PRODUCTION OF BIOHYTHANE FROM ALGAE VIA DARK FERMENTATION COUPLED WITH ANAEROBIC DIGESTION PROCESS

Abstract

This study focused on the use of response surface methodology (RSM) in the optimization of process parameters for efficient biohythane production using chlorella sp. via two-stage anerobnic digestion process. A quadratic model has been suggested to predict the behavior of samples. The box-behnken design matrix was applied in designing 15 batch experimental runs for the evaluation of hydrogen yield and methane yield by varying initial substrate concentration (6, 8 and 10gmVS), initial pH (5.0, 6.0 and 7.0) and temperature (35, 45 and 55℃). Results showed that the optimal biohydrogen yield (HY) of 46.97 ml H2/gm-VS was obtained in Run-9 at a substrate concentration of 10 gm-VS, Temperature of 55℃ and initial pH of 6.0. This has been validated by carrying out a verification experiment which gave an average hydrogen yield of 48.32 ml H2/gm-VS with a bias of 15.08 %. Further methanogenesis has been carried out from hydrogen effluent of the most optimal run which provided us with a yield of 184.69 mlCH4/gm-VS with a total production of 277.03 ml CH4 in a time period of 14 days. Mathematical modeling done on experimental yield of hydrogen and methane revealed the suitability of cone model (R2 = 1.000, bias = - 0.02%, AIC = - 28.57) for biohydrogen fermentation (R2 = 0.99, bias = + 3.91%, AIC = 59.98) for biomethane production respectively. An energy assessment on Chlorella sp. powder revealed a higher heating value of 22.70 MJ/kg VS and an energy yield and recovery of 0.51 kJ/gm-VS and 2.34 % from dark fermentation and 7.11 kJ/gm-vs and 31.43 % from dark fermentation and methanogenesis respectively. This optimization study clearly showed that the Yield of H2 and CH4 is being significantly affected by substrate concentration, temperature, and pH and hence we can conclude that the use of RSM with appropriate experimental design can help in achieving the optimum hydrogen and methane yield, which could serve as an alternative source of energy that could replace traditional petroleum-based fuels.