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The acceleration of urbanization has intensified the strain on sewage treatment systems. Research on reducing, rendering harmless, and resourcefully treating organic solid waste has gained significant attention. This study begins by outlining the current state of sludge treatment in China, followed by a review of advancements in pyrolysis, biological treatment, and gasification technologies. It systematically categorizes, compares, and summarizes influencing factors, and process mechanisms of various technologies. The paper focuses on the distinctive features of different processes, emphasizing the high-value utilization of three-phase products and the optimization of reaction conditions. In addition, it provides insights into enhancing the resource utilization of sludge and solid waste, as well as optimizing treatment technologies. This paper aims to consider the ecological environment and economic benefits of the efficient treatment of solid organic waste. It provides reference for industrial application, and contributes to the building of a resource-saving and environmentally friendly society. [ABSTRACT FROM AUTHOR]

The efficiency of anaerobic digestion of sludge can be significantly improved through a combination of acid or alkali hydrolysis with low-temperature hydrothermal (LTH) pretreatment. The impact of various agents in conjunction with LTH treatment on sludge properties and high-temperature anaerobic digestion (HTAD) systems was comprehensively examined in this study. Comparative analyses reveal that NaOH-LTH pretreatment surpasses HCl-LTH pretreatment in enhancing sludge organic matter solubilization and enhancing HTAD system. Contrary to expectations, the use of acetic acid (HAc) pretreatment does not further enhance organic matter solubilization in sludge. Instead, it inhibits gas production efficiency and diminishes the removal efficiency of total chemical oxygen demand (TCOD) during HTAD. Among the pretreatments, NaOH (pH 11, 24 h)-LTH (90 °C, 30 min) co-treatment emerges as the optimal condition. This configuration results in a 12.5-fold increase in sludge soluble chemical oxygen demand (SCOD) compared to untreated samples, a 34.1% improvement in methane yield in the HTAD system, and a remarkable TCOD removal efficiency of 36.8%. Notably, this combined pretreatment induces significant alterations in the microbial community structure of the sludge HTAD system. Following NaOH-LTH pretreatment, the total relative abundance of methanogenic archaea increases from 80.2 to 92.3% compared to untreated systems. [ABSTRACT FROM AUTHOR]

The treatment of sludge is one of the main sources of carbon emissions throughout the entire life cycle of sewage treatment. This study conducted carbon emission analysis on the sludge treatment process of a sewage treatment plant in Guangzhou, China, and offered a carbon accounting boundary calculation process for the sludge called the deep dehydration–drying–incineration process. An international standard method was improved to offer a carbon emissions accounting method for direct carbon emissions, indirect carbon emissions, and carbon sink for the sludge treatment of the effluent treatment plant. Research has found that the amount of sludge treatment is directly proportional to carbon emissions and carbon sinks. When the sludge treatment capacity reaches 600 t or more, almost zero carbon emissions are achieved, and the carbon emissions generated during the incineration stage of sludge treatment are the highest in all process steps. In addition, there is a significant positive correlation between dry sludge treatment capacity and carbon emissions from drying/integration. There is a significant positive correlation between dry sludge treatment capacity and direct emissions caused by incineration, but there is no correlation with carbon emissions generated by the use of electricity/chemicals. This study offered important data support and technical reference for the resource development and low-carbon disposal regulation of sludge, and a basis for the calculation of carbon emissions throughout the entire process of sludge treatment. Practical Applications: The paper explored the carbon emission accounting method for sludge treatment. An international standard method has been improved to offer an accounting method for direct carbon emissions, indirect carbon emissions, and carbon sequestration of sludge treatment in sewage treatment plants, providing possibilities for carbon accounting throughout the entire life cycle of sewage and sludge in sewage treatment plants. The results show that the sludge treatment capacity is directly proportional to carbon emissions and carbon sinks. When the sludge treatment capacity reaches 600 t or more, almost zero carbon emissions are achieved, and the carbon emissions generated during the sludge treatment incineration stage are the highest in all process steps. In addition, there is a significant positive correlation between dry sludge treatment capacity and carbon emissions from drying/integration. There is a significant positive correlation between dry sludge treatment capacity and direct emissions caused by incineration, but there is no correlation with carbon emissions generated by the use of electricity/chemicals. The research results contribute to the resource utilization and low-carbon disposal of sludge. [ABSTRACT FROM AUTHOR]

