Pretreatment and biodegradation of wastewater from a textile dyeing and finishing industry

Abstract

Pretreatment is a common approach for removing color and reducing the organic load of textile dyeing and finishing wastewater. Subsequent aerobic treatment is often employed to complete organic removal as well as remove toxicity and metals. The wastewater from the textile dyeing and finishing industry studied was not treated efficiently and often failed effluent toxicity and metals tests. In this research project, various pretreatment alternatives were studied in an attempt to identify the most efficient and economical method(s). Also, aerobic, biological treatment was performed in bench-scale reactors to determine the biological kinetic coefficients of the wastewater so that the overall efficiency and performance of the biological treatment system might be improved. Effluent toxicity of the wastewater was also evaluated in hopes that improved treatment efficiency would yield subsequent improved effluent toxicity. The performance of a sequencing batch reactor was compared to that of the continuous-flow reactors.

In regard to pretreatment with various polymers, coagulation with a blend of inorganic aluminum and a polyamine (AL220, Polymer Systems, Inc.) produced the most economical and efficient results. Subsequent addition of an anionic polymer improved the settling characteristics of the chemical flocs. Color removal ranged from 71-90% and DOC removal averaged 25% with AL220 doses between 400-600 mg/L.

Increased sludge ages (θ_c) of the continuous-flow reactors produced improved removal efficiencies. Sludge ages of 8-30 days resulted in an average of 55-68% COD removal. Kinetic analysis produced values of 0.032 d⁻¹ and 0.619 for k_d, and Y, respectively. K_s and k could not be determined accurately. This difficulty was attributed to possible inhibitory effects and a residual, biorefractory COD that was not quantified in this study.

The SBR, operated with a cycle time of one day and an average MLSS concentration of 4,266 mg/L, achieved an average 69% COD removal and 59% color removal. Addition of nutrients did not appear to improve these efficiencies. Settling characteristics of the sludge were excellent.

Preliminary acute toxicity testing of the SBR effluent and effluent from the 8 day θ_c reactor produced encouraging results. Subsequent chronic toxicity testing of the 15, 20 and 30 day θ_c reactors yielded a maximum No Observed Effect Concentration of 50-75%.