Enhancement of Water Hyacinth Juice Treatment in an Anaerobic Sequential Batch Reactor with Coffee Husk–Derived Biochar

Abstract

The proliferation of water hyacinths is a global issue with significant environmental and social implications, and its proper management is a critical issue. Anaerobic digestion (AD) of compressed water hyacinth juice (WHJ) is key to efficiently utilizing water hyacinth biomass, but a simpler and more cost-effective method has yet to be established. In this study, the effectiveness of biochar carriers derived from local waste biomass (i.e., coffee husk) for WHJ treatment was evaluated in a sequential batch reactor. This was compared to conventional AD carriers (polyurethane sponge) and no-carrier conditions. The no-carrier condition resulted in process failure after 40 days due to the accumulation of volatile fatty acids from the substrate overload. In contrast, the biochar condition showed a significant CH4 yield (472 mL/g-VS) and total organic carbon removal (88.6%), comparable to the sponge carrier condition. Scanning electron microscope observation revealed an aggregation of mainly rod-shaped microorganisms in the biochar pores, indicating biofilm formation and a rise in microbial concentration. Nano-archaea (Candidatus Diapherotrites archaeon ADub.Bin253), which have a symbiotic relationship with methanogens, were detected, particularly in carrier-filled conditions, with a relative archaea abundance of 12.9–28.6%. This study highlights the effectiveness of using coffee husks to treat WHJ, which can both exist in the same region, and suggests an alternative way of using locally generated biomass for local waste treatment.