Anaerobic Co-digestion Of Sewage Sludge Research Articles

Coupling of biogas residue biochar and low-magnitude electric fields promotes anaerobic co-digestion of sewage sludge and food waste.

Biochar-assisted anaerobic digestion (AD) remains constrained due to the inefficient decomposition of complex organics, even with the direct interspecies electron transfer (DIET) pathway. The coupling of electrochemistry with the anaerobic biological treatment could shorten lengthy retention time in co-digestion by improving electron transfer rates and inducing functional microbial acclimation. Thus, this work investigated the potential of improving the performance of AD by coupling low-magnitude electric fields with biochar derived from the anaerobically digested biogas residue. Different voltages (0.3, 0.6, and 0.9 V) were applied at various stages to assess the impact on biochar-assisted AD. The results indicate that an external voltage of 0.3 V, coupled with 5 g/L of biochar, elevates CH4 yield by 45.5% compared to biogas residue biochar alone, and the coupled approach increased biogas production by up to 143% within 10 days. This finding may be partly explained by the enhanced utilization of substrates and the increased amounts of specific methanogens such as Methanobacterium and Methanosarcina. The abundance of the former increased from 4.0 to 11.3%, which enhances the DIET between microorganisms. Furthermore, the coupling method shows better potential for enhancing AD compared to preparing iron-based biochar, and these results present potential avenues for its broader applications.

Development of separation and recovery technology of cultured Euglena gracilis using activated sludge for anaerobic digestion

The combination of microalgae cultivation and anaerobic co-digestion of sewage sludge and microalgae is a promising system for increased energy efficiency in sewage treatment plants. This study proposed an innovative separation and recovery technology for microalgae from liquid media after culturing using combined heating and co-sedimentation with activated sludge. Sedimentation and anaerobic digestion experiments were conducted using Euglena gracilis cultures and activated sludge. Combining heating at 40 °C and co-sedimentation resulted in a maximum recovery of 92 %. Activated sludge adsorbed E. gracilis at a ratio of 0.644 μg-Chl. a/mg-MLSS. In anaerobic digestion experiments, no adverse effects such as fermentation inhibition were caused by mixing the activated sludge and E. gracilis. Total energy balance was evaluated assuming a sewage treatment plant with a capacity of 50,000 m3/day. The proposed system is shown to be energy efficient, and increase methane recovery by 24 %.

Anaerobic co-digestion of low Chemical oxygen demand concentration sludge mixture by different pretreatment methods

<p>Three laboratory scale systems were operated to study the anaerobic co-digestion of sewage sludge with the excess activated sludge and cattle manure which contained low COD concentration. The experiments were performed to evaluate the effects of different methods of pretreatment. Since the poor organic substrate, the organic loading rate(OLR) was designed about 1.6kg total solids(TS)(l *d)-1 and the hydraulic retention time was controlled from 78days to 53days throughout the experiment to investigate the effects of the input on overall stability. When the digesters got stabilized, the COD removal efficiencies were 61%, 89% and 54%, respectively, and the pH value fluctuated little in the three digesters. The results indicated that the treatment of 1g volatile solids(VS) of SSEASCM on semi-continuous co-digestion generated more than 200ml of biogas on average. Thus, anaerobic co-digestion of the mixed sludge provided a means for low COD waste treatment and produced renewable energy.</p>

Investigation into the effects of different recycled magnetic additives on anaerobic co-digestion of sludge and straw

The addition of magnetic additives has been found to enhance the anaerobic co-digestion of sludge and straw. Due to strong magnetic properties, these additives can be easily separated from the digestate, allowing for recycling during the continuous anaerobic digestion process. This study aimed to investigate the impact of different recycled magnetic additives (specifically, magnetic biochar and Fe3O4) on the anaerobic co-digestion of sewage sludge with corn straw. The results showed that the addition of recycled Fe3O4 with an initial amount of 10 g/kg resulted in the highest cumulative methane yield of 295.70 mL/g VSadded, which increased by 79.81% as compared to the control. The results suggest that magnetic biochar with higher carbon content exerts a more noticeable impact on shortening the digestion lag phase time, as indicated by kinetic analysis. With the addition of recycled Fe3O4, the Methanosaeta and Methanosarcina enhanced significantly. Especially Methanosarcina, which was increased from 3.85% to 6.28%, resulting in a 2.43% increase. Furthermore, the predominant aceticlastic pathway of digestion process was consolidated, and the enriched Methanosarcina broadened the pathways of methanogenesis. This research provides a potential utilization strategy of recycling Fe3O4 for accelerating the anaerobic degradation of urban and rural areas solid waste.

