Sewage Sludge Treatment Processes Research Articles

Change characteristics, bacteria host, and spread risks of bioaerosol ARGs/MGEs from different stages in sewage and sludge treatment process

The spread of antibiotic resistance genes (ARGs) in the atmospheric environment has seriously threatened human health. Wastewater treatment plants (WWTPs) are an important source of aerosol ARGs. A large WWTP, including sewage treatment process (SWP) and sludge treatment process (SDP), was selected in North China for sampling in this study. The content of ARGs, mobile genetic elements (MGEs), and bacterial genera in sewage/sludge and aerosols from different process stages was detected. The possible correlation between ARGs/ MGEs and bacteria was analyzed. The risk of antibiotic-resistant bacteria was evaluated and the diffusion of ARGs/MGEs was simulated. The results showed that the concentration of ARGs/MGEs varied as the process progressed, and which in the aeration tank was relatively high. The ARGs/MGEs content in SWP aerosol (8.35–163.27 copies/m3) was higher than that in SDP (5.52–16.36 copies/m3). The main ARGs/MGEs detected in SWP aerosol were tnpA-05, tnpA-04, and ermF, while the main ARGs/MGEs detected in SDP aerosol were sul1, ermF, and blaPAO. ARGs were positively correlated with most bacteria and Escherichia coli with ARGs carries higher cytotoxicity. ARGs/MGEs mainly diffused towards the southeast, which may cause harm to urban residents with the diffusion of aerosols. This study provides clues and theoretical basis for preventing the hazards of ARGs from WWTP sources.

Comparative Environmental Evaluation of Sewage Sludge Treatment and Aggregate Production Process by Life Cycle Assessment

This study evaluated the environmental impact of landfill, incineration, and lightweight aggregate production for sewage sludge management techniques and compared the utilization of sewage-produced lightweight aggregates with natural aggregates in terms of building material production. Two scenarios were established for the life cycle assessment (LCA) of the sludge and associated product that was carried out after sludge generation. Sludge incineration and landfill deposition includes emissions from the drying, transportation, incineration of sludge, and landfill, and the production of lightweight aggregates and natural aggregates includes transportation to manufacturing facilities, the manufacturing processes themselves, and transportation of the produced aggregates to construction sites. We calculated the amount of pollutant emissions for each process in each scenario and analyzed the environmental impact index considering the environmental impact of each pollutant using the Open LCA program. The parameters used for the environmental impact index analysis for sludge management are potential acidification, climate change, eutrophication potential, human toxicity, photochemical oxidation, and stratospheric ozone depletion. The environmental impact values of lightweight aggregates (LWA) are GWP 100 441 kg CO2_Eq, AP 2.73 × 10−2 kg SO2_Eq, EP 4.46 × 10−3 kg PO4−_Eq, HTP 4.15 × 10−2 kg, 1,4-DCB_Eq, POCP 1.64 × 10−3 kg CH4_Eq, and ODP 3.41 × 10−7 kg CFC-11_Eq. We found that these values were low compared to landfill and incineration as a sewage sludge disposal method and compared to natural aggregate as a construction material production method. The environmental impact index analysis during LCA of lightweight aggregates produced from the sludge verified its positive environmental impact compared to the other potential methods of sludge management.

IDENTIFIKASI DAMPAK LINGKUNGAN PADA PROSES PENGOLAHAN LUMPUR TINJA (IPLT) JABON DENGAN METODE LIFE CYCLE ASSESSMENT (LCA)

Pengolahan lumpur tinja di IPLT adalah suatu kegiatan pengolahan lanjutanlumpur tinja di tangki septik belum layak dibuang ke lingkungan karena masihmengandung beban organik yang tinggi. IPLT Jabon Sidoarjo menjadi objek dalampenelitian dan bertujuan untuk menentukan dampak lingkungan yang ditimbulkanoleh proses pengolahan lumpur tinja di IPLT Jabon Sidoarjo dengan Metode LifeCycle Assessment (LCA). Life cycle assessment (LCA) digunakan untukmelakukan penilaian dampak lingkungan dengan metode Impact 2002+ danmenggunakan pendekatan gate to gate. Data setiap proses pengolahan dianalisisdengan software SimaPro 9.0. Kontribusi tiga dampak terbesar dari analisis LCApada proses pengolahan lumpur tinja adalah non-renewable energy, globalwarming, dan respiratory inorganic. Untuk alternatif program perbaikan yang disarankan yaitu Penerapan green building di daerah sekitar pengolahan, penggunaaninverter dalam upaya menghemat listrik, pemantauan secara berkala pembersihanataupun pembaruan pada unit pengolahan.

