Anaerobic Digestion Of Sewage Sludge Research Articles

Impact of High-Intensity Static Magnetic Field on Chemical Properties and Anaerobic Digestion of Sewage Sludge

The increasing production of sewage sludge at global level has addressed the search for technical solutions to take advantage from it, reducing the environmental burden originating from its disposal. Anaerobic digestion is a suitable option to handle sewage sludge in accordance with circular economy principles, as it generates a methane-rich biogas and a digestate with potential fertilizing properties. Several techniques have been proposed to enhance anaerobic digestion performances and, among these, the application of static magnetic field (SMF) has recently gained attention. Nonetheless, the effects of high-intensity SMF on the sewage sludge destined to anaerobic digestion and its impact on the anaerobic digestion process have not been evaluated yet. This study aims to determine the effects of a 1.5 T SMF on the chemical composition of sewage sludge as well as on methane generation during anaerobic digestion. The main parameters influencing the SMF (i.e., flow rate, mixing ratio of magnetized to non-magnetized sludge, number of pumping cycles, and total solid content) were varied to evaluate the impact of different exposure conditions on the chemical characteristics and methane potential of sewage sludge. An extensive exposure to the high-intensity SMF applied resulted in a 24% decrease of methane production, reduced the concentration of the monitored ionic species (i.e., NH4+, NO3−, PO43−, SO42− and Mg2+) in the liquid phase of sewage sludge, and promoted the precipitation of compounds with valuable fertilizing properties, e.g., struvite. These outcomes suggest that high-intensity SMF, although negatively influencing methane generation, can promote the precipitation, and possibly the recovery/recycle of valuable compounds from sewage sludge, enhancing its proper management in a circular economy perspective.Graphical abstract

Comparative anaerobic digestion of sewage sludge at different temperatures with and without heat pre-treatment

Anaerobic digestion of sewage sludge is generally conducted under mesophilic (around 35 °C) or thermophilic (around 55 °C) conditions, whereas it is conducted at lower temperatures in some wastewater treatment plants without heating. In this study, we compared the anaerobic digestion of sewage sludge at 15, 25, 30, 35, 45, and 55 °C following hyperthermophilic pre-treatment at 80 °C for 24 h. Laboratory-scale reactors were operated continuously for more than 1000 days, and batch experiments were performed to evaluate the reaction kinetics. Biogas production rates at 15 °C with and without pre-treatment divided by that at 35 °C without pre-treatment were 0.73 and 0.78, respectively. The dewaterability of the digested sludge was evaluated by the capillary suction time (CST). The CST was approximately 50 s at 15 °C with and without pre-treatment and was slower than the CST at 35 °C. Compared to the shear rate, viscosity was higher at lower temperatures; however, it decreased with pre-treatment, which reduced the energy required for mixing in the reactors. Pre-treatment eliminated Escherichia coli from the sludge; however, E. coli (approximately 105 colony forming unit/g-total solids) was detected after digestion at temperatures ≤30 °C. Pre-treatment was also useful to replace a part of heat treatment required for digested sludge before it was used as fertilizer. Gene sequencing analyses indicated the effects of pre-treatment and digestion temperature on the microbial community in the digested sludge. Co-generation of biogas is useful to obtain both electricity and heat; however, heat from co-generation is sometimes limited. To maximize electricity recovery, the use of low temperature digesters has the potential to reduce fuel costs. The results indicate that anaerobic digestion at low temperatures with or without heat pre-treatment can be an efficient and cost-effective method of treating sewage sludge.

