The residual organic matter in conventionally treated drinking waters may be sufficient for the formation of harmful disinfection by-products, and for supporting bacterial growth in distribution networks. Thus, nanofiltration has been proposed as an option for enhancing the organic matter removal from high organic load containing source waters. Given that little is known of the success of nanofiltration in removing residual organic matter from chemically pre-treated and rather pure surface waters, further research was required. In addition, more information was needed regarding fouling, operation, cost and environmental impact of nanofiltration process as a refining phase in surface water treatment. Long-term pilot-scale studies at an operating water treatment plant as well as laboratory-scale test runs using real and model feed waters were employed to evaluate the applicability of the nanofiltration process. Nanofiltration resulted in high and stable removal of organic matter after conventional surface water treatment in all circumstances that were studied. However, the nanofiltered water showed surprisingly high potential for microbial growth, and contained enough microbially available carbon and phosphorus for bacterial growth. Thus, disinfection using small dosage of chlorine is recommended as a safety barrier and for suppressing microbial growth in distribution systems after nanofiltration. In the cases studied, the use of nanofiltration membranes with high organic matter, and lowered inorganic matter retention, optimally met the requirements for treated water quality, as well as for the productivity and fouling of the membranes. However, the studied pre-treated feed waters caused intense flux decline of nanofiltration membranes and required short membrane cleaning intervals at the studied operational parameters. The results of the study also indicate that most feed water constituents, organic material, inorganic precipitates and micro-organisms, affect membrane fouling. Accordingly, it seems impossible to remove the membrane fouling tendency from surface waters. The study supports the consideration of nanofiltration as an efficient and reliable option for improving the quality of conventionally treated surface water in varying circumstances. However, in applications not requiring substantial improvement of organic matter or ion removals other process options may be more suitable and cost effective compared to nanofiltration.
|Tila||Julkaistu - 2006|
|OKM-julkaisutyyppi||G5 Tohtorinväitöskirja (artikkeli)|