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]

With the increasing shortage of land resources and the aggravation of soil pollution in mining areas, the remediation of soil in abandoned mining areas has gradually attracted people's attention. The remediation of heavy metal contaminated soil in mining areas is the key to reduce the harm of heavy metals to the environment and human health. In this study, municipal sludge and phytoremediation technology were combined to investigate the migration and transformation of heavy metals at the soil-plant interface in improved mining areas through indoor pot experiments. The results showed that heavy metals in non-rhizosphere soil entered the rhizosphere environment with the growth of plants, leading to the increase of heavy metal content in rhizosphere soil. The cumulative amounts of Cu, Zn, Pb and Cd were 1299.32, 832.10, 347.89 and 71.34 mg/kg, respectively. The content of oxidized Cu and Zn decreased with increasing planting days, while the oxidized Pb and Cd showed an increasing trend. Under acidic conditions, H+ is easy to compete with heavy metal ions for exchangeable positions in the clay mineral layer, so that the reducible heavy metals are easy to be converted into exchangeable states. In this paper, the effects of various factors on the distribution of heavy metals were discussed by adjusting soil pH, adding humic acid and root exudates, so as to analyse the migration and transformation mechanism of heavy metals at the soil-plant interface, and provide a reliable theoretical basis for soil remediation in mining areas. [ABSTRACT FROM AUTHOR]

The production of municipal solid waste incineration fly ash (MSWI-FA) and municipal sludge (MS) has been increasing annually, raising concerns about proper disposal. In this study, a thermal treatment method with attributes of energy efficiency and complete detoxification was applied to synergistically convert MSWI-FA and MS into precursors for the synthesis of high-strength alkali-activated materials (AAMs). The impact of mass ratios of MSWI-FA and MS on the mineralogy, microstructure, and reactivity of obtained precursors were investigated. The mechanism of alkali activation was deeply studied by characterizing the evolution of reaction products. The strength development of synthesized AAMs was characterized in a one-year time scale, as well as the environmental compatibility. The results revealed that strength, with values ranging from 12.8–33.0 MPa at 3 d, 29.5–44.1 MPa at 28 d and 39.3–54.8 MPa at 365 d. Furthermore, after one year of curing, the release of Ni, Cr, Cu, Pb, Zn, Mn, and Ba from synthesized AAMs into both deionized water and acetic acid were far below the regulatory limits in China. All these contribute to promoting the safe disposal and effective valorization of MSWI-FA and MS. [ABSTRACT FROM AUTHOR]

The management of solid waste pollution in the Yangtze River Economic Belt is crucial for the ecological environment protection and restoration campaign. In order to gain a deep understanding of solid waste management and carbon emissions along the river, this study conducts quantitative analyses on the generation characteristics, treatment and disposal features, and comprehensive environmental impacts (in terms of carbon emissions) of typical solid wastes such as domestic waste and municipal sludge. The analyses are based on data from statistical analysis and model prediction methods. The results indicate that in 2022, the total generation of domestic waste and municipal sludge in the provinces and cities along the Yangtze River was approximately 105 million tons and 5.08 million tons, respectively. It is projected to reach approximately 122 million tons and 6.46 million tons by 2025, with Jiangsu Province having the largest total generation (approximately 25.85 million tons and 1.74 million tons for domestic waste and municipal sludge, respectively). The downstream areas showed the largest gaps (approximately 13.20 million tons and 1.63 million tons). Incineration is the primary disposal method for both domestic waste and municipal sludge, accounting for around 76.1% and 77.8% on average, respectively. The total carbon emissions from domestic waste and municipal sludge are estimated to reach 22.89 million tons and 90.21 million tons, respectively, with unit emission intensities of approximately 0.24 CO_(2-eq) t/ t and 2.21 CO_(2-eq) t/ t. Based on the generation characteristics and carbon emission intensities of domestic waste and municipal sludge in various provinces and cities along the Yangtze River Economic Belt, this paper proposes optimization management recommendations to promote low-carbon treatment and disposal of solid waste in the Yangtze River Economic Belt.

In order to prevent ecological environment pollution and water resource waste effectively, the study of pyrolysis treatment technology is of great significance in guiding the scientific treatment of municipal sludge. Thermogravimetric analysis was used to investigate the TG (thermogravimetric analysis) and DTG (derivative thermogravimetry) curves of five typical municipal sludges in Chongqing under different heating rates. The distribution characteristics of volatile analysis parameters such as characteristic index D, comprehensive combustion characteristic index, activation energy, and pre-exponential factor under pyrolysis and combustion conditions were analyzed, revealing its pyrolysis and combustion characteristics and kinetic laws. The results show that the volatile and ash contents of the five municipal sludges is higher, while the fixed carbon content is lower. As the heating rate increases, the comprehensive pyrolysis and combustion performance of various sludges improve. Based on the pyrolysis and combustion characteristics parameters at all heating rates, the comprehensive pyrolysis performance of Tuzhu and Yudong sludge is the best, while Tangjiaqiao sludge exhibits the best comprehensive combustion performance. Kinetic analysis are used to toinvestigate regular pattern, the results show that the average activation energy of the pyrolysis process for Yudong sludge is lower than the other four types of sludge, at 112. 34 kJ/mol. Similarly, the average activation energy of the combustion process of Tangjiaqiao sludge is lower than the other four types of sludge, at 67. 46 kJ/mol. It is concluded that Yudong and Tangjiaqiao sludge exhibit excellent pyrolysis and combustion characteristics, respectively. [ABSTRACT FROM AUTHOR]