Design of Urban Sludge Emission Reduction Optimisation Strategy Based on Fuzzy Neural Network

Abstract Urban sewage sludge treatment is important for sustainable utilisation and virtuous cycle of freshwater resources. However, with the improvement of sewage discharge standards, ensuring stable operation of sewage sludge treatment plants is becoming an urgent problem to be solved in the sewage treatment industry. This paper proposes a FNN control framework based on different working conditions to optimise the whole process of municipal sewage sludge treatment and discharge. The framework first divides the working conditions according to the weather, forming a separate feature and an input vector together with the typical indicators of other sewage treatment plants. Then the FNN is used to complete the control and optimisation of various indicators, achieving the dual objectives of reducing energy consumption and optimising water quality. Finally, the model is tested for the tracking index of sewage flow. The results demonstrate that the FNN control method used has significantly lower MAE than the single method in the two indexes of energy consumption and water quality evaluation. This provides new ideas for the optimisation of urban sewage sludge treatment process in the future. Overall, the paper effectively highlights the importance of urban sewage sludge treatment and presents a well-designed FNN control framework for optimising the treatment process. Additionally, the paper could benefit from further elaboration on the significance of the results obtained, and suggestions for future research in this area.

Contemporary Drift in Emerging Micro(nano)plastics Removal and Upcycling Technologies from MunicipalWastewater Sludge: Strategic Innovations and Prospects.

Annually, huge amounts of microplastics (MPs) are added to farmlands through sewage sludge (SS)/biosolid applications as a fertilizer. Most research emphasizes the enormity of the problem and demonstrates the fate, impacts, and toxicity of MPs during SS treatment processes and land applications. None has addressed the management strategies. To address the gaps, the current review evaluates the performance analysis of conventional and advanced sludge treatment methods in eliminating MPs from sludge. The review uncovers that the occurrence and characteristics of MPs in SS are highly governed by factors such as population density, speed and level of urbanization, citizens' daily habits, and treatment units in wastewater treatment plants (WWTPs). Furthermore, conventional sludge treatment processes are ineffective in eliminating MPs from SS and are accountable for the increased small-sized MPs or micro(nano)plastics (MNPs) along with altered surface morphology facilitating more co-contaminant adsorption. Simultaneously, MPs can influence the operation of these treatment processes depending on their size, type, shape, and concentration. The review reveals that research to develop advanced technology to remove MPs efficiently from SS is still at a nascent stage. This review provides a comprehensive analysis of MPs in the SS, by corroborating state-of-the-knowledge, on different aspects, including the global occurrence of MPs in WWTP sludge, impacts of different conventional sludge treatment processes on MPs and vice versa, and efficiency of advanced sludge treatment and upcycling technologies to eliminate MPs, which will facilitate the development of mitigation measures from the systematic and holistic level.

Production of Cationic Starch-Based Flocculants and Their Application in Thickening and Dewatering of the Municipal Sewage Sludge

