Zhonglin Chen

Evaluation of disinfection by-products formation during chlorination and chloramination of dissolved natural organic matter fractions isolated from a filtered river water.

Dissolved natural organic matter (DOM) in a filtered river water was isolated and fractionated into six different fractions. Trihalomethanes (THMs) and haloacetic acids (HAAs) formed from these isolated DOM fractions during chlorination and chloramination were determined. Results show that the hydrophobic acid, hydrophilic acid, hydrophilic base and hydrophobic neutral are major precursors of THMs and HAAs. There exist good correlations between the values of specific ultraviolet absorbance at 254nm of the individual DOM fractions and their disinfection by-products formation potential, indicating that aromatic moieties are responsible for disinfection by-products formation for both hydrophobic and hydrophilic DOM fractions. Chloramination of the DOM fractions yields much less THMs and HAAs than chlorination. For the dominant DOM fraction (i.e. hydrophobic acid) in the water, the yields of THMs and HAAs increase more significantly in chlorination than those in chloramination with the increase of disinfectant dosage, contact time and dissolved organic carbon content.

Ozone enhanced activity of aqueous titanium dioxide suspensions for photodegradation of 4-chloronitrobenzene

The TiO(2)/UV/O(3) process has been employed to remove 4-chloronitrobenzene (4-CNB) and compared to UV/air, O(3), TiO(2)/O(3), TiO(2)/UV/O(2) and UV/O(3) five parallel oxidation pathways. The reaction activities of these six processes were tested in aqueous using electron paramagnetic resonance (EPR) spin trapping technique with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trap. Moreover, the effects of ozone dosage, catalyst dosage and initial solution pH on the degradation of 4-CNB by TiO(2)/UV/O(3) process were also investigated. Results showed that the TiO(2)/UV/O(3) is the most efficient process for complete mineralization of 4-CNB since the combination of photocatalytic oxidation with ozone has a synergistic effect. The relative intensity of DMPO-OH follows the order of UV/air<O(3)<TiO(2)/O(3)<UV/O(3)<TiO(2)/UV/O(2)<TiO(2)/UV/O(3). In TiO(2)/UV/O(3) process, the ozone and catalyst dosage are found to have a significant impact on the process efficiency whereas initial pH has relatively less effect. Chlorine atoms of 4-CNB are absolutely oxidized to chloride anions when the ozone dosage in the range of 5-18 mg/min, or the catalyst dosage ranging from 1.0 to 2.0 g/L. Part of chloride anions would be further oxidized to chlorate(V) ions if the ozone dosage exceeds 24 mg/min, or the catalyst dosage exceeds 2.0 g/L.

Hydrothermal synthesis of TiO2 hollow microspheres for the photocatalytic degradation of 4-chloronitrobenzene

TiO(2) hollow microspheres were synthesized by a simple hydrothermal method followed by calcination at different temperatures ranging from 400 to 800°C. The prepared samples were characterized by XRD, SEM, TEM, SAED, HRTEM, N(2) adsorption, and UV-vis spectroscopy. The photocatalytic activities of the hollow microspheres were evaluated by photocatalytic decomposition of 4-chloronitrobenzene (4-CNB). Results showed that the TiO(2) hollow microspheres, which had an average external diameter of 1.75 μm, were composed of numerous TiO(2) nanoparticles. Photocatalysis experiments indicated that the TiO(2) hollow microspheres calcined at 500°C exhibited the highest photocatalytic activity, which was nearly 2 and 1.5 times higher than that of the uncalcined sample and Degussa P25, respectively. The catalyst crystallinity, catalyst dosage and 4-CNB concentration were found to have a significant impact on the degradation efficiency whereas solution pH has relatively less effect. The removal of total organic carbon (TOC) and formation of chloride, nitrate (V) anions were monitored to follow the mineralization process of 4-CNB. In addition, it was demonstrated that these TiO(2) hollow microspheres could be recycled easily without decreasing their photocatalytic activities.

Ozonation catalyzed by the raw bauxite for the degradation of 2,4,6-trichloroanisole in drinking water.