In the realm of water supply and the management of residues arising from water treatment plants (WTP), an essential challenge lies in understanding and characterising sludge, and assessing whether these characteristics impact sludge dewatering, an essential step to reduce the management costs of these wastes. This review focuses specifically on the characterisation of sludge properties relevant to dewatering performance, addressing an underexplored aspect within recent literature on water treatment plant sludge (WTS). Unlike prior studies, which predominantly focus on sludge reuse after dewatering, this review systematically examines the direct correlations and interdependencies between sludge characteristics and dewatering outcomes, addressing gaps in literature. A bibliometric analysis of global WTS research revealed an annual average of fewer than 14 publications since 1957. Keywords related to sludge characteristics are notably scarce in connection with 'dewatering', highlighting a specific gap that this review aims to address. This review categorises sludge characteristics into 'micro-properties' and 'macro-properties', providing detailed descriptions of each. The latter primarily influence dewatering and are generally unmeasured in WTPs due to the inherent difficulties in their determination. However, it's possible to derive macro-properties from micro-properties, establishing their relationship and subsequently selecting an appropriate dewatering technique. Main findings underscore direct proportionality between: viscosity (micro) and capillary suction time – CST (macro), solid concentration – SC (micro) and CST; and inverse proportionality between: SC and specific resistance to filtration – SRF (macro). These findings contribute a refined understanding of parameters affecting sludge dewatering processes, supporting further research focused on enhancing efficiency in WTS management. [ABSTRACT FROM AUTHOR]

Sludge flocs encapsulate a significant amount of bound water, resulting in poor dewatering efficiency. To address this issue, the addition of alum (KAl(SO4)2·12H2O) has emerged as an effective strategy for enhancing sludge dewatering performance. This research specifically investigates the effects of various alum dosages on the dewatering characteristics of sludge. The introduction of alum alters internal temperature, pH levels, and intracellular osmotic pressure, which facilitates the release of trapped water within the flocs. Additionally, alum accelerates sludge sedimentation and promotes the agglomeration of smaller particles into larger ones, further improving dewatering efficiency. However, determining the optimal alum dosage for sludge conditioning is essential, as excessive amounts can lead to a decrease in dewatering performance. [ABSTRACT FROM AUTHOR]

This study investigated treatment methods for urban wastewater sludge, specifically examining natural drying over five years, accelerated freeze–thaw–drying cycles, and composting with and without a zeolite additive. The findings reveal that composting effectively stabilized the sludge while retaining essential nutrients crucial for agriculture. Notably, with the addition of 2% zeolite by total mass, approximately 40% of the total nitrogen was preserved. Adequate aeration during composting maintained acceptable levels of phosphorus compounds, with the phosphorus content expressed as P2O5 showing significant retention compared with the natural drying methods. Composting also demonstrated a substantial reduction in petroleum hydrocarbon concentrations, which decreased from 30 mg/kg to 3 mg/kg, thereby showcasing its potential for processing contaminated sludge. The inclusion of zeolite enhanced the nitrogen retention by an additional 10–20% compared with the composting without zeolite, aligning with previous studies on its effectiveness. While composting and thermal treatments, like accelerated freeze–thaw cycles, influenced the physical properties of the sludge—such as reducing the moisture content and altering the volatile substance concentrations—they did not significantly affect the heavy metal levels. Natural drying over five years resulted in reduced metal quantities, which possibly reflected changes in the wastewater characteristics over time. Given that the heavy metal concentrations remained largely unchanged, additional treatment methods are recommended when the initial sludge contains high levels of these contaminants to ensure the safe use of the final product as fertilizer. This study underscored the significant role of biochemical and microbiological processes during composting and natural drying in transforming sludge properties. Future research should focus on establishing upper contamination thresholds and exploring microbiological safety measures to enhance the viability of sludge reuse in agriculture, balancing nutrient preservation with environmental safety. [ABSTRACT FROM AUTHOR]

The use of coagulants, such as ferric chloride hexahydrate, in wastewater treatment processes is known to induce pipe corrosion and to contribute to the discoloration of treated water. This study explores alternative approaches to sludge dewatering by evaluating the effectiveness of polymeric aluminum chloride (PAC) as a coagulant and polyoxyethylene alkyl ether (POAE) as a surfactant. The impacts of coagulation/flocculation were assessed using time to filtration (TTF) and a pressure filter press. The effects of certain coagulant and surfactant dosages were studied. The inputs were in the range of 105–1750 mg/L for PAC and 28–152 mg/L for POAE, which were determined based on zeta potential (ZP) measurements. The optimal concentrations were 876 mg/L for PAC and 114 mg/L for POAE, resulting in a TTF of less than 1 min. Moreover, the effect of pH on anaerobic sludge dewaterability was investigated. At a low pH below 8, the ZP reached the maximum value, and a higher pH resulted in a reduction in ZP. Under low-pH adjustments, it was observed that the dewatering performance of the POAE surfactant improved more significantly than that of the PAC coagulant. In addition, the effect of pressure was analyzed using a pressure filter under conditions favoring POAE, with relatively lower dosages and greater cost-effectiveness. In order to evaluate the solubility of organic matter under pressurized conditions, the filtrate's removal efficiency, chemical oxygen demand (COD), and total phosphorus (TP) were investigated. Solubilization did not occur at an increased pressure of around 10 bars. The findings presented in this study provide technical assistance for sludge treatment. [ABSTRACT FROM AUTHOR]

