Two-phase Anaerobic Digestion Research Articles

Effect of acidification pretreatment on two-phase anaerobic digestion of acidified food waste

Acidified food waste significantly disrupts anaerobic digestion, highlighting the need for effective solutions to mitigate its impact. This study presents a method that utilizes acidified sludge to pretreat acidified food waste, thereby significantly improving the efficiency of hydrolysis and acidogenesis. After acidification pretreatment, hydrolysis efficiency improved from 64.54 % to 96.51 %, while acidogenesis efficiency increased from 34.82 % to 49.95 %. Additionally, the concentration of short-chain fatty acids and hydrogen production in the acidification pretreatment group increased by 45.89 % and 48.67 %, respectively. The pretreatment group exhibited a biochemical methane potential of 512.84 ± 13.73 mL/(g volatile suspended solids), which was 35.77 % higher than that of the control group. Mechanism analysis revealed that the higher abundance of genes associated with lactate dehydrogenase in the acidified sludge facilitated the rapid degradation of lactic acid. Moreover, the abundant Clostridium butyricum in the acidified sludge promoted the targeted conversion of lactic acid and other organic matter into butyric acid within the food waste system. This efficient butyric acid fermentation improved the fermentation environment and provided abundant substrates for methane production. This study introduces a promising bio-based strategy to improve the anaerobic digestion efficiency of acidified food waste.

Effect of Biochar Addition on Biogas Production Using Konjac Waste through Mesophilic Two-Phase Anaerobic Digestion

Effect of Biochar Addition on Biogas Production Using Konjac Waste through Mesophilic Two-Phase Anaerobic Digestion

Mass flow and microbial shifts in recirculated two-phase anaerobic digestion for biohythane production: Effect of hydraulic retention time

Biohythane, the promising gaseous biofuel, can be produced by the recirculated two-phase anaerobic digestion (R-TPAD). The effect of hydraulic retention time (HRT) as 30, 20 and 10 days on biohythane production via R-TPAD (recirculation ratio = 0.4) was investigated with co-digestion of food waste and paper waste. The results showed that HRTs of 30 and 20 days maintained stable performance for R-TPAD but HRT of 10 days led to the final decrease in biogas production. The failure in the end was attributed to the wash-out of microbes. The removal efficiencies for COD and carbohydrates were decreased by short HRTs while for VS it remained relatively stable at about 75.7 ± 4.0%. All through the operation, acidogenic phase and methanogenic phase were separated stably and butyrate pathway was the dominant pathway for hydrogen fermentation in the first stage. The microbial community in the first stage reached the highest diversity when total HRT was 20 days, where the hydrogen production rate was the highest. The genera Lactobacillus and Caproiciproducens kept dominating the dark fermentation in the acidogenic phase, and Ruminococcus and Methanosarcina were decreasing in the methanogenic phase. The biohythane yields were 411 mL/g-VSfed, 332 mL/g-VSfed and 253 mL/g-VSfed, respectively, where the H2 contents were 18.4%, 14.7% and 8.8%, respectively.

Metagenomic analysis reveals the mechanisms of biochar supported nano zero-valent iron in two-phase anaerobic digestion of food waste: microbial community, CAZmey, functional genes and antibiotic resistance genes

The mechanisms of biochar supported nano zero-valent iron (BC/nZVI) on two-phase anaerobic digestion of food waste were investigated. Results indicated that the performance of both acidogenic phase and methanogenic phase was effectively facilitated. BC/nZVI with the amount of 120 mg/L increased methane production by 32.21%. In addition, BC/nZVI facilitated direct interspecies electron transfer (DIET) between Geobacter and methanogens. Further analysis showed that BC/nZVI increased the abundance of most CAZymes in acidogenic phase. The study also found that BC/nZVI had positive effects on metabolic pathways and related functional genes. The abundances of acdA and ackA in acidogenic phase were increased by 151.75% and 36.26%, respectively, and the abundances of pilA and TorZ associated with DIET were also increased. Furthermore, BC/nZVI mainly removed IMP-12, CAU-1, cmeB, ErmR, MexW, ErmG, Bla2, vgaD, MuxA, and cpxA from this system, and reduced the antibiotic resistance genes for antibiotic inactivation resistance mechanisms.

