Inline coagulation – ultra fi ltration as the pretreatment for reverse osmosis brine treatment and recovery

• Low cost pretreatment for RO brine recovery using inline coagulation-UF method. • Outstanding performance of FeCl3 in foulant removal compared to PACl and ACH. • 55% and N99% of DOC and phosphate removed when FeCl3 was used as the coagulant. • Highest removal of humic substances, building blocks and LMW neutrals using FeCl3.

1) 2) 3) 4) 5) 230/303 nm — protein-like fluorescence, such as tyrosine 230/355 nm — protein-like fluorescence, such as tryptophan 230/407 nm — fulvic acid-like fluorescence 310/353 nm — soluble microbial byproduct-like fluorescence 330/410 nm — humic acid-like fluorescence The fluorescence intensity for the wavelength pairs could provide quantitative information for the corresponding organic matter. According to Fig. 8, FeCl3 targets the removal of almost all the DOC fractions with the highest efficiency among the three coagulants, except for soluble microbial byproducts. FeCl3 exhibited the highest removal efficiency of protein-like fluorescence (Peaks 1 and 2), which had been identified as the tracer in wastewater effluent and this is consistent with the OND signal displayed in Fig. 5 [47]. The reduction of proteinaceous content in treated water is highly recommended because it accounts for 19–25% of We describe the first study of inland RO brine treatment and recovery using inline coagulation-UF as the pretreatment method which potentially requires shorter coagulation time of one minute, smaller footprint and lower operating cost for the treatment system. The following conclusions can be drawn from the present study investigating the performance of three different coagulants for removal of RO foulants. - Inline coagulation-UF with PACl and ACH attained TOC removals of up to 30% and 18% at the optimal pH 6.5. FeCl3 presented the best performance among the three coagulants, achieving up to 55% of TOC removal at optimal pH of 7. Optimal molar dose for the three inorganic coagulants was 0.556 mM as Fe or Al. FeCl3 demonstrated the highest phosphate removal efficiency of N 99% while PACl and ACH could only achieve up to 72% and 50% respectively at 0.556 mM as Fe or Al. FeCl3 also elucidated a relatively high silica removal efficiency of 14%, after ACH with 15%, and PACl displayed the lowest removal efficiency of 7% at the optimum conditions. - FeCl3 showed the highest removals of nearly all the DOC fractions, namely humic substances, building blocks and LMW neutrals in contrast to the other two coagulants as well as proteins as illustrated in the EEM spectra. This suggests that the use of FeCl3 in the inline coagulation-UF process is highly recommended because the removal of low molecular weight DOC and proteinaceous material could potentially reduce the fouling tendency in the downstream RO process. - These results provide a basis for the selection of coagulants for the inline coagulation-UF pretreatment of RO brine which could potentially be useful in the mitigation measures of brine handling for inland water reuse plants. This study also provides information on the optimal operating conditions for each particular coagulant in order to obtain the required water quality suitable for the downstream membrane process and a database for the pilot study in the next step.