Dominant Volatile Fatty Acids Research Articles

Microbial community dynamics and volatile fatty acid production during anaerobic digestion of microaerated food waste under different organic loadings

This study examined the effects of microaeration pretreatment and varying organic loading rates (OLRs) on volatile fatty acids (VFAs) production from food waste (FW) via anaerobic digestion process. FW was pretreated with 6 mL O2/g VS and digested at OLRs ranging from 10 to 25 g/L VS. Microaeration pretreatment increased the VFA yield to 7.4 g/L, whereas without pretreatment, it was 5.19 g/L, with butyrate as the dominant VFA (92 % at 25 g/L OLR) due to Firmicutes enrichment. A relatively high OLR initially increased VFA production but later favored propionate without pretreatment. Microbial analysis revealed that aerobic conditions promoted lactic acid bacteria such as Lactobacillus, increasing lactic acid production, whereas anaerobic conditions promoted Prevotella and butyrate producers such as Clostridium, which specialize in acetate and butyrate production. This study highlights that microaeration and an optimal OLR can increase and stabilize VFA yields, modulating the microbial community for tailored VFA profiles that are useful in biofuel and biochemical applications.

Performance, interaction, and metabolic pathway of novel dry–wet anaerobic digestion for treating high-solid agricultural waste

Anaerobic digestion (AD) with high-solid content of agricultural waste often leads to the accumulation of volatile fatty acids (VFAs) due to the imbalance of the functions of hydrolytic acidification bacteria and methanogenic archaea. This study developed a novel dry–wet AD of high-solid content was developed to make acidogenic bacteria and methanogenic archaea having higher collaboration ability. The results showed that the dry–wet AD system achieved a dynamic balance and synergistic effect between hydrolytic acidification and the methane production process, which shortened the lag phase to a minimum of 1.21 days. Additionally, the system exhibited a highest volumetric biogas production rate of 1.76 L L−1 d−1 when CM:CS and the initial pH were 6:4, 8.0, respectively. The total VFA concentration reached a maximum of 4.69 g L−1 d−1 and acetic acid (HAc) and butyric acid (HBu) were dominant VFAs (88.75%–93.27%) in the leachate in hydrolytic acidification phase. Metagenomic analysis indicated Pseudomonadales, Clostridiales, Bacteroidales, Spirochaetales, and Methanosaeta were dominant microorganism in hydrolytic acidification phase and methanogenic phase, respectively. The gene abundance of key enzymes in the acetoclastic methanogenic pathway significantly exceeded that of the hydrotrophic methanogenic pathway. This study provides a novel AD technology and insights into the energy conversion of agricultural waste.

Increasing biohydrogen production from swine wastewater influenced by anaerobic consortium and nickel ferrite nanoparticles

Screening of efficient microbial consortia and supplementing nanoparticles for pure hydrogen gas evolution have recently become urgent issues in the field of wastewater-derived hydrogen production. In this study, a newly isolated anaerobic consortium combining with nickel ferrite (NiFe2O4) nanoparticles (NPs) was applied to increase the biohydrogen production from swine wastewater. The suitable swine-wastewater-to-rice-straw-hydrolysate proportion was determined as 2:3, which corresponded to a cumulative hydrogen production of 1560.4 ± 10.3 mL/L. The addition of 200 mg/L NiFe2O4 NPs was found to be the most favorable for hydrogen gas evolution, resulting in a cumulative hydrogen production that was 21.8 % higher than that of the control (0 mg/L). Moreover, with the optimal dose (200 mg/L) of NiFe2O4 NPs, butyric acid was converted to the dominant volatile fatty acid, the microbialcommunity was dominated by Clostridium_sensu_stricto and Rummeliibacillus, and the relative expression of hydrogenase gene increased 175.4 ± 31.7-fold after 24 h of fermentation. The changes in microbial metabolism, distribution, and hydrogenase gene expression are helpful to increase the biohydrogen production with the addition of optimal dose of NiFe2O4 NPs.

