Search

[Display omitted] • Six machine learning models were used to predict MR and CT. • GPR model demonstrated the best predictive performance. • SHAP and PDP were introduced for model interpretation. • An easy-to-use GUI was developed for the prediction of MR and MC. Preparation of activated carbons is an important way to utilize municipal sludge (MS) resources, while drying is a pretreatment method for making activated carbons from MS. In this study, machine learning techniques were used to develop moisture ratio (MR) and composting temperature (CT) prediction models for the thermally assisted biodrying process of MS. First, six machine learning (ML) models were used to construct the MR and CT prediction models, respectively. Then the hyperparameters of the ML models were optimized using the Bayesian optimization algorithm, and the prediction performances of these models after optimization were compared. Finally, the effect of each input feature on the model was also evaluated using SHapley Additive exPlanations (SHAP) analysis and Partial Dependence Plots (PDPs) analysis. The results showed that Gaussian process regression (GPR) was the best model for predicting MR and CT, with R2 of 0.9967 and 0.9958, respectively, and root mean square errors (RMSE) of 0.0059 and 0.354 ℃. In addition, graphical user interface software was developed to facilitate the use of the GPR model for predicting MR and CT by researchers and engineers. This study contributes to the rapid prediction, improvement, and optimization of MR and CT during thermally assisted biodrying of MS, and also provides valuable guidance for the dynamic regulation of the drying process. [ABSTRACT FROM AUTHOR]

• Pathways of carbon-containing compounds in municipal sludge pyrolysis were Mapped. • In terms of gas pollution, most carbon was fully pyrolyzed into CO 2. • The pyrolysis liquid below 300 °C exhibited a potential for resource utilization. • The yield of CO in pyrolysis gas rapidly increased at temperature above 500 °C. • The insights hold practical implications for environmental management. Municipal sludge contains abundant amounts of carbon, with contents ranging from 14 % to 38 %. The various carbon-containing group compounds can be converted into beneficial products, but pollutants and greenhouse gases are also released through the municipal sludge pyrolysis process. Ascertaining the pathways by which carbon-containing group compounds is converted and transformed is crucial for addressing pollution concerns and promoting recycling. This study explored the transformation pathways of carbon-containing group compounds during the pyrolysis process of municipal sludge. The results showed that the three major carbon-containing group compounds including protein (61 %), cellulose (9 %), and hemicellulose (7 %), had significantly different pyrolysis temperature of 600 °C, 400 °C and 300 °C. In terms of gas pollution, most carbon was fully pyrolyzed into CO 2. While the temperature raised up to 500 °C, a part of the CO 2 converted into CO. Meanwhile, the various carbon-containing compounds exhibited distinct effects on gas production, which CH 4 was produced more with cellulose and protein presenting in the sludge. When temperature increased to 700 °C, the 60 % of the carbon-containing group compounds were transformed into liquid and solid. The pyrolysis liquid in the low-temperature stage (30–300 °C) contained a relatively high aliphatics content and lower organooxygen species (OOSs) content (at 200 °C), suggesting a potential for resource utilization. The yield of CO in the gas rapidly increased as the temperature increased in the high-temperature stage (500–700 °C). The insights from this study hold practical implications for enhancing municipal sludge pyrolysis efficiency, reducing pollution, and facilitating more sustainable and resource-efficient practices. [ABSTRACT FROM AUTHOR]

[Display omitted] • CaMn 0.5 Fe 0.5 O 3-δ -washed can ensure 61% of the effective gas fuel components. • Nanometer-sized MnO 2 can facilitate the oxygen uncoupling regeneration. • The anti-deposition performance of the oxygen carrier enhanced by washing red mud. • The reacted oxygen carrier exhibits a hollow structure that is easily fluidized. Chemical looping gasification (CLG) is a promising technology that utilizes lattice oxygen for partial oxidation of solid organic waste to produce high-quality syngas. The utilization of low-cost and high-performance oxygen carriers (OCs) is important for the success of this technology. The red mud from aluminum production was mixed with calcium and manganese oxides to prepare CaMn 0.5 Fe 0.5 O 3-δ perovskite OCs. The comparative redox tests were carried out to analyze the reactivity using a thermogravimetric analyzer (TGA). Multiple cycle CLG experiments were conducted on a wet municipal sludge in a lab-scale fluidized bed to produce the hydrogen-rich gas. The results showed that the CaMn 0.5 Fe 0.5 O 3-δ -washed demonstrated higher oxygen transfer capacity and better cycling stability with a maximum weight loss of 7.3096 %. After the 5th cycle in CLG, the syngas obtained using CaMn 0.5 Fe 0.5 O 3-δ -washed maintained a H 2 volume fraction exceeding 40%. However, an increase in CO 2 production was also observed, which could be due to the catalytic effect of MnO in the OC on the steam-reforming reaction. The XRD curves showed that fresh CaMn 0.5 Fe 0.5 O 3-δ -washed exhibited prominent diffraction peaks characteristic of perovskite. It was observed that after undergoing 5 cycles, the presence of iron calcium silicate structures containing Mn became evident due to the attachment of sludge ash, leading to the increased impurities on the surface of OCs with a decrease in the specific surface area. Additionally, some of the reacted OC particles exhibited a hollow structure, facilitating the fluidization. This preliminary study provides the basis for the improvement of the OC performance in sludge gasification. [ABSTRACT FROM AUTHOR]

Oxygen-fuel combustion is an effective and promising method of steadily minimizing municipal sludge volume at the same time exploiting available heat and falling emissions. The effects of temperature, oxygen concentration, and CaO addition on SO 2 and NO x emissions from municipal sludge combustion in CO 2 /O 2 atmosphere were systematically explored via a lab-scale electrically heated tubular furnace in this work. The results show that the minimum average emissions of both SO 2 and NO x were observed at 800 °C. Compared with air, all oxygen-fuel atmospheres reduced SO 2 emission, and a salient effect was observed with 30% of oxygen concentration. In contrast, the inhibition of NO x emission was inconspicuous and exacerbated in some cases. With a lower oxygen concentration (21%), CaO evidently reduced SO 2 emission and 8 wt% addition performed the best. The removal efficiency of NO by CaO addition was poor and only exhibited slight inhibition with 5 wt% addition. • SO 2 and NO x emissions during oxygen-fuel combustion of municipal sludge were studied. • Effects of oxygen concentration on SO 2 and NO x emissions were compared. • CaO evidently reduced SO 2 emission with appropriate addition amount. • Optimal addition ratio of CaO for NO removal was obtained. [ABSTRACT FROM AUTHOR]

Because proper disposals of municipal sewage sludge and lead-containing wastewater are still open questions, the novel sludge-derived mesoporous nanospinel ferrite adsorbents were prepared from municipal sewage sludge (S-MZF) and its incineration ash (A-MZF) for Pb(II) removal from water. S-MZF and A-MZF had similar mesoporous structures with an average pore size at around 4.13–5.51 nm. A-MZF displayed a larger specific surface area (254 m2/g) and pore volume (0.3 m3/g) but inferior magnetic property, while S-MZF showed abundant surface functional groups and higher saturation magnetization (12.3 emu/g). The adsorption capacity of S-MZF and A-MZF for Pb(II) was close to each other at 50 °C, reaching 160 mg/g. Initial adsorption of A-MZF for Pb(II) was dominated by intraparticle diffusion, while the evident liquid film diffusion existed in that of S-MZF. Advanced statistical physics modeling found that multiple divalent lead ions were anchored simultaneously by each site of S-MZF mainly via multi-interactions where physical force and precipitation played a key role, while each site of A-MZF anchored only one Pb(II) ion by the physical interaction. As a result, the adsorption capacity of S-MZF mainly depended upon the number of Pb(II) ions adsorbed by each active site, while the available density of active sites on the surface of A-MZF primarily controlled its adsorption capacity for Pb(II). [Display omitted] • Sludge-based mesoporous nanospinel ferrite adsorbents were prepared. • Municipal sewage sludge and its incineration ash were used as feedstocks. • Statistical physics modelling was used to explain special adsorption mechanism. • Multiple Pb(II) ions were simultaneously anchored by each active site of S-MZF. • A-MZF has a higher adsorption site density than S-MZF to capture Pb(II). [ABSTRACT FROM AUTHOR]

