VFA Accumulation Research Articles

Use of embedding immobilized biofillers to improve hydrolysis acidification efficiency in domestic wastewater treatment

This study evaluated the effectiveness of embedding immobilization technology in wastewater treatment and its capacity to enhance the hydrolysis acidification process. Based on this technology, a stable anaerobic environment has been maintained. Results showed that the rates of dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) conversion both exceeded 98 % under short hydraulic retention time (HRT = 2h) and ambient temperature. Notably, acetic acid and propionic acid comprised up to 90.9 % of the total volatile fatty acids in the effluent, providing suitable carbon sources for downstream denitrification. 16S rRNA gene sequencing indicated that biofillers effectively enriched and retained functional bacteria, causing norank_Anaerolineaceae (11.6 %-29.7 %) and norank_Bacteroidetes_vadinHA17 (10.8 %-14.9 %) as the dominant genera in the reactor, which were crucial for refractory organic matter degradation. Immobilized biofillers effectively improved wastewater biodegradability, supporting a stable microbial community with high DON and DOP conversion rates as well as increased VFA accumulation.

The Possibility of Using Waste from Dye Sorption for Methane Production

The aim of this study was to determine the effect of sorption of Basic Red 46 (BR46) dye by lignocellulosic biomass on the susceptibility of the sorbed waste to anaerobic decomposition by anaerobic digestion. The research material used in the experiment consisted of two types of biomass: stalks with leaves and inflorescences after mowing Canadian goldenrod (Solidago canadensis L.) (GB), and rapeseed hulls (RHs) after oil pressing. During the anaerobic decomposition of RHs, 732.30 NmL/gVS and 646.63 NmL/gVS of methane were obtained from the non-sorbed substrate and the plant material after dye sorption, respectively. Similarly, in the variants using Canadian goldenrod, the production was 220.70 NmL/gVS and 183.20 NmL/gVS. The GB sorbent sorbed 34% more BR46 dye than the RH sorbent, which is likely to have resulted in the accumulation of VFA and contributed to the partial inhibition of methane production. In light of the obtained results and the literature data, it is concluded that there is a possibility of effective use of dye sorption waste for methane production.

A novel strategy combining hydrogenotrophic methanogens' bioaugmentation and biochar biostimulation for simultaneous polycyclic aromatic hydrocarbon biodegradation and bioenergy recovery.

A novel strategy combining bioaugmentation using methanogenic archaea and biostimulation using biochar was proposed for the first time to obtain simultaneous improvement of mixed PAHs' anaerobic biodegradation and bioenergy production. The results showed that the addition of PHAs immediately resulted in inhibition in methane production and accumulation of VFA, indicating that PHAs are more toxic to methanogens than the acetogenic bacteria. The coupling of biochar with hydrogenotrophic methanogen alleviated the inhibitory effects of PAHs, allowing the anaerobic fermentation system to recover its methane production capability rapidly. Compared to the Fe3+ + bioaugmentation group, the biochar + bioaugmentation group exhibited a 7.5% higher restored cumulative methane production. This coupling strategy ultimately facilitated the degradation of most PAHs, achieving a removal rate of over 90%. Moreover, the coupled biochar and bioaugmentation induced significant changes in the archaeal community structure. Direct interspecies electron guilds (i.e., Streptococcus and Methanosarcina) were enriched in the presence of biochar and bioaugmentation, responsible for prominent PAH removal and methane recovery. This study demonstrated the feasibility of simultaneous PAH biodegradation and bioenergy production using electron acceptor and enriched microorganisms.

Anaerobic digestion of winery solid waste in a two-stage membrane process: Effect of loading rate on biomethane production

