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Food waste is categorized as organic solid waste, which has a negative impact on environmental sustainability. Food waste was simultaneously used for the feasible generation of mixed volatile fatty acids (VFAs) and bio-hydrogen by deploying dark fermentation. Original anaerobic digested sludge was prepared via the shock technique with 50 g/L glucose under thermophilic temperature (55 °C). The pretreated inoculum was found capable of converting 10 g VS/L food waste to hydrogen with a rather high yield of 135.2 ± 7 mL H2/VSadded. The effect of various concentrations of food waste, including 10.2, 16.3, 20.3, and 26.4 g VS/L, on mixed VFAs production was subsequently carried out in batch dark fermentation. The highest butyric acid concentration (5.26 ± 0.22 g/L) in soluble metabolites was obtained from batch dark fermentation with 26.4 g VS/L of food waste. The dominant Clostridium thermobutyricum,Clostridium sporogenes, and Octadecobacter sp. found in the batch of dark fermentation of food waste could confirm the effectiveness of the load shock pretreatment method for inoculum preparation. The continuous stirred tank reactor (CSTR) inoculated with mixed cultures, also prepared via the load shock pretreatment method and without the addition of external nutrients, was operated by feeding 26.4 g VS/L food waste at the kinetically designed HRT for 4 days, corresponding to an organic loading rate (OLR) of 7.6 g VS/L·d. Under steady state conditions, promising butyric acid (5.65 ± 0.51 g/L)-rich mixed VFAs were achieved along with the hydrogen yield of 104.9 ± 11.0 mL-H2/g VSadded, which is similar to the upper side of the previously reported yields (8.8 ± 0.6–103.6 ± 0.6 mL-H2/g VS).

Acceleration of the anaerobic digestion (AD) process is crucial to achieving energy-efficient recycling of organic wastes. Hydrochar is produced by hydrothermal liquefaction of biomass, yet its application in the AD process is rarely reported. The present study showed that sewage sludge-derived hydrochar (SH) enhanced the methane production rate of glucose by 37%. SH increased the methane production rate from acetate but did not affect acidification and the methane production rate from H2/CO2. SH enhanced hydrogenotrophic methanogenesis, which could be due to direct interspecies electron transfer (DIET) by converting H+, e-, and CO2 to methane. Trichococcus and Methanosaeta were dominant in the AD process with SH. Label-free proteomic analysis showed Methanosaeta was involved in DIET as reflected by the up-regulation of proteins involved in hydrogenotrophic methanogenesis. Hydrochars derived from corn straw (CH), Enteromorpha algae (EH), and poplar wood (PH), as well as activated carbon (AC), were also tested in the AD process. SH, CH, and EH obviously increased the methane production rates, which were 39%, 15%, and 20% higher than the control experiment, respectively. It was neither electrical conductivity nor the total redox property of hydrochars and AC but the abundances of surface oxygen-containing functional groups that correlated to the methane production rates.

This study attempted to find potential effective thermotolerant microorganisms producing complex enzymes for use in the hydrolyzing empty fruit bunch (EFB) to reduce cost of enzyme and enhance the efficiency of saccharification. The enrichment process at 45 °C was employed as a strategy to obtain four effective thermotolerant microorganisms. Streptomyces thermocarboxydus ME742, Bacillus subtilis ME751 and Bacillus amyloliquefaciens ASB/TRE produced the highest activity of xylanase (226.2 U/mL), CMCase (3.84 U/mL) and FPase (69.55 U/mL), respectively, while Aspergillus fumigatus A4112 exhibited the highest specific activity of xylanase (637.9 U/mg), CMCase (5.55 U/mg) and FPase (21.58 U/mg). Xylanase of isolated ME742 and A4112, CMCase of isolated ASB/TRE, FPase of isolated ME742, ME751 and ASB/TRE possessed thermostability with 80% remaining activity at 60 °C after 1 h incubation. These four strains were capable to reduce 49–78% (w/w) lignin in raw EFB with simultaneous enzyme production. The EFB residue was reused as substrate for saccharification with the highest amount of reducing sugar using the crude enzymes from S. thermocarboxydus ME742 (9.24 mg/g EFB). The sugar was 3.76 and 3.61 fold higher than that obtained from saccharification of acid- and alkaline-pretreated EFB, respectively. Moreover, the crude enzymes from A. fumigatus A4112 and B. amyloliquefaciens ASB/TRE hydrolyzed palm oil mill effluent (POME) to generate high yield of reducing sugar (61.01–64.63 mg/g TS-POME). Therefore, these selected strains were considered as the potent biological tool applicable in the bioconversion of oil palm biomass to fermentable reducing sugars.

