Effects of process,operational and environmental variables on biohydrogen production using palm oil mill effluent (POME)

A batch study for biohydrogen production was conducted using raw palm oil mill effluent (POME) and POME sludge as a feed and inoculum respectively. Response Surface Methodology (RSM) was used to design the experiments. Experiments were conducted at different reaction temperatures (30–50 °C), inoculum size to substrate ratios (I:S) and reaction times (8–24 h). An optimum condition of biohydrogen production was achieved with COD removal efficiency of 21.95% with hydrogen yield of 28.47 ml H₂ g^?1 COD removed. The I:S ratio was 40:60, with reaction temperature of 50 °C at 8 h of reaction time. The study showed that a lower substrate concentration (less than 20 g L^?1) for biohydrogen production using pre-settled POME was achievable, with optimum HRT of 8 h under thermophilic condition (50 °C). This study also found that pre-settled POME is feasible to be used as a substrate for biohydrogen production under thermophilic condition.     

Simultaneous thermophilic hydrogen production and phenol removal from palm oil mill effluent by Thermoanaerobacterium-rich sludge

Thermoanaerobacterium-rich sludge was used for hydrogen production and phenol removal from palm oil mill effluent (POME) in the presence of phenol concentration of 100–1000 mg/L. Thermoanaerobacterium-rich sludge yielded the most hydrogen of 4.2 L H₂/L-POME with 65% phenol removal efficiency at 400 mg/L phenol. Butyric acid and acetic acid were the main metabolites. The effects of oil palm ash, NH₄NO₃ and iron concentration (Fe²⁺) on hydrogen production and phenol removal efficiency from POME by Thermoanaerobacterium-rich sludge was investigated using response surface methodology (RSM). The RSM results indicated that the presence of 0.2 g Fe²⁺/L, 0.3 g/L NH₄NO₃ and 20 g/L oil palm ash in POME could improved phenol removal efficiency, with predicted hydrogen production and phenol removal efficiency of 3.45 L H₂/L-POME and 93%, respectively. In a confirmation experiment under optimized conditions highly reproducible results were obtained, with hydrogen production and phenol removal efficiency of 3.43 ± 0.12 L H₂/L-POME and 92 ± 1.5%, respectively. Simultaneous hydrogen production and phenol removal efficiency in continuous stirred tank reactor at hydraulic retention time (HRT) of 1 and 2 days were 4.0 L H₂/L-POME with 85% and 4.2 L H₂/L-POME with 92%, respectively. Phenol degrading Thermoanaerobacterium-rich sludge comprised of Thermoanaerobacterium thermosaccharolyticum, Thermoanaerobacterium aciditolerans, Desulfotomaculum sp., Bacillus coagulans and Clostridium uzonii. Phenol degrading Thermoanaerobacterium-rich sludge has great potential to harvest hydrogen from phenol-containing wastewater.     

Feasibility of bio-hythane production by co-digesting skim latex serum (SLS) with palm oil mill effluent (POME) through two-phase anaerobic process

Hydrogenogenic batch fermentation without nutrients addition was investigated at different SLS: POME mixing ratios of 100:0, 95:5, 90:10, 85:15, 80:20, 75:25, 70:30, 65:35, 60:40, 55:45,50:50, and 0:100 (Volatile Solid, VS basis) at initial organic concentrations of 21 and 7 g-VS/L. Satisfactory hydrogen yield of 84.5 ± 0.7 mL H₂/g-VS_added was achieved from 7 g-VS/L batch having SLS: POME-VS mixing ratio of 55:45. Adding NaHCO₃ 3 g/L or 0.43 g-NaHCO₃/g-VS) in the two-stage anaerobic system at 7 g-VS/L could provide sufficient buffering capacity. Hydrogenogenic effluent from 7 g-VS/L batch at SLS: POME mixing ratio of 55:45 (VS basis) could further generate rather high methane yield of 311.2 ± 8.0 mL- CH₄/g-VS_added in themethanogenic stage.According to the experimental results, bio-hythane approximately 55.5 × 10⁶ m³/year with 21% (V/V) of hydrogen, equivalent to51.0 × 10⁶ l-gasoline could be produced potentially from 3.88 × 10⁶ m³ of mixed SLS and POME through the two-stage anaerobic co-digestion.     

Pilot-scale of biohythane production from palm oil mill effluent by two-stage thermophilic anaerobic fermentation

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.     