Polymer flocculants are used to promote solid-liquid separation processes in wastewater treatment technologies, and bio-based flocculants possess many advantages over conventional synthetic polymers. Potato starch microgranules were chemically modified and mechanically sheared to produce modified starch flocculants. The effectiveness of produced cationic starch (CS) and cross-linked cationic starch (CCS) flocculants in the thickening and dewatering of surplus activated sewage sludge was evaluated and compared with that of synthetic cationic flocculants (SCFs) The flocculation efficiency of SCF, CS, and CCS in sludge thickening was determined by measuring the filtration rate of treated surplus activated sludge. Comparing the optimal dose of SCFs and CCS flocculants needed for thickening, the CCS dose was more than 10 times higher, but a wide flocculation window was determined. The impact of used flocculants on the dewatering performance of surplus activated sludge at optimal dose conditions was investigated by measuring capillary suction time. The filtration efficiencies (dewaterability) of surplus activated sludge using SCF, CS, and CCS were 69, 67, and 72%, respectively. The study results imply that mechanically processed cross-linked cationic starch has a great potential to be used as an alternative green flocculant in surplus activated sludge thickening and dewatering operations in municipal sewage sludge treatment processes.

Comparative life-cycle energy and environmental analysis of sewage sludge and biomass co-pyrolysis for biofuel and biochar production

To address the gaps in current research on sewage sludge (SS) pyrolysis, this study examined the feasibility of the environmental and energy demands of co-pyrolysis as an SS treatment process. The analyses included a cradle-to-gate life cycle assessment, carbon emission and credit assessment, energy recovery calculations, and sensitivity analysis. Sawdust (SD) and wheat straw (WS) were chosen as co-feeds for the co-pyrolysis scenarios; four mixing ratios (20, 40, 60, and 80 wt%) were examined for each co-feed. The functional unit was 1000 kg of bio-oil. Mixing the co-feed biomass with SS reduced the overall environmental burden by 58–83 %; WS/SS co-pyrolysis performed better than SD/SS in this respect. All examined scenarios reduced the global warming potential (GWP) and achieved a net positive energy balance; SD/SS co-pyrolysis was more desirable owing to high energy recovery. The additional gas turbine operation generated a process energy demand of 23–224 %. GWP and terrestrial ecotoxicity potential are indicators that are significantly affected by co-feed material transportation. Sensitivity analysis revealed that the transportation of feedstock and pyrolysis products should be prioritised to limit the environmental burden of the process. Co-pyrolysis is an eco-friendly SS treatment method, and its economic viability should be further investigated.

Understanding of mercury and methylmercury transformation in sludge composting by metagenomic analysis

Municipal sewage especially the produced sewage sludge is a significant source releasing mercury (Hg) to the environment. However, the Hg speciation especially methylmercury (MeHg) transformation in sewage sludge treatment process remains poorly understood. This study investigated the transformation of Hg speciation especially MeHg in sludge composting. The distribution of Hg transformation related gene pairs hgcAB and merAB, and their putative microbial hosts were comprehensively analyzed. Both Hg (from 3.16±0.22 mg/kg to 3.20±0.19 mg/kg) and MeHg content (from 4.77±0.64 ng/g to 4.36±0.37 ng/g) were not obviously changed before and after composting, but about 19.69% of Hg and 27.36% of MeHg were lost according to mass balance calculation. The metagenomic analysis further revealed that anaerobes (Desulfobacterota and Euryarchaeota) were the mainly putative Hg methylators especially carrying high abundance of hgcA gene in the initial periods of composting. Among the 151 reconstructed metagenome-assembled genomes (MAGs), only 4 hgcA gene carriers (Myxococcota, Firmicutes, Cyclobacteriaceae, and Methanothermobacter) and 16 merB gene carriers were identified. But almost all of the MAGs carried hgcB gene and merA gene. The merA gene was widely distributed in genomes, which indicated the widespread functionality of microbes for reducing Hg(II) to Hg(0). The hgcA carrying microbes tends to present the similar metabolic pathways including methanogenesis and sulfur metabolism. Besides, both the irregular distribution of hgcA in various species (including Actinobacteria, Archaea, Bacteroidetes, Desulfobacterota, Euryarchaeota, and Nitrospirae, etc.) and opposite evolution trends between hgcA gene abundance and its host genome abundance can be an indication of horizontal gene transfer or gene deletions of hgcA during composting. Our findings thus revealed that sludge composting is not only a hotspot for Hg speciation transformation, but also a potential hotspot for MeHg transformation.