Effect of Pretreatment of Anaerobic Acid Fermentation Sludge from Mixed Swine Wastewater and Food Waste Leachate on Biohydrogen Generation

Objectives:This study aims to investigate the effects of heat shock and 2-bromoethanesulfonate (2-BES) injection on hydrogen production and methanogens inhibition in anaerobic acid fermenter sludge and methane fermenter sludge using mixed swine wastewater and food waste leachate as substrates. Additionally, the analysis of biogas, fermentation products such as volatile fatty acids (VFAs) and alcohols, and microbial community changes were conducted to derive efficient pretreatment conditions for anaerobic hydrogen generation.Methods:Sludge samples were collected from two-phase anaerobic digesters treating swine wastewater and food waste leachate. Heat shock (90°C, 15 min) and 2-BES injection (1, 5, 10, 50, and 100 mmol/L) pretreatments were applied to the each sludge, along with control reactor without pretreatment before anaerobic digestion. Batch experiments were conducted at 30°C to assess biogas, organic compounds (COD, VS, VFAs, and alcohols), and microbial community composition.Results and Discussion:In methanogenic sludge, hydrogen gas was not produced under all conditions, but heat shock method inhibited methane production more effectively than 2-BES injection method. As the concentration of 2-BES increased, methane production decreased. Conversely, hydrogen was produced from the all acid fermentation sludges, mainly attributed to the butyric acid production by dominant Clostridium spp., but the pattern of biogas production varied over time. In the experimental group injected with 2-BES, even at a low concentration of 1 mmol/L, methane gas did not produce due to the inhibition of methanogens. However, in the control group, produced hydrogen was entirely converted to methane by hydrogenotrophic methanogens such as Methanobrevibacter and Methanosphaera. The heat shock group showed delayed hydrogen production due to prolonged lag phase of hydrogen-producing bacteria, with hydrogenotrophic methanogen metabolism starting after 12 days. Heat shock and 2-BES injection reduced bacterial diversity in the acid fermentation process compared to the initial stage.Conclusion:For efficient anaerobic hydrogen production from swine wastewater and food waste leachate, 2-BES injection into the acid fermentation sludge was found to be a preferable method over heat shock, considering hydrogen production efficiency and sustained methanogen inhibition. Further research is needed to find more economical and efficient pretreatment methods and operational strategies considering subsequent methane production processes for practical application in the field.

Assessing two-phase anaerobic digestion systems for demand-driven electricity and biobutanol transport fuel at a large distillery

Decarbonisation of industry will necessitate innovative technological solutions that allow for both reduced carbon footprint and security of supply. Biogas systems can allow electricity production on-demand. This study evaluated and compared different two-phase anaerobic digestion systems for continuous volatile fatty acid (VFAs) production and demand-driven biogas production at a whiskey distillery using by-products as feedstock. The systems analysed were a two-phase continuously stirred tank reactor (CSTR) and a leach bed-expanded granular sludge bed reactor (LBR-EGSB) system. Both systems exhibited continuous VFA production (up to 10.4 g. L−1VFA made up of primarily butyric acid and acetic acid) and rapid biogas production, achieving peak flow rates within 30 min. The peak biogas production from the demand-driven EGSB was 3.1 L. L−1reactor. d−1 compared to the CSTR, which recorded 1.8 L. L−1reactor. d−1. Three kinetic models of both systems were assessed, which were able to describe the cumulative biogas production. A theoretical evaluation of processing butyric acid into biobutanol, to be blended with diesel, could produce a more sustainable transport fuel than diesel, reducing distillery-associated transport emissions by 16%.

