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Lignocellulosic biomass is a promising substrate for biogas production. However, its recalcitrant structure limits conversion efficiency. This study aims to design a microbial consortium (MC) capable of producing the cellulolytic enzyme and exploring the taxonomic and genetic aspects of lignocellulose degradation. A diverse range of lignocellulolytic bacteria and degrading enzymes from various habitats were enriched for a known KKU-MC1. The KKU-MC1 was found to be abundant in Bacteroidetes (51%), Proteobacteria (29%), Firmicutes (10%), and other phyla (8% unknown, 0.4% unclassified, 0.6% archaea, and the remaining 1% other bacteria with low predominance). Carbohydrate-active enzyme (CAZyme) annotation revealed that the genera Bacteroides,Ruminiclostridium,Enterococcus, and Parabacteroides encoded a diverse set of cellulose and hemicellulose degradation enzymes. Furthermore, the gene families associated with lignin deconstruction were more abundant in the Pseudomonas genera. Subsequently, the effects of MC on methane production from various biomasses were studied in two ways: bioaugmentation and pre-hydrolysis. Methane yield (MY) of pre-hydrolysis cassava bagasse (CB), Napier grass (NG), and sugarcane bagasse (SB) with KKU-MC1 for 5 days improved by 38–56% compared to non-prehydrolysis substrates, while MY of prehydrolysed filter cake (FC) for 15 days improved by 56% compared to raw FC. The MY of CB, NG, and SB (at 4% initial volatile solid concentration (IVC)) with KKU-MC1 augmentation improved by 29–42% compared to the non-augmentation treatment. FC (1% IVC) had 17% higher MY than the non-augmentation treatment. These findings demonstrated that KKU-MC1 released the cellulolytic enzyme capable of decomposing various lignocellulosic biomasses, resulting in increased biogas production.

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

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.

Medium-chain fatty acids (MCFAs) and their derivatives have important applications in the energy and chemical industries. The sustainable production of MCFAs from renewable biomass resources using microbial fermentation has become promising. A particular set of anaerobic pathways known as chain elongation can occur under specific conditions producing MCFAs with a higher value than biogas and broader applicability. MCFAs formation occurs through a carboxylic acid chain elongation process, which mainly uses reverse beta-oxidation of acetic acid, n-butyric acid, and caproic acid with an electron donor (ethanol, lactic acid, methanol, and hydrogen). The MCFAs fermentation by chain elongation is mainly composed of caproic acid (C6), heptylic acid (C7), and caprylic acid (C8). Therefore, we have summarized the current knowledge on the mechanism of chain elongation, a substrate for MCFAs production, microbial strains for MCFAs production, environmental factors affect on MCFAs production, process development for MCFAs production, improvement methods for MCFAs production and discussed the current state of the art on the use of complex organic feedstock and reviewed key operational parameters and their interactions.

Hydrothermal liquefaction of sewage sludge to produce bio-oil and hydro-char unavoidably results in the production of high-strength organic wastewater (HTLWW). However, anaerobic digestion (AD) of HTLWW generally has low conversion efficiency due to the presence of complex and refractory organics. The present study showed that granular activated carbon (GAC) promoted the AD of HTLWW in continuous experiments, resulting in the higher methane yield (259 mL/g COD) compared to control experiment (202 mL/g COD). It was found that GAC increased the activities of both aceticlastic and hydrogenotrophic methanogens. The molecular transformation of organics in HTLWW was further analyzed. It was shown GAC promoted the degradation of soluble microbial by-products, fulvic- and humic-like substances as revealed by 3-dimensional fluorescence excitation-emission matrix (3D-EEM) analysis. Gas chromatography mass spectrometry (GC–MS) analysis showed that GAC resulted in the higher degradation of N-heterocyclic compounds, acids and aromatic compounds and less production of new organic species. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) analysis also showed that GAC promoted the degradation of nitrogenous organics. In addition, it was shown that GAC improved the removal of less oxidized, higher nitrogen content, and higher double bond equivalent (DBE) organic compounds. Microbial analysis showed that GAC not only increased the microbial concentration, but also enriched more syntrophic bacteria (e.g., Syntrophorhabdus and Synergistes), which were capable of degrading a wide range of different organics including nitrogenous and aromatic organics. Furthermore, profound effects on the methanogens and the enrichment of Methanothrix instead of Methanosarcina were observed. Overall, the present study revealed the molecular transformation and microbial mechanism in the AD of HTLWW with the presence of GAC. Keywords: Wastewater treatment, Sludge hydrothermal liquefaction, Granular activated carbon, Anaerobic digestion, Molecular analysis, Microbial analysis

