Effects of UV-based oxidation processes on the degradation of microplastic: Fragmentation, organic matter release, toxicity and disinfection byproduct formation.

The occurrence and transformation of microplastics (MPs) remaining in the water treatment plants has recently attracted considerable attention. However, few efforts have been made to investigate the behavior of dissolved organic matter (DOM) derived from MPs during oxidation processes. In this study, the characteristics of DOM leached from MPs during typical ultraviolet (UV)-based oxidation was focused on. The toxicity and disinfection byproduct (DBP) formation potentials of MP-derived DOM were further investigated. Overall, UV-based oxidation significantly enhanced the aging and fragmentation of highly hydroscopic MPs. The mass scales of leachates to MPs increased from 0.03% - 0.18% at initial stage to 0.09% - 0.71% after oxidation, which were significantly higher than those leached by natural light exposure. Combined fluorescence analysis with high resolution mass spectrometer scan confirmed that the dominant MP-derived DOM are chemical additives. PET-derived DOM and PA6-derived DOM showed inhibition of Vibrio fischeri activity with corresponding EC50 of 2.84 mg/L and 4.58 mg/L of DOC. Bioassay testing with Chlorella vulgaris and Microcystis aeruginosa showed that high concentrations of MP-derived DOM inhibited algal growth by disrupting the cell membrane permeability and integrity. MP-derived DOM had a similar chlorine consumption (1.63 ± 0.41 mg/DOC) as surface water (1.0 - 2.0 mg/DOC), and MP-derived DOM mainly served as precursors for the investigated DBPs. Contrary to the results of previous studies, the DBP yields from MP-derived DOM were relatively lower than those of aquatic DOM under simulated distribution system conditions. This suggests that MP-derived DOM itself rather than serving as DBP precursor might be potential toxic concern.

Does Snowfall Introduce Disinfection By-product Precursors to Surface Water?

Snow with large specific surface area and strong adsorption capacity can effectively adsorb atmospheric pollutants, which could/might lead to the increase of disinfection by-product (DBP) precursors in surface water. In this study, the contents and characteristics of dissolved organic matter (DOM) in meltwater were investigated, and DBP formation and the DBP-associated cytotoxicity index during chlorination of meltwater was first explored. Overall, meltwater exhibited high nitrogen contents. Meltwater-derived DOM was mainly composed of organics with low molecular weights, low aromaticity, and high unsaturated degrees. DBP formation potentials and cytotoxicity indexes in chlorinated meltwater were positively correlated with air quality index and were significantly impacted by snowfall stages. The trihalomethane and haloacetic acid yields from meltwater were relatively low, while yields of highly cytotoxic DBPs, especially halonitromethanes (6.3-10.8 µg-HNMs/mg-DOC), were significantly higher than those of surface water (1.7 µg-HNMs/mg-DOC). Notably, unsaturated nonaromatic organic nitrates in meltwater were important precursors of halonitromethanes. The actual monitoring results showed that snowfall significant increased the haloacetaldehydes and nitrogenous DBP formation levels of surface water. Considering increased DBP formation and DBP-associated toxicity, it was demonstrated that DOM derived from snowfall in atmosphere-polluted areas could deteriorate surface water quality and pose potential risks to drinking water.

Degradation of 2,6-dichloro-1,4-benzoquinone by UV/H2O2/O3 treatment: Effectiveness, water matrix effects, and degradation mechanism.