Microbiome assembly and stability during start-up of a full-scale, two-phase anaerobic digester fed cow manure and mixed organic feedstocks

Carbon transformations during anaerobic digestion are mediated by complex microbiomes, but their assembly is poorly understood, especially in full-scale digesters. Gene-centric metagenomics combining functional and taxonomic classification was performed for an on-farm digester during start-up. Cow manure and organic waste pre-treated in a hydrolysis tank were fed to the methane-producing digester and the volatile solids loading rate was slowly increased from 0 to 3.5 kg volatile solids m−3 d−1 over one year. The microbial community in the anaerobic digester exhibited a high ratio of archaea, which were dominated by hydrogenotrophic methanogens. Bacteria in the anaerobic digester had a high abundance of genes for ferredoxin cycling, H2 generation, and more metabolically complex fermentations than in the hydrolysis tank. In total, the results show that a functionally stable microbiome was achieved quickly during start-up and that the microbiome created in the low-pH hydrolysis tank did not persist in the downstream anaerobic digester.

Study on the Effect of Two-Phase Anaerobic Co-Digestion of Rice Straw and Rural Sludge on Hydrogen and Methane Production

Hydrogen and methane, as chemical raw materials with broad application prospects in the future market, can be produced by the two-phase anaerobic co-digestion of rice straw and sludge. The study was carried out using a medium-temperature batch experiment with rice straw, a rural crop residue from Sichuan, and residual sludge from a sewage treatment station. The effect of the mixing ratio of rice straw and rural sludge on hydrogen and methane production from anaerobic digestion was investigated with a view to alleviating the energy crisis and efficient resource utilization. The experimental results showed that hydrogen production was most favorable when rice straw/sludge = 5:1, with a cumulative hydrogen yield as high as 38.59 ± 1.12 mL/g VSadded, while methane production was most favorable when 3:1, with a cumulative methane yield as high as 578.21 ± 29.19 mL/g VSadded. By calculating the energy yield, it was determined that 3:1 is more favorable for the two-phase anaerobic digestion capacity of rice straw and sludge, which is as high as 20.88 ± 1.07 kJ/g VSadded, and its conversion of hydrogen and methane is 0.75% and 78.19%, respectively. The hydrogen production pathway was dominated by the butyric acid type, whose hydrogen production phase pH (5.84 ± 0.13) was slightly higher than the optimal pH for hydrogen-producing bacteria, while the methanogenic phase could meet the optimal pH for methanogenic bacteria (6.93 ± 0.17).

Microalgae and co-culture for polishing pollutants of anaerobically treated agro-processing industry wastewater: the case of slaughterhouse

Anaerobically treated slaughterhouse effluent is rich in nutrients, organic matter, and cause eutrophication if discharged to the environment without proper further treatment. Moreover, phosphorus and nitrogen in agro-processing industry wastewaters are mainly removed in the tertiary treatment phase. The objective of this study is to evaluate the pollutant removal efficiency of Chlorella and Scenedesmus species as well as their co-culture treating two-phase anaerobic digester effluent through microalgae biomass production. The dimensions of the rectangular photobioreactor used to conduct the experiment are 15 cm in height, 20 cm in width, and 30 cm in length. Removal efficiencies between 86.74–93.11%, 96.74–97.47%, 91.49–92.91%, 97.94–99.46%, 89.22–94.28%, and 91.08–95.31% were attained for chemical oxygen demand, total nitrogen, nitrate, ammonium, total phosphorous, and orthophosphate by Chlorella species, Scenedesmus species, and their co-culture, respectively. The average biomass productivity and biomass yield of Chlorella species, Scenedesmus species, and their co-culture were 1.4 ± 0.1, 1.17 ± 0.12, 1.5 ± 0.13 g/L, and 0.18, 0.21, and 0.23 g/L*day, respectively. The final effluent quality in terms of chemical oxygen demand, total nitrogen, and total phosphorous attained by Chlorella species and the co-culture were below the permissible discharge limit for slaughterhouse effluent standards in the country (Ethiopia). The results of the study showed that the use of microalgae as well as their co-culture for polishing the nutrients and residual organic matter in the anaerobically treated agro-processing industry effluent offers a promising result for wastewater remediation and biomass production. In general, Chlorella and Scenedesmus species microalgae and their co-culture can be applied as an alternative for nutrient removal from anaerobically treated slaughterhouse wastewater as well as biomass production that can be used for bioenergy.Graphical

Comparison of Thermophilic-Mesophilic and Mesophilic-Thermophilic Two-Phase High-Solid Sludge Anaerobic Digestion at Different Inoculation Proportions: Digestion Performance and Microbial Diversity.

