Dechlorination membrane performance

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... 

As remarkable as the performances of these membranes are, aU aromatic PA membranes have one severe drawback their susceptibility to degradation by chlorine. The removal of chlorine prior to membrane separation by activated carbon, sodium sulphite (Na2S03), or sodium bisulphite (NaHSOa) addition is, therefore, mandatory. Dechlorination by NaHSOs in stoichiometric excess can, however, be ineffective in seawater feed because dissolved oxygen in seawater reacts with the chemical. Further, the absence of chlorine can lead to biofouling that is often irreversible. 

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