Efficient removal of natural organic matter from drinking water for reducing disinfection by-products

Tafvizi, Hoda (2022) Efficient removal of natural organic matter from drinking water for reducing disinfection by-products. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Chlorine as a low-cost bactericide has been used for more than a century for the disinfection of drinking water. However, the contact between chlorine-based disinfectants and natural organic matter (NOM) leads to the production of hazardous disinfection by-products (DBPs). Trihalomethanes (THMs) and haloacetic acids (HAAs) as two groups of regulated DBPs by U.S. EPA and Health Canada have been of concern in the last two decades for the water treatment facilities around the world, specifically small communities of Newfoundland. Enhanced coagulation (EC) and adsorption with activated carbon (AC) are two recommended methods by U.S. EPA for the removal of NOM. Although many studies have tested these methods in full scale and lab scale for the removal of dissolved organic carbon as the main precursor of THMs and HAAs, certain environmental factors in NL (e.g., seasonal variations) and treatment factors (i.e., fast mixing and settling time in EC, and aluminum coating in AC) have not been considered so far. This research aims to (i) examine the effect of five factors of pH, coagulant dosage, coagulant type, fast mixing speed, and settling time simultaneously on the removal of DBPs rather than DOC. (ii) establish prediction models for the removal of DOC and reduction of THMs and HAA5 based on NL water characteristics. (iii) decrease the power consumption of EC. (iv) to reduce the coagulant dosages (v) improve the mesoporosity of activated carbon for NOM removal by chemical activation using nitric acid and physical activation, (vi) enhance the removal of DOC and humic acids by surface charge modification through metal impregnation, (vii) study the efficient removal of NOM by combination of EC and AC (viii) study the variations of NOM characteristics in four communities of NL over two years. (ix) to figure out the most crucial factors affecting the production of HAA5 and THM4. The results of this research on EC confirmed that optimization of EC parameters based on THMs and HAAs reduction, reduced the dosage of coagulant from 6.51-7.85 mg/mg DOC for DOC to 3.83-5.95 mg/mg DOC. Moreover, the energy consumption in the fast-mixing stage was reduced by 59.8%. The fly ash of pulp and paper company in corner brook was used to produce AC. Nitric acid at 10% concentration increased the Brunauer, Emmett and Teller (BET) surface area and pore width of the developed AC in comparison with chemical treatment with nitric acid at 5% concentration. Moreover, metal impregnation with 0.75% Fe and 1.00% Al enhanced the THM4 and HAA5 reduction by 33-44%. The investigation on the NOM characterization in four sources of drinking water in NL over two years revealed that very hydrophobic acid NOM and neutral hydrophilic are the main contributors to the production of HAA5 while very hydrophobic acids (VHAs) are the main precursors of THM4. The highest level of DOC was observed in summer and the highest contributor to the NOM content was VHAs in all seasons.

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