• The Cu-Fe oxygen carriers are welcome for CLC, but the Fe phase separation is found. • Perovskite-form oxygen carriers demonstrate better performance stability. • Sludge rich in iron can in-situ inhibition of Fe phase separation of OCs. • Sludge ash containing iron can be used to prepare low-cost OCs. A high-performance and low-cost oxygen carrier (OC) is the key for industrialization of chemical looping gasification (CLG) technology for sludge treatment. In this work, four OCs (RM_15 %CuO, RM_10 %CuO, RM, RM_POC) were prepared in an industrial-scale granulation equipment. The red mud was composited by mixing with different amounts of CuO and MnO 2 , then subjecting to different calcination temperatures. Firstly, the oxygen decoupling and oxygen carrying capacities of the OCs were compared using 5% H 2 as the reducing agent. RM_15%CuO and RM_POC showed excellent oxygen release capabilities, with oxygen release loss of −1.99 % for RM_15%CuO. The catalytic gasification performances of RM_15%CuO and RM_POC were evaluated in a lab-scale fluidized bed reactor with wet sludge as the feedstock. Both OCs were able to maintain the H 2 concentration of over 44.6% and no less than 79.2% sludge gasification efficiency after 30 cycles. However, the H 2 content was clearly higher in case of RM_POC. SEM-EDS was used to analyze the influence of sludge ash, rich in Fe, on the performance of two OCs after the fluidized bed operation. The results showed that the sludge ash sample with more than 20% Fe 2 O 3 could transfer its lattice oxygen to assist OC and prevent the in-situ segregation of Fe phase in the POC surface. However, the inhibitory effect of RM_15%CuO was much lower. The degradation performance of RM_POC carrier was slower and thus the H 2 content was higher. This performance evaluation provides a theoretical guide for chemical looping gasification of sludge in future with an idea of mixed ratio of recycling sludge ash to the RM_POC. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxygen could trigger complex trends due to the enhanced sludge dissolution. • Formic acid could also be prevalent at low temperatures except for acetic acid. • Three fluorescent components containing 8 peaks were identified as common features. • Lipids and lignins were important components of dissolved organic matter. • C 19 H 32 O 3 S and C 18 H 30 O 3 S served as crucial intermediates during the reaction. The impact of temperature and oxygen pressure on the basic performance of hydrothermal reactions and dissolved organic matter (DOM) was investigated. The results showed that total chemical oxygen demand and volatile suspended solids removal rate achieved a maximum of 72 % and 99 %, respectively, at 260 °C and 0.9 MPa oxygen pressure. Oxygen demonstrated a significant role in enhancing sludge particle dissolution. The interaction with temperature resulted in a complex trend for dissolved organic carbon (DOC) and specific ultraviolet absorbance at 254 nm. Acetic acid and formic acid were identified as the prominent volatile fatty acids, with formic acid prevalent at lower temperatures, while acetic acid accumulated with increasing temperature and oxygen pressure. Three-dimensional excitation emission matrix and Fourier transform ion cyclotron resonance mass spectrometry was also employed to analyse DOM as over half of the DOC remained unknown. Parallel factor analysis indicated that three components with 8 peaks in total might represent a universal feature for fluorescent DOM in hydrothermal reaction solution. The deciphered data from FTICR-MS indicated that lipids and lignins as well as CHOS and CHON molecules were the main components of DOM. Meanwhile, condensed hydrocarbons were formed at high temperatures in wet oxidation runs. Moreover, identification of C 19 H 32 O 3 S, C 18 H 30 O 3 S and C 18 H 26 N 2 O 3 as crucial intermediates further enriched the understanding of hydrothermal reactions in municipal sludge. [ABSTRACT FROM AUTHOR]

This study investigated the effects of two-step activated carbon cloth (CC) on the syntrophic microbial associations during anaerobic digestion (AD) of municipal sludge. A simple two-step activation, acid pretreatment (H 2 SO 4 /HNO 3) followed by air calcination (550 °C), was used to convert commercial untreated CC (U-CC) into high performance activated CC (A-CC). Biochemical methane potential (BMP) assays conducted at different CC dosages indicated that A-CC, at a dose of 0.80 g A-CC {1.48 g A-CC/g-VS (volatile solids) substrate }, enhanced methane yield from by 3.7× and reduced the lag phase up to 15.6-fold, compared to non-CC Control within 3 days. Characterization of CC surfaces and kinetic modeling indicated indicated that A-CC pore size area increased by 435× a (Barrett, Joyner, and Halenda, BJH) with the potential to promote electron transfer and accelerate kinetic rates of methane production. Consistent with these results, microbial community composition profiles of CC surfaces indicated rapid adherence of methanogenic archaea and bacterial syntrophs to A-CC within 3 days. Multi-variate statistical analyses indicated that these populations were highly enriched on 0.80 g A-CC dosage compared to U-CC and Controls. Based on these results it can be concluded that A-CC provides a robust selective environment for syntrophic energy metabolism driving enhanced methane production from municipal sludge. Two-step activation of CC on rate and extent of methane production. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The occurrence of SMX and K ALE decreases as pH increases. • With the increase of pH, SMX concentration in ALE decreased. • SMX concentration of ALE extracted via dialysis lower than ethanol extraction. • ALE holds potential in agricultural and other application sectors. The recovery of biopolymers, particularly alginate-like extracellular polymers, from municipal sludge represents a promising step toward sustainable sludge treatment practices. Originating from wastewater plants in complexly polluted environments, alginate-like extracellular polymers carry potential environmental risks concerning their reuse. This study employs ultrahigh-performance liquid chromatography–tandem mass spectrometry to investigate the distribution coefficients and occurrence of alginate-like extracellular polymers and sulfamethoxazole. Results demonstrate a negative distribution coefficient, suggesting an inhibitory effect on sulfamethoxazole dissolution. The ethanol-extracted alginate-like extracellular polymers exhibits higher sulfamethoxazole levels (approximately 52%) than those obtained via dialysis extraction. Three-dimensional excitation-emission matrix analysis and adsorption studies indicate the absence of tyrosine-like substances in the alginate-like extracellular polymers, unlike in other extracellular polymeric substances. This absence diminishes hydrophobic interactions, highlighting that electrostatic interactions play a more important role. These insights are crucial for understanding the adsorption behavior of alginate-like extracellular polymers and optimizing their large-scale extraction processes. [ABSTRACT FROM AUTHOR]

The co-pyrolysis of municipal sludge (MS) and papermaking sludge (PS) is beneficial for improving the quality of co-pyrolysis biochar and the stability of heavy metals in it. This study investigated the synergistic effect of co-pyrolysis of MS and PS, as well as the influence of different mass ratios (1:9, 3:7, 5:5, 7:3, and 9:1; MS:PS) and pyrolysis temperatures (400–600 ℃) on the physicochemical properties of pyrolysis char, chemical speciation of heavy metals, and their potential ecological risk index. Furthermore, thermodynamic equilibrium calculations were used to study the transformation and stabilization mechanisms of heavy metals during co-pyrolysis. The results indicated that the addition of PS increased the comprehensive pyrolysis index of MS (by 2.09–16.72 times) and the specific surface area of co-pyrolysis char. The inclusion of MS effectively promoted the transformation of heavy metals from unstable fractions to stable fraction, significantly reducing the potential ecological risk index of pyrolysis biochar (by 21.93–41.58 %). The combination of thermodynamic equilibrium calculations and experimental data demonstrated that heavy metals in sludge could be stabilized through the formation of stable heavy metal compounds or their encapsulation within the lattice of inorganic components during co-pyrolysis. These findings suggest that co-pyrolysis of MS and PS is a feasible and promising approach for producing high-quality pyrolysis char with low risk of heavy metals. [Display omitted] • The co-pyrolysis of municipal sludge and papermaking sludge was researched. • Adding municipal sludge elevates the stability of heavy metals in biochar. • Adding papermaking sludge improved the pyrolysis characteristics of mixed sludge. • The inorganic components play a key role in stabilizing heavy metals. [ABSTRACT FROM AUTHOR]

[Display omitted] • The research timeline of alginate-like extracellular polymers (ALE) are mapped. • The key factors of ALE recovery in wastewater plant was summarized and discussed. • Sludge treatment requires reconstruction with ALE recovery. • Environmental and economic sustainability of ALE requires detailed assessment. • The environmental health risk of ALE products deserves further exploration. The recovery of alginate-like extracellular polymer (ALE) from municipal sludge is a highly anticipated approach for addressing resource and climate crises, achieving sustainable development, and transforming water-resource factories. This review begins with the recovery of ALE from sludge and analyzes the current status of ALE-recovery research. The goal of ALE recovery is product-centered, and the approach considers the entire recovery chain. For the first time, this study presents a timeline of ALE research and clarifies the sequence of events in this research. Two aspects of a series of critical issues in ALE recycling are discussed: the value-added benefit of ALE recycling and its external influence. Different types of sludge and extraction methods are among the many key factors in a sewage-treatment plant that affect the recovery rate of ALE. We believe that introducing ALE recovery into the sludge-treatment process will have a series of external effects (such as changes in the properties of the treated sludge) that will affect further treatment. In addition, the environmental and economic sustainability of ALE recovery still requires further analysis, and the environmental risks due to the presence of pollutants in products that utilize ALE need to be investigated further. Herein, we summarize the current status of research regarding ALE recovery, which is expected to provide useful reference information for the large-scale recovery of ALE anticipated in the future. [ABSTRACT FROM AUTHOR]