The critical challenge of hydrothermal liquefaction (HTL) for bio-oil production from biomass is the production of large amounts of aqueous products (HTL-AP) with high organic contents. The present study investigated the anaerobic digestion (AD) performances of HTL-AP under both thermophilic and mesophilic conditions, and molecular and metabolic analysis were conducted to provide insights into the different performances. The results showed that thermophilic AD had lower COD removal efficiency compared to mesophilic AD (45.0% vs. 61.6%). Liquid chromatography coupled with organic carbon detection and organic nitrogen (LC-OCD-OND) analysis showed that both high molecular weight (HMW) and low molecular weight (LMW) compounds were degraded to some extent and more LMW acids (LMWA) and recalcitrant aromatic compounds were degraded in the mesophilic reactor, which was the main reason of higher COD removal efficiency. Phenyl compounds (e.g. phenol and 2 methoxyphenol), furans and pyrazines were the recalcitrant chemicals detected through GC-MS analysis. Fourier transform ion cyclone resonance mass spectrometry (FT-ICR-MS) analysis demonstrated the complexity of HTL-AP and the proportions of phenolic or condensed aromatic compounds increased especially in the thermophilic effluents. Metabolites analysis showed that the reasons contributing to the differences of mesophilic and thermophilic AD were not only related to the degradation of organic compounds (e.g. benzoate degradation via CoA ligation) in HTL-AP but also related to the microbial autogenesis (e.g. fatty acid biosynthesis) as well as the environmental information processing. In addition, the enrichment of Mesotoga, responsible for the high degradation efficiency of LMWA, and Pelolinea, involved in the degradation of phenyl compounds, were found in mesophilic reactor, which was consistent with higher removal of corresponding organics.

Thermotolerant cellulolytic consortium for improvement biogas production from oil palm empty fruit bunches (EFB) by prehydrolysis and bioaugmentation strategies was investigated via solid-state anaerobic digestion (SS-AD). The prehydrolysis EFB with Clostridiaceae and Lachnospiraceae rich consortium have maximum methane yield of 252 and 349 ml CH4 g−1 VS with total EFB degradation efficiency of 62% and 86%, respectively. Clostridiaceae and Lachnospiraceae rich consortium augmentation in biogas reactor have maximum methane yield of 217 and 85.2 ml CH4 g−1 VS with degradation efficiency of 42% and 16%, respectively. The best improvement of biogas production was achieved by prehydrolysis EFB with Lachnospiraceae rich consortium with maximum methane production of 113 m3 CH4 tonne−1 EFB. While, Clostridiaceae rich consortium was suitable for augmentation in biogas reactor with maximum methane production of 70.6 m3 CH4 tonne−1 EFB. Application of thermotolerant cellulolytic consortium into the SS-AD systems could enhance biogas production of 3–11 times.

