Hydrogen production from alcohol distillery wastewater containing high potassium and sulfate using an anaerobic sequencing batch reactor

In this study, the feasibility of hydrogen production from alcohol distillery wastewater containing high potassium and sulfate was investigated using an anaerobic sequencing batch reactor (ASBR). The seed sludge taken from an anaerobic tank treating the distillery wastewater was boiled for 15 min before being fed to the ASBR. The ASBR system was operated under different feed chemical oxygen demand (COD) values and different COD loading rates at a mesophilic temperature of 37 °C, a controlled pH at 5.5, and a cycle time of 6 cycles per day. When the studied ASBR was operated under the best conditions (providing a maximum hydrogen production efficiency) of a feed COD of 40,000 mg/l, a COD loading rate of 60 kg/m³ d, and a hydraulic retention time of 16 h, the produced gas was found to contain 34.7% H₂ and 65.3% CO_2, without any methane being detected. Under these best conditions, the specific hydrogen production rate (SHPR) of 270 ml H₂/g MLVSS d (or 3310 ml H₂/l d), and hydrogen yield of 172 ml H₂/g COD removed, were obtained. When the feed COD exceeded 40,000 mg/l, the process performance in terms of hydrogen production decreased because of the potassium and sulfate toxicity.     

Hydrogen production from alcohol wastewater by an anaerobic sequencing batch reactor under thermophilic operation: Nitrogen and phosphorous uptakes and transformation

The objective of this study was to investigate hydrogen production from alcohol wastewater using an anaerobic sequencing batch reactor (ASBR) under thermophilic operation and at a constant pH of 5.5. Under the optimum COD loading rate of 68 kg/m³d, the produced gas contained 43% H₂ without methane and the system provided a hydrogen yield and specific hydrogen production rate of 130 ml H₂/g COD removed and 2100 ml H₂/l d, respectively, which were much higher than those obtained under the mesophilic operation. Under thermophilic operation, both nitrogen and phosphate uptakes were minimal at the optimum COD loading rate for hydrogen production and most nitrogen uptake was derived from organic nitrogen. Under the thermophilic operation for hydrogen production, the nutrient requirement in terms of COD:N:P was found to be 100:6:0.5, which was much higher than that for the methenogenic step for methane production under both thermophilic and mesophilic operations and for the acidogenic step for hydrogen production under mesophilic operation.     

Hydrogen production from cassava wastewater using an anaerobic sequencing batch reactor: Effects of operational parameters,COD:N ratio,and organic acid composition

In this work, hydrogen production from cassava wastewater using anaerobic sequencing batch reactors (ASBR) was investigated to determine the optimum number of cycles per day, chemical oxygen demand (COD) loading rate, and COD:N ratio. The system operated at a COD loading rate of 30 kg/m³d and 6 cycles per day provided maximum hydrogen production performance in terms of specific hydrogen production rate (SHPR) (388 ml H₂/g VSS d or 3800 ml H₂/l d) and hydrogen yield (186 ml H₂/g COD removed). The effect of nitrogen supplementation was also studied by adding NH₄HCO₃ into the system at the COD:N ratios of 100:2.2, 100:3.3, and 100:4.4 under the COD loading rate of 30 kg/m³d and 6 cycles per day. The maximum SHPR and hydrogen yield of 524 ml H₂/g VSS d (5680 ml H₂/l d) and 438 ml H₂/g COD removed, respectively, were obtained at the stoichiometric COD:N ratio of 100:2.2. An excess nitrogen was found to promote the productions of higher organic acids and ethanol, resulting in lowering hydrogen production efficiency.     

Optimization and microbial community analysis for production of biohydrogen from palm oil mill effluent by thermophilic fermentative process

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 60 gCOD l⁻¹ d⁻¹ gave a maximum hydrogen yield of 0.27 l H₂ g COD⁻¹ with a volumetric hydrogen production rate of 9.1 l H₂ l⁻¹ d⁻¹ (16.9 mmol l⁻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 (1 d) and OLR (80 gCOD l⁻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).     

