High-rate anaerobic digestion of water hyacinth juice in an upflow anaerobic sludge blanket reactor with observations on granule formation

Abstract

Water hyacinth, due to its rapid growth rate and widespread, presents an opportunity for sustainable utilization, necessitating further research. Recent attention toward high-rate anaerobic digestion, especially of green or organic juices, suggests that juice from the water hyacinth plant could serve as an appropriate substrate. This study aims to assess the long-term performance, maximize treatment capacity limits across different phases, microbial community dynamics, and granule characteristics of an up-flow anaerobic sludge blanket (UASB) reactor in response to increasing loadings of water hyacinth juice (WHJ). The findings demonstrated that the reactor maintains stable effluent pH levels (7.2–8.9) and supports high biogas production rates throughout the process. At an optimal hydraulic retention time (HRT) of 1.2 day, the process remained stable, achieving a biogas production rate of 2.2 L L-reactor⁻¹ day⁻¹ and organic carbon removal of around 90 %. For the first time, this study revealed that the use of water hyacinth, despite being an aquatic weed, effectively facilitated granule formation during anaerobic digestion process. Scanning electron microscopy revealed, robust, and stable granule textures. Microbial analyses indicated a diverse bacterial and archaeal community, with a Shannon index of 5.0 for bacteria and 2.3 for archaea, confirming the efficient degradation of water hyacinth juice. Overall, the results indicate that high-rate anaerobic digestion of water hyacinth juice is feasible, enabling the sustainable utilization and removal of excess water hyacinth. The high biogas production rate and granule formation observed in this study highlights the potential for large-scale bioenergy production and effective waste management.