In this manuscript, CH4 emissions from sludge treatment centres are quantified using an unmanned aerial vehicle (UAV) framework, with particular focus on anaerobic digesters and digestate storage tanks. The outcomes are compared to those obtained using the carbon accounting workbook (CAW), which is the most commonly used industry tool by UK and Irish water companies to estimate the annual greenhouse gas emissions from their process operations. Path integrated concentrations are monitored with the use of an open-path tuneable diode laser absorption spectroscopy sensor embedded on a UAV. Measurements are interpolated using geostatistics (Kriging) and coupled with the mass balance approach to estimate emissions. The findings show that the CAW seems to underestimate emissions from digestate storage tanks by up to an order of magnitude. The results also show that CH4 emissions are linked with the residence time in the tank and temperature of the digestate. This study highlights the limitations of assumptions made using current reporting methods based on the carbon accounting workbook. This study proves that the UAV framework, together with the mass balance approach, provides high spatial resolution data; it captures the dynamic nature of emissions compared to the CAW and can be a cost-effective solution to estimate CH4 fluxes compared to other sensor-based systems. [ABSTRACT FROM AUTHOR]

The effects of reaction temperature, time, and medium on the properties of sludge hydrochar were experimentally studied. The results demonstrated that hydrothermal carbonization (HTC) treatment enhanced sludge dewatering and volume reduction, with a higher water removal rate (42.8%--53.3%) observed under acidic conditions compared to neutral conditions (28.9%--45.2%). Notably, the highest dehydration rate was achieved after HTC at 240°C for 1 hour. Increased reaction temperatures and longer reaction times led to reduced hydrochar yield due to enhanced dehydration and decarboxylation reactions. The H/C and O/C atomic ratios gradually decreased as a result. Furthermore, the regular and compact structure of sludge was disrupted to varying degrees following HTC treatment, resulting in the formation of holes and grooves that increased the specific surface area, pore volume, and pore size of the hydrochar produced. Specifically, hydrochar obtained from HTC at 220°C for 1 hour exhibited the highest specific surface area (129.98 m2/g) and pore volume (0.66 cm3/g). The composition and crystalline structure of hydrochar were primarily influenced by factors such as reaction medium > reaction temperature > reaction time. With the increase of HTC reaction temperature and residence time, the volatile content of hydrochar decreased while the fixed carbon and ash content increased. The main exothermic range during combustion of hydrochar occured between 250--550°C. [ABSTRACT FROM AUTHOR]

Phosphorus is an important element for agriculture and industry, but its deposits are not uniformly distributed. Countries that do not have primary sources are dependent on imports or regeneration from secondary materials. A widely available secondary source is sewage sludge. Used environmental standards govern sludge treatment, but its inclusion in the raw material policy is often missing. We focus on the Czech Republic (a European Union member) and Japan, countries without phosphorus deposits. Based on our analysis of sewage sludge flows, legislation, and technologies used, we aimed to evaluate approaches towards sustainable phosphorus policy. We figured out that in the Czech Republic, sludge application to soil continues due to legislation deregulation and thus, various pollutants enter the soil along with the sludge. In Japan, thermal treatment predominates, but ash is not processed, and phosphorus is irreversibly lost in landfills or construction. By not implementing a functional P-recovery policy, both countries lose more than 13 % replacement of phosphorus fertilisers from their sources. [ABSTRACT FROM AUTHOR]

This study demonstrates the potential of an innovative anaerobic treatment technology for municipal biosolids (IntensiCarb), which relies on vacuum evaporation to decouple solids and hydraulic retention times (SRT and HRT). We present proof-of-concept experiments using primary sludge and thickened waste activated sludge (50-50 v/v mixture) as feed for fermentation and carbon upgrading with the IntensiCarb unit. IntensiCarb fully decoupled the HRT and SRT in continuously stirred anaerobic reactors (CSAR) to achieve two intensification factors, that is, 1.3 and 2, while keeping the SRT constant at 3 days (including in the control fermenter). The intensified CSARs were compared to a conventional control system to determine the yields of particulate hydrolysis, VFA production, and nitrogen partitioning between fermentate and condensate. The intensified CSAR operating at an intensification factor 2 achieved a 65% improvement in particulate solubilization. Almost 50% of total ammonia was extracted without pH adjustment, while carbon was retained in the fermentate. Based on these results, the IntensiCarb technology allows water resource recovery facilities to achieve a high degree of plant-wide intensification while partitioning nutrients into different streams and thickening solids. PRACTITIONER POINTS: The IntensiCarb reactor can decouple hydraulic (HRT) and solids (SRT) retention times in anaerobic systems while also increasing particulate hydrolysis and overall plant capacity. Using vacuum as driving force of the IntensiCarb technology, the system could achieve thickening, digestion, and partial dewatering in the same unit-thus eliminating the complexity of multi-stage biosolids treatment lines. The ability to partition nutrients between particulate, fermentate, and condensate assigns to the IntensiCarb unit a key role in recovery strategies for value-added products such as nitrogen, phosphorus, and carbon, which can be recovered separately and independently.