Optimizing energy harvest in wastewater treatment by combining anaerobic hydrogen producing biofermentor (HPB) and microbial fuel cell (MFC)

This study focused on the optimization of energy harvest from wastewater treatment by integrating two novel biotechnologies: anaerobic hydrogen production and microbial fuel cell (MFC). The simultaneous production of hydrogen and electricity from wastewater was examined at continuous flow at different organic loading rates (OLR) by changing chemical oxygen demand (COD) and hydraulic retention time (HRT). The experimental results showed that the specific hydrogen yield (SHY, mole H₂/mole glucose) increased with the decrease in OLR, and reached at the maximum value of 2.72 mol H₂/mole glucose at the lowest OLR of 4 g/L.d. The effluent from hydrogen producing biofermentor (HPB) was fed to a single chamber MFC (SCMFC), obtaining the highest power density and coulombic efficiency (CE) of 4200 mW/m³ and 5.3%, respectively. The energy conversion efficiency (ECE) increased with OLR and reached the peak value of 4.24% at the OLR of 2.35 g/L.d, but decreased with higher OLR. It was demonstrated that the combination of HPB and MFC improved the ECE and COD removal with the maximum total ECE of 29% and COD removal of 71%. The kinetic analysis was conducted for the HPB-MFC hybrid system. The maximum hydrogen production was projected to be 2.85 mol H₂/mole glucose. The maximum energy recovery and COD removal efficiency from MFC were projected to be 559 J/L and 97%, respectively.     

A bench scale study of fermentative hydrogen and methane production from food waste in integrated two-stage process

A two-stage fermentation process combining hydrogen and methane production for the treatment of food waste was investigated in this paper. In hydrogen fermentation reactor, the indigenous mixed microbial cultures contained in food waste were used for hydrogen production. No foreign inoculum was used in the hydrogen fermentation stage, the traditional heat treatment of inoculum was not applied either in this bench scale experiment. The effects of the stepwise increased organic loading rate (OLR) and solid retention time (SRT) on integrated two-stage process were investigated. At steady state, the optimal OLR and SRT for the integrated two-stage process were found to be 22.65 kg VS/m³ d (160 h) for hydrogen fermentation reactor and 4.61 (26.67 d) for methane fermentation reactor, respectively. Under the optimum conditions, the maximum yields of hydrogen (0.065 m³ H₂/kg VS) and methane (0.546 m³ CH₄/kg VS) were achieved with the hydrogen and methane contents ranging from 29.42 to 30.86%, 64.33 to 71.48%, respectively. Biodegradability analysis showed that 5.78% of the influent COD was converted to the hydrogen in H₂-SCRD and 82.18% of the influent COD was converted to the methane in CH₄-SCSTR under the optimum conditions.     

Anaerobic fermentative system based scheme for green energy sustainable houses

The green energy sustainable house based on bio-hydrogen and bio-methane energy technologies proposed in this study employs dark fermentation technology to complete a scheme for green energy sustainable house that includes energy production, storage, distribution control, load applications, recycling, waste treatment, and reuse. In order to resolve the problem of wastewater discharge from hydrogen production in green energy sustainable houses, this study proposes wastewater chemical oxygen demand (COD) treatment research, and suggests the use of two-stage anaerobic treatment to produce two types of bio-energy i.e. hydrogen and methane, while simultaneously reducing COD levels.Methane production employed a condensed molasses fermentation solubles (CMS) and hydrogen fermentation tank effluent as a substrate to test the COD reducing efficiency and overall efficiency of methane production. It was found that if CMS is used during the hydrolysis and acidogenesis stages, the maximum carbohydrate degradation rate will be approximately 70% (F/M ratio of 1.9-2.3), and the COD removal rate will increase from 15 to 20% (F/M ratio of 1.9-2.3) to 68% (F/M ratio of 0.5). This study showed that the total gas (H₂ and CH₄) production yield from effluent of hydrogen fermentation tank (56.2 KJ/mol substrate) is greater than the value for CMS.In this study, a 3.2 m³ anaerobic hydrogen reactor is evaluated to provide a family with 3-4 kW of power. When acclimatization is performed under conditions of 20 g COD/L substrate and hydraulic retention time (HRT) of 8 h, the COD removal rate can reach approximately 50%. If a methane-generating reactor with a 95% COD removal rate is used to degrade effluent from the hydrogen reaction tank, it will be possible to reduce the COD of organic effluent to under 500 mg/L. Since this water quality is not far from that of ordinary untreated household wastewater (approximately 300-500 mg COD/L), the effluent can be discharged into a community sewer system and treated in a community sewage treatment facility.     

