Adding benefits to phytoremediation of sugar mill effluent by growing water hyacinth (Eichhornia crassipes): Evaluation of biomass for biogas production

Abstract

In this experiment, we assessed the phytoremediation potential of water hyacinth (Eichhornia crassipes) for pollutants removal from sugar mill effluent amended at different concentrations and further biogas production from its grown biomass co-digested with cow dung in a laboratory scale anaerobic digester. The results showed that the maximum values of kinetic growth rate (2.56gg^-1d^-1), total chlorophyll content (4.10±0.10mg/gfwt.) and fresh plant biomass (393.87±4.67g/Kg) of E. crassipes were achieved in 75% concentration of sugar mill effluent after 60 days of phytoremediation experiments. Also, the enrichment factor (E_f) and bioaccumulation factor (B_f) of heavy metals were greater than or equal to 1 in the roots and leaves of E. crassipes which indicated efficient elimination of these metals from the sugar mill effluent. Significant values of cumulative biogas production (5195 ml) and predicted by modified Gompertz kinetic model (5238.71 ml) were found after 15 days of anaerobic digestion at 40°C with maximum reduction of COD (83.11%) of the substrate slurry. The plot of log(COD) vs. t (HRT) suggested good fitness of first order kinetic equation (R²= 0.9746) for reduction of co-substrate COD. The different kinetic parameters of COD reduction for biogas production viz., a_, xc and k were noted as 6096.12, 7.73 and 0.26, with R² value of 0.99, respectively. The findings of this study concluded that E. crassipes can be used for the phytoremediation of heavy metals and other pollutants most efficiently in 75% concentration of the sugar mill effluent. Additionally, the biomass of E. crassipes grown during phytoremediation can be used for enhanced biogas production.