In the process of sewage treatment, a large amount of activated sludge will be produced, the problem of high treatment cost will inevitably arise due to the large output of sludge. The traditional sludge treatment method is to dry the sludge left by the water treatment process and then incineration, landfill, which will not only occupy a lot of land resources, but also produce harmful substances or gases will cause impact on the surrounding environment and soil, so it is necessary to take some reasonable pretreatment measures before sludge treatment. Sludge pretreatment can destroy the floccule stable structure in the sludge more effectively, release as much water in the sludge as possible, and then reduce the output of the sludge and the impact of it on the surrounding environment in the subsequent resource treatment process. The relevant technologies of sludge pretreatment in present are summarized from the physical aspects, providing some ideas for the scientific research and utilization of sludge pretreatment. [ABSTRACT FROM AUTHOR]

The production of municipal sludge is increasing with the development of urbanization in these years. The municipal sludge usually has a high moisture content and contains large number of organic pollutants. Inappropriate treatment methods will lead to secondary pollution. Conventional mechanical dehydration can hardly meet the moisture content requirements for subsequent disposal. Flocculation is widely used in the sludge dewaterability enhancement for its economic efficiency and reliability. This paper provides a comprehensive review of flocculation-based techniques for municipal sludge dewatering. Firstly, the advantages and disadvantages of pretreatment techniques is elaborated. Even though flocculation is widely applied in sludge dewatering, deep dehydration always faces bottleneck in area such as removing cell bound water and changing the structure of EPS, etc. when using individual flocculation. Limited understanding of mechanisms and behaviors of joint technology of flocculation and physical/chemical/biological methods, have been highlighted as knowledge gaps in sludge dewatering. Some specific cases, mechanisms of action, practical considerations, dewatering effects and economic analyses of flocculation-coupled multiple technologies for deep sludge dewatering are analyzed in detail, Finally, the limitations, challenges and outlook of flocculants applied in sludge dewatering are comprehensively discussed. [ABSTRACT FROM AUTHOR]

This research aimed to examine the compound effects of polyacrylamide (PAM) and cadmium (Cd) on plant growth subsequent to the mixing of municipal sludge with soil and to explore the potential ecological risks associated with the use of sludge. A pot experiment was performed wherein four gradients (0, 5, 15, and 20 g/[kg dry sludge]) were established corresponding to different PAM concentrations to assess the effects on the physiological and biochemical parameters of Brassica campestris L. ssp. chinensis Makino and Brassica campestris L. and the effects on Cd and PAM concentrations in soil. The findings indicated that the biomass of both plants increased when the total PAM concentration ranged from 5 g to 15 g/(kg dry sludge). Concurrently, polyacrylamide (PAM) downplayed the uptake of Cd by the plants, reduced phytotoxicity, and increased the activities of antioxidant enzymes such as superoxide dismutase (SOD) and peroxidase (POD) in the roots. However, the biomass of Brassica campestris L. ssp. chinensis Makino and Brassica campestris L. decreased significantly when the total PAM concentration was exceeded 15 g/(kg dry sludge), and the toxic effect of Cd on pants was enhanced to some extent. Especially when the PAM concentration was 20 g/(kg dry sludge), apparent cell damage was observed in root cells. It was further noted that Brassica campestris L. portrayed a higher tolerance towards higher proportions of sludge compared with Brassica campestris L. ssp. chinensis Makino. Sludge holds a wider scale of applicability in landscaping than in agriculture. A fusion of polyacrylamide (PAM) and antioxidant enzymes could potentially counteract the effects of Cd within a specific concentration range, serving as a defense mechanism against stress. The data obtained from this study are crucial for unraveling anti‐stress responses and detoxification mechanisms employed by different plant species under the influence of factors such as PAM, Cd, and others, thus providing novel insights into research related to land use involving sludges. [ABSTRACT FROM AUTHOR]

Aerobic composting is one of the most potential disposal methods realizing sludge reduction, innocuity and resource utilization simultaneously. To strengthen the aerobic composting process of sludge and improve composting quality, compound bacterial agent were formed by mixing Azotobacter chroococcum,Bacillus cereus and Bacillus amyloliquefaciens with the equal ratio. The sludge was mixed with corn straw according to the volume ratio of 1 ∶ 1. 5, the moisture content of the mixture was adjusted to 60% by drying, then the mixture was inoculated with 10% compound microbial agent and put into the composting device, and the air flow is adjusted to 0. 20 L/ min for aeration fermentation for 15 d, the TN, TC, TP and TK of the sludge composting were (23. 20±0. 21) g / kg, (230. 80±0. 56) g / kg, (3. 13±0. 03) g / kg and (1. 55±0. 01) g / kg, respectively, the germination index was (129. 95±5. 42)%. Compared with the control group, the contents of nutrient substrate were increased, and the contents of heavy metals were decreased significantly, except As, other heavy metal indexes were lower than the limits of national standard of organic fertilizer. The decrease of total nitrogen, the increase of total phosphorus and the decrease of heavy metals in the compost of the compound microbial agent fermentation indicated that the compound microbial agent had the functions of nitrogen fixation, phosphorus accumulation and passivation of heavy metals, this will help to solve the problems of low composting efficiency, high nutrient loss and excessive heavy metals in municipal sludge composting. [ABSTRACT FROM AUTHOR]

