Optimization of Hydraulic Retention Time (HRT) Employing Contemporary Statistical Tools for Treatment of NUST Domestic Wastewater Using Lab Scale Sequencing Batch Reactor (SBR)

Abstract

This study evaluates and compares the SBR treatment performance for synthetic and real wastewater which was observed through effluent quality, sludge parameter and the removal efficiency in terms of COD, TSS, nitrate, nitrite, ammonia, total phosphate and ortho-phosphate. The study on Sequencing Batch Reactors was conducted in two phases. Before the analysis both the reactors were calibrated statistically. In Phase-1, wastewater parameters were analyzed for the treatment of synthetic wastewater at four different Hydraulic Retention Times (HRT= 1, 2, 3 and 4 hours). The mixed liquor suspended solids (MLSS) was maintained in range of 4 to 6 g/L. The reactor with HRT 1 hour had a Sludge Volume Index (SVI) greater than 150 ml/g which lead to poor sludge settling and sludge bulking. While HRT 2, 3 and 4 hours showed an increase in COD removal with the acclimation of sludge. Two optimal HRTs were selected based upon statistical analysis. In Phase 2 of the project, the optimized HRT (2 hours and 3 hours) were run for the treatment of real wastewater of NUST H-12.The SVI of both HRTs remained in a good range but the MLSS of HRT 2 hours was higher than 3 hours. A lot of variation in the inlet COD concentration was observed and the removal efficiency of COD varied accordingly. But the effluent COD concentration remained within the NEQS limit of 150 mg/L. For the nutrient removal it was observed that, on the average the Ammonium-N and nitrite nitrogen removal efficiency was higher for HRT 3 hours compared to 2 hours. Whereas, HRT=2 hours showed a higher efficiency for orthophosphate and total phosphate removal. Based on the wastewater parameters, 3 hours was the optimal hydraulic retention for real wastewater.