The wine industry causes a high amount of solid waste with high organic content at different parts of the production line. One of the best strategies to overcome organic solid waste management problem is anaerobic digestion, as It allows renewable energy production and waste reduction together. The OLR is considered one of the most important operating parameters in continuous or semi-continuous anaerobic operations, as it affects the overall performance of anaerobic digestion systems. Therefore, appropriate OLR determination plays a crucial role in anaerobic digestion. This study investigated the effect of OLR on the performance of a TAnMBR treating (winery solid waste) WSW in terms of biogas and biomethane production. To this end, the production of biogas and biomethane from WSW via a TAnMBR at four different OLRs (0.5 0.75 1.0 1.5 gVS/Lreac d) was investigated. Biogas production rates were 677, 850, 1265, and 566 ml/gVS and biomethane production rates were 352, 450, 679, and 251 ml/gVS respectively, during 0.5 0.75 1.0 1.5 gVS/Lreac d OLR operating conditions. Results revealed that proper biogas and biomethane production can continue until the OLR is 1.5. VFA accumulation can be considered as the main inhibition reason, at 1.5 OLR VFA/Alk ratio increased up to 1.6 with 1864 mgHAc/L VFA concentration. Additionally, phenol and sulfate concentrations were below 45 and 48 mg/L during operation, respectively, therefore it is considered that no inhibition occurred due to these parameters.

Dual disintegration of microalgae biomass for cost-effective biomethane production: Energy and cost assessment

The present study aims to enhance the biomethane production potential of microalgae via a dual disintegration process. During this process, the microalgae biomass was firstly subjected to cell wall weakening by thermochemical disintegration (TC) (50 to 80 °C), pH adjustment with alkali, NaOH (6 to 10) and time (0 to 10 min) and, secondly, by bacterial disintegration (BD). TC-BD disintegration was comparatively higher (33 %) than BD (24 %), TC (8.5 %), and control (7 %). A more significant VFA accumulation of 2816 mg/L was recorded for TC-BD. Similarly, a greater substrate anaerobic biodegradability was achieved in TC-BD (0.32 g COD /g COD) than BD (0.21 g COD /g COD), TC alone (0.09 gCOD/g COD) and control (0.08 g COD /g COD), respectively. The TC-BD achieves a positive net profit and an energy ratio of + 0.12 GJ/d and 1.03. The proposed dual disintegration has a promising future for commercialization.

Revealing the occurrence of refractory melanoidins and inhibitions on anaerobic fermentation via thermal hydrolysis pretreatment

Thermal hydrolysis pretreatment (THP) is widely used to promote the hydrolysis of polysaccharides and proteins in waste activated sludge (WAS). However, it also generates unwanted refractory organics of melanoidins products (MPs), which should not be overlooked, especially concerning the occurrence and inhibition of hydrolases and anaerobes. In this study, the MPs occurrence by THP was investigated and inhibition mechanism on anaerobic fermentation was revealed for the first time. The results showed that SCOD in WAS significantly increased from 0.5±0.02 g/L in control to 4.1±0.02 g/L in THP at 180 °C. However, the color of MPs under a higher temperature (>120 °C) changed from colourless to dark brown. The components of MPs were mainly nitrogenous and humic acid-like refractory organics. Unwanted MPs generated above 160 °C reduced methane production by 49.1 %–89.8 %, which was due to the inhibition of protease, acidogenic bacteria, and acetoclastic methanogens. Inhibition of acetoclastic methanogens also resulted in the accumulation of VFAs. The microbial diversity clearly showed that the toxicity of MPs altered the microbial community structure, reducing the proportion of both acidogenic bacteria and acetoclastic methanogens. Therefore, the negative effect of MPs on anaerobic digestion demonstrated that THP should be re-evaluated in the production of biochemicals, which is important for achieving carbon neutrality of WWTPs in the future.

Comparative study of high-solid anaerobic digestion at laboratory and industrial scale – Process performance and microbial community structure

High-solid anaerobic digestion (HSD) for biogas production, compared with wet digestion, is attracting interest due to advantages such as reduced fresh water usage, improved digestate quality and potential for high organic loading rates. However, the underlying processes are not well described and evaluated for HSD. In this study, two laboratory-scale reactors (46 L) of plug-flow type were designed to simulate an industrial-scale HSD process co-digesting food waste, agricultural waste and garden residues under thermophilic conditions. Performance of the laboratory-scale HSD process under stable and disturbed conditions was compared with that in industrial-scale reactors. The results showed that the laboratory- and industrial-scale processes had similar efficiency (93 %) and VS-reduction (43 % and 41 %, respectively) and relatively similar specific methane production (339 and 366 NL CH4/kg VS, respectively). Results from tracer studies combined with chemical analyses showed no phase-separation or plug-flow behaviour along the horizontal axis in either laboratory- or industrial-scale reactors, indicating a need for further process optimisation. Analyses of microbial community structure showed high similarity between laboratory- and industrial-scale, but with some differences caused by downscaling. During the experiment, the laboratory- and industrial-scale processes both showed signs of disturbance, i.e. VFA accumulation at NH4+-N levels > 4 g/L, accompanied by a shift in microbial community structure at both scales, with significant increases in relative abundance of e.g. genera Defluviitoga and Methanothermobacter. In conclusion, this study confirmed the validity of simulating HSD at laboratory scale, thus providing valuable insights into biogas production from high-solid substrates, both in laboratory- and industrial-scale processes.

