Combined anaerobic-aerobic treatment of a simulated textile effluent
This work aimed to treat a simulated textile effluent (STE) with combined anaerobic­ aerobic treatment. A simple simulated cotton processing effluent was generated that was similar to real effluents in terms of COD, BOD, COD:BOD, pH and TSS. An upflow anaerobic sludge blanket reactor (UASB) was more effective in treatment of STE than an inclined tubular digester (ITD) as it treated larger volumes of effluent and showed superior colour removal. Coagulation/flocculation was investigated as a pre-treatment but was found to be unsuitable. It was also aimed to discover whether amines were produced during anaerobic treatment, and if so, were they degraded anaerobically. Anaerobic treatment reduced the COD load to the aerobic stage and thus reduced the quantity of aerobic sludge produced. However, aerobic treatment alone removed a quantity of COD comparable to that achieved by combined treatment. Unlike anaerobic treatment, aerobic treatment alone did not remove colour. When step increases in load were carried out, or when the UASB was not operating at its optimum, the aerobic stage removed excess anaerobic effluent COD. It was necessary to adjust the activated sludge stage to pH 7 and to feed it a concentrate of OECD synthetic sewage in order to maintain the MLSS. The treatment efficiency of the combined anaerobic-aerobic system remained constant despite intervening step changes indicating that the system could tolerate such changes without any alteration in effectiveness of operation. The optimum starch:dye ratio for overall colour removal varied with the dye concentration present in the STE. At the same dye concentration the presence of extra starch greatly increased colour removal. It was therefore recommended that if colour removal efficiency decreases, starch to the maximum volumetric loading rate of UASB be added. A combination of HPLC-UV, Total Organic Nitrogen analysis and respiration inhibition tests indicated that anaerobic degradation of the dye used in this STE produced aromatic amines that were removed aerobically. As the amines were degraded aerobically, some aerobic COD removal was due to their degradation.
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