Deficiency in the nutrient supply such as nitrogen usually results in activated sludge bulking and this phenomenon often takes place in the industrial wastewater treatment plants with activated sludge process. The effects of nitrogen deficiency on activated sludge bulking were studied specially in some experiments carried out in a sequencing batch reactor fed with brewing process wastewater in this paper. The experimental results showed that the sludge settled properly at an influent BOD/N value of 100/4. When the value of BOD/N was 100/3, filaments had an excessive growth at one time during the reaction process. Afterwards, the number of filamentous bacteria began to reduce and simultaneously an excessive growth of viscous Zoogloea with high percentage of moisture was observed and non-filamentous activated sludge bulking occurred. When the influent BOD/N value was 100/2, the excessive growth of filamentous microorganisms could not be observed at all times and the sludge characterization was similar to the case in which BOD/N value was 100/3. When the value of influent BOD/N was 100/0.94, more serious non-filamentous bulking occurred. Furthermore, the effects of nitrogen deficiency on the nitrogen sources and phosphorus sources utilization rate and the COD removal rate were investigated in the experiments.

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