Soil heavy metal pollution poses a serious threat to the eco-environment. Municipal sludge-based passivators and clay minerals have been widely applied to immobilize heavy metal contamination in soils. However, little is known about the immobilization effect and mechanisms of raw municipal sludge and clay in reducing the mobility and bioavailability of heavy metals in soils. Here, municipal sludge, raw clay and mixtures of thereof were used to remediate Pb-contaminated soil from a Pb-acid battery factory. The remediation performance was evaluated through acid leaching, sequential extraction, and plant assay. Results showed that the leachable Pb content in the soil decreased from 5.0 mg kg−1 to 4.8, 4.8 and 4.4 mg kg−1 after 30 d of remediation with MS and RC added at equal weights to give total dosage of 20, 40 wt% and 60 wt %, respectively. The leachable Pb further decreased to 1.7, 2.0 and 1.7 mg kg−1 after 180 d of remediation. Speciation analysis of the soil Pb indicated that the exchangeable and Fe-Mn oxide-bound Pb were transformed into residual Pb in the early stage of remediation, and the carbonate-bound Pb and organic matter-bound Pb were transformed into residual Pb in the later stage of remediation. As a result, Pb accumulation in mung beans decreased by 78.5%, 81.1% and 83.4% after 180 days of remediation. These results indicate that the leaching toxicity and phytotoxicity of Pb in remediated soils were significantly reduced, presenting a better and low-cost method for soil remediation. [ABSTRACT FROM AUTHOR]

To investigate the influence of carbonization process parameters on the characteristics of municipal sludge carbonization products, this study selected carbonization temperatures of 300–700 °C and carbonization times of 0.5–1.5 h to carbonize municipal sludge. The results showed that with an increase in temperature and carbonization time, the sludge was carbonized more completely, and the structure and performance characteristics of the sludge changed significantly. Organic matter was continuously cracked, the amorphous nature of the material was reduced, its morphology was transformed into an increasing number of regular crystalline structures, and the content of carbon continued to decrease, from the initial 52.85 to 38.77%, while the content of inorganic species consisting continued to increase. The conductivity was reduced by 87.8%, and the degree of conversion of salt ions into their residual and insoluble states was significant. Natural water absorption in the sludge decreased from 8.13 to 1.29%, and hydrophobicity increased. The dry-basis higher calorific value decreased from 8,703 to 3,574 kJ/kg. Heavy metals were concentrated by a factor of 2–3, but the content of the available state was very low. The results of this study provide important technological support for the selection of suitable carbonization process conditions and for resource utilization. HIGHLIGHTS Temperature and time are used to investigate the properties of carbonized sludge.; The structure and performance characteristics of the sludge changed significantly.; The EC, water absorption, particle size and calorific value tends to decrease.; Carbon content continues to decrease with the rising of temperature and time.; Heavy metals were concentrated, but the content of the soluble state was very low.;

Municipal sludge generated from wastewater treatment plants can cause a serious environmental and economic burden. A novel hybrid conditioning strategy was developed to enhance the dewatering performance of sludge, employing 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([C4mim][CF3SO3]) treatment combined with H2SO4 acidification. Following conditioning, the capillary suction time ( CST normalized ), the specific resistance of filtration (SRF), and moisture content of the treated sludge were decreased to 1.99 ± 0.24 (s·L/g TSS), 1.33 ± 0.05 (1012 m/kg), and 72.01 ± 0.94%, respectively. The results were superior to those achieved with sludge treated solely by H2SO4 acidification or [C4mim][CF3SO3] alone. The biomacromolecules within the sludge flocs were dissolved by [C4mim][CF3SO3], while simultaneously, the microorganisms were inactivated. Consequently, the colloidal-like structures of the sludge flocs were destroyed. Additionally, the ionizable functional groups of the biomacromolecules were instantly protonated by the introduced H+ ions, and their negative charges were neutralized during the H2SO4 acidification process. The presence of H+ ions promoted the weakening of electrostatic repulsion between the sludge flocs. As a result, an enhancement of sludge dewaterability was obtained after treatment with [C4mim][CF3SO3] and H2SO4 acidification. The finding of the intensification mechanism of sludge dewaterability brought by hybrid treatment of acidification and [C4mim][CF3SO3] provides novel insights into the field of sludge disposal. [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]

The production of municipal sludge is steadily increasing in line with the production of sewage. A wealth of organic contaminants, including nutrients and energy, are present in municipal sludge. Anaerobic fermentation can be used to extract useful resources from sludge, producing hydrogen, methane, short-chain fatty acids, and, via further chain elongation, medium-chain fatty acids. By comparing the economic and use values of these retrieved resources, it is concluded that a high-value resource transformation of municipal sludge can be achieved via the production of medium-chain fatty acids using anaerobic fermentation, which is a hotspot for future research. In this study, the selection of the pretreatment method, the method of producing medium-chain fatty acids, the influence of the electron donor, and the technique used to enhance product synthesis in the anaerobic fermentation process are introduced in detail. The study outlines potential future research directions for medium-chain fatty acid production using municipal sludge. These acids could serve as a starting point for investigating other uses for municipal sludge. [ABSTRACT FROM AUTHOR]

Municipal sludge is rich in nutrients and microbial populations, making it a potential soil amendment to enhance fertility. This study aimed to investigate the impact of municipal sludge application on microbial populations and assess its suitability as a fertilizer. The results indicated a significant increase in organic matter content in sandy soil after municipal sludge application (from 9.57 to 23.62 mg·kg−1). Available potassium and phosphorus levels improved from poor to intermediate, and available nitrogen reached an excellent level. Plant parameters such as wet weight, diameter, root length, and aboveground height also showed improvement with municipal sludge addition. High-throughput sequencing revealed Shannon and Simpson indices exceeding 5.26 and 0.98, respectively, across all substrates except B1, indicating enhanced microbial community structure and diversity in sandy soil. Redundancy analysis highlighted the pivotal role of total phosphorus, available phosphorus, organic matter, available nitrogen, total nitrogen, and available potassium in enriching microbial abundance and diversity. In conclusion, using municipal sludge as fertilizer is feasible and beneficial for soil safety, fertility, and microbial populations enhancement.