Some species of the genus Clostridium are efficient acetate producers and have been deemed useful for upgrading industrial biogas. An acetogenic, strictly anaerobic, Gram-stain-positive, subterminal endospore-forming bacterium designated strain PL3T was isolated from peatland soil enrichments with H2 and CO2. Cells of strain PL3T were 0.8–1.0×4.0–10.0 µm in size and rod-shaped. Growth of strain PL3T occurred at pH 6.0–7.5 (optimum, pH 7.0), at 20–40 °C (optimum, 30 °C) and with 0–1.5 % (w/v) NaCl (optimum, 0.5%). Biochemical analyses revealed that strain PL3T metabolized lactose, maltose, raffinose, rhamnose, lactic acid, sorbitol, arabinose and glycerol. Acetic acid was the predominant metabolite under anaerobic respiration with H2/CO2. The major cellular fatty acids were C16 : 0, C16 : 1 cis 9 and C17 : 0 cyc. The main polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, aminolipid and aminophospholipid. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain PL3T belongs to the genus Clostridium with the highest sequence similarity to Clostridium aciditolerans DSM 17425T (98.6 %) followed by Clostridium nitrophenolicum (97.8 %). The genomic DNA G+C content of strain PL3T was 31.1 mol%.The genomic in silico DNA–DNA hybridization value between strain PL3T and C. aciditolerans DSM 17425T was 25.1 %, with an average nucleotide identity of 80.2 %. Based on phenotypic, chemotaxonomic and phylogenetic differences, strain PL3T was suggested to represent a novel species of the genus Clostridium , for which the name Clostridium thailandense sp. nov. is proposed. The type strain is PL3T (=DSM 111812T=TISTR 2984T).

High-strength waste activated sludge (WAS) and greasy sludge (GS) were largely generated from canned tuna processing. This study reports the performance of the two-stage anaerobic process for co-digesting WAS and GS. Various WAS:GS mixing ratios of 0:100, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, and 100:00 (volatile solids (VS) basis) were investigated in batch acidogenic stage at ambient (30 °C ± 3 °C), 55 °C, and 60 °C temperatures. Subsequently, the effluents from the first stage were used to produce methane in the second methanogenic stage at an ambient temperature. The highest methane yield of 609 mL CH

The sulfate-reducing bacteria (SRB) consortium (Desulfovibrio sp. Desulfitibacter sp. Dethiosulfatibacter sp. and Clostridium sp.) was investigated for sulfate removal and biohythane production from rubber sheet wastewater (RSW). The RSW at COD/ SO 4 2 − ratio of 13 and pH 6 was suitable for sulfate reduction and biohythane production. Hydrogen yield, sulfate removal efficiency, and methane yield were 101 mL H2·gVS−1, 87%, and 629 mL CH4·gVS−1, respectively. The hydrogen and methane production rate was 14.53 mL H2·d−1and 45 mL CH4·d−1, respectively. Hydrogen effluent with trace element supplemented improved hydrolysis rate (kh) from 0.19 d−1 to 0.23 d−1 and methane production rate from 31–48 to 42–97 mL CH4·d−1. The COD removal of RSW in acidogenic stage and methane stage was 11.3% and 72.4–76.2%, respectively. The sulfate removal of RSW in acidogenic stage and methane stage was 87% and 9%, respectively. Two-stage anaerobic fermentation obtained simultaneous biohythane production and sulfate removal with efficiently for energy recovery from RSW.

Biohydrogen production from palm oil mill effluent by two-stage dark fermentation and microbial electrolysis was investigated under thermophilic condition. The optimum chemical oxygen demand (COD) concentration and pH for dark fermentation were 66 g·L−1 and 6.5 with a hydrogen yield of 73 mL-H2·gCOD−1. The dark fermentation effluent consisted of mainly acetate and butyrate. The optimum voltage for microbial electrolysis was 0.7 V with a hydrogen yield of 163 mL-H2·gCOD−1. The hydrogen yield of continuous two-stage dark fermentation and microbial electrolysis was 236 mL-H2·gCOD−1 with a hydrogen production rate of 7.81 L·L−1·d−1. The hydrogen yield was 3 times increased when compared with dark fermentation alone. Thermoanaerobacterium sp. was dominated in the dark fermentation stage while Geobacter sp. and Desulfovibrio sp. dominated in the microbial electrolysis cell stage. Two-stage dark fermentation and microbial electrolysis under thermophilic condition is a highly promising option to maximize the conversion of palm oil mill effluent into biohydrogen.

