Abstract
The use of C. utilis TISTR No. 5001 as a substitute for bacterial sludge in the SBR system was examined in this study. To stimulate and maintain Candida utilis TISTR No. 5001 as the dominant strain in the SBR system, the initial pH of wastewater had to be controlled in the acidic range (5-6). The laboratory scale SBR system (10-L reactor volume) with C. utilis TISTR No. 5001 (Y-SBR system) operating at 1 cycle/day, ambient temperature (25-29oC), impeller speed of 60 rpm, dissolved oxygen of 2.0-2.5 mg/l and replacement volume of 2.50 L/d, showed the highest COD, BOD5 and total nitrogen (TN) removal efficiencies of 97.2±1.6, 97.6±1.6 and 53.1±0.6%, respectively, with synthetic waste water, SWW (pH5), under an organic loading of 0.45 kg BOD5/m3-d. The effluent NO3 - and effluent NO2 - of the system were only 0.42±0.06 mg/l and 0.05±0.007 mg/l, respectively. The sludge age (SRT) and sludge volume index (SVI) of the system were 19±2.3 days and 72±8.2 ml/g, respectively. The SBR system with a mixed culture of C. utilis TISTR No. 5001 and bacterial sludge (Y-SBS-SBR system) showed high organic removal efficiencies of higher than 95% with both acidic-SWW and alkaline-SWW. Furthermore, it showed the highest total nitrogen (TN) removal efficiency with SWW (pH 5). The TN removal efficiency with SWW (pH 8) under the lowest organic loading of 0.13 kg BOD5/m3-d was only 22.1±10.2%, while it increased to 35.4±1.0% for SWW (pH 5).
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