The high-solid anaerobic digestion (AD) for anaerobic co-digestion of palm oil mill effluent (POME) and oil palm empty fruit bunches (EFB) has low degradation efficiency. The enhancement of biogas production and EFB degradation efficiency by Bacteroides and Clostridium-rich methanogenic consortium was investigated. A Bacteroides and Clostridium-rich methanogenic consortium have xylanase, FPase, endo-glucanase, and exo-glucanase activity of 9.2, 1.3, 2.1, and 1.5 IU·mL−1, respectively with EFB degradation efficiency of 57.5%. Methane production (79 m3-CH4·tonne−1-EFB) by Bacteroides and Clostridium-rich methanogenic consortium augmentation was increased by 67.2%. The real application of bioaugmentation in the feedstock mixing tank before a feed to the AD reactor significantly increased methane yield (376.7 mL-CH4·g-1-VS−) by 85.5%. Bioaugmentation of Bacteroides and Clostridium-rich methanogenic consortium increased the number of hydrolytic bacteria and strengthened symbiotic relationships with indigenous microorganisms resulting in high biogas production, accelerated hydrolysis, and reduced solids accumulation of the high-solid AD process.

A novel reactor was developed in this research to simultaneously produce biogas from solid- and liquid-state anaerobic digestions in one container for the first time. Excess heat from the outer liquid-state anaerobic digestion (OL-AD) of POME was transferred to the inner solid-state anaerobic digestion (IS-AD) of EFB for promoting thermophilic digestions (55 °C and 70 °C). Continuous operations at various hydraulic retention times were performed. Bacteria and archaea communities were identified. The results showed that the maximum methane yields were 507.07 and 125.84 mL-CH4/g-VS for OL-AD and IS-AD, respectively. In OL-AD, raising temperature increased the methane yield by 6.4%. In IS-AD, the yield was not significantly affected by elevated temperature. However, the pretreatment of EFB with NaOH increased the methane yield by 14.1%. The main bacteria and archaea communities in OL-AD and IS-AD were found similar. The novel reactor could save energy, reduce costs and digester space, and increase the methane yield.

Valorization of biodiesel-derived crude glycerol and its hydrolysis product (ethanol) as a co-substrate supplemented to palm oil mill effluent (POME) to enhance biogas production efficiency under mesophilic anaerobic digestion was investigated. Based on our previous studies, the concentrations of each co-substrate were varied in the range of 1–5% v⋅v−1. The optimum concentrations of crude glycerol and ethanol were 1% and 5% v/v, respectively. They could increase both methane production (nearly 2 fold) and methane yield (1.98–2.09 fold based on volatile solids (VS) and 1.6–1.87 fold based on COD). However, they exhibited oppositely in the methane production rate; the 1% crude glycerol was 38% lower while 5% ethanol exhibited a 67% higher methane production rate than the control (POME). The results clearly indicated that the methane production rate from 5% ethanol was 2.7 times higher than that from the 1% crude glycerol. Microbial community analysis revealed that the dominant bacteria in both co-substrates biogas production process were Sandarakinotalea sp., Lachnobacterium sp., Blautia sp., Marinobacter sp., Anaerotruncus sp., Clostridium sp., Enterobacter sp., and Acinetobacter sp. The Blautia sp. was dominant in the presence of 1% crude glycerol than 5% ethanol. The archaea communities were dominated by hydrogenotrophic methanogen (Methanoregula sp. and Methanoculleus sp.) and acetoclastic methanogen (Methanosarcina sp. and Methanospirillum sp.). Therefore, ethanol was a better co-substrate than crude glycerol. Nevertheless, biogas production from POME with crude glycerol as co-substrate was anticipated to strongly increase by enhancing the growth (or bioaugmentation) of Blautia sp. and Methanosarcina sp.

This study aimed to investigate the biohydrogen and biomethane potential of palm oil mill effluent (POME) in a two-stage anaerobic digestion (AD) system under thermophilic (55 ± 3 °C) and mesophilic (30 ± 3 °C) conditions, respectively. Among the initial loadings of 0.5 g-COD, 1.0 g-COD, or 1.5 g-COD, the best production potentials of 106.13 mL-H2/g-COD and 334.56 m L-CH4/g-CODadded, corresponding to the total energy production of 13.61 kJ/g-CODadded, were obtained from POME with an initial 0.5 g-COD loading. The investigation also revealed that the energy yield (CH4+H2) achieved from two-stage AD was approximately 38.95 % higher than single-stage anaerobic digestion (single-stage AD), where only methane energy carrier was produced. Continuous hydrogen and methane production were subsequently performed in a series of continuous stirred tank reactor (CSTR) and anaerobic horizontal baffled channel (AHBC) reactor to treat POME without external supplement. The results revealed that the highest hydrogen yield of 86 m L-H2/g-CODadded was generated at 3-day HRT, while the highest methane production was obtained from HRT over 35 days with a yield of 250.33 m L-CH4/g-CODadded. Additionally, the overall COD removal in the continuous process was approximately 66.27 %. As a highly efficient organic matter removal and higher energy recovery, the continuous two-stage AD can be further developed to industrial-scale mixed hydrogen and methane production from POME.

