Bio-electrochemical systems (BESs) are the microbial systems which are employed to produce electricity directly from organic wastes along with some valuable chemicals production such as medium chain fatty acids; acetate, butyrate and alcohols. In this review, recent updates about value-added chemicals production concomitantly with the production of gaseous fuels like hydrogen and methane which are considered as cleaner for the environment have been addressed. Additionally, the bottlenecks associated with the conversion rates, lower yields and other aspects have been mentioned. In spite of its infant stage development, this would be the future trend of energy, biochemicals and electricity production in greener and cleaner pathway with the win-win situation of organic waste remediation. Henceforth, this review intends to summarise and foster the progress made in the BESs and discusses its challenges and outlook on future research advances.
Biohydrogen is regarded as an attractive future clean energy carrier due to its high energy content and environmental-friendly conversion. It has the potential for renewable biofuel to replace current hydrogen production which rely heavily on fossil fuels. While biohydrogen production is still in the early stage of development, there have been a variety of laboratory- and pilot-scale systems developed with promising potential. This work presents a review of advances in bioreactor and bioprocess design for biohydrogen production. The state-of-the art of biohydrogen production is discussed emphasizing on production pathways, factors affecting biohydrogen production, as well as bioreactor configuration and operation. Challenges and prospects of biohydrogen production are also outlined.
Hydrogen production by cyanobacteria could be one of the promising energy resources in the future. However, there is very limited information regarding the kinetic modeling of hydrogen production by cyanobacteria available in the literature. To provide an in-depth understanding of the biological system involved during the process, the Haldane's noncompetitive inhibition equation has been modified to determine the specific hydrogen production rate (HPR) as a function of both dissolved CO2 concentration (CTOT) and oxygen production rate (OPR). The highest HPR of 15 [Formula: see text] was found at xCO2 of 5% vol/vol and the rate consequently decreased when the CTOT and OPR were 0.015 k mol m(-3) and 0.55 mL h(-1), respectively. The model provided a fairly good estimation of the HPR with respect to the experimental data collected.
This study aims to investigate the impact of utilizing lactic acid fermentation (LAF) as storage method of food waste (FW) prior to dark fermentation (DF). LAF of FW was carried out in batches at six temperatures (4 °C, 10 °C, 23 °C, 35 °C, 45 °C, and 55 °C) for 15 days followed by biological hydrogen potential (BHP) tests. Different storage temperatures resulted in different metabolites distribution, with either lactate or ethanol being dominant (159.2 ± 20.6 mM and 234.4 ± 38.2 mM respectively), but no negative impact on BHP (averaging at 94.6 ± 25.1 mL/gVS). Maximum hydrogen production rate for stored FW improved by at least 57%. Microbial analysis showed dominance of lactic acid bacteria (LAB) namely Lactobacillus sp., Lactococcus sp., Weisella sp., Streptococcus sp. and Bacillus sp. after LAF. Clostridium sp. emerged after DF, co-existing with LAB. Coupling LAF as a storage method was demonstrated as a novel strategy of FW management for DF, for a wide range of temperatures.
The aim of this study was to investigate the influence of some environmental factors on bacterial metabolism. Fermentative hydrogen production by C. acetobutylicum, using glucose as the substrate. The effect of initial pH (4-8), inoculum size (1-20% (v/v)) and glucose concentration (1-30 g L(-1)) on hydrogen production were studied. The optimum cultivation temperature for hydrogen production was at 30 degrees C. The results show that substrate concentration and inoculum size resulted in hydrogen yield (Y(P/S)) of 391 mL g(-1) glucose utilized with maximum hydrogen productivity of 77.5 mL/L/h. Higher substrate concentration or inoculum size adversely affects hydrogen production, which decreases hydrogen yield by 15% to 334 mL g(-1) glucose utilized when 30% (v/v) inoculum size was used. The use of 30 g L(-1) substrate concentration resulted in a 75% decrease to 97 mL g(-1) glucose supplied. Concluded that proper Xo/So enhanced the hydrogen production.
The effect of removal of resultant gas resulted in enhancement of the H2 yield. The technique of CO2 scavenging resulted in H2 yield being improved from 408 mL g(-1) to reach the maximum of 422 mL g'. The highest hydrogen productivity of 87.9 ml L(-1) h(-1) was obtained by CO2 scavenging. Biomass concentration was enhanced to 1.47 g L(-1), Y(P,X) of 287 ml g(-1) L(-1), Y(X/S) of 0.294 and Y(H2/s) of 0.0377 by the use of CO2 scavenging. The results suggested that the presence of the gaseous products in fermentation medium and headspace adversely effect biomass growth and hydrogen production.