Dealing with municipal sludge in an effective way is crucial for urban development and environmental protection. Co-processing the sludge by burning it in a decomposition furnace in the cement production line has been found to be a viable solution. This work aims to analyze the effects of the co-disposal of municipal sludge on the decomposition reactions and NOx emissions in the decomposing furnaces. Specifically, a practical 6000 t/d decomposition furnace was taken as the research object. To achieve this, ANSYS FLUENT with a UDF (user-defined function) was applied to establish a numerical model coupling the limestone decomposition reaction, fuel combustion, and NOx generation and reduction reactions. The flow, temperature, and component field distributions within the furnace with no sludge were firstly simulated with this model. Compared with site test results, the model was validated. Then, with sludge involved, the structure and operation parameters of the decomposition furnace for the co-disposal of municipal sludge were investigated by simulating the flow field, temperature field, and component field distributions. Parametric studies were carried out in three perspectives, i.e., sludge mixing ratio, preheating furnace arrangement height, and sludge particle size. The results show that all three aspects have great importance in the discomposing process. A set of preferable values, including a sludge mixing ratio of 10%, preheating furnace height of 21.5 m, and sludge particle diameter of 1.0 mm, was obtained, which resulted in a raw material decomposition rate of 89.9% and a NO volume fraction of 251 ppm at the furnace outlet. [ABSTRACT FROM AUTHOR]

Resource utilization of sludge is critical because traditional sludge treatment methods cause a large amount of nutrient loss. This study investigated the impact of hydrochloric acid quantity, reaction temperature, and time on phosphorus release and migration from municipal sludge during hydrothermal treatment and designed a sludge disposal method for the recovery and utilization of phosphorus resources. We know that hydrochloric acid destroys the complexation of calcium and phosphorus precipitates, leading to the selective transfer of phosphorus to the liquid phase, and that the addition of 1–5% hydrochloric acid corresponds to a phosphorus extraction rate in the range of 0.3–98%. When hydrochloric acid is added, a change in temperature and reaction time has a negligible effect on phosphorus. Phosphorus can be recovered using the liquid product obtained under the optimal hydrothermal reaction conditions (adding 5% HCl at 205 °C for 30 min). After adjusting the pH value and adding the magnesium source, struvite (MgNH4PO4·6H2O) can be precipitated quickly and with high purity. At a cost of USD 27.8/ton of sludge, this method can recover 94% of the phosphorus in the sludge, and the bioavailable phosphorus ratio of the product is 93%, therefore, providing an important alternative to existing phosphorus recovery technologies. [ABSTRACT FROM AUTHOR]

Magnetite tailings and municipal sludge is two different solid wastes. Large stockpiles of magnetite tailings and municipal sludge create serious environmental problems. In this study, a new method for preparing ceramsite from magnetite tailings and municipal sludge is proposed. The effects of factors including preheating temperature, preheating time, roasting temperature, roasting time, and municipal sludge dosage on the physical properties of ceramsite were investigated. The optimal conditions for ceramsite preparation were determined as follows: magnetite tailings:municipal sludge quality ratio of 85:15, preheating temperature of 325°C, preheating time of 40 min, roasting temperature of 1120°C, and roasting time of 6 min. Under these conditions, the ceramsite with an apparent density of 1.22 g/cm3, bulk density of 0.63 g/cm3, 1‐h water absorption of 3.58%, particle strength of 231 N, and cylinder pressure strength of 3.5 MPa was obtained; the resulting ceramsite met the standard requirements and was evaluated as having high quality. A toxic leaching test indicated that the ceramsite had a much lower concentration of heavy metals than the limits described by the USA Environmental Protection Agency, meeting the environmental quality standard requirements for surface water. [ABSTRACT FROM AUTHOR]

Copyright of Chemical Engineering (China) / Huaxue Gongcheng is the property of Hualu Engineering Science & Technology Co Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The co-pyrolysis effect of municipal sludge (MS) and polyethylene terephthalate (PET) was estimated using kinetic analysis via thermogravimetric (TG) analysis and pyrolyzer-gas chromatography/mass spectrometry (Py-GC/MS). The co-feeding of MS and MS ash to PET pyrolysis decreased the PET decomposition temperature, from 427 °C to 409 °C by MS and to 420 °C by MS ash. The production amount of mono aromatic hydrocarbons (MAHs) on the pyrolysis of PET and MS was also increased by 2.5 times compared to the theoretical value by applying their co-pyrolysis. Additional use of MS ash for the co-pyrolysis of PET and MS further increased MAHs by 4.1 times compared to the theoretical value because of the radical enhancement and the catalytic effect of ash in MS. The amount of MAHs on the co-pyrolysis of PET and MS was increased by 9 times larger than the theoretical value for the co-pyrolysis of PET (0.5 mg) and MS (0.5 mg) at 500 °C by applying the increased reaction temperature (from 500 °C to 600 °C) and MS co-feeding amount (from 0.5 mg to 1.0 mg) to the pyrolysis of PET (0.5 mg). [ABSTRACT FROM AUTHOR]

To achieve high value-added resource utilization of solid waste and reduce the cost of rubber manufacturing, this study utilizes finely structured municipal sludge (MS) with small particle size and abundant organic matter as the main raw materials. Through organic surface modification, rubber reinforcing fillers with surface affinity and compatibility are prepared. The effect of the amount of coupling agent bis-(triethoxysilyl-propyl)-tetrasulfide (Si69) on the properties of modified sludge powder (Si69-MS) reinforced styrene butadiene rubber (SBR) and its reinforcing mechanism were also studied. The results showed that when the mass fraction of Si69 was 1.5% of the MS, the adhesion work between Si69-MS and SBR increased from 88.34 to 101.42 mJ m−2, and the interfacial tension decreased from 25.45 to 0.34 mJ m−2. The tensile strength of the composite SBR reached 14.86 MPa, and the elongation at break reached 1829.1%. These findings indicate that the increased interface affinity between Si69-MS and the surface of SBR improves its dispersion within the SBR matrix, promoting the formation of a highly elastic composite rubber. [ABSTRACT FROM AUTHOR]

