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The research experimentally investigated biohydrogen production with a light intensity of 4500 lux using indigenous bacteria in DEPOME. The study was conducted in three stages: identified indigenous bacteria through next-generation sequencing (NGS) DNA, analyzed DEPOME characteristics, and produced biohydrogen. Biohydrogen production was carried out under two initial substrate pH conditions: neutral (pH 7) and natural pH substrate (4.9–5.4) for 88 h at a controlled temperature of 30 °C, with measurements of gas production and observations of changes in dissolved oxygen (DO), oxidation-reduction potential (ORP), and substrate pH taken at 4-h intervals. Rhodopseudomonas palustris bacteria was identified as indigenous bacteria for photo-fermentation in POME. The yield, gas production rate, and light conversion efficiency (LCE) were found to be 147.65 mg-H 2 /L-Depome, 1.68 mg-H 2 /L-Depome/h, and 11.75 % under the initial pH neutralization treatment, while without initial pH treatment, the values were 78.5 mg-H 2 /L-Depome, 0.89 mg-H 2 /L-Depome/h, and 6.25 %. [Display omitted] • Rhodopseudomonas palustris was found as indigenous bacteria on POME. • pH is one of the most influential factors for good bacterial growth. • Changes in ORP and pH during the process have an impact on biohydrogen yields. • DEPOME has good potential as a photo-fermentation substrate. [ABSTRACT FROM AUTHOR]

Microbial fuel cells (MFCs) are a viable source of clean and renewable energy from wastewater and gaining attention on a global scale. Thus, this research work focuses on the energy production from high-strength palm oil mill wastewater using MFCs. A state-of-the-art technique for improving the performance of MFCs by covering a carbon fibre anode with various sized powdered activated carbon (PAC) particles was investigated. In addition, the MFCs were tested at various hydraulic retention times (HRT) to assess the performance displayed by modified MFCs. Results showed that a relatively smaller amount of PAC with a diameter of 13 μm coated at the anode during the cultivation stage at a shorter hydraulic retention time (4 days) would produce 504.1 ± 8.7 mW m−3 of power, 39.9 ± 2.9% of chemical oxygen demand removal efficiency, and 299 ± 63 mL of biogas. While, MFC running at a longer hydraulic retention time (12 days) was able to produce more power and had better effluent quality than those operating at a shorter hydraulic retention period. [Display omitted] • Ability of MFC to produce energy and treat palm oil wastewater simultaneously. • MFC-carbon cloth anode coated PAC produced almost doubled energy than control. • About 10% higher COD removal with MFC-carbon cloth anode coated PAC than control. • Inverse relationship between biogas production and power generation was identified. [ABSTRACT FROM AUTHOR]

Facultative hydrogen-producing bacteria hold immense potential for fermentative hydrogen and valuable metabolite production. In this study, a mesophilic hydrogen-producing bacterium was isolated from palm oil mill effluent (POME) and identified as Enterococcus faecalis isolate VT-H1 using hybrid sequencing technologies. Our investigation encompassed the growth of the isolate and its capacity for hydrogen and volatile fatty acid (VFA) production. The results revealed that optimal growth occurred when glucose was utilized at 37 °C and initial pH of 7.0, resulting in a final OD 600 of 2.58. The isolate demonstrated exceptional hydrogen production capabilities, achieving a maximum cumulative hydrogen yield of 2.22 mol-H 2 /mol-glucose at 30 °C and pH 7.0, outperforming previously reported E. faecalis strains by 5.84-fold. Kinetic analysis revealed favorable parameters for hydrogen production at 30 °C, with maximum hydrogen production (H m = 2.63 mol-H 2 /mol-glucose), maximum hydrogen production rate (R m = 0.03 mol-H 2 /mol-glucose·h), and lag-phase time (LPT = 18.34 h). Additionally, E. faecalis isolate VT-H1 exhibited significant butyric acid production (63.0 mM) alongside acetic acid (7.0 mM). Genome analysis unveiled the presence of key enzymes associated with hydrogen production, including formate hydrogen lyase (FHL) complex with formate dehydrogenase subunit alpha (FDH-α), bidirectional [NiFe] hydrogenase, NADH-dependent oxidoreductase subunit E, and NADH-quinone oxidoreductase subunit F. Moreover, genes associated with butyric acid production were also identified. These findings highlight the potential of E. faecalis isolate VT-H1 as a promising candidate for sustainable hydrogen and VFA production. Its unique characteristics, distinct genetic profile, and exceptional hydrogen and VFA production capabilities bring exciting opportunities for future biotechnological applications and further research to optimize and scale-up its potential for industrial use. [Display omitted] • A novel hydrogen-producing bacterium, Enterococcus faecalis VT-H1 , was isolated. • E. faecalis VT-H1 shows high hydrogen yield, 2.22 mol-H 2 /mol-glucose. • Butyric acid was found to be the dominant volatile fatty acid in the system. • Optimal hydrogen and butyric acid production conditions were 30 °C with pH 7.0. • E. faecalis VT-H1 contains multicomplexes in its formate hydrogenlyase system. [ABSTRACT FROM AUTHOR]