Biohydrogen production has received widespread attention from researchers in industry and academic fields. Response surface methodology (RSM) was applied to evaluate the effects of several key variables in anaerobic fermentation of glucose with Clostridium butyrium, and achieved the highest production rate and yield of hydrogen. Highest H2 yield of 2.02 mol H2/mol-glucose was achieved from 24 h bottle fermentation of glucose at 35 °C, while the composition of medium was (g/L): 15.66 glucose, 6.04 yeast extract, 4 tryptone, 3 K2HPO4, 3 KH2PO4, 0.05 L-cysteine, 0.05 MgSO4·7H2O, 0.1 MnSO4·H2O and 0.3 FeSO4·7H2O, which was very different from that for cell growth. Sugarcane bagasse and Jatropha hulls were selected as typical tropical biomass wastes to produce sugars via a two-step acid hydrolysis for hydrogen production. Under the optimized fermentation conditions, H2 yield (mol H2/mol-total reducing sugar) was 2.15 for glucose, 2.06 for bagasse hydrolysate and 1.95 for Jatropha hull hydrolysate in a 3L fermenter for 24 h at 35 °C, with H2 purity of 49.7-64.34%. The results provide useful information and basic data for practical use of tropical plant wastes to produce hydrogen.
The stimulant and toxicity effects of reported organic (acetic acid, propionic acid, butyric acid, formic acid, oil & grease) and inorganic (copper) by-products presented in palm oil mill effluent on anaerobic bacterial population were examined in this paper. The toxicity test had shown that acetic, propionic and butyric acids tend to stimulate the bacterial density level (survival rate more than 50%), while formic acid, copper, oil and grease were shown to have suppressed the density level (survival rate less than 50%). The highest biomass recorded was 1.66 mg/L for the concentration of acetic acid at 216 mg/L and lowest biomass concentration, 0.90 mg/L for copper at 1.40 mg/L. Biohydrogen-producing bacteria have a favourable growth rate around pH 5.5. The comparison of half maximal effective concentration (EC50) values between two test duration on the effects of organic and inorganic by-products postulate that bacteria had a higher tolerance towards volatile fatty acids. While acetic, butyric and propionic acids had exhibited higher tolerance EC50 values for bacteria, but the opposite trend was observed for formic acid, copper and oil & grease.
Microbial electrolysis cells (MECs) are perceived as a potential and promising innovative biotechnological tool that can convert carbon-rich waste biomass or wastewater into hydrogen (H2) or other value-added chemicals. Undesired methane (CH4) producing H2 sinks, including methanogens, is a serious challenge faced by MECs to achieve high-rate H2 production. Methanogens can consume H2 to produce CH4 in MECs, which has led to a drop of H2 production efficiency, H2 production rate (HPR) and also a low percentage of H2 in the produced biogas. Organized inference related to the interactions of microbes and potential processes has assisted in understanding approaches and concepts for inhibiting the growth of methanogens and profitable scale up design. Thus, here in we review the current developments and also the improvements constituted for the reduction of microbial H2 losses to methanogens. Firstly, the greatest challenge in achieving practical applications of MECs; undesirable microorganisms (methanogens) growth and various studied techniques for eliminating and reducing methanogens activities in MECs were discussed. Additionally, this extensive review also considers prospects for stimulating future research that could help to achieve more information and would provide the focus and path towards MECs as well as their possibilities for simultaneously generating H2 and waste remediation.
Photo fermentation is a biological process that can be applied for hydrogen production. The process is environmental friendly which is operated under mild conditions using renewable resources. In order to increase yield of H2 produced by Rhodobacter sphaeroides, some experimental factors that may enhance H2 production were studied. The effect of operating parameters including agitation, aeration and light on hydrogen production using R. sphaeroides NCIMB 8253 was investigated. Rhodobacter sphaeroides NCIMB 8253 was grown in 100 mL serum bottle containing growth medium with maliec acid as the sole organic carbon source. The cultures were incubated anaerobically at 30 degrees C with tungsten lamp (100 W) as the light source (3.8 klux) and argon gas was purged for maintaining anaerobic condition. The results show that maximum hydrogen produced was higher (54.37 mL) in static culture with 69.98% of H2 in the total gas compared with shake culture (11.57 mL) with 57.86% of H2. By using static culture, H2 produced was five times higher compared with non-static in both aerobic and anaerobic condition. It was found that growth and H2 production with fluorescent lamp showed better results than growth and H2 production with tungsten light.