Population genetic structure of Varuna litterata living along the coast of Thailand were examined in this study. The samples were collected from 3 coastal regions: The Andaman sea (Satun, Trang, Phang Nga), the lower Gulf of Thailand (Pattani, Songkhla, Nakhon Si Thammarat) and the upper Gulf of Thailand (Petchburi, Samut Songkram, Rayong, Trat). Intraspecific variation was determined based on partial sequences of the cytochrome oxidase subunits I gene. A total of 182 samples were collected but only 32 haplotypes were obtained from these samples. An excess of rare haplotypes indicated that the female effective population size of V. litterata living along the coast of Thailand is large. Estimated values of haplotype diversity and nucleotide diversity were 0.790 and 0.003, respectively. The AMOVA (analysis of molecular variance) and phylogenetic analysis results showed that based on genetic variation, the population of this organism was found to have 2 genetically different populations: The Andaman sea population and the Gulf of Thailand population. Genetic exchange of V. litterata among populations inhabiting along the coast of Thailand could be described by the stepping stone model. The results of neutrality tests, both Tajima’s D and Fu’s Fs statistics, yielded negative values (-1.992 and -26.877, respectively) and statistically significant deviation from the neutrality, indicating that the V. litterata living along the Thailand coast had experienced population expansion. Mismatch distribution analysis indicated that a possible expansion occurred 211,428 years ago during the Pleistocene glaciations period.

Bacterial Cellulose (BC) was produced by Acetobacterxylinum TISTR 086 use mixing of oil palm shoot juices (OPSJ) and coconut juice (CJ) medium with or without nutrient supplemented or OPSJ was digested with α-amylase. Results showed the highest yield was obtained at OPSJ with CJ at mixing ratios of 50% (4.70±0.11 g/L) and the lowest yield was obtained at OPSJ with CJ at mixing ratios of 0% (3.54±0.11 g/L). OPSJ was digested with 1300 lU/gm at concentration enzyme 650 IU/L at 37 °C for 24 h has highest sugar concentration of 73.93±0.12 g/L. Amylase digested OPSJ mixed with coconut juice’s highest bacterial cellulose production at OPSJ with CJ at mixing ratios of 50% (4.94±0.13 g/L), respectively. Moreover, the BC obtained had molecular weight from 332,122 to 503,233 g/mol. The chemical structure of BC produced was studied using Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray defections. The morphology of BC was investigated by Scanning Electron Microscopy (SEM). Thermal property was further studied using Differential Scanning Calorimetry (DSC) and Thermogravimetic Analysis (TGA). This study obviously showed the ability of OPSJ, a suitable and cheap carbon source, to be used as a substrate in a fermentation medium for production of cellulose by Acetobacterxylinum TISTR 086.

Thermophilic solid-state anaerobic digestion (SS-AD) of biomass from palm oil mill industry, including empty fruit bunches (EFB), oil palm fronds (OPF) and oil palm trunks (OPT) were investigated under different feedstock-to-inoculum ratios (F:I), carbon-to-nitrogen ratios (C:N) and total solids contents (TS). The optimal condition for biogas production was achieved at F:I ratio of 2:1, C:N ratio of 40:1 and TS content of 16%. The highest methane yield from EFB, OPF and OPT were 223, 207 and 161 m 3 CH 4 tonne −1 VS, respectively. Bacterial community structure in thermophilic SS-AD of oil palm biomass was dominated by Thermoanaerobacterium sp. and Clostridium sp. Archaeal community structure was dominated by Methanosaeta sp. and Methanoculleus sp. The highest methane production of 45 m 3 CH 4 tonne −1 fresh biomass was achieved from EFB. Solid waste residues from palm oil mill industry have great potential for methane production via thermophilic SS-AD.

