Enrichment and adaptation of extreme-thermophilic (70o C) hydrogen producing bacteria to organic household solid waste by repeated batch cultivation

Adaptation of biohydrogen producing extreme-thermophilic bacteria to household solid waste (HSW) at extreme-thermophilic temperature (70 °C) was investigated. Inocula received from an extreme-thermophilic glucose fermentation reactor were exposed to increasing HSW concentrations from 1 g-VS/L to 10 g-VS/L via repeated batch cultivation. It was found that repeated batch cultivation was a very useful method to adapt and enrich biohydrogen producing mixed cultures that could ferment HSW with high hydrogen yield and without significant lag phase. For unadapted cultures (inocula from simple substrate-glucose to complex substrate-HSW), hydrogen was produced only in the HSW concentration of 1-2 g-VS/L and the lag phase required more than 2 days. After adaptation, hydrogen was produced directly in the HSW feedstock (10 g-VS/L) with the maximum yield of 101.7 ± 9.1 mL H /g VS . Acetic acid was the main fermentation product in all HSW concentration cultivation. Furthermore, hydrogen production was demonstrated in continuous system with adapted cultures while process failure was found with unadapted cultures

Hydrogen and methane production from household solid waste in the two-stage fermentation process

A two-stage process combined hydrogen and methane production from household solid waste was demonstrated working successfully. The yield of 43 mL H-2/g volatile solid (VS) added was generated in the first hydrogen production stage and the methane production in the second stage was 500 mL CH4/g VS added. This figure was 21% higher than the methane yield from the one-stage process, which was run as control. Sparging of the hydrogen reactor with methane gas resulted in doubling of the hydrogen production. PH was observed as a key factor affecting fermentation pathway in hydrogen production stage. The optimum PH range for hydrogen production in this system was in the range from 5 to 5.5. The short hydraulic retention time (2 days) applied in the first stage was enough to separate acidogenesis from methanogenesis. No additional control for preventing methanogenesis in the first stage was necessary. Furthermore, this study also provided direct evidence in the dynamic fermentation process that, hydrogen production increase was reflected by acetate to butyrate ratio increase in liquid phase. (c) 2006 Elsevier Ltd. All rights reserved