Effect of different concentrations of sodium selenite on anaerobic digestion of waste sewage sludge

The effect of sodium selenite on anaerobic digestion of waste sewage sludge (WSS) was studied. Interestingly, methane production was enhanced at 2 mg/L and inhibited at 100 mg/L of sodium selenite during the anaerobic digestion of WSS. Hydrolytic activity increased in correlation with increased concentrations of sodium selenite (0 to 100 mg/L). At the acidogenesis stage, acetic acid accumulated at the concentrations more than 25 mg/L of sodium selenite whereas it was consumed for 10 days at the concentration of 2 mg/L of sodium selenite. Also, the concentration of propionic acid decreased and that of butyric acid increased at 100 mg/L of sodium selenite. Although methanogenic activities were totally inhibited at 100 mg/L of sodium selenite, a high hydrogenotrophic methanogenic activity was observed at 2 mg/L of sodium selenite. The abundance of hydrogenotrophic methanogens ( Methanospirillum and Methanocorpusculum ) increased in the WSS at 2 mg/L of sodium selenite. Moreover, the results of pure-culture experiments using Methanosarcina acetivorans C2A show that the growth promotion or inhibition was observed at 2 mg/L or at 100 mg/L of sodium selenite. In conclusion, sodium selenite has the double-sided effect during the anaerobic digestion of WSS as shown by the results that methane production was promoted at a low concentration and inhibited at a high concentration. • Sodium selenite affects methane production through the anaerobic digestion of sewage sludge. • Methanogenic activities were totally inhibited at 100 mg/L of sodium selenite. • Sodium selenite at 2 mg/L enhanced the activity of hydrogenotrophic methanogenesis. • The growth of Methanosarcina acetivorans C2A was promoted at 2 mg/L and inhibited at 100 mg/L of sodium selenite.

Enzymatic integrated in-situ advanced anaerobic digestion of sewage sludge for the removal of antibiotics and antibiotic resistance genes

Antibiotics and antibiotic resistance genes (ARGs) in sewage sludge can cause high ecotoxicological risks in the environment and public health concerns. The aims of this study were to establish enzymatic integrated in-situ advanced anaerobic digestion (AAD) by adding cellulase and papain as well as the two enzymes combined with zero valent iron (ZVI) directly into the anaerobic digesters to explore the removal of antibiotics and ARGs under the mesophilic condition (35 °C). The methane production potential during in-situ AAD was effectively improved. Papain and cellulase at 30 mg/gTSS were most effective in improving antibiotic removal. The removal of sulfamerazine (SMZ) and sulfadiazine (SMR) could reach 89.10 % and 71.75 %. Combined enzymes with ZVI also enhanced the removal of all target antibiotics, especially roxithromycin (ROX), SMZ and SMR most significantly. Except for sul1, tetA and tetB, the removal of ARGs by papain reached 6.33 %-82.15 %. The addition of cellulase effectively improved tetA removal. The combination of biological enzymes further enhanced the removal of qnrS and ermX. The tetG, tetB, sul3, ermX, ermT, qnrS, and aac(6′)-IB-CR by combined enzymes with ZVI could even not be detected after digestion. Addition of papain, cellulase, and ZVI caused variations in the dominant bacteria. All target antibiotics presented significant positive correlations with the genera norank_f__Bacteroidetes_vadinHA17, norank_f__norank_o__SJA-15, norank_f__norank_o__Aminicenantales. Redundancy analysis showed archaea Methanosaeta and Candidatus_ Methanoacidiosum genera greatly contributed to antibiotics removal with the combination of enzymes and ZVI. Co-occurrence network analysis indicated the removal of ARGs was mainly based on the changes of existence of host bacteria.

Anaerobic digestion of sewage sludge for biogas & biohydrogen production: State-of-the-art trends and prospects

Advancement in the anaerobic digestion of sewage sludge for biogas production is constantly required for effective commercialization. There is great interest in exploring the scientometric and technical assessment in biogas production using sewage sludge from various sources in the anaerobic digestion process. Therefore, this work provides a bibliometric and technical study of anaerobic digestion for biogas production from sewage sludge in the last ten years, based on Web of Science data. The vital parameters of the bibliometric study are authors, countries, and institutional collaboration along with the authors' keywords. In terms of technical assessment, challenges are highlighted with critical analysis of previous work performed both on a laboratory scale and on a pilot scale. The study recommends key considerations and new combination techniques to enhance biohydrogen production with optimized process conditions which will provide vital economic impact for technological adaptation and commercialization.