This study investigated the performance of thermophilic-mesophilic (T-M) and mesophilic-thermophilic (M-T) two-phase sludge anaerobic digestion at different inoculation proportions after a change in digestion temperature. After temperature change, the pH, total ammonia nitrogen (TAN), free ammonia nitrogen (FAN), solubility chemical oxygen demand (SCOD), and total alkalinity (TA) levels of two-phase digesters were between thermophilic control digesters and mesophilic control digesters. However, the volatile fatty acid (VFA) levels of two-phase digesters were higher than those of thermophilic or mesophilic control digesters. The bacteria communities of M-T two-phase digesters were more diverse than those of T-M. After a change in digestion temperature, the bacterial community was dominated by Coprothermobacter. After a change of digestion temperature, the relative abundance (RA) of Methanobacterium, Methanosaeta, and Methanospirillum of M-T two-phase digesters was higher than that of T-M two-phase digesters. In comparison, the RA of Methanosarcina of T-M two-phase digesters was higher than that of M-T two-phase digesters. The ultimate methane yields of thermophilic control digesters were greater than those of mesophilic control digesters. Nevertheless, the ultimate methane yield levels of M-T two-phase digesters were greater than those of T-M two-phase digesters. The ultimate methane yields of all two-phase digesters presented an earlier increase and later decrease trend with the increasing inoculation proportion. Optimal methane production condition was achieved when 15% of sludge (T-M15) was inoculated under mesophilic-thermophilic conditions, which promoted 123.6% (based on mesophilic control) or 27.4% (based on thermophilic control). An optimal inoculation proportion (about 15%) balanced the number and activity of methanogens of high-solid sludge anaerobic digestion.

The integrated production of hydrochar and methane from lignocellulosic fermentative residue coupling hydrothermal carbonization with anaerobic digestion

The popularization of large-scale biogas project makes the disposal of fermentative residue an urgent issue to be solved. Hydrothermal carbonization (HTC) technology is suitable for treating wet biomass to produce carbonaceous materials. In this study, the solid residue from the two-phase anaerobic digestion (AD) was hydrothermally converted in the range of 180–240 °C, and the hydrochar and aqueous components were characterized for subsequent utilization. The heating values of hydrochar were indicated to be increased by 14.2% and 16.6% at 210 °C and 240 °C as compared with feedstock, and also the specific surface areas were 34.8 m2/g and 27.1 m2/g with 17.4- and 13.3-fold enhancement, respectively. The migration of elements such as S, Cl, K to aqueous phase was beneficial for fuel application. The mesoporous pores were dominant in hydrochars with ample oxygenated functional groups. In addition, the wastewater involved organic acids, phenols, and nitrogen-containing compounds, etc. Evaluating the biodegradability by AD, it was found that when the initial concentration was ≤8 g COD/L, the maximum methane yields up to 275.9 mL CH4/g CODremoval and 277.6 mL CH4/g CODremoval were obtained. The enhanced toxicity/inhibition of representative pollutants on microorganisms was significant at higher organic loading, which could be indicated in the microbial structure and diversity. As a conclusion, the integrated production of hydrochar and methane will provide an extended route for further processing of lignocellulosic fermentative residue.

