Biohydrogen production from anaerobic fermentation of pineapple peels by immobilized co-cultured bacteria

Abstract

Pineapple peel is one of the potential biomass feedstocks for biohydrogen production. The most convenient way to produce biohydrogen from lignocellulosic materials is through fermentation. The process is environmentally friendly and consumes low energy but has low production yield. One of the ways to increase the biohydrogen production is by utilising more than one species of hydrogen-producing bacteria, also known as co-culture, and immobilising them in a stable anaerobic condition. The suitability of the bacterial co-culture and their stability in immobilisation matrix were tested to achieve maximum biohydrogen production. The objective of this study was to improve biohydrogen production from pineapple peels via batch fermentation process using the most suitable immobilised co-culture. Pineapple peel was chosen due to its abundance and availability. Three different H2- producing bacteria were selected, namely Escherichia coli, Enterobacter aerogenes, and Clostridium sporogenes, which were used as a single culture or combined as a co- culture. Their performances in free cell and immobilised form were then compared. For the immobilisation, activated carbon sponge and loofah sponge were used and compared. Finally, the cumulative production of biohydrogen and biohydrogen production rate were analysed by kinetics study. The modified Gompertz equation was fitted to the kinetics of cumulative biohydrogen production via Excel solver application. All fermentation processes were carried out at pH 7 and 32 ± 1 °C, with 30 % v/v inoculum of working volume in batch process. In terms of biohydrogen production rate in immobilized co-culture fermentation, activated carbon sponge was found to be a better support material compared than loofah sponge. The obtained biohydrogen production rate using immobilized co-culture on activated carbon sponge was 0.768 L H2/h/Lsubstrate at 24 h fermentation, approximately 45 % higher than using loofah sponge for the immobilization. In comparison with fermentation of free co- culture, the average biohydrogen production rate using co-culture immobilized onto activated carbon sponge was 67 % higher than that without immobilization. The highest cumulative and production rate of biohydrogen were achieved by the co- cultured bacteria Escherichia coli and Clostridium sporogenes, with 15.42 L of H2 and 1.416 L H2/h/Lsubstrate. The best fitting curve result for the cumulative biohydrogen production prove that the modified Gompertz equation fitted well with most experimental results. This finding would be useful for scaling up of biohydrogen production. In conclusion, the combination of activated carbon sponge and co-culture enhanced the biohydrogen production from pineapple residues. The activated carbon sponge was identified as a reasonable, easily obtained, and durable support material, which is suitable to be used in any plug flow bioreactor system in the future.