Due to accelerating global efforts toward decarbonization, a clean hydrogen (H 2) producing technology, Microbial Electrolysis Cell (MEC), has garnered considerable attention. However, MEC's external energy requirement has raised concerns about its sustainability, scalability and application costs. The objective of this research was to build a renewable energy generating system for MECs' performance enhancement during the treatment of Palm oil mill effluent (POME). A novel integration of a pico-hydro-power generator (PHP) with single-chambered MECs exceptionally improved its performance. The performance boost was observed as 1.16 m3-H 2 /m3d H 2 and 113 A/m3current production in concomitant with 73% organics removal from Palm Oil Mill Effluent (POME) wastewater, which is higher than the previous single-chambered MECs studies. 78% H 2 recovery r cat (H 2) along with 57% coulombic efficiency (CE) corroborated the removal of a high percentage of electrons from POME organic materials to generate >96% pure H 2. The MEC nourished POME wastewater degrading communities while stimulating growth of electroactive Geobacter in the anodic biofilm which produced H 2. The overall H 2 recovery, COD removal rate and energy efficiency of PHP-MEC are superior than other MECs powered by other external renewable energy sources reported to date. The PHP-MEC prototype paves the path of scale up studies to build a renewable energy dependent future. [Display omitted] • PHP-MEC exceptionally transforms environmental toxic waste to renewable energy. • PHP-MEC yielded >96% pure H 2 during toxic industrial effluent (POME) treatment. • MEC's energy requirement was exceedingly met by a novel Pico-hydro power (PHP). • H 2 yield and COD removal by PHP-MECs are superior than non-PHP-MECs to-date. • PHP-MEC is economic and scalable option to reduce the carbon footprint. [ABSTRACT FROM AUTHOR]

Palm oil mill effluent (POME), a wastewater from the most significant agricultural industry in Southeast Asia is produced in tremendous amounts that requires proper management to mitigate its negative environmental effects. The feasibility of treating POME in a closed dark fermentation (DF) system to replace the existing inefficient open ponding treatment has been thoroughly investigated. Theoretically, the maximum H 2 yield obtained by DF process is 4 mol H2 /mol glucose , however, it is not achievable due to the nature of POME. In this study, several enhancement methods for increasing H 2 yield and DF process stability were discussed. An apprehension into the different pre-treatment methods on POME including physicochemical, chemical and biological and their effects on the characteristics of POME including pH, temperature, sugar content, solid content, viscosity, nutrients and by-product toxicity on the biohydrogen production and effluent quality were reviewed. Various bioreactor designs were used for biohydrogen from POME, the modifications applied on the system design to increase the stability and productivity of POME treatment have been examined. Moreover, higher biohydrogen productivity could be obtained with the addition of nanoparticle nutrients and introducing genetically modified H 2 -producing bacteria. Finally, further investigation in the future shall focus on the development of a more inclusive and efficient POME treatment via DF process that favours biohydrogen production, environmental benign and economically viable. [Display omitted] • Enhancement of H 2 production from POME in DF was reviewed. • Enhancement efficiency was based on increase in H 2 yield and pollutant removal. • Dilute acid pretreatment has a promising effect on the performance of DF. • Simple modification in bioreactor design could greatly improve process performance. • Genetic engineering and nanoparticle technology on H 2 were discussed. [ABSTRACT FROM AUTHOR]