Effect of composition of volatile fatty acids on yield of polyhydroxyalkanoates and mechanisms of bioconversion from activated sludge

Polyhydroxyalkanoates (PHA) is green biodegradable natural polymer. Here PHA production from volatile fatty acids (VFAs) was investigated in sequential batch reactors inoculated with activated sludge. Single or mixed VFAs ranging from acetate to valerate were evaluated, and the dominant VFA concentration was 2 times of that of the others in the tests. Results showed that mixed substrates achieved about 1.6 times higher yield of PHA production than single substrate. The butyrate-dominated substrates maximized PHA content at 72.08% of VSS, and the valerate-dominated substrates were followed with PHA content at 61.57%. Metabolic flux analysis showed the presence of valerate in the substrates caused a more robust PHA production. There was at least 20% of 3-hydroxyvalerate in the polymer. Hydrogenophaga and Comamonas were the main PHA producers. As VFAs could be produced in anaerobic digestion of organic wastes, the methods and data here could be referred for efficient green bioconversion of PHA.

A Novel Fermentation Method for the Target Production of Propionic Acid Dominant Volatile Fatty Acids from Food Waste for Pathogen Inactivation

A Novel Fermentation Method for the Target Production of Propionic Acid Dominant Volatile Fatty Acids from Food Waste for Pathogen Inactivation

Effect of Temporal Variation in Chemical Composition on Methane Yields of Rendering Plant Wastewater

The effect of temporal variation in chemical composition on methane yields of rendering plant wastewater was studied in batch experiments at 37 °C. In total, 14 grab samples were collected from Monday through Friday (Day 1 to 5) from a rendering plant located in Queensland, Australia. Each day, three samples were collected: early morning (S1), midday (S2) and afternoon (S3). Chemical analyses showed that a significant different in total solids (TS), volatile solids (VS), and chemical oxygen demand (COD) was noticed among the samples. TS content ranged from 0.13% to 1.82% w/w, while VS content was between 0.11% and 1.44% w/w. Among the samples, S2 of Day 3 had the highest COD concentration (10.5 g/L) whilst S1 of Day 1 had the lowest COD (3.75 g/L) and total volatile fatty acid (VFA) concentration (149.1 mg/L). In all samples, acetic acid was the dominant VFA and accounted for more than 65–90% of total VFAs. Biochemical methane potential studies showed that the highest methane yield of 270.2 L CH4/kgCODadded was obtained from S3 of Day 3. Whilst the lowest methane yield was noticed for S1 of Day 1 (83.7 L CH4/kgCODadded). Results from kinetic modelling showed the modified Grompetz model was best fit than the first order model and a large variation was noticed between the experimental and the modelled data. Time delay ranged from 2.51 to 3.84 d whilst hydrolysis constant values were close to 0.21 d−1. Thus, the study showed that chemical composition of incoming feed to a biogas plant varies throughout the week and is dependent on the chemical composition of organic materials received and the amount of steam used for rendering process.

Effect of Volatile Fatty Acids Accumulation on Biogas Production by Sludge-Feeding Thermophilic Anaerobic Digester and Predicting Process Parameters

Sewage sludge represents an important resource for reuse in the wastewater treatment field. Hence, thermophilic anaerobic digestion (TAD) could be an alternative technique to recover renewable resources from sludge. In the TAD biodegradation process, volatile fatty acids (VFAs) are the intermediate products of methanogenesis. However, the higher formation and accumulation of VFAs leads to microbial stress, resulting in acidification and failure of the digester. Therefore, several batch TADs have been investigated to evaluate the VFAs production from sludge and their impact on biogas generation and biodegradation efficiency. Three types of sewage sludges, e.g., primary sludge (PS), secondary sludge (SS), and mixed sludge (MS) were used as substrates to estimate the accumulation of VFAs and yield of methane gas. The system showed the maximum total VFAs accumulation from both PS and MS as 824.68 ± 0.5 mg/L and 236.67 ± 0.5 mg/L, respectively. The dominant VFA accumulation was identified as acetic acid, the main intermediate by-product of methane production. The produced biogas from PS and MS contained 66.75 ± 0.5% and 52.29 ± 0.5% methane, respectively. The high content of methane with PS-feeding digesters was due to the higher accumulation of VFAs (i.e., 824.68 ± 0.5 mg/L) in the TAD. The study also predicted the design parameters of TAD process by fitting the lab-scale experimental data with the well-known first-order kinetic and logistic models. Such predicted design parameters are significantly important before the large-scale application of the TAD process.