Energy Potential of Biogas from Sewage Sludge after Thermal Hydrolysis and Digestion

This paper presents the energy potential of biogas obtained from the anaerobic digestion (AD) of sewage sludge (SS) preceded by thermal hydrolysis (THP) using Cambi THP® technology. The presented data are for the Tarnów (Poland) wastewater treatment plant for the year 2020. A detailed energy balance of biogas and its use in the cogeneration process and in the production of heat in the water boiler and the steam boiler is presented. The article contains data on the amount of processed SS and the content of dry matter and dry organic matter at different stages of the technological process. The annual plant operation resulted in the production of 3,276,497 Nm3 of biogas as a result of processing 8684 tonnes of dry solids (tDS) of municipal SS from the Tarnów wastewater treatment plant (WWTP) and regional WWTPs. The energy potential of the produced biogas was 75,347.06 GJ. The average calorific value of biogas was 23,021 kJ/Nm3.. The obtained biogas production allowed us to cover the thermal energy demand of the THP 100%. The annual average specific biogas conversion rate during the study period was 0.761 Nm3/kg of dry organic matter reduced and the average organic matter content reduction in the sludge was 64.60%.

Anoxic desulphurisation of biogas from full-scale anaerobic digesters in suspended biomass bioreactors valorising previously nitrified digestate centrate

Nitrification of centrate from anaerobic sewage sludge digestion presents a major opportunity as an electron acceptor in anoxic biogas biodesulphurisation. Nitritation and nitrification inhibition by free ammonia was detected at laboratory scale, but was avoided during the scale-up operation in a 4 m3 reactor treating ammonium loads up to 19 gN m−3 h−1. This nitrate-rich stream was fed to two pilot-scale suspended biomass bioreactors (SBBs) treating real biogas for 220 days. After an adaptation period of 21 days, nitrate and alkalinity concentrations in the liquid medium below 10 mgN L−1 and 100 mgCaCO3 L−1 were found to limit hydrogen sulphide (H2S) oxidation. Once controlled, 95% of the H2S was removed in SBB1 and 90% in SBB2, at a gas residence time (GRT) of 5.9 min, treating average values of 321 ± 205 ppmv and 457 ± 205 ppmv, respectively. Outlet H2S concentrations of 16 ± 24 ppmv in SBB1 and 46 ± 39 ppmv in SBB2 were obtained, which are below the requirements of biogas combustion heat and power engines. Unlike H2S, siloxanes were not removed with these GRTs. The results demonstrate the feasibility of the combined process for H2S treatment, potential valorisation of precipitated elemental sulphur and a reduction in the reagents currently used to control H2S.

Principles and potential of thermal hydrolysis of sewage sludge to enhance anaerobic digestion

Sewage sludge is rich source of carbon, nutrients, and trace elements and can be subjected to proper treatment before disposal to fulfill government legislation and protect receiving environments. Anaerobic digestion (AD) is a well-adopted technology for stabilizing sewage sludge and recovering energy-rich biogas and nutrient-rich digestate. However, a slow hydrolysis rate limits the biodegradability of sludge. In the present study we have attempted to explain the potential of thermal hydrolysis to enhance anaerobic digestion of sewage sludge. Thermal pretreatment improves biodegradability and recycling of the sludge as an excellent energy and nutrients recovery source at reasonable capital (CAPEX) and operational (OPEX) costs. Other pretreatments like conventional (below/above 100 °C), temperature-phased anaerobic digestion (TPAD), microwave and chemically mediated thermal pretreatment have also been accounted. This review provides a holistic overview of sludge's characterization and value-added properties, various techniques used for sludge pretreatment for resource recovery, emphasizing conventional and advanced thermal pretreatment, challenges in scale-up of these technologies, and successful commercialization of thermal pretreatment techniques.