An economic and global warming impact assessment of common sewage sludge treatment processes in North America

This study details a probabilistic life cycle assessment model to evaluate the environmental (i.e., global warming potential) and economic impact of four common sewage sludge treatment methods (anaerobic digestion, incineration, composting and pyrolysis) coupled with their most common end-of-life scenarios for the North American context. The model is subsequently applied to a realistic case study where each technology is assessed over a 10-year analysis period based on data made available by a Canadian municipality. For the case study, pyrolysis and anaerobic digestion coupled with agricultural land application have an expected global warming impact at least 46% and 60% lower, respectively, than the alternative treatment methods. Conversely, composting and pyrolysis have an expected life cycle cost at least 32% and 27% lower, respectively, than the competing treatment alternatives. Composting is able to achieve its relatively low life-cycle costs through the affordability of the required capital investments; conversely, pyrolysis is able to reduce its life-cycle cost through the recovery of valuable resources such as energy, fertilizer, and fuel. These findings and the resulting tool from this work will aid decision-makers as they seek sustainable sewage sludge treatment strategies.

Comparative life-cycle assessment of pyrolysis processes for producing bio-oil, biochar, and activated carbon from sewage sludge

This study aimed to determine the feasibility of pyrolysis scenarios as sewage sludge treatment processes through cradle-to-gate life-cycle assessment and additional energy consumption, carbon emission, and economic benefit analyses, considering circular economy principles. The examined pyrolysis scenarios include slow pyrolysis with various residence times to produce activated carbon (AC) or biochar and fast pyrolysis to produce bio-oil, all with internal gas energy recovery. The functional unit (FU) in this study comprises 1000 kg of dried sludge entering the pyrolysis reactor. The overall evaluation and new product application routes address gaps in current studies on sludge treatment via pyrolysis. Environmentally, the bio-oil (-0.31 kg CO2-eq/kg FU) and biochar (-0.05 kg CO2-eq/kg FU) scenarios show considerable improvement over contemporary pyrolysis and other conventional sludge treatment methods. The AC scenarios have higher toxicity but lower carbon emissions (1.50–1.70 kg CO2-eq/kg FU) than contemporary AC production processes. Chemical reagent usage has significant effects on the environmental burden of AC production processes. The biochar and bio-oil pyrolysis scenarios achieve net energy recovery through product applications. Although the AC scenarios still require energy input, this demand can be significantly reduced by optimising moisture removal processes. Operating cost analysis indicates that the examined pyrolysis scenarios are potentially profitable. Primary product yield and market value are significant factors determining the net profit of these pyrolysis scenarios, but further assessment of capital costs is required. This study shows that bio-oil and biochar pyrolysis are eco-friendly sewage sludge treatment methods.

Enhanced hydrogen production from anaerobically digested sludge using microwave assisted pyrolysis

Sewage sludge production has increased worldwide in recent years owing to continuous increase in the number of wastewater treatment plants. In Korea, disposal of sewage sludge in landfills is prohibited. Thus, an alternative, environmental-friendly sewage sludge treatment process is needed. Given its high organic matter content, sewage sludge is a potential energy source. In the present study, a pyrolysis method was utilized to produce energy from anaerobically digested sludge. In particular, to overcome limitations of conventional pyrolysis (CP) method, the microwave-assisted pyrolysis method (MWP), which is faster and more efficient, was applied. The efficiency of CP and MWP methods was compared at 400, 600, 800, and 1000 °C. The yield of 48% H2 in the gas generated using the MWP significantly surpassed that in the gas produced using CP. When the energy required for increases in temperature and H2 yield were compared, 800 °C was found to be the optimum temperature for both the methods. The microwave utilization improved the decomposition efficiency during the pyrolysis through rapid increases in temperature and direct internal heating. The application of heating element for maintaining the temperature of MWP was possible using bio-char generated in pyrolysis. The higher efficiency of the MWP relative to the CP was attributed to the associated lower energy required to raised and maintain the pyrolysis.