Treatment of dairy wastewater using anaerobic and solar photocatalytic methods

The present study was aimed to treat the dairy wastewater by using anaerobic and solar photocatalytic oxidation methods. The anaerobic treatment was carried out in a laboratory scale hybrid upflow anaerobic sludge blanket reactor (HUASB) with a working volume of 5.9 L. It was operated at organic loading rate (OLR) varying from 8 to 20 kg COD/m³ day for a period of 110 days. The maximum loading rate of the anaerobic reactor was found to be 19.2 kg COD/m³ day and the corresponding chemical oxygen demand (COD) removal at this OLR was 84%. The anaerobically treated wastewater at an OLR of 19.2 kg COD/m³ day was subjected to secondary solar photocatalytic oxidation treatment. The optimum pH and catalyst loading for the solar photochemical oxidation was found to be 5 and 300 mg/L, respectively. The secondary solar photocatalytic oxidation using TiO₂ removed 62% of the COD from primary anaerobic treatment. Integration of anaerobic and solar photocatalytic treatment resulted in 95% removal of COD from the dairy wastewater. The findings suggest that anaerobic treatment followed by solar photo catalytic oxidation would be a promising alternative for the treatment of dairy wastewater.     

Evolution of methane and hydrogen from ethanol wastewater with maximization of energy yield by three-stage anaerobic sequencing batch reactor system

A new anaerobic sequencing batch reactor (ASBR) unit with three stage concept was proposed and tested for spontaneous generation of hydrogen (H₂) and methane (CH₄) from ethanol wastewater with maximum energy yield. The system was controlled at 37 °C, a fixed pH of 5.5 in the first bioreactor and a recycle ratio of unity from the third bioreactor to the first bioreactor to lower the amount of sodium hydroxide for pH regulation in the first bioreactor and to increase total alkalinity and process stability. Under the optimum organic loading rate of 15 kg COD/m³d (based on the total liquid holding volume), it exhibited the highest yields and specific generation rates of both gases, resulting in the uppermost overall energy yield which was much higher than those of all other anaerobic systems. The lactic acid was found to be about 4–8 times more toxic than acetic acid to methanogens. The higher the solution pH in any anaerobic system, the greater the reduction of micronutrients.     

Improved hydrogen gas production in electrohydrolysis of vinegar fermentation wastewater by scrap aluminum and salt addition

Scrap aluminum particles and salt (NaCl) were added to the vinegar fermentation wastewater to improve hydrogen gas formation by electrohydrolysis of the wastewater organics. The applied DC voltage and initial COD of the wastewater were constant at 4 V and 33.16 g L⁻¹, respectively. The highest cumulative hydrogen gas formation (2877 mL) was obtained with scrap Al (1 g L⁻¹) and NaCl (1 g L⁻¹) additions within 72 h as compared to 1925 mL H₂ gas formation from raw wastewater. Hydrogen gas formation from Al and NaCl added water was 302 ml as compared to 260 ml from raw water. The highest H₂ gas formation rate (952 mL d⁻¹), the yield (1660 mL H₂ g⁻¹ COD) and the highest current intensity (163 mA) were also obtained with combined effects of scrap Al and NaCl additions. Almost pure hydrogen gas (99%) was produced using the raw wastewater. Initial conductivity of the raw wastewater increased from 1.80 mS cm⁻¹ to 5.01 mS cm⁻¹ with the addition of scrap Al and salt for which the final conductivities were 4.0 mS cm⁻¹ and 6.91 mS cm⁻¹, respectively. The highest energy conversion efficiency was obtained with only scrap Al addition (37.8%) as compared to 30.5% efficiency obtained with Al and salt additions. Additions of NaCl and scrap Al particles was found to be very beneficial for H₂ gas formation by electrohydrolysis of vinegar fermentation wastewater.     

