Evaluation of methods for preparing hydrogen-producing seed inocula under thermophilic condition by process performance and microbial community analysis

Five methods for preparation of hydrogen-producing seeds (base, acid, 2-bromoethanesulfonic acid (BESA), load-shock and heat shock treatments) as well as an untreated anaerobic digested sludge were compared for their hydrogen production performance and responsible microbial community structures under thermophilic condition (60 °C). The results showed that the load-shock treatment method was the best for enriching thermophilic hydrogen-producing seeds from mixed anaerobic cultures as it completely repressed methanogenic activity and gave the a maximum hydrogen production yield of 1.96 mol H2 mol−1 hexose with an hydrogen production rate of 11.2 mmol H2 l−1 h−1. Load-shock and heat-shock treatments resulted in a dominance of Thermoanaerobacterium thermosaccharolyticum with acetic acid and butyric acid type of fermentation while base- and acid-treated seeds were dominated by Clostridium sp. and BESA-treated seeds were dominated by Bacillus sp. The comparative experimental results from hydrogen production performance and microbial community analysis showed that the load-shock treatment method was better than the other four methods for enriching thermophilic hydrogen-producing seeds from anaerobic digested sludge. Load-shock treated sludge was implemented in palm oil mill effluent (POME) fermentation and was found to give maximum hydrogen production rates of 13.34 mmol H2 l−1 h−1 and resulted in a dominance of Thermoanaerobacterium spp. Load-shock treatment is an easy and practical method for enriching thermophilic hydrogen-producing bacteria from anaerobic digested sludge.