Removal of dissolved organic matter in municipal effluent with ozonation, slow sand filtration and nanofiltration as high quality pre-treatment option for artificial groundwater recharge

In the paper the combination process of ozonation, slow sand filtration (SSF) and nanofiltration (NF) was investigated with respect to dissolved organic matter (DOM) removal as high quality pre-treatment option for artificial groundwater recharge. With the help of ozonation leading to breakdown of the large organic molecules, SSF preferentially removes soluble microbial by-product-like substances and DOM with molecular weight (MW) less than 1.0 kDa. NF, however, removes aromatic, humic acid-like and fulvic acid-like substances efficiently and specially removes DOM with MW above 1.0 kDa. The residual DOM of the membrane permeate is dominated by small organics with MW 500 Da, which can be further reduced by the aquifer treatment, despite of the very low concentration. Consequently, the O3/SSF/NF system offers a complementary process in DOM removal. Dissolved organic carbon (DOC) and trihalomethane formation potential (THMFP) can be reduced from 6.5 ± 1.1 to 0.7 ± 0.3 mg L−1 and from 267 ± 24 to 52 ± 6 μg L−1, respectively. The very low DOC concentration of 0.6 ± 0.2 mg L−1 and THMFP of 44 ± 4 μg L−1 can be reached after the aquifer treatment.

Research highlights
► The O3/SSF/NF process provides a high quality pretreatment for groundwater recharge.
► This process reduces DOC from 6.54 mg L−1 to 0.69 mg L−1 and THMFP from 267.2 μg L−1 to 52.0 μg L−1.
► This process also offers reciprocal DOM removal by SUVA, EEM and HPSEC analysis.