This study investigated treatment methods for urban wastewater sludge, specifically examining natural drying over five years, accelerated freeze–thaw–drying cycles, and composting with and without a zeolite additive. The findings reveal that composting effectively stabilized the sludge while retaining essential nutrients crucial for agriculture. Notably, with the addition of 2% zeolite by total mass, approximately 40% of the total nitrogen was preserved. Adequate aeration during composting maintained acceptable levels of phosphorus compounds, with the phosphorus content expressed as P2O5 showing significant retention compared with the natural drying methods. Composting also demonstrated a substantial reduction in petroleum hydrocarbon concentrations, which decreased from 30 mg/kg to 3 mg/kg, thereby showcasing its potential for processing contaminated sludge. The inclusion of zeolite enhanced the nitrogen retention by an additional 10–20% compared with the composting without zeolite, aligning with previous studies on its effectiveness. While composting and thermal treatments, like accelerated freeze–thaw cycles, influenced the physical properties of the sludge—such as reducing the moisture content and altering the volatile substance concentrations—they did not significantly affect the heavy metal levels. Natural drying over five years resulted in reduced metal quantities, which possibly reflected changes in the wastewater characteristics over time. Given that the heavy metal concentrations remained largely unchanged, additional treatment methods are recommended when the initial sludge contains high levels of these contaminants to ensure the safe use of the final product as fertilizer. This study underscored the significant role of biochemical and microbiological processes during composting and natural drying in transforming sludge properties. Future research should focus on establishing upper contamination thresholds and exploring microbiological safety measures to enhance the viability of sludge reuse in agriculture, balancing nutrient preservation with environmental safety.

Nature-based solutions (NBS) imitate natural processes and serve to generate multi-benefit values and services to the local communities. Sustainable solutions are multi-purpose measures implemented at the site, and offer communities targeted environmental water-related solutions in wastewater treatment, water retention, and pollution mitigation that result in a climate-resilient landscape. Numerous good cases combine NBS for environmental pollution mitigation, prevention, and management. They can be implemented and managed locally, and are stimulated as zero-emission and climate-resilient technology. The main areas of intervention where NBS is best applied are agricultural run-off mitigation (constructed ecosystems), wastewater and leachate treatment (constructed wetlands), revitalisation of standing water bodies (floating wetlands), stormwater retention measures (rain gardens), and nutrient reuse (sludge drying reed beds). A new report by the Sustainable sanitation Task Force (active in Global Water Partnership Central and Eastern Europe) on NBS in wastewater treatment indicates a moderate improvement in NBS application, but also relevant progress in engineering knowledge and innovation. It also estimates the application of several NBS treatment technologies for rural sanitation improvement and water reuse potentials.

At present, the treatment method for urban sludge is mainly sludge landfill, which requires the water content of sludge to be less than 60%. Therefore, many researchers have proposed different methods to reduce sludge water content. Freeze–thaw (F/T) and chemical conditioning of sludge, combined with vacuum pressure and vertically inserted drainage board, has been proven to be an effective method to reduce the moisture content of landfill sludge (LS). Based on the consolidation theory of radial drainage, the characteristics of LS in the process of vacuum preloading were studied. A method of instantaneous multistage loading was proposed. The concept of free drainage stage before consolidation drainage is proposed, and the correction of the consolidation coefficient is introduced. Finally, the rationality of the theory was verified by experimental data. The results showed that the consolidation theory is rational for deep dewatering of LS in the vacuum preloading method. The difference between sludge dewatering after F/T pretreatment and chemical pretreatment was mainly reflected in the consolidation coefficient and the free drainage stage. The sludge after F/T pretreatment has higher permeability, more water precipitation, and low moisture content after vacuum preloading. [ABSTRACT FROM AUTHOR]

Vermi-wetland is a sustainable technology for recycling excess sludge in small-town areas. Although biochar (BC) amendment into the vermi-wetland could considerably boost the effectiveness of treating sludge, its impact on the nitrogen transformation in vermi-wetland remains unclear. Hence, this study aimed to explore the mechanism and performance of BC amendment into the vermi-wetland for enhancing nitrogen transformation during excess sludge recycling. The semi-aquatic plant Acorus calamus and the earthworm Eisenia fetida were planted in the designed vertical vermi-reactor, with corncob BC added to the upper and lower layers of one vermi-reactor, in comparison with the vermi-reactor without BC. The vermi-reactor with BC significantly lowered (p < 0.05) ammonia nitrogen (NH4+-N) and nitrite nitrogen (NO2−-N) in the effluent by 1.63 and 4.85-fold, respectively, and increased considerably nitrate nitrogen (NO3−-N) in the effluent by 1.5-fold. The numbers of ammonia-oxidizing bacteria (AOB) and archaea (AOA) in the vermi-reactor with BC were greatly enriched by 6 and 1.42-fold, compared with their counterparts (p < 0.05). Moreover, nirS and nirK gene copies in the vermi-reactor with BC were considerably improved (p < 0.05) by 2.03 and 1.82-fold, respectively. BC significantly enhanced the growth of earthworms by 6.92-fold and promoted plant growth by 1.28-fold. In addition, the AOB members like Nitrosomonas and Nitrosospira and the AOA members like Crenarchaeota and Thaumarchaeota cohabited in BC. Overall, these results suggest that a vermi-reactor amended with BC could enhance the nitrification processes of excess sludge, thereby improving the treatment performance of vermi-wetland. [ABSTRACT FROM AUTHOR]