Nitrite acts as the key “switch” governing the free nitrous acid pretreatment in anaerobic digestion: A comprehensive mechanism of abiotic, bioinformatics and bioenergetics effects

Free nitrous acid (FNA) pretreatment has been an effective and environmentally-friendly strategy to improve anaerobic digestion (AD) performance, and the mechanism was generally ascribed to the abiotic role of enhancing substrate solubilization. However, a comprehensive understanding of FNA is lack considering the different biotic roles on various steps, microbes and functional genes, as well as the variation of thermodynamic conditions. Herein, FNA pretreatment significantly enhanced the AD performance of food waste (FW), and the maximum increment of methane yield (36.45 %) was observed for FNA level of 1.42 mg HNO2 − N/L. Nevertheless, FNA exhibited an inhibition-to-enhancement effects as the AD process proceeds, and the introduced nitrite was the key “switch”. Initially, the abiotic effects of FNA reduced the molecular weight of components in FW, benefiting the solubilization and formation of available organics (glucose and amino acid). The individual steps experiment confirmed that residual nitrite severely inhibited methanogenesis rather than hydrolysis and acidogenesis, which resulted in the decrement of methane yield and accumulation of VFAs. Meanwhile, the methanogens (Methanothrix and Methanobacterium) and genes involved in methanogenesis metabolisms (aceticlastic and hydrogenotrophic pathways) were downregulated. However, with the elimination of nitrite, the microbial activities and gene expressions restored and were even enhanced, and Gibbs-energy-based analysis suggested that accumulated VFAs provided favorable thermodynamic conditions for subsequent methanogenesis. This study firstly proved that the abiotic breakdown of macromolecule components, selective and reversible inhibition on microbes and functional genes induced by nitrite and varying thermodynamic conditions together governed the FNA affecting the AD process of FW.

Enhancing acidification efficiency of vegetable wastes through heat shock pretreatment and initial pH regulation.

Anaerobic digestion (AD) technology is a practical approach to alleviate severe environmental issues caused by vegetable wastes (VWs). However, its primary product is methane-rich biogas converted from the precursors (mainly volatile fatty acids, VFAs) after long fermentation periods, making traditional AD projects of low economic profits. Intervening in the methanogenesis stage artificially to produce high value-added VFAs can shorten the reaction time of the AD process and significantly improve profits, posing a promising alternative for treating VWs. Given this, this study applied heat shock (HS) pretreatment to inoculum to prevent methane production during AD and systemically investigated the effects of HS pretreatment and initial pH regulation on VFA production from VWs. The results showed that appropriate HS pretreatment effectively inhibited methane generation but promoted VFA accumulation, and VFA production was further enhanced by adjusting the initial pH to 8.0 and 9.0. The highest total VFA concentration of 14,883 mg/L witha VFA yield of 496.1 mg/gVS, 26.98% higher than that of the untreated group, was achieved at an initial pH 8.0 with HS pretreatment of 80 °C for 1 h. Moreover, pH regulation influenced the metabolic pathway of VFA production from VWs during AD, as butyrate was the dominant product at an initial pH of 6.0, while the increased initial pH improved the acetate proportion.

