Influence of hydraulic shock loads and TDS on the performance of large-scale CETPs treating textile effluents in India

Abstract

The present study relates to the influence of hydraulic shock loads and total dissolved solids (TDS) on the performance of three large-scale common effluent treatment plants (CETPs) treating textile effluents, which is generated from clusters of small-scale industries in the state of Rajasthan in India. Of the three CETPs, two having capacities 7.0 and 9.0 million liters per day (mld) are located in Pali and one of capacity 6.0 mld in Balotra, District Barmer. Wastewater from about one thousand small-scale industries is treated in these CETPs. The effects of hydraulic shock loads and TDS on effluent data from secondary clarifier for parameters biochemical oxygen demand (BOD) and suspended solids (SS) for CETPs at Pali, and chemical oxygen demand (COD) and SS for the CETP at Balotra were studied. It was observed that the effluent BOD and SS remained within the prescribed limits for CETP Pali at 30% increased flow rate, whereas effluent COD and SS at 30% increased flow rate for CETP Balotra exceeded the prescribed limits and the CETP could sustain 20% increased flow rate. The shock loading analysis revealed that CETP Balotra had reduced capacity to sustain shock loads by 10% as compared to CETP Pali due to the presence of high TDS (15 000–20 000 mg/l). High TDS interfered with the oxygen transfer necessary for biological metabolism, thereby affected the efficiency of activated sludge process. Hence, activated sludge process treating high TDS effluents are more sensitive to hydraulic shock loads and prone to process upsets.