Evaluation of the biodegradability of a heat-treated anaerobic inoculum

The citrus industry produces a considerable amount of solid and liquid waste, which are mostly wasted. Anaerobic digestion of sewage sludge is an attractive option as it can produce fuels in the form of methane gas. However, the presence of complex organic compounds and pathogenic microorganisms significantly hinders the effectiveness of this process. The objective of this work is the selection of a source of inoculum free of pathogenic microorganisms by means of a thermal pretreatment and in this way is conducive to the treatment of residual sludge from the Citrus industry. The inoculum was taken from a geomembrane reactor which uses cattle manure as a substrate. 6 biodegradability kinetics were performed, varying the substrate-inoculum ratio, three of them with inoculum without pretreatment and another three with treatment, all under mesophilic conditions. SV parameters, pH, and biogas production were determined.

Viscosity and Total Organic Carbon Removal in High-Solid Anaerobic Digestion of Sewage Sludge

Viscosity and Total Organic Carbon Removal in High-Solid Anaerobic Digestion of Sewage Sludge

Sludge Management at the Kraków-Płaszów WWTP—Case Study

Municipal wastewater treatment plants are good examples of facilities where the concept of a circular economy model can be effectively implemented by the recovery of energy as well as secondary and natural materials. That is why anaerobic co-digestion has become one of the most appealing renewable energy pathways and takes a key position within sludge-handling processes. This research looked into the feasibility of the utilization of water sludge from a water treatment plant in anaerobic co-digestion with sewage sludge. The experiments confirmed that anaerobic digestion of sewage sludge together with water sludge significantly improved fermentation gas (biogas) production. The best results were observed when water treatment sludge constituted 30% of the mass of sewage sludge (as volatile solids, VS). At this ratio, approximately 20% more biogas was produced in laboratory experiments compared to the biogas production from sewage sludge only. The results, once confirmed on a semi-technical scale, will help to develop a sequence of processes which would enhance biogas production. Both the technology and the final product offer a comprehensive solution for waste generated at water and wastewater treatment plants. The innovative approach allows for the use of various waste streams and their combined processing following the principle of the circular economy.

Composting and Anaerobic Digestion of Food Waste and Sewage Sludge for Campus Sustainability: A Review

Composting and anaerobic digestion have emerged as better options for managing food waste and sewage sludge at the campus level. This review highlights the characteristics of food waste and sewage sludge from various global higher education institutions. The composting and anaerobic digestion processes of food waste and sewage sludge will be reviewed and evaluated. Also, the adoption of composting and anaerobic digestion at various campus levels has been reviewed. The challenges and future direction, focusing on managing university campus composting and anaerobic digestion, are discussed as well. This review paper will significantly contribute to the understanding of the potential for managing and handling campus waste in a natural-friendly manner.

Impact of Metal Oxide Nanoparticles (NiO, CoO and Fe3O4) on the Anaerobic Digestion of Sewage Sludge

Impact of Metal Oxide Nanoparticles (NiO, CoO and Fe3O4) on the Anaerobic Digestion of Sewage Sludge

Artificial neural network modeling of biochar enhanced anaerobic sewage sludge digestion

Despite the considerable amount of data generated with respect to biochar application in the anaerobic digestion of sewage sludge, there is a research gap for correlations linking biochar physico-chemical parameters to anaerobic digestion performance. In the current study, cumulative methane production (CMP) from anaerobic digestion of sewage sludge amended with biochar is modeled by an Artificial Neural Network (ANN) (2 hidden layers, 12 neurons each) based on data compiled from 51 published biomethane potential tests (BMP). The model reflects the effects of 13 operational parameters covering physico-chemical properties of biochar, sludge characterization and operating conditions. Various types of sewage sludge and biochar under both mesophilic and thermophilic conditions have been successfully modeled with an R2 of 0.9924. An importance analysis is conducted to evaluate the significance of the model input parameters to CMP. Results indicate that operating conditions are more significant to CMP and that CMP is strongly correlated with biochar physical properties and chemical composition where chemical composition has the dominant effect. Overall, this study proves that biochar physico-chemical parameters are correlated to CMP and enables its forecasting under unexamined conditions thus assisting in process optimization, scale up and techno-economic analyses without resorting to BMP tests.