Microbiologically induced calcite precipitation (MICP), as a newly developing bioremediation technology, could redeem heavy metal contamination in diverse scenarios. In this study, MICP bacterium Sporosarcina ureilytica ML-2 was employed to suppress the pollution of Pb, Cd and Zn in municipal sludge nutrient soil. After MICP remediation, the exchangeable Cd and Zn in sludge nutrient soil were correspondingly reduced by 31.02 % and 6.09 %, while the carbonate-bound Pb, Cd and Zn as well as the residual fractions were increased by 16.12 %, 6.63 %, 13.09 % and 6.10 %, 45.70 %, 3.86 %, respectively. In addition, the extractable Pb, Cd and Zn either by diethylenetriaminepentaacetic acid (DTPA) or toxicity characteristic leaching procedure (TCLP) in sludge nutrient soil were significantly reduced. These results demonstrated that the bio-calcite generated via MICP helped to immobilize heavy metals. Furthermore, MICP treatment improved the abundance of functional microorganisms related to urea cycle, while reduced the overall abundance of metal resistance genes (MRGs) and antibiotic resistance genes (ARGs). This work confirmed the feasibility of MICP in remediation of heavy metal in sludge nutrient soil, which expanded the application field of MICP and provided a promising way for heavy metal pollution management. [Display omitted] • MICP tech could improve the stability of Pb, Cd and Zn in sludge nutrient soil. • The exchangeable Cd reduced by maximum 31.2 % contents after MICP remediated. • The carbonated and residual contents of Pb, Cd and Zn increased after remediated. • The extracted contents of DTPA & TCLP-Pb, Cd and Zn were reduced after remediated. • MICP improved the abundance of functional microbes and reduced resistance genes. [ABSTRACT FROM AUTHOR]

• UF fractionation of hydrothermal liquefaction aqueous product from sludge applied. • In molecular weight range of 1-300 kDa, most organics are fractionated into <1 kDa. • Cumulative specific methane yield is not affected by molecular weight distribution. • Methane production rate is the highest for less than 1 kDa molecular weight range. • Compared to theoretical yield, all fractions yielded 45 % lower specific methane. Hydrothermal liquefaction (HTL) is a promising thermo-chemical technology for municipal sludge treatment due to its potential for biocrude oil recovery and minimizing biosolids management costs. However, the process generates a high volume of an aqueous byproduct that needs to be treated due to its high chemical oxygen demand (COD) and various organic and inorganic compounds. Although the aqueous phase is known to contain recalcitrant and potentially inhibitory substances that may affect its biological treatment, their molecular weight distribution (MwD) and its impact on anaerobic biodegradability are poorly understood. Ultrafiltration (UF) was conducted to fractionate HTL aqueous into different molecular weight (Mw) fractions using 300, 100, 10, and 1 kDa membranes. Mesophilic biochemical methane potential (BMP) assays were conducted to assess the anaerobic biodegradability of each fraction, and the first-order model was used to calculate the degradation kinetics of potential inhibitory compounds. The highest percentage of organics (65 %) was found in the Mw<1 kDa range, whereas the 10>Mw>1 kDa had the lowest percentage (8 %). There was no significant difference in the cumulative specific methane produced from various Mw fractions (p>0.05). The Mw<1 kDa fraction had the highest first-order specific methane production rate (0.53 day−1), whereas the unfiltered HTL had the lowest (0.38 day−1). Although UF fractionation increased the rate of anaerobic degradation of HTL aqueous for the Mw<1 kDa fraction, the observed methane potential was only 55 % of the theoretical value. This implies that 45 % of COD remains undegraded even after permeation through the lowest Mw cut-off membrane. Therefore, further characterization of HTL aqueous is needed for compounds with molecular weights below 1 kDa to fully understand the nature of inhibitory organics and their impact on anaerobic digestion. Furthermore, pretreatments utilizing techniques such as adsorption and advanced oxidation may be necessary to enhance the specific methane yields from various HTL aqueous fractions, thereby bringing them closer to the theoretical yield. [Display omitted] [ABSTRACT FROM AUTHOR]

The nitrogen content of municipal sludge is as high as 2.5～9.0 wt%, which has become an important problem in pollution control during pyrolysis. Recycling nitrogen from municipal sludge not only enables resource utilization, but also reduces the nitrogen-related pollution. In this study, the transformation pathways of nitrogen to resource material and typical pollutants during the municipal sludge pyrolysis process were analyzed. The results showed that the nitrogen species in municipal sludge were mainly protein-N (64.41%), pyridine-N (19.47%) and inorganic-N (16.13%). After pyrolysis at 300 °C, the peptide bond of protein-N was gradually broken down, resulting in the formation of three nitrogenous intermediates (amine-N, nitrile-N and heterocyclic-N) were produced. These intermediates can be transformed to NH 3 for resource recovery or to HCN pollutants. Moreover, the full nitrogen transformation pathways of municipal sludge pyrolysis were constructed by the method of Spearman's correlation coefficient and experiment analysis. It was found that NH 3 and HCN were mostly generated from the cracking of three nitrogenous intermediates at 600–800 °C. In addition, there was a prominent effect on the transformation of HCN to NH 3 with co-presence of calcium minerals in raw sludge. By adding inorganic calcium minerals, NH 3 as a recyclable component was prominently improved by 10.30% at 700 °C, while HCN yield was decreased by 53.02% accordingly under the inhibitory effect. The results systematically provided a theoretical support to the possibility of nitrogen recycling for utilization during municipal sludge pyrolysis, as well as to control the transformation of nitrogen elements into pollutants. [ABSTRACT FROM AUTHOR]

Sludge pyrolysis, as a new sludge disposal technology, can realize the reduction and resource utilization of municipal sludge. Based on TG-FTIR-MS technology, pyrolysis behaviors such as pyrolysis reaction kinetics, pyrolysis product composition and other pyrolysis behaviors of four common municipal sludges (SD, NJ, CS, TJ) at different pyrolysis rates were investigated in this paper, and the migration and transformation of nitrogen elements in municipal sludge were analyzed. The results showed that the pyrolysis of municipal sludge was mainly divided into three stages: dewatering (below 160 °C), volatile decomposition (160–550 °C), and carbonization stage (550–900 °C). The activation energies of the four sludge pyrolysis stages were 189.75 kJ/mol, 138.13 kJ/mol, 300.76 kJ/mol, and 237.83 kJ/mol, respectively. It was found that the sludge pyrolysis stage followed the stochastic nucleation and subsequent growth mechanism through the study of SD and CS sludge. The pyrolysis gaseous product content was affected by the rate of heating and pyrolysis temperature. Moderate temperatures (400–550 °C) favored complete sludge decomposition. Sludge is more likely to decompose in a narrow temperature range at higher heating rates, and increasing the heating rate accelerates sludge decomposition. The nitrogenous compounds in sludge are mainly pyrrole nitrogen, protein nitrogen, and pyridine nitrogen. During sludge pyrolysis, the nitrogenous compounds decompose and precipitate in the form of heterocyclic nitrogen (pyridine, pyrrole), and release small molecules of nitrogenous compounds (NH 3 , HCN, HCNO). The experimental results can provide a reference for the disposal of municipal sludge by pyrolysis. • Sludge pyrolysis is divided into dewatering, volatile decomposition, carbonization. • Sludge pyrolysis follows random nucleation and subsequent growth mechanism. • Increasing the heating rate can accelerate the decomposition of sludge. • Nitrogenous compounds decompose and precipitate as heterocyclic nitrogen. • Small molecule nitrogenous compounds are precipitated during decomposition. [ABSTRACT FROM AUTHOR]

[Display omitted] • 40% more methane was recovered via "thermal hydrolysis + two-stage AD" process. • Integrated thermal and fermentation process achieved up to 40% COD solubilization. • Maximum VFAs recovery was achieved via sequential "thermal/fermentation process". • The produced VFAs primarily contained acetic, propionic, and isobutyric acids. • Fermentation reduced the adverse effect of thermally-formed intermediates on AD. The purpose of this research was to investigate the impact of two process configurations integrating two-phase anaerobic digestion (AD) of municipal sludge with thermal hydrolysis (TH). The TH was positioned either before or after the acidogenic fermentation phase. The fermentation process was carried out under the semi-continuous flow regime with a retention time of three days. The TH was done at a temperature of 170 °C and for 30 min. Among all the tested scenarios, the TH of sludge followed by the acidogenic fermentation resulted in the highest COD solubilization ratio (39.5%) and volatile fatty acids production (6,420 ± 400 mg/L), which was 630% and 500% more than that of the raw sludge, respectively. The sequential TH/fermentation process achieved 40% higher ultimate methane yield (240 mL/g COD) than the non-pretreated (raw) sludge. Positioning TH after the fermentation process reduced the ultimate methane yield to 231 240 mL/g COD, although it was still 32% higher than that of the raw sludge. The analysis of methane production rate and biodegradation kinetics data suggested the formation of refractory intermediates during the thermal process of sludge, which reduced the overall performance rate during the first week of the AD process. It was also revealed that acidogenic fermentation of thermally-processed sludge could diminish the adverse effect of the recalcitrant compounds formed during the thermal hydrolysis on the subsequent AD process. [ABSTRACT FROM AUTHOR]