Optimising organic composition of feedstock to improve microbial dynamics and symbiosis to advance solid-state anaerobic co-digestion of sewage sludge and organic waste

This study provided new insight to the underlying mechanisms, by which organic compositions, including protein, fat, degradable carbohydrates and lignocellulose, regulate the performance of solid-state anaerobic digestion (SSAD) for synergistic treatment of organic wastes. Results show that the feedstock with a balanced composition of protein, fat, degradable carbohydrates and lignocellulose could maintain SSAD homeostasis to enhance methane (CH4) production by 14–487%. On the other hand, organic waste with a high content of degradable carbohydrates and fat at 39 and 14%, respectively, showed an initially high CH4 production at the beginning but a lower overall CH4 production. This was because of the accumulation of volatile fatty acids (VFAs) and ammonium nitrogen (NH4+-N) at up to 17.3 and 7227.7 mg·L−1, respectively, leading to anaerobic activity inhibition. Microbial dynamic and modular network analyses indicated that the balanced feedstock secured stepwise biodegradation of different organic substances to reduce the relative abundance of hydrolytic bacteria (e.g. Rikenellaceae_RC9_gut_group and Tepidimicrobium), thus alleviating VFAs and NH4+-N stresses. In particular, fat in the balanced feedstock could not only enrich the phylum Firmicutes for macromolecular biodegradation and genes for VFAs production, but also inhibit relative oxidizers (e.g. Synergistes and Acinetobacter) to facilitate propionate and acetate production to strengthen acetotrophic methanogenesis for effective CH4 yield. Results in this study show that a balanced organic composition could regulate microbial dynamics and symbiosis to advance SSAD homeostasis and methanation in synergistic organic waste treatment.

Enhancing Methane Production through Anaerobic Co-Digestion of Sewage Sludge: A Modified ADM1 Model Approach

The International Water Association’s (IWA) established Anaerobic Digestion Model No. 1 (ADM1) was created to serve as a backup for experimental findings regarding the actual anaerobic digestion process. The previous model idea was adjusted and used to simulate an anaerobic digestion process in this study. Testing procedures, such as benchmark tests and balance checks, were performed in order to verify the accuracy of the implementation. These measures worked in tandem to ensure that the model was implemented flawlessly and without inconsistencies. The primary objective of this article is to construct a method that is based on the ADM1 for evaluating co-digestion and predicting the performance of the digestion process or methane yield based on the analyzed substrates’ physicochemical properties. Additional equations and simulations have been added to the standard model to create tools for evaluating the feasibility of anaerobic co-digestion. The study’s two most intriguing aspects are the optimal mixture and parameter dependence. The adjusted ADM1 is accurate in predicting the measured values of effluent COD, pH, methane, and produced biogas flows with a reasonable degree of accuracy, according to the validation results. This research shows how to use ADM1 in a wastewater treatment plant and other settings where anaerobic digestion is of interest.

Anaerobic Co-digestion of sewage sludge and organic fraction of municipal solid waste: Focus on mix ratio optimization and synergistic effects

The utilization of municipal solid waste (MSW) and sewage sludge (SS) as a source of renewable energy is crucial in achieving sustainable and integrated MSW management. SS and organic fraction of municipal solid waste (OFMSW) can be anaerobically digested to produce methane for energy. However, anaerobic digestion of specific substrates is challenging with respect to substrate characteristics. The problem of mono-digestion can be mitigated by co-digestion of these two major organic wastes because of their complementary characteristics. Moreover, there is a lack of studies on optimization of different mix ratios of organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS) based on total solids (TS). The study aims to optimize the mix ratio for anaerobic co-digestion of OFMSW and SS. The study further elucidates synergistic effects associated with the co-digestion process. Different mix ratios of SS and OFMSW (0:100, 20:80, 40:60, 60:40, 80:20, 100:0) at 5, 7.5 and 10% TS were assessed for biomethane potential assessment. The results showed that with an increase in SS in the mix ratio feed the methane yield increased by 91% and 50% as compared to mono digestion of sewage sludge and OFMSW respectively at TS 7.5%. Based on the kinetic analysis, it was observed that the lag phase reduced for 60:40 mix ratio leading to higher rate of biodegradation. Positive synergistic effects were observed for 40:60, 60:40 and 80:20 mix ratio of SS:OFMSW based on co-digestion impact factor value. Response surface modelling was used to get the optimized mix ratio and TS %. The optimum mix ratio with the highest methane yield (388 ml/gVS added) was 70:30 (SS: OFMSW) at TS 7.5% with a desirability value of 0.98. These findings demonstrate that co-digesting SS and OFMSW is a preferable alternative for harnessing renewable energy and managing organic waste in a sustainable manner.