2,6-dichloro-1,4-benzoquinone (DCBQ), a typical representative of Halobenzoquinones, is an emerging aromatic disinfection by-product (DBP) with high toxicity and carcinogenicity, generated commonly through the chlorination in the drinking water disinfection process while there is still a lack of research on its removal. In this study, the effects of ultraviolet-based advanced oxidation processes (UV-AOPs) on the degradation of DCBQ were evaluated. The results showed that UV-AOPs are effective in degrading DCBQ. The removal of DCBQ by UV/H2O2/O3 was more significant than by UV/H2O2 or UV/O3, achieving a 96.7% removal rate at both the O3 and H2O2 doses of 1 mg/L. The results also indicated the alkaline and weakly acidic environments could facilitate the degradation of DCBQ, inorganic anions could inhibit DCBQ degradation and the degree of inhibition increased as the matrix concentration increased. The degradation of DCBQ was inhibited more by the CO32- than the other matrix components, such as Cl- and NO3-. It was shown by the density functional theory simulations and the ultrahigh-performance liquid chromatography (UPLC) - Orbitrap mass spectra that the electrons in DCBQ are mainly on the chlorine atom connected to the carboatomic ring and that OH• can attack the chlorine atom to cause de-chlorination. The DCBQ degradation pathway may involve the oxidation of DCBQ to 3-hydroxy-2,6-DCBQ (HO-DCBQ) and 3,5-dichloro-1,2,4-pyrogallol, the further degradation of intermediate products by OH• to dechlorinated forms of HO-DCBQ and DCBQ.

The characteristic of N-nitrosodimethylamine precursor release from algal organic matter and degradation performance of UV/H2O2/O3 technology.

Seasonal cyanobacterial blooms in eutrophic water releases algal organic matter (AOM), which contains large amount of dissolved organic nitrogen (DON) and is difficult to be removed effectively by conventional treatment processes (e.g., coagulation and sand filtration) because of its high hydrophilicity. Moreover, N-nitrosodimethylamine (NDMA) can be generated by the reaction of AOM with disinfectants in the subsequent disinfection process. In this study, the formation of NDMA from different AOM components was explored and the control of algal-derived NDMA precursors by UV/H2O2/O3 was evaluated. The results showed that the hydrophilic and polar components of AOM with the low molecular weight had higher NDMA yields. UV-based advanced oxidation process (AOPs) is effective in degrading NDMA precursors, while the removal rate can be affected greatly by UV doses. The removal rate of NDMA precursors by UV/H2O2/O3 is higher than by UV/H2O2 or UV/O3 which can reach 95% at the UV dose of 400 mJ/cm2. An alkaline environment reduces the oxidation efficiency of UV/H2O2/O3 technology, while an acidic environment is conducive to its function. Inorganic anions such as HCO3-, SO42-, Cl- and NO3- are potential to compete with target algal-derived NDMA precursors for the oxidants reaction and inhibit the degradation/removal of these precursors. The degradation of algal-derived NDMA precursors by UV/H2O2/O3 is mainly accomplished by the oxidation of DON with secondary amide groups, and the main degradation mechanism by UV/H2O2/O3 was through the initial decomposition of macromolecular organic compounds such as biopolymers and humic substances and the further degradation of resulting small molecular components.

Removal of organic pollutants by contact oxidation of biological carbon sludge.

A pilot-scale (5 m3 /day) study was conducted for the treatment of micro-polluted low-turbidity water using a biological contact oxidation high-density sedimentation tank system with biochar sludge. First, the best operating conditions were found through system debugging; then, biological characteristics were investigated during system debugging; and finally, the performance in terms of pollutant elimination was investigated. The carbon sludge tank biomass was stable, which provided good stability for the removal of organic matter in raw water. The average reduction in absorbance of UV254 and total organic carbon were 36.71% and 29.63%, respectively, when compared with conventional coagulation. The adsorption and degradation of the mixture comprising carbon and sludge played an important role in removing organic pollutants; most of the humic and fulvic acid content of the water was removed during the coagulation processes. PRACTITIONER POINTS: The contact oxidation of biological carbon sludge system can effectively treat low-turbidity water. The extracellular polymeric substances and the filamentous bacteria connecting the structure provided good settling for the carbon sludge mixture. The adsorption and degradation of the mixture comprising carbon and sludge played an important role in removing organic pollutants. With the carbon sludge reflux, organic matter with molecular weight >30K and 10K-3K was greatly reduced. The contact oxidation of biological carbon sludge system was successful in reducing the concentrations of DBPs and their precursors.

Effect of a nanofiltration combined process on the treatment of high-hardness and micropolluted water.