• Metals recovered from pickling sludge by using municipal sludge (MS) as agent. • Under optimized conditions, Fe, Cr and Ni recovery rates are 70.1%, 53.7% and 60.3%. • CO 2 /N 2 improves the MS pyrolysis, and favors for the reduction of pickling sludge. • Pickling sludge riches in Cr, and Ni, and their migration rates are smaller than 10%. A new method for recovering metals from ferritic stainless steel pickling sludge using municipal sludge as a reducing agent is proposed. The effects of temperature, municipal sludge blending ratio, and reaction atmosphere on the recovery characteristics were studied. The migration characteristics of heavy metals (HMs) at different temperatures were also investigated. The results showed that municipal sludge can be used as a reducing agent for metal recovery from pickling sludge. Under optimized conditions (temperature of 650 °C and blending ratio of 5%), the recovery fractions of Fe, Cr, and Ni were 70.1, 53.7, and 60.3%, respectively. The CO 2 atmosphere was beneficial for increasing the recovery fraction of the pickling sludge. The migration fractions of Cr, Mn, and Ni were approximately 10%. The migration fractions of Zn, Cu, and Pb, which are semi-volatile HMs, varied significantly with temperature. The migration fractions of Cd and As, which are volatile HMs, could exceed 70%. [ABSTRACT FROM AUTHOR]

The harmless disposal, resource recovery, and synergistic efficiency reduction of municipal sludge have been the research focuses for the last few years. Calcium peroxide (CaO 2) is a multifunctional and safe peroxide that produces an alkaline oxidation environment to promote the fermentation of municipal sludge to produce hydrogen (H 2) and volatile fatty acids (VFAs), thus realizing sludge resource recovery. This review outlines the research achievements of CaO 2 in sludge resource recovery, improvement of sludge dewaterability, and removal of pollutants from sludge in recent years. Meanwhile, the mechanism of CaO 2 and its influencing factors have also been comprehensively summarized. Finally, the future development direction of the application of CaO 2 in municipal sludge is prospected. This review would provide theoretical reference for the potential engineering applications of CaO 2 in improving sludge treatment in the future. [Display omitted] • Recent advances in CaO 2 application in primary sludge treatment are reviewed. • Various influencing factors of CaO 2 performance were summarized. • The performance of CaO 2 was compared with other oxidants in sludge resource recovery. • The research blank of CaO 2 in sludge resource recovery field is pointed out. [ABSTRACT FROM AUTHOR]

Municipal sludge treatment in urban contexts faces significant challenges, especially when dealing with sludge characterized by exceptionally high water content and organic content. This study investigates the application of sodium persulfate oxidation activated by ferrous ions (Fe2+/SPS) in conjunction with waste steel slag as a conditioning agent for municipal sludge, capillary suction time and specific resistance filtration experiments were conducted on conditioned sewage sludge, along with dewatering tests under ultrahigh pressure conditions. Additionally, to investigate the potential underlying mechanisms, Scanning Electron Microscopy analysis, Zeta potential measurements, and comprehensive sample analyses were performed. The research reveals substantial improvements in sludge dewatering performance when steel slag is combined with Fe2+/SPS treatment. This combined treatment introduces additional ferrous ions into the sludge, generating radicals that disrupt the structure of extracellular polymeric substances and cells within the sludge. Steel slag also acts as a skeleton builder material, creating larger drainage pathways within the sludge cake under ultrahigh pressure, enhancing permeability, and accelerating moisture release. This combined treatment method holds promise for achieving deep sludge dewatering, under ultrahigh filtration pressure, with water content reduced to below 40%. The study not only highlights the advantages of using steel slag in combination with Fe2+/SPS treatment for sludge dewatering but also provides insights into the underlying mechanisms. This comprehensive treatment method reduces the excessive use of ferrous ions and costs while significantly enhancing dewatering performance, offering a promising solution for municipal sludge treatment and management. [Display omitted] • Steel slag in combination with Fe2+/Na 2 S 2 O 8 for sludge conditioning is firstly proposed. • Ultrahigh filtration pressure reaches 30 MPa. • Steel slag reduces the excessive use of ferrous ions. • Larger drainage pathways within the sludge cake under ultrahigh pressure are created by steel slag. • The bound water was released and reduced significantly. [ABSTRACT FROM AUTHOR]

Hydrothermal liquefaction (HTL) is an effective technology for municipal sludge (MS) conversion. In this study, the performances of biochar catalysts in HTL were investigated using MS as raw material. The solid product (hydrochar) of MS HTL was collected and prepared into three types of catalysts, namely BC, KOH/BC, and H 2 SO 4 /BC, to investigate the effects of different catalysts and catalyst loadings on MS HTL under fixed reaction conditions (350 °C, 40 min). The results show that the highest yield of biocrude could be achieved at 5 wt% BC, 15 wt% KOH/BC, and 5 wt% H 2 SO 4 /BC catalysts under used conditions, which could reach 17.84 wt%, 16.99 wt%, and 18.00 wt%, respectively. They were all higher than that of the non-catalytic condition (16.86 wt%). H 2 SO 4 /BC gave the greatest boost to the biocrude yield (18.00 wt%) and the highest energy recovery (ER up to 51.15% at 5 wt% loading), 8.85% higher than the energy recovery without catalyst (42.30%). H 2 SO 4 /BC also increased the hydrocarbon content and decreased the phenol content in biocrude. [Display omitted] • Solid by-products from MS HTL were used as biochar catalysts in MS HTL for green recycling. • The highest biocrude yield (18.00 wt%) and energy recovery (51.15%) were achieved at 5 wt% H 2 SO 4 /BC. • The highest C (74.68 wt%) and the lowest O contents (6.67 wt%) of biocrude were obtained at 15 wt% KOH/BC. • 5 wt% H 2 SO 4 /BC reduced phenol from 2.94% to 1.7% and increased hydrocarbon from 10.76% to 11.67% in biocrude. [ABSTRACT FROM AUTHOR]

[Display omitted] • Glass-ceramics of MFA and MS were prepared. • Melting temperature of preparation process was below 1300 °C. • Vickers hardness and fracture toughness are 7.35GPa and 5.85 MPa•m1/2. Utilization of municipal solid waste, such as incineration fly ash (MFA) and municipal sludge (MS), is currently the focus area of research. In this paper, glass ceramics were prepared from these two types of municipal solid waste. The melting temperature could be reduced through the component regulation, thus lowering the production cost of glass ceramics. The results indicated that glass ceramics were successfully prepared at the temperatures below 1300 °C and the MFA/MS ratio of 1:1 – 3:7. The morphostructural analysis of glass ceramics revealed the formation of abundant crystals and fine grains. The volume density of ceramics was 2.82–2.92 g/cm3. The Vickers hardness of glass ceramics was greater than 6.68 GPa and the best fracture toughness was 5.85 MPa•m1/2; meanwhile, the acid and alkali corrosion resistance was above 96 %. These results suggest the feasibility of preparation of glass ceramics with good performance from MFA and MS at relatively low temperatures. [ABSTRACT FROM AUTHOR]

A novel Fe/La decorative biochar filled in sodium alginate beads (SA-KBC-Fe/La) was prepared by a simple sol-gel method and applied to adsorb phosphate (P) efficiently from water in this study. The morphology, structure and chemical component of the hydrogel beads were characterized in detail. And the synthesized bead exhibited easy separation and high P uptake of 46.65 mg/g when the Fe: La was of 1: 2 at 298 K with initial P of 100 mg/L, which was much higher than SA gel bead. The adsorption showed that the optimal pH was 6, and the adsorption was met with pseudo-second-order kinetics and Langmuir isothermal models, indicating a chemical adsorption process. The adsorption capacity remained 82 % after 5 cycles of adsorption. The adsorption mechanism of P was mainly of ligand exchange and electrostatic attraction. Compared with other reported adsorbents, the modification of Fe/La could enhance the mechanical property of SA-KBC-Fe/La beads with increasing active sites. Additionally, the involved biochar could lead to excellent thermal stability and hierarchical porous structure of beads with larger specific surface area (54.22 m2/g). The study could provide new ideas for P removal and strategy for the final disposal of municipal sludge. [Display omitted] • Fe/La decorative biochar/sodium alginate beads were prepared to adsorb P from water. • Concrete adsorption property and mechanism of the beads for P were discussed. • Fe/La and biochar modification could greatly enhance P adsorption capacity. • New idea for P removal and strategy for disposal of municipal sludge was provided. [ABSTRACT FROM AUTHOR]

In this study, modified municipal sludge was used in place of fine aggregate to manufacture concrete, and it's revealed how different quicklime and sludge contents affect concrete. The best modified sludge concrete group was used for the performance improvement test, after which the constitutive model, the carbonation depth prediction model, and the freeze-thaw damage model were fitted. The results showed that the compressive strength of the L10S10 was best in experiment of modified municipal sludge concrete. Under alkali activation, fly ash absorbed the remaining alkali in modified municipal sludge, promoted concrete hydration, and improved the mechanical characteristics of concrete. The F10N4 group had the best activation effect, with a compressive strength of 50.61 MPa. Test results could be accurately reflected by the constitutive model and carbonation depth prediction model that were devised. The freeze-thaw damage model based on relative dynamic elastic modulus has a correlation coefficient greater than 0.98. • The effect of modified municipal sludge on the mechanical properties of concrete is revealed. • The microscopic mechanism of alkali-activated modified municipal sludge concrete is studied. • The carbonation depth prediction model, freeze-thaw damage model of modified municipal sludge concrete is fitted. [ABSTRACT FROM AUTHOR]

