Renewable and sustainable bioenergies production from palm oil mill effluent (POME): win-win strategies toward better environmental protection

Palm oil industry is one of the leading agricultural industries in Malaysia with average crude palm oil production of more than 13 million tonne per year. However, production of such huge amount of crude palm oil has consequently resulted to even larger amount of palm oil mill effluent (POME). POME is a highly polluting wastewater with high chemical oxygen demand (COD) and biochemical oxygen demand (BOD) in which can caused severe pollution to the environment, typically pollution to water resources. On the other hand, POME was identified as a potential source to generate renewable bioenergies such as biomethane and biohydrogen through anaerobic digestion. In other words, a combination of wastewater treatment and renewable bioenergies production would be an added advantage to the palm oil industry. In line with the world's focus on sustainability concept, such strategy should be implemented immediately to ensure palm oil is produced in an environmental friendly and sustainable manner. This review aims to discuss various technologies to convert POME to biomethane and biohydrogen in a commercial scale. Furthermore, discussion on using POME to culture microalgae for biodiesel and bioethanol production was included in the present paper as a new remedy to utilize POME with a greater beneficial return.     

Bioconversion of wheat stalk to hydrogen by dark fermentation: effect of different mixed microflora on hydrogen yield and cellulose solubilisation

This study determined hydrogen production, volatile fatty acids (VFAs) generation and cellulose solubilisation from anaerobic dark fermentation of wheat stalk and showed the effect of different mixed microflora. The cumulative hydrogen yields of anaerobic digested activated sludge (AS)-inoculated and anaerobic digested dairy manure (DM)-inoculated system were 23.3 and 37.0 mL/g VS at 204 h, respectively. A modified Gompertz equation was able to adequately describe the production of hydrogen from the batch fermentation by both mixed microflora. During the process, acetate and butyrate accounted for more than 76.1% of total VFAs for both fermentations. The extent of cellulose solubilisation approached 46.6% and 75.2% for AS- and DM-inoculated fermentation, respectively. The X-ray diffraction (XRD) showed that the crystallinities of both fermented stalks were partly disrupted by the mixed microflora, and DM-inoculated fermentation had more disruption than AS-inoculated one.     

Evaluation of dairy cattle manure as a supplement to improve net energy gain in fermentative hydrogen production from sucrose

This study evaluated fermentative biohydrogen production from sucrose supplemented with dairy cattle manure at different sucrose:manure ratios. Hydrogen yields found in this study (2.9-5.3 M hydrogen/M sucrose) at ambient temperature are higher than literature results obtained at mesophilic temperatures. This study demonstrated that dairy cattle manure could serve as a buffering agent to maintain recommended pH levels; as a nutrient source to provide the required nutrients for hydrogen production; as a seed to produce hydrogen from sucrose; and as a co-substrate to improve the hydrogen yield. Based on an analysis of the net energy gain, it is concluded that positive net energy gains can be realized with non-thermal pretreatment and/or by combining dark fermentation with anaerobic digestion or microbial fuel cells to extract additional energy from the aqueous products of dark fermentation.     

Photofermentative hydrogen production from wastes

In many respects, hydrogen is an ideal biofuel. However, practical, sustainable means of its production are presently lacking. Here we review recent efforts to apply the capacity of photosynthetic bacteria to capture solar energy and use it to drive the nearly complete conversion of substrates to hydrogen and carbon dioxide. This process, called photofermentation, has the potential capacity to use a variety of feedstocks, including the effluents of dark fermentations, leading to the development of various configurations of two-stage systems, or various industrial and agricultural waste streams rich in sugars or organic acids. The metabolic and enzymatic properties of this system are presented and the possible waste streams that might be successfully used are discussed. Recently, various immobilized systems have been developed and their advantages and disadvantages are examined.     

Fermentative biohydrogen production systems integration

Acidogenic fermentation can be used to produce hydrogen from a range of biomass sources. The effluent from this process can be utilised in a number of biological processes enabling further recovery of energy from the biomass. In this review a number of candidate technologies are assessed including conventional methanogenic anaerobic digestion, dark fermentative hydrogen production, photo-fermentation, and bioelectrochemical systems. The principles, benefits and challenges associated with integrating these technologies are discussed, with particular emphasis on integration with fermentative hydrogen production, and the current state of integrative development is presented. The various system configurations for potential integrations presented here may simultaneously permit an increase in the conversion efficiency of biomass to energy, improved adaptability to varying operating conditions, and improved stability. Such integration, while increasing system complexity, may mean that these bioprocesses could be deployed in a wider range of scenarios and be used with a greater range of substrates.     

Optimization of fermentative biohydrogen production by response surface methodology using fresh leachate as nutrient supplement

Fresh compost leachate was used as a nutrients source to facilitate anaerobic fermentative hydrogen production from glucose inoculated with mixed culture. The optimum condition for hydrogen production was predicted by response surface methodology (RSM). The model showed the maximum cumulative hydrogen volume (469.74 mL) and molar hydrogen yield (1.60 mol H₂/mol glucose) could be achieved at 6174.93 mg/L glucose and 3383.20 mg COD/L leachate. According to the predicted optimal condition, four tests were carried out to validate the predicted values and evaluate the leachate’s effect on co-fermentation with juice wastewater. A maximum cumulative hydrogen volume of 587.05 ± 15.08 mL was obtained in co-fermentation test, and the molar hydrogen yield reached 2.06 ± 0.06 mol H₂/mol glucose. The co-fermentation of fresh leachate and glucose/juice wastewater was a combination of acetic acid and butyric acid type-fermentation. The results demonstrated that leachate can serve as a nutrients source for biohydrogen production.     

