Enriched biogas and biofertilizer production from Eichhornia weed biomass in cow dung biochar-amended anaerobic digestion system

Abstract The effect of cow dung biochar on water hyacinth anaerobic digestion of with control setup (without biochar (T 0 ) was investigated using a batch scale setup (at 35 °C). Biochar was applied in three doses (v/v) 0.5% (T 0 . 5 ), 1% (T 1 ), and 1.5% (T 1 . 5 ) in anaerobic digestion setups and daily and cumulative biogas formation was recorded in all setups. Results revealed that biochar addition reduced the lag phase from 3 d to 1 d but extended in a higher dose (1.5%). The cumulative biogas production was fund to be 2721 mL in T 1 followed by, 2388 mL (T 0 . 5 ), 1940 mL (T 1 . 5 ), and 1153 mL (T 0 ) ( p 0 . 001 for all) by the end of 35 days of the AD process. The maximum biogas production improved by 40.6–57.6%, in biochar setups than T 0 . Spent slurry was analyzed for its possible use as biomanure for plant production and results revealed a considerable amount (g kg − 1 ) of total nitrogen (14.07–16.69), total phosphorous (15.76–17.8), total potassium (21.56–24.12) in spent slurry from biochar-amended setups. Carbon-to-nitrogen ratio (14.2–19.6), NH 4 + /NO 3 -N ( − 1 ) ratio, and germination index of spent slurry was also in the acceptable limit as decided for biomanure, indicating its possible in plant production. Biochar addition (up to 1%) improves the biomethane contents (4.4–11%) in biogas and nutritional value of spent slurry. This study indicates that weed Eichhornia biomass could be managed effectively by anaerobic digestion for methane-rich biogas and biofertilizer production simultaneously under the circular economy model.