Biohydrogen production by Clostridium butyricum EB6 from palm oil mill effluent

A hydrogen producer was successfully isolated from anaerobic digested palm oil mill effluent (POME) sludge. The strain, designated as Clostridium butyricum EB6, efficiently produced hydrogen concurrently with cell growth. A controlled study was done on a synthetic medium at an initial pH value of 6.0 with 10 g/L glucose with the maximum hydrogen production at 948 mL H₂/L-medium and the volumetric hydrogen production rate at 172 mL H₂/L-medium/h. The supplementation of yeast extract was shown to have a significant effect with a maximum hydrogen production of 992 mL H₂/L-medium at 4 g/L of yeast extract added. The effect of pH on hydrogen production from POME was investigated. Experimental results showed that the optimum hydrogen production ability occurred at pH 5.5. The maximum hydrogen production and maximum volumetric hydrogen production rate were at 3195 mL H₂/L-medium and 1034 mL H₂/L-medium/h, respectively. The hydrogen content in the biogas produced was in the range of 60–70%.     

Enhancement of biohythane production from solid waste by co-digestion with palm oil mill effluent in two-stage thermophilic fermentation

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 (k_h) from 0.07 to 0.113 to 0.120–0.223 d⁻¹. The hydrolysis constant (k_h) 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.     

In-situ methane enrichment of biogas from anaerobic digestion of palm oil mill effluent by addition of zero valent iron (ZVI)

Palm oil mill effluent (POME) is a wastewater effluent that is generated from palm oil milling. Treatment of POME, especially using biological treatment methods, is a challenge as it contains high amounts of organic and sulfur compounds, and it is highly acidic. In this research, the effects of zero-valent iron (ZVI) on the enhancement of methane production from POME via anaerobic digestion were investigated. Furthermore, to identify the reactor operation modes that were suitable for the addition of ZVI, anaerobic digestion of POME was tested in three reaction configurations: batch reactor, fed-batch reactor, and continuous stirred-tank reactor (CSTR). In the batch mode, where acidic POME was fed with 16 g/L of ZVI dose just once, methane production increased by 74%. However, as the oxidation of ZVI under anaerobic conditions led to the production of hydroxyl ions, the pH of the medium continuously increased from approximately 7 to 9, which is not suitable for methanogenesis. In the fed-batch mode that involved intermittent feeding of acidic POME, the pH of the culture media was maintained at 6.8. This is because the extra hydroxyl ions generated from the oxidation reaction of ZVI tended to neutralize the acids in the feeding substrate. In addition, ZVI promoted the production of methane from POME and increased the average methane content in biogas from 62% to 76%. In the CSTR mode, which involved continuous feeding of acidic POME, ZVI increased methane production by 86% (from 1.79 to 3.32 L/day), methane content in biogas from 60 to 75%, and total chemical oxygen demand (tCOD) removal efficiency from 78 to 89 to 88–95%. Thus, the addition of ZVI can be a potential strategy for in-situ methane enrichment of biogas by anaerobic digestion of POME. This is because ZVI acts as a buffer for acid generation and provides extra electrons, ferrous ions, and ferric ions, which promote key microbial activities in the anaerobic digestion process.     

High efficient biohydrogen production from palm oil mill effluent by two-stage dark fermentation and microbial electrolysis under thermophilic condition

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.     

Dark fermentation of acid hydrolyzed ground wheat starch for bio-hydrogen production by periodic feeding and effluent removal

Dark fermentation of acid hydrolyzed ground wheat starch for bio-hydrogen production by periodic feeding and effluent removal was investigated at different feeding intervals. Ground wheat was acid hydrolyzed at pH = 3 and T = 121 °C for 30 min using an autoclave. The resulting sugar solution was subjected to dark fermentation with periodic feeding and effluent removal. The feed solution contained 9 ± 0.5 g L⁻¹ total sugar supplemented with some nutrients. Depending on the feeding intervals hydraulic residence time (HRT) was varied between 6 and 60 h. Steady-state daily hydrogen production increased with decreasing HRT. The highest daily hydrogen production (305 ml d⁻¹) and volumetric hydrogen production rate (1220 ml H₂ L⁻¹ d⁻¹) were obtained at HRT of 6 h. Hydrogen yield (130 ml H₂ g⁻¹ total sugar) reached the highest level at HRT = 24 h. Effluent total sugar concentration decreased, biomass concentration and yield increased with increasing HRT indicating more effective sugar fermentation at high HRTs. Dark fermentation end product profile shifted from acetic to butyric acid with increasing HRT. High acetic/butyric acid ratio obtained at low HRTs resulted in high hydrogen yields.