The efficacy of concentrated enzymes from Trichoderma koningiopsis TM3 in hydrolyzing palm oil mill effluent (POME) and oil palm trunk residues (OPTr) at 40 and 50 °C was evaluated prior to methane fermentation. POME hydrolysate containing total sugar concentration of 15.40 g L−1 was obtained from enzymatic hydrolysis using 15 Unit g−1 TVS at 50 °C for 18 h incubation with the hydrolysis yield of 0.35 g total sugars g−1 TVS. The OPTr hydrolysate contained slightly higher total sugar concentration (18.90 g L−1) with the hydrolysis yield of 0.85 g total sugars g−1 TVS under the same condition. Methane production from POME hydrolysate was 6.29% higher than the raw POME. Co-digestion of POME hydrolysate with OPTr gave the maximum methane yield (369 ml CH4 g−1 VS-added) with the increase of 9.28% compared to the raw POME. The methane production rate (Rmax) and the hydrolysis rate constant (kh) of the co-digestion of POME hydrolysate with OPTr were 1.2-fold higher than those of the POME hydrolysate. PCR-DGGE analysis revealed that Clostridium sp. and Petrimonas sp. were dominated bacteria while Methanosarcina sp. and Methanospirillum sp. played an important role in methane production. These results indicated that enzymatic pretreatment and co-digestion of POME hydrolysate with OPTr could improve methane yield from anaerobic fermentation of POME.

In this study, the performance of immobilized cells on granular activated carbon (GAC) for thermophilic biohydrogen production is determined using POME as a fermentation substrate. The immobilized cells are formed at different pH medium using sugar composition characterized in the POME. The pH 6 revealed the optimum pH used for biofilm development with HPR of 2.8 mmol H2/L h. The effect of sugar utilization by the immobilized cells on GAC are determined at different sugar concentration using the Monod model prior validated the performance of the cells in the fluidized bed reactor (FBR). From the model, 0.316 ± 0.013 h−1 of maximum specific growth rate was obtained at 20 g/L sugar used and was keep increasing to the maximum of 30 g/L of sugar used with HPR 2.6–2.8 mmol H2/L h. Lastly, the POME-enriched nutrients are used as the carbon source in the fluidized bed reactor (FBR). The highest HPR obtained was at HRT 12 h, (5.2 mmol H2/L h) and HY of 1.24 mol H2/mol sugar. The screening of the microbial population by DGGE revealed that the Thermoanaerobacterium thermosaccharolyticum sp. was dominant for all the HRTs, thereby indicating that this bacterium is resilient towards environmental disturbances.

Methane production from solid-state anaerobic digestion (SS-AD) of empty fruit bunches (EFB) using recycling solid-anaerobic digested (S-AD) sludge and liquid-anaerobic digested (L-AD) sludge as inoculum was investigated under thermophilic (55 °C) and mesophilic conditions (40 °C). The methane production rate of L-AD sludge (2.98–3.27 L-CH4 L−1 reactor d −1) was 1–2 times higher than recycling S-AD sludge (1.36 L-CH4 L−1 reactor d −1) as inoculum. Methane production of L-AD and S-AD sludge inoculum was 53.5–54.1 and 31.2–39.0 m3 CH4 tonne-1 EFB, respectively. The SS-AD of EFB with L-AD and S-AD sludge under thermophilic condition had specific methane activity of 34–96 times higher than the mesophilic condition. Clostridium sp., Methanosaeta sp., and Methanoculleus sp. were responsible for the SS-AD of EFB with L-AD sludge inoculum. The L-AD sludge was suitable inoculum for SS-AD of EFB in terms of methane production rate, cellulose degradation efficiency, biogas production, and microbial activity.

The suitability of molasses, Napier grass (Pennisetum purpureum), empty fruit bunches (EFB), palm oil mill effluent (POME), and glycerol waste as a co-substrate with Chlorella sp. TISTR 8411 biomass for biohythane production was investigated. Mono-digestion of Chlorella biomass had hydrogen and methane yield of 23–35 and 164–177 mL gVS−1, respectively. Co-digestion of Chlorella biomass with 2–6% TS of organic wastes was optimized for biohythane production with hydrogen and methane yield of 17–75 and 214–577 mL gVS−1, respectively. The hydrogen and methane yield from co-digestion of Chlorella biomass with molasses, POME, and glycerol waste was increased by 8–100% and 80–264%, respectively. The biohythane production of co-digestion of Chlorella was 6–11 L L-mixed waste−1 with an optimal C/N ratio range of 19–41 and H2/CH4 ratio range of 0.06–0.3. Co-digestion of Chlorella biomass was significantly improved biohythane production in term of yield, production rate, and kinetics.

