Optimization of substrate composition for biohydrogen production from buffalo slurry co-fermented with cheese whey and crude glycerol, using microbial mixed culture

Biohydrogen production from buffalo slurry (BS) co-fermented with cheese whey (CW) and crude glycerol (CG) was investigated using a suitable microbial community (F210) as inoculum. Mixture Design was used to find the optimal composition (%) of the three substrate components and to investigate the effect of the mixing ratio on Bio-H-2 yields. Maximum H-2 yield estimated through the model was around 117 mL H-2/g VSadded, while the maximum experimentally detected was 111.6 +/- 21.8 mL H-2/g VSadded, obtained for a mixing ratio of substrate composition of 66% BS and 33% CW (R-2 = 0.962; p-value = 0.0001). CW was clearly the most suitable substrate (with a relative contribution higher than 46%), but led to a rapid drop in pH from 6.5 to 4, while BS showed high buffering capacity by maintaining the pH above 6. Interestingly, the co-digestion of the different substrates decreased the H-2 production lag phase lambda; in particular the presence of BS shortened the lag period (lambda < 3 h) and increased the degradation efficiency of CG. The results demonstrate the usefulness of the mixture design for finding the optimal substrate composition, using BS as co-fermentation substrate to obtain high H-2 production yields. Moreover the response surface shows the possibility of mixing the substrates in different ways, while maintaining H-2 production within an optimum range: 105-117 mL H2/g VSadded. This might offer a considerable advantage in the effective management of systems or processes, in which the substrates availability may change over the time. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.