The effects of digestate pyrolysis liquid on the thermophilic anaerobic digestion of sewage sludge — Perspective for a centralized biogas plant using thermal hydrolysis pretreatment

The use of pyrolysis process to valorize digestate from anaerobic digestion (AD) of municipal sewage sludge for biochar production was piloted in a central biogas plant. The pyrolysis also generates pyrolysis liquid with high organics and nutrient contents that currently has no value and requires treatment, which could potentially be done in AD. As the pyrolysis liquid may contain inhibitory compounds, we investigated the effects of adding the pyrolysis liquid on AD of sewage sludge and thermal hydrolysis pretreated sewage sludge (THSS) simulating the full-scale centralized biogas plant conditions. In batch assays, the pyrolysis liquid as such did not produce any methane, and the 1% and 5% (v/w) shares suppressed the methane production from THSS by 14–19%, while a smaller decrease in methane production was observed with sewage sludge. However, in the semi-continuous reactor experiments, pyrolysis liquid at a 1% (v/w) share was added in sewage sludge or THSS feed without affecting the methane yields or digestate characteristics. The laboratory results indicated that pyrolysis liquid can be treated in AD, while extrapolating the results to the centralized biogas plant indicated minor increase in the overall methane production and an increased potential for ammonium recovery.

Effect of nitrite on hydrolysis-acidification, biogas production and microbial community in semi-continuous two-phase anaerobic digestion of sewage sludge

Previous study found that the pre-treatment of sewage sludge with nitrite improves the biogas production during the mono/two-phase anaerobic digestion (AD) using batch biochemical methane potential tests. In this study, the effects of nitrite on hydrolysis-acidification, biogas production, volatile solids destruction and microbial composition in semi-continuous two-phase AD of sewage sludge were investigated. The addition of nitrite promotes sludge organic matter solubilization (+484%) and VFAs production (+98.9%), and causes an increase in the VS degradation rate during the AD process (+8.7%). The comparison of biogas production from the acidogenic and methanogenic reactors with or without the addition of nitrite implies that the nitrite has no significant effect on the overall biogas production of two-phase sludge AD process. High-throughput sequencing analysis shows that the microbial communities of bacteria and archaea in two-phase AD reactors significantly changes after the addition of nitrite. Vulcanibacillus (bacteria) and Candidatus Methanofastidiosum (archaea) become the dominant genera in the acidogenic and methanogenic reactors with the nitrite respectively. These findings provide new insights about using nitrite to promote the organic matter degradation of sewage sludge in a semi-continuous two-phase AD system.

Effects of Stepwise Temperature Shifts in Anaerobic Digestion for Treating Municipal Wastewater Sludge: A Genomic Study.

In wastewater treatment plants (WWTP), anaerobic digester (AD) units are commonly operated under mesophilic and thermophilic conditions. In some cases, during the dry season, maintaining a stable temperature in the digester requires additional power to operate a conditioning system. Without proper conditioning systems, methanogens are vulnerable to temperature shifts. This study investigated the effects of temperature shifts on CH4 gas production and microbial diversity during anaerobic digestion of anaerobic sewage sludge using a metagenomic approach. The research was conducted in lab-scale AD under stepwise upshifted temperature from 42 to 48 °C. The results showed that significant methanogen population reduction during the temperature shift affected the CH4 production. With 70 days of incubation each, CH4 production decreased from 4.55 L·g−1-chemical oxygen demand (COD) at 42 °C with methanogen/total population (M·TP−1) ratio of 0.041 to 1.52 L·g−1 COD (M·TP−1 ratio 0.027) and then to 0.94 L·g−1 COD ( M·TP−1 ratio 0.026) after the temperature was shifted to 45 °C and 48 °C, respectively. Methanosaeta was the most prevalent methanogen during the thermal change. This finding suggests that the Methanosaeta genus was a thermotolerant archaea. Anaerobaculum, Fervidobacterium, and Tepidanaerobacter were bacterial genera and grew well in shifted-up temperatures, implying heat-resistant characteristics.