BACKGROUND AND OBJECTIVE Toxic nitrogen compounds are one cause decreasing of shrimp production and water pollution. Indigenous Halomonas spp., isolated from Pacific white shrimp farm are benefitted for saline ammonium waste water treatment. This study aimed to isolate the heterotrophic-halophilic Halomonas spp. and investigate their ammonium removal efficiency. MATERIALS AND METHODS Halomonas spp., were isolated by culturing of samples collected from shrimp farm into modified Pep-Beef-AOM medium. Ammonium converting ability was tested and monitored by nitrite reagent. Ammonium removal efficiency was measured by the standard colorimetric method. Identification and classification of Halomonas spp., were studied by morphological, physiological and biochemical characteristics as well as molecular information. RESULTS There were 5 strains of heterotrophic-halophilic nitrifying bacteria including SKNB2, SKNB4, SKNB17, SKNB20 and SKNB22 were isolated. The identification result based on 16S rRNA sequence analysis indicated that all 5 strains were Halomonas spp., with sequence similarity values of 91-99 %. Ammonium removal efficiency of all strains showed a range of 23-71%. The production of nitrite was low detected of 0.01-0.15 mg-N L-1, while the amount of nitrate was almost undetectable. CONCLUSION This might suggest that the indigenous Halomonas spp., as nitrifying bacteria involved biological nitrification process for decreasing and transforming of ammonia. Due to being heterotrophic, halophilic and ammonium removing bacteria, these Halomonas spp., could be developed for use in treatment of saline ammonium waste water.

Two-stage thermophilic fermentation and mesophilic methanogenic process with methanogenic effluent recirculation to hydrogen reactor for biohythane production from palm oil mill effluent (POME) was investigated. Maximum hydrogen (4.1 L H2/L-POME) and methane production (16.6 L CH4/L-POME) from POME in batch tests were achieved at 30% recirculation rate of methanogenic effluent. Continuous hydrogen production of without and with recirculation phase was 2.2 and 3.8 L H2/L-POME, respectively. Continuous methane production of without and with recirculation phase was 12.2 and 14 L CH4/L-POME, respectively. Both reactor effluents were effective to keep at optimal pH with 2 times increasing in hydrogen production. The hydrogen and methane yield were 135 mL H2/gVS and 414 mL CH4/gVS, respectively. Biohythane gas composition was composed 13.3% of hydrogen, 54.4% of methane and 32.2% carbon dioxide. Two-stage process with methanogenic effluent recirculation flavored Thermoanaerobacterium sp. in the hydrogen reactor and efficiently for energy recovery from POME.

Co-fermentation of palm oil mill effluent (POME) for hydrogen production by Thermoanaerobacterium thermosaccharolyticum PSU-2 under thermophilic condition was investigated. Hydrogen production from co-fermentation POME with 5 g/L decanter cake and without was 2.6 and 1.7 L-H 2 /L-POME. Co-fermentation of POME with decanter cake enhanced hydrogen production. Tbm. thermosaccharolyticum PSU-2 augmentation at 20% v/v was found to be an efficient start-up strategy in continuous hydrogen production from co-fermentation of POME with decanter cake. Tbm. thermosaccharolyticum PSU-2 augmentation could suppress normal flora bacteria in POME and decanter cake. Hydrogen production of 7.2 L-H 2 /L-POME and hydrogen production rate of 18.1 mmol-H 2 /L/h was achieved from continuous hydrogen in long term operation. The soluble metabolites were dominated by acetic acid and butyric acid. Tbm. thermosaccharolyticum PSU-2 augmentation could use for control undesired bacteria in the hydrogen production system with flavored Thermoanaerobacterium sp. as dominant species.