Microbial electrolysis cells (MECs) are a new bio-electrochemical method for converting organic matter to hydrogen gas (H 2). Palm oil mill effluent (POME) is hazardous wastewater that is mostly formed during the crude oil extraction process in the palm oil industry. In the present study, POME was used in the MEC system for hydrogen generation as a feasible treatment technology. To enhance biohydrogen generation from POME in the MEC, an empirical model was generated using response surface methodology (RSM). A central composite design (CCD) was utilized to perform twenty experimental runs of MEC given three important variables, namely incubation temperature, initial pH, and influent dilution rate. Experimental results from CCD showed that an average value of 1.16 m3 H 2 /m3 d for maximum hydrogen production rate (HPR) was produced. A second-order polynomial model was adjusted to the experimental results from CCD. The regression model showed that the quadratic term of all variables tested had a highly significant effect (P < 0.01) on maximum HPR as a defined response. The analysis of the empirical model revealed that the optimal conditions for maximum HPR were incubation temperature, initial pH, and influent dilution rate of 30.23 ∘C, 6.63, and 50.71%, respectively. Generated regression model predicted a maximum HPR of 1.1659 m3 H 2 /m3 d could be generated under optimum conditions. Confirmation experimentation was conducted in the optimal conditions determined. Experimental results of the validation test showed that a maximum HPR of 1.1747 m3 H 2 /m3 d was produced. [Display omitted] • POME used in MEC for H 2 as a feasible method and effective treatment technology. • To enhance H 2 production from POME, an empirical model was generated using RSM. • Results from CCD showed 1.16 m3 H 2 /m3 d for maximum HPR was produced. • The confirmation test results showed a maximum HPR of 1.1747 m3 H 2 /m3 d. [ABSTRACT FROM AUTHOR]

This study aims to analyse the life-cycle assessment of biohydrogen production from palm oil mill effluent (POME) in a pilot-scale up-flow anaerobic sludge blanket fixed-film reactor. The SimaPro LCA software and ReCiPe 2016 impact assessment method were used. Electricity usage was found to be a significant source of environmental impacts, with 50–98% of the total impacts. Furthermore, an improvement analysis was conducted, resulted in a reduction in all impacts, especially global warming impact with 77% reduction from 818 to 189 kg CO 2 -eq per kg biohydrogen. While shifting the pilot reactor to Sarawak may further lessen the impact to 142 kg CO 2 -eq due to cleaner grid in that region. Besides, if the environmental burden avoided due to usage of POME is considered, the global warming impact can be further reduced to 54.9 kg CO 2 -eq. Thus, the pilot reactor has huge potential, especially in utilizing waste to produce bioenergy. • The LCA of bio-H 2 production from POME in the pilot-scale reactor was conducted. • Electricity usage contributed highest impact especially in global warming potential. • Improvement analysis was conducted to reduce impact to 54.9 kg CO 2 eq per kg H 2. [ABSTRACT FROM AUTHOR]

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. • ZVI provided suitable pH values for acidogenesis, acetogenesis and methanogenesis. • ZVI provided extra electrons and iron ions, which promoted key microbial activities. • 16 g/L was an optimal ZVI concentration in terms of methane yields in batch reactors. • In a fed-batch, ZVI increased the methane content in biogas from 62 to 76%. • In a CSTR, ZVI increased the methane content in biogas from 60 to 75%. [ABSTRACT FROM AUTHOR]

Methods are investigated to prepare active hydrogen (H 2)-producing cultures originating from palm oil mill sludge using dark fermentation. The first successful method that produces potent H 2 -producing cultures and avoids growing H 2 -consuming methanogens involves heat pretreatment of the sludge at 100 °C for 2 h and then the sludge sample is shocked in an ice bath for 15 min. Subsequently, a glucose solution rich in nutrients (glucose-based substrate) of 14.80 g chemical oxygen demand (COD)/L is fed in to enrich the H 2 -producing cultures. The H 2 production reaches 78.63% on day 31. The second method involves acid pretreatment of sludge with 10 M hydrochloric acid at pH 3 for 48 h. Glucose-based substrate of 25.47 g COD/L is fed into the system. The H 2 production is 69.41% on day 27. For both methods, the H 2 production is stable after the H 2 content reached its maximum. The operation is performed semi-continuously using a hydraulic retention time of 1 day and at 30 °C. The optimum bacterial cells-to-COD level of substrate is approximately 0.60 in the start-up medium. The fermentation medium has an optimum initial pH of 5 and a final pH of 5.2–5.3. These two methods are recommended to produce active H 2 -producing cultures for plant start-up in bio-H 2 production. • Active H 2 -producing cultures are prepared for system start-up. • Pretreatment of palm oil mill sludges and preparation methods are proposed. • Glucose-based substrate is used in maximizing consistency for bacterial growth. • The fermentation medium has initial pH 5 and final pH 5.2–5.3. • The H 2 content reaches 78.63% on day 31 with production stable thereafter. [ABSTRACT FROM AUTHOR]

