Treatment of Railway Laundry Wastewater through a Chain of Physicochemical Processes and an Aerobic Sequential Batch Reactor

Abstract

This paper introduces a comprehensive approach to treating industrial laundry wastewater collected from a railway laundry, employing a novel unique sequential combination of coagulation–flocculation, neutralization, ultraviolet (UV)-H2O2 treatment, and biological processes. Typical characterization of laundry wastewater reveals high pH, suspended solids, dissolved organic content, and low biodegradability. The researched treatment sequence involved turbidity reduction (65%) using FeCl3 and cationic polyelectrolyte coagulants followed by pH neutralization (7–8), UV-H2O2 treatment [83% and 23% chemical oxygen demand (COD) and biochemical oxygen demand (BOD) removal, respectively) and aerobic biological treatment (88% and 97% for COD and BOD removal, respectively). During the UV-H2O2 process, when the H2O2 dosage exceeded 30 mg·L−1, inefficiency in COD removal was observed owing to the scavenging of hydroxyl radicals. With the increase in flow rate, the COD removal was reduced nominally. The effluent from the UV-H2O2 process was treated by an aerobic sequential batch reactor, demonstrating high efficacy in removing both BOD and COD. The biokinetics parameters, such as half-saturation coefficient (ks), maximum specific rate of substrate utilization (k), yield coefficient (Y), decay rate (Kd), and maximum specific growth rate (µm) were determined, and they were observed to be 130 mg of COD·L−1, 0.3 day−1, 0.9 mg volatile suspended solids/mg COD, 0.055 day−1, and 0.42 day−1, respectively. Overall, a reduction of approximately 95% of COD and 97% of BOD was attained, rendering the wastewater suitable for safe disposal into inland surface waters. This showcases an effective and sustainable method for treating laundry wastewater. The present work deals with the characterization and treatment of industrial laundry wastewater. The typical laundry wastewater is mainly characterized by high suspended solids and chemical oxygen demand (COD) due to nonbiodegradable organics. The biodegradability index of the wastewater was very poor (0.15–0.25), which made it difficult to treat by conventional biological processes. Hence, a treatment chain consisting of coagulation–flocculation–sedimentation, neutralization, ultraviolet-H2O2 advanced oxidation process, and sequential batch reactor (SBR) was used. Alum coagulation at high pH, along with the addition of cationic polyelectrolyte, removed the suspended solids to a great extent. Sulfuric acid was found to be the most efficient to neutralize the wastewater after coagulation. In the UV-H2O2 process, the COD of the wastewater was reduced to < 250 mg·L−1, below the discharge standard specified in the Central Pollution Control Board, India guidelines. However, the biochemical oxygen demand (BOD) was much higher compared to the discharge standard. The biodegradability index increased to 0.8, which indicated that nonbiodegradable organics were converted to biodegradable organics. The BOD of the wastewater was reduced to < 30 mg·L−1 through SBR. The proposed wastewater treatment chain led to an overall 95% of COD and 97% of BOD removal.