Dark fermentative biohydrogen production is a complex multiproduct process and is affected by many parameters. In the present review, effect of a wide range of parameters such as inoculum, temperature, pH, hydraulic retention time, bioreactor configuration, hydrogen partial pressure, substrate type and concentration, nutrient type and concentration in dark fermentative biohydrogen production is addressed. Most of the studies on dark fermentative biohydrogen production have been conducted in batch mode using glucose and sucrose as substrate, thus future studies in continuous mode using organic wastes and inexpensive substrates are desirable.

Hydrogen gas is the cleanest energy carrier and could be produced by biological process. Dark fermentation is one of the biohydrogen production methods that carried out just on organic wastes conversion. In this study, the batch tests were conducted to compare the biohydrogen production and glucose fermentation via acetate‑butyrate and acetate‑ethanol metabolic pathway induced by NaOH and KOH (10 M) pretreatment. In batch test, the glucose concentration in the feed was varied from 3.75 to 15 g/L under mesophilic conditions (37°C ± 1°C). In order to sludge pretreatment, NaOH and KOH (as an alkaline agent) was used. Batch tests showed that maximum biohydrogen production under NaOH (2.7 ± 0.5 L) and KOH (2.2 ± 0.7 L) pretreatment was achieved at 15 g/L of influent glucose. In the batch test, with increasing influent glucose concentration, the lower yields of hydrogen were observed. The biohydrogen reactions had good electron closure (5.2 –13.5%) for various glucose concentrations and pretreatments. For NaOH and KOH pretreatment, the biohydrogen yield decreased from 2.49 to 1.63 and from 2.22 to 1.2 mol H2/mol glucose, respectively, when glucose concentration increased from 3.75 to 15 g/L. By applying alkaline sludge pretreatment by NaOH and KOH, the glucose fermentation was followed with acetate‑butyrate and acetate‑ethanol metabolic pathway, respectively. The lower biohydrogen yields were observed under acetate‑ethanol metabolic pathway and related to metabolically unfavorable for biohydrogen production.

Biofuels are a new priority to reduce fossil fuel consumption, its contamination and the problem of waste disposal, hence extensive research has been done on biofuels production, effective factors, and optimization of the process. Production of biodiesel and bioethanol from organic waste is possible on an industrial scale. Volatile fatty acids can be produced from organic waste and then turn to biogas, biohydrogen, and biodiesel. In this paper, the production of biodiesel fuel, biohydrogen, volatile fatty acids and its conversion to biodiesel are discussed. Biodiesel production by transesterification in the presence of a catalyst is an appropriate method. Moreover, dark fermentation produces the most amount of biohydrogen and it needs the lowest volume reactor among other biological methods. In this paper, firstly different methods of biodiesel production and effective parameters and then, biohydrogen production and effective parameters have been discussed

The Palm Oil Mill Effluent (POME) still contains a significant quantity of organic substances that can potentially serve as raw materials for biohydrogen production. This research explores the influence of initial substrate pH and light intensity on the conversion of POME into biohydrogen through photo-fermentation. The study begins by analyzing certain characteristics of POME that may have an impact and identifying indigenous bacteria present in the substrate. The initial substrate pH (neutralized and unaltered) and light intensity (7000 lux and 9500 lux) are tested in combination. A modified Gompertz equation is used to analyze the kinetics of biohydrogen production. The substrate pH neutralization and 9500 lux light intensity resulted in the highest yields and production rates, with values of 516.18 mL-H2/L-POME, 7.17 mL-H2/L-POME/hour, and 2.14% Light Conversion Efficiency (LCE). Changes in ORP (Oxidation-Reduction Potential) values during the treatments indicated an inverse relationship with biohydrogen production. Simulation results and data fitting using the modified Gompertz model yielded excellent coefficients of determination for all treatment data, exceeding 0.99.