A start-up study of lab-scale up-flow anaerobic sludge blanket fixed-film reactor (UASFF) was conducted to produce biohydrogen from palm oil mill effluent (POME). The reactor was fed with POME at different hydraulic retention time (HRT) and organic loading rate (OLR) to obtain the optimum fermentation time for maximum hydrogen yield (HY). The results showed the HY, volumetric hydrogen production rate (VHPR), and COD removal of 0.5–1.1 L H 2 /g COD consumed , 1.98–4.1 L H 2 L−1 day−1, and 33.4–38.5%, respectively. The characteristic study on POME particles was analyzed by particle size distribution (PSD), Scanning electron microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDX). The microbial Shannon and Simpson diversity indices and Principal Component Analysis assessed the alpha and beta diversity, respectively. The results indicated the change of bacterial community diversity over the operation, in which Clostridium sensu stricto 1 and Lactobacillus species were contributed to hydrogen fermentation. • Fermentative hydrogen production from palm oil mill effluent. • Substrate particle size, surface morphology, elemental identification were studied. • Maximum H 2 production at HRT 8 h/OLR 45.4 g COD L−1 day−1. • Evolution in microbial community before and after dark fermentation. • Clostridium sensu stricto 1 mostly contributed to biohydrogen production. [ABSTRACT FROM AUTHOR]

The shift from conventional hydrogen production that utilised fossil-based energy towards a more sustainable practice is essential. Recently, the interest in utilising renewable hydrogen sources associated with bio-gas has risen. This work aims to develop a P-graph methodology for bio-hydrogen network synthesis, where oil refineries and ammonia plants act as bio-hydrogen sinks, while palm oil mills serve as the bio-hydrogen sources. The latter produces huge amount of palm oil mill effluent (POME) which may be converted to bio-hydrogen. The model is optimised with the aim to minimise the total network cost, whilst fulfilling the demand of all hydrogen sinks. Two case studies in Malaysia are used to illustrate the effectiveness of the proposed model. Results show that the overall network cost can be reduced by 45.6% (first case study) and 85.8% (second case study) when bio-hydrogen is supplied from the abundant POME in the study areas. Besides, the capability of the proposed P-graph framework in conducting uncertainty analysis and technology benchmarking study, are also demonstrated. Image 1 • A P-graph approach to synthesise the bio-hydrogen network is developed. • Bio-hydrogen network can be more economic feasible compared to the existing one. • Two case studies in Malaysia are used to illustrate the proposed method. • The framework can be used to analyse supply chain uncertainty. • The framework can be used to benchmark the feasibility of new technology. [ABSTRACT FROM AUTHOR]

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-H 2 ·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-H 2 ·gCOD−1. The hydrogen yield of continuous two-stage dark fermentation and microbial electrolysis was 236 mL-H 2 ·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 two-stage fermentation and microbial electrolysis were investigated for biohydrogen production. • H 2 yield of 236 mL-H 2 ·gCOD−1 was achieved from two-stage biohydrogen processes. • COD removal of 86% was achieved from two-stage biohydrogen processes. • The overall energy yield of 4.48 kJ·gCOD−1 was achieved in the two-stage biohydrogen processes. • The hydrogen yield was 3 times increased when compared with dark fermentation alone. [ABSTRACT FROM AUTHOR]

Methane (CH 4) production from palm oil mill effluent (POME) pre-treated by ozonation was conducted under mesophilic (37 °C) condition. The results demonstrated that methane can be produced from both non-ozonated and ozonated POME at a concentration range of 3,000 to 15,000 mg COD L−1. Methane yield rised 54% when POME was pre-treated by ozonation at POME concentration of 15,000 mg COD L−1. The methane yield increased the POME concentration was increased. At POME above 15,000 mg COD L−1, the methane yield was dropped dramatically. The methane production rates (R max) and yields exerted similar trend regarding the POME concentration. Accumulation of volatile fatty acids in the reactor posed the drop of methane production. Ozonation pretreatment process of POME can improve the biodegradability of the complex organic matter in POME and enhanced methane yield and rate at POME concentration range of 3,000–15,000 mg COD L−1. • Mesophilic fermentation setup for methane production from POME. • Ozonation pre-treatment raised POME biodegradability. • Ozonation pre-treated POME raised yield 54%. [ABSTRACT FROM AUTHOR]

