UV Fenton and sequencing batch reactor treatment of chlorpyrifos, cypermethrin and chlorothalonil pesticide wastewater

Abstract

This study examined the effect of operating conditions of UV Fenton pretreatment combined with aerobic sequencing batch reactor on degradation and biodegradability (BOD5/COD ratio) improvement of chlorpyrifos, cypermethrin and chlorothalonil pesticide wastewater. The optimum operating conditions in the pretreatment phase were H2O2/COD molar ratio 2.0, H2O2/Fe2+ molar ratio 25, pH 3 and reaction time 60 min and achieved COD and TOC removal were 64.8 and 45.9% for COD and TOC removal, respectively and biodegradabilty (BOD5/COD ratio) improved from 0.02 to 0.31. In the aerobic SBR phase, five different UV Fenton operating conditions were investigated and UV F-SBR 1 appeared to be the most significant (p < 0.05). Increasing UV Fenton pretreatment time and combining the pretreated pesticide wastewater and municipal treatment plant wastewater enabled sustenance of the SBR operation. The UV Fenton-SBR (C) achieved COD and TOC removal efficiency of 96.2 and 97.4%, respectively after 40 d operation at 12 hr HRT. Effluent COD, TOC and BOD5 were 24, 19 and 18 mg L−1, respectively and BOD5/COD ratio was 0.75. Applying the Monod model, values of the biological first order kinetic constant (Kob), cell yield (Yx/s) and decay coefficients (kd) were 0.1332 hr−1, 0.5301 (mg COD mg−1 MLSS) and 0.0072 hr−1, respectively. The UV Fenton-SBR (C) process is effective in treatment of pesticide wastewater containing chlorpyrifos, cypermethrin and chlorothalonil to meet Malaysian industrial effluent discharge standard.