Kinetic modeling of anaerobic co-digestion with glycerol: Implications for process stability and organic overloads

The energy crisis, depletion of fossil fuels, and global waste issue highlight the need for sustainable and eco-friendly energy processes. In this study, the anaerobic co-digestion of sewage sludge (DS), milk sludge (MS), and food waste (FW) with glycerol (GL) from biodiesel production was investigated. Binary co-digestion of MS-GL, DS-GL, and FW-GL, as well as ternary co-digestion of MS-FW-GL and DS-FW-GL, were examined to determine the optimal combinations for biogas production and process stability. Adding 5% GL (v/v) increased methane yields by 88.78%, 405.82%, and 40.03% for binary mixtures and 55.57% and 298.53% for ternary mixtures, respectively. In addition, the ternary mixtures resulted in the accumulation of volatile fatty acids at 2136.96 mg/L and 1843.62 mg/L, respectively, causing a reduction in methane yield compared to that in binary mixtures. GL added to binary and ternary mixtures delayed optimal methanogenic activities, with higher hydrolysis rates and shorter lag times observed in single substrate-contained and binary mixture reactors. Ternary mixtures showed lower hydrolysis rates and longer lag times, indicating that methanogens required more time to adjust to the increased organic content. Co-digestion procedures using different substrate ratios should consider the risk of organic overloads, which can lead to system instability or failure.

The effect and mechanism of polyethylene terephthalate microplastics on anaerobic co-digestion of sewage sludge and food waste

This research investigated the impact of polyethylene terephthalate (PET) microplastics on the anaerobic co-digestion of sewage sludge and food waste. The performance of anaerobic digester was investigated with different particle sizes (30 µm and 250 µm) PET at concentrations of 0, 0.45, 1.35, and 2.70 mg/g total solid (TS). Results suggested that the CH4 production at 2.70 mg/g TS level decreased by 21.63% (30 µm) and 15.87% (250 µm) compared with the control group, respectively. PET microplastics exerted negative influence through leaching toxic diisobutyl phthalate (DIBP) and dibutyl phthalate (DBP). Microbial community analysis and redundancy analysis showed that DIBP and DBP reduced the abundances of key hydrolysis bacteria (Bacteroides vadin HA17) and acidification bacteria (Clostridium and Sphaerochaeta). Structural equation model analysis showed that DBP and DIBP were the key factors that reduced the methane production, and they had stronger impact on daily methane production in the 30 µm group compared with the 250 µm group.

Anaerobic co-digestion of sewage sludge and wine vinasse mixtures in single-stage and sequential-temperature processes

The present work consisted of the energetic valorization of sludge from wastewater treatment plants and discharges from the wine sector by means of anaerobic co-digestion. The valorization was approached through the application of two different processes: a) single-stage mesophilic anaerobic digestion process (35 °C) and, b) Temperature - Phased Anaerobic Digestion (TPAD) with separation of microorganisms: thermophilic acidogenic (55 °C) and mesophilic methanogenic (35 °C) phases.Mesophilic methanogenic biodegradability tests (BMP) were developed to determine the biogas (methane) production yield in single-stage process and sequential thermophilic hydrogen (BHP) and BMP were developed to study the biogas (hydrogen and methane) production yield in anaerobic co-digestion processes in TPAD process.The results obtained showed that the single-stage mesophilic anaerobic co-digestion process was more effective for methane generation with yields of 55.39 mL CH4/g VSadded for the sludge and vinasse mixture, compared to 45.79 mL CH4/g VSadded for the TPAD process.

