Experimental and kinetics study for phytoremediation of sugar mill effluent using water lettuce (Pistia stratiotes L.) and its end use for biogas production.

In present study, the performance of phytoremediation by Pistia stratiotes on sugar mill effluent (SME) and its end use for biogas production are investigated. The objectives of the study are to determine the nutrient and pollution reduction efficiency of P. stratiotes from SME and evaluation of its biomass as a feedstock for biogas production. Various concentrations of SME (25, 50, 75, and 100%) were remediated by Pistia stratiotes (initial weight; 150 g) outdoor for 60 days under batch mode experimental setup. The results showed that P. stratiotes achieved marked reduction in nutrient (TKN, 72.86%; TP, 71.49%) and pollutant load (EC, 25.69%; TDS, 57.26%; BOD, 69.40%; COD, 61.80%; Ca2+, 56.79%; Mg2+, 55.01%; Na+, 42.86%; K+, 54.38%; MPN, 78.13%; SPC, 60.13%) from 75% SME at the end of the experiment. The highest biomass (328.48 ± 2.04 g) and chlorophyll content (3.62 ± 3.04 mg/g) were also achieved with 75% SME. The dried biomass of P. stratiotes (from 75% SME) was inoculated with cow dung (10% w/v) and diluted with distilled water (1:10). The whole content was used as a substrate for the biogas production within hydraulic retention time (HRT) of 30 days at room temperature. Substrate parameters such as pH, TS (%), COD (mg/L), TKN (%), TOC (%), VS (%), and C/N ratio were reduced from 7.85 to 6.0, 66.65 to 28.65%, 12,900 to 2800 mg/L, 0.95 to 0.75%, 45.54 to 19.5%, 76.87 to 28.78%, and 47.94 to 26.00, respectively, in 30 days of HRT. About 8478.6 mL of cumulative biogas production was evaluated by modified Gompertz equation. Thus, the present investigation not only achieved efficient nutrient and pollution reduction from SME but also proved the potential of P. stratiotes for biogas production.