A start-up study was conducted to produce biohydrogen and biomethane from Palm Oil Mill Effluent (POME) using a two-stage up-flow anaerobic sludge fixed-film (UASFF) bioreactor. 100% molasses was used to start the system, and POME was added at 10% increments until it reached 100% after 59 days. During this period of continuous operation, the HRT and temperature were adjusted in order to optimize the condition for biogas production. Hydrogen and methane gas production fluctuated between 53–70% and 90–95%, respectively, in the last four days of operation (days 56–59), with POME percentage being increased from 70% to 100% (30%–0% molasses). Using 100% raw POME led to a total COD removal of 83.70%, average gas production rates of 5.29 L H 2 d−1 (57.11% H 2) and 9.60 L CH 4 d−1 (94.08% CH 4), in their respective units. This output is comparable to, if not better than using 100% molasses as substrate. This work concludes that based on the relative consistency of biogas production on days 56–59, the two-stage UASFF bioreactor operating at a final HRT of 4 h and temperature of 43 °C has taken a period of two months for start-up. Image 1 • A total COD removal efficiency of 83.70% was achieved using raw POME in two-stage UASFF reactor. • Short-term and stable H 2 and CH 4 production were established in thermophilic UASFF bioreactor. • Highest H 2 percentage and HPR was 57.11% and 5.29 L d−1 using 100% raw POME. • Highest CH 4 percentage and MPR was 94.08% and 9.60 L d−1 using 100% raw POME. [ABSTRACT FROM AUTHOR]

In current paper, thermodynamics study of palm oil mill effluent (POME) steam reforming was performed to investigate its feasibility for syngas production. By using the minimization of total Gibbs free energy method, the thermodynamic simulation is executed to study the effect of reaction temperature (573–1173 K) on product yield (Y i) and syngas ratio (H 2 :CO). Based on preliminary analysis, the POME liquor composed of 99.73% water and 0.27% organic contents by mole. Complete conversion of POME's organic contents is accomplished regardless of reforming temperature. However, the equilibrium constant reveals that not every organic constituent in POME are reformed into syngas via steam reforming at ≤673 K, so their disappearance hints at the occurrence of thermal decomposition. The steam reforming of all organic contents in POME is only viable at ≥773 K. From POME steam reforming at 573–1173 K, H 2 -rich syngas (H 2 :CO ratio = 25–3457) is produced. For syngas production, the optimum temperature is 1073 K because it gives highest Y s y n g a s (58348 μmol syngas/mol POME) with a Q r e q u i r e d of 12.05 kJ/mol POME. In a nutshell, the POME steam reforming is an alluring process that viable for syngas production as it potentially mitigates the environmental issue inflicted by palm oil processing. • Thermodynamics analysis of POME steam reforming was completed for 573–1173 K. • Complete conversion of POME's organic contents regardless of reforming temperature. • Amelioration of all POME's organic contents into syngas viable at ≥773 K. • H 2 -rich syngas is generated from POME steam reforming. • Maximum Y s y n g a s (58348 μmol syngas/mol POME) accomplished at 1073 K. [ABSTRACT FROM AUTHOR]

This paper reports on the novel application of catalytic steam reforming process to convert palm oil mill effluent (POME) into syngas over a 20wt%Ni/80wt%Al 2 O 3 catalyst. The catalyst possessed high degree of crystallinity and was impurity-free, judging from the obtained XRD pattern. Furthermore, the BET specific surface area of catalyst was low (2.09 m2 g−1), consistent with smooth surface captured by the FESEM images. CO 2 -desorption and NH 3 -desorption profiles showed a presence of both acid and basic sites on the surface of catalyst. In the absence of catalyst, about 7.0% reduction of chemical oxygen demand (COD) was achieved at 6.0 mL h−1 flow rate of POME, reforming temperature of 873 K and 20 mL min−1 of N 2 -flow. Significantly, the COD reduction shot up to 93.7% in the presence of catalyst and liquid-hourly-space-velocity (LHSV) of POME of 90 mL h−1 g cat −1 at 873 K. The corresponding biochemical oxygen demand (BOD) reduction recorded was 93.8%. However, normalized carbon loss indicates that a high LHSV would favour carbon deposition. In addition to high LHSV, the carbon deposition was also influenced by reaction temperature. High reaction temperature has reduced carbon deposition, as well as organics removal. COD reduction was 99.41% and BOD reduction was 99.52% at 1173 K when LHSV was 60 mL h−1 g cat −1. In the gas phase, four species were consistently detected, viz. H 2 , CO 2 , CO and CH 4 , with H 2 as the major component. The H 2 selectivity increased with both LHSV and reaction temperature. • More than 99% of organics in POME was degraded in the presence of catalyst. • The H 2 selectivity increased with both LHSV and reaction temperature. • Carbon deposition was reduced at elevated reaction temperature. [ABSTRACT FROM AUTHOR]

