Browsing by Author "Sibiya, Simon Muzi"

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    An investigation into the effect of inline coagulation and air scouring to minimize ultrafiltration membrane fouling
    (Stellenbosch : Stellenbosch University, 2020-12) Sibiya, Simon Muzi; Pillay, Visvanathan Lingamvrthi; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: The quality of raw water is an essential factor that determines the treatment technologies and level of treatment required to attain specified treatment objectives. Water utilities such as Rand Water currently use conventional water treatment processes to purify water to drinking water standards. However raw water quality had been gradually deteriorating due to agricultural and industrial activities and poorly performing wastewater treatment plants. Low-pressure membrane filtration processes such as microfiltration(MF) and ultrafiltration(UF) have become an attractive alternative treatment technology to replace or supplement conventional water treatment for surface waters, as they consistently produce drinking water of high quality. However, the major disadvantage of membrane filtration is membrane fouling. The objective of this study was to determine the effect of coagulant dosage, air scouring rate and the frequency of air scouring on the rate of membrane fouling and final water quality, for Vaal Dam raw water. The investigation into the effect of the polymeric coagulant dosage, air scouring rate and the frequency of air scouring on the rate of membrane fouling was conducted using a bench-scale outside-in hollow fibre PVDF submerged UF module. Firstly, ranges for polymeric coagulant dosage, air scouring rate, and the frequency of air scouring were selected and independently validated using an OFAT approach. These validated ranges were then used in a full factorial design of experiments (DoE). The purpose of conducting the DoE was to determine the combined effects of the factors and factors interactions on the rate of membrane fouling.In the scanning and validation investigation, the rate of membrane fouling reduced by 60% when the polymeric coagulant dosage was in the range of 1 to 8 mg/l, relative to no polymeric coagulant dosage. Excessive polymeric coagulant dosage increased the rate of membrane fouling. The rate of membrane fouling decreased with increasing air scouring rates range of 1 to 5 m3/m2.h. Air scouring rates above 5 m3/m2.h increased the rate of membrane fouling. The rate of membrane fouling reduced with increasing air scouring frequency from 0% to 100%. The air scouring frequency of 0% and 25% resulted in a similar rate of membrane fouling. Similarly, the air scouring frequency of 75% and 100% resulted in a similar rate of membrane fouling. The results from the DoE were analysed with statistical software and a regression model was obtained. This showed that 0 mg/l polymeric coagulant dosage and 10 min off / 10 min on air scouring frequency, irrespective of the air scouring rates resulted in the highest rate of membrane fouling. The treatment combination of 1 mg/l polymeric coagulant dosage, continuous air scouring resulted in the lowest rate of membrane fouling, irrespective of the air scouring rates. A Pareto plot indicated that the polymeric coagulant dosage, followed by the air scouring rate were the most critical factors in reducing the rate of membrane fouling. The frequency of air scouring had a moderate effect on the rate of membrane fouling, while the interaction of the air scouring rate and frequency of air scouring had a marginal effect.