Treatment of malathion pesticide wastewater with nanofiltration and photo-Fenton oxidation

Pesticide industry wastewater treatment combining nanofiltration (NF) and advanced oxidation process (AOP) using photo-Fenton's reagent was investigated in the laboratory. During the first stage of study, NF and AOP were used independently to treat malathion as a model substrate in pesticide industry wastewater (10 mg/L) to produce high quality effluent (less than 0.1 mg/L). Of the three types of NF membranes used (NF-A, NF90, and NF270), NF270 membrane has the largest water flux, but did not meet the desired effluent concentration of 0.1 mg/L. NF90 and NF-A membranes could reduce the malathion concentration to 0.06 mg/L, but provided a lower flux rate compared to NF270 membrane. AOP experiments were conducted at pH 3 to determine the optimum initial ratios of chemicals, which were malathion: H2O2 = 1:100 and H2O2:Fe(II) =40:1. Experiments were also carried out at different initial malathion concentrations to determine the reaction time for the desired effluent under the optimum conditions. It took 1 h, 2.25 h and 3 h to reduce the malathion from different initial concentrations (1, 10, and 33 mg/L) to the desired level. During the second stage of study, a specific energy consumption was determined for each treatment scheme to evaluate the economic feasibility of the NF-AOP combination. AOP is the significant energy consumer in the combined process and hence should be minimized by enhancing NF.