The Quick Wash (QW) treatment extracts phosphorus (P) from manure and municipal sludge (MS), producing an organic acidified by-product with adequate nitrogen (N):P ratio to meet crop N requirements. Yet, data on crop response to N using QW by-products are lacking. We evaluated the response of annual ryegrass (Lolium multiflorum Lam.) and potential N leaching in sandy soil to N applications using raw wastes, their corresponding QW by-products, and ammonium sulfate (AMS) fertilizer. Treatments included a control (no amendment added), raw and acid-washed chicken litter, dairy and swine manure, MS, and AMS at 100, 200, and 400 kg N ha−1. We found no significant differences in annual ryegrass yield and N uptake between the raw and acidified organic QW by-products. However, ryegrass produced 4–30% more biomass with AMS than organic amendments. The total residual soil inorganic N under AMS treatments ranged between 6.3 and 67.9 mg pot−1 and accounted for 5–17% of the total N applied, but it was <1% for all the organic amendments. We found no differences in soil N leaching between raw and acid-washed forms of each organic soil amendment. Our results indicated that acidified organic QW by-products can improve environmental quality by substantially reducing the amount of applied P with no penalties for crop yield losses compared to raw manure and MS. [ABSTRACT FROM AUTHOR]

Copyright of Environmental Science & Technology (10036504) is the property of Editorial Board of Environmental Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As a by product of municipal sewage treatment, municipal sludge contains a lot of organic matter and rich nutrients such as nitrogen, phosphorus and potassium, but also contains a variety of heavy metals. After mining, the mine soil is poor and barren, therefore, a large amount of guest soil and timely fertilization are needed in ecological restoration. This paper investigates the amount of sludge products added to the guest soil by detecting the chemical composition of the guest soil, calculation, experiment, and expert argumentation. Based on the effective control of heavy metal content, the goal of utilizing and treating the urban sludge to save soil costs is achieved, which is also verified through engineering practice. The results show that it is feasible to use sludge products in improving the soil quality of the abandoned mine land. The application of sludge products not only meets the soil pollution requirements, but also enhances soil fertility to a certain extent, with good ecological restoration. The innovation is that sludge products can replace part of the substrate materials for mine restoration, and generally save about 10% 30% of soil cost. In addition, the fertilizer cost can also be reduced. Moreover, the sludge products containing about 50% water reduces the water requirement of vegetation growth and the cost of labor and equipment for irrigation during the maintenance process. Therefore, this study can be used as a reference for similar engineering practice in the future. [ABSTRACT FROM AUTHOR]

The utilization of metallurgical waste heat for urban sludge drying and dewatering not only affects the subsequent cost of sludge treatment but also provides a pathway for the rational utilization of metallurgical waste heat. The influence of different experimental conditions on sludge drying characteristics, such as drying temperature and thickness, was analyzed based on metallurgical waste heat. Based on the analysis and evaluation of the drying kinetics parameters of commonly used drying mathematical models, a modified Midilli drying kinetic model is proposed. The kinetic parameters and effective diffusivity of sludge drying were analyzed in three stages of sludge drying: rising rate, constant rate, and falling rate. By utilizing the Arrhenius equation, the relationship between the effective diffusion coefficient and thermodynamic temperature is established, revealing the apparent activation energies for the three stages of urban sludge drying as 29.772 kJ·mol−1, 37.129 kJ·mol−1, and 39.202 kJ·mol−1, respectively. This is closely related to the migration, diffusion, and mass transfer resistance of sludge moisture, indicating that the thickness of sludge accumulation affects the drying time of sludge during the treatment of municipal sludge. [ABSTRACT FROM AUTHOR]

The production of municipal sludge is steadily increasing in line with the production of sewage. A wealth of organic contaminants, including nutrients and energy, are present in municipal sludge. Anaerobic fermentation can be used to extract useful resources from sludge, producing hydrogen, methane, short-chain fatty acids, and, via further chain elongation, medium-chain fatty acids. By comparing the economic and use values of these retrieved resources, it is concluded that a high-value resource transformation of municipal sludge can be achieved via the production of medium-chain fatty acids using anaerobic fermentation, which is a hotspot for future research. In this study, the selection of the pretreatment method, the method of producing medium-chain fatty acids, the influence of the electron donor, and the technique used to enhance product synthesis in the anaerobic fermentation process are introduced in detail. The study outlines potential future research directions for medium-chain fatty acid production using municipal sludge. These acids could serve as a starting point for investigating other uses for municipal sludge.

Fluoride contamination in water is a global health concern. While many studies have used simulated fluoride-containing solutions in labs, few have conducted defluorination experiment on natural fluoride-contaminated water. In this study, we prepare three defluorination pellets (P1, P2, P3) using cement, sludge, and rice husk powder with mass percentages of 75%: 20%: 5%, 70%: 20%: 10%, and 65%: 20%: 15%, respectively, and tested their defluorination efficiency in water samples taken from the South Jiaolai River in Shandong Province, China. An outdoor experiment was conducted in May and June in Jiaozhou, Shandong Province, which lasted for 24 days. For each treatment, 10 g/L of pellets were added to 50 L of natural water samples with 3 replicates. The initial fluoride concentration of the water samples was 1.90 mg/L, and the fluoride concentration and pH value were measured every 3 days. SEM, EDS, XRD, and FTIR were used for analyzing potential defluorination mechanisms. The results showed that 3 types of pellets were effective in fluoride removal. On the 24th day, the fluoride concentrations in the water samples treated with pellets were significantly lower than that of the control group. The fluoride concentration in water samples treated with P1, P2, and P3 decreased to 0.74, 0.75, and 0.99 mg/L, respectively. AlF3 and MgF2 could be found in the composition of the pellets after the treatment of water samples, and hydroxylated metal oxides and CaCO3 both contributed to the defluorination process. The prepared pellets have potential for application in defluorination of fluoride-contaminated surface water. [ABSTRACT FROM AUTHOR]

