Browsing by Author "Deelie, Malcolm"
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- ItemEnergy reduction in a woven-fabric immersed membrane bioreactor(Stellenbosch : Stellenbosch University, 2017-03) Deelie, Malcolm; Pillay, V. L.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH SUMMARY: Most developing countries, including South Africa, currently face a substantial challenge in providing satisfactory sanitation for all its inhabitants. Small-scale sanitation plants have the greatest potential to overcome this challenge, especially for decentralized areas. Currently such systems are available; however these systems are extremely expensive and complicated, especially in terms of the running costs. In recent years there has been a major shift towards immersed membrane bioreactor (IMBR) technology in the wastewater treatment industry due to the advantages that IMBRs offer over conventional wastewater treatment plants. The major hindrance to the implementation of IMBRs in developing economies is due the costliness and the lack of durability of the current membranes being used. A novel woven-fabric microfilter (WFMF) is currently produced in South Africa from woven polyester which resembles the features of a microfilter and harbours the characteristics to make IMBRs sustainable and affordable. An IMBR which makes use of the WFMF is known as the woven-fabric immersed membrane bioreactor (WF IMBR). The overall aim of this study is to reduce the energy consumption in the WF-IMBR to make it an affordable technology. The following are the key objectives of this study: I. Improve the mechanical design of the WFMF membrane module; II. Improve the air-scour regime of the WF-IMBR; To start the investigation, a pilot plant rig was constructed and set-up at Zandvliet wastewater treatment works (WWTW). Preliminary experiments were done to evaluate the WFMF module design and modify it in order to decrease the inherent pressure drop which would reduce the energy consumed to withdraw permeate from the system. By inserting a more rigid spacer and by including two larger permeate outlets the overall pressure drop was decreased by 90%. Experiments were then performed to investigate the effect of different process conditions. A surprising result, which suggested that less fouling occurred when operating the system without scouring the membrane; led to further investigation of this phenomenon on a lab-scale basis. Lab-scale results confirmed this phenomenon and also gave rise to a new operating regime, known as intermittent air-scouring. Across all three activated sludge feeds from different WWTWs investigated, there was a clear indication that operating with intermittent air-scouring and with air scouring resulted in the lowest fouling rate. This was significantly less than operating with continuous air-scouring. Furthermore, increasing the air-scour rate during continuous air-scouring trials resulted in higher fouling rates. A three factor two level factorial experiment was then performed to investigate the effect of the three main parameters which could potentially increase the effectiveness of the intermittent air-scouring regime. Results showed that filtration duration was one of the more important operational parameters during intermittent air-scour trials. It was hypothesised that longer filtration durations allowed for a protective cake layer to form on the membrane surface which kept the membrane clear of organic substances which has a higher fouling potential. Implementing these findings on the pilot plant rig, confirmed intermittent air-scouring to be the most practical and feasible air-scour regime which reduced air-scour costs by 95%. Further investigations should be done to determine an optimum operating point for intermittent air-scour regime on the pilot plant rig.