Effect of hydraulic retention time on nutrients and organics removal by fegac/h2 o2 –sbr treatment of pesticide wastewater

Abstract

The study investigated the effects of 6, 12, and 24 h hydraulic retention time (HRT) in terms of nutrients and organics removal by combined iron granular activated carbon–hydrogen peroxide– sequencing bath reactor (FeGAC/H2 O2 –SBR) process from pesticide wastewater. The operating conditions of the pretreatment phase (FeGAC 15 g/L, H2 O2 concentration 300 mg/L, reaction time 120 min) achieved chemical oxygen demand (COD), total organic carbon (TOC) removal, and biode-gradability (BOD5 /COD ratio) index which made the wastewater amenable to biological treatment. The SBR was operated for a period of 88 d in three different reactors at HRTs 6, 12, and 24 h. The volumetric exchange ratio was kept at 50%. At HRT 12 h, COD removal efficiency (96.5% ± 2%) was maximum. An increase in HRT from 6 to 12 h, led to increased nutrients removal. Ammonia–nitrogen removal efficiency was 38.0% ± 4% and 61.0% ± 5% at 6 and 12 h respectively; while phosphorus removal efficiency was 84.4% ± 3%, 90.7% ± 4%, and 74.1% ± 5% at HRTs 6, 12, and 24 h, respec-tively. SBR was cycled for 12 h period, the first-order-kinetic constant (k1) was obtained and substrate removal was observed at 3.5 mg/L/h while the coefficient of determination (R2) was 0.94. These results indicate that HRT can affect biomass content, nutrients, and organics removal.