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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.

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.

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%.

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.

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.

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.

Five bacterial strains were screened for polymer production in five synthetic media (GP, PS, GL, PL and PR). The highest polymer yield was obtained from Bacillus subtilis WD161 in PR medium (8.89 g/L). Cultivation at 30, 45 and 60 °C indicated that they were thermotolerant with the maximum biopolymer yield at 45 °C. Using palm oil mill effluent (POME) as medium, the nitrogen had to be supplemented to 1.28 g/L (equal to that in PR medium) with the initial pH adjusted to 7.0 and cultivation at 30 °C. Characterization based on its composition and functional groups revealed that the biopolymer WD161 was glycoprotein with the molecular weight of 1.54 × 10 6 Da. FT-IR analysis revealed the presence of amine (NH 2 ), hydroxyl, carboxyl and carbonyl groups. It was also a bioflocculant and its flocculating activity to precipitate the suspended solid in POME increased by 35% under the optimum condition.

A two-stage thermophilic fermentation for hydrogen and methane production from wastewater of cassava rice and corn starch at different concentration (5,10 and 15 g/L) was studied. The hydrogen production from cassava starch at concentrations of 5 g/L gave the highest hydrogen yield and followed by cassava starch at a concentration 10 g/L, rice starch at concentrations of 15 g/L. The hydrogen and methane yields from cassava starch processing wastewater by two-stage was 81.5 L H2 kgCOD-1 and 310.5 L CH4 kgCOD-1, respectively with total energy yield of 13363 kJ kgCOD-1. Mixed hydrogen and methane (biohythane) production was 9.51 L biogas l-1 with containing of 55% CH4, 11% H2 and 34% CO2.

Ethanol was produced from oil palm frond juice (OPFJ) by using Saccharomyces cerevisiae yeast cells. Experiments were operated in a batch mode by varying the oil palm age between 3-4, 4-7, 7-10, 10-20 and 20-25 years. Experimental results showed that OPFJ at 3-4 years gave the highest concentrations of glucose and ethanol as 31.26 and 11.50 g/l. Ethanol yield was 0.39 g-ethanol/g-glucose, which estimated as 76.47% of the theoretical yield (0.51 g-ethanol/g-glucose). Additionally, the Monod and modified Gompertz equations were used to describe the kinetics of substrate utilizationand product formation. The values of the kinetic parameters in Monod and modified Gompertz equations of OPFJ extracted from oil palm aged 3-4 years were evaluated: maximum specific growth rate ( μ max ) was 0.29 g/g-VSS.hr, saturation concentration ( K s ) 47.05 g/l, maximum ethanol concentration ( P m ) 11.50 g/l, maximum ethanol production rate ( r p,m ) 0.24 g./l.hr and lag phase 0.12 hr. Both models fitted well to the experimental data, which had the high regression coefficient values (R 2 >0.95).

Old oil palm trunk (OPT) is available in large quantity in Southeast Asia and a potential lignocellulosic biomass resource for bioethanol production. Dilute acid (DA) pretreatment was applied to the old oil palm trunk for enzymatic saccharification. The pretreatment conditions were investigated through a fractional factorial experiment design. The pretreated substrates were analyzed for chemical composition, and their enzymatic digestibility was investigated and compared. The results indicated that the DA pretreatment was able to improve enzymatic hydrolysis by removing hemicelluloses from OPT. Mild pretreatment preserved more hemicellulose and cellulose in pretreated OPT, but severe pretreatment was necessary to achieve satisfactory enzymatic hydrolysis of OPT. For example, the DA pretreatment with 3% H 2 SO 4 at 180 °C for 40 min could achieve an 80% enzymatic hydrolysis.

Solid state anaerobic digestion is a safe and environmental friendly technology to dispose solid wastes, could produce methane and reduce the volume of wastes. Three biomass residues from palm oil mill plant including empty fruit bunches (EFB), palm press fiber (PPF) and decanter cake (DC) were evaluated for methane production by solid state anaerobic digestion. Oil palm biomass was mixed with inoculum at F/I ratio of 2:1, 3:1, 4:1, 5:1 and 6:1 based on the volatile solid (VS). Results show that among the five F/I ratios tested, the F/I ratio of 2:1 gave the highest methane yield and methane production for all biomass residues. The highest cumulative methane production of 2180 mLCH 4 was obtained from EFB followed by PPF (1964 mL CH 4 ) and DC (1827 mL CH 4 ) at F:I ratio of 2:1. The highest methane yield of 144 mL CH 4 /gVS was obtained from EFB followed by PPB (140 mL CH 4 /gVS) and DC (130 mL CH 4 /gVS) at F/I ratios of 2:1. Methane production from EFB, PPF and DC by SS-AD was 55, 47 and 41 m 3 CH 4 /ton, respectively. These results collectively suggested that EFB could be a promising substrate for methane production by SS-AD