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. Image 1 • Biohythane from co-digestion of POME with solid waste was 26.5–34 m3/ton wastes. • Co-digestion POME with solid waste increased biohythane production of 67–114%. • Co-digestion increased hydrolysis constant 10 times higher than single digestion. • The synergistic effect occurred during co-digestion POME with palm oil waste residues. • Clostridium sp. and Methanosphaera sp. were dominated in co-digestion system. [ABSTRACT FROM AUTHOR]

Abstract In this work, the syngas production rate ( F S y n g a s ) of LaNiO 3 -catalysed steam reforming of palm oil mill effluent (POME) was optimized with respect to POME flow rate ( V ˙ P O M E ), catalyst weight ( W c a t ), and particle size ( d c a t ). With a net acidity, the synthesized LaNiO 3 catalysed POME steam reforming by cracking the bulky compounds and valorising simpler intermediates into syngas. The degradation efficiencies ( X P ) were also evaluated by assessing wastewater parameters, viz. pH, chemical oxygen demand (COD), biochemical oxygen demand (BOD 5), total suspended solids (TSS), and colour intensity (A). After steam reforming at 873 K, the liquid condensate has neutral pH and zero TSS. The parallel trend of F S y n g a s and X P verified syngas generation from degradation of POME's organics. At higher V ˙ P O M E (0.05–0.09 mL/min), greater POME partial pressure promoted its steam reforming and water gas shift, which enhanced catalytic performance. Beyond optimum V ˙ P O M E (0.09 mL/min), coke-forming Boudouard reaction deteriorated catalytic activity. Catalytic performance was boosted for a longer residence time at higher W c a t (0.1–0.3 g); nonetheless, it was reduced by agglomerated catalyst when W c a t > 0.3 g. Finer LaNiO 3 ( d c a t > 74 μm) with greater surface area to volume ratio exhibited better performance; however, ultrafine LaNiO 3 ( d c a t < 74 μm) had poor performance because of occluded pores. Remarkably, optimized POME steam reforming over LaNiO 3 (T = 873 K, V ˙ P O M E = 0.09 mL/min, W c a t = 0.3 g, d c a t = 74–105 μm) has generated 132.47 μmoL/min of H 2 -rich syngas, whilst achieved 99.53% X C O D , 99.88% X A , 99.75% X B O D 5 , and 100% X T S S . Graphical abstract Image 1 Highlights • POME steam reforming over LaNiO 3 was studied at 873 K and 1 atm. • Reaction was optimized at V ˙ P O M E = 0.09 mL/min, W c a t = 0.3 g, and d c a t = 74 – 105 μm. • At optimised conditions, 132.47 μmol/min of H 2 -rich syngas was generated. • The treatment can achieve 99.53% X C O D , 99.88% X A , 99.75% X B O D 5 , and 100% X T S S . [ABSTRACT FROM AUTHOR]

