The influence of self-immobilization of enriched acidogenic mixed consortia on fermentative H2 production was studied on different supporting materials [SBA — 15 (mesoporous) and activated carbon (granular; GAC and powder; PAC)] [126].

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Suspended growth (SG-control) of cultures showed inhibition in terms of both H2 production and substrate degradation, especially at higher loading rates. On the other hand, attached growth showed marked improvement in both H2 yields and substrate degradation efficiency, particularly at higher loading rates. Self­immobilization on SBA-15 showed nine times higher H2 production than the non-attached (SG) operation. Attached growth on GAC and PAC also showed marked improvement in the process performance at higher OLRs compared to SG operation. Immobilization of microflora on the support medium as biofilm results in high biomass hold up, which enabled the operation of the process at signifi­cantly higher liquid throughputs and OLRs. Immobilization protects the cells from environmental/chemical toxicity and from predation by other organisms and may enhance survival under extreme environments with relatively high survival rates even after prolonged storage [26, 92, 126]. Immobilized cells survive even at high temperatures.