Experimental approaches for identifying the impact of enhanced flotation technology using hollow microspheres.

Hollow microspheres should be characterized in terms of physicochemical aspects to understand the flotation effect principle. There have been insufficient studies on the effect of hollow microspheres in water treatment in terms of flotation. In this study, various analytical and experimental approaches were utilized to identify the flotation characteristics and understand the effect of hollow microspheres on flotation. These approaches included analytical methods such as particle count and zeta potential measurements, scanning electron microscopy-energy dispersive X-ray spectroscopy analysis, X-ray photoelectron spectroscopy, a floc breakage experiment, and a collision efficiency model. The hollow microspheres were spherical shape with an average size of 50 µm. The microspheres were identified to have a higher negative charge (-69.1 mV) than microbubbles (-51.1 and -30.5 mV). The binding energy of Si-O from the hollow microspheres showed the highest peak at 103.18 eV and 61,503.7 counts/s. Si-O binding structure and the molecular structure of the SixOx series were considered to be a structure in which Si32- is bonded to oxygen ion. The optimum floc breakage condition was determined to be 15 min. The number of particles increased because the average particle size is increased with the concentration of hollow microspheres injection. The turbulent flocculation (TF) model was confirmed to be consentient to the experimental data in comparison with the white-water bubble blanket (WWBB) model. As a result, the hollow microspheres had the characteristic of increasing floc size so that flocs can be floated easily.

Process analysis of microplastic aging during the photochemical oxidation process and its effect on the adsorption behavior of dissolved organic matter.

Information on microplastics (MPs) interactions with dissolved organic matter (DOM) is essential for understanding their environmental impacts. However, research is scarce regarding the adsorption behavior of DOM with different characteristics onto pristine and aged MPs. This research thus investigates MPs aging behavior accelerated by UV/Persulfate and UV/chlorine oxidation processes and the adsorption behavior of organic matter with low-specific ultraviolet absorbance (L-SUVA) and high-SUVA (H-SUVA) characteristics. MPs were degraded by UV/Cl and UV/Persulfate for 30 days. Changes in thermal properties, surface morphology, and chemistry were studied using different analytical techniques. The adsorption behavior was assessed by adsorption kinetic and isotherm study. After oxidation, the surface of the MPs showed a significant increase in the oxygen-containing functional groups, contact angle, surface roughness, and surface energy, and a decrease in crystallinity. The oxidation effect follows the order of UV/Cl > UV/Persulfate. The kinetic and equilibrium data of H-SUVA adsorption on pristine and aged MPs well-fitted the pseudo-second-order and Langmuir model. In contrast, L-SUVA well-fitted the pseudo-first-order and Freundlich model. The adsorption capacity (qm) increased in the following orders: 8.11 > 5.87>4.29 mg g-1 for H-SUVA and 19.81 > 6.662>5.315 mg g-1 for L-SUVA by MPs aged with UV/Cl, UV/Persulfate and pristine MPs, respectively. The larger the surface damage of MPs, the greater the adsorption affinity of DOM. The result was attributed to the physical adsorption process, hydrophobic interactions, electrostatic, hydrogen, and halogen bonding. These findings are beneficial to provide new insights involving the adsorption behavior and interaction mechanisms of DOM onto MPs for the environmental risk assessment.

Low-energy high-rate flotation technology for reduction of organic matter and disinfection by-products formation potential: A pilot-scale study.

