Simultaneous hydrogen gas formation and COD removal from cheese whey wastewater by electrohydrolysis
Highlights
► H2 gas production and COD removal was realized by electrohydrolysis of cheese whey. ► Effects of DC voltage on H2 gas formation and COD removal was investigated. ► High volumes of H2 gas formation with high rates and yields were obtained.
Introduction
There has been considerable interest in developing clean fuels to replace fossil fuels over the last fifty years. Coal and petroleum-based fuels are responsible for emission of COx, NOx, SOx and volatile organic compounds (VOC) to atmosphere causing air pollution problems. It is widely believed that hydrogen gas is an attractive energy carrier of the future with high energy content of 122 kJ g−1 and reduced green house gas emissions as compared to fossil fuels. Hydrogen gas can also be used in fuel cells to generate electricity [1], [2]. However, hydrogen gas is not readily available in nature and is produced by costly processes such as steam reforming of natural gas or electrolysis of water requiring high energy inputs [1], [2].
Hydrogen gas production by fermentation of renewable resources such as biomass has been considered as a viable approach due to operation under mild conditions. Due to low rates and yields of hydrogen gas production fermentative processes are not feasible for large scale operations [3], [4].
Electrolysis of water for hydrogen gas production has been studied extensively despite the negative energy balance [5], [6], [7], [8]. Energy requirement for electrolysis of water is 4 kW h m−3 H2 while the energy content of hydrogen gas is 3.55 kW h m−3 H2. Three major electrolysis processes used for H2 gas production are alkaline electrolysis, proton exchange membrane (PEM) and solid oxide electrolysis cells (SOEC). Photoelectrochemical (PEC) water splitting is a newly developed technology for H2 gas production. Catalytic or high temperature steam electrolysis was also developed to improve H2 gas production by electrolysis. Proton exchange membrane (PEM) containing electrolysis cells were used for H2 gas production from water with net energy input [8].
Hydrogen gas production by electrohydrolysis of organics present in waste materials is a newly developed approach. A few recent patents on hydrogen gas production by DC current application to organic wastes and fermentation effluents have been reported [9], [10], [11]. Hydrogen gas production from wastewater using microbial electrolysis cells (MEC) has also been investigated [12], [13], [14]. In our previous studies on H2 gas production from electrohydrolysis of organic wastes, anaerobic sludge, olive mill wastewater (OMW) and landfill leachate were used as raw materials [15], [16], [17], [18], [19], [20].
Cheese whey (CW) is a high strength wastewater (COD = 50–60 g L−1) of cheese manufacturing processes and is considered as a nutritionally rich medium for production of fuels (ethanol, methane) and chemicals (organic acids) by fermentation due to high carbohydrate (5–6% w v−1 lactose), protein (0.8–1%), and fat (0.06%) contents [21], [22], [23], [24]. Cheese whey has also been used for bio-hydrogen production by dark fermentation [25], [26], [27], [28]. Hydrogen gas production by electrohydrolysis of cheese whey has not been reported in literature. Therefore, this study constitutes the first report on hydrogen gas production by electrohydrolysis of cheese whey solution. DC voltages between 0.5 and 5.0 V were applied to diluted CW solution for hydrogen gas production using aluminum electrodes. CW control experiments with no voltage application and water control experiments with DC voltage application were also carried out to determine the extent of hydrogen gas production by bacterial fermentation and by electrolysis of water, respectively.
Section snippets
Experimental setup and procedure
Batch electrohydrolysis experiments were performed using 1 L serum bottles with 500 mL working volume. The bottles contained two aluminum electrodes (L = 24.5 cm, Dcathode = 8 mm, Danode = 6 mm) immersed in cheese whey solution and connected to DC power suppliers (TT-T-ECHNI-C MCH-305T and MCH-305D-II, China). The bottles were closed tightly by silicone rubber stoppers and screw caps and were sealed carefully using silicone to avoid any gas leakage. Duplicate bottles were placed on magnetic
Results and discussion
Batch electrohydrolysis experiments were performed to determine the effects of applied DC voltage on hydrogen gas production and COD removal from the CW solution. The first set of experiments was consisted of 6 duplicate serum bottles containing diluted CW with DC voltage application (0.5–5 V) and a CW control bottle with no DC voltage. The second set of experiments consisted of 6 bottles containing water (water controls) with different DC voltages to determine H2 production by electrolysis of
Conclusions
Hydrogen gas production with simultaneous COD removal was realized by electrohydrolysis of cheese whey solution by applying different DC voltages between 0.5 and 5 V. Hydrogen ions released from dissociation of VFAs produced by bacterial fermentation reacted with the electrons provided by DC power supply to form H2 gas. The highest cumulative hydrogen volume (5551 mL), hydrogen gas formation rate (913 mL d−1), hydrogen yield (1709 mL H2 g−1 COD) and percent hydrogen (99%) in the gas phase were
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