Copyright of Clean Coal Technology is the property of Clean Coal Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the acceleration of urbanization and the continuous increase of urban population, more and more municipal sludge is produced. So it is extremely urgent to deal with municipal sludge. The contents of organic matter, ammonia nitrogen, total nitrogen, total phosphorus and unstable heavy metals in municipal sludge are reduced by adding different amounts of denitrifying bacteria. The optimum amount of denitrifying bacteria is determined to be 15 g/m³ according to the experimental results. From the single variable experiment, it is concluded that the denitrification is most favorable when the temperature is 25 ℃ and the pH of overlying water is 6.5. After comparison between single carbon source with composite carbon source, the removal rate of organic matter by adding composite carbon source is 14.1% higher than that by single carbon source. Finally, composite carbon source is selected as the carbon source of denitrifying bacteria. The sludge treated by microorganism in advance is added with quicklime for decontamination and dewatering, and cement is used as solidification material. Through the orthogonal test, the final ratio of solidified soil is 25%（sludge/dry soil）, 13% water and 8% cement, and its unconfined compressive strength in 28 days is 550.17 kPa. The treated sludge solidified soil is determined to meet the discharge standard of heavy metals after acid rain leaching, and can be used as geotechnical materials. [ABSTRACT FROM AUTHOR]

The effect of potassium ferrate (PF) and straw fiber (SF) on the strength of cement-based solidified municipal sludge, including the influence of reducing the organic matter in the sludge on the efficiency of the hydration of the cement, was studied. Single-factor tests, orthogonal tests, and linear weighted optimization methods were used to obtain suitable ratios to meet practical requirements, and then SEM and XRD analyses were used to explore the solidification mechanism. The results showed that PF and SF had significant influence on the strength, with SF having the greatest influence and the strength increasing with the amount of both admixtures, and cement had no significant influence on the strength. After linear weighting optimization, the ideal dosage was found to be 20% cement, 20% PF, and 5% SF, which produced a solidified sludge that had an strength of 126.87 kPa, far higher than the 50 kPa required to qualify for disposal in landfills. Analysis of the mineral content and microstructure showed that PF and SF could promote cement hydration and produce more hydration products, and the density of the optimized sample was much higher than that of the raw sludge and a sludge sample mixed with 20% cement alone. HIGHLIGHTS Potassium ferrate and straw fibers synergistically enhanced the effect of cement-based solidification of municipal sludge and had significant influence.; Orthogonal tests were combined with linear weighted optimization to obtain the suitable ratio.; Potassium ferrate and straw fibers could reduce the influence of organic matter in municipal sludge on cement hydration efficiency and promote cement hydration reaction.;

In thus study, municipal sludge was treated by wet oxidation coupled with alkali hydrolysis for recycling as a carbon source for biological denitrification and struvite crystallization. The effects of the reaction variables on the soluble chemical oxygen demand (SCOD) yield were investigated. To obtain the optimal reaction conditions for the SCOD yield, a response surface method was used, and a quadratic regression equation model was established. The optimal reaction conditions were as follows: H2O2 dosage: 5.9 g, reaction time: 30 min, reaction temperature: 214°C, and NaOH dosage: 2.7 g. A SCOD yield of 58% was obtained, which is consistent with the predicted value. The results indicate that an alkaline hydrolytic solution can be effectively used as a carbon source for biological denitrification. When the ratio of C/N = 6, the highest denitrification rate of 0.51 mg/(g·h) was obtained. Struvite crystallization was used to recover phosphorus from the alkaline solution. The ratio of Mg/P and pH significantly affected struvite production. The analytical results from scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy indicated that struvite was the main substance in the crystallization production. The results of this study demonstrate the feasibility of reusing sewage sludge as a carbon source and struvite. [ABSTRACT FROM AUTHOR]

Copyright of Inorganic Chemicals Industry is the property of Editorial Office of Inorganic Chemicals Industry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, amino acids, proteins, and microbial communities in sludge from different wastewater treatment plants (WWTPs) were analyzed. The results showed that the bacterial communities of different sludge samples were similar at the phylum level, and the dominant bacterial species in sludge samples with the same treatment process were the consistent. The main amino acids in EPS of different layers were different, and the amino acid results of different sludge samples were quite different, but the content of hydrophilic amino acids in all samples was higher than that of hydrophobic amino acids. And the total content of glycine, serine, and threonine related to sludge dewatering was positively correlated with protein content in sludge. In addition, the content of nitrifying bacteria and denitrifying bacteria in sludge was also positively correlated with the content of hydrophilic amino acids. In this study, the correlations between proteins, amino acids, and microbial communities in sludge were analyzed respectively, and the internal relationship was found. And it provided ideas for further study of sludge dewatering characteristics in the future. [ABSTRACT FROM AUTHOR]

