Recovering biomethane and nutrients from anaerobic digestion of water hyacinth (Eichhornia crassipes) and its co-digestion with fruit and vegetable waste

The potential to recover bioenergy from anaerobic digestion of water hyacinth (WH) and from its co-digestion with fruit and vegetable waste (FVW) was investigated. Initially, biogas and methane production were studied using the biochemical methane potential (BMP) test at 2 g volatile solids (VS) L⁻¹ of substrate concentration, both in the digestion of WH alone and in its co-digestion with FVW (WH-FVW ratio of 70:30). Subsequently, the biogas production was optimized in terms of total solids (TS) concentration, testing 4 and 6% of TS. The BMP test showed a biogas yield of 0.114 m³ biogas kg⁻¹ VS_added for WH alone. On the other hand, the biogas potential from the WH-FVW co-digestion was 0.141 m³ biogas kg⁻¹ VS_added, showing an increase of 23% compared to that of WH alone. Maximum biogas production of 0.230 m³ biogas kg⁻¹ VS_added was obtained at 4% of TS in the co-digestion of WH-FVW. Using semi-continuously stirred tank reactors, 1.3 m³ biogas yield kg⁻¹ VS_added was produced using an organic loading rate of 2 kg VS m⁻³ d⁻¹ and hydraulic retention time of 15 days. It was also found that a WH-FVW ratio of 80:20 improved the process in terms of pH stability. Additionally, it was found that nitrogen can be recovered in the liquid effluent with a potential for use as a liquid fertilizer.