The quality of raw water and the current high level of pollution presents a phenomenon of high hardness and micropollution. An experimental study was conducted of the nanofiltration (NF) pilot-scale process combined with biological contact oxidation precipitation and ultrafiltration (UF) as the pretreatment process to treat this water. The study investigated the removal efficiency and membrane fouling of the NF process under the continuous and stable operating conditions of the combination process and studied the influence of high-hardness water on the membrane pollution of the combination process. The results showed that the combined process had a positive removal effect on conventional pollutants and characteristic pollutants, and the removal rates of conventional pollutants, such as turbidity, UV254 and CODMn, were 95%, 90% and 85%, respectively. The removal efficiency of total hardness, total alkalinity and soluble total solids reached 98%, 86% and 91%, respectively, and that of total desalination was above 95%. The removal rates of fluorescent organic substances, such as tryptophan, tyrosine, soluble microbial products (SMPs), fulvic acid and humus-like substances, as well as the precursors of disinfection byproducts reached over 88% and 50%, respectively. The pollutant removal efficiency of the combined process was mainly concentrated in the NF unit. The pretreatment process had certain removal effects on turbidity and macromolecular organic substances in the raw water, which provided a perfect operating environment for the NF process. Under long-term operation, the main elements of scaling on the surface of the NF membrane included C, O, Na, Mg, Al, Si, S, Cl, Ca, Ti and Fe, which were mainly concentrated at the outlet of the membrane and mainly came from monomers or compounds composed of inorganic salts in the raw water and some organic compounds. High-hardness water accelerated the change in membrane process parameters, and the surface of the membrane had abundant inorganic scaling. The inorganic scale on the surface of the NF membrane increased noticeably when filtering water with high hardness. Regular cleaning of the UF and NF membranes could effectively restore the parameters of the process and prolong the service life of the membrane process.

Research on CFD numerical simulation and flow field characteristics of countercurrent-cocurrent dissolved air flotation.

Countercurrent-cocurrent dissolved air flotation (CCDAF), the popular water purification device, which consists of collision and adhesion contact zones, showed favorable flotation conditions for micro-bubble adhesion and stability. In this study, computational fluid dynamics (CFD) numerical simulation was employed to confirm that the unique CCDAF configuration create reasonable and that the flow field characteristics were good no matter for single phase or gas-liquid two-phase conditions. In addition, the turbulence of the flow field was enhanced with the increasing influent load; the swirling was remarkably reduced with the increase of gas holdup. Meanwhile, a thick micro-bubble filter layer was formed in the separation zone, which favored bubble-flocs agglomerating and rising. The force analysis also showed that the cross section within the tank contribute to the uniformity of the bottom water collection as well as enlargement of the bottom outflow area, therefore improving the overall flotation performance. The simulation results revealed for the CCDAF process can provide technical guidance for engineering design and application.

Adsorption-desorption behavior of magnetic amine/Fe3O4 functionalized biopolymer resin towards anionic dyes from wastewater.

In this work, a new kind of magnetic amine/Fe3O4 functionalized biopolymer resin (amine/Fe3O4-resin) was prepared and applied to remove various anionic dyes from water. Methyl Orange (MO), Reactive Brilliant Red K-2BP (RBR) and Acid Red 18 (AR) were selected as the typical anionic dye for this research. Meanwhile, amine/Fe3O4-resin was characterized by VSM, XRD, FT-IR, SEM, TEM and XPS. Three anionic dyes removed by amine/Fe3O4-resin were investigated using batch adsorption technique, and the parameters including adsorbent dosage, pH, contact time and temperature were considered. Due to a large number of amine groups and high surface areas, amine/Fe3O4-resin exhibited a remarkably high adsorption capacity for all three dyes, reaching 101.0mg/g, 222.2mg/g and 99.4mg/g for RBR, MO and AR at 25°C, respectively. The pseudo second order model and Langmuir model agreed well with the experimental data, and regeneration experiments indicated its merit of separability and reusability.

