Effects of Hydraulic Retention Time on the Pilot-Scale Activated Sludge and Floating Aquatic Macrophytes Wetland System for Treatment of Cafeteria Wastewater
Selection of a suitable method for treatment of domestic wastewater depends on its efficiency, simplicity, and cost-effectiveness. This study investigated the effects of hydraulic retention time (HRT) on the treatment efficiency of an activated sludge process (AS) and floating aquatic macrophytes (water hyacinth) constructed wetland (FAMCW) system. Experiments were conducted in pilot-scale reactor under steady-state conditions and varying HRT (6, 12 and 18 h). Total suspended solid (TSS), Biochemical Oxygen Demand (BOD), Nitrate Nitrogen (NO3-N), Ammonium Nitrogen (NH4-N) and ortho–Phosphate (o-PO4) were measured to evaluate the removal efficiency. The average removal efficiencies were 46.4%, 81.0% and 91.9% of TSS, 49.9% ,79.9% and 95.6% of BOD, 25.2% ,54.6% and 76.14 % of NO3--N, 36.7% ,-149.0% and 89.0% of NH4+-N and 89.3%, 96.2% and 90.8% of o-PO43- under HRT of 6, 12 and 18 h, respectively. The results indicated that average removal efficiencies of BOD, TSS, NO3-N and NH4-N increased with an increase in HRT. Average removal efficiency of o-PO4 in AS was highest at the shortest HRT. Limiting dissolved oxygen level resulted in an increase of NH4-N concentration in FMACW. Highest and lowest relative growth rates (RGR) of water hyacinth were found in 12h HRT (0.0265 d-1) and 18h HRT (0.0150 d-1), respectively. These findings confirmed hydraulic retention time is a key factor in determining the effectiveness of wastewater treatment in an AS-FAMCW reactor.
Index Terms - Hydraulic Retention Time, Activated Sludge Process, Floating Aquatic Macrophytes Constructed Wetland, Removal Efficiency