Unravelling the resilience of magnetite assisted granules to starvation and oxytetracycline stress

Starvation and antibiotics pollution are two frequent perturbations during breeding wastewater treatment process. Supplying magnetite into anaerobic system has been proved efficient to accelerate microbial aggregates and alleviate the adverse effect caused by process disturbance. Nevertheless, whether these magnetite-based granules are still superior over normal granules after a long-term starvation period remains unknown, the responsiveness of these granules to antibiotics stress is also ambiguous. In current study, we investigated the resilience of magnetite-based anaerobic granular sludge (AnGS) to starvation and oxytetracycline (OTC) stress, by unravelling the variations of reactor performance, sludge properties, ARGs dissemination and microbial community. Compared with the AnGS formed without magnetite, the magnetite assisted AnGS appeared more robust defense to starvation and OTC stress. With magnetite supplement, the average methane yield after starvation recovery, 50 mg/L and 200 mg/L OTC stress was enhanced by 48.95%, 115.87% and 488.41%, respectively, accompanied with less VFAs accumulation, improved tetracycline removal rate (76.3–86.6% vs. 51.0–53.5%) and higher ARGs reduction. Meanwhile, magnetite supplement effectively ameliorated the potential sludge breakage by triggering more large granules formation. Trichococcus was considered an important impetus in maintaining the stability of magnetite-based AnGS process. By inducing more syntrophic methanogenesis partnerships, especially for hydrogenotrophic methanogenesis, magnetite ensured the improved reactor performance and stronger resilience at stress conditions.

Improving removal of combined veterinary antibiotics and mitigating their negative impacts during anaerobic digestion of swine manure using modified bentonite

This study investigated the potential of modified bentonite (MB) material in mitigating the negative effects of combined veterinary antibiotics (CVAs) on anaerobic digestion (AD) process treating swine manure. Four CVAs (i.e., Oxytetracycline (OTC), Tetracycline (TC), Norfloxacin (Norf), and Sulfadiazine (SDZ)) were selected as they are most frequently detected in swine manure; and anaerobically incubated for 30 days under mesophilic conditions (37 °C) and with addition of different MB weights (1, 5, and 10 g L−1). Results showed that 1, 5, and 10 g L−1 of MB enhanced the removal of CVAs from 61.5 (no MB addition) to 72.7, 86.4, and 91.4 %, respectively. CVAs removal was accredited to biodegradation rather than adsorption to MB. Norf was rapidly transferred to solids causing an adsorption competition and decreasing co-antibiotics removal, while it was fast removed when MB was added. When 10 g L−1 of MB were added, the CVAs' adsorption competition diminished and their inhibition on CH4 production decreased from 27 % to 1.7 %. MB addition lowered the impact of CVAs significantly by maintaining pH stability, enhanced COD removal, decreased the VFAs accumulation, and improved the activity of bacteria and archaeal communities. The cost analysis showed that MB additions to AD would reduce cost by 52 % than applied methods for animal slurry pre-treatment or post-digestive treatment for reducing antibiotic residues. These findings suggests that using MB as an environmentally-friendly and commercial additive holds promise for reducing CVAs and eradicating their negative impacts with safe digestate disposal to land applications.

Process stability in expanded granular sludge bed bioreactors enhances resistance to organic load shocks

Environmental perturbations such as changes in organic loading rate (OLR) can have deleterious effects on the anaerobic digestion process, leading to VFA accumulation and process failure. However, the operational history of a reactor, such as prior exposure to VFA build up, can impact a reactor's resistance to shock loads. In the present study, the effects of long term (>100 days) bioreactor (un)stability on OLR shock resistance were assessed. Three 4 L EGSB bioreactors were subjected to varying levels of process stability. Operational conditions such as OLR, temperature and pH were maintained stable in R1; R2 was subjected to a series of minor OLR perturbations and R3 was subjected to a series of non-OLR perturbations, including ammonium, temperature, pH and sulfide. The effect of these different operational histories on each reactor's resistance to a sudden 8-fold increase in OLR were assessed by monitoring COD removal efficiency and biogas production. The microbial communities of each reactor were monitored using 16S rRNA gene sequencing to understand the relationship between microbial diversity and reactor stability. It was determined that the stable (un-perturbed) reactor performed best in terms of its resistance to a large OLR shock, despite its lower microbial community diversity.

