Development of a recycling technology for abnormally occurring oysters using molten alkali hydroxide

The management of marine fouling organisms on coastal infrastructure-especially the treatment and disposal of shellfish waste-poses a persistent environmental and operational challenge. This study seeks to develop a simplified and effective treatment strategy for addressing "abnormally occurring" shellfish populations. Oysters sourced from Shirako-cho, Chiba Prefecture, Japan, served as the primary material for the experiment. The hydroxide alkali fusion method was applied to reduce the final volume and weight of the oysters. This study involved varying the alkali hydroxide mixing ratio (KOH:NaOH = 1:0, 3:1, 1:1, 1:3, 0:1) and reaction temperature (200-500 °C) to investigate the potential self-powdering of oyster shells and the decomposition process of oyster meat. The results indicated that without the addition of molten hydroxide, the shell samples maintained their original form within the 200-500 °C range without powderization. Conversely, when molten hydroxide was introduced, all shell samples achieved self-pulverization at temperatures ≥ 200 °C across all mixing ratios. The decomposition of oyster meat exceeded 80% at 200 °C for all mixing ratios (KOH:NaOH = 1:0, 1:1, 0:1). Furthermore, alkali fusion treatment of a whole oyster with KOH at 200 °C resulted in simultaneous shell powdering and meat decomposition. These findings highlight the method's ability to reduce oyster shell and meat concurrently at low temperatures without the need for prior crushing or incineration, offering insights for developing novel approaches to manage shellfish waste.