Wet Anaerobic Codigestion of Sewage Sludge and OFMSW in Pilot-Scale Continuously Stirred Tank Reactors: Focus on the Reactor Microbial Communities

Dark fermentation (DF) is a simple method for hydrogen (H2) production through the valorization of various organic wastes that can be used as feedstock. In particular, an organic fraction of municipal solid waste (OFMSW) is a fermentation substrate that can easily be gathered and provides high yields in biogas and value-added organic compounds such as volatile fatty acids (VFAs). DF is coupled with a methanogenic reactor to enhance biogas production from the OFMSW. In this study, a two-stage reactor was conducted and monitored to optimize the methane yield by reducing the HRT at the DF reactor. A focus of the functional inference based on a next-generation sequence (NGS) metabarcoding analysis and comparison of microbial communities that populate each reactor stage was performed. Concerning gas quality, the two-stage system observed a hydrogen-rich biogas in the first fermentative reactor (on average 20.2%) and an improvement in the methane content in the second methanogenic digester, which shifted from 61.2% obtained for the one-stage experiment to 73.5%. Such increases were due to the improvement in substrate hydrolysis. As for the specific biogas production, the results showed an overall increase of 50%.

Anaerobic Co-Digestion of Sewage Sludge and Trade Wastes: Beneficial and Inhibitory Effects of Individual Constituents

Anaerobic digestion (AD) of sewage sludge can be optimised by adding trade wastes (TWs) because of their nutrient content and boost in biogas formation if non-inhibitory. However, some components in TWs might have an inhibitory impact, such as nitrogen compounds, sulphate, heavy metals, metalloids, halogens and organic pollutants (e.g., phenol). This study aimed to understand the impact of TWs on the co-digestion with sewage sludge to identify appropriate TW loads for sustainable AD operation. The composition of 160 TWs was evaluated and the constituents with potential to cause inhibition or toxicity were tested in bio-methane potential (BMP) tests. The compounds studied in BMP tests included ammonia, zinc, copper, aluminium, mercury, arsenic, chloride, sulphate and nitrate. An improvement was observed at concentrations 2–746 mg Zn/L, 1066–2821 mg Cl/L as zinc sulphate and sodium chloride in biogas production, and 2–746 mg Zn/L, 162 mg SO4/L, 25 mg Hg/L as zinc sulphate, sodium chloride and mercury sulphate in methane production, respectively. Considering the TWs characterised and the results of the BMP tests, a volumetric ratio of 10/90 of TWs and sewage sludge is proposed as a suitable feedstock for co-digestion.

Anaerobic co-digestion of sewage sludge and Cladophora green algae: Investigation of synergistic effects and Optimization of substrate composition ratio

Anaerobic co-digestion of primary and secondary sewage sludge and <i>Cladophora</i> green algae was investigated under mesophilic temperature conditions. The design of experiment method and the optimal mixture design were used to systematically optimize the substrate composition ratios and elucidate the possible synergistic effects for an anaerobic digestion system. A reduced cubic model was created by Design-Expert software as a function of substrate composition ratios. The model was validated by ANOVA experimentally. Also, the substrate composition ratio's effects on variations in biogas production were studied. All linear impacts on changes in biogas production were significantly observed, and interactions between substrates in combined digestion had synergistic impacts on biogas production rate. The highest amount of biogas (235.17-296.03 ml/g VS) was obtained with ratios of equal to 70-60%, B equal to 0-17%, and C equal to 18-30%. Eventually, the model optimization was performed to predict the optimal conditions to achieve the maximum biogas production rate. It was seen that the predicted and actual values of produced biogas in favorable conditions with an error of about 1.3% are well consistent. The authors conclude that the optimal mixture design can be utilized to assess the optimal composition of substrates in an anaerobic digestion system.

