Year

2011

Degree Name

Master of Engineering

Department

University of Wollongong. School of Civil, Mining and Environmental Engineering

Abstract

This project aimed to enhance the removal efficiency of pharmaceutically active compounds (PhACs) by membrane bioreactor treatment. Two chemically different PhACs namely sulfamethoxazole and carbamazepine were selected for the investigation. The performance of a laboratory-scale microfiltration membrane bioreactor (MBR) was continuously examined over a period of 160 days. The first 45 days was under a near anoxic condition, from day 46 onwards, the MBR was operated under an aerobic condition with and without the addition of powdered activated carbon (PAC) and various PhACs loading.

Within the first 45 days, although low specific oxygen uptake rate values indicated that the microbes within the reactor were under stress, the MBR showed excellent performance in terms of reducing the concentration of basic water quality parameters including TOC (>96%), TN (94%), UV-absorbance and turbidity. Furthermore, significant reducing of the selected PhACs sulfamethoxazole (66%) and carbamazepine (68%) under a high loading of 0.75 mg/L.d was accomplished. Of special interest was the unprecedented high removal of carbamazepine, which is a known persistent PhAC. The PhACs removal rate remained unchanged beyond aMLSS concentration of 5 g/L, indicating that biodegradation, in contrast to biosorption, was the main removal mechanism in the MBR. Nevertheless, in line with the relative hydrophobicity (Log D) of the compounds, the cake-layer on the membrane contributed to a 2.5% and 6% additional retention of sulfa methoxazole and carbamazepine, respectively. Possible approaches to mitigate rapid TMP build up due to the inefficient scouring of the membrane under weakly aerated conditions were also discussed.

From day 46 to 160, significant adsorption of sulfamethoxazole and carbamazepine to PAC was confirmed by a series of adsorption tests (adsorption contributed around 40% to the overall removal). In contrast, adsorption of these PhACs to the sludge was negligible. The removal of these compounds in MBR was dependent on their hydrophobicity and loading as well as the PAC dosage. Sulfamethoxazole exhibited better removal rate during operation under no or low (0.1 g/L) PAC dosage. Whenthe PAC concentration in MBR was raised to 1.0 g/L, a sustainable and significantly improved performance in the removal of both compounds was observed - the removal efficiencies of sulfamethoxazole and carbamazepine increased to 82±11 and 92±15% from the levels of 64±7%, and negligible removal, respectively (under anaerobic condition and without any PAC addition). The higher removal efficiency of carbamazepine at high (1.0 g/L) PAC dosage could be attributed to the fact that carbamazepine is relatively more hydrophobic than sulfmethoxazole, which consequently resulted in its higher adsorption affinity toward PAC.

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