Despite operating complexity and high energy costs associated with its operation and maintenance, dissolved air flotation (DAF) is widely used in drinking water treatment processes. Recently, the focus has shifted to designing and developing DAF with high surface loading rates. This research compares the performance of pilot-scale high-rate DAF and low-energy high-rate flash-pressurized flotation (FPF) based on the removal behavior of natural organic matter, different molecular weight size fractions, and the formation potential of disinfection by-products. For a surface-loading rate of 30 m/h, the residual dissolved organic matter (DOC) concentrations in treated samples from high-rate DAF and FPF were 1.35 ± 0.02 (30.25 ± 0.15% removal) mg/L and 1.37 ± 0.03 (29.12 ± 1.72% removal) mg/L, respectively. In contrast, the removal of high-molecular-weight fractions, i.e., biopolymers and humic substances, showed similar removal performance for both treatment processes but not for building blocks. The removal rates were 27.10% and 6.64% for high-rate DAF and FPF, respectively. The formation potential of trihalomethanes/DOC for high-rate DAF with reaction times of 1, 3, 6, and 9 days 14.12 ± 0.18, 17.84 ± 0.22, 23.04 ± 0.29, and 29.73 ± 0.37 µg/mg C, respectively, and 16.83 ± 0.34, 22.69 ± 0.46, 27.08 ± 0.55, and 28.54 ± 0.58 for high-rate FPF. In the case of haloacetonitriles/dissolved organic nitrogen-humic substances and chloral hydrate/DOC, there were no significant differences. Thus, low-energy high-rate FPF with a reduction of energy of 55% provides an alternative to high-rate DAF.

Degradation effect of ultraviolet-induced advanced oxidation of chlorine, chlorine dioxide, and hydrogen peroxide and its impact on coagulation of extracellular organic matter produced by Microcystis aeruginosa.

Implementation of an ultraviolet (UV)-induced advanced oxidation process (AOP) before coagulation was found to enhance the removal of algae cells. However, the effect of UV-induced AOPs on extracellular cellular organic matter (EOM) and on its coagulation and removal was neglected. This study investigated the impact of UV-induced AOPs (UV/Cl2, UV/ClO2, and UV/H2O2) on EOM from Microcystis aeruginosa, and its coagulation and removal by a conventional gravity system (CGS), dissolved air flotation, and a low-energy flash-pressurized flotation (FPF) process. The changes in EOM characteristics before and after the UV-induced AOPs were based on UV absorbance (UV254) and liquid chromatography with organic carbon detection analysis. The reduction in UV254 increased with an increasing dose of oxidant and UV irradiation. The reduction in UV254 for UV/Cl2, UV/ClO2 and UV/H2O2 was 59.5%, 26.5%, and 17.5% respectively, for 0.71 mM equimolar concentration of oxidant and 1920 mJ/cm2 UV irradiation, as evident from a pseudo-first order kinetics study. Similarly, degradation of the high molecular weight to low molecular weight (LMW) fraction was pronounced for UV/Cl2. The coagulation efficiency decreased after UV-induced AOP in the following order: UV/H2O2 > UV/ClO2 > UV/Cl2. By contrast, the low-energy FPF process showed a higher removal of LMW fractions than CGS. Thus, low-energy FPF could be an alternative technology for the UV-induced AOP treatment system.

Assessing the efficacy of dissolved air and flash-pressurized flotations using low energy for the removal of organic precursors and disinfection byproducts: a pilot-scale study.

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.

Models for predicting carbonaceous disinfection by-products formation in drinking water treatment plants: a case study of South Korea.

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.

Formation characteristics of carbonaceous and nitrogenous disinfection by-products depending on residual organic compounds by CGS and DAF.

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.

Arsenate removal from simulated groundwater with a Donnan dialyzer.

A simple point of use (POU) device based on the theory of Donnan dialysis was developed for the removal of arsenate (As(V)) in the present study. A commercial anion exchange membrane was used as a semipermeable barrier between the feed and stripping solution (As(V)-spiked groundwater and a 12gL(-1) table salt solution, respectively). The proposed POU device could be operated 26 times before replacing the stripping solution. In each batch, approximately 80% of the arsenate anions were transported across the membrane within 24h, and the arsenic concentration of the stripping solution was finally more than 180 times greater than that of the treated water. Cations were well preserved in treated water; however, a slight increase in the sodium ion concentration was observed due to electrolyte leakage. Alternatively, the chloride ion concentration significantly increased at the expense of a loss of sulfate and bicarbonate. The quality of treated water was in compliance with drinking water standards. Membrane fouling was investigated, and a reduction in the As(V) removal rates was not observed when the membrane was used repeatedly. Our results showed that the proposed Donnan dialysis POU device could effectively remove arsenic from drinking water in rural areas in a sustainable manner.