NOM characterization and removal at six Southern African water treatment plants

Abstract

Organic pollution is a major concern during drinking water treatment. Major challenges attributed to organic pollution include the proliferation of pathogenic micro-organisms, prevalence of toxic and physiologically disruptive organic micro-pollutants, and quality deterioration in water distribution systems. A major component of organic pollution is natural organic matter (NOM). The operational mechanisms of most unit processes are well understood. However, their interaction with NOM is still the subject of scientific research. This paper takes the form of a meta-study to capture some of the experiences with NOM monitoring and analysis at a number of Southern African Water Treatment Plants. It is written from the perspective of practical process selection, to try and coax some pointers from the available data for the design of more detailed pilot work. NOM was tracked at six water treatment plants using dissolved organic carbon (DOC) measurements. Fractionation of the DOC based on biodegradability and molecular weight distribution was done at a water treatment plant in Namibia. A third fractionation technique using ion exchange resins was used to assess the impact of ozonation on DOC. DOC measurements alone did not give much insight into NOM evolution through the treatment train. The more detailed characterization techniques showed that different unit processes preferentially remove different NOM fractions. Therefore these techniques provide better information for process design and optimisation than the DOC measurement which is routinely done during full scale operation at these water treatment plants

Reversibility of fouling on ultrafiltration membrane by backwashing and chemical cleaning: differences in organic fractions behaviour

“…The LMWA fraction was always found below limit detection. This composition is in accordance with previous studies that also applied HPSEC for the fractionation of NOM after sand filtration of river water [33,34]. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 finding is in agreement with Peter-Varbanets et al [35], who also observed that "only biopolymers and the humic acid fraction of NOM were retained to some extent during filtration" of different types of water.…”

Substitution of conventional pre-treatment units by membrane based processes in drinking water treatment

“…The LMWA fraction was always found below limit detection. This composition is in accordance with previous studies that also applied HPSEC for the fractionation of DOC in drinking water plants (Haarhoff et al, 2010, Velten et al, 2011. The removal of TOC by the UF membrane was 10%, while the corresponding one for DOC was fairly low (4%).…”

Making Rainwater Harvesting a Key Solution for Water Management: The Universality of the Kilimanjaro Concept

“…For low-income communities, the extended Kilimanjaro Concept should strive for a disinfectant-free water supply. This is because, chlorination, which is widely recommended by the WHO is not really affordable, and reacts with organic matter in water to form trihalomethanes, which are carcinogenic [71,72]. In cases, where contamination of rainwater with pathogenic microbes is expected or suspected, stored water can be intermittently heated (e.g., once per week) to about 80 degrees and kept for some 10 minutes at this temperature (pasteurization).…”

“…However, in the case of the East The harvesting and storage of both rainwater and stormwater enable the subsequent conjunctive use of both water resources. On the one hand, subject to its quality, clean rainwater can be used for drinking water provision in its raw state or after affordable treatment [72][73][74][75]. On the other hand, stormwater, which is likely to be contaminated by anthropogenic pollutants, can be used for livestock watering and irrigation of household nutritional and herbal gardens [76].…”