Effect of Acid Pretreatment on the Anaerobic Codigestion of Sewage Sludge, Chicken Litter, and Sugarcane Waste (SCW) for Biogas Production

Effect of Acid Pretreatment on the Anaerobic Codigestion of Sewage Sludge, Chicken Litter, and Sugarcane Waste (SCW) for Biogas Production

Techno-economic analysis of single-stage and temperature-phase anaerobic co-digestion of sewage sludge, wine vinasse, and poultry manure

Anaerobic co-digestion (AcoD) is a mature and consolidated waste management technology that can transform agro-industrial by-products into biogas and digestate. This study conducted a techno-economic assessment of bioenergy and agricultural fertilizer production from AcoD of sewage sludge, wine vinasse, and poultry manure. In this case study, three configurations were investigated: i) Scenario 1, AcoD in thermophilic temperature; ii) Scenario 2, AcoD in mesophilic temperature; and iii) Scenario 3, AcoD in a temperature phase (TPAD) system, where the digestate produced in the first reactor (thermophilic) feeds the second reactor (mesophilic). The process was designed to manage 24,022 m³ wine vinasse y−1, 24,022 m³ sewage sludge y−1, and 480 m³ poultry manure y−1. The major cost was the fixed capital investment for the single-stage (320,981 USD) and TPAD processes (379,698 USD). The TPAD process produced the highest electricity (1058.99 MWh y−1) and heat (4765.47 GJ y−1) with the lowest cost of manufacturing for electricity (84.99 USD MWh−1), heat (0.019 USD MJ−1), and fertilizer (30.91 USD t−1). Regarding the profitability indicators, the highest net present value (509,011 USD) and the lowest payback time (4.24 y) were achieved for Scenario 3. In conclusion, TPAD is a profitable and sustainable waste-to-energy management technology that can be applied in a circular economy framework to recover bioenergy and fertilizer, contributing to decreasing the carbon footprint of the agri-food sector.

Enhancing methane production in anaerobic co-digestion of sewage sludge and food waste by regulating organic loading rate

This study presented mechanistic insights into the long-term effects of stepwise-increasing organic loading rates (OLRs) on anaerobic co-digestion (AcoD) of sewage sludge and food waste. The maximum methane (CH4) yield of 500.0 ± 10.5 mL CH4/g VSfed was achieved at medium OLR of 3.5 g VS/L/d. This excellent performance was associated with the high hydrolysis efficiency (78.4%), three-fold enhancement in the acidogenesis enzyme activity, and 87.0% enhanced methanogen activity. Soluble intermediates (carbohydrates and proteins) were largely degraded (>98.5%), especially tyrosine-like and tryptophan-like aromatic proteins. The particulates were effectively decomposed from macromolecules to micromolecules, and the crystallinity of cellulosic substances decreased by 24.5%. The newly-shaped combined syntrophic acetate oxidation-hydrogenotrophic methanogenesis pathway dominated enhanced CH4 production. Energy balance analysis based on medium OLR demonstrated the high energy recovery potential in full-scale AcoD. These findings suggest the optimal medium OLR can facilitate the bioconversion of organics to CH4 through a new metabolic pathway.

Temperature-phased enhanced the single-stage anaerobic co-digestion of sewage sludge, wine vinasse and poultry manure: Perspetives for the circular economy

The effect of hydraulic retention time (HRT) on single-stage (mesophilic and thermophilic range) and temperature-phase anaerobic co-digestion processes (TPAD) of sewage sludge, wine vinasse, poultry manure was studied. The HRTs studied were 20, 15, 13 and 10 days for the single-stage and TPAD process. For the TPAD with an HRT of 20 days, 65 % of total chemical oxygen demand (TCOD) were removed, which was higher than the single-stage process (26 % and 17 % TCOD removal, respectively for the thermophilic and mesophilic phases). Regarding the volatile solids (VS) removal, TPAD process presented a higher efficiency (90 %) when compared with the thermophilic (41 %) and mesophilic (43 %) single-stage digesters. At an HRT of 13 days 155 mLCH4/gVSadded (thermophilic), 260 mLCH4/gVSadded (mesophilic), and 202 mLCH4/gVSadded (TPAD) were obtained. The maximum methane yield was achieved for the TPAD process operated at an HRT of 20 days (320 mLCH4/gVSadded) with the additional benefit of obtaining hydrogen in the first stage (40.41 mLH2/gVSadded). The digestate obtained from the TPAD process were classified as class A biosolids, and could be used for agriculture fertilizer. In conclusion, TPAD waste management process presented better operational performance and methane yield when compared to a single-stage conventional system, direcly contributing for the framework of a circular economy transition of the agri-food industry.