The pyrolysis kinetics of two types of sewage sludge (municipal sludge and pharmaceutical sludge) were studied by thermogravimetry. The collected samples were pretreated and tested with nitrogen as carrier gas at different heating rates (10, 20, 30, and 40 °C/min) using a thermogravimetric analyzer. Model-free methods and master plots method were used to calculate the pyrolysis kinetic parameters of the samples. TG/DTG results showed that the thermal decomposition of the two types of sewage sludge may be divided into three stages (Dehydration, Decomposition, and Coking stage). The activation energies of the two kinds of sewage sludge were 366.58 KJ/mol (municipal sludge) and 268.36 KJ/mol (pharmaceutical sludge), respectively. The pyrolysis mechanism of two kinds of sewage sludge was discussed by the master plots method. The results showed that under a low conversion rate, the phase interface reaction model can better explain the pyrolysis mechanism of pharmaceutical sludge; under high conversion rate, the nucleation and growth model was more suitable. For municipal sludge, power law model was most suitable in the whole range. The pyrolysis characteristic of the samples was further studied. The results showed that the organic matter in sewage sludge can be decomposed into bio-oil and bio-gas at elevated temperatures and can be used as an attractive energy source. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermochemical technologies are suitable for municipal sludge (MS) recycling. • Hydrothermal methods show a great potential on energy and resource recovery of MS. • Machine learning (ML) guides process optimization, mechanism mining in MS recycling. • Application of ML for thermochemical conversion of MS still remains challenging. • Comprehensive ML models considering successive reaction processes deserve further study. The sustainable disposal of high-moisture municipal sludge (MS) has received increasing attention. Thermochemical conversion technologies can be used to recycle MS into liquid/gas bio-fuel and value-added solid products. In this review, we compared energy recovery potential of common thermochemical technologies (i.e., incineration, pyrolysis, hydrothermal conversion) for MS disposal via statistical methods, which indicated that hydrothermal conversion had a great potential in achieving energy recovery from MS. The application of machine learning (ML) in MS recycling was discussed to decipher complex relationships among MS components, process parameters and physicochemical reactions. Comprehensive ML models should be developed considering successive reaction processes of thermochemical conversion in future studies. Furthermore, challenges and prospects were proposed to improve effectiveness of ML for energizing thermochemical conversion of MS regarding data collection and preprocessing, model optimization and interpretability. This review sheds light on mechanism exploration of MS thermochemical recycling by ML, and provide practical guidance for MS recycling. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is an effective way to harmlessly dispose municipal sludge (MS). This work comprehensively reviewed critical hydrothermal parameters of HTC, reaction mechanisms, physicochemical characteristics, applications of target products, technology coupling, energy balance, economic evaluation and life cycle analyses. The formation of hydrochar is predominantly attributed to the polymerization of remarkably reactive intermediates generated through the degradation of biopolymers in MS, as well as the solid-solid conversion of their insoluble components. Physicochemical properties of target products are closely related to process parameters and chemical compositions of MS, which provide a promising opportunity to acquire desired products by optimizing reaction conditions. The combination of other wastes with MS, and the coupling of different processes (e.g., pyrolysis) are potential optimization methods of HTC. The synergy of technological coupling enables the augmentation of value within the product. Typical energy balances of HTC indicate that net energy recovery exists even when the moisture content of municipal sludge is up to 91%. The combination of hydrochar as a substitute for fossil fuels and anaerobic digestion or recycling of process water is very favorable for the life cycle assessment of HTC of MS. Ultimately, some prospects for HTC of MS are highlighted. [Display omitted] • The influence of process factors on mechanisms and products properties are discussed. • Physicochemical properties of key products from municipal sludge are summarized. • Potential applications of main products from municipal sludge are evaluated. • Synergy of technological coupling enables augmentation of value within the product. • Hydrothermal carbonization is competitive in process, economy and life cycle. [ABSTRACT FROM AUTHOR]

A 20-day sludge biodrying process was coupled with photocatalysis to improve biodrying efficiency and investigate the effect of photocatalysis on biodegradation. After biodrying, the moisture content in the coupled photocatalytic group (T CA) and the control group (T UCA) decreased from 63.61% to 50.82% and 52.94%, respectively, and the volatile solids content decreased from 73.18% to 63.42% and 64.39%, respectively. Neutral proteinase activity decreased by 9.38% and 28.69%, and lipase activity decreased by 6.12% and 26.17%, respectively, indicating that photocatalysis helped maintain neutral proteinase and lipase activities. The Chao1 and Shannon indices showed that photocatalysis increased fungal diversity and reduced bacterial richness and diversity. The β diversity clustering analysis indicated that the bacterial community structure during the thermophilic phase in T CA differed from that in T UCA. The Kyoto Encyclopedia of Genes and Genomes annotation showed that photocatalysis has the potential to promote the synthesis and degradation of ketone bodies. Biodrying coupled with photocatalysis can improve the dewatering of sludge without negatively affecting biodegradation. [Display omitted] • Photocatalysis was applied to sludge biodrying. • The negative effects of TiO 2 addition on biodegradation and microbial communities were not observed. • Coupled photocatalysis helped the maintenance of enzyme activity. • The functional metabolism of microorganisms was analyzed using KEGG. [ABSTRACT FROM AUTHOR]

Nitrogen-rich pyrolysis of sewage sludge has a potential benefit being one way of resource utilization. But a new environmental pollutant, environmentally persistent free radicals (EPFRs), can be formed in sludge-based pyrolysis biochar. In this study, EPFRs formed in different kinds of sludge pyrolysis were investigated, and the impact of the controlled pyrolysis conditions on EPFRs was deeply analyzed, including the changing temperatures, residence times, and oxygen content. Results reveal that the F-centered, carbon-centered, as well as oxygen-centered radicals were spotted in the resultant biochar, which was dependent on pyrolysis conditions. All the biochar derived from papermaking sludge pyrolysis contribute a higher spin concentration of EPFRs, compared to other sludge-based biochar. The pyrolysis temperature of 600 °C resulted in the highest spin concentration of 6.5159 × 1016 spins/g in Municipal sludge. The residence time research showed that most EPFRs were generated in the first hour of pyrolysis treatment. In addition, the increase of a limited oxygen content could promote EPFRs formation in the resulted biochar. The findings concentration on EPFRs formation provide valuable insights for estimating EPFRs generation and associated risk during pyrolyzed sewage sludges, providing an opportunity to control EPFRs production. • Different sludge source has an impact on the evolvement of EPFRs. • A high spin concentration of EPFRs was found in papermaking sludge-based biochar. • Most EPFRs were formed in the first one hour of pyrolysis treatment. • The presence of oxygen affected the types and spin concentrations of EPFRs. • Pyrolysis temperature above 500 °C can effectively limit EPFRs forming. [ABSTRACT FROM AUTHOR]

At present, the comprehensive utilization of bulk industrial solid waste has attracted wide attention. The recycling of industrial solid waste in building materials not only provides valuable insights for the management of solid waste, but also alleviates the over-exploitation of natural clay resources in the construction industry. In this study, municipal sludge (MS) and blast furnace slag (BFS) were incorporated into kaolin clay (KC) to synthesize sustainable composite bricks, and the sintering effects and engineering properties of bricks were adjusted by changing BFS dosages. The results indicated that the addition of BFS would promote liquid glassy phase production in bricks due to the higher content of alkali/alkaline-earth metal oxides, and the ingredient, viscosity and content of liquid glassy phases could also be regulated through varying the dosage of BFS (0-15%), thereby affecting the pore structure, particle arrangement/consolidation and performance of bricks. Among all synthesized bricks, the optimum dosages of BFS, MS and KC for satisfying the building standard thresholds were 10%, 40% and 50%, with corresponding linear shrinkage, porosity, density, water absorption, compressive and flexure strengths of 12.97%, 18.15%, 1.83 g/cm3, 0.82%, 15 MPa and 38 Mpa, respectively. Finally, mechanism analysis further demonstrated that the formation and evolution of liquid glassy phases were the key responsibility for adjusting the brick micromorphology and performance. Based on this study, using MS and BFS in brick manufacturing benefited the value-added utilization of industrial solid wastes, clean protection of environments and sustainable production of building materials, providing a reference for the process optimization and potential application of MS and BFS wastes in masonry construction. [ABSTRACT FROM AUTHOR]

Municipal sludge production has been growing due to urbanization, and the sludge co-combustion process has been proven to be a promising alternative. Bituminous coal, straw, and general industrial solid waste (GISW) were used as fuel with sludge co-combustion power generation (CPG). The life cycle cost (LCC) theory and life cycle assessment (LCA) were applied to study the techno-economic and environmental impact of three CPG processes. The results show that the sludge CPG process demonstrates significant economic benefits. Using 1 ton of wet sludge as the functional unit. The net gains for using GISW, rice straw, and bituminous coal as fuel are ¥947.38, ¥261.31, and ¥135.78, respectively. However, the sludge CPG process imposes a burden on the environment, and incineration is the main stage leading to environmental degradation. Therefore, it is essential to focus on the emission of pollutants during this stage. This study can promote the economic sustainable development of sludge CPG. • Techno-economic and environmental study on co-combustion of different fuels and sludge for power generation. • The raw material collection model and economic evaluation model were established. • The economic evaluation indexes NPV, IRR, and DPP were analyzed. • The sludge CPG process has high economic benefits, while simultaneously increasing the environmental burden. [ABSTRACT FROM AUTHOR]

