Mesophilic Anaerobic Digestion as a Post-treatment for Biofouling Blue Mussels

In the last 80 years, the blue mussels of the genus Mytilus have been introduced by shipping and anthropogenic activities to the Japanese waters, resulting in biofouling which lead to lower plant efficiency and problems in treatment and disposal. Despite many on-going researches into the development of preventive, removal, and control strategies, treatment and disposal of the removed blue mussels are still ecologically, socially, and economically challenging. In this study, the possibility of using anaerobic digestion as an alternative to direct disposal and incineration of blue mussels was examined, and the effect of salinity (0 g/L, 10 g/L, 20 g/L, 3 5g/L, and control) on solubilization and methanogenesis of these marine biofoulers was evaluated in five batch reactors maintained at mesophilic temperature (37degC) over a period of 100 days. Rapid progression in the hydrolysis and acidogenesis of complex organic matter in mussel tissues, denoted by a sharp decrease in pH and increases in VFAs and SCOD in the first four days, were observed in all blue mussels-containing batch reactors. This suggests that solubilization of blue mussels in anaerobic digestion was not rate limiting. Salinity was also not found to have a significant effect on the degree of solubilization. A high cumulative methane production of above 8 L was obtained from batch reactors of low salinity (0 g/L and 10 g/L), in contrast to that of less than 3 L of methane from those of high salinity (20 g/L and 35 g/L). These results have thus proven that the concept of using anaerobic digestion for the treatment of the removed blue mussels will be feasible, and methanogenesis can be best optimized under salinity conditions below 10 g/L.