Effect of Oyster Shell on Mesophilic Anaerobic Digestion of Fish Waste. 

Marine product processing industry discharges large amounts of fish waste, which could be used for anaerobic digestion because of its high organic matter content. Fish waste, however, is a protein-rich substrate and its degradation products (ammonium nitrate and ammonia) inhibit anaerobic digestion. Such inhibition could be reduced by oyster shell as it contains high levels of calcium ion. In this study, the effects of oyster shell on anaerobic digestion were investigated. Results showed that the addition of oyster shell accelerated methane production in both batch tests and semi-continuous experiments. Oyster shell also acted as a substrate for the attachment of hydrogenotrophic methanogenic Methanoculleus spp. In conclusion, oyster shell is effective for the anaerobic digestion of fish waste because it can play two roles: as a source of calcium ions that counteract the inhibitory effect of ammonia and as a carrier that ensures microbial retention.

Key words: Oyster shell, calcium ion, ammonium nitrate, anaerobic digestion, fish waste.

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