In the modern world, wheat, a vital global cereal and the second most consumed, is vulnerable to climate change impacts. These include erratic rainfall and extreme temperatures, endangering global food security. Research on hydrogen-rich water (HRW) has gained momentum in plant and agricultural sciences due to its diverse functions. This study examined the effects of different HRW treatment durations on wheat, revealing that the 4-h treatment had the highest germination rate, enhancing potential, vigor, and germination indexes. This treatment also boosted relative water content, root and shoot weight, and average lengths. Moreover, the 4-h HRW treatment resulted in the highest chlorophyll and soluble protein concentrations in seeds while reducing cell death. The 4-h and 5-h HRW treatments significantly increased H2O2 levels, with the highest NO detected in both root and shoot after 4-h HRW exposure. Additionally, HRW-treated seeds exhibited increased Zn and Fe concentrations, along with antioxidant enzyme activities (CAT, SOD, APX) in roots and shoots. These findings suggest that HRW treatment could enhance wheat seed germination, growth, and nutrient absorption, thereby increasing agricultural productivity. Molecular analysis indicated significant upregulation of the Dreb1 gene with a 4-h HRW treatment. Thus, it shows promise in addressing climate change effects on wheat production. Therefore, HRW treatment could be a hopeful strategy for enhancing wheat plant drought tolerance, requiring further investigation (field experiments) to validate its impact on plant growth and drought stress mitigation.
Pseudogenes are considered to be nonfunctional genes that lack a physiological role. By screening 3985 Escherichia coli mutants using chemochromic membranes, we found four pseudogenes involved in hydrogen metabolism. Knockouts of pseudogenes ydfW and ypdJ had a defective hydrogen phenotype on glucose and formate, respectively. Also, the knockout of pseudogene yqiG formed hydrogen from formate but not from glucose. For the yqiG mutant, 100% hydrogen recovery was obtained by the complementation of YqiG via a plasmid. The knockout of pseudogene ylcE showed hydrogen deficiency in minimal media which suggested that the role of YlcE is associated with cell growth. Hence, the products of these four pseudogenes play an important physiological role in hydrogen production in E. coli.
The simultaneous production of hydrogen and ethanol by microorganisms from waste materials in a bioreactor system would establish cost-effective and time-saving biofuel production. This review aims to present the current status of fermentation processes producing hydrogen accompanied by ethanol as a co-product. We outlined the microbes used and their fundamental pathways for hydrogen and ethanol fermentation. Moreover, we discussed the exploitation of renewable and sustainable waste materials as promising feedstock and the limitations encountered. The low substrate bioconversion rate in hydrogen and ethanol co-production is regarded as the primary constraint towards the development of large scale applications. Thus, microbes with an enhanced capability have been generated via genetic manipulation to diminish the inefficiency of substrate consumption. In this review, other potential approaches to improve the performance of co-production through fermentation were also elaborated. This review will be a useful guide for the future development of hydrogen and ethanol co-production using waste materials.
Lower temperature biohydrogen production has always been attractive, due to the lower energy requirements. However, the slow metabolic rate of psychrotolerant biohydrogen-producing bacteria is a common problem that affects their biohydrogen yield. This study reports on the improved substrate synthesis and biohydrogen productivity by the psychrotolerant Klebsiella sp. strain ABZ11, isolated from Antarctic seawater sample. The isolate was screened for biohydrogen production at 30°C, under facultative anaerobic condition. The isolate is able to ferment glucose, fructose and sucrose with biohydrogen production rate and yield of 0.8 mol/l/h and 3.8 mol/g, respectively at 10 g/l glucose concentration. It also showed 74% carbohydrate uptake and 95% oxygen uptake ability, and a wide growth temperature range with optimum at 37°C. Klebsiella sp. ABZ11 has a short biohydrogen production lag phase, fast substrate uptake and is able to tolerate the presence of oxygen in the culture medium. Thus, the isolate has a potential to be used for lower temperature biohydrogen production process.