The present work aims to elucidate substrate utilization from palm oil mill effluent (POME) for biohydrogen production. The experiment was performed in 150 mL serum bottles and the cultures were supplemented with autoclaved-pretreated POME or 0.05 M individual technical grade substrates to investigate the potential use of POME and substrates in preference towards biohydrogen production. The cultures were incubated at 37 °C for 24 h with mild agitation. The maximum hydrogen yield (MHY) obtained was 0.66 mol H 2 /mol total monomeric sugars and productivity of 3551 μmol/10 10 cfu were obtained from engineered Escherichia coli . The POME oligomeric sugars were not metabolized further, which render insignificant conversion of carbohydrates into hydrogen from POME. The yield of hydrogen production increased by 3.5 folds by engineered E . co li BW25113 compared to wild type E . coli BW25113. The preference of the substrates for biohydrogen production is in the following order; glucose > fructose > formic acid. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the maximum hydrogen yield as well as the chemical oxygen demand (COD) reduction from palm oil mill effluent (POME) by using two stage sequential dark and photo fermentation. The first stage operation was carried out using Clostridium butyricum LS2, which has the maximum hydrogen yield of 0.784 ml H 2 /ml POME and COD removal of 57%. The dark fermentative effluent was diluted with 50% of tap water (DEPOME-50), for better penetration of light and was subsequently used as substrate to the second stage fermentation using Rhodopseudomonas palustris as hydrogen producer. Hydrogen production was monitored under optimized light illumination of 7 klux, in batch mode. The two-stage fermentation enhanced the total hydrogen yield from 0.784 (dark fermentation) to 3.064 ml H 2 /ml POME (dark/photo-fermentation). Meanwhile, a 93% of total COD removal was also achieved. [ABSTRACT FROM AUTHOR]

The present study investigates the technical possibilities of hydrogen and methane production from palm oil mill effluent (POME). The production was carried out in two stage (thermophilic and mesophilic) continuous phase with recirculation of the digestate sludge. The reactors used for the present study, up-flow anaerobic sludge blanket reactor (UASB) and continuous stirred tank reactor (CSTR) were operated under thermophilic and mesophilic conditions, respectively. The UASB reactor was operated at 2 days hydraulic retention time (HRT) and 75 kgCOD m 3 d −1 organic loading rate (OLR) for hydrogen production. The effluents from UASB reactor containing mainly with acetate and butyrate were directly fed into CSTR for methane production and 5 days HRT was maintained. Both UASB and CSTR reactors were operated for 120 days continuously, and a stable production of the hydrogen and methane was obtained in the separate reactors. The maximum hydrogen and methane production rate achieved was 1.92 L H 2 L − d −1 and 3.2 L CH 4 L −1 d −1 , respectively. The cumulative hydrogen and methane yields were 215 L H 2 /kgCOD −1 and 320 L CH 4 /kgCOD −1 , respectively with the total COD removal efficiency of 94%. Thermoanaerobacterium species was dominant in hydrogen reactor, while methane reactor was dominated with Methanobrevibacter sp. [ABSTRACT FROM AUTHOR]

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 H 2 mol −1 hexose 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. [ABSTRACT FROM AUTHOR]

Abstract: Thermotolerant consortia were obtained by heat-shock treatment on seed sludge from palm oil mill. Effect of the initial pH (4.5–6.5) on fermentative hydrogen production palm oil mill effluent (POME) showed the optimum pH at 6.0, with the maximum hydrogen production potential of 702.52 mL/L-POME, production rate of 74.54 mL/L/h. Nutrients optimization was investigated by response surface methodology with central composite design (CCD). The optimum nutrients contained 0.25 g urea/L, 0.02 g Na2HPO4/L and 0.36 g FeSO4·7H2O/L, giving the predicted value of hydrogen production of 1075 mL/L-POME. Validation experiment revealed the actual hydrogen production of 968 mL/L-POME. Studies on the effect of temperature (25–55 °C) revealed that the maximum hydrogen production potential (985.3 mL/L-POME), hydrogen production rate (75.99 mL/L/h) and hydrogen yield (27.09 mL/g COD) were achieved at 55, 45 and 37 °C, respectively. Corresponding microbial community determined by the DGGE profile demonstrated that Clostridium spp. was the dominant species. Clostridium paraputrificum was the only dominant bacterium presented in all temperatures tested, indicating that the strain was thermotolerant. [Copyright &y& Elsevier]