Anaerobic co-digestion of agro-industrial wastes using anaerobic sequencing batch reactor for bio-energy recovery: Focus on process performance and stability of the methanogenic step

Anaerobic co-digestion of tannery wastewater (TWW) with dairy wastewater (DWW) using a two-phase anaerobic sequencing batch reactor (ASBR) was evaluated. For this purpose, laboratory-scale anaerobic digesters, one for acidogenesis and the other for methanogenesis, with 0.4 and 0.6 L of working volume, respectively, operated in semi-continuous mode, were used. The results showed that a methanogenic reactor treating the effluent acidogenic reactor (50 % TWW and 50 % DWW) exhibits the best process performances in terms of daily biogas (64.7 mL/day), methane production (461 mL/day), specific methane yield (892 mL CH4/g COD), methane content (71.2 %), and total chemical oxygen demand (TCOD) removal efficiency (85.6 %) when operated at a hydraulic retention time (HRT) of 15 days. This indicated that the addition of DWW improves the anaerobic co-digestion process, increasing biogas production (64.7 mL/day) by about 41 % as compared with anaerobic co-digestion of 100 % TWW (27.4 mL/day). The process stability of the methanogenic stage of the two-stage anaerobic digestion process was also evaluated, and the obtained result showed suitable pH (6.70), no total volatile fatty acid (TVFA) accumulation (VFA/alkalinity: 0.363), alkalinity (3350 mg CaCO3/L), and ammonia (231 mg/L) within the optimum operating range. Furthermore, high overall performance efficiency in terms of TCOD reduction (88.8 %) in the two-phase (acidogenesis and methanogenesis) anaerobic digester of 50:50 (TWW:DWW) was obtained when operated at a HRT of 18 days (3 days for acidogenesis and 15 days for methanogenesis). Anaerobic co-digestion of TWW with DWW generally resulted in increased process stabilities and performances compared to mono-digestion of TWW.

A Novel Batched Four-Stage–Two-Phase Anaerobic Digestion System to Facilitate Methane Production from Rice Straw and Cow Manure with Low Inoculum/Substrate Ratios

In order to improve the performance of methane production from agro-waste, a batched four-stage–two-phase anaerobic digestion (4S2P-AD) system was designed to combine the advantages of both anaerobic co-digestion (co-AD) and two-phase AD. The initial separation of two phases was performed using rice straw (RS) as a feedstock in acidogenic phase and cow manure (CM) in methanogenic phase at low inoculum/substrate (I/S) ratios of 0.5 and 0.2 and a high organic loading of 60 g volatile solid (VS)/L. The periodic round-trip reflux of leachate during the 4S2P-AD process facilitated re-inoculation throughout the four stages. The results showed that this round-trip reflux also dispersed toxic ammonia, balanced the carbon/nitrogen ratio, unified the microbial community structure, and led to the selection of Methanosarcina (relative abundance > 80%) as the dominant methanogens. With the abilities to overcome volatile fatty acid accumulation, shorten lag times, improve biodegradability, and foster synergistic effects, it was verified that the 4S2P-AD process can maintain efficient and stable methanogenesis from high-solid lignocellulosic feedstock. The averaged methane production throughout the four stages of 4S2P-AD was 234 mL/g VS. This result is 96% higher than the averaged methane production obtained from the four one-step AD groups using mono-feedstock, and 91% higher than that obtained using co-feedstock. This study provides a scientific reference for the development of new processes of bio-methane production from agro-waste with a high fermentation capacity and stability in the future.

Two-phase anaerobic digestion for enhanced valorisation of whiskey distillery by-products

The valorisation of whiskey by-products was assessed and compared in three anaerobic digestion systems. The systems produced similar methane yields, which could satisfy up to 44% of the thermal energy demand at a distillery. Using methane generated from by-products would displace natural gas and reduce the distillery's carbon footprint. Two-phase systems had higher methane content (ca. 75 %vol) than the traditional system (54 %vol) and furthermore, unlocked opportunities for volatile fatty acid production. The potential value that could be generated from the extraction of butyric acid and caproic acid was approximately €6.76 million for a 50 million litre alcohol facility (0.14 € per litre of whiskey). All three anaerobic digestion systems showed the potential to valorise whiskey by-products and convert current linear distillery production processes into circular repurpose and reuse production processes.

