Treatment of Industrial Paper Mill Effluent with Sequencing Batch Reactor Technology

Abstract

Sequencing batch reactor (SBR) is a variant of the activated sludge process that instead of operating continuously, runs on a batch mode. Effluents from industrial paper mills converting old corrugated container board (OCC) to corrugating medium and liner typically have very high pollutant loading. A study was conducted to treat effluent from the primary sedimentation tank of an OCC mill with a bench-scale SBR unit. Various 8-h cycles consisting of fill, react, settle, draw, and idle stages were imposed, and hydraulic retention times of the system varied from 1.33 to 3.0 d. Influents with an average COD of 300(superscript +) mg/L, BOD5 of 1800 mg/L and SS of 400 mg/L, could be treated with a single SBR cycle to about 200 mg/L COD, single-digit BOD5 values, and SS of about 30 mg/L as evaluated at steady-state conditions. Despite the significant variations in values of the influent COD, there was no apparent effect on the filtered COD concentrations in the treated effluent. About 90 to 94% of the unfiltered influent COD was removed, and more than 98% of the BOD5 was removed. These are extremely high removal efficiencies. The reaction kinetics during the react period of a steady-state system was determined to be a first-order reaction. The oxygen uptake rate (OUR) and specific oxygen utilization rate (SOUR) at the beginning of the react period were 4.32g O2/(L×d) and 0.64 O2/(g MLSS×d), respectively; much higher than the corresponding values of 0.89g O2/(L×d) and 0.13 O2/(g MLSS×d) measured near the end of the period, reflecting the fact that the batch process created a feast/famine cycle in the system with the substrate removal rate substantially higher at the start of aeration. Despite the encouraging results, certain scale-up parameters need to be defined before its practical application is possible.