Physicochemical and biological treatment of a textile dyeing and finishing wastewater
Wastewaters from textile dyeing and finishing industries are often high in color, organic matter, metals and toxicity. Treatment is usually required before discharge into a sewer or body of water. Pretreatment often consists of chemical coagulation to remove color and solid matter. Aerobic biological treatment is incorporated to remove degradable organic matter and additional color and solid matter.
The wastewater studied in this research project consisted of thermosol dye, print, and bleach and finish waste streams. The goal of this research project was to continue work on this wastewater that was initiated by Weber (1994). Pretreatment experiments were performed on the bleach and finish stream in an attempt to reduce organic content. Also, bench scale, aerobic biological reactors were operated at hydraulic residence times (HRT) of 4 and 7 days, to determine if higher reductions in color, organic matter or solids would be seen compared to Weber’s results from the 3 day HRT operation. Toxicity tests were performed on reactor effluents to determine if toxicity remained after treatment was performed.
The bleach and finish did not respond favorably to the majority of pretreatments. An 84% color reduction was produced with adjustment of the pH to 4.5 and chemical coagulation with 400 mg/L of a blend of inorganic aluminum and a polyamine (AL220; Polymer Systems, Inc.). A 65% reduction in COD resulted from coagulation using 100 mg/L of Nalco polymer 9764, a polyamine.
The bench scale reactors were-operated at sludge ages of 15, 20 and 30 days and hydraulic residence times of 4 and 7 days. The 4 day HRT COD removal results were similar to Weber’s (1994) results, while the 7 day HRT operation resulted in COD removals of 89 to 92%. Analysis of the steady state data produced kinetic coefficient values K₆, k, Y and k𝖽 for the 7 day operation of 2.6 mg/L, 0.16 day⁻¹, 0.74, and 0.05 day⁻¹.
Toxicity tests performed on effluent from the 7 day HRT operations were passed. Short term chronic tests, using Pimephales promelus, resulted in No Observed Effect Concentrations of 100%. Acute tests, using Ceriodaphnia dubia, yielded LC50 values of greater than or equal to 100%.