Behaviour of Fossil and Biogenic Carbon in Sewage Sludge Treatment Processes and Their Impacts on Greenhouse Gas Emissions

Behaviour of Fossil and Biogenic Carbon in Sewage Sludge Treatment Processes and Their Impacts on Greenhouse Gas Emissions

Circulation of fibrous microplastic (microfiber) in sewage and sewage sludge treatment processes

The fate of microplastics (MPs) in the sewage treatment process has been investigated worldwide, and novel results have been reported; few studies have also clarified the fate of MPs in the sewage sludge treatment process. Although most MPs in sewage are transferred to sludge, some flow back from the sludge treatment process to the sewage treatment process. Therefore, throughout the sewage treatment plant, the removal rate of MPs may increase via a countermeasure during the sludge treatment process. In this study, samples obtained from sewage and sewage sludge treatments were used to degrade organic matter with hydrogen peroxide. Water sample particles were trapped on Ni filters with 20-μm-sized pores, dried at room temperature and then the MPs were detected and identified by FTIR microscopy. Note that sludge samples were treated with hydrogen peroxide and separated by specific gravity using NaI solution. The concentration of MPs per unit volume was then calculated and the MPs load was estimated using flow rates of water and sludge. Subsequently, we clarified the fate of MPs with sizes of 20 μm or greater in a sewage treatment plant. When the MPs load in the influent sewage is 100%, 12% of the MPs were found to return to the sewage treatment process via the sidestream of the sludge treatment process. Per this observation, it was made evident that MPs are in fact circulating throughout the sewage and sludge treatment processes. MPs in the sidestream mainly consisted of the effluent from the sludge concentration process, and most MPs were thought to be fibrous polyethylene terephthalate (fibrous MPs, i.e. microfibers [MFs]). The results show that MFs circulate throughout the sewage and sludge treatment processes, and for effectively increasing the removal rate of MPs, the removal of MFs proves correspondingly effective during the sludge treatment process.

Solid-Embedded Microplastics from Sewage Sludge to Agricultural Soils: Detection, Occurrence, and Impacts

Microplastics (MPs) have been increasingly identified as a global concern because of their ubiquitous distribution and the threats they pose. MPs embedded in the solid matrix remain an underexplored field compared to MPs in aquatic environments. This review focuses on solid-embedded MPs in a binary system consisting of sewage sludge and agricultural soils, which are interconnected through land application of sewage sludge to agricultural soils. The detection, occurrence, and impacts of MPs were summarized for sewage sludge and agricultural soils. Specifically, the latest techniques for detecting solid-embedded MPs are summarized and compared. The occurrence of MPs is presented from three aspects, i.e., the origin, transformation, and properties. Lastly, the impacts of solid-embedded MPs on sewage sludge treatment processes and the agroecosystem are reviewed. As a cutting-edge overview of the current knowledge, this review proposes key challenges to be further investigated with respect to solid-embedded MPs, including a uniform detection procedure, worldwide monitoring programs, rigorous assessments of potential risks, and mitigation measures through collaborative efforts by related liable parties.

Synergism of uncoupler dicoumarin and nonmetallic mineral tourmaline for the sewage sludge treatment process: Reducing sludge generation

Environmental concerns linked to the recycling of sewage sludge on land involve the hazard of nutrient leaching, impacts on soil biodiversity and greenhouse gas emissions. Sludge reduction in a wastewater treatment plant has recently received considerable attention worldwide. Large amounts of excess sludge needs to be disposed of in a cost-effective and environmentally friendly manner. In this study, dicoumarin was used as a metabolic uncoupler, its effect on the sludge reduction, effluent quality and sludge performance at the low concentration range (≤10 ​mg/L) and at high concentration (40 ​mg/L) in the sequencing batch reactor (SBR) system was investigated. It showed that Yobs was decreased with high dicoumarin concentration. Chemical oxygen demand (COD) and total nitrogen (TN) removal efficiency are also decreased while the sludge activity was enhanced. Tourmaline, a low cost natural nonmetallic mineral with unique physical properties and a promising environmental material could improve the negative effects caused by high concentration of dicoumarin without increasing the sludge yield in the SBR system. Synergistic effect of tourmaline with high concentration dicoumarin showed COD and TN removal efficiency increase. Yobs value was 0.13. The decrease in nitrite accumulation and increase in microbial activity may correlate to the existence of electrostatic fields and far infrared rays generated by tourmaline. Tourmaline also improved the sludge settling performance due to its adsorption characteristics. Effect of optimum environmental conditions; pH (6.5 ​± ​0.3, 7.5 ​± ​0.3, and 8.5 ​± ​0.3), temperature (15 ​°C, 25 ​°C, and 35 ​°C) and other factors on the synergistic action of dicoumarin and tourmaline was also studied. It is recommended to use dicoumarin as the main component and tourmaline as the auxiliary component. The synergistic effect of the two can solve the negative impact caused by the uncoupling agent administration alone.