Waste-to-energy innovative system: Assessment of integrating anaerobic digestion and pyrolysis technologies

Anaerobic digestion (AD) of sewage sludge is an already well-developed technology to convert waste to bioenergy and digestate. Despite its deployment, AD process still raises environmental, technical and economic issues and many researches have been done to improve the process yield, reduce environmental burdens from digestate application and allow a better distribution of energy. The integration of thermal processes with anaerobic digestion is explored to overcome some of the anaerobic digestion limitations. In this study, a cradle-to-grave life cycle assessment (LCA) is performed to compare a system integrating anaerobic digestion and pyrolysis (PY) with single anaerobic digestion, for the co-digestion of sewage sludge and quinoa residue. The results suggest that the environmental impacts of the two pathways are quite similar except for three impact categories: single anaerobic digestion is the best scenario in terms of global warming potential (−769 vs. -604 kg CO 2 eq./t substrate), ozone depletion (−33.7 vs −2.11 mg CFC-11 eq./t substrate) and fossil resources use (−9900 vs −6900 MJ/t substrate). The multifunctional process could be a viable competitor to single anaerobic digestion by improving pyrolysis products upgrading. The application of liquid digestate to crop field revealed to have significant burdens to particulate matter, acidification and terrestrial eutrophication impact categories and must be carefully monitored in both pathways.

Roadmap from Microbial Communities to Individuality Modeling for Anaerobic Digestion of Sewage Sludge.

Biological models describing anaerobic digestion (AD) of sewage sludge have been widely applied to test various control and operation strategies. Anaerobic digestion model 1 (ADM1) provides a generic platform that includes the main processes of AD, excluding homoacetogenesis and the microbial structure. Homoacetogenic bacteria have been identified as important competitors for hydrogen consumption and acetate production. Although recent advances in meta-omics techniques have improved our characterization of AD microbial communities, conventional models treat functional groups as homogeneous and overlook the physiology and behavior of microbial individuality, limiting insights into mechanisms governing process performance. A novel microbial individuality model (MIM) that integrates kinetics, energetics, and agent-based modeling to describe a microbiome's behavior as heterogenic populations, including homoacetogenesis, was developed. The MIM was validated with two datasets from previous studies through daily biogas production, methane content, compound concentrations, and microbial relative abundance changes. The MIM identified the emergence of Methanosaeta at low concentrations of acetate. Moreover, this simulation supports experimental studies confirming that the overlooked homoacetogenesis is an important hydrogen sink in AD. Validated MIMs are expected to provide insights into syntrophic and competitive interactions among microbiomes in AD systems while testing different operational parameters in a virtual environment. The MIM offers a methodological framework to other biological treatment systems and their microbial community dynamics.

Polyethylene terephthalate microplastic fibers increase the release of extracellular antibiotic resistance genes during sewage sludge anaerobic digestion

Microplastic fibers (MFs), as the most frequently detected microplastic shape in sewage sludge, have posed emerging concern for sludge treatment and disposal. However, the effect of MFs on antibiotic resistance genes (ARGs), especially extracellular ARGs (eARGs) during sludge treatment remains far from explicit. Therefore, this study investigated the potential impact of MFs on eARGs during sludge anaerobic digestion (AD), a commonly used sludge treatment method, through long-term operation. The qPCR results showed that both absolute and relative abundances of eARGs increased with the MFs exposure during sludge AD. The average absolute and relative abundances of eight tested eARGs in the AD reactor with the highest MFs dosage (170 items/gTS) were 1.70 and 2.15 times higher than those in the control AD reactor. The metagenomics results further comfirmed the increase of eARGs abundance during sludge anaerobic digestion after MFs exposure and the enhancement did not show significant selectivity. The identification of the potential hosts of eARGs suggested the host numbers of eARGs also increased with MFs exposure, which may suggest enhanced horizonal transformation as a result of increased eARGs. Further exploring the mechansims showed that the genes involved in type IV secretion system was upregulated after MFs exposure, suggesting the active release of eARGs was enhanced with MFs exposure. In contrast, the MFs may not affect the passive release of eARGs as its impact on cell membrance damage was insignificant. The enhanced eARGs in sludge AD process may further accelerate the transport of ARGs in environment, which should be considered during sludge treatment and disposal.