Improvement of biohythane production from oil palm industry solid waste residues by co-digestion with palm oil mill effluent (POME) in two-stage thermophilic fermentation was investigated. A two-stage co-digestion of solid waste with POME has biohythane production of 26.5–34 m3/ton waste. The co-digestion of solid waste with POME increased biohythane production of 67–114% compared to digestion POME alone. Co-digestion of solid waste with POME enhanced hydrolysis constant (kh) from 0.07 to 0.113 to 0.120–0.223 d−1. The hydrolysis constant (kh) of co-digestion was 10 times higher than the single digestion of solid waste. Clostridium sp. was predominated in the hydrogen stage, while Methanosphaera sp. was predominant in methane stage. The co-digestion of solid waste with readily biodegradable organic matter (POME) could significantly increase biohythane production with achieving the significant cost reduction for pretreatment of solid wastes.

A mathematical model of minimum fluidization velocity (Umf) was developed based on the hydrodynamic characteristics of the fluidized bed reactors (FBR) with immobilised cells attached to activated carbon at thermophilic biohydrogen fermentation. The maximum hydrogen productivity rate of 7.8 mmolH2/L.h and hydrogen yield of 2.2 molH2/mol of sugar consumed was obtained when the HRT was shortened from 48 h to 6 h. The presence of the immobilised cells enriched the biomass composition in the FBR from 4.9 to 7.1 g VSS/L and maximum energy generated was 58.7 KJ H2/L.d. The FBR had to be operated at a high Umf of 0.05–0.44 cm/s and a low terminal velocity of 2.11 cm/s to prevent the immobilised cells from washed out from the FBR, hence achieved an adequate fluidization system. A screening of the microbial population by DGGE revealed that the T. thermosaccharolyticum sp. was dominant for all the HRTs, thereby indicating that this bacterium is resilient towards environmental disturbances.

The pilot-scale of two-stage thermophilic (55 °C) for biohythane production from palm oil mill effluent (POME) was operated at hydraulic retention time (HRT) of 2 days and organic loading rate (OLR) of 27.5 gCOD/L⋅d) for first stage and HRT of 10 days and OLR of 5.5 gCOD/L⋅d for second stage. Biohythane production rate was 1.93 L-gas/L⋅d with biogas containing 11% H2, 37% CO2, and 52% CH4. Recirculation of methane effluent mixed with POME at a ratio of 1:1 can control pH in the first stage at an optimal range of 5.0–6.5. Microbial community in hydrogen stage dominated by Thermoanaerobacterium sp., while methane stage dominated by Methanosarcina sp. The H2/CH4 ratio of biohythane was 0.13–0.18 which suitable for vehicle fuel. Biohythane production from POME could be promising cleaner biofuel with flexible and controllable H2/CH4 ratio.

Continuous H2 production from xylose by granules and biofilm up-flow anaerobic reactor using moderate thermophilic mixed cultures was investigated. The maximum H2 yield of 251 mL H2/g-xylose with H2production rate of 15.1 L H2/L⋅d was obtained from granules reactor operating at the organic loading rate (OLR) of 60 g-xylose/L⋅d and hydraulic retention time (HRT) of 4 h. Meanwhile the highest H2 production rate of 13.3 L H2/L⋅d with an H2 yield of 221 mL H2/g–xylose was achieved from the biofilm reactor. Both reactors were dominated by Thermoanaerobacterium species with acetate and butyrate as main fermentation products. The microbial community of the biofilm reactor was composed of Thermoanaerobacterium species, while granules reactor was composed of Clostridium sp., Thermoanaerobacterium sp. and Caloramator sp. The granular reactor was more microbial diversity and more balance between economic efficiency in term of the hydrogen production rate and technical efficiency in term of hydrogen yield.

The effect of trace metals supplementation into palm oil mill effluent on biohythane production and responsible microbial communities in thermophilic two-stage anaerobic fermentation was investigated. High biohythane yields were linked to Ni/Co/Fe supplementation (10, 6 and 20 mg L−1, respectively) with maximum H2 and CH4 yields of 139 mL H2 gVS−1 and 454 mL CH4 gVS−1, respectively. The Ni/Co/Fe supplementation resulted in higher numbers of Bacillus sp., Clostridium sp. and Thermoanaerobacterium sp. together with increasing hydrogenase expression level leading to increasing hydrogen yields of 90.4%. The numbers of Methanosarcina, Methanomassiliicoccus, and Methanoculleus were enhanced by Ni/Co/Fe addition, accompanied by 21.7% higher methane yields. No correlation between methyl coenzyme-M reductase expression level and methane yields was observed. The Ni/Co/Fe supplementation improved gas production in the two-stage biohythane process via enhancing a number of viable hydrogen-producing bacteria together with hydrogenase activity in H2 stage and enhancing number methanogens in the CH4 stage.