Abstract: Substrate bioavailabity is one of the critical factors that determine the relative biohydrogen (bioH2) yield in fermentative hydrogen production and bioelectricity output in a microbial fuel cell (MFC). In the present undertaking, batch bioH2 production and MFC-based biolectricity generation from ultrasonically pretreated palm oil mill effluent (POME) were investigated using heat-pretreated anaerobic sludge as seed inoculum. Maximum bioH2 production (0.7mmolH2/gCOD) and COD removal (65%) was achieved at pH 7, for POME which was ultrasonically pretreated at a dose of 195J/mL. Maximum value for bioH2 productivity and COD removal at this sonication dose was higher by 38% and 20%, respectively, than unsonicated treatments. In batch MFC experiments, the same ultrasound dose led to reduced lag-time in bioelectricity generation with concomitant 25% increase in bioelectricity output (18.3W/m3) and an increase of COD removal from 30% to 54%, as compared to controls. Quantitative polymerase chain reaction (qPCR) tests on sludge samples from batch bioH2 production reflected an abundance of gene fragments coding for both clostridial and thermoanaerobacterial [FeFe]-hydrogenase. Fluorescence in situ hybridization (FISH) tests on sludge from MFC experiments showed Clostridium spp. and Thermoanaerobacterium spp. as the dominant microflora. Results suggest the potential of ultrasonicated POME as sustainable feedstock for dark fermentation-based bioH2 production and MFC-based bioelectricity generation. [Copyright &y& Elsevier]

Abstract: This study investigated the microbial community of an anaerobic sequencing batch reactor (ASBR) operating at mesophilic temperature under varying hydraulic retention times (HRTs) for evaluating optimal hydrogen production conditions, using palm oil mill effluent (POME) as substrate. POME sludge enriched by heat treatment with hydrogen-producing bacteria was used as inoculum and acclimated with the POME. The microbial community was determined by first isolating cultivable bacteria at each operating HRT and then using polymerase chain reaction (PCR). The PCR products were sequenced and sequence identification was performed using the BLAST algorithm and Genbank database. The findings revealed that about 50% of the isolates present were members of the genus Streptococcus, about 30% were Lactobacillus species and around 20% were identified as species of genus Clostridium. Scanning electron microscopy (SEM) analysis also confirmed the presence of spherical and rod-shaped microbial morphologies in the sludge samples of bioreactor during prolonged cultivation. [Copyright &y& Elsevier]

Abstract: Clostridium butyricum EB6 successfully produced hydrogen gas from palm oil mill effluent (POME). In this study, central composite design and response surface methodology were applied to determine the optimum conditions for hydrogen production (P c) and maximum hydrogen production rate (R max) from POME. Experimental results showed that the pH, temperature and chemical oxygen demand (COD) of POME affected both the hydrogen production and production rate, both individually and interactively. The optimum conditions for hydrogen production (P c) were pH 5.69, 36°C, and 92g COD/l; with an estimated P c value of 306ml H2/g carbohydrate. The optimum conditions for maximum hydrogen production rate (R max) were pH 6.52, 41°C and 60g COD/l; with an estimated R max value of 914ml H2/h. An overlay study was performed to obtain an overall model optimization. The optimized conditions for the overall model were pH 6.05, 36°C and 94g COD/l. The hydrogen content in the biogas produced ranged from 60% to 75%. [Copyright &y& Elsevier]

Abstract: The optimum values of hydraulic retention time (HRT) and organic loading rate (OLR) of an anaerobic sequencing batch reactor (ASBR) for biohydrogen production from palm oil mill effluent (POME) under thermophilic conditions (60°C) were investigated in order to achieve the maximum process stability. Microbial community structure dynamics in the ASBR was studied by denaturing gradient gel electrophoresis (DGGE) aiming at improved insight into the hydrogen fermentation microorganisms. The optimum values of 2-d HRT with an OLR of 60gCODl−1 d−1 gave a maximum hydrogen yield of 0.27l H2 gCOD−1 with a volumetric hydrogen production rate of 9.1l H2 l−1 d−1 (16.9mmoll−1 h−1). The hydrogen content, total carbohydrate consumption, COD (chemical oxygen demand) removal and suspended solids removal were 55±3.5%, 92±3%, 57±2.5% and 78±2%, respectively. Acetic acid and butyric acid were the major soluble end-products. The microbial community structure was strongly dependent on the HRT and OLR. DGGE profiling illustrated that Thermoanaerobacterium spp., such as Thermoanaerobacterium thermosaccharolyticum and Thermoanaerobacterium bryantii, were dominant and probably played an important role in hydrogen production under the optimum conditions. The shift in the microbial community from a dominance of T. thermosaccharolyticum to a community where also Caloramator proteoclasticus constituted a major component occurred at suboptimal HRT (1d) and OLR (80gCODl−1 d−1) conditions. The results showed that the hydrogen production performance was closely correlated with the bacterial community structure. This is the first report of a successful ASBR operation achieving a high hydrogen production rate from real wastewater (POME). [Copyright &y& Elsevier]