A kind of inexpensive and environmental friendly mineral, the raw bauxite has been used successfully as a catalyst combined with ozonation in the degradation of 2,4,6-trichloroanisole (TCA). The catalyst was characterized by using various analytical techniques. X-ray powder diffraction (XRD) characterization showed that the raw bauxite containing boehmite (gamma-AlOOH), kaolinite (Al(2)Si(2)O(5)(OH)(4)) and quartz (SiO(2)), and gamma-AlOOH was the major composition. The catalytic ozonation removal effectiveness of TCA was investigated under various physicochemical conditions. Both the adsorption and the single ozonation were not effective for the degradation of TCA, and the presence of the raw bauxite in ozonation enhanced the TCA removal effectiveness. Both the hydroxyl radicals (OH) scavenging experiment and R(ct) characterization confirmed that the generation of OH was accounted for the enhancement of the degradation of TCA. The generation of OH was inhibited faintly by the presence of both natural organic matters (NOMs) and alkalinity in the natural water during catalyzed ozonation with the raw bauxite. The increasing of both the bauxite dosage and the ozone dosage enhanced the removal effectiveness of TCA. The raw bauxite was an efficient green catalyst for TCA degradation in drinking water.

Chemical cleaning of fouled PVC membrane during ultrafiltration of algal-rich water.

Cleaning of hollow-fibre polyvinyl chloride (PVC) membrane with different chemical reagents after ultrafiltration of algal-rich water was investigated. Among the tested cleaning reagents (NaOH, HCl, EDTA, and NaClO), 100 mg/L NaClO exhibited the best performance (88.4% +/- 1.1%) in removing the irreversible fouling resistance. This might be attributed to the fact that NaClO could eliminate almost all the major foulants such as carbohydrate-like and protein-like materials on the membrane surface, as confirmed by Fourier transform infrared spectroscopy analysis. However, negligible irreversible resistance (1.5% +/- 1.0%) was obtained when the membrane was cleaning by 500 mg/L NaOH for 1.0 hr, although the NaOH solution could also desorb a portion of the major foulants from the fouled PVC membrane. Scanning electronic microscopy and atomic force microscopy analyses demonstrated that 500 mg/L NaOH could change the structure of the residual foulants on the membrane, making them more tightly attached to the membrane surface. This phenomenon might be responsible for the negligible membrane permeability restoration after NaOH cleaning. On the other hand, the microscopic analyses reflected that NaClO could effectively remove the foulants accumulated on the membrane surface.

Comparison of N-nitrosodiethylamine degradation in water by UV irradiation and UV/O3: Efficiency, product and mechanism

N-nitrosodiethylamine (NDEA) is a member of nitrosamines, which is strong carcinogenic. In order to explore an effective treatment method for NDEA removal from water, sole UV irradiation and UV/O(3) were carried out in this study. The removal efficiency, degradation products and pathways were compared between those two processes. Results showed that NDEA removal efficiency achieved 99% within 15 min by both UV and UV/O(3). Degradation reaction well followed pseudo-first-order kinetics. Water pH had different effect on NDEA degradation in those two processes. Acidic and neutral conditions were good for NDEA degradation by sole UV irradiation. However, NDEA underwent rapid degradation under various pH conditions in the UV/O(3) process. Though the ozone introduction in the UV/O(3) process had little effect on NDEA degradation efficiency, it had significant effect on its degradation products and pathways. Methylamine, dimethylamine, ethylamine and diethylamine were observed as aliphatic amine products of NDEA degradation in both two processes. They were assumed to arise due to N-N bond fission under UV irradiation, or due to the reaction of NDEA and hydroxyl radicals in the UV/O(3) process.

Inhibiting the regeneration of N-nitrosodimethylamine in drinking water by UV photolysis combined with ozonation

N-Nitrosodimethylamine (NDMA) is a highly carcinogenic compound that is suspected of carcinogenic activity in the human body. A variety of methods are used to remove NDMA from water, but the main degradation products, dimethylamine (DMA) and NO(2)(-), are also precursors for NDMA formation. UV irradiation combined with ozonation (UV/O(3)) was examined in this investigation for its ability to inhibit the regeneration of NDMA after degradation. Both the degradation products and the regeneration potential of NDMA were compared between UV irradiation alone and UV/O(3). The yields of DMA and NO(2)(-) in the UV/O(3) process were less than for UV irradiation alone. Yields of DMA and NO(2)(-) were 2.25 mg L(-1) and 3.22 mg L(-1) from UV irradiation, while they were 0.92 mg L(-1) and 0.45 mg L(-1) from the UV/O(3) process. Furthermore, the regeneration of NDMA was also less after the UV/O(3) process than after UV irradiation. The concentration of regenerated NDMA was more than 51.8 microg L(-1) after UV irradiation regardless of the dosage of Cl(2). However, the concentration of regenerated NDMA in the UV/O(3) process was less than 7.37 microg L(-1) under the same conditions. Consequently, the UV/O(3) process was more effective than UV irradiation alone in inhibiting NDMA regeneration. The inhibition of NDMA regeneration was due to a decrease in DMA and NO(2)(-) produced by the UV/O(3) process. As the major products generated from NDMA, NO(2)(-) and DMA were likely to be oxidized by ozone and hydroxyl radicals (OH). In addition, the reaction between NDMA and OH would possibly generate methylamine as the only product, leading to a decrease in the production of DMA by the UV/O(3) process.