Anaerobic membrane bioreactors (AnMBRs) are formed through the combination of anaerobic digestion and membrane technology. The upgraded technology separates SRT from HRT in the anaerobic digester, shortening the treatment period, reducing the digester's volume and improving effluent quality. Furthermore, AnMBRs have a strong tolerance for the existing forms of objects and can handle liquids, high-solid materials and gases. Up to now, AnMBRs have been utilized in the treatment of various types of industrial and municipal wastewater, organic solid waste and also biogas upgrading, and they have achieved excellent performance. However, there are few studies which have discussed their multiple utilization, especially following the flow of wastewater treatment. This study summarizes the application of AnMBRs in their diverse roles in the municipal wastewater treatment process. The discussion revolves around energy generation and the fouling issue of AnMBRs in the treatment of municipal wastewater, the digestion of sewage sludge generated in conventional municipal wastewater treatment and the upgrading of biogas after anaerobic digestion. In addition to controlling operating parameters, strategies used to improve the treatment effectiveness are also introduced. Lastly, online methods for preventing membrane fouling, which is the main operational obstacle to AnMBRs' wider spread, are also discussed. This review aims to provide a fresh perspective on how AnMBRs are utilized in waste treatment. [ABSTRACT FROM AUTHOR]

Copyright of Kemija u Industriji is the property of Croatian Society of Chemical Engineers 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.)

This research examines whether ultrasonic waves can enhance the hydrolysis, stability, and dewatering of activated sludge from raw urban wastewater. Sampling and physical examination of the activated sludge that was returned to the aeration pond were carried out using ultrasonic waves that were guided at frequencies of 30 and 50 kHz for periods of 0.5, 1, 3, 5, 10, 15, and 30 min. Various tests, including volatile suspended solids, inorganic solids, volatile solids, sludge resistant time, capillary suction time, total suspended solids, total solids, and volatile soluble solids, were carried out to advance further the processes of hydrolysis, stabilization, and dehydration of samples. According to the observations, the volatile soluble solids at a frequency of 30 kHz and t = 15 min were raised by 72%. The capillary suction time of 30 and 50 kHz in 1 min demonstrated a drop of 29 and 22%, respectively. It is crucial to consider that, at 10 min and the frequency of 50 kHz, the greatest efficiency was found. The 30 kHz and 1 min yielded the optimum sludge dewatering conditions. Finally, artificial neural networks (ANN) are utilized to propose predictive models for concentration, and the results were also very accurate ( M A E = 1.37 % ). Regarding the computational costs, the ANN took approximately 5% of the time spent on experiments. [ABSTRACT FROM AUTHOR]

Based on the best dehydration effect, this study compared the adsorption phosphorus effect of sludge biochar after sludge conditioning with FeCl3, KMnO4, and cationic polyacrylamide (CPAM). This provided insights into the effects of chemical conditioning during the sludge dewatering stage on the overall phosphate adsorption of the dewatered sludge biochar. The phosphorus adsorption mechanism of the dewatering sludge biochar was analysed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy. Under the optimal pyrolysis temperature (300°C), the phosphate adsorption capacity of FeCl3-conditioned sludge biochar (SB-FeCl3) was increased 77 times of the unconditioned sludge biochar. In different solution environments (e.g. pH and coexisting anions), Phosphate adsorption of SB-FeCl3 was srtrongest when the pH of 9 and contained CO32-. Through the analysis of surface elements and functional groups, it was explained that the phosphorus removal effect of SB-FeCl3 comes from abundant active sites containing iron. Phosphorus release occurred in sludge biochar (SB) during the study. SB-FeCl3 solved SB the release of phosphorus, and improved the adsorption capacity of phosphorus. [ABSTRACT FROM AUTHOR]