Waste-activated sludge (WAS) and greasy sludge (GS) discharged from the canned tuna industry are considerably characterized as harsh organic wastes to be individually treated by using traditional anaerobic digestion. This study was attempted to anaerobically co-digest WAS and GS in continuous pilot scale two-stage process, comprising the first 50 L continuous stir tank reactor (CSTR

A sudden pH drops always inhibits the anaerobic digestion (AD) reactor for biogas production from palm oil mill effluent (POME). The pH adjustment of POME by oil palm ash addition and the biogas effluent recycling effect on the preventing of pH drop and change of the archaea community was investigated. The pH adjustment of POME to 7.5 increased the methane yield two times more than raw POME (pH 4.3). The optimal dose for pH adjustment by oil palm ash addition was 5% w/v with a methane yield of 440 mL-CH4/gVS. The optimal dose for pH adjustment by biogas effluent recycling was 20% v/v with a methane yield of 351 mL-CH4/gVS. Methane production from POME in a continuous reactor with pH adjustment by 5% w/v oil palm ash and 20% v/v biogas effluent recycling was 19.1 ± 0.25 and 13.8 ± 0.3 m3 CH4/m3-POME, respectively. The pH adjustment by oil palm ash enhanced methane production for the long-term operation with the stability of pH, alkalinity, and archaea community. Oil palm ash increased the number of Methanosarcina mazei and Methanothermobacter defluvii. Oil palm ash is a cost-effective alkali material as a source of buffer and trace metals for preventing the pH drop and the increased methanogen population in the AD process.

Background Anaerobic digestion (AD) is a suitable process for treating high moisture MSW with biogas and biofertilizer production. However, the low stability of AD performance and low methane production results from high moisture MSW due to the fast acidify of carbohydrate fermentation. The effects of organic loading and incineration fly ash addition as a pH adjustment on methane production from high moisture MSW in the single-stage AD and two-stage AD processes were investigated. Results Suitable initial organic loading of the single-stage AD process was 17 gVS L−1 at incineration fly ash (IFA) addition of 0.5% with methane yield of 287 mL CH4 g−1 VS. Suitable initial organic loading of the two-stage AD process was 43 gVS L−1 at IFA addition of 1% with hydrogen and methane yield of 47.4 ml H2 g−1 VS and 363 mL CH4 g−1 VS, respectively. The highest hydrogen and methane production of 8.7 m3 H2 ton−1 of high moisture MSW and 66.6 m3 CH4 ton−1 of high moisture MSW was achieved at organic loading of 43 gVS L−1 at IFA addition of 1% by two-stage AD process. Biogas production by the two-stage AD process enabled 18.5% higher energy recovery than single-stage AD. The 1% addition of IFA into high moisture MSW was useful for controlling pH of the two-stage AD process with enhanced biogas production between 87–92% when compared to without IFA addition. Electricity production and energy recovery from MSW using the coupled incineration with biogas production by two-stage AD process were 9,874 MJ ton−1 MSW and 89%, respectively. Conclusions The two-stage AD process with IFA addition for pH adjustment could improve biogas production from high moisture MSW, as well as reduce lag phase and enhance biodegradability efficiency. The coupled incineration process with biogas production using the two-stage AD process was suitable for the management of MSW with low area requirement, low greenhouse gas emissions, and high energy recovery.

Empty fruit bunches (EFB) have low biodegradability and restrict their commercial utilization in biogas plants. Integration of straw mushroom (Volvariella volvacea) cultivation as a function of bio-pretreatment on EFB to improve biodegradability and methane production by solid-state anaerobic digestion (SS-AD) was investigated. The mushroom yield was 47.3 kg·tonne−1 EFB with remaining weight in spent mushroom-EFB (S-mEFB) of 82%. The cellulose, hemicellulose, and lignin of EFB were degraded by 3.3%, 21.3%, and 17.6%, respectively, with an increased surface area of S-mEFB. The biodegradability of S-mEFB (62.7%) was 2 times higher than raw EFB (33.5%) with the highest methane yield and production of 281 mL CH4·g−1 VS and 50.6 m3·tonne−1 S-mEFB, respectively. The co-digestion of S-mEFB with 5% v/w POME had highest methane yield of 405 mL CH4·g−1 VS with biodegradability of 90.8%. Integrating straw mushroom cultivation with SS-AD is a promising strategy for achieving an environmentally friendly and economically feasible process.

