Microfiltration water treatment

Filtration (water treatment) Refers to the physical separation of particles, colloids, or other contaminants from water by passing the liquid through permeable or semipermeable materials (compare with microfiltration, nanofiltration, reverse osmosis, and ultrafiltration). 

In the last few years, a third type of microfiltration operating system called semi-dead-end filtration has emerged. In these systems, the membrane unit is operated as a dead-end filter until the pressure required to maintain a useful flow across the filter reaches its maximum level. At this point, the filter is operated in cross-flow mode, while concurrently backflushing with air or permeate solution. After a short period of backflushing in cross-flow mode to remove material deposited on the membrane, the system is switched back to dead-end operation. This procedure is particularly applicable in microfiltration units used as final bacterial and virus filters for municipal water treatment plants. The feed water has a very low loading of material to be removed, so in-line operation can be used for a prolonged time before backflushing and cross-flow to remove the deposited solids is needed. 

Beginning in about 1990, the first microfiltration/ultrafiltration plants were installed to treat municipal surface water supplies [14,15], The driver was implementation of an EPA surface water treatment rule requiring all utilities in the United... 

Cross-flow filtration is also referred to as tangential flow filtration or microfiltration, but all three terms refer to a process by which membranes are used to separate components in a liquid solution (or suspension) on the basis of their size. The development of robust membranes in polymeric and ceramic materials has provided a powerful new technology for bioseparations, which is already widespread in the process industries as well as for water treatment processes. 

Davies, W. J., M. S. Le, and C. R. Heath (1998). Intensified activated sludge process with submerged membrane microfiltration. Water Science and Technology Wastewater Industrial Wastewater Treatment, Proc. 199819th Biennial Conf. Int Assoc, on Water Quality. Part 4, June 21-26, Vancouver, Canada, 38, 4-5, 421 28. Elsevier Science Ltd., Exeter, England. 

Membrane filters are made in a wide variety of pore sizes (Fig. 1). The effective pore size for membranes vary, and membranes can be used in reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF). RO membranes are widely used in water treatment to remove ionic contaminations from the water. These membranes have an extreme small pore size and, therefore, require excellent pretreatment steps to reduce any fouling or scaling of the membrane, which would reduce the service lifetime. RO membranes are used by extensive pressures on the upstream side of the filter membrane to force the liquids through the pores. 

Nanofiltration is one of promising technologies for the treatment of natural organic matters and inorganic pollutants. Low-pressure operation of nanofiltration is possible [115, 116]. The nanofiltration system, which has a pretreatment process of microfiltration or ultrafiltration, may be applicable to drinking water treatment. 

Eor water-treatment processes such as drinking water or potable water production, reverse osmosis (desalination), nanofiltration, and ultrafiltration are mainly used. In these processes often a microfiltration stage is implemented as the first cleaning stage for the removal of dissolved organic matter, colloids and particles from the source. 

In this chapter, membrane filtration in water treatment is reviewed. The aim is to assess the current status and reveal gaps in knowledge firom the wealth of literature. The background on models and principles is summarised for the relevant processes microfiltration (MF), ultrafiltration fUFJ, and nanofiltration (NF). Reverse osmosis is brifily considered to put NF, which is often described as a process "in between" UF and RO, in perspective. 

Johnson W.T. (1999), Recent advances in microfiltration for drinking water treatment, AVCWA Annual Meeting, Chicago, June 99. 

Membrane operations in water treatment processes include (in order of decreasing pore size) microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. In general, microfiltration and ultrafiltration would have little effect on the removal of transformation products due to their relatively large pore... 

Huang et al. [19] explains that based on the operating transmembrane pressure, membranes for water treatment use can be broadly classified as high pressure and low pressure. The latter are operated at relatively low transmembrane pressures (less than 1-2 bar, typically) and include microfiltration (MF) membranes and UF membranes. With pore sizes ranging from 10 to 100 nm, low-pressure membranes are effective in removing suspended solids and particulates to reduce turbidity and pathogens, but they are not effective for substances such as organic micropollutants. 

Hemodialysis/hemofiltration alone had sales of over US 2200 million in 1998. Reverse osmosis (RO), ultrafiltration (UF) and microfiltration (MF) together accounted for 1.8 billion dollars in sales in 1998. At that time about US 400 million worth of membranes and modules were sold each year worldwide for use in reverse osmosis. About 50% of the RO market was controlled by Dow/FihnTec and Hydranautics/Nitto. They were followed by DuPont and Osmonics. Membranes are apphed during sea-water desahnation, municipal/ brackish water treatment and in the industrial sectors. The market for RO and nanofiltration is growing at a rate higher than 10%/year. The market for desali-... 

Microfiltration tertiary treatment units and bioreactors capture more than 50% of the new water treatment plant market. 

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