Enhancement of hydrogen production by recycling of methanogenic effluent in two-phase fermentation of food waste

The feasibility of operational strategies was investigated for hydrogen and methane production from food waste. Food waste was heat-treated at 70 °C and fed to a two-phase anaerobic sequencing batch fermenting system. Maximum hydrogen productivity of 1.19 m³ H₂/m³ d was observed at a food waste concentration of 30 g carbohydrate/L, a hydraulic retention time of 2 d, and a solids retention time of 3.4 d. The effluent from hydrogenesis was efficiently converted to methane at an organic loading rate of up to 3.6 kg COD/m³.d. The methanogenic effluent was then recycled to the hydrogenesis reactor without any pretreatment. The recycled effluent not only successfully replaced external dilution water and decreased alkaline dosage by 75%, but also increased hydrogen production by 48%, resulting in hydrogen productivity of 1.76 m³/m³ d. The two-phase digestion with recycling would convert 91% of organic pollutants in food waste to hydrogen (8%) and methane (83%) without any external dilution water.     

Hydrogen gas production from vinegar fermentation wastewater by electro-hydrolysis: Effects of initial COD content

Vinegar fermentation wastewater with different initial COD contents (9.66–48.6 g L⁻¹) were used for hydrogen gas production with simultaneous COD removal by electro-hydrolysis. The applied DC voltage was constant at 4 V. The highest cumulative hydrogen production (3197 ml), hydrogen yield (2766 ml H₂ g⁻¹ COD), hydrogen formation rate (799 ml d⁻¹), and percent hydrogen (99.5%) in the gas phase were obtained with the highest initial COD of 48.6 g COD L⁻¹. The highest energy efficiency (48%) was obtained with the lowest COD content of 9.66 g L⁻¹. Hydrogen gas production by water electrolysis was less than 250 ml and wastewater control resulted in less than 25 ml H₂ in 96 h. The highest (12%) percent COD removal was obtained with the lowest COD content. Hydrogen gas was produced by reaction of (H⁺) ions present in raw WW ( pH = 3.0) and protons released from acetic acid with electrons provided by electrical current. Electro-hydrolysis of vinegar wastewater was proven to be an effective method of H₂ gas production with some COD removal.     

Effect of hydraulic retention time on biohydrogen production from palm oil mill effluent in anaerobic sequencing batch reactor

The feasibility of hydrogen generation from palm oil mill effluent (POME), a high strength wastewater with high solid content, was evaluated in an anaerobic sequencing batch reactor (ASBR) using enriched mixed microflora, under mesophilic digestion process at 37 °C. Four different hydraulic retention times (HRT), ranging from 96 h to 36 h at constant cycle length of 24 h and various organic loading rate (OLR) concentrations were tested to evaluate hydrogen productivity and operational stability of ASBR. The results showed higher system efficiency was achieved at HRT of 72 h with maximum hydrogen production rate of 6.7 LH₂/L/d and hydrogen yield of 0.34 LH₂/g COD_feeding, while in longer and shorter HRTs, hydrogen productivity decreased. Organic matter removal efficiency was affected by HRT; accordingly, total and soluble COD removal reached more than 37% and 50%, respectively. Solid retention time (SRT) of 4-19 days was achieved at these wide ranges of HRTs. Butyrate was found to be the dominant metabolite in all HRTs. Low concentration of volatile fatty acid (VFA) confirmed the state of stability and efficiency of sequential batch mode operation was achieved in ASBR. Results also suggest that ASBR has the potential to offer high digestion rate and good stability of operation for POME treatment.     