Environmental life cycle assessment of treatment and management strategies for food waste and sewage sludge

A consequential life cycle assessment (LCA) was utilized to compare the environmental impacts of food waste and sewage sludge management strategies. The strategies included a novel two-phase anaerobic digestion (AD) system and alternatives including landfill, waste-to-energy, composting, anaerobic membrane bioreactor, and conventional AD (wet continuous stirred-tank reactor [CSTR]). The co-management of food waste with sewage sludge was also considered for the two-phase AD system and for a conventional AD reactor. A multidimensional LCA approach was taken, considering the five-midpoint impact categories of global warming, smog, human health particulate, acidification, and eutrophication estimated using the U.S. EPA Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts. Co-management of food waste and sewage sludge using the novel two-phase AD system was shown to maximize energy recovery and had a net global warming benefit while reducing other environmental impacts compared with the alternative management strategies. It had similar relative environmental advantages across all categories as conventional AD, with the advantage of a smaller physical footprint. However, both approaches featured net environmental burdens when the background electric grid intensity fell below 0.25 kg CO2-eq kWh−1, as could be expected in a decarbonized electric future. Upgrading the biogas produced from AD to renewable natural gas can displace the use of fossil natural gas for other non-electricity energy requirements that are difficult to decarbonize and may extend the time period of significant environmental benefits of utilizing AD for organic waste management. Treatment of the nutrient-rich supernatant generated by the novel two-phase AD system could be an obstacle for utilities with stringent nutrient discharge limits. Future research and full-scale implementation are needed to demonstrate the benefits of the two-phase AD system predicted through this analysis.

Design, Construction, and Concept Validation of a Laboratory-Scale Two-phase Reactor to Valorize Whiskey Distillery By-products.

The by-products generated from the whiskey distillation process consist of organic liquids with a high chemical oxygen demand (COD) and residues with a high solid content. Low-carbon strategies that repurpose and valorize such by-products are now imperative to reduce the carbon footprint of the food and beverage industries. The operation of a two-phase anaerobic digester to produce volatile fatty acids (VFAs) and biogas may enable distilleries to transition toward a low-carbon bioeconomy. An example of such a system is a leach bed reactor connected to an expanded granular sludge bed (LBR-EGSB) which was designed, commissioned, and conceptually validated in this paper. Several design improvements progress the LBR-EGSB beyond previous reactor designs. An external gas-liquid-solid separator in the EGSB was used to capture any residual gases produced by the effluent and may reduce the amount of methane slippage and biomass washout. The implementation of a siphon-actuated leachate cup is a low-cost alternative that is less prone to actuation malfunction as compared to electrically actuated solenoid valves in previous reactor designs. Furthermore, replacing fresh water with distillery's liquid by-products as leachate promotes a circular repurpose and reuse philosophy. The system proved to be effective in generating VFAs (10.3 g VFAs L-1Leachate), in EGSB COD removal (96%), and in producing methane-rich biogas (75%vol), which is higher than the values achieved by traditional anaerobic digestion systems. The LBR-EGSB could ultimately provide more by-product valorization and decarbonization opportunities than traditional anaerobic digestion systems for a whiskey distillery.

Effects of biochar supported nano zero-valent iron with different carbon/iron ratios on two-phase anaerobic digestion of food waste

The promotion effects of biochar supported nano zero-valent iron (BC/nZVI) with different carbon/iron ratios on two-phase anaerobic digestion (AD) of food waste (FW) were studied. Results suggested that when the carbon/iron ratio was 3:1 AD system showed the best performance, with the concentration of volatile fatty acids (VFAs) in acidogenic phase (AP) and the cumulative methane production in methanogenic phase (MP) increased by 31.4% and 24.8%, respectively. Metagenomic analysis demonstrated that BC/nZVI increased the relative abundance of Defluviitoga in AP, and promoted the growth of Methanothrix in MP. Metabolic pathway analysis in AP indicated that BC/nZVI mainly promoted the abundances of acetate kinase and butyrate kinase to enhance acid production. Methane metabolism pathway analysis in MP revealed that BC/nZVI increased methane production by promoting the module of M00357 and activating related enzymes. The results of this sutdy showed that BC/nZVI promoted AD of FW mainly through acetoclastic methanogenic pathway.