Evaluation of volatile fatty acids (VFAs) production in thermophilic and mesophilic anaerobic digestion of oil palm empty fruit bunch (OPEFB)

Palm oil is one of the leading global commodities, and Indonesia is one of the largest palm oil producers in the world. One of the solid wastes generated from oil palm industrial activities is oil palm empty fruit bunches (OPEFB). The annual accumulation of OPEFB in Indonesia is 126,317.54 tons/year, and it increases with increasing palm oil production. The cellulosic content of OPEFB is a potential substrate for anaerobic digestion to produce volatile fatty acids (VFAs). This study used chemical pretreatment (NaOH 8% w/V) for OPEFB delignification before the anaerobic digestion for VFAs production. Digested cow manure (DCM) was used as the inoculum. Process optimization of producing VFAs is challenging because VFAs act as intermediate products in the metabolic pathway of anaerobic digestion. In general, the temperature can affect the activity of hydrolytic and acidogenic facultative microorganisms. It increases the hydrolysis rate of organic polymers to more soluble forms and improves the performance of anaerobic reactors for the formation of VFAs. This study examines the effect of temperature on the anaerobic digestion process of OPEFB for VFAs production in a batch reactor. The temperature varied in mesophilic (29 °C) and thermophilic (55 °C) conditions. This study showed that anaerobic digestion in the thermophilic conditions produces almost thrice VFAs compared to the mesophilic process. The highest accumulation of VFAs in both reactors occurred on the seventh day, i.e., 3311.57 ± 89 mg.L−1 at ORP -163 ± 16 mV in the thermophilic reactor and 1307 ± 42 mg.L−1 at ORP -224 ± 32 mV in the mesophilic reactor. Acetic acid was the dominant VFA in each reactor. The VFA production in thermophilic reactor (RT) reached 59% of the stoichiometric potential. Although the thermophilic condition improves the VFA yield compared to the mesophilic condition, further study is still needed to increase the VFA production from OPEFB.

Chicken manure-based bioponics: Effects of acetic acid supplementation on nitrogen and phosphorus recoveries and microbial communities.

Bioponics has the potential to recover nutrients from organic waste streams, such as chicken manure and digestate with high volatile fatty acid (VFA) contents through crop production. Acetic acid, a dominant VFA, was supplemented weekly (0, 500, 1000, and 1500mg/L) in a chicken manure-based bioponic system, and its effect on the performance of bioponics (e.g., plant yield and nitrogen and phosphorus availabilities) was examined. Microbial communities were analyzed using 16S rRNA gene sequencing, and the functional gene abundances were predicted using PICRUSt. Although acetic acid negatively affected plant yield, no significant difference (p>0.05) was noted in the average nitrogen or phosphorus concentration. In terms of nutrient recovery, the bioponic systems still functioned well, although higher concentrations of acetic acid decreased plant yield and altered the bacterial communities in plant roots and chicken manure sediments. These data suggest that an acetic acid concentration of<500mg/L or a longer loading interval is recommended for the effective operation of chicken manure and digestate-based bioponics.

Improvement of Hydrogen Production during Anaerobic Fermentation of Food Waste Leachate by Enriched Bacterial Culture Using Biochar as an Additive.

It has become urgent to develop cost-effective and clean technologies for the rapid and efficient treatment of food waste leachate, caused by the rapid accumulation of food waste volume. Moreover, to face the energy crisis, and to avoid dependence on non-renewable energy sources, the investigation of new sustainable and renewable energy sources from organic waste to energy conversion is an attractive option. Green energy biohydrogen production from food waste leachate, using a microbial pathway, is one of the most efficient technologies, due to its eco-friendly nature and high energy yield. Therefore, the present study aimed to evaluate the ability of an enriched bacterial mixture, isolated from forest soil, to enhance hydrogen production from food waste leachate using biochar. A lab-scale analysis was conducted at 35 °C and at different pH values (4, no adjustment, 6, 6.5, 7, and 7.5) over a period of 15 days. The sample with the enriched bacterial mixture supplemented with an optimum of 10 g/L of biochar showed the highest performance, with a maximum hydrogen yield of 1620 mL/day on day three. The total solid and volatile solid removal rates were 78.5% and 75% after 15 days, respectively. Acetic and butyrate acids were the dominant volatile fatty acids produced during the process, as favorable metabolic pathways for accelerating hydrogen production.

Bioaugmented Mixed Culture by Clostridium aceticum to Manipulate Volatile Fatty Acids Composition From the Fermentation of Cheese Production Wastewater.