As a by-product of wastewater treatment, sludge has dual attributes of pollutant and resource. Proper disposal of sludge is significant for reducing pollution and carbon emissions in sewage treatment. The sludge treatment in China has shifted from emphasis on wastewater treatment over sludge treatment to equal emphasis on sludge and wastewater treatment, and the technologies and standards system have been rapidly developed. However, against the background of carbon peaking and carbon neutrality, there remain shortcomings in sludge treatment in China. In this paper, we reviewed the current status of slug treatment in China from the aspects of urban sludge production and characteristics, slug treatment technologies, and policy and standards systems, and summarized the prominent problems of slug treatment in terms of management system, technical standards, and routes selection. Considering the development stage and international development trends, we proposed a development concept of “green and lowcarbon, resource recycling, environmental friendliness, and adapting measures to local conditions.” Corresponding key measures are also proposed. Specifically, the top-level design should be strengthened to coordinate facility planning and layout, and treatment routes should adapt to local conditions. The standards system and price subsidy mechanism for sludge treatment should be improved to clarify the division of responsibilities and strengthen the supervision mechanism. The integration level of the whole chain should be promoted by strengthening the weaknesses to form a technology model that can be applied widely. Research on frontier technologies should be conducted to innovate and upgrade the technologies and equipment for sludge disposal and recycling.

Sludge treatment is an important part of wastewater treatment and the recovery and utilization of phosphorus from wastewater treatment plant (WWTP) is a challenge for sludge treatment and product disposal. In this paper, eight Chinese typical sludge treatment projects were selected to analyze the species and fractions, and characterization of phosphorus during the sludge treatment process. Furthermore, the nutritional value of phosphorus in the sludge treatment process and the land resource utilization value of phosphorus in the sludge treatment product were discussed. The results showed that the insufficient release of phosphorus to supernatant during anaerobic digestion (AD) of sludge is an important factor restricting phosphorus recovery. Phosphorus in sludge aerobic composting treatment products is mainly in the solid phase, and the concentration effect is beneficial for the phosphorus recovery potential. Phosphorus in sludge treatment products mainly exists in the form of non-apatite inorganic phosphorus, which indicates that improving the bioavailability of phosphorus in sludge treatment products is the key to realizing the nutritional value of the sludge products. [ABSTRACT FROM AUTHOR]

The microwave enhanced advanced oxidation process (MW-AOP) has been applied to pre-treat different sludge types and high solids content. Secondary sludge not only had the highest solids and nutrient content but also yielded higher treatment efficiency than primary or mixed sludge. In the case of secondary sludge with 4% total solids (TS), the total suspended solids (TSS) concentration was reduced by 32% while soluble chemical oxygen demand concentration increased from 1% to 40% after treatment at 110°C. A high level of nutrient release was also achieved; about 65% total phosphate (TP) solubilized at 110°C. The degree of secondary sludge disintegration was dictated by temperature and hydrogen peroxide dosage. The optimal operating temperature for the system was 110°C, and sludge containing TS up to 8% was treated effectively. Secondary sludge with 8% TS had a TSS reduction of 41% after treatment at 110°C while COD solubilization was about 45%; about 55% TP was solubilized at 10 min holding time. Treatment of sludge with higher solids content would allow for handling larger amounts of sludge at a given period and reduce heating cost per unit of treated sludge. The inter-relationship between the degree of sludge disintegration and changes in chemical and physical properties was also clearly demonstrated here. The treated sludge would be an ideal substrate for anaerobic digestion or phosphorous recovery processes. High levels of nutrients (phosphorus and nitrogen) and metal release, and solids disintegration from sludge containing high solids content would make subsequent resource recovery processes more effective and economical. [ABSTRACT FROM AUTHOR]

In the light of high energy consumption in sludge drying, a new process for sludge drying coupled with pyrolysis was proposed. The factors affecting the heat transfer of combustible gas (such as pyrolysis temperature and addition rate of poplar sawdust) and the influence of heating rate on pyrolysis products and system energy consumption were analyzed through the simulation with Aspen Plus software. The results indicated that when the co-pyrolysis of poplar sawdust and sludge was carried out, the addition rate of poplar sawdust must reach 43.5 % to maintain a normal and stable operation of the system. When the pyrolysis temperature was 550 °C, the yield of pyrolysis oil as the main component of combustible gas reached the maximum of 51.7%, and the system had the maximum heating capacity of 12.619 MJ/h. Additionally, it was found that when the heating rate increased, the yield of solid residue decreased, while the overall yield of pyrolysis oil and combustible gas increased. And when the heating rate decreased, the yield of pyrolytic oil and gas also decreased. Finally, the pilot plant scale-up test results showed that at a sludge feeding rate of 3 kg/h, the desired drying goal could be achieved at a minimum of residence time of 45 min and air flowrate of 40 L/min. [ABSTRACT FROM AUTHOR]

The use of aluminum coagulants for drinking water treatment generates a large amount of sludge that is typically destined to landfills, wasting valuable urban land with potential environmental risks. An innovative approach was presented to recycling aluminum-rich sludge from water treatment, alongside coal fly ash, into bricks for construction. By varying fly ash ratios (0–50 %) and firing temperatures (900–1200 °C), optimal conditions were determined: 1050 °C firing temperature and 30 %-50 % fly ash addition. The resulting bricks meet construction material standards, boasting compressive strength (>7 MPa), porosity (15–30 %), water absorption (10–20 %), and permeability (>1.0 × 10−2 cm/s). Incorporating fly ash mitigates shrinkage and crack formation. Organic matter ignition in sludge during brick-making creates a porous structure, ideal for low-impact development like permeable pavements in sponge cities. This method promotes waste reduction, aluminum recycling, heavy metal stabilization, and sustainable urban development, offering a cost-effective solution for safe, permeable bricks. [Display omitted] [ABSTRACT FROM AUTHOR]

