H2 production through anaerobic mixed culture: effect of batch S0/X0 and shock loading in CSTR

Biological production of H2 has received considerable attention lately. The present study was undertaken to observe the effects of substrate/seeding ratios (S0/X0) on batch H2 generation. The H2-producing seeding spores were obtained from the heat treatment (88 °C for 12 h) of the compost from a grass composting facility. A dehydrated brewery mixture was used as feed substrate. The results indicate that the pattern of the cumulative H2 production with time is similar to the growth curve with a typical lag, exponential and stationary phase; the results were successfully modeled with a modified Gompertz equation. It appears that maximum H2 yield potential (27 ml g−1 CODadded) occurs at an S0/X0 ratio of about 4, whereas the maximum specific H2 yield (205 ml g−1 VSS d−1) occurs at approximately S0/X0 = 3. The S0/X0 ratios higher than 4 would inhibit H2 production. An attempt was made to waste a certain amount of reactor content and replaced it with fresh substrate in order to enhance H2 production. After this medium replacement, the H2 production was initially inhibited and the system then exhibited a long lag before it reached an active H2 production stage. For a continuous-stirred tank-reactor (CSTR) system, the results of replacing 25% of the reactor content indicate that there is still a lag time before a sudden increase in H2 production after the addition of the new substrate feed. The major low molecular weight acids identified are HAc and HBu with total volatile acids of about 6000–8000 mg l−1. The ratio of HAc/HBu in the present study is relatively constant (about 5) and appears not significantly affected by the medium replacement. The concentration of total alcohols is about 2000 mg l−1. All in all, the CSTR system is able to recover to its previous performance after such a dramatic 25% medium replacement.