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The effect of different modes of cleaning of RO membranes fouled by wastewater treatment plant effluent has been investigated. Characterization of the wastewater effluent revealed the presence of foulants containing carboxylic and phenolic functional groups as well as calcium ions. The chemical cleaning agents, sodium hydroxide (NaOH), ethylenediaminetetraacetic acid (EDTA), sodium dodecyl sulfate (SDS), and sodium chloride (NaCl), were selected as models for alkaline solutions, metal chelating agents, surfactants, and salt cleaning, respectively. Specifically, we examined the impact of a sequence or a combination of two cleaning agents compared to the use of single cleaning agents. Increased cleaning efficiency was demonstrated when two cleaning agents were applied in a certain order and mixture. In particular, it was shown that addition of NaOH can enhance the overall cleaning performance when introduced with other chemical agents, due to its ability to loosen the fouling layer. Cleaning efficiency as high as 94% was obtained by simply increasing the pH of an NaCl cleaning solution, compared to 65% in the case of the individual salt solution with no pH adjustment. On the other hand, combining chemical cleaning agents was not advantageous in some cases, possibly because of the competing cleaning mechanisms of some of the agents. The most and the least effective cleaning modes were highlighted, suggesting a rationale for the design of chemical cleaning of RO membranes fouled by wastewater effluent. This study demonstrates that careful selection of cleaning agents and the steps through which those agents are applied allows the regeneration of high water productivity after fouling while minimizing both the cleaning time and the amount of chemicals.

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A two-year comprehensive advanced oxidation processes (AOPs) pilot test was completed for a Singapore waterworks in 2011–2013. This study focused on oxidative removal of spiked organic contaminants with ozone and ozone-based AOPs (ozone application together with hydrogen peroxide, which is necessary for AOPs). The ‘optimized H2O2 dosage’ test philosophy was verified during the test period – keeping the residual ozone at 0.3 mg/L in the water for disinfection purpose by minimizing the H2O2 dosage. This study also monitored the bromate concentration in both ozone- and AOP-treated water, and all the samples reported below the laboratory detection limit (<5 µg/L), which is also lower than the WHO Guidelines for Drinking Water Quality (<10 µg/L). For comparison, a low pressure UV-based AOP test was conducted in the final stage of the study. The electrical energy per order (EEO) value is compared with ozone- and UV-based AOPs as well. The results indicated that ozone-based AOP with an optimized hydrogen peroxide dosage could be the most energy efficient option for this specific water matrix in terms of most selected compounds.