Municipal sludge is a sedimentation waste produced during the wastewater process in sewage treatment plants. Among recent studies, pilot and field tests showed that chemical conditioning combined with vacuum preloading can effectively treat municipal sludge. To further understand the drainage and consolidation characteristics of the conditioning sludge during vacuum preloading, a large deformation nonlinear numerical simulation model based on the equal strain condition was developed to simulate and analyze the pilot and field tests, whereas the simulation results were not satisfactory. The results of the numerical analysis of the pilot test showed that the predicted consolidation degree was greater than that measured by the field tests, which is attributed to the relatively low permeability layer formed during the preloading process of the prefabricated vertical drain. To better reflect the consolidation process of the conditioned sludge, a simplified analysis method considering the low permeability layer around the prefabricated vertical drain was proposed. The initial permeability coefficient of the low permeability layer is determined via numerical simulations using finite difference method. The predicted settlement curve was in good agreement with the measured results, which indicated that the numerical simulation based on the equal strain condition considering the relatively low permeability layer can better analyze the consolidation process of ferric chloride-conditioning sludge with vacuum preloading. [ABSTRACT FROM AUTHOR]

At higher ammonium concentrations, nitritation can be easily attained by picking out the inhibitor. In low-concentrated reactors, nitrite accumulation without using any chemical inhibitor is a challenging process. In this study, two continuous stirred-tank reactors (CSTR) with biofilm and without biofilm were operated with total ammonium nitrogen feed concentrations of ~50 mg/L and ~30 mg/L and effluent concentrations of ~1 mg/L. A CSTR without biofilm was operated in three phases. In phase 1, a substrate-shock concentration of 1 to 2000 mg total ammonium nitrogen (TAN)/L was tested. It was found that the shock concentration was not successful in long-term operations because nitrite-oxidizing bacteria (NOB) recovered rapidly. In phases 2 and 3, the sludge-treatment method was applied, and a high nitrite accumulation efficiency was achieved (~98%). In a CSTR with biofilm, the free ammonia shock concentration was ~91.7 mg/L, and a nitrite accumulation efficiency of ~90% was achieved. [ABSTRACT FROM AUTHOR]

On-site sanitation systems such as pit latrines are extensively used around the world, while there is a growing number of evidence documenting the impact of pit latrines on groundwater quality that may affect human health. Hence, this paper summarizes the various safe-sanitation technologies by broadly categorizing them into fecal pathogen disinfection methods (anaerobic digestion, chemical disinfection, biological additives, solar pasteurization and vermicomposting) and capturing methods (pit lining and permeable reactive barriers, the latter of which simultaneously capture and sanitize fecal sludge in pit latrines). While some of the reviewed technologies have been widely practiced for mitigating microbial contamination of the groundwater, others are still in the early stage of commercialization and field validation. Though there are challenges to the selection and adoption of the most appropriate technology, this paper discusses the readiness of each technology as a stand-alone fecal sludge management solution. HIGHLIGHTS Pit latrines impact groundwater quality that may affect human health.; Low-cost treatment techniques are discussed to capture and treat pathogens in pit latrines.; Pit liners such as peat, clay, hydrophobic membranes and permeable reactive barriers help capture pathogens.; When compared with other methods, the chemical disinfection method with chlorine, lime, Ikati and Soda ranked best with the highest score.;

In order to effectively solve the increasingly serious environmental problems caused by sewage sludge emissions, the deep dewatering technology of urban sludge was reviewed at home and abroad in recent years, focusing on the mechanism of physical, chemical, biological and other combined technologies on deep dewatering of sludge, the dewatering effect, advantages and disadvantages of different dehydration methods were also compared in detail. It provides a theoretical reference for the sustainable development of sludge treatment and disposal technology. It is pointed out that for complex and changeable sludge, it is an important direction for future development to clarify its physical and chemical properties and dynamic change characteristics, develop efficient and low-consumption conditioning technology, and establish accurate analysis methods. [ABSTRACT FROM AUTHOR]