Production of targeted volatile fatty acid (VFA) composition by fermentation is a promising approach for upstream and post-stream VFA applications. In the current study, the bioaugmented mixed microbial culture by Clostridium aceticum was used to produce an acetic acid dominant VFA mixture. For this purpose, anaerobic sequencing batch reactors (bioaugmented and control) were operated under pH 10 and fed by cheese processing wastewater. The efficiency and stability of the bioaugmentation strategy were monitored using the production and composition of VFA, the quantity of C. aceticum (by qPCR), and bacterial community profile (16S rRNA Illumina Sequencing). The bioaugmented mixed culture significantly increased acetic acid concentration in the VFA mixture (from 1170 ± 18 to 122 ± 9 mgCOD/L) compared to the control reactor. Furthermore, the total VFA production (from 1254 ± 11 to 5493 ± 36 mgCOD/L) was also enhanced. Nevertheless, the bioaugmentation could not shift the propionic acid dominancy in the VFA mixture. The most significant effect of bioaugmentation on the bacterial community profile was seen in the relative abundance of the Thermoanaerobacterales Family III. Incertae sedis, its relative abundance increased simultaneously with the gene copy number of C. aceticum during bioaugmentation. These results suggest that there might be a syntropy between species of Thermoanaerobacterales Family III. Incertae sedis and C. aceticum. The cycle analysis showed that 6 h (instead of 24 h) was adequate retention time to achieve the same acetic acid and total VFA production efficiency. Biobased acetic acid production is widely applicable and economically competitive with petroleum-based production, and this study has the potential to enable a new approach as produced acetic acid dominant VFA can replace external carbon sources for different processes (such as denitrification) in WWTPs. In this way, the higher treatment efficiency for WWTPs can be obtained by recovered substrate from the waste streams that promote a circular economy approach.

Bioconversion of food waste to volatile fatty acids: Impact of microbial community, pH and retention time

Bio-based production of materials from waste streams is a pivotal aspect in a circular economy. This study aimed to investigate the influence of inoculum (three different sludge taken from anaerobic digestors), pH (5 & 10) and retention time on production of total volatile fatty acids (VFAs), VFA composition as well as the microbial community during anaerobic digestion of food waste. The highest VFA production was ∼22000 ± 1036 mg COD/L and 12927 ± 1029 mg COD/L on day 15 using the inoculum acclimated to food waste at pH 10 and pH 5, respectively. Acetic acid was the dominant VFA in the batch reactors with initial alkaline conditions, whereas both propionic and acetic acids were the dominant products in the acidic condition. Firmicutes, Chloroflexi and Bacteroidetes had the highest relative abundance in the reactors. VFA generation was positively correlated to the relative abundance of Firmicutes.

Butyric acid dominant volatile fatty acids production: Bio-augmentation of mixed culture fermentation by Clostridium butyricum

The most sustainable and environmentally friendly butyric acid production method is fermentation; however, low production yield and high substrate cost limit the competition with petrol-based production. The study is aimed to enhance butyric acid production via bioaugmentated mixed culture by Clostridium butyricum. Anaerobic sequencing batch reactors (bioaugmented and control) were operated under alkali pH (pH 10) at 35 °C and fed by dairy industry wastewater as substrate. The performance of bioaugmentation was monitored in three stages: before the application, during the application (C. butyricum was injected as %10 of active reactor volume on a daily basis for seven days), after bioaugmentation. The VFA concentration and composition (by GC-FID) with the copy gene number of C. butyricum (by Q-PCR) were monitored in the bioaugmented reactor during the operation. The bioaugmentation of C. butyricum increased butyric acid production (mgCOD L-1) from 260 ± 36 to 2889 ± 180. The total VFA production (mgCOD L-1) was increased from 1434 ± 217 to 4642 ± 1778 in control and bioaugmented reactors, respectively. There was a positive correlation between the gene copies of C. butyricum with butyric, hexanoic, n-heptanoic, valeric acids production. Furthermore, the bioaugmented mixed culture had better performance than pure culture regarding butyric acid production. The cycle analysis showed that the similar butyric acid production efficiency would be obtained in the first 6 h in the bioaugmented reactor, in the first 14 h in the control reactor of the cycle. The study provides a fundamental solution to step forward to achieve next-generation biorefineries by using both monocultures modularity and mixed culture robustness and stability regarding.

