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The objective of this study was to evaluate the potential of nanofiltration (NF) and ozonation for indirect potable reuse in terms of pharmaceutical residuals. To simultaneously obtain a reasonable retentate volume for further treatment, the tests were performed at a high volume reduction factor (VRF) of 60. The feed to the pilot plant was the effluent from a BNR plant with a final process step of chemical precipitation and rapid sand filtration. Two tests were performed 1) nanofiltration of treated wastewater followed by ozonation and 2) ozonated treated wastewater as feed to NF. Of the 95 pharmaceuticals analysed, three were not removed to the quantification limit, oxazepam in the first test and glibenclamide and ketoprofen in the second. The water quality after the two processes was similar, with an overall removal of pharmaceutical residuals of 99%. There are two advantages of ozonated water as feed to NF-a higher specific flux of 35% and a potential removal of ozonation by-products. The retention of some pharmaceuticals by NF was lower than anticipated, the major removal occurring in the ozonation. A tighter NF or RO is required in order to achieve higher pharmaceutical retention for further treatment of the retentate.

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Several years of trouble-free operation with pre-denitrification at the Himmerfjärden WWTP concerning bulking and foaming have been followed by an unstable period. Two bulking incidents with no foaming by Microthrix parvicella were found to be caused by ethanol addition. Other bulking and foaming occurrences by Microthrix could be correlated to the production of volatile fatty acids in some of the sludge treatment steps. It is possible that a more widespread use in society of washing and cleaning products based on vegetable oils has promoted the ability of Microthrix to compete with floc-forming organisms, especially when ethanol or volatile fatty acids are present.

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