Phosphate ore is a non-renewable resource, so finding a replacement is necessary. Municipal sludge has significant recycling potential because of its high phosphorus content and large discharge characteristics. The migration and transformation of phosphorus in municipal sludge treated with different concentrations of HCl were studied using the standards, measurements, and testing phosphorus extraction protocol from two aspects: phosphorus complexation and mineral form. After the hydrothermal carbonization treatment without HCl, the hydrochar retained 99.7% of phosphorus in the sludge, and the organophosphorus percentage was about 30%. In the hydrothermal carbonization treatment with the addition of 0.5–2.5% HCl, the phosphorus content in the hydrochar decreased gradually from 99.5% (46.18 mg/g) to 91.8% (64.17 mg/g) that of the original sludge, and the proportion of non-apatite inorganic phosphorus increased from 34% to 94%. Hydrochloric acid provides a low-pH environment and promotes the dissolution of calcium-related phosphorus precipitates and enhances the dehydration reaction. This study provides technical support for the recovery of phosphorus resources from municipal sludge. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To investigate the temporal behaviors of heavy metals in sewage sludge in typical cities of industrial, industrial-agricultural, agricultural, or energy focused. Samples were collected every 10 days for a period of 1 year in four types of cities of Lanzhou, Tianshui, Qingyang, and Zhangye. The average annual values for all four cities were Cd (1.59–3.16 mg/kg), Pb (41.9–55.1 mg/kg), Cr (63.8–92.0 mg/kg), Cu (75.7–92.6 mg/kg), Zn (498–612 mg/kg), and Ni (3.66–4.25 mg/kg). The highest values were observed in June for Cd, Cr, and Zn, at Lanzhou and Tianshui. At Qingyang and Zhangye, the Cd, Cr, and Zn contents were stable throughout the year. There was a similar monthly change among the four cities regarding the levels of Ni content, and it was far below the background value. The monthly fluctuations in Cd, Pb, Cr, and Zn are mainly due to street dust effect. For cities with a developed industry, the impact of street dust during the first rains of the year on sewage sludge's heavy metal content must be highlighted as being of particular importance. [ABSTRACT FROM AUTHOR]

Water in municipal sludge has an electric double layer (EDL), and can be rapidly removed via electroosmosis. However, the understanding of the physical mechanisms of electroosmosis is limited owing to the complex pore structure of sludge porous media, which may restrict the development of electric dewatering (EDW) technology. In this study, the sludge microstructure was measured using the computerized tomography technique and quantitatively characterized using fractal geometry. A new pore-scale physical model for the electroosmotic flow through sludge porous media was developed based on the EDL theory, and the analytical expressions for the electroosmotic flow rate and permeability coefficient were determined. The proposed fractal pore-scale model for electroosmotic flow was validated by comparing it with the measured electroosmotic flow rate using a self-designed EDW device for municipal sludge composed of a hydraulic system and applied electric field. The results show that the electroosmotic flow rate of sludge porous media depends not only on the applied electric field, but also on the sludge microstructure including porosity, maximum pore size, and pore and tortuosity fractal dimensions. However, the correlation between the electroosmotic flow rate and the voltage gradient was usually nonlinear, and became linear only if the tortuosity fractal dimension equaled to one (straight flow path). The electroosmotic permeability coefficient increases with an increase in porosity; however, it is lowered by the increased pore and tortuosity fractal dimensions under a certain porosity. The electroosmosis phenomenon can effectively remove part of the interstitial water and surface water in sludge porous media, and the proposed electroosmotic physical model provides a useful theoretical basis for the development of EDW technology for municipal sludge. [ABSTRACT FROM AUTHOR]

In this study, hydrogels were prepared from municipal sludge to recycle and realize the value-added utilization of the carbon components in this abundant waste material. The carbon sources were extracted from the municipal sludge using synthesised nano CaO2 as an oxidant, and the carbon sources were graft copolymerised with acrylic acid monomer using N, N'-methylenebisacrylamide as a crosslinking agent and ammonium persulfate as an initiator. The factors influencing the hydrogel preparation were investigated by single-factor experiments. Based on the results of the single-factor experiments, a hydrogel with a swelling ratio of up to 19768.4% at 12 h was prepared with an oxidant dosage of 0.20 g, a monomer dosage of 5.8 g, a neutralisation degree of the monomer of 70%, an initiator dosage of 0.15 g, and a crosslinking agent dosage of 0.15 g. The hydrogel preparation conditions were optimized using the response surface method, and the interactions between the different reaction conditions were analysed to obtain the best preparation conditions. X-ray diffraction results showed that hydrogels were amorphous in structure. Scanning electron microscopy images showed that the SiO2 particles from the sludge acted as crosslinking points between different layers of hydrogel chains. The crosslinking polymerisation and crosslinking agent worked together to form hydrogels with an inorganic-organic double network structure, and this structure was highly stretchable, resulting in hydrogels with good swelling properties. [ABSTRACT FROM AUTHOR]

To solve the problem that the traditional microbial classification and identification methods cannot output the corresponding results in time when the number of microorganisms to be identified changes, this paper studies the classification and identification methods of microorganisms in urban domestic sludge. The microorganisms in municipal sewage sludge are collected by sedimentation, and the classification standard of microorganisms in municipal sewage sludge is established. Extract the DNA sequence of microorganisms and analyze the information in the DNA sequence by PCR. Collect protozoan images in the sludge, and extract image features after pre-processing. Using DNA information characteristics and protozoan image characteristics as the basis for classification and identification, and using support vector machines to complete the classification and identification of microorganisms in urban domestic sludge, the design of methods for classification and identification of microorganisms was realized. Through comparison experiments with traditional classification and identification methods, it is proved that the studied microbial classification and identification methods can quickly respond when the number of microorganisms in the identification target changes. [ABSTRACT FROM AUTHOR]

Dealing with municipal sludge in an effective way is crucial for urban development and environmental protection. Co-processing the sludge by burning it in a decomposition furnace in the cement production line has been found to be a viable solution. This work aims to analyze the effects of the co-disposal of municipal sludge on the decomposition reactions and NOx emissions in the decomposing furnaces. Specifically, a practical 6000 t/d decomposition furnace was taken as the research object. To achieve this, ANSYS FLUENT with a UDF (user-defined function) was applied to establish a numerical model coupling the limestone decomposition reaction, fuel combustion, and NOx generation and reduction reactions. The flow, temperature, and component field distributions within the furnace with no sludge were firstly simulated with this model. Compared with site test results, the model was validated. Then, with sludge involved, the structure and operation parameters of the decomposition furnace for the co-disposal of municipal sludge were investigated by simulating the flow field, temperature field, and component field distributions. Parametric studies were carried out in three perspectives, i.e., sludge mixing ratio, preheating furnace arrangement height, and sludge particle size. The results show that all three aspects have great importance in the discomposing process. A set of preferable values, including a sludge mixing ratio of 10%, preheating furnace height of 21.5 m, and sludge particle diameter of 1.0 mm, was obtained, which resulted in a raw material decomposition rate of 89.9% and a NO volume fraction of 251 ppm at the furnace outlet.