Oil palm frond (OPF) is one of the major oil palm biomass from agricultural waste. It can be potential to be valorised into cellulose. Cellulose can be extracted from natural fibers, which environmentally sustainable products. The aim of this work is to extract cellulose from oil palm frond biomass by two different treatments: (i) extraction cellulose fiber using pressure and (ii) extraction cellulose fiber non-pressure. The fibers were chemically treated with various concentrations of alkaline solution. Subsequently, the properties of raw material and cellulose were determined by utilizing X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The functional group of raw material and cellulose microfibers of palm-based lignocellulosic biomass were determined using Fourier transform infrared spectroscopy (FTIR), morphological studies were viewed using Scanning Electron Microscopy (SEM). According to the experimental analysis, the results of the chemical compositions revealed that the alkaline treatments were under-pressure and non-pressure able to remove a large fraction of lignin and hemicelluloses compared to non-alkaline treatment. The extraction condition at 150 °C using 15 wt.% NaOH under 7 bar pressure showed the highest content and high crystallinity of α-cellulose fibers.

Background The co-fermentation of syngas (mainly CO, H2 and CO2) and different concentrations of carbohydrate/protein synthetic wastewater to produce volatile fatty acids (VFAs) was conducted in the present study. Results It was found that co-fermentation of syngas with carbohydrate-rich synthetic wastewater could enhance the conversion efficiency of syngas and the most efficient conversion of syngas was obtained by co-fermentation of syngas with 5 g/L glucose, which resulted in 25% and 43% increased conversion efficiencies of CO and H2, compared to syngas alone. The protein-rich synthetic wastewater as co-substrate, however, had inhibition on syngas conversion due to the presence of high concentration of NH4+-N (> 900 mg/L) produced from protein degradation. qPCR analysis found higher concentration of acetogens, which could use CO and H2, was present in syngas and glucose co-fermentation system, compared to glucose solo-fermentation or syngas solo-fermentation. In addition, the known acetogen Clostridium formicoaceticum, which could utilize both carbohydrate and CO/H2 was enriched in syngas solo-fermentation and syngas with glucose co-fermentation. In addition, butyrate was detected in syngas and glucose co-fermentation system, compared to glucose solo-fermentation. The detected n-butyrate could be converted from acetate and lactate/ethanol which produced from glucose in syngas and glucose co-fermentation system supported by label-free quantitative proteomic analysis. Conclusions These results demonstrated that the co-fermentation with syngas and carbohydrate-rich wastewater could be a promising technology to increase the conversion of syngas to VFAs. In addition, the syngas and glucose co-fermentation system could change the degradation pathway of glucose in co-fermentation and produce fatty acids with longer carbon chain supported by microbial community and label-free quantitative proteomic analysis. The above results are innovative and lead to achieve effective conversion of syngas into VFAs/longer chain fatty acids, which would for sure have a great interest for the scientific and engineering community. Furthermore, the present study also used the combination of high-throughput sequencing of 16S rRNA genes, qPCR analysis and label-free quantitative proteomic analysis to provide deep insights of the co-fermentation process from the taxonomic and proteomic aspects, which should be applied for future studies relating with anaerobic fermentation.

Homoacetogens consortium was enriched from peatland soil, digested sludge, and rumen fluid for simultaneous carbon dioxide (CO2) consumption and acetic acid production in the biogas upgrading process. The homoacetogens consortium enriched from peatland soil (PL3) has a maximum CO2 consumption and acetic acid production of 95% and 120 mg/L, respectively. The methane content in upgraded biogas and acetic acid production of 98% and 543 mg/L was obtained at optimum hydrogen (H2) to CO2 at a ratio of 2:1, pH 8, and temperature 30 °C. The upgraded biogas (CH4 > 95%) can be used as vehicle fuel or injected into the natural gas grid. The homoacetogens consortium PL3 was dominated by Clostridium sp., Proteiniclasticum sp., and Petrimonas sp. Clostridium species are the main homoacetogens responsible for CO2 reduction using H2 as an energy source. The homoacetogens consortium PL3 could provide an opportunity for simultaneous biogas upgrading to biomethane and acetic acid production.

Two-stage thermophilic solid state anaerobic digestion (SS-AD) processes for biohythane production from Chlorella sp. biomass was investigated. The hydrogen and methane yield from fresh Chlorella sp. biomass was 124.9 mL H2 gVS−1 and 230.1 mL CH4 gVS−1, respectively, at 16% TS with biodegradation efficiency of 34%. Hydrogen and methane production from hydrothermal pretreated Chlorella sp. biomass was 190.0 mL H2 gVS−1 and 319.8 mL CH4 gVS−1, respectively at 16% TS with biodegradation efficiency of 47%. Pretreatment of Chlorella sp. biomass with hydrothermal follow by two-stage thermophilic SS-AD improved 150% biogas production comparing with fresh biomass. Clostridium sp. was the main bacteria responsible for hydrogen production. Clostridium sp. and Ruminococcus sp. was main bacteria in methane stage, while Methanoculleus sp. and Methanothermobacter sp. was dominated archaea in methane production process. Chlorella sp. biomass with hydrothermal pretreatment has great potential for hydrogen and methane production via two-stage thermophilic SS-AD.