Improved methane production of two-phase anaerobic digestion by cobalt: Efficiency and mechanism

Two-phase anaerobic digestion (AD) is a promising technology, but its performance is sensitive to methanogen. In this study, the effect of cobalt (Co) on two-phase AD was investigated and the enhanced mechanism was revealed. Though no obvious effect of Co2+ was observed in acidogenic phase, the activity of methanogens was significantly affected by Co2+ with an optimal Co2+ concentration of 2.0 mg/L. Ethylenediamine-N'-disuccinic acid (EDDS) was the most effective for improving Co bioavailability and increasing methane production. The role of Co-EDDS in improving methanogenic phase was also verified by operating three reactors for two months. The Co-EDDS supplement increased the level of Vitamin B12 (VB12) and coenzyme F420, and enriched Methanofollis and Methanosarcina, thereby successfully improving methane production and accelerating reactor recovery from ammonium and acid wastewater treatment. This study provides a promising approach to improve the efficiency and stability of anaerobic digester.

Pilot-scale two-phase anaerobic digestion of deoiled food waste and waste activated sludge: Effects of mixing ratios and functional analysis

Anaerobic co-digestion of deoiled food waste (dFW) and waste activated sludge (WAS) can address the challenges derived from mono-digestion of FW. In the present study, a pilot-scale methanogenic bioreactor of a two-phase anaerobic digestion system was developed to explore the impact of dFW/WAS volatile solids ratios on the overall performance, microbial community, and metabolic pathways. Besides, the tech-economic of the system was analyzed. The results showed that the degradation efficiency of soluble chemical oxygen demand (SCOD) was more than 84.90% for all the dFW/WAS ratios (v/v) (1:0, 39:1, 29:1, 19:1 and 9:1). Moreover, the dominant genus of bacteria and archaea with different ratios were Lactobacillus (66.84–98.44%) and Methanosaeta (53.66–80.09%), respectively. Co-digestion of dFW and WAS (29: 1 in v/v ratios) obtained the highest yield of methane (0.41 L CH4/Ladded) with approximately 90% of SCOD being removed. In the pilot-scale experiment, the co-digestion of FW and WAS makes positive contribution to reusing solid waste for improving solid management.

Optimization of Operating Parameters for Two-Phase Anaerobic Digestion Treating Slaughterhouse Wastewater for Biogas Production: Focus on Hydrolytic–Acidogenic Phase

In a two-phase anaerobic digestion process, enhanced biogas production and organic pollutant removal depend on the stability and performance of the hydrolytic–acidogenic and methanogenic phases. Additionally, the hydrolytic–acidogenic phase is a rate-limiting step, which calls for the further optimization of operating parameters. The objective of this study was to optimize the operating parameters of the hydrolytic–acidogenic reactor (HR) in the two-phase anaerobic digestion treating slaughterhouse wastewater. The experiment was carried using bench-scale sequential bioreactors. The hydrolytic–acidogenic reactor operating parameters were optimized for six different hydraulic retention times (HRTs) (6–1 day) and organic loading rates (OLRs) (894.41 ± 32.56–5366.43 ± 83.80 mg COD/L*day). The degree of hydrolysis and acidification were mainly influenced by lower HRT (higher OLR), and the highest values of hydrolysis and acidification were 63.92% and 53.26% at an HRT of 3 days, respectively. The findings indicated that, at steady state, the concentrations of soluble chemical oxygen demand (SCOD) and total volatile fatty acids (TVFAs) decrease as HRT decreases and OLR increases from HRTs of 3 to 1 day and 894.41–1788.81 mg COD/L*day, respectively, and increase as the HRT decreases from 6 to 4 days. The concentration of NH4+-N ranges from 278.67 to 369.46 mg/L, which is not in the range that disturbs the performance and stability of the hydrolytic acidogenic reactor. It was concluded that an HRT of 3 days and an ORL of 1788.81 mg COD/L*day were selected as optimal operating conditions for the high performance and stability of the two-phase anaerobic digestion of slaughterhouse wastewater in the hydrolytic–acidogenic reactor at a mesophilic temperature. The findings of this study can be applicable for other agro-process industry wastewater types with similar characteristics and biowaste for value addition and sustainable biowaste management and safe discharge.