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Dissolved air flotation (DAF) is a widely used treatment process in drinking water and wastewater treatment plants despite high energy cost associated with operation and maintenance (accounts 50% of the total annual operation cost). In recent years, the focus has been diverted to optimizing or reducing energy, and a microbubble generation without a saturator was developed and used in small treatment facilities because of its simple structure. Thus, in this study, DAF and low-energy flash-pressurized flotation (FPF) efficacies were investigated in a pilot plant based on organic precursors, different molecular weight (MW) fractions, and disinfection byproduct reduction. The organic fractions with different MW was analyzed by liquid chromatography-organic carbon detector. Both DAF (550 kPa) and FPF (300 kPa) showed similar removal of dissolved organic carbon (DOC) and chromatographic DOC; however, the removal tendency of different MW fractions found was different. There was no significant difference in the removal of biopolymers, building blocks, and low molecular weight (LMW) neutrals for both DAF and FPF. Interestingly, the removal of LMW acids was found to be higher (93.8%) for DAF, whereas only 35.8% removal was observed for FPF. The total trihalomethanes concentration in a DAF-treated water sample was found to be 10% lower than that of FPF. Also, the reduction in haloacetonitriles was found to be slightly higher for a water sample treated by using DAF than by using FPF (1.5 and 1.8 μg L−1, respectively). Moreover, the formation of chloral hydrate was observed to be the same (1.9 μg L−1) for DAF- and FPF-treated water, with a total reduction of 40.6%. FPF with low pressure enabled a reduction in energy of around 55% when compared with DAF. Thus, FPF with low-pressure energy provides an alternative to DAF by reducing the annual operation cost and carbon footprint. [ABSTRACT FROM AUTHOR]

Chlorination in a drinking water treatment plant is the critical process for controlling harmful pathogens. However, the reaction of chlorine with organic matter forms undesirable, harmful, and halogenated disinfection by-products. Carbonaceous disinfection by-products, such as trihalomethanes (THMs) and haloacetic acids (HAAs), are genotoxic or carcinogenic and are reported at high concentration in drinking water. This study is aimed at developing a mathematical model for predicting concentration levels of THMs and HAAs in drinking water treatment plants in South Korea because no previous attempts to do so have been reported for the country. The THMs concentration levels ranged from 29 to 39 μg/L, and those for the HAAs from 6 to 7 μg/L. Multiple regression models, i.e., both linear and nonlinear, for THMs and HAAs were developed to predict their concentration levels in water treatment plants using datasets (January 2015 to December 2016) from three treatment plants located in Seoul, South Korea. The constructed models incorporated principal factors and interactive and higher-order variables. The principal factor variables used were dissolved organic carbon, ultraviolet absorbance, residual chlorine, bromide, contact time, chlorine dose and temperature for treated water, and pH for both raw and treated water at the plant. The linear models for both THMs and HAAs were found to give acceptable fits with measured values from the water treatment plants and predictability values were found to be 0.915 and 0.772, respectively. The models developed were validated with a later dataset (January 2017 to July 2017) from the same water treatment plants. In addition, the models were applied to two different water treatment plants. Application and validation results of the constructed model showed no significant differences between predicted and observed values. [ABSTRACT FROM AUTHOR]

Allogenic organic matter (AOM) composed of extracellular and intracellular organic matter (EOM and IOM) is a major precursor of halogenated carbonaceous and nitrogenous disinfection by-products (C-DBPs and N-DBPs) upon chlorination. The EOM and IOM extracted from Microcystis aeruginosa were analyzed based on bulk parameters and organic fractions with different molecular weight by liquid chromatography with organic carbon detection (LC-OCD). It investigated the efficiency of a conventional gravity system (CGS) and dissolved air flotation (DAF) in the removal of organic precursors, together with measurement of the formation of four major trihalomethanes (THMs) and haloacetonitriles (HANs) in treated water upon chlorination. The results showed that EOM accounted for 59% of building blocks and humic substances, whereas for IOM, 54% were low molecular weight (LMW) neutrals. Both CGS and DAF showed 57–59% removal of dissolved organic carbon (DOC) from EOM and IOM. Regarding DON removal, DAF was found to be more effective, i.e., 8% higher than CGS for EOM. Moreover, the removal of LMW acids and neutrals (not easy to remove and are major precursors of DBPs) from EOM and IOM by DAF was higher than from CGS. The amounts of DBPs measured in all the samples treated for interchlorination were much lower than in the samples for prechlorination. Although the precursors of EOM had a higher concentration than in IOM, THMs and HANs were detected for IOM at a higher concentration, which might be attributed to higher amounts of aromatic, aliphatic moisture and protein compounds in the IOM. Comparatively, DAF showed lower THM and HAN values than CGS water, particularly for IOM. Also, DAF showed a sharp decrease in THMs and an insignificant increase in HANs according to time. [ABSTRACT FROM AUTHOR]