A comparitive evaluation of membrane bioreactor technology at Darvill Wastewater Works
Thesis (MEng)--Stellenbosch University, 2017.
ENGLISH SUMMARY: Water scarcity is one of the overriding concerns of the 21st century. Improving wastewater treatment is a relatively cost-effective solution that reduces strain on the available water supply. Reducing and improving the quality of wastewater discharges should be at the forefront of integrated water management. The aim of the research was to investigate the ability of different Membrane Bioreactor (MBR) configurations to treat municipal wastewater to a standard above that achieved by conventional processes. The research objective was to install two MBR pilot plants with different configurations to run parallel (using the same influent wastewater) to the Darvill Wastewater Works (WWW). The performance of the two MBR pilot plants and the Darvill WWW is compared in terms of their treatment efficacy and performance reliability. A number of MBR comparative studies have been undertaken internationally, but none in South Africa. The two MBRs tested (Toray and Norit) have previously been pilot tested on municipal sewage by other researchers and therefore the results from these studies have proved useful for comparing performance. The MBR pilot plants were operated for an extended period of one year in order to take into account seasonality and variability of influent quality. Samples of influent and effluent were taken and analysed on a daily basis. The Darvill WWW is currently operational so these samples were already taken on a routine basis. The performance of the MBR pilot plants and Darvill WWW were compared by analysing the effluent water quality data using statistical techniques (t-test and F-test). A reliability analysis was also undertaken to determine performance against set water quality discharge standards. Based on the operating experience at Darvill and recorded MBR performance the average flux for the submerged Toray MBR system was 17 lmh, whereas that for the sidestream Norit MBR system was 37.5 lmh. The predicted peak flux for the Toray membrane was 20 lmh whereas for the Norit sidestream membrane it was 45 lmh. The predicted cleaning frequency for the Toray MBR is 5-6 weeks and 7-8 weeks for the Norit MBR. The MBR pilot plants out-perform the conventional activated sludge and secondary clarification process that is operated at the Darvill WWW for all determinands measured with the exception of phosphate removal. The performance of the MBRs could not be separated in terms of treatment efficacy with regard to all determinands as both outperformed the other depending on the determinand measured. The results showed that MBRs produce an effluent water quality that exceeds the capability of the conventional activated sludge process (CASP) operated at the Darvill WWW. The reliability of the MBR pilot plants was also higher than that of the Darvill WWW. MBRs thus have an advantage if compliance with stricter discharge standards is required or if treatment of the effluent for reclamation is the goal.
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