Hydrogen production from cassava starch processing wastewater by two-stage thermophilic dark fermentation and microbial electrolysis was investigated. Single-chamber membrane-free microbial electrolysis cell with applied voltage of 0.6 V was optimum for hydrogen production with hydrogen yield of 245 ml H 2 gCOD −1 . Continuous microbial electrolysis reactor has a maximum hydrogen yield of 182 ml H 2 gCOD −1 at HRT of 48 h with energy recovery efficiency of 217%. The continuous integrated two-stage dark fermentation and microbial electrolysis have hydrogen yield of 465 ml H 2 gCOD −1 with 2 times hydrogen yield improving compared with a single stage and a maximum COD removal of 58% was achieved. Dominated bacteria at an anode of microbial electrolysis cell were exoelectrogens belong to Brevibacillus sp. Caloranaerobacter sp. and Geobacillus sp. Continuous two-stage thermophilic dark hydrogen fermentation and microbial electrolysis were efficient processes for hydrogen production from cassava starch processing wastewater.

Palm oil mill industry generates a large amount of palm oil mill effluent (POME) and empty fruit bunches (EFB) as byproducts. Biogas production from anaerobic co-digestion of POME with EFB was investigated under mesophilic condition. The amount of POME and EFB was varied from 2 to 10 gVS and size of EFB was varied from 0.5-6 centimeter. High methane yield and high biodegradability were achieved at the size of 0.2 mm with 63-70% biodegradability with a methane yield of 320 mL CH4/gVS. The POME:EFB ratio of 4.5-7.5 and size EFB of 3.3-6 centimeters shown acceptable biodegradability value of 40-50% with a methane yield of 282 mL CH4/gVS. The POME:EFB ratio of 4.5-7.5 and size EFB of 3.3-6 centimeters was more practical for biogas production due to reducing the cost of size reduction

The sulfate-rich wastewater from rubber smoked sheet industry could generate hydrogen sulfide (H2S) under anaerobic condition, which created bad smell to the community and might cause toxicity and damage to the environment. The H2S can be removed from the biogas by sulfur-oxidizing bacteria (SOB) with the ability to converted H2S to sulfate. Sulfate-reducing bacteria (SRB) could remove sulfate in wastewater before anaerobic treatment for biogas production. The microbial sludge from wastewater and anaerobic digestion system was collected and test for sulfate and H2S removal efficiency. Anaerobic microbial sludge has a high ability to produced methane from gelatin with a specific methane production rate of 92.4 ml CH4 gVSS-1 day-1. Anaerobic microbial sludge has lower methane production when gelatin and sulfate used as a substrate with a specific methane production rate of 81.4 ml CH4 gVSS-1 day-1. The biomethane potential, hydrogen sulfide removal and sulfate removal in anaerobic digestion system by addition of enriched cultures of SOB and SRB were investigated. The methane yield of SRB consortium was 60.1 ml CH4/gCOD with 20% sulfate reduction from wastewater and no sulfide reduction. The methane yield of SOB consortium was 41.9 ml CH4/gCOD with no sulfate and sulfide reduction from wastewater. The addition of SRB consortium could increase methane production by reducing sulfate concentration in wastewater consequently to a reduced concentration of H2S in biogas.

Hydrogen sulfide (H2S) is one of the most problematic contaminants in biogas. The removal of H2S from biogas is necessary in order to clean biogas and prevent gas engine. The efficiency evaluation on H2S removal from palm oil mill biogas by biofilter was investigated. Eight sludge samples from biofilter systems of palm oil mill biogas were tested for H2S removal by grown in thiosulfate mineral medium under an anaerobic condition at atmospheric pressure. Analytical data demonstrated that average amounts of CH4, CO2, and H2S in inlet biogas were 62%, 35%, and 0.95%, respectively. The highest H2S removal rate of 0.35 g/L/d was found sludge A (Asian palm oil company). It also found that the major product for sludge A was elemental sulfur of 13,650 mg/L and could produce the highest sulfate concentration of 300 mg/L. In contrast, sludge I (Thai Indo palm oil factory) has the lowest H2S removal with rate (0.09 g/L/d.) Microbial activity for H2S removal was increased with the decrease in pH from 7.12 to 6.40 due to H2S dissolved medium. The suitable condition for the growth of sulfur oxidizing bacteria affected on H2S removal efficiency from palm oil mill biogas by biofilter systems.