Pre-treatment study on two-stage biohydrogen and biomethane productions in a continuous co-digestion process from a mixture of swine manure and pineapple waste

This study involves continuous co-digestion of swine manure and pineapple waste mixture using two-stage anaerobic reactors and examines hydraulic retention time (HRT) and substrate heat pre-treatment. The maximum hydrogen and methane production rates of 1488.62 and 991.57 mL/L/d, respectively, reached optimal HRTs of 4.5 h in the hydrogen production fermenter (HPF) and 9 d in the methane production fermenter (MPF) using heat pre-treatment. Acetic acid is a dominant volatile fatty acid of the soluble metabolites with values 70%–73% under all the tested conditions and increased values under heat pre-treatment and high HRT. Firmicutes and Euryarchaeota are the main bacteria species detected in HPF and MPF, respectively. The optimal total energy of 196.47 kJ/L/d and chemical oxygen demand (COD) removal efficiency of 90% were obtained by a complete anaerobic co-digestion process at a high substrate concentration of 105 g COD/L and low HRT of 4.5 h. This shows that the two-stage co-digestion process could increase the COD removal efficiency, hydrogen production rate, and net energy gains and produce high quality biogas and significantly reduce fermentation time.

Acidogenic and methanogenic properties of corn straw silage: Regulation and microbial analysis of two-phase anaerobic digestion

Corn straw silage (CSS) is one of the organic solid residues available for biogas production. The aim of this study was to investigate the possibility and optimal controlling strategy for anaerobic digestion (AD) of CSS. Four leaching bed reactors (LBR) were operated at different pH. Maximum volatile fatty acids (VFAs) concentration of 19.34 g/L was reached at pH 8.0 with acetic and propionic acids as dominant VFAs. The subsequent microbial analysis indicated that abundant bacteria were Firmicutes, Bacteroidetes and Proteobacteria. UASB as methanogenic reactor was integrated with the LBR. The organic loading rate (OLR) could reach 8 g COD/L·d with effective conversion of VFAs. Acetotrophic Methanosaeta and hydrogenotrophic Methanobacterium played major roles in methanogenic process. In the whole process, the results showed that methane yield of 143.4 mL CH4/g volatile solid (VS) was obtained. pH and OLR controls in two-phase AD were feasible for methane production from CSS.

Anaerobic digestion of swine manure using aqueous pyrolysis liquid as an additive

As a very typical agricultural organic waste, the anaerobic treatment of swine manure requires more mechanistic exploration to improve the efficiency and quality of its conversion to renewable energy. The feasibility of using aqueous pyrolysis liquid (APL) as anaerobic digestion (AD) substrate has been verified, however only few applications of APL as an additive to AD have been reported. The application of diluted APLs (5 times dilution (A5), 50 times dilution (A50), and 100 times dilution (A100)) as an additive in AD of swine manure was investigated. The result showed that the effects of different concentrations of APL on AD are different. A50 improved methanogenic capacity by 22.98 ± 5.82% compared to control because of trace elements in APL, which both enhanced resistance of microorganisms to high ammonia nitrogen (TAN) concentration, and reduced TAN accumulation. Accordingly, the average dissolved organic carbon (DOC) concentration for A50 was lower than in the control. Based on microbial communities, the dominant volatile fatty acids (VFAs) were degraded mainly by Methanosarcina and Methanobrevibacter. The versatile metabolic pathways and high relative abundance of Methanosarcina for A50 rationalized the high methane production. Therefore, the use of APL as an additive has considerable potential of application.

Dynamic behaviors of batch anaerobic systems of food waste for methane production under different organic loads, substrate to inoculum ratios and initial pH