Optimal operational conditions for biohydrogen production from sugar refinery wastewater in an ASBR

The performance of biohydrogen production in an anaerobic sequencing batch reactor (ASBR) was evaluated with respect to variations in the key operational parameters – pH, hydraulic retention time HRT, and organic loading rate OLR using sugar refinery wastewater as substrate. Analysis of variance (ANOVA) indicated HRT had less significant influence on hydrogen content and yield in comparison to pH and OLR, whereas OLR has much impact on hydrogen production rate. Taxonomic analysis results showed that diverse bacterial species contributed to hydrogen production and the dominant species in the bioreactor were governed by all operational parameters. Even without pretreatment of the seed sludge, a high proportion of Clostridium spp. over the other bacterial species was observed at pH 5.5, and this is compatible with the high hydrogen productivity. Consequently, pH 5.5, HRT 10 h, and OLR 15 kg/m³ d were delineated as the optimal operational conditions for an ASBR fed with sugar refinery wastewater.     

Hydrogen and methane production in extreme thermophilic conditions in two-stage (upflow anaerobic sludge bed) UASB reactor system

Two-stage hydrogen and methane production in extreme thermophilic (70 °C) conditions was demonstrated for the first time in UASB-reactor system. Inoculum used in hydrogen and methane reactors was granular sludge from mesophilic internal circulation reactor and was first acclimated for extreme thermophilic conditions. In hydrogen reactor, operated with hydraulic retention time (HRT) of 5 h and organic loading rate (OLR) of 25.1 kg COD/m³/d, hydrogen yield was 0.73 mol/mol glucose_added. Methane was produced in second stage from hydrogen reactor effluent. In methane reactor operated with HRT of 13 h and OLR of 7.8 kg COD/m³/d, methane yield was 117.5 ml/g COD_added. These results prove that hydrogen and methane can be produced in extreme thermophilic temperatures, but as batch experiments confirmed, for methane production lower temperature would be more efficient.     

Psychrophilic hydrogen production from petrochemical wastewater via anaerobic sequencing batch reactor: techno-economic assessment and kinetic modelling

Independent hydrogen production from petrochemical wastewater containing mono-ethylene glycol (MEG) via anaerobic sequencing batch reactor (ASBR) was extensively assessed under psychrophilic conditions (15–25 °C). A lab-scale ASBR was operated at pH of 5.50, and different organic loading rates (OLR) of 1.00, 1.67, 2.67, and 4.00 gCOD/L/d. The hydrogen yield (HY) progressed from 134.32 ± 10.79 to 189.09 ± 22.35 mL/gMEG_initial at increasing OLR from 1.00 to 4.00 gCOD/L/d. The maximum hydrogen content of 47.44 ± 3.60% was achieved at OLR of 4.0 gCOD/L/d, while methane content remained low (17.76 ± 1.27% at OLR of 1.0 gCOD/L/d). Kinetic studies using four different mathematical models were conducted to describe the ASBR performance. Furthermore, two batch-mode experiments were performed to optimize the nitrogen supplementation as a nutrient (C/N ratio), and assess the impact of salinity (as gNaCl/L) on hydrogen production. HY substantially dropped from 62.77 ± 4.09 to 6.02 ± 0.39 mL/gMEG_initial when C/N ratio was increased from 28.5 to 114.0. Besides, the results revealed that salinity up to 10.0 gNaCl/L has a relatively low inhibitory impact on hydrogen production. Eventually, the cost/benefit analysis showed that environmental and energy recovery revenues from ASBR were optimized at OLR of 4.0 gCOD/L/d (payback period of 7.13 yrs).     

Direct fermentation of Laminaria japonica for biohydrogen production by anaerobic mixed cultures

A few studies have been made on fermentative hydrogen production from marine algae, despite of their advantages compared with other biomass substrates. In this study, fermentative hydrogen production from Laminaria japonica (one brown algae species) was investigated under mesophilic condition (35 ± 1 °C) without any pretreatment method. A feasibility test was first conducted through a series of batch cultivations, and 0.92 mol H₂/mol hexose_added, or 71.4 ml H₂/g TS of hydrogen yield was achieved at a substrate concentration of 20 g COD/L (based on carbohydrate), initial pH of 7.5, and cultivation pH of 5.5. Continuous operation for a period of 80 days was then carried out using anaerobic sequencing batch reactor (ASBR) with a hydraulic retention time (HRT) of 6 days. After operation for approximately 30 days, a stable hydrogen yield of 0.79 ± 0.03 mol H₂/mol hexose_added was obtained. To optimize bioenergy recovery from L. japonica, an up-flow anaerobic sludge blanket reactor (UASBr) was applied to treat hydrogen fermentation effluent (HFE) for methane production. A maximum methane yield of 309 ± 12 ml CH₄/g COD was achieved during the 90 days operation period, where the organic loading rate (OLR) was 3.5 g COD/L/d.     

