Enhanced biohydrogen production from carbohydrate rich wastewater through anaerobic fermentation

Abstract

In recent times,“the world has faced serious problems emanating from the use of fossil fuels which are detrimental to the environment at large. On the other hand, due to the industrial boom, many industries produce wastewater that is harmful to the environment hence, carbohydrate-rich industrial wastewater can be advantageously used to reduce impact on the environment. If subjected to anaerobic fermentation, organic wastewater has the potential to produce renewable energy sources that have less impact on the environment, including biohydrogen, which has little or no carbon footprint. While reducing the impact of the problems caused by the disposal of wastewater to the environment, the biological methods also offer a solution to the detrimental effects of fossil fuels and their after use effects. The study was mainly based on environmental protection and clean, renewable alternative energy production by generating biohydrogen from organic industrial wastewater as a substrate. Anaerobic digestion has been extensively studied, but dark fermentation, which is an emerging technology within anaerobic digestion that involves the production of hydrogen from carbohydrate-rich substrates, has less information documented regarding this technology. This technology is crucial in the because it forecasts beyond fossil fuel usage and is accompanied with long-term economic expansion and energy security as there are many reservations about fossil fuel reserves and their high risk of exploitation.” Biohydrogen potential tests (BHP) were performed on five different wastewater streams (yeast, alcohols, brewery, sugar, and dairy industries) to determine the stream with the best hydrogen potential. Rigorous characterisation of various wastewater streams was conducted; the main parameters of interest were COD, BOD, VS, TS, pH, among others. The BHP tests were conducted in triplicates in 600 mL Schott bottles charged independently with various wastewater streams and inoculated by the seed sludge from a local wastewater treatment plant at the different substrate to biomass ratios. The highest hydrogen composition was recorded with the brewery wastewater, which had 40.1% H2 in the off-gas as analysed by the gas chromatograph; and the minimum was found in alcohol wastewater, 21.4%. The Kepner-Tregor decision-making tool was conducted to determine the most suitable stream for the scaled-up reactor. A conclusion to use the brewery wastewater in the scaled-up Anaerobic Baffled Reactor (ABR) was reached.

Four 10 L Anaerobic Baffled Reactors were used as the scaled-up reactors to optimise operating conditions for the production of biohydrogen using the brewery wastewater. Design-Expert software, under response surface methodology, was used to produce the matrix of combinations of the experimental runs by varying temperature (32-38℃), batch time (4-16 h), and pH (3.5-7.5); in total 20 runs were formulated.” The highest hydrogen production rate of 18.16 mL/h and the hydrogen yield of 30.98 mmol/gCOD were observed at temperature, batch time, and pH of 35℃, 4-10 h, and 5, respectively. The optimum operating conditions were determined to be a temperature of 36℃, batch time of 10.2 h, and a pH of 5.6. A predictive model, quadratic polynomial in nature, was developed after an intensive analysis of variance, a regression coefficient between predicted and actual hydrogen production rates was found to be 0.92. A system was run on optimum conditions to validate the developed mathematical model. The maximum hydrogen potential rate (HPR) determined in this study was 6.11% higher than the predicted value. The validation runs were also performed as control experiments for comparison between a system with nanoparticles and a system without nanoparticles with regards to the HPR. 25.37% H2 and 21.85% H2 were determined for with magnetite nanoparticle system and a system without nanoparticles, respectively. The experiments with nanoparticles garnered 44% higher HPR (23.41 mL/h) than a system without nanoparticles.