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UBC Theses and Dissertations

Sludge reduction by mixed liquor ozonation Zheng, Xiaoyu


In this comparative study, a combination of mixed liquor ozone treatment and an enhanced biological phosphorus removal (EBPR) process with long SRT operations (25 d and 50 d) was tested for sludge reduction. An equivalent to about 80% sludge reduction was achieved in an EBPR system with mixed liquor ozonation and with long SRT operation. The effluent quality was not affected with mixed liquor ozonation at SRT = 50 d. Both the control and the ozone-treated systems achieved about 90 ± 1% COD, 99 ± 1 % ammonia, 79 ± 1% inorganic nitrogen, and about 94 ± 1% ortho-phosphorus removal efficiencies at SRT = 50 d. The mixed liquor in both systems hosted a similiar fraction of active organisms. The mixed liquor in the ozonated system exhibited a different composition of the bacteria community compared with that in the control by the Analysis of 16S rDNA. The low diversity of microbial community was observed in the ozonated reactor. The nitrification was not affected in the ozonated system. The specific ammonium removal efficiency was comparable to that in the control. Similar fraction and diversity of nitrifiers were identified in the ozonated system and in the control. The phosphorus removal performance was not adversely affected in the ozonated system at SRT = 50 d. The maximum P-release rate and the maximum P-uptake rate in the ozonated reactor were similar to the control. The heterotrophic decay coefficients in both reactors had no statistically siginficant difference. The maximum specific growth rate in the ozonated system (6.21 ± 0.31 d-¹) was less than that in the control reactor (8.31 ± 0.55 d-¹). The mixed liquor ozonation batch tests indicated that there was an optimum TSS/VSS concentration at which the maximum soluble COD was achieved. Carbonate/bicarbonate addition may reduce the efficiency of sludge disintegration. The solids solubilization was significantly improved under high pH conditions. The zero sludge EBPR SBR process at lab-scale was proposed and tested. The optimum ozone dosage was determined and no inorganic matter accumulation was observed. By the batch P-release and discharge operations, the system maintained P mass balance and no P accumulation were observed.

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