Biogas production from anaerobic co-digestion of sewage sludge and food waste in continuously stirred tank reactor

The purpose of current investigation was to explore the scope of integrating an anaerobic digester in a decentralized municipal wastewater treatment plant for in-situ treatment of household waste. The present work intends to identify the potential of sewage sludge and food waste for biogas generation. The study was conducted in lab scale continuous stirred tank reactor having a working volume of 6.5 L at mesophilic temperature. The paper mill sludge was used as inoculum and was stabilised using food waste substrate for initial 50 days in batch mode. Co-digestion of food waste (FW) and bio-flocculated sewage sludge (BFS) was performed using continuous feeding for maintaining OLR of 2.5 gVSL−1D−1at HRT of 4 days for 120 days. 2% FW and 98% BFS (by volume) was feeded in the reactor throughout the experimental duration. The highest VFA accumulation of 1902 mg L−1 were observed and maximum bio-methane yield was found to be 127.05 mLCH4 g−1 VSadded. The pH with current feeding ratio was found stable during the reactor operation without adding external alkalinity source.

Anaerobic co-digestion of sewage sludge pretreated by thermal hydrolysis and food waste: gas production, dewatering performance, and community structure

ABSTRACT Anaerobic co-digestion can effectively break the limitations of mono-digestion. However, there are still some problems such as long residence time, unsatisfactory methane yield, and unstable performance for co-digestion of sewage sludge (SS) and food waste (FW). Therefore, the SS in the reactor treating co-digestion of SS and FW is considered to be pretreated by thermal hydrolysis. In this work, the anaerobic co-digestion of SS of thermal hydrolysis pretreatment (THP) and FW significantly improved the stability, methane production of the digestive reactor, and dewaterability of the digested sludge. The R6 obtained the most cumulative methane production (315.76 mL/g VS). In addition, compared to R3, the cumulative methane production and maximum methane production rate of R5 increased by 9.93% and 14.56%, respectively. The dewaterability of R4, R5, and R6 was improved, while the dewatering performance of the R3 decreased to a greater extent. The results of the kinetic model fitting were consistent with the experimental results. Among them, the hydrolysis constants (Kh) of anaerobic co-digestion of THP-SS and FW were 0.121, 0.130, and 0.114 d−1, respectively, which were higher than those of other groups. And the estimated lag time (λ) of co-digestion was also lower than that of mono-digestion groups. Microbial community analysis indicated that the bacterial diversity and richness of anaerobic co-digested groups of THP-SS and FW were enhanced, while the methanogens with acetoclastic pathway became the main methanogenic microorganisms. This work provides essential information on anaerobic co-digestion containing different THP-SS contents.

Kinetic modelling of anaerobic co-digestion of sewage sludge and Sherry-wine distillery wastewater: Effect of substrate composition in batch bioreactor

Batch thermophilic anaerobic co-digestion of sewage sludge (SS) and Sherry-wine distillery wastewater (SW-DW) was investigated through biochemical methane potential tests (BMP). The results pointed out that biodegradability and biomethane potential were enhanced proportionally to the percentage of SW-DW of the feedstock, whose soluble biodegradability fraction is 10-fold higher than SS. Specifically, organic matter removal increases from 37 % (employing sole SS as feedstock) to 60 % (employing sole SW-DW as feedstock). SW-DW almost doubles methane yield in comparison to SS (302 ± 15 and 175 ± 9 NL/kg, respectively).A structured kinetic model was developed considering hydrolysis, acidogenic and methanogenic steps of anaerobic digestion. A non-linear multiple-response regression was employed to estimate the kinetic parameters for each feedstock (0%(v/v) SW-DW, 25%(v/v) SW-DW, 50%(v/v) SW-DW, 75%(v/v) SW-DW, and 100%(v/v) SW-DW). The first-order kinetic parameter estimated of the hydrolysis step varies inversely proportional to the percentage of SW-DW content in the feedstock. Whereas, there is no significant influence of feedstock composition on kinetic parameters value regarding acidogenesis and methanogenesis. These results showed that rate–limiting step switched during the fermentation and the addition of SW–DW favours acidogenic and methanogenic steps. In summary, the proposed kinetic model was able to predict batch experimental data, supporting the application of biogas production from anaerobic co-digestion of SS and DW-DW.