Biohythane production from co-digestion of palm oil mill effluent (POME) with empty fruit bunches (EFB) and decanter cake (DC) by two-stage solid state anaerobic digestion process was investigated. The first stage, thermophilic hydrogen fermentation of co-digestion of POME with DC at 10, 30, 50 and 70% of DC in POME has hydrogen yield of 16, 14, 3 and 1 ml H 2 /gVS, respectively. Co-digestion of POME with 10% DC gave the best hydrogen yield of 16 ml H 2 /gVS with hydrogen production of 1.4 m 3 /ton mixed waste. Co-digestion of POME with 10% EFB gave the best hydrogen yield of 16 ml H 2 /gVS with hydrogen production of 1.4 m 3 /ton mixed waste. The effluent from the hydrogen production was further converted to methane in the second stage. The methane yield from POME mixed withn10% DC was 391 mlCH 4 /gVS and from POME mixed with 10% EFB was 240 mlCH 4 /gVS. The hydrogen and methane content in biogas was 25.33% and 65.21% respectively. The two-stage solid stage anaerobic digestion process can be removal efficiently of cellulose 57-59%, hemicelluloses 35-40% and lignin 16-27%. Result obtained make practical use for the development of two-stage anaerobic digestion process providing hydrogen and methane co-production from palm oil waste residues.

Hydrogen production from crude glycerol by two-stage processes of dark fermentation using Klebsiella sp. TR17 and photo fermentation using Rhodopseudomonas palustris TN1 (Rps. palustris TN1) was investigated in batch experiments. In dark fermentation, the cumulative hydrogen production and hydrogen yield was 64.24 mmol H2/L and 5.74 mmol H2/g COD consumed, respectively with 80.21% of glycerol conversion rate. The dark fermentation effluent (DFE) was employed for photo fermentation. Effect of DFE concentrations (0–5 times dilution), with and without supplementation of yeast extract (2.3 g/L) + NaHCO3 (0.63 g/L), and glutamate (2–8 mM) were optimized. The optimal conditions for hydrogen production from Rps. palustris TN1 were 5 times dilution of DFE without the supplement of yeast extract + NaHCO3, and 2 mM glutamate. Under the optimum conditions, the cumulative hydrogen production of 3.12 mmol H2/L and hydrogen yield of 0.68 mmol H2/g COD consumed was obtained. The total hydrogen yield of two-stage processes was estimated to be 6.42 mmol H2/g COD consumed which was 10.4% of the theoretical yield.

A two-stage thermophilic fermentation and mesophilic methanogenic process for biohythane production from palm oil mill effluent (POME) was investigated. The hydrogen and methane potential from POME were 170–200 L H 2 kgCOD −1 and 210–292 L CH 4 kgCOD −1 , respectively. A continuous two-stage process with hydraulic retention time (HRT) of 2 d for hydrogen reactor and 15 d for methane reactor, obtained 34% higher energy yield than single stage methane production. The hydrogen and methane yields from two-stage were 210 L H 2 kgCOD −1 and 315 L CH 4 kgCOD −1 , respectively with total energy yield of 15.34 MJ kgCOD −1 . Mixed hydrogen and methane (biohythane) production rate was 4.4 L biogas L −1 d −1 with containing of 51% CH 4 , 14% H 2 and 35% CO 2 . Hydrogen reactor was dominated with hydrogen producing bacteria of Thermoanaerobacterium thermosaccharolyticum , while acetoclastic Methanoculleus sp. was the dominant methanogen in methane reactor. Two-stage process for biohythane production could efficiently for energy recovery from POME.

A series of up-flow anaerobic sludge blanket (UASB) reactors operated under thermophilic conditions was used to investigate the two-stage anaerobic process for continuous hydrogen and methane production from skim latex serum (SLS). The first reactor for producing hydrogen was operated by feeding 38 g-VS/L-SLS at various hydraulic retention times (HRTs) of 60, 48, 36, and 24 h. The optimum hydrogen production yield of 2.25 ± 0.09 L-H 2 /L-SLS was achieved at a 36 h HRT. Meanwhile, the effluents containing mainly with acetate was fed to the second UASB reactor for methane production at 9-day HRT and could be converted to methane with the production yield of 6.41 ± 0.52 L-CH 4 /L-SLS. The efficiency of organic matters removal obtained from this two-stage process was 62%. The present study shows high value fuel gases in a form of hydrogen and methane can be potentially generated by using a continuous two-stage anaerobic process, in which available organic matters is simultaneously degraded.