Pyrolysis treatment of municipal sludge is a promising sludge treatment technology. However, due to the presence of heavy metals in sludge, the practical application of sludge pyrolysis products, especially biochar, is greatly affected. In this paper, the enrichment characteristics of different heavy metals in municipal sludge and its pyrolysis biochar and their leaching characteristics in the environment were studied. The environmental risks of municipal sludge and biochar were also assessed. The experimental results revealed that pyrolysis would promote the enrichment of different heavy metals in sludge in pyrolysis biochar. And with higher pyrolysis temperature, the enrichment is stronger. But for metals with high volatility such as Hg, Cd, Se, increasing the pyrolysis temperature will reduce their enrichment. Pyrolysis can inhibit the heavy metals in sludge leaching, and the effect of pyrolysis temperature on different kinds of heavy metals is different. The leaching rates of Se, As and Cr first increased and then decreased as the temperature of pyrolysis increased. The leaching rate of Cd increased as the temperature of pyrolysis increased. Considering the leaching rate of each heavy metal, the leaching toxicity of heavy metals in pyrolysis biochar is the lowest at the pyrolysis temperature of 400 °C. The risk assessment of municipal sludge and biochar revealed that the most harmful heavy metals in the original sludge were Hg, Cd and Se, followed by Cu and Zn. Sludge pyrolysis into biochar can reduce the content of Hg, Cd and Se. The use of copper and zinc water pipes should be reduced for sewage pipe laying to decrease the contents of Cu and Zn in municipal sludge. • Higher pyrolysis temperature promotes the enrichment of heavy metals. • Pyrolysis inhibits the leaching of heavy metals from sludge. • The comprehensive leaching toxicity of heavy metals is minimum at 400 °C. • The most hazardous heavy metals in raw sludge are mainly Hg, Cd and Se. [ABSTRACT FROM AUTHOR]

Orthogonal experiments were conducted to determine for the effect of frequency, power, reaction time, and mixing ratio on the co-pyrolysis characteristics and products of bagasse and municipal sludge. After ultrasonic pretreatment, the carbon content in the sample increased and the nitrogen content decreased. The thermogravimetric analysis results revealed that the pyrolyzed ultrasonic samples only had one peak, and the maximum mass loss rate and comprehensive pyrolysis characteristic index (D) values increased. Range analysis revealed that experimental conditions of 45 kHz, 200 W, and 2 h assisted in decreasing the residue, whereas 45 kHz, 200 W, 1 h assisted in increasing D. The GC/MS results revealed that the main components of the co-pyrolyzed bagasse and sludge were hydrocarbon, ketone, phenol, ether, alcohol, aldehyde, acid, ester, furfural, furan, allose, and nitrogen-containing. The proportion of ketones, phenols and alcohols increased rather noticeably after pretreatment. The proportion of hydrocarbon, furan, allose, and nitrogen-containing compounds decreased noticeably. The acid proportion decreased when CaO was added. Lower frequencies and lower powers assisted in increasing the phenol and alcohol ratios and decreasing the acid ratio. The addition of CaO could promote the formation of phenol and alcohol, and might reduce the proportion of acid. • C content increased and the N content decreased after ultrasonic pretreatment. • Pyrolysis products include 12 compounds including hydrocarbon, phenol and alcohol. • Low frequency increases the pyrolysis performance and the phenol and alcohol ratio. • Alcohol and phenol ratio increase after adding CaO, especially under power of 500 W. [ABSTRACT FROM AUTHOR]

Both huge volume and high moisture content of municipal sludge have brought great troubles and attracted extensive concerns in the world. In this paper, the mechanical press filtration (MPF) dewatering was performed under ultrahigh pressure in order to improve the dewatering performance of municipal sludge. Low-Field Nuclear Magnetic Resonance (NMR) technique was used to study the effect of MPF parameters on dewatering performance. Based on the pore characteristics of municipal sludge, a capillary bundle model was developed to explore the mesoscopic mechanisms of MPF dewatering. The results indicate that moisture content of sludge cake decreases gradually with the increase of compressed pressure and dewatering time as well as the decrease of sludge weight , and the moisture content of municipal sludge can be reduced to as low as 30% with MPF dewatering. According to the peak and envelope area of relaxation time curve in NMR, it can be found that the size of pores decreases and the percentage of small pores increases during the dewatering process. Therefore, the capillary water cannot be removed by MPF method because the capillary pressure in very small pores increases evidently. Furthermore, the compaction degree of the outmost layer is generally higher than that of the middle layer, and the difference of moisture content between the middle and outmost layers of cake is 25%–28.4%. The present work may be helpful to understand the MPF dewatering mechanism and shed light on the new dewatering techniques of municipal sludge. Image 1 • Ultrahigh pressure mechanical dewatering of municipal sludge is performed. • Pore structures are measured with low-field nuclear magnetic resonance technique. • Effect of dewatering parameters and pressurization model are illustrated. • Pore-scale model is present to understand the dewatering mechanism. [ABSTRACT FROM AUTHOR]

• The advantages of ultrasonic technique for municipal sludge treatment are studied. • Ultrasound can improve the final biogas production. • Ultrasound can improve the efficiency of anaerobic digestion process. Ultrasonic technique has attracted wide attention due to its advantages of no secondary pollution, high decomposition speed and simple equipment in the treatment of municipal sludge. In this paper, study on ultrasound-chemical treatment for municipal sludge in investigated. Results indicate that ultrasonic waves can destroy sludge floc structure and cell walls, release intracellular organic matter, and accelerate the hydrolysis process; ultrasonic can improve the sedimentation and dewatering performance of sludge; ultrasonic wave can produce a sponge effect on sludge, which makes the water flow through the channel more easily from the wave surface, thereby agglomerating the sludge particles and increasing the particle size; ultrasound can promote coagulation; ultrasound can also improve the activity of excess sludge, and improve the efficiency of anaerobic digestion process and the final biogas production. Ultrasound-Cationic polyacrylamide (CPAM) treatment can undermine the repulsion between particles to a certain extent and destabilizes sludge flocs. In addition, the adsorption and bridging action of the flocculant CPAM further agglomerates the sludge particles, and the water in the sludge is squeezed out to be converted into free water, which further improves the dewatering performance of the sludge, thereby reducing the moisture content of the filter cake. [ABSTRACT FROM AUTHOR]

This study presents the research results acquired from conducting municipal sludge gasification in a downdraft type gasifier at pilot scale. The assessment of the results was not only focused on syngas characteristics, but also on the gasification residues: char ash and glassy material. The gasification temperature was varied from 1000 to 1150 °C during the gasification trials. The produced high quality syngas was transferred to the engine to generate the electricity. About 1 kWh electrical power was achieved for approximately 1.2 kg municipal sludge gasified. Most of the heavy metals available in the sludge was found as fixed form in the glassy material. The gasification residues evaluated as valuable materials regarding their characteristics have reuse potential for different beneficial usage alternatives. Based on the costs for the investment and operation and incomes, the return on the investment for this pilot scale system was roughly found as 3.3 years. This study showed that the municipal sludge had an important fuel merit and the energy recovery from the sludge was possible via the gasification application. In this paper, the research results were discussed in detail to make better insight to full-scale applications as a promising alternative for sludge disposal. Image 1 • The municipal sludge gasification experiments were conducted in a pilot-scale downdraft fixed bed gasifier. • The sludge showed high gasification potential. • Approximately 1 kWh electrical energy was produced per 1.2 kg sludge gasified. [ABSTRACT FROM AUTHOR]