Three newly discovered H2 producing bacteria namely Clostridium perfringens strain JJC, Clostridium bifermentans strain WYM and Clostridium sp. strain Ade.TY originated from landfill leachate sludge have demonstrated highly efficient H2 production. The maximum H2 production attained from these isolates are in the descending order of strain C. perfringens strain JJC > C. bifermentans strain WYM > Clostridium sp. strain Ade.TY with yield of 4.68 ± 0.12, 3.29 ± 0.11, and 2.87 ± 0.10 mol H2/mol glucose, respectively. The result has broken the conventional theoretical yield of 4 mol H2/mol glucose. These isolates were thermodynamically favourable with Gibbs free energy between -33 and -35 kJ/mol (under process conditions: pH 6, 37 °C and 5 g/L glucose). All three isolates favour butyrate pathway for H2 production with the ratio of acetate and butyrate of 0.77, 0.65 and 0.80 for strain JJC, WYM and Ade.TY, respectively. This study reported provides a new insight on the potential of unique bacteria in H2 production.
The objective of this study is to investigate the effect of salts addition to fermentation medium on hydrogen production, under anaerobic batch culture system. In this study, batch experiments were conducted to investigate the inhibitory effect of both NaCl and sodium acetate on hydrogen production. The optimum pH and temperature for hydrogen production were at initial pH of 7.0 and 30 degrees C. Enhanced production of hydrogen, using glucose as substrate was achieved. In the absence of Sodium Chloride and Sodium Acetate enhanced hydrogen yield (Y(P/S)) from 350 mL g(-1) glucose utilized to 391 mL g(-1) glucose utilized with maximum hydrogen productivity of 77.5 ml/L/h. Results also show that sodium chloride and sodium acetate in the medium adversely affect growth. Hydrogen yield per biomass (Y(P/X)) of 254 ml/L/g, biomass per substrate utilized (Y(X/S)) of 0.268 and (Y(H2/S) of 0.0349. The results suggested that Sodium at any concentration resulted to inhibit the bacterial productivity of hydrogen.
A two-stage fermentation process consisting of dark and photo-fermentation periods was carried out in a batch reactor. In the first stage, glucose was fermented in the dark stage using Clostridium saccharoperbutylacetonicum N1-4 (ATCC 13564; CSN1-4) to produce acetate, CO2 and H2. The acetate produced in the first stage is fermented to H2 and CO2 by Rhodobacter sphaeroides NCIMB 8253 for further hydrogen production in the second, illuminated stage. The yield of hydrogen in the first stage was about 3.10 mol H2 (mol glucose)(-1) at a glucose concentration of 10 g L(-1), pH 6 +/- 0.2 and 37 degrees C and the second stage yield was about 1.10-1.25 mol H2 (mol acetic acid)(-1) at pH 6.8 +/- 0.2 and 32 degrees C, without removal of the Clostridium CSN1-4. The overall yield of hydrogen in the two-stage process, with glucose as the main substrate was higher than single-stage fermentation.
In this study the kinetics of autohydrogenotrophic denitrification was studied under optimum solution pH and bicarbonate concentration. The optimal pH and bicarbonate concentration were firstly obtained using a design of experiment (DOE) methodology. For this purpose a total of 11 experiments were carried out. Sodium bicarbonate concentrations ranging of 20-2000 mg/L and pH values from 6.5 to 8.5 were used in the optimization runs. It was found that the pH has a more pronounced effect on the denitrification process as compared to the bicarbonate dose. The developed quadratic model predicted the optimum conditions at pH 8 and 1100 mg NaHCO(3)/L. Using these optimal conditions, the kinetics of denitrification for nitrate and nitrite degradation were investigated in separate experiments. Both processes were found to follow a zero order kinetic model. The ultimate specific degradation rates for nitrate and nitrite remediation were 29.60 mg NO(3)(-)-N/g MLVSS/L and 34.85 mg NO(3)(-)-N/g MLVSS/L respectively, when hydrogen was supplied every 0.5h.
Bio-hydrogen production from wastewater using sludge as inoculum is a sustainable approach for energy production. This study investigated the influence of initial pH and temperature on bio-hydrogen production from dairy wastewater using pretreated landfill leachate sludge (LLS) as an inoculum. The maximum yield of 113.2 ± 2.9 mmol H2/g chemical oxygen demand (COD) (12.8 ± 0.3 mmol H2/g carbohydrates) was obtained at initial pH 6 and 37 °C. The main products of volatile fatty acids were acetate and butyrate with the ratio of acetate:butyrate was 0.4. At optimum condition, Gibb's free energy was estimated at -40 kJ/mol, whereas the activation enthalpy and entropy were 65 kJ/mol and 0.128 kJ/mol/l, respectively. These thermodynamic quantities suggest that bio-hydrogen production from dairy wastewater using pretreated LLS as inoculum was effective and efficient. In addition, genomic and bioinformatics analyses were performed in this study.