Membrane cleaning chlorine

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. 

Particular attention was devoted to the control of membrane fouling and membrane cleaning. Acid-alkaline washing was tested and low concentration chlorine solutions were also used. The recovery of initial fluxes was generally 50% with the new modulus, and higher then 95% with a used modulus. These results indicate the existence of a certain irreversible fouling of the new membranes, which come to steady state values, and does not increase with membrane reuse. 

Tessaro, I. C., Da Silva, J. B. A., and Wada, K. 2005. Investigation of some aspects related to the degradation of polyamide membranes Aqueous chlorine oxidation catalyzed by aluminum and sodium lauryl sulfate oxidation during cleaning. Desalination 181 275-282. 

Kim, Y.W., Hong, Y.K. and Hong, W.H. 2001. Removal of chlorinated organic componnds using crosslinked PDMS membrane. Clean Technol. 7(3) 195-202. 

Microbial fouling is best dealt with before biofilm becomes mature. Biofilm protects the microorganisms from the action of shear forces and biocidal chemicals used to attack them. Microbes can be destroyed using chlorine, ozone, ultraviolet radiation, or some non-oxidizing biocides (see Chapters 8.2.1, 8.2.2, and 8.1.8). An effective method to control bacteria and biofilm growth usually involves a combination of these measures. Specifically, chlorination or ozonation of the pretreatment system, followed by dechlorination to protect the membranes, or UV distraction followed by periodic disinfection with a non-oxidizing biocide used directly on the membranes to keep the membranes clean. 

Thermoplastics. There are five elastomeric membranes that are thermoplastic. Two materials, chlorinated polyethylene (CPE) and polyisobutylene (PIB), are relatively obscure. Thermoplastic materials can be either heat-fused or solvent-welded. In contrast to Hypalon and uncured EPDM, this abiHty to fuse the membranes together remains throughout the life of the material. However, cleaning of the membrane surface after exposure to weather is required. Correct cleaning procedures for specific membranes are available from the individual manufacturer. 

Chemical attack is often a result either of fouling prevention or cleaning in response to fouling. Chlorine and hypochlorite damage most RO and NF membranes, as do oxidants generally (see discussion of chlorine tolerance below). 

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... 

R/0 unit Reverse Osmosis Unit for water purification in small aquariums and miniature yard-ponds, utilizes a membrane under pressure to filter dissolved solids and pollutants from the water. Two different filter membranes can be used the CTA (cellulose triacetate) membrane is less expensive, but only works with chlorinated water and removes 50-70% of nitrates, and the TFC membrane, which is more expensive, removes 95% of nitrates, but is ruined by chlorine. R/0 wastes water and a system that cleans 100 gallons a day will cost ft-om 400 to 600 with membrane replacement adding to the cost. A unit that handles 140 gallons a day will cost above 700,00. 

RO membranes can be fouled or damaged. This can result in low flow or holes in the membrane and passage of the concentrated solution to clean water, and thus a release to the environment. In addition, some membrane materials are susceptible to attack by oxidizing agents, such as free chlorine. 

The SBP slurry-phase bioremediation system can treat a wide range of organic contamination, especially wood-preserving wastes and solvents. A modified version can also treat polynuclear aromatic hydrocarbons (PAHs) such as creosote and coal tar pentachlorophenol (PCP) total petroleum hydrocarbons (TPH) and chlorinated aliphatics, such as trichloroethene (TCE). The technology can be combined with SBP s membrane filtration system to form a soil cleaning system to handle residuals and contaminated liquids. 

Sterilization of a membrane system is also required to control bacterial growth. For cellulose acetate membranes, chlorination of the feed water is sufficient to control bacteria. Feed water to polyamide or interfacial composite membranes need not be sterile, because these membranes are usually fairly resistant to biological attack. Periodic shock disinfection using formaldehyde, peroxide or peracetic acid solutions as part of a regular cleaning schedule is usually enough to prevent biofouling. 

Most chemical cleaning protocols consist of an alkali detergent step followed by an acid step, with appropriate rinses in between. However, for polymeric membranes, it is also common to follow the acid cleaning step with a second alkali cleaning step supplemented with chlorine as this further improves flux [176,179]. In some cases, acid cleaning has been recommended as the first step, especially for whey applications, where mineral fouling maybe more important than protein fouhng [176]. 

Plants are cleaned, sanitized, and rinsed immediately after processing, and right before processing to ensure satisfactory initial process conditions from microbiological standpoint [3]. Because chlorine is freely permeable to most membranes that it is able to sanitize the permeate side of the system as well as the retentate side, using solutions of sodium hypochlorite containing 100-200 ppm of active chlorine is a common sanitation technique for many membranes, except cellulose acetate reverse osmosis membranes, which can only tolerate brief exposure to chlorine at 10-50 ppm level [3]. 

Chlorine gas, released during the use of hypochlorite, can cause mucous membrane irritation, bronchospasm, pneumonia, and pulmonary edema. It is beheved that when hypochlorite is used as a cleaning substance in low concentrations it does not cause respiratory damage, but in a comparison of pulmonary function tests in 23 cleaning workers and 14 technical personnel, as a control group, even low concentrations of hypochlorite affected pulmonary function, causing irritation in the airways (8). 

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