Concentration and fraction distribution of organics and heavy metals in municipal sludge treated by modified phosphogypsum and acetic acid (signed as MPG/HAC) were studied. The results showed that MPG/HAC conditioning significantly produce synergistic enhancement effect to dissolution of unstable heavy metals wrapped in the stable colloid network. Simultaneously, after conditioning, about 45.16% of organics such as proteins, polysaccharides and humic acid in supernatant was degraded, thus dissociating large amount of active group which accelerated immobilization of dissolved heavy metals and weaken its toxicity. In addition, MPG with a porous structure could adsorb unstable heavy metals and transform them into residual fraction, leading to a considerable decrease in their mobility risk level. Besides, linear regression models showed that a strong oxidizability of sludge, and destruction of colloidal network could greatly promote dissolution of unstable heavy metals. Simultaneously, sludge oxidizability and organics degradation rate, and disintegration of extracellular polymeric substances (EPS) layer highly accelerate immobilization of unstable metals. Excepting Cd, environmental risk of Cr, Cu, Pb, Zn, Ni and As can be effectively weakened after conditioning. Additionally, MPG/HAC conditioning might be appropriate for stabilization of Cd, Cr and Zn in water supply sludge, especially for Zn. Graphical abstract Image 1 Highlights • 45.16% of organics were degraded and dissociated large amount of active groups. • Unstable heavy metals were dissolved from colloid network after pretreatment. • MPG with a porous structure could immobilize unstable metals. • Lower pH and higher oxidation-reduction potential could promote reduction of metals. • Immobilization of unstable metals was largely affected by organics variation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Char derived from municipal and industrial sludge pyrolysis examined for fuel. • Increase in pyrolysis temperature improved the thermal stability of the char. • Char reactivity increased with the accumulation of catalytic inorganic compounds. • Heavy metals transformation by pyrolysis was not significant during combustion. • Slagging and fouling tendencies of char were comparable to that of raw sludge. Abstract A comprehensive study was conducted to evaluate the fuel properties of the char produced from pyrolysis of municipal sludge (MS) and industrial sludge (IS) at different pyrolysis temperatures (500–700 °C). A detailed characterisation of the char was performed to investigate the impact of the decomposition and the accumulation of organic and inorganic compounds during pyrolysis on the fuel properties of the derived char. Increase in pyrolysis temperature increased the fuel ratios especially in the MS-derived char. On the other hand, ash accumulation resulted in decreased higher heating values (HHVs). Dehydration and decarboxylation were the main reactions, which caused the decomposition of the organic compounds in raw sludge during pyrolysis. Thermogravimetric analysis results showed that high temperature pyrolysis could improve the thermal stability of the derived char. The accumulation of catalytic inorganic compounds improved the combustion reactivity of both the IS and MS-derived char. The MS-derived char showed higher slagging and ash fouling indices compared to the IS-derived char despite the lower ash content. However, slagging and ash fouling indices of the char were comparable to that of raw sludge samples. The results indicate that the accumulation and physicochemical transformations of heavy metals during pyrolysis process would not be significantly affected during combustion of the char. For practical application in combustion, the MS-derived char has a greater potential due to considerable HHVs, improved thermal stability, efficient combustion characteristics, lower heavy metals leaching and comparable ash related issues. [ABSTRACT FROM AUTHOR]

Abstract Electrolysis is a promising technology to improve sludge dewaterability efficiently with negligible environmental impact. To intensify the electrolytic efficiency, the effect of electrolytes (NaCl, Na 2 SO 4 , NaNO 3 , and NaClO 4) on electrolysis pretreatment of municipal sludge and its mechanisms was investigated using Ti/PbO 2 electrodes. The electrolytes, which enhanced the production of oxidative radicals, showed a significant synergetic effect in reducing the capillary suction time (CST) of sludge. NaCl was distinguished from the other electrolytes since it formed a large amount of active chlorine species, which oxidized the sludge cells to improve the sludge dewaterability. The surface morphologies as well as the soluble proteins and polysaccharides were analyzed to unravel the underlying mechanisms of sludge dewaterability. Additionally, an economic assessment showed that NaCl addition in the electrolysis pretreatment can be a suitable technique for enhancing municipal sludge dewaterability. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Highlights • Determination of NH 3 and GHG emissions on-site provides more value than lab tests. • Increasing ambient temperature promotes NH 3 and GHG emissions. • Improving aeration frequency decreases GHG but promotes NH 3 emissions. • In addition to CO 2 , N 2 O is a key GHG with an 11.19–43.30% CO 2 -eq contribution. Abstract This study analyzed emissions characteristics of NH 3 and greenhouse gases (i.e. N 2 O, CH 4 , and CO 2) from a municipal sewage sludge aerobic composting plant. Samples were collected during different seasons in which ambient temperatures and aeration frequencies varied. Results revealed (1) the maximum gas emissions occurred during the mesophilic phase for N 2 O (22%–56%) and CH 4 (65%–95%), and in the thermophilic phase for NH 3 (84%–86%) and CO 2 (65%–74%); (2) raising ambient temperatures promoted emissions of NH 3 and greenhouse gases, while improved aeration frequency increased NH 3 but decreased greenhouse gas emissions; (3) CO 2 and N 2 O were found to be the key greenhouse gases emitted during aerobic composting according to assessment of the CO 2 equivalent. The results obtained from this study suggest that adjusting ambient temperature to −3 to 5 °C and aeration frequency in composting workshops can be useful approaches for the reduction of NH 3 and greenhouse gas emissions from municipal sewage sludge composting plants. [ABSTRACT FROM AUTHOR]

[Display omitted] • Composites with excellent photocatalytic performance were synthesized. • Synthesis process sequence has an effect on material morphology and properties. • Sludge-based biochar has multiple roles in the complex system. • Application to degrade humic acid provides new ideas for sludge disposal. CeO 2 /sludge-based biochar composites were prepared by a combination of carbonization and oxidation and applied to photocatalytic degradation of humic acid reactions. The effects of the preparation process sequence on the products were investigated from the perspectives of microscopic morphology and phase composition. The results showed that when the carbonization temperature was selected as 700 °C and the oxidation temperature was selected as 650 °C, accompanied by a certain holding time, structurally stable composites were obtained. In the composites, the biochar increased the adsorption property of the system, as well as facilitated the improvement of CeO 2 photocatalytic activity. The adsorption degradation rates of S ICO and S CIO on humic acid after 3 h of illumination were 57.92% and 82.88%, respectively, which were much better than those of pristine CeO 2 and pure sludge-based biochar. This study provided new path for the practical application of municipal sludge disposal products. [ABSTRACT FROM AUTHOR]

Black soldier fly larvae (BSFL) are used to digest municipal sludge, and its excretion and the sludge residue (BSFL sand) have attracted much attention. However, little research has been conducted on the quality of the BSFL sand produced with high concentrations of copper (Cu) and cadmium (Cd) and its effect on plant growth. We collected BSFL sand from previous studies to assess its feasibility as an organic fertiliser. The results showed that with the increase in Cu and Cd concentrations, pH (5.84–6.73), electrical conductivity (2.38–3.37), and organic matter (82–96%) increased continuously, moisture (20–25%), and total nutrients (4.19–5.26%, TN + P 2 O 5 +K 2 O) content decreased. Cu and Cd stress significantly (P < 0.05) reduced the content of free amino acids and fatty acids in the BSFL sand, and the germination index of cucumber seed also decreased continuously (30–73%), especially the mildew phenomenon that occurred in the Cu-1500 (mg/kg) group. In conclusion, BSFL sand can be considered a fertiliser when Cu and Cd concentrations in the initial sludge are lower than 900 and 120 mg/kg, respectively. However, considering the problems of Cu and Cd enrichment, their concentrations should be lower than 222 and 2.54 mg/kg, respectively. This study provides a theoretical basis for applying BSFL sands in agricultural production. Studies on the effects of Cu and Cd on the quality of insect and sludge co-composting products. [Display omitted] • Municipal sludge can be used as a raw material for BSFL composting. • A high concentration of Cu and Cd stress will reduce the quality of composting. • In the control group, BSFL sand meets the quality standard for fertilizer. • High EC (2.4–3.4) is the biggest problem in the final composting product. • In the initial MS, we recommend Cu and Cd below 222 and 2.54 mg/kg, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Activation of carbon cloth improves surface area for enhanced methanogenesis. • Metal-impregnation controls the efficacy of carbon cloth for methane enrichment. • Surface area dominates over electrical conductivity for improved microbial syntrophy. • Rapid adhesion of syntrophic microbes to larger surface of carbon cloth in 3 days. This study investigated the effect of metal-impregnated carbon cloth (CC) supplementation on thermophilic anaerobic digestion (AD) improvement by utilizing municipal sludge as a biomass input. Four types of metal-impregnated CC nanocomposites (Fe/CC, Ni/CC, Ni/Fe/CC, NiPcS/Fe/CC) were synthesized from activated CC (A-CC) using hydrothermal synthesis and compared with untreated CC (U-CC) to evaluate their functional significance for enhanced AD. The main factors inspected were electrical conductivity (EC) and Brunauer–Emmett–Teller (BET) surface area. A-CC had the highest surface area of 386.15 m2/g, followed by Fe/CC, NiPcS/Fe/CC, Ni/CC and Ni/Fe/CC with 140.96, 52.27, 43.52 and 36.07 m2/g, respectively. The A-CC and Fe/CC reactors produced 3.45 and 2.70 times more methane than Control (without CC) in the first 9 days. In contrast, the methane production for U-CC, Ni/CC, Ni/Fe/CC and NiPcS/Fe/CC was only 0.87, 1.26, 1.01 and 1.29 times, respectively, compared to Control. At a higher BET surface (>350 m2/g), the surface area becomes a more dominant factor, and the increase of EC value (>2.9*104 1/Ω.m) does not have an impact on methane enhancement. Microbial community analysis revealed that A-CC had the highest abundances of Syntrophomonas, Coprothermobacter and methanogenic populations, including Methanothermobacter and Methanosarcina , within 3 days compared to Control and metal-impregnated CC. There were minimal changes in microbial community composition in metal-impregnated CC compared to the U-CC. The result implies that the efficacy of CC supplementation for AD upgrading largely depends on the higher surface area compared to metal impregnation or conductivity. [ABSTRACT FROM AUTHOR]