Integrated microbial electrolysis with high-alkali pretreated sludge digestion: Insight into the effect of voltage on methanogenesis and substrate metabolism

Integrated microbial electrolysis with anaerobic digestion is proved to be an effective way to improve methanogenesis efficiency of waste activated sludge (WAS). WAS requires pretreatment for efficient improvement of acidification or methanogenesis efficiency, but excessive acidification may inhibit the methanogenesis. In order to balance these two stages, a method for efficient WAS hydrolysis and methanogenesis has been proposed in this study by high-alkaline pretreatment integrated with microbial electrolysis system. The effects of pretreatment methods and voltage on the normal temperature digestion of WAS have also been further investigated with emphasis on the effects of voltage and substrate metabolism. The results show that compared to low-alkaline pretreatment (pH = 10), high-alkaline pretreatment (pH > 14) can double the SCOD release and promote the VFAs accumulation to 5657 ± 392 mg COD/L, but inhibit the methanogenesis process. Microbial electrolysis can alleviate this inhibition effectively through the rapid consumption of VFAs and speeding up of the methanogenesis process. The optimal methane yield of the integrated system is 120.4 ± 8.4 mL/g VSS at the voltage of 0.5 V. Enzyme activities, high-throughput and gene function prediction analysis reveal that the cathode and anode maintain the activity of methanogens under high substrate concentrations. Voltage positively responded to improved methane yield from 0.3 to 0.8 V, but higher than 1.1 V is found to be unfavorable for cathodic methanogenesis and results in additional power loss. These findings provide a perspective idea for rapid and maximum biogas recovery from WAS.

Reduced graphene oxide-nano zerovalent iron assisted anaerobic digestion of dairy wastewater: A potential strategy for CH4 enrichment

Efficient waste management and alternatives for waste reduction have been the prime factors in achieving sustainable development goals. Large quantities of waste biomass can be transformed to energy by anaerobic fermentation. This study focused on improving the electron transport and subsequent CH4 enrichment in the anaerobic digestion of dairy wastewater by adding reduced graphene oxide-nano zerovalent iron (RGO-NZVI) composite. Different ratios (wt/wt) of RGO and NZVI were added to the anaerobic digesters and monitored their effects on biogas volume, composition, COD removal and VFA accumulation. There was 86.27 ± 2.8% high CH4 and 47.37 ± 1.3% improved COD removal in the digester containing the conductive additive compared to control. Comparing different ratios of RGO-NZVI revealed that a proportion of 2:1 was beneficial for maximum CH4 generation. Further, it was found that higher concentrations of the conductive additives could be fatal for microbial metabolism. A ratio of 0.5:1 had minimal support on degradation and the composition of CH4 in this digester was 34.14 ± 1.5% less than control. The metagenomic analysis showed that the diversification of microbial community and switching of major mechanism to direct interspecies electron transfer caused higher CH4 generation.

Potential of hydrochar/pyrochar derived from sawdust of oriental plane tree for stimulating methanization by mitigating propionic acid inhibition in mesophilic anaerobic digestion of swine manure

VFAs accumulation in anaerobic digestion systems can lead to disturbance of the acid base balance, which has brought major challenges for methane production. Meanwhile, less research explored the potential of biochar derived from wood wastes of oriental plane tree (Platanus orientalis L.) for stimulating methanization in mesophilic anaerobic digestion. In this study, the effects of pyrochar and hydrochar derived from sawdust of oriental plane tree on mesophilic anaerobic digestion of swine manure were compared for the first time. Fourier infrared transform analysis indicated that more functional groups existed on the surface of hydrochar, whereas higher ash content and BET specific surface area were found in pyrochar. The maximum methane production rate during anaerobic digestion was observed in the pyrochar treatment, which increased by 59.5% compared with the control without biochar. Although stimulative effects on dissolved organic carbon and volatile fatty acids production were both observed in the pyrochar and hydrochar treatments, the pyrochar treatment was much easier to trigger multipath methanogenesis and direct interspecific electron transport and subdue propionic acid accumulation compared to the hydrochar treatment. Moreover, redundancy analysis indicated that the variations in acetic acid and dissolved organic carbon were mostly associated with microbial succession. These results suggest that pyrochar has better promoting effects than HC in terms of methane generation and propionic acid inhibition alleviation owing to its special porous structures, functional groups (e.g., C=O, C–O and O–H), and physicochemical properties. These excellent properties play a greater role in recruiting functional archaea and bacteria to regulate the levels of volatile fatty acids and dissolved organic carbon to enhance the methane yield of anaerobic digestion. This study provides novel and valuable information for further engineering applications of pyrochar and hydrochar derived from sawdust of oriental plane tree in energy production and environmental waste treatment.