The cultivation of Chlorella sp. TISTR 8411 on biogas effluent of seafood processing wastewater was investigated. Chlorella sp. biomass was used for biogas production by anaerobic co-digestion with seafood processing. Chlorella sp. biomass cultivated on 50, 60, 70, 80, 90, and 100% of biogas effluent was 0.184, 0.121, 0.061, 0.048, 0.039, and 0.032 g/L, respectively. The highest growth of Chlorella sp. biomass was 0.184 g/L from 50% biogas effluent. Methane yield from anaerobic co-digestion of seafood processing wastewater with 10, 20, 30, 40, and 50% v/v Chlorella sp. biomass was 131, 152, 173, 188 and 193 ml CH4/gVS, respectively. Methane yield from Chlorella sp. biomass was 44 ml CH4/gVS. Methane yield from seafood processing wastewater was 18 ml CH4/gVS. 10 times of methane yield was improve in anaerobic co-digestion seafood processing wastewater with Chlorella sp. biomass at 40 and 50 % v/v. Anaerobic co-digestion seafood processing wastewater with Chlorella sp. biomass has great potential for biogas production.

Oil palm trunk (OPT) an abundant agriculture waste was evaluated as an alternative lignocellulosic biomass resource for bioethanol production. Sulfite-based SPORL pretreatment (Sulfite Pretreatment to Overcome Recalcitrance of Lignocellulose) was applied to the OPT to enhance its enzymatic saccharification. The pretreatment conditions were optimized through a designed experiment within the ranges of temperature 170–190oC, time for 30 min, 2–6% sulfite, and initial H2SO4 concentrations 3–7% (w/w). The overall saccharides (hexoses and pentoses) recovery of SPORL pretreated was 62.5%. SPORL pretreatment removed 38.8% lignin from the OPT as lignosulfonate in the liquor with great potential for co-product development, and 93.9% xylose was dissolved, which were the main reasons why the SPORL pretreatment could enhance the enzymatic hydrolysis of the OPT. The results indicated that over 92% of the cellulose in the pretreated OPT with 7% H2SO4 and 6% Na2SO3 at 190oC was enzymatically hydrolyzed to glucose within 48 h with a cellulase loading of 15 FPU/g cellulose, and overall glucose yield was 66%.

Background: Biohydrogen effluent contains a high concentration of volatile fatty acid (VFA) mainly as butyric, acetic, lactic and propionic acids. The presence of various VFAs (mixture VFAs) and their cooperative effects on two-stage biohythane production need to be further studied. The effect of VFA concentrations in biohydrogen effluent of palm oil mill effluent (POME) on methane yield in methane stage of biohythane production was investigated. Results: The methane yield obtained in low VFA loading (0.9 and 1.8 g/L) was 15–20% times greater than that of high VFA loading (3.6 and 4.7 g/L). Butyric acid at high concentrations (8 g/L) has the individual significantly negative effect the methane production process ( P P Geobacillus sp., Thermoanaerobacterium thermosaccharolyticum , Methanoculleus thermophilus and Methanothermobacter delfuvii resulting in low methane yield. Conclusion: Preventing the high concentration of butyric acid, and propionic acid in the hydrogenic effluent could enhance methane production in two-stage anaerobic digestion for biohythane production. Normal 0 false false false ES-CL X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabla normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:8.0pt; mso-para-margin-left:0cm; line-height:107%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri",sans-serif; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-ansi-language:ES-CL;} Normal 0 false false false EN-US X-NONE TH

Additional file 1. Figures S1–S8 and Table S1–S6.

Recovery of bioenergy and biochemicals from industrial and agricultural wastewater has attracted growing and widespread interests. The two-stage fermentation process offers an appealing avenue to achieve stepwise and directional substrate conversion in separated stages. The two-stage fermentation process could enhance the degradation of the substrate with high product yield and quality. The two-stage fermentation process has been developed for the production of biomethane, biohydrogen, biohythane, bioelectricity, and medium-chain carboxylic acids (MCCAs) with advantages over the conventional one-stage process. Two-stage fermentation process promising for future applications in industrial and agricultural wastewater treatment with simultaneous value-added production and pollution control. This chapter provides an overview of the various two-stage fermentation process for bioenergy and biochemicals production, introduces the recent advances, biochemical pathways, microorganisms, process parameters, technology assessment, and discusses the significant challenges with future perspectives for practical application.