Proposal for the Use of Fouling Potential in Water Purification andApplication of a Submerged Membrane Filtration System

Abstract

This paper presents our proposed fouling potential (FP) as an index measuring the quality of membrane feed wateras well as an application of a submerged membrane filtration system using an existing sedimentation tank in the renew-al of a water treatment plant.FP gives the organic fouling potential of membrane feed water through simple laboratory–scale membrane filtrationtesting. The value of FP varies depending on the raw water type, including river water, lake water, and groundwater. Ittends to agree with empirical criteria for the determination of membrane permeate flux and is anticipated to reflect thefouling characteristics of raw water. At the same time, FP correlates less well with typical organic matter indices (DOCand UVA260), which thus cannot provide an estimation of FP. This fact suggests that the organic matter indices, such asDOC, are not necessarily appropriate for the evaluation of irreversible membrane fouling during water purification. FParises dominantly from high molecular materials with a molecular weight of 100 kDa or more in membrane feed water;therefore, this group of materials may significantly affect membrane fouling during water purification.Upon renewal of water treatment plants, a space–saving submerged membrane filtration system allows the use of anexisting confined tank, e.g., a sedimentation tank or a filtration tank, as a membrane–submerged tank. Compared tothe construction of new water treatment plants, the use of an existing tank is expected to reduce the huge costs associ-ated with the securing of a site and the re–installation of large diameter water transmission/distribution pipes. It mayalso reduce construction waste by eliminating the installation of a new membrane–submerged tank or the demolition ofan existing water treatment plant. A submerged membrane filtration system operating at low trans–membrane pres-sure can replace existing processes to allow for membrane filtration by gravity flow due to the water level differencebetween the receiving well and the treated water reservoir, as is the case with conventional rapid filtration systems.Depending on the design membrane permeate flux, the submerged membrane filtration system can perform membranefiltration based only on the water level difference and without consuming power even during low water temperatureperiods or in the presence of irreversible membrane fouling, thus contributing to significant operational energy savings.