Efficiency of Chemical Toilet Sewage (CTS) Co-Fermentation with Typical Energy Crops

Chemical toilets are becoming more and more common. Large volumes of chemical toilet sewage (CTS) are generated in popular tourist destinations, where waste conveyance and treatment systems are not an option, which necessitates new methods for neutralizing such waste. Anaerobic digestion is, potentially, one such solution. The aim of the present study was to test the treatability of chemical toilet sewage (CTS) co-fermented with maize silage biomass using anaerobic digestion (AD). It was found that CTS does not impair AD, as long as the fluid used to dilute the feedstock does not contain more than 30% CTS. Biogas yield reached 400 cm3/gVS, and the biogas produced contained 57 ± 2.6% CH4 methane. Higher doses of CTS inhibited anaerobic digestion. This inhibition was directly linked to CTS toxicity, which reduced methanogen populations. This, in turn, slowed down VFA-to-biogas conversion, triggered VFA accumulation, and ultimately increased FOS/TAC and decreased pH.

Role of pine needle biochar in operation and stability of anaerobic processes.

Utility of biochar addition in anaerobic processes for promoting direct interspecies electron transfer (DIET) is demonstrated in this research. Biochar produced from pyrolysis of pine needle forest residue was used as conductive material for DIET. Three CSTRs were operated in parallel with and without biochar addition in fed-batch mode. Reactor without biochar which represented indirect interspecies electron transfer (IIET) exhibited wide variation in pH and VFA and took longer period during startup. All the rectors were operated at steady state with an OLR ranging from 0.5 to 1.75kg-COD/m3.d. As OLR increased, performance of reactor without biochar resulted in rapid pH drop and increase in VFA, leading to its eventual failure at OLR of 1.75kg-COD/m3.d. As against to this, performance of reactors with biochar remained robust and relatively unaffected at higher OLR values. Daily VFA accumulation from fed-batch mode always remained highest in reactor without biochar.

Effect of Different Acid and Base Potassium Ferrate Pretreatment on Organic Acid Recovery by Anaerobic Digestion of Sludge.

Potassium ferrate has strong oxidation in both acid and alkali environments, which has attracted extensive attention. However, the impact of the pH environment on this coupling process with the goal of resource recovery has not received attention. Under the goal of the efficient recovery of organic acid, the changes of solid-liquid characteristics of sludge after acid and alkaline ferrate pretreatment and during anaerobic digestion were discussed. The results showed that compared with blank control groups, after alkaline ferrate pretreatment, the volatile suspended solids (VSSs) decreased the most, reaching 28.19%. After being pretreated with alkaline ferrate, the sludge showed the maximum VFA accumulation (408.21 COD/g VSS) on the third day of digestion, which was 1.34 times higher than that of the acid ferrate pretreatment. Especially in an alkaline environment, there is no need to add additional alkaline substances to adjust the pH value, and the effect of sludge reduction and acid production is the best.

The Three-stage High Solid Anaerobic Digestion (TSHS- AD) under Ambient Temperature for Enhanced Biogas Production from Cow Manure

This research aimed to investigate the three-stage high solid anaerobic digestion (TSHS-AD) at ambient temperature. BMP was conducted at the various substrate to inoculum (S: I) ratios of 2:1, 4:1, and 6:1 on a volatile solid (VS) basis, each of which was conducted at different total solid concentrations (15%, 20%, and 30%). The highest methane yield of 343.97 mL-CH4·gVS-1 was achieved at 2:1-S: I ratio and 15 %TS. Meanwhile, TSHS-AD operated at S: I 2:1 and 15 %TS (20g-TS/L-R1) provide a maximum methane yield of 316.09 mL-CH4·gVS-1. The stage separation of TSHS-AD reduces inhibitors in the methanogenesis step. Moreover, it could create a full microbial function in each stage. Accumulation of VFA and semi-continuous feeding have considerable influence in enhancing anaerobic microbes involved in the biogas system. The annual income from biogas has the greatest impact on the investment attractiveness of TSHS-AD, according to the computation of IRR, NPV, and PB. The results obtained in this research could be potentially helpful to scale up the TSHS-AD system.

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.