The aim of this work was to investigate the migration and transformation of sulfur in the municipal sewage sludge during disposal in cement kiln, and better understand the emission of the sulfur related pollutants in this process. In consideration of the temperature conditions in the practical operation, municipal sewage sludge was pre-dried at 105 °C, and then dried at 210, 260 and 310 °C, co-combusted with cement raw mill at 800, 900 and 1000 °C, and 1350, 1400 and 1450 °C respectively in the laboratory. X-ray photoelectron spectroscopy (XPS) was used to determine the S2p spectral lines of the municipal sewage sludge treated in the different process. Besides, The Thermal Analysis-Thermogravimetry (DTA-TG), Back Scattered Electron (BSE) and Energy Dispersive Spectrometer (EDS) were also employed to explore the mechanism of sulfur subsistence at 1450 °C. The results indicate that sulfide, thiophene, sulfone and sulfate are mainly sulfur compound in the municipal sewage sludge dried at 105 °C. Sulfoxide, a new sulfur compound, appears after it is further dried at 210 °C. The relative contents of sulfide and thiophene are continuously declined as the drying temperature increases due to their evaporation, decomposition and transformation in this process. The transformation of sulfide and thiophene makes the relative contents of sulfoxide and sulfate accordingly increased. However, the relative content of sulfone experiences an elevating-lowering process while the dry temperature elevated from 210 to 310 °C. This case is related to its evaporation and decomposition, as well as its production for the transformation of sulfide and thiophene. In the co-combustion process, sulfide, thiophene and sulfone are entirely vanished for their evaporation, decomposition and transformation. Sulfone is still contained at 800 °C, but when the temperature unceasingly rises, it is completely decomposed or evaporated and sulfate is the only sulfur compound. The microstructures left by the gas release are also observed in the mixtures sintered at 1450 °C, however sulfate still exists even at 1450 °C. The BSE and EDS results show that the melt phase is the important contribution to the appearance of sulfate at the high temperature. These results will sever as a theoretically reference for the pollution control of the sulfur related pollutants in the disposal process of the municipal sewage sludge in cement kiln. [ABSTRACT FROM AUTHOR]

Recently, bioproduction of short-chain fatty acids (SCFA) from waste activated sludge (WAS) has attracted much attention. Many pretreatment methods were investigated to improve the hydrolysis efficiency of WAS. However, studies on sludge pretreatment employing ferrate (VI) remain limited. Therefore, this literature explored how the potassium ferrate affects the SCFA production as well as the underlying correlation between the microbial community and the system performance. It was found that the ferrate pretreatment promoted the SCFA production significantly after 8 days’ digestion from 475 mg COD/L of the control to 2835 mg COD/L at a dosage of 0.9 g/g. The analysis of extracellular polymeric substance (EPS) showed that the extracted EPS had a positive linear relationship with the final SCFA production, which indicated that the extracted EPS could be adopted as an excellent indicator to reveal the pretreatment effect of this method. The concentrations of protein and carbohydrate both showed uptrends with the increasing dosage of potassium ferrate, whereas it imposed a negative impact on the phosphate concentration, which could be explained by precipitation of Fe ion and phosphate. Terminal restriction fragment length polymorphism (T-RFLP) analysis showed that the biodiversity and population distribution evenness were reduced markedly and it further indicated that ferrate pretreatment enhanced the community function by giving rise to acid-producing bacteria, which was in accord with the observed SCFA yield. [ABSTRACT FROM AUTHOR]

Food waste has a high energy potential that can be converted into useful energy in the form of methane via anaerobic digestion. Biochemical Methane Potential assays (BMPs) were conducted to quantify the impacts on methane production of different ratios of food waste. Anaerobic digester sludge (ADS) was used as the inoculum, and BMPs were performed at food waste:inoculum ratios of 0.42, 1.42, and 3.0 g chemical oxygen demand/g volatile solids (VS). The 1.42 ratio had the highest CH 4 -COD recovery: 90% of the initial total chemical oxygen demand (TCOD) was from food waste, followed by ratios 0.42 and 3.0 at 69% and 57%, respectively. Addition of food waste above 0.42 caused a lag time for CH 4 production that increased with higher ratios, which highlighted the negative impacts of overloading with food waste. The Gompertz equation was able to represent the results well, and it gave lag times of 0, 3.6 and 30 days and maximum methane productions of 370, 910, and 1950 mL for ratios 0.42, 1.42 and 3.0, respectively. While ratio 3.0 endured a long lag phase and low VSS destruction, ratio 1.42 achieved satisfactory results for all performance criteria. These results provide practical guidance on food-waste-to-inoculum ratios that can lead to optimizing methanogenic yield. [ABSTRACT FROM AUTHOR]

Municipal sludge can be utilized as a resource despite its polluting nature. However, the presence of heavy metals lowers its resource value, and their uniform dispersion in conventional biological processes because of sludge reflux poses enormous difficulties for the subsequent separation/recovery. In this study, the enrichment strategies of Cu and Zn in simulated wastewater based on a new biological process named oxic-hydrolytic & denitrification-oxic (O1/H/O2 or O/H/O) combination were investigated and the influence mechanisms of pH, chelate, operating parameters, and denitrification reaction control were illustrated. Results showed that the amount Cu and Zn in the sludge of H reactor exceeded those of both O1 and O2 when pH of O1＜6.5. The maximum sludge-water partition coefficients (K d) of Cu and Zn in H reactor were 3128 and 3421 times when the influent concentration of NH 3 –N was at a certain value (210 mg/L NH 4 Cl for Cu and 140 mg/L NH 4 Cl for Zn). This was ascribed to the control of nitrification rate, ammonification/nitrosation in the O1 reactor, anaerobic ammonia oxidation combined with autotrophic denitrification in the H reactor, optimal hydraulic retention time (HRT) and sludge retention time (SRT). Under the pre-set conditions of water quality and operation parameters, the precipitates in the sludge were found to be Cu(OH) 2 , Zn(OH) 2 , CuS, ZnS which were theoretically and instrumentally characterized. In sum, the joint regulation of biological combination and biochemical reaction will provide new enrichment/separation strategies for heavy metals in municipal sludge management. • Cu and Zn can be enriched in the H-unit sludge of a new biological process named O/H/O process. • Enrichment of Cu and Zn was the coupling of ammonization, complexation and precipitation regulated by pH. • The O/H/O process can realize the collaborative management of wastewater and sludge. [ABSTRACT FROM AUTHOR]

A significant amount of the aqueous phase (HTAP) (∼90% by mass) produced by hydrothermal carbonization (HTC) is considered a burden. This study investigated, for the first time, the possibility of using the HTAP obtained from HTC of municipal sludge (at 180 °C and 220 °C) as liquid fertilizer in agricultural applications. The HTAP is rich in nitrogen, and its heavy metal concentration is significantly lower than the limits imposed by agricultural application standards in various countries. The highest dry weight of pakchoi (Brassica chinensis L.) was obtained when the electrical conductivity of HTAP was 0.2 mS cm−1. The HTAP has a relative abundance of 67% and 75% N-containing compounds at 180 °C and 220 °C, respectively. In hydroponics, lipid-like and aliphatic/protein-like structures, and those with low saturation, are preferentially consumed and converted into compounds with relatively high saturations, whereas S-containing compounds are difficult to remove. These findings provide new insights into the design and implementation of management strategies for HTAP. [Display omitted] • The use of the HTAP from HTC of municipal sludge as liquid fertilizer was studied. • The dry weight of pakchoi treated with HTAP at EC = 0.2 mS cm−1 was the largest. • The molecular composition of HTAP was investigated by ESI-FT-ICR MS. • S-containing compounds are difficult to be used by pakchoi. [ABSTRACT FROM AUTHOR]

With the popularization of municipal sewage treatment facilities, the improvement of sewage treatment efficiency and the deepening degree of sewage treatment, the sludge production of sewage plant has been sharply increased. Carbon emission during the process of municipal sewage treatment and disposal has become one of the important sources of greenhouse gases that cause greenhouse effect. How to reduce carbon dioxide emissions during sewage treatment and disposal process is of great significance for reducing air pollution. Kitchen waste and excess sludge, as two important organic wastes, once uses anaerobic synergetic digestion technology in the treatment process can on the one hand, avoid instability of sludge individual anaerobic digestion, improve sludge degradation rate and marsh gas production rate, and on the other hand, help increase the reduction of carbon dioxide emissions to a great extent. The paper uses material balance method, analyzes and calculates the carbon dioxide emissions from kitchen waste and sludge disposed by the anaerobic synergetic digestion technology, compares the anaerobic synergetic digestion technology with traditional sludge sanitary landfill technology and works out the carbon dioxide emission reductions after synergetic digestion. It takes the kitchen waste and sludge synergetic digestion engineering project of Zhenjiang city in Jiangsu province as an example, makes material balance analysis using concrete data and works out the carbon dioxide daily emission reductions. The paper analyzes the actual situation of emission reduction by comparing the data, and found that the synergetic digestion of kitchen waste and sludge can effectively reduce the carbon dioxide emission, and the reduction is obvious especially compared with that of sludge sanitary landfill, which has a certain effect on whether to promote the use of the technology. [ABSTRACT FROM AUTHOR]