Adsorptive purification of heavy metal contaminated wastewater with sewage sludge derived carbon-supported Mg(II) composite.

A rod-like SDBC-Mg(II) composite was synthesized and optimized in the conditions of 25% Mg(II) loading and 500 °C calcination temperature. As-prepared SDBC-25%Mg(II)-500 adsorbent attained equilibrium in 30 min, with an extraordinary capacity of 2931.76 mg g-1 (Pb(II)) and 861.11 mg g-1 (Cd(II)), revealing a promising adsorbent for the removal of such metals so far. The adsorption kinetics was well described by the pseudo-second-order model while the adsorption isotherm could be fitted by Redlich-Peterson model. Furthermore, SDBC-25%Mg(II)-500 has a high anti-interference and selectivity in the presence of competing ions/other environmental factors and, also effectively eliminates >99% of Pb2+, Cd2+, Ag+ and Cu2+ ions from pond water, lake water and tap water. The adsorption process demonstrated a synergetic adsorption mechanism comprised of ion exchange with Mg(II), coordination with surface and inner carboxylic or carbonyl functional groups and co-precipitations as metal silicates, which is responsible for its superb adsorption performance. Besides, surface carvings of Mg(II) and tunnels on the rods resulting from the sludge carbonization provided a high surface area (91.57 m2 g-1), extra sorption sites and room for easy pollutant diffusion which contributed to surface physical adsorption. Furthermore, this technique demonstrate an alternative pathway that will relieve the burdens of sewage sludge treatment process and turn this solid waste into highly efficient adsorbent for eliminating heavy metal ions from wastewater. This can be considered as a feasible waste resource utilization to meet with the requirement from both ecology and economy for auspicious applications in industries.

Life cycle assessment of sewage sludge treatment in China

Taking sewage sludge (SS) as the research object, establish 6 scenarios of sludge treatment, S1: concentration and dehydration-cement preparation (CdCpd); S2: concentration and dehydration-lime stable-cement preparation (CdLsCpd); S3:concentration and dehydration-drying-landfill (CdDrL); S4: concentration and dehydration-drying-incineration-landfill (CdDrIL); S5: concentration and dehydration-drying-incineration-concrete preparation (CdDrICp); S6: concentrate-anaerobic digestion-land use (CALu), LCA is used to compare the environmental impacts of S1-S6 in China, find the unit that has a greater impact on environment in different treatments and substances and energy that have a greater impact on the environment in different units. The results show that the environmental impacts dealing with 1t SS (water content 80%) can be sequenced as S3 > S4 > S5>S6 > S1 > S2; the direct pollutants generated in the unite of direct landfill and incineration and the thermal energy required for drying have a great impact on the environment; after a series of treatments of SS for concrete preparation and cement preparation, that is, resource utilization can fix certain elements in the sludge, so that the environmental impact can be alleviated; the transfer of contaminants during the SS treatment process is a matter of concern, so that the focus of the SS treatment should be on the fixation of pollutants in the future.