This study characterized dynamic behaviors of batch anaerobic digesters treating food waste in terms of methane production, organics destruction and process stability under different organic loads (OLs), substrate to inoculum (S/I) ratios [on volatile solid (VS) basis] and initial pH. The results showed that OL, S/I ratio and initial pH significantly affected batch anaerobic process. Methane yield was proved to be inversely proportional to OL and S/I ratio. Digester with lowest OL (5g VS/L) obtained greatest methane yield (551.4mL/g VS), highest organics removal (94.1%) and good stability. Enhancing OL to 10g VS/L was recommended for satisfactory stability and higher volumetric methane productivity. When OL was designated as 10g VS/L, digester with low S/I ratio (1/2) achieved satisfactory methane yield (539.3mL/g VS), high organics removal (92.3%) and stable performance. When OL was relatively high (20g VS/L), adjusting initial pH to 7.5 contributed to stable performance via enhancing buffering capacity against volatile fatty acids (VFA) disturbance. Strong VFA inhibition occurred under high OL (40g VS/L) or great S/I ratio (2/1) or acidic initial pH (6.5). In this case, acetate was dominant VFA, followed by butyrate. However, when digester was stable, acetate was main VFA, followed by propionate. This study provided practical guidance on process configurations for batch digesters of food waste needed to achieve satisfactory performance and stability.

Upgrading volatile fatty acids production through anaerobic co-fermentation of mushroom residue and sewage sludge: Performance evaluation and kinetic analysis

Due to complex inherent structure of lignocellulosic biomass, inefficient hydrolysis and acidification limits fermentative volatile fatty acids (VFA) production of mushroom residues. Meanwhile, the mushroom residues present insufficient nutrient with a high C/N ratio. To solve this issue, anaerobic co-fermentation of cellulose-rich Oyster champost and sewage sludge was tested to enhance the VFA production, and the effect of proportion of mixed substrate was investigated in this study. The results indicated that the sewage sludge yielded higher VFAs than the Oyster champost in single-substrate fermentative system. The maximal VFA yield of 595 mgCOD/gVSadded was achieved when the proportion of sewage sludge increased to 50% in the mixed substrate. In the co-fermentation system, the optimal C/N ratio and features of mixed substrate contributed to the enhancement in hydrolysis and acidification in terms of organic solubilization and VFA production, respectively. But the co-fermentation could not increase VFA/SCOD ratio, probably due to the existence of refractory products such as humic-like and protein-like materials. Besides, this co-fermentation system had strong buffer capacity and it was not necessary to dose chemicals to control the system pH for stable VFA production. Acetate was the dominant VFA product in co-fermentation systems. A modified-Logistic model fitted co-fermentation of sludge and Oyster champost well, and presented a faster rate and higher efficiency of VFA production.

The effect of mixing on fermentation of primary solids, glycerol, and biodiesel waste.

In this study, the effect of mixing on volatile fatty acid (VFA) production and composition was investigated through running five identical bench-scale reactors that were filled with primary solid and dosed with either pure glycerol or biodiesel waste. Experimental results revealed that there was an inverse correlation between the mixing intensity and the VFA production. The total VFA production in the un-mixed reactor was 9,787 ± 3,601 mg COD/L, whereas in the reactor mixed at 100 rpm this dropped to 3,927 ± 1,175 mg COD/L, while both types of reactor were dosed with pure glycerol at the beginning of each cycle to reach the initial concentration of 1,000 mg/L (1,217 mg COD/L). Propionic acid was the dominant VFA in all the reactors except the reactor mixed at 30 rpm. It is hypothesized that low mixing facilitated hydrogen transfer between obligate hydrogen producing acetogens (OHPA) and hydrogen consuming acidogens in these non-methanogenic reactors. Also, in a narrower range of mixing (0 or 7 rpm), the total VFA production in biodiesel waste-fed reactors was considerably higher than that of pure glycerol-fed reactors.

Biological hydrolysis pretreatment on secondary sludge: Enhancement of anaerobic digestion and mechanism study

The performance of biological hydrolysis (BH) pretreatment on municipal secondary sludge was evaluated in this study. During 6-day BH at 42°C (BH42), soluble chemical oxygen demand (sCOD) increased from 175.2±38.2mg/L to 3314.5±683.4mg/L; the dominant volatile fatty acid (VFA) was acetic acid, and its concentration increased from 41.5±2.1mg/L to 786.0±133.2mg/L. The extracted extracellular polymeric substances (EPS) from untreated secondary sludge contained three main fractions, and Fraction I gradually decreased from 133.9kDa to 24.9kDa during 6-day BH42. The BH pre-treatment at 42°C and 55°C both achieved more than 4-log reduction of total coliforms and 3-log reduction of E. coli. The BH pretreated secondary sludge at 15-day biochemical methane potential (BMP) test was comparable with the untreated secondary sludge after 30-day BMP, showing a significant enhancement on the acceleration of biogas production by BH pretreatment.