For the first time, the ability of a Microbial Fuel Cell (MFC) to produce value-added products from the high content of oily kitchen waste was evaluated. A Single-chamber, air-cathode MFC containing 30% solids was designed for evaluation of the rate of biohydrogen and bioelectricity production. Food wastes were studied in four states: oil-free (0%), containing 3% oil, 6%, and 9% oil during 30 days of operation. Experiments showed with increasing the amount of oil, the amount of biohydrogen produced increased from 0 to 6% of the oil, and with the addition of 9% of oil, no significant change was observed in the biohydrogen production rate. The average daily production of biohydrogen for 0, 3, 6 and 9% of the oil was estimated at 42.5, 58.7, 69.6 and 70.1 mL per day, respectively, which showed that adding oil up to 6% could increase the efficiency of the system for biohydrogen production. On the other hand, with the increase in the amount of oil, the production of bioelectricity decreased, so that the maximum output voltage was recorded for the fourth day of zero state: 472 mV, and the lowest voltage on most of the days recorded for 9% of oil. The results of Chemical Oxygen Demand (COD) removal showed with increasing the amount of oil, although the amount of initial COD increased, the amount of COD removal decreased, which is consistent with the process of electricity production. Volatile fatty acids including acetate, butyrate, and propionate were other valuable products of the system, although the accumulation of VFA was indicated as an inhibitor for biohydrogen production The results showed kitchen waste without oil separation can be used as a useful substrate in MFC systems to produce value-added products, in this way, sewage pollution by oil resulted from food waste could be prevented.

The ever increase in global population and consequently daily increase in energy consumption are casing various environmental pollution and worldwide climate changes. Replace fossil with different type of clean and renewable energy or decreasing the consumption of petroleum-based fuels will greatly reduce the hazardous effects of fossil fuels. Biohydrogen is a suitable alternative source of energy that can reduce dependency on conventional fuels. In this research the effect of the external oxido-reduction system on biohydrogen production from glucose fermentated in a dark medium was carried out and the effect of oxidation potential on biohydrogen production from clostridium acetobutylicum was investigated.  The maximum hydrogen production rate and accumulative hydrogen were calculated using the modified Gompertz equation.  Results show that the increase of voltage to 600 mV, leads to an increase of 25% in hydrogen production rate and a 19% increase in yield. It was also observed that the amount of undesired end products like ethanol and lactate decreased with the increase of oxidation potential and the acetate to butyrate ratio (A/B) increased from 0.82 to 1.52 when the voltage was raised to 600 mV.

Energy resources will play an important role in the world’s future. Increasing atmospheric concentrations of greenhouse gases and their projected consequences, in particular global warming, have caused widespread consideration of feasible remedies and transformation of the energy system from fossil fuels towards the use of renewable resource. Fossil fuels can be replaced by Biofuels such as bioethanol, biomethanol, biohydrogen and biodiesel. Bioethanol is the most important biofuel and can be produced by molasses, starch and cellulose. Biomethanol as a good fuel can be produced by methane gas. One of the drawbacks of methanol as a fuel is its corrosivity to some metals, including aluminum. Biohydrogen is hydrogen produced via biological processes or from biomass and it is a suitable biofuel because produces the least air pollution. Biodiesel can be produced from consumed vegetable oils and is very appropriate for diesel fuel replacement. Generally speaking, biofuels are generally considered as offering many benefits, including sustainability, reduction of greenhouse gas emissions, regional development, social structure and agriculture and security of supply.

The production of biohydrogen from industrial food wastewater is feasible using innovative, and renewable methods. In particular, dark fermentation with Fe3O4/ZSM-5 catalysts and industrial food wastewater as a carbon source has been successfully implemented by bacteria. The optimization of three parameters including the concentration of Fe3O4/ZSM-5 nanoparticles, temperature, and pH were input into the software environment. It was carried out using RSM software and the Central Composite Design model.  The software was set to run 20 experiments for replicating the tests. The optimal conditions were found to be a nanoparticle concentration of 300 mg/L, a pH of 5.5, and a temperature of 36 degrees Celsius, leading to a hydrogen production efficiency of 250.8 mL. These results show that nanoparticles at specific concentrations enhance bacterial activity by affecting intracellular enzymes, thereby improving efficiency. Consequently, the green synthesis of Fe3O4/ZSM-5 nanoparticles and the dark fermentation process have great potential for biohydrogen production from industrial food wastewater.