Enhancement in adsorption potential of microplastics in sewage sludge for metal pollutants after the wastewater treatment process

Microplastics (MPs) as new pollutants of environmental concern have been widely detected in sewage sludge, and may act as significant vectors for metal pollutants due to their adsorption property. Our findings show that Cd, Pb, and Co, but not Ni, contents in sewage sludge are lower than that of corresponding metal irons adsorbed on sludge-based MPs, indicating that the MPs accumulate such metal pollutants as Cd in the sludge samples. In contrast to virgin MPs, sludge-based MPs are one order of magnitude higher adsorption capacity for Cd, which reaches up to 2.523 mg g−1, implying that there is a considerable enhancement in adsorption potential of the MPs for metals after the wastewater treatment process. SEM analysis shows that sludge-based MPs have rougher and more porous surface than virgin MPs, and FTIR spectra reveal that functional groups such as CO and OH are found on sludge-based MPs. Further, two-dimensional FTIR correlation spectroscopy indicates that CO and NH functional groups play a vital role in the process that sludge-based MPs adsorb Cd, which are not found in virgin MPs. The results imply that increased adsorption potentials of the sludge-based MPs to Cd are attributed to changes in the MP physicochemical properties during wastewater treatment process. In addition, such factors as pH value, and sludge inorganic and organic components also have an effect on the MP adsorption to Cd. Principal component analysis shows that the MPs could be divided into three categories, i.e. polyamide, rubbery MPs (polyethylene and polypropylene) and glassy MPs (polyvinyl chloride and polystyrene). Their adsorption potentials to Cd follow the decreasing order: polyamide > rubbery MPs > glassy MPs. In summary, these findings indicate that MPs may exert an important influence on fate and transport of metal pollutants during sewage sludge treatment process, which deserves to be further concerned.

Operation performance of an A/O process combined sewage sludge treatment and phosphorus recovery using human urine

A novel sewage sludge treatment process is developed in which sludge anaerobically phosphorus (P) released with the temperature control/ultrasonic treatment and recovery with human urine are incorporated to a conventional anaerobic/aerobic (A/O) process. The results showed that temperature affected the anaerobic P release and the maximum orthophosphate (PO4 3-P) release rate was 21.68 mg PO4 3-P/(g MLVSS.h) at 20 °C. The optimal specific energy of ultrasonic treatment was 15,000 kJ/kg TS, at which the solubilization degree of soluble chemical oxygen demand (SCOD) was 37.93%, which verified that the anaerobic sludge flocs were broken and the organic matter was obviously released. Human urine and P-rich sludge stream could be verified as a feasible way of P recovery in the form of struvite. The output of P in the combined A/O treatment process consisted of three pathways (i.e., effluent wastewater, sewage sludge, and P recovery). The influent P could be recovered by 22.84% and about 1.48 g/d potential struvite could be recovered from the anaerobic sludge flow using 0.27 L/d-human urine. The mass balances of COD and nitrogen (N) indicated that the combined A/O process also improved the organic mineralization and the removal of N.

A two-step process for sewage sludge treatment: Hydrothermal treatment of sludge and catalytic hydrothermal gasification of its derived liquid

The worldwide increase in amount of sewage sludge has recently attracted considerable interest in developing an efficient and economical sludge disposal method. A sewage sludge treatment process combining the hydrothermal treatment (HT) of sludge and the catalytic hydrothermal gasification (CHTG) of its derived liquid (HT&CHTG-Process) is proposed in this paper. Liquid hourly space velocity (LHSV) value of 25–100 h−1 and liquid flow rate of 10–40 mL/min were employed with a self-designed CHTG experimental setup. During the first stage of the HT-Process, approximately 56% of the carbon in the sludge was transferred into the derived liquid at 300 °C. During the second stage of the CHTG-Process, the derived liquid was gasified into CH4, H2, and CO2 using a Ni/carbon catalyst, and the carbon conversion reached 88% at 350 °C and 20 MPa with a LHSV of 25 h−1. Using the integrated HT&CHGT-Process, approximately 0.78 Nm3 of CH4, 0.62 Nm3 of H2 and 0.31 Nm3 of CO2 were generated from 1 kg of carbon in the sewage sludge. The combined process was expected to be an efficient method for sewage sludge treatment due to its mild conditions (≤350 °C and ≤20 MPa) and high yield of fuel gases.