Enhanced H2 production from corn stalk by integrating dark fermentation and single chamber microbial electrolysis cells with double anode arrangement

The low conversion efficiency of substrate is one of the main bottlenecks in dark fermentation for bio-H₂ production. Herein, an enhanced H₂ yield from corn stalk was achieved by integrating dark fermentation and single chamber microbial electrolysis cells (MECs). In the dark fermentation stage, a H₂ yield of 129.8 mL H₂/g-corn stalk and an average H₂ production rate of 1.73 m³/m³ d were recorded at 20 g/L of corn stalk and initial pH 7.0. The effluent from dark fermentation was diluted and further employed as feedstock to generate H₂ by MECs. A H₂ yield of 257.3 mL H₂/g-corn stalk, an HPR of 3.43 ± 0.12 m³/m³ d and an energy efficiency of 166 ± 10% were obtained with the effluent COD of 3995.5 mg/L under 0.8 V applied voltage. During MECs operation stage, about 90 ± 2% of acetate was converted to H₂ and the corresponding COD removal reached 44 ± 2% in MECs. Overall, the H₂ yield can reach 387.1 mL H₂/g-corn stalk by integrating dark fermentation and MECs, which had nearly tripled as against that of dark fermentation.     

Comparison of thermophilic and hyperthermophilic dark fermentation with subsequent mesophilic methanogenesis in expanded granular sludge bed reactors

Herein, dark fermentation (DF, V = 5.5 L) and subsequent mesophilic methanogenesis (V = 43.5 L) are run as expanded granular sludge bed reactors (EGSB) at thermophilic (υDF = 60 °C) and hyperthermophilic (υDF = 80 °C) temperatures. A synthetic glucose wastewater is run with a 22.5 g/L chemical oxygen demand (COD) and 48–9 h hydraulic retention times (HRTs), giving organic loading rates (OLRs) of 11–60 g COD/L/d for DF. The maximum hydrogen production rate (HPR) is HPR = 3.0 m³/m³/d for HRT = 9 h with a 50 L/kg COD hydrogen yield (HY) and 40 vol% H₂. Methane production rate (MPR) reaches MPR = 2.6 m³/m³/d with 70 vol% CH₄ at HRT = 2.8 d. The highest H₂ yields are HY = 180 L/kg COD with 53 vol% H₂ (thermophilic, HRT = 48 h). Hyperthermophilic temperatures led to lower HPRs (0.7 m³/m³/d) and MPRs (1.6 m³/m³/d). 53% of Thermoanaerobacterium thermosaccharolyticum as an H₂ producer are found. Discoloration of granular sludge from black to white and granule stability was observed in DF.     

Different ratios of carbon sources in the fermentation of cheese whey and glucose as substrates for hydrogen and ethanol production in continuous reactors

The fermentation of glucose, cheese whey and the mixture of glucose and cheese whey were evaluated in this study from two inocula sources (sludge from a UASB reactor for swine wastewater treatment and poultry slaughterhouse) for hydrogen production in continuous anaerobic fluidized bed reactors (AFBR). For all fermentations, a hydraulic retention time (HRT) of 6 h and a substrate concentration of 5 g COD L⁻¹ were used. In glucose fermentation, the maximum hydrogen yield (HY) was 1.37 mmol H₂ g⁻¹ COD. The co-fermentation of the cheese whey and glucose mixture was favorable for the concomitant production of hydrogen and ethanol, with yields of up to 1.7 mmol H₂ g⁻¹ COD and 3.45 mol EtOH g⁻¹ COD in AFBR2. The utilization of cheese whey as a sole substrate resulted in an HY of 1.9 mmol H₂ g⁻¹ COD. Throughout the study, ethanol fermentation was evident.