Comparison of epichlorohydrin-dimethylamine with other cationic organic polymers as coagulation aids of polyferric chloride in coagulation-ultrafiltration process.

Epichlorohydrin-dimethylamine (DAM-ECH) copolymer was acquired by polycondensation of hazardous reagents: epichlorohydrin (analytical reagent, A.R.) and dimethylamine (A.R.) with ethanediamine (A.R.) as cross-linker. Its coagulation and membrane performance as coagulation aid of polyferric chloride (PFC) was evaluated by comparing with other two cationic coagulation aids: poly dimethyl diallyl ammonium chloride (PDMDAAC) and polyacrylamide (PAM) in humic acid-kaolin (HA-Kaolin) simulated water treatment. Firstly, optimum dosages of PFC&DAM-ECH, PFC&PDMDAAC and PFC&PAM were identified according to their coagulation performance. Then their impacts (under optimum dosages) on membrane fouling of regenerated cellulose (RC) ultra-membrane disc in coagulation-ultrafiltration (C-UF) process were reviewed. Results revealed that small addition of DAM-ECH was the effective on turbidity and DOC removal polymer. Furthermore, in the following ultra-filtration process, external membrane fouling resistance was demonstrated to be the dominant portion of the total membrane fouling resistance under all circumstances. Meanwhile, the internal membrane fouling resistance was determined by residual of micro-particles(1) that cannot be intercepted by cake layer or ultrafiltration membrane.

Adsorption of nitrate from aqueous solution by magnetic amine-crosslinked biopolymer based corn stalk and its chemical regeneration property.

A novel adsorbent of magnetic amine-crosslinked biopolymer based corn stalk (MAB-CS) was synthesized and used for nitrate removal from aqueous solution. The characters and adsorption mechanisms of this bio-adsorbent were determined by using VSM, TGA, XRD, SEM, TEM, FT-IR and XPS, respectively. The results revealed that the saturated magnetization of MAB-CS reached 6.25 emu/g. Meanwhile, the studies of various factors indicated that this novel magnetic bio-adsorbent performed well over a considerable wide pH range of 6.0 ∼ 9.0, and the presence of PO4(3-) and SO4(2-) would markedly decrease the nitrate removal efficiency. Furthermore, the nitrate adsorption by MAB-CS perfectly fitted the Langmuir isotherm model (R(2)=0.997-0.999) and pseudo second order kinetic model (R(2)=0.953-0.995). The calculated nitrate adsorption capacity of MAB-CS was 102.04 mg/g at 318 K by Langmuir model, and thermodynamic study showed that nitrate adsorption is an spontaneous endothermic process. The regeneration experiments indicated its merit of regeneration and stability with the recovery efficient of 118 ∼ 147%. By integrating the experimental results, it was found that the removal of nitrate was mainly via electrostatic attraction and ion exchange. And this novel bio-adsorbent prepared in this work could achieve effective removal of nitrate and rapid separation from effluents simultaneously.

Influence of Enteromorpha polysaccharides on variation of coagulation behavior, flocs properties and membrane fouling in coagulation-ultrafiltration process.

Enteromorpha polysaccharides (Ep) were used as a new coagulant aid together with polyaluminum chloride (PACl) in coagulation-ultrafiltration process to purify Yellow River water. The evolution of flocs size, growth rate, strength, recoverability and fractal structure due to Ep addition were systematically studied in this paper. On this basis, membrane fouling caused by the coagulation effluents of PACl and Ep were also investigated. Results indicated that Ep addition lead to 20% increase in coagulation performance, and meanwhile generate flocs with bigger sizes, faster growth rates and higher recovery abilities. Additionally, the flocs formed by PACl presented more compact structure with a larger D(f) value, while much looser flocs were obtained when Ep was added. Results of ultrafiltration experiments implied that with Ep addition, membrane fouling could be significantly reduced due to large size and loosely structures of flocs in coagulation effluents. Considering both the coagulation efficiency and ultrafiltration membrane performance, 0.2 mg/L Ep was determined as the optimal dosage in coagulation-ultrafiltration process in this study.