Efficiency and products investigations on the ozonation of 2-methylisoborneol in drinking water.

2-Methylisobomeol (MIB) is a terpenoid produced as a secondary metabolite by some cyanobacteria and actinomycetes and thus can be present in some drinking water source waters. The removal efficiency, products, and degradation pathway of MIB in drinking water by ozonation were studied. The results showed that ozone is efficient in removing MIB from an aqueous solution, regardless of the initial MIB concentration. Hydroxyl radicals (OH) scavenger experiments indicated that hydroxyl radicals are involved in MIB degradation. The degradation products of MIB were identified by gas chromatography-mass spectrometry. Camphor was identified as a primary degradation product, which was further oxidized to form other degradation intermediates, such as aldehydes, ketones, and carboxylic acids. A possible degradation pathway for the ozonation of MIB was proposed. Qualitative and quantitative analysis of the formation of aldehydes was carried out. It was found that six aldehydes are the main aldehydes products of ozonation of MIB, namely formaldehyde, acetaldehyde, propanal, butanal, glyoxal, and methyl glyoxal.

SMX degradation by ozonation and UV radiation: A kinetic study

The rate constants of sulfamethoxazole (SMX) degradation by ozonation and UV(254) radiation were investigated under various parameters including influent ozone gas concentration, initial SMX concentration, UV light intensity, ionic strength, water quality in terms of varying anions (bicarbonate, sulfate and nitrate), humic acid (HA) and pH. The results indicated that the removal of SMX by ozonation and UV(254) radiation fitted well to a pseudo first-order kinetic model and the rate constants were in the range of (0.9-9.8)×10(-3) and (1.7-18.9)×10(-3) s(-1), respectively. The second-order rate constants of SMX with ozone (ko(3)), under varying operational parameters, were also determined and varied in the range of (0.60-3.38)±0.13×10(5)M(-1) s(-1). In addition, SMX degradation through UV pretreatment followed by ozonation in the presence of HA was proved to be an effective method which can remove SMX with a low ozone dose. The results suggested that ozonation of SMX was more affected by concentration of influent ozone gas, alkalinity, and HA, while incident UV light intensity, pH, and HA were the dominant factors influencing UV degradation of SMX.

Degradation and detoxification of microcystin-LR in drinking water by sequential use of UV and ozone.

Microcystins (MCs) produced by cyanobacteria are strong hepatotoxins and classified as possible carcinogens. MCs pose a considerable threat to human health through tainted drinking and surface waters. Herein filtrated water from a waterworks in Harbin, China, was spiked with microcystin-LR (MC-LR) extracted from a toxic scum of microcystis aeruginosa, and the spiked sample waters were treated using UV irradiation with consequent ozonation process (UV/O3), compared with ozonation at a dose range commonly applied in water treatment plants, UV irradiation at 254 nm and UV irradiation combined with ozonation (UV+O3), respectively. The remaining of toxins were analyzed using high-performance liquid chromatography and also determined using a protein phosphatase type 2A inhibition assay, which was utilized to evaluate the reduction in toxicity. Results indicated that in comparison to other three processes (O3, UV, and UV+O3), UV/O3 process could effectively decrease both the concentration and toxicity of MC-LR at 100 microg/L level after 5 min UV irradiation with consequent 5 min ozonation at 0.2 mg/L (below 1 microg/L), while 0.5 mg/L ozone dose was required for the level below 0.1 microg/L. The addition of an UV treatment step to the existing treatment train may induce significant transformation of micropollutants and breaks down the natural organic matters into moieties unfavorable for ozone decomposition, stabilizing the ozone residual. These findings suggested that sequential use of UV and ozone may be a suitable method for the removal of these potentially hazardous microcystins from drinking water.