Microfiltration pretreatment

Chlorination of secondary effluent prior to membrane pretreatment may extend membrane run times between clean. Over 90 h of MF operation was achieved with prechlorinated secondary effluent compared to 42 h operation reported when secondary effluent was not chlorinated (72,73). Similar observations were reported with dosage of chloramine prior to microfiltration pretreatment (77). It was speculated that preoxidation due to chlorination altered the chemistry of extracellular polymeric substance (EPS) produced by the microorganisms in the secondary effluent. This could weaken the attachment of the EPS on the membrane and thus offset the detrimental effect on the membrane flux. However, care must be taken to verify compatibility of membrane with chlorination as some membranes are not tolerant to the aggressive action of chlorine. 

Pretreatment For most membrane applications, particularly for RO and NF, pretreatment of the feed is essential. If pretreatment is inadequate, success will be transient. For most applications, pretreatment is location specific. Well water is easier to treat than surface water and that is particularly true for sea wells. A reducing (anaerobic) environment is preferred. If heavy metals are present in the feed even in small amounts, they may catalyze membrane degradation. If surface sources are treated, chlorination followed by thorough dechlorination is required for high-performance membranes [Riley in Baker et al., op. cit., p. 5-29]. It is normal to adjust pH and add antisealants to prevent deposition of carbonates and siillates on the membrane. Iron can be a major problem, and equipment selection to avoid iron contamination is required. Freshly precipitated iron oxide fouls membranes and reqiiires an expensive cleaning procedure to remove. Humic acid is another foulant, and if it is present, conventional flocculation and filtration are normally used to remove it. The same treatment is appropriate for other colloidal materials. Ultrafiltration or microfiltration are excellent pretreatments, but in general they are... 

Microfiltration (MF) and ultrafiltration (UF) membranes can be used as forms of pretreatment for nanofiltration (ISIF) or reverse osmosis (RO) desalination processes. Membrane pretreatment reduces the amount of chemicals that are required and hence reduces the environmental impact of the final discharge. MF membranes can be used to filter particles with diameters of 0.1-10 pmm and typically remove bacteria, viruses, precipitates, coagulates and large colloidal particles. UF can remove particles with diameters as small as 0.002 pm, and... 

Colloidal materials present in surface waters can also plug RO membranes, causing a decrease in permeate flux. Colloidal plugging can be avoided by using one of several possible pretreatment steps. Ultrafiltration (qv) (UF) or microfiltration (MF), depending on the size of the colloid, can be used to filter out the colloidal material. Alternatively, a coagulant such as alum can be added to the water to form aggregates of the colloid, which can then be filtered in a similar manner as suspended solids. 

Microfiltration - pLTRAFILTRATION] (Vol 24) -hollow-fiber technology [HOLLOW-FIBERMEMBRANES] (Vol 13) -pretreatment for membrane feed [REVERSE OSMOSIS] (Vol 21)... 

Among the numerous approaches studied so far to minimize such phenomena in ED, it is worth citing pretreatment of the feed solution by coagulation (De Korosy et al., 1970) or microfiltration (MF) or ultrafiltration membrane processing (Ferrarini, 2001 Lewandowski et al., 1999 Pinacci et al., 2004), turbulence in the compartments, optimization of the process conditions, as well as modification of the membrane properties (Grebenyuk et al., 1998). However, all these methods are partially effective and hydraulic or chemical cleaning-in-place (CIP) is still needed today, thus... 

Microfiltration, ultrafiltration, and nanofiltration are becoming standard in feed pretreatment for water desalination, wastewater treatment and fruit-juice concentration. 

Membrane pretreatment includes microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF). Microfiltration and UF membrane processes can remove microbes and algae. However, the pores of MF and UF membranes are too large to remove the smaller, low-molecular weight organics that provide nutrients for microbes. As a result, MF and UF can remove microbes in the source water, but any microbes that are introduced downstream of these membranes will have nutrients to metabolize. Therefore, chlorination along with MF and UF is often recommended to minimize the potential for microbial fouling of RO membranes. The MF or UF membranes used should be chlorine resistant to tolerate chlorine treatment. It is suggested that chlorine be fed prior to the MF or UF membrane and then after the membrane (into the clearwell), with dechlorination just prior to the RO membranes. See Chapter 16.1 for additional discussion about MF and UF membranes for RO pretreatment. 

In this chapter, the impact of other membrane technologies on the operation of RO systems is discussed. Technologies considered include microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) as pretreatment to RO, and continuous electrodeionization (CEDI) as post-treatment to RO. This chapter also describes the HERO (high efficiency RO—Debasish Mukhopadhyay patent holder, 1999) process used to generate high purity water from water that is difficult to treat, such as water containing high concentrations of silica. 

Microfiltration as pretreatment to RO is used for bulk removal of suspended solids and bacteria. Microfiltration is a barrier technology that can in many cases replace conventional clarification and filtration. Advantages of MF over conventional clarification and filtration include the following ... 

In many cases, additional pretreatment is required prior to the HERO process. Additional pretreatment can include cold lime softening, sodium softening, and ultrafiltration or microfiltration. These pretreatment unit operations are required when the total hardness is very high and/or the concentration of suspended solids is high. 

Zhu, B.T., Cliford, D.A., Chellam, S. (2005). Comparison of electrocoagulation and chemical coagulation pretreatment for enhanced virus removal using microfiltration membranes. Water Res. 39, 3098-3108. 

Chakravorty, B. and A. Layson (1997). Ideal feed pretreatment for reverse osmosis by continuous microfiltration. Desalination Int. Symp. Pretreatment of Feedwater for Reverse Osmosis Desalination Plants, March 31-April 2, 110,1-2,143-150. Elsevier Science B.V., Amsterdam, Netherlands. 

Surface water can also be processed to become drinking water but it requires some pretreatment prior to the microfiltration step. A filtrate flux of 1,000-1,500 L/hr-m can be realized [Guibaud, 1989]. 

Kokugan K and Kokugan T. The effect of molasses pretreatment by ceramic microfiltration membrane on ethanol fermentation. 

Karleskind D, Laye I, Mei FI, and Morr CV. Chemical pretreatment and microfiltration for making delipidized whey protein concentrate. J. Pood Sci. 1995 60(2) 221-226. 

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