Pesticide Effluent Treatment Using Bacteria and Microalgae

Over the past 5 decades, the pesticide production in India has increased from 5000 tons/year to 95000 tons/year. This has raised concern about the treatment of pesticide effluent. Low biodegradability and high Chemical Oxygen Demand (COD) cause major problems to pesticide effluent treatment. Though the physical treatments like advanced oxidation processes (AOPs) are effective, they are not economical as compared with biological treatment systems. The present study was conducted to examine 1. the performance of aerobic bacteria and mixed microalgae in treating a pesticide industry effluent and to quantify the biodegradation in terms of biokin etic parameters at steady state and 2. the inhibition caused by the pesticide effluent on unacclimated ethanol enriched aerobic and anaerobic culture. The pesticide effluent was collected from a pesticide formulating industry, which manufactures 13 insecti cides, 2 fungicides, and 5 herbicides. The effluent has a COD of 35000 mg/L and the COD/Total Organic Carbon (TOC) ratio was 2.38. The experiment was performed in 1000 mL plastic bottles at six different Solid Retention Time (SRTs) - 6, 8, 10, 12, 14, and 16 days in continuous mode with mixing at 60 rpm. The influent and effluent parameters were analyzed for COD, TOC, Total nitrogen (TN), sulfates and Volatile Suspended Solids (VSS). The performance of the treatment was monitored based on TOC, TN, sulfates removal at different SRTs. In aerobic reactors, the removal efficiency progressively increased with increasing SRTs. The COD removal was above 80% for SRTs greater than 8 days. In mixed microalgal rectors the effluent TOC and was found to be very higher th an influent possibly due to carbon dioxide fixation from atmosphere . The steady - state kinetic parameters of aerobic bacteria for organic carbon removal were estimated by fitting experimental data to linearized Michaelis - Menten and Monod model at steady - stat e conditions. The steady state kinetic parameters k, Ks, Y, and kd were 2.52 d - 1 , 49.68 mg COD/L, 0.25 mg VSS/mg COD and 0.46 d - 1 respectively. The unacclimated ethanol enriched aerobic and anaerobic culture reactors were dosed with the different percentag es (0, 0.1, 0.2, 0.4, 0.8, 1.6, 3.2 and 4.8%) of pesticide effluent to study the inhibitory effect of the pesticide effluent on ethanol utilization. Inhibition result shows that the pesticide effluent caused a competitive inhibition above a dose of 1.6% to unacclimated ethanol enriched aerobic culture. However, under anaerobic conditions, the inhibitory effect was more severe and substrate utilization was not observed. Above studies show high treatment efficiency can be achieved in aerobic biological treatm ent when the biomass gets acclimatized to the pesticide industrial effluent. The effect of pesticide industry effluent was more severe on anaerobic bacteria and mixed microalgal culture under similar conditions.