Methanogenic recovery under organic overload using starfish-derived powder.

INTRODUCTION

Starfish overpopulation causes ecological and economic problems, and the collected biomass is typically discarded by incineration or landfilling. Given its high CaCO3 content and biodegradable fraction, starfish biomass could be valorized as a multifunctional additive in anaerobic digestion (AD). This study evaluated the buffering and recovery effects of starfish powder (SF) under starch-induced overloading.

METHODS

Starfish (Asterina pectinifera and Asterias amurensis) were dried, pulverized (<1.7 mm), and characterized for physicochemical properties and theoretical biochemical methane potential (TBMP). Long-term (257 days) batch assays compared starch overload (30 g volatile solids (VS)/L) alone, CaCO3 supplementation, and SF addition at equivalent or higher CaCO3 doses.

RESULTS

As a sole substrate, SF yielded 490 mL CH4/g VS (59-73% of TBMP). Under starch overloading, CaCO3 supplementation failed to restore activity (≤5.4% of expected yield), whereas SF enabled recovery with triphasic methane production, reaching 60-78% of the expected yield. Microscopy indicated more open pores with microbial colonization in the SF trials, and 16S rRNA sequencing analysis indicated a shift in fermentative bacterial communities accompanied by enrichment of hydrogenotrophic methanogens.

DISCUSSION: These findings suggest that SF promotes recovery through combined physicochemical buffering and microbial restructuring, serving as a slow-acting alkalinity source in overloaded digesters where long-term stability is prioritized.