Abstract
Textile wastewater contains organics and color dyes which need to be treated before discharging into receiving water bodies. Sequencing batch reactor (SBR) is proved promising against textile wastewater due to its high organic and nutrient removal efficiencies. In this study the influence of variable hydraulic retention time (HRT) on the performance of SBR in treating combined textile and domestic wastewater was evaluated. Six SBRs were operated in parallel at 12 and 8 hrs HRTs respectively, three for synthetic and three for real textile plus domestic wastewater. SBRs were operated at constant temperature 25 +/- 1 degrees C and pH 7 +/- 1 to avoid seasonal effects. The biological oxygen demand (BOD) removal efficiency was consistent at 73% while, total suspended solids (TSS) removal efficiency increased from 52 to 63% in SBRs with decrease in HRT from 12 to 8 hrs. The organic loading rate (OLR) increased from 0.45 to 0.68 Kg/m(3)/d, SVI decreased from 94 to 84 mL/g and chemical oxygen demand (COD) removal efficiency increased in real waste water (RWW) SBRs from 59 to 63% with decrease in HRT from 12 to 8 hrs. Low COD removal at 12 hr HRT can be attributed to poor settling characteristics of sludge due to possible filamentous growth at low F/M (0.03) and greater SRT (28 days) as compared to 8 hr HRT condition, where F/M was 0.05 and SRT of 20 days.