Treatment of woolen textile wastewater using membrane bioreactor, nanofiltration and reverse osmosis for reuse in production processes

Abstract

The reuse opportunities of separate wastewater streams and end-of-pipe composite wastewater were investigated in an integrated woolen textile mill. The main purpose was to reuse either the treated composite wastewater and/or treated/untreated separate streams depending on the water quality demand of different water use points in the production processes. In this context, three separate wastewater streams (tops-fiber, bobbins thread and fabric dyeing-finishing wastewaters) and composite wastewater were analyzed in terms of quality and quantity. Moreover, raw groundwater, softened process water, cationic ion exchangers’ regeneration wastewater, and reverse osmosis (RO) concentrates were also characterized. Wastewater treatability studies were conducted in pilot-scale employing membrane bioreactor (MBR), nanofiltration (NF) and brackish water reverse osmosis (BWRO) processes at different test conditions. In the wastewater characterization studies, peaks and oscillations were found in the separate wastewater streams depending on the production schedules and applied dyeing recipes. Therefore, due to mixing effects of separate streams, it was decided to employ pilot-scale treatability tests on the composite wastewater. In the MBR process, the average chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP), and color removals were 70, 74, 86, 28, 43, and 62%, respectively. In MBR + NF and MBR + RO tests, the removals of all analyzed parameters were 40–99 and 52–99%, respectively. The pH, conductivity, turbidity, color, and TN concentrations in MBR + RO effluent were 7.6–7.8, 57–65 μS/cm, 0.6–1.2 NTU, 25–44 PtCo, and 14–16 mg/L, respectively. In addition, the COD, BOD5 and total hardness values were found under 1 mg/L. The treated water was finally disinfected with ultraviolet (UV) light to ensure microbial safety before reuse in dyeing process. Treated water samples were tested in different dyeing recipes in lab-scale to determine their impacts on woolen textile product quality. Dry-wet rubbing, water fastness, dry-cleaning and alkali-acid perspiration fastness tests were performed on the fabrics dyed with MBR + UV, MBR + NF + UV and MBR + RO + UV effluents and the results were compared with those dyed with process water (softened groundwater). It was found that especially MBR + NF + UV and MBR + RO + UV effluents did not negatively affect product quality. Surprisingly, the color depth was increased in some shades with MBR + UV effluent, possibly due to the presence of already existing salts. Overall, the product quality tests with reclaimed wastewaters exhibited very promising results. Therefore, capital and operational costs were estimated for a potential full-scale wastewater treatment and reclamation plant in the textile mill.