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Background and Objective: Wastewater treatment and stabilization always imposes costs and consequently a lot of energy on wastewater treatment plants. To achieve the purification and stabilization of as much sludge as possible, breaking complex components into simpler components is considered a critical step. Therefore, this study aimed to evaluate the feasibility of treating the produced sludge in the municipal wastewater treatment plant using ozonation method. Materials and Methods: In this study, sludge was obtained from the return line of activated sludge from the wastewater treatment plant in the south of Tehran. An ozonation generator with a discharge rate of 3 L/min and an ozone concentration of 40-35 mg/L was discharged to the reactor and the residual ozone concentration was measured by iodometric method. Finally, the total suspended solids and volatile, soluble chemical oxygen demand, total organic carbon, and biochemical oxygen demand during ozonation processes were measured using the Standard Method. Results: The results of this study showed that the amount of TSS and VSS in the activated return sludge decreased from 4060 to 2100 mg/L and from 3300 to 1850 mg/L during the ozonation process, respectively. However, SCOD, TOC, and SBOD had an upward trend of about 18, 11.7, and 14 times in the same reaction time, respectively. Conclusion: According to the results of this study, it can be concluded that the ozonation system can be proposed as a suitable process for the decomposition of sludge produced in wastewater treatment plants and increasing the biodegradability of these sludges.

The huge worldwide use of antibiotics triggers the accumulation of these substances in sludge from wastewater treatment plants (WWTP) and the possible contamination of soils amended with it, as well as of crops growing in these soils. In this work we analyzed the presence of the antibiotics amoxicillin (AMO), cefuroxime (CEF), ciprofloxacin (CIP), clarithromycin (CLA), levofloxacin (LEV), lincomycin (LIN), norfloxacin (NOR), sulfadiazine (SUL), and trimethoprim (TRI), in sludge from different WWTPs in Galicia (NW Spain), as well as in sludge technically treated by waste-managers, in soils where treated sludge was applied, and in crops (corn and vineyard) growing in the amended areas. The antibiotics were quantified by means of high resolution HPLC-mass-chromatography. The results indicate that almost all the sludge samples contained antibiotics, being ciprofloxacin and levofloxacin the most abundant reaching maximum values of 623 and 893 ng/g, respectively. The sludge treatment significantly reduced the number and the concentrations of antibiotics. In 12% of the soil samples where sludge was applied, some antibiotics were detected, but always in small concentrations. Regarding the crops, no antibiotic was detected in the roots, stalk, leaves and grain of corn, neither in grapes sampled in vineyards. It can be concluded that the treatments currently applied in the WWTPs under study are not totally effective in removing antibiotics from the sludge, although the findings of this research suggest that the additional specific treatment of the sludge derived from these WWTPs is effective in reducing the risk of environmental pollution due to a variety of antibiotics, and specifically in the case of soils amended with these organic materials and crops growing on it.

The minimization of sludge produced by municipal wastewater treatment plants (MWWTPs) is critical as its handling accounts for approximately 50% of the total operating cost. The challenges in predicting dewatering performance can be overcome by optimizing the sludge treatment process, especially conditioning and dewatering. This study aimed to investigate sludge dewaterability at four different MWWTPs, using a gravity drainage test unit and a bench-scale press. The effect of differently treated effluent used as a solvent to mix the flocculation polymers was observed during dewatering. The membrane bioreactor (MBR) treated effluent yielded the highest filtrate volume in the lowest amount of time, with the least polymer flocculant dosage. The Box Behnken Design model fitted the data and proved a relationship between polymer dosage, cake solids concentration, and cake height during the bench-scale press tests. Highlights The type of water used for polymer flocculant dissolution has, to an extent, a considerable impact on the gravity drainage of the sludge.; Increasing polymer flocculant dosing is not directly proportional to the cake height and cake dryness.; Significant correlation between sludge characteristics (e.g. feed solids) and the cake formed.;

The interaction between extracellular polymeric substances (EPS) in municipal sludge and antibiotics in wastewater is critical in wastewater treatment, resource recovery, and sludge management. Therefore, it is increasingly urgent to investigate the distribution coefficient (Log K) of sulfonamide antibiotics (SAs) in EPS, particularly in sludge-derived dissolved organic carbon (DOC) and aqueous phase systems. Herein, through balance experiments, the concentrations of SAs were determined using alkaline extraction EPS (AEPS) and alginate-like extracellular polymer (ALE) systems, and the Log K DOC values were determined. The results showed that the Log K DOC of AEPS was higher than that of ALE, which exhibited a negative K DOC value, indicating an inhibitory effect on dissolution. For the three SAs studied, the Log K DOC values were in the following order: sulfamethoxazole > sulfapyridine > sulfadiazine. This order can be attributed to the differing physicochemical properties, such as polarity, of the SAs. Three-dimensional excitation–emission matrix fluorescence spectra and fitting results indicated a lack of aromatic proteins dominated by tryptophan and humus-like substances in ALE. Meanwhile, the hydrophobic interaction of aromatic proteins dominated by tryptophan was the main driving force in the binding process between AEPS and SAs. [Display omitted] • The distribution characteristics of sulfonamides in two systems were different. • Proportion of tryptophan and humus-like substances is different. • Hydrophobic substances tryptophan play a key role in the binding. • The binding potential is sulfamethoxazole > sulfapyridine > sulfadiazine. [ABSTRACT FROM AUTHOR]