In this research, wheat, rice, and corn residue were used as a substrate for biogas production. Due to the high amount of lignin in all three substrates (> 9.9) and in order to increase the degradability of these substrates, an ultrasonic pretreatment with a power of 150 w at 15 min was used prior to initiating enzymatic digestion process. Some physical and chemical properties including solid and volatile particles and contents of lignin, cellulose and hemicellulose were measured before and after digesting the substances; and in addition, the biogas compounds including hydrogen, methane, hydrogen sulfide and carbon monoxide was measured during digestion. The metabolic pathways of converting glucose as the main constituent of all three waste types into biogas were studied to determine the factors affecting biogas compounds. The results showed that use of ultrasonic pretreatment in all three wastes increased the breakdown of lignin structures, which decreased the content of these structures in the feedstock compared to the substrate. The amount of solid and volatile particles of the feedstock obtained from the substrate of wheat residue was 35.1% and 95.3%, respectively, which was more than that of the other substrates. The highest amounts of reduction of solid particles (19.6%), volatile particles (18%), cellulose (12.6%), hemicellulose (4.4%) and lignin (3.6%) were related to the feedstock obtained from wheat residue. Analyses of biogas compounds showed that the highest biohydrogen production obtained for wheat substrate (ppm 18000), but its biomethane production was lower than the other substrates. The highest amounts of biohydrogen production of all the substrates occurred after seven days, which was related to the butyrate acidification stage. With increasing digestion time, hydrogen production decreased while the other biogas compounds increased. One of the probable reasons was the consumption of hydrogen produced in the stages of hydrolysis, acidification and acetate formation in the stages of alcoholization and methanation. The highest amount of hydrogen production was related to the stage of butyrate formation and then acetate formation. The higher production of biohydrogen by wheat residue is most likely due to its high volume of volatile, hydrocarbon and hemicellulose compounds. While the low production of hydrogen by corn residue was due to driving the reactions towards the production of ethanol and consuming hydrogen.

Increasing global consumption of fossil fuels leads to greenhouse gas emissions, climate change and environmental pollution. Agricultural, animal and food industrial waste is one of the main sources of pollution. The bioethanol industry is one of 17 highly polluted industries. In the process of producing bioethanol, vinasse is produced, and so far 22.4 Giga litter of vinasse has been produced worldwide.With fossil fuel resources running out, energy production from renewable sources, including organic waste, has been considered in recent years and has transformed biological hydrogen production into a new approach to replace it with fossil fuels. The purpose of this study was to evaluate Biohydrogen production from Vinasse bioethanol processing industry as clean and renewable energy.

In this review study conducted in 1398, 150 indexed articles from the past 15 years were used in the databases of ProQuest, Science Direct, Pubmed, Google Scholar and Scopus.

The results showed that vinasse is the most effective organic material for high-efficiency Biohydrogen production and dark fermentation hydrogen is the most promising biological hydrogen production method. Microbial species, reactor type, pH, temperature, substrate type and concentration, organic loading rate (OLR), hydraulic retention time (HRT), nitrogen, phosphate and iron concentrations are among the parameters influencing the process to maximize biohydrogen productivity and efficiency and concentration. High volatile fatty acids are also a major inhibitor of Biohydrogen production.

Compared to the thermal energy content of methane, ethanol and gasoline, hydrogen thermal energy is high (142 kj/g) and water is the only by-product of hydrogen burning. Anaerobic treatment is the most effective way to reduce the pollution of Vinasse. In addition to reducing environmental pollution, the economical result of Biohydrogen production as a clean energy source is that by optimizing the operating conditions of the process we can achieve maximum efficiency and productivity of Biohydrogen production.