Exploitation results of seven RO plants for recovery and reuse of treated effluents in textile industries

The paper comprises a case study on the implementation of the advance treatment process (ATP) in seven small-scale textile industries. The ATPs installed and commissioned are in compliance with the Statutory Board directions for recovery and reuse of treated effluent leading to zero effluent discharge. The textile effluents are treated in effluent treatment plants comprising a physicochemical option followed by biological activated sludge process, pressure sand filtration and activated carbon adsorption. The tertiary treated effluents (25-65 m(3)/d) are high in total dissolved solids, chlorides and hardness, and partly reused for ashing screens, cloth and ash quenching. The tertiary treated effluent contained suspended solids and total dissolved solids in the range, 4-30 mg/L and 1980-2682 mg/L, respectively, with COD concentrations in the range, 125-410 mg/L and did not meet the stipulated standards for discharge into inland surface waters. A part of the tertiary treated effluent (4.0-9.5 m(3)/d) is routed to ATP for recovery of boiler feed quality water. The ATP comprises a multi-grade filter, ultrafiltration (UF) unit and a reverse osmosis (RO) unit. The multi-grade filter ensured complete removal of suspended solids with a marginal decrease in COD. The fouling index (b) for the feed to the ultrafiltration was estimated to be varying in the range 0.6-2.1 x 10(-3) s(-1.) The UF operated at 200-300 kcals with 88-95% permeate recovery. This unit achieved 80-90% removal of BOD and COD and 65-90% removal of phosphates. The RO unit at a pressure range of 1270-1670 kPascals produced 68-84% permeate. The permeate characteristics conforms the boiler water quality as prescribed by the Indian Standards Institution for low-pressure drum type boilers. The pH of the recovered water was adjusted with alkali to pH 10-11 and mechanically deaerated for use in boilers. Recycle/reuse of tertiary treated effluents for various purposes and reuse of the recovered water from advance treatment process as boiler water make-up has resulted in a reduction in water requirements by 30-35% in each industry.