Development of net energy ratio and emission factor for biohydrogen production pathways

This study investigates the energy and environmental aspects of producing biohydrogen for bitumen upgrading from a life cycle perspective. Three technologies are studied for biohydrogen production; these include the Battelle Columbus Laboratory (BCL) gasifier, the Gas Technology Institute (GTI) gasifier, and fast pyrolysis. Three different biomass feedstocks are considered including forest residue (FR), whole forest (WF), and agricultural residue (AR). The fast pyrolysis pathway includes two cases: truck transport of bio-oil and pipeline transport of bio-oil. The net energy ratios (NERs) for nine biohydrogen pathways lie in the range of 1.3-9.3. The maximum NER (9.3) is for the FR-based pathway using GTI technology. The GHG emissions lie in the range of 1.20-8.1 kg CO? eq/kg H?. The lowest limit corresponds to the FR-based biohydrogen production pathway using GTI technology. This study also analyzes the intensities for acid rain precursor and ground level ozone precursor.     

Hydrogen production by the newly isolated Clostridium beijerinckii RZF-1108

A fermentative hydrogen-producing strain, RZF-1108, was isolated from a biohydrogen reactor, and identified as Clostridium beijerinckii on the basis of the 16S rRNA gene analysis and physiobiochemical characteristics. The effects of culture conditions on hydrogen production by C. beijerinckii RZF-1108 were investigated in batch cultures. The hydrogen production and growth of strain RZF-1108 were highly dependent on temperature, initial pH and substrate concentration. Yeast extract was a favorable nitrogen source for hydrogen production and growth of RZF-1108. Hydrogen production corresponded to cell biomass yield in different culture conditions. The maximum hydrogen evolution, yield and production rate of 2209 ml H₂/l medium, 1.97 mol H₂/mol glucose and 104.20 ml H₂/g CDW h⁻¹ were obtained at 9 g/l of glucose, initial pH of 7.0, inoculum volume of 8% and temperature of 35 °C, respectively. These results demonstrate that C. beijerinckii can efficiently produce H₂, and is another model microorganism for biohydrogen investigations.     

Performance evaluation and phylogenetic characterization of anaerobic fluidized bed reactors using ground tire and pet as support materials for biohydrogen production

This study evaluated two different support materials (ground tire and polyethylene terephthalate [PET]) for biohydrogen production in an anaerobic fluidized bed reactor (AFBR) treating synthetic wastewater containing glucose (4000 mg L⁻¹). The AFBR, which contained either ground tire (R1) or PET (R2) as support materials, were inoculated with thermally pretreated anaerobic sludge and operated at a temperature of 30 °C. The AFBR were operated with a range of hydraulic retention times (HRT) between 1 and 8 h. The reactor R1 operating with a HRT of 2 h showed better performance than reactor R2, reaching a maximum hydrogen yield of 2.25 mol H₂ mol⁻¹ glucose with 1.3 mg of biomass (as the total volatile solids) attached to each gram of ground tire. Subsequent 16S rRNA gene sequencing and phylogenetic analysis of particle samples revealed that reactor R1 favored the presence of hydrogen-producing bacteria such as Clostridium, Bacillus, and Enterobacter.     

H<Subscript>2</Subscript> enrichment from synthesis gas by <Emphasis Type="Italic">Desulfotomaculum</Emphasis><Emphasis Type="Italic">carboxydivorans</Emphasis> for potential applications in synthesis gas purification and biodesulfurization

Desulfotomaculum carboxydivorans, recently isolated from a full-scale anaerobic wastewater treatment facility, is a sulfate reducer capable of hydrogenogenic growth on carbon monoxide (CO). In the presence of sulfate, the hydrogen formed is used for sulfate reduction. The organism grows rapidly at 200 kPa CO, pH 7.0, and 55°C, with a generation time of 100 min, producing nearly equimolar amounts of H₂ and CO₂ from CO and H₂O. The high specific CO conversion rates, exceeding 0.8 mol CO (g protein)⁻¹ h⁻¹, makes this bacterium an interesting candidate for a biological alternative of the currently employed chemical catalytic water–gas shift reaction to purify synthesis gas (contains mainly H₂, CO, and CO₂). Furthermore, as D. carboxydivorans is capable of hydrogenotrophic sulfate reduction at partial CO pressures exceeding 100 kPa, it is also a good candidate for biodesulfurization processes using synthesis gas as electron donor at elevated temperatures, e.g., in biological flue gas desulfurization. Although high maximal specific sulfate reduction rates (32 mmol (g protein)⁻¹ h⁻¹) can be obtained, its sulfide tolerance is rather low and pH dependent, i.e., maximally 9 and 5 mM sulfide at pH 7.2 and pH 6.5, respectively.