The microbial community structure of thermophilic mixed culture sludge used for biohydrogen production from palm oil mill effluent was analyzed by fluorescence in situ hybridization (FISH) and 16S rRNA gene clone library techniques. The hydrogen-producing bacteria were isolated and their ability to produce hydrogen was confirmed. The microbial community was dominated by Thermoanaerobacterium species (∼66%). The remaining microorganisms belonged to Clostridium and Desulfotomaculum spp. (∼28% and ∼6%, respectively). Three hydrogen-producing strains, namely HPB-1, HPB-2, and HPB-3, were isolated. 16S rRNA gene sequence analysis of HPB-1 and HPB-2 revealed a high similarity to Thermoanaerobacterium thermosaccharolyticum (98.6% and 99.0%, respectively). The Thermoanaerobacterium HPB-2 strain was a promising candidate for thermophilic fermentative hydrogen production with a hydrogen yield of 2.53 mol H2 mol−1hexose from organic waste and wastewater containing a mixture of hexose and pentose sugars. Thermoanaerobacterium species play a major role in thermophilic hydrogen production as confirmed both by molecular and cultivation-based analyses.

Biohydrogen production from crude glycerol by immobilized Klebsiella sp. TR17 was investigated in an up-flow anaerobic sludge blanket (UASB) reactor. The reactor was operated under non-sterile conditions at 40 ○ C and initial pH 8.0 at different hydraulic retention times (HRTs) (2–12 h) and glycerol concentrations (10–30 g/L). Decreasing the HRT led to an increase in hydrogen production rate (HPR) and hydrogen yield (HY). The highest HPR of 242.15 mmol H 2 /L/d and HY of 44.27 mmol H 2 /g glycerol consumed were achieved at 4 h HRT and glycerol concentrations of 30 and 10 g/L, respectively. The main soluble metabolite was 1,3-propanediol, which implies that Klebsiella sp. was dominant among other microorganisms. Fluorescence in situ hybridization (FISH) revealed that the microbial community was dominated by Klebsiella sp. with 56.96, 59.45, and 63.47% of total DAPI binding cells, at glycerol concentrations of 10, 20, and 30 g/L, respectively.

A thermotolerant Klebsiella sp. TR17 for production of hydrogen from crude glycerol was investigated. Results from Plackett–Burman design indicated that the significant variables, which influenced hydrogen production, were KH 2 PO 4 and NH 4 Cl (for buffer capacity and nitrogen source). Subsequently, the two selected variables and crude glycerol were optimized by the Central Composite design for achieving maximum hydrogen and ethanol yield. The concentration of crude glycerol, KH 2 PO 4 , and NH 4 Cl had an individual effect on both hydrogen and ethanol yield ( p 2 PO 4 and NH 4 Cl had an interactive effect on ethanol yield ( p 2 PO 4 , and 6.03 g/L NH 4 Cl. The predicted maximum simultaneous hydrogen and ethanol yield were 0.27 mol H 2 /mol glycerol and 0.63 mol EtOH/mol glycerol, respectively. Validation of the predicted optimal conditions exhibited similar hydrogen and ethanol yield of 0.26 mol H 2 /mol glycerol and 0.58 mol EtOH/mol glycerol, respectively.

Anaerobic co-digestion of canned seafood wastewater (CSW) with glycerol waste (GW) and wolffia arrhiza (WA) for methane production was investigated. Methane yields from anaerobic co-digestion of CSW with 1%GW, CSW with 1%GW and 5%WA, CSW with 1%GW and 10%WA and CSW with 1%GW and 15%WA were 577, 789, 545 and 474 mL CH4/g VS-added, respectively. Methane production from CSW with 1%GW and 5%WA increased approximately 4-fold when compared with CSW alone (278 mLCH4/g VS-added). Co-digestion of CSW with 1% GW and 5% WA was the best condition and gave the maximum methane production of 8.8 m3 CH4/m3 mixed wastewater and 96.8% biodegradability. The maximum methane production rate and yield were 3.71 L CH4/L-reactor.day and 858 mL CH4/g VS-added (352 mLCH4/g COD-removed) at OLR of 4 g COD/L. day in UASB reactor. The methane composition in biogas was 62.3%. The Monod, Modified Stover–Kincannon and Grau second-order models were used to explain the performance of UASB reactor. The results showed that the kinetic coefficient of the Modified Stover–Kincannon model could explain the performance of UASB reactor in term of COD removal efficiency and microbial growth by having the regression coefficient (R2) as 0.987.