Resource utilization of sludge is critical because traditional sludge treatment methods cause a large amount of nutrient loss. This study investigated the impact of hydrochloric acid quantity, reaction temperature, and time on phosphorus release and migration from municipal sludge during hydrothermal treatment and designed a sludge disposal method for the recovery and utilization of phosphorus resources. We know that hydrochloric acid destroys the complexation of calcium and phosphorus precipitates, leading to the selective transfer of phosphorus to the liquid phase, and that the addition of 1–5% hydrochloric acid corresponds to a phosphorus extraction rate in the range of 0.3–98%. When hydrochloric acid is added, a change in temperature and reaction time has a negligible effect on phosphorus. Phosphorus can be recovered using the liquid product obtained under the optimal hydrothermal reaction conditions (adding 5% HCl at 205 °C for 30 min). After adjusting the pH value and adding the magnesium source, struvite (MgNH4PO4·6H2O) can be precipitated quickly and with high purity. At a cost of USD 27.8/ton of sludge, this method can recover 94% of the phosphorus in the sludge, and the bioavailable phosphorus ratio of the product is 93%, therefore, providing an important alternative to existing phosphorus recovery technologies.

Due to the annual increase in wastewater treatment in most Chinese cities, a major environmental issue has arisen: safe treatment, disposal, and recycling of municipal sludge. Municipal sludge has a high content of carbon and essential nutrients for plant growth; hence, it has gained interest among researchers as a soil fertilizer. This study discusses the potential usage of municipal sludge as soil fertilizer (indicators include nitrogen (N), phosphorus (P), and trace elements) along with its shortcomings and drawbacks (potentially toxic elements (PTEs), organic matter (OM), pathogens, etc.) as well as reviews the latest reports on the role of municipal sludge in land use. The use of municipal sludge as a soil fertilizer is a sustainable management practice and a single application of sludge does not harm the environment. However, repeated use of sludge may result in the accumulation of harmful chemicals and pathogens that can enter the food chain and endanger human health. Therefore, long-term field studies are needed to develop ways to eliminate these adverse effects and make municipal sludge available for agricultural use. [ABSTRACT FROM AUTHOR]

Copyright of Advances in New & Renewable Energy is the property of Editorial Office of Advances in New & Renewable Energy and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Municipal sludge is the main by-product in the process of sewage treatment, and the primary problem to be solved for its harmless disposal or energy utilization is its poor dehydration property. In this paper, biological conditioning technology was used to ferment municipal sludge with methanogens under different carbon to nitrogen ratios (C/N) through an anaerobic fermentation system. The mechanism of improving sludge dewatering performance under fermentation and the effect of C/N of sludge on its dehydration property were investigated. The results showed that the flocculent structure of the sludge was destroyed by the fermentation of methanogens, the sludge's inherent moisture was released, and the dehydration property was promoted. With the change of C/N from 8 to 20, the hydrophilic oxygen-containing functional group content of the sludge decreased first and then increased. When C/N was 16, the content of hydrophilic oxygen-containing functional groups diminished to the lowest level. Meanwhile, the surface of the sludge showed dense microscopic cavities and small holes, indicating that the sludge flocs had been cracked to a large extent, and thus the ability of the sludge to bind water was weakened. The bound water content of the fermented sludge from low to high was 48.9, 59.0, 64.3, and 71.7% respectively, with C/N of 16, 12, 20, and 8. Therefore, within the scope of this experiment, the optimal C/N for the sludge dehydration property could be identified as around 16, which could reduce the bound water content of the sludge from 87% to 48.9%. [ABSTRACT FROM AUTHOR]

The reasonable pyrolysis temperature of sludge was determined to make the biochar have good Cu(II) adsorption capacity and maximum carbon sequestration potential. Biochar was prepared from the sludge of wastewater treatment plant in Chongqing at different pyrolysis temperatures, and its physical properties was characterized by X-ray diffraction, X-ray fluorescence and Fourier transform infrared spectroscopy, the effect of pyrolysis temperature on the adsorption of Cu(II) was evaluated by the adsorption of biochar; and the carbon sequestration potential of biochar at different pyrolysis temperatures was evaluated by carbon retention (YC), fixed carbon yield (YFC) and thermal stability. The results showed that the adsorption capacity difference of biochar for Cu(II) was little when the pyrolysis temperature was lower than 300 ℃. However, with the increase of pyrolysis temperature above 300 ℃, the adsorption capacity of Cu(II) on biochar decreased. The ash in biochar is mainly SiO2, it did not contribute to the adsorption of Cu(II) on biochar, the adsorption capacity of biochar for Cu(II) was restricted by oxygen-containing functional groups and specific surface area. In addition, YFC could comprehensively measure the carbon sequestration effect of biochar than YC or thermal stability alone. The YFC of 300 ℃ biochar was the largest and the carbon fixation effect was the best. Considering the adsorption capacity of Cu(II) and carbon sequestration potential, it was suggested that the pyrolysis temperature of biochar prepared from municipal sludge in mountainous cities should be set at 300 ℃. [ABSTRACT FROM AUTHOR]