Comparison of pre-treatment technologies towards improving reverse osmosis desalination of cooling tower blow down

• CTBD of high DOC shows to be challenging for membrane treatment.
• Membrane based desalination of CTBD is affected by pre-treatment conditions.
• PAC dosage proves beneficial for membrane filtration performance on CTBD.

The suitability of three different pre-treatment technologies namely powdered activated carbon (PAC) adsorption, coagulation with ferric chloride and ultrafiltration (UF) as pre-treatment to reverse osmosis (RO) desalination of a cooling tower blow down (CTBD) was investigated. Special attention was paid to the capability of the pre-treatment options to remove dissolved organic carbon (DOC) from the CTBD by applying advanced DOC characterization. Furthermore, the direct effect on the performance of reverse osmosis (RO) desalination was investigated.Advanced DOC analysis showed clear differences between the pre-treatment technologies in removal of total DOC and in removal of certain DOC fractions. By investigation of RO normalized flux decline after different pre-treatments an improvement of 10–20% by UF treatment and an additional improvement of 10–20% by PAC/UF treatment were found in comparison to RO performance on not pre-treated CTBD. The achieved results indicate the negative influence of chemical additives in the CTBD matrix on RO fouling and performance as well as pre-treatment efficiency.With PAC/UF pre-treatment resulting in the least fouling development the normalized flux decline remained high with roughly 40%–50% over 5 days of RO operation indicating the challenging nature of high DOC CTBD treatment for re-use.

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