Zongping Wang

Textile Dyeing Wastewater Treatment

Textile industry can be classified into three categories viz., cotton, woolen, and synthetic fibers depending upon the used raw materials. The cotton textile industry is one of the oldest industries in China. The textile dyeing industry consumes large quantities of water and produces large volumes of wastewater from different steps in the dyeing and finishing processes. Wastewater from printing and dyeing units is often rich in color, containing residues of reactive dyes and chemicals, such as complex components,many aerosols,high chroma,high COD and BOD concentration as well as much more hard-degradation materials. The toxic effects of dyestuffs and other organic compounds, as well as acidic and alkaline contaminants, from industrial establishments on the general public are widely accepted. At present, the dyes are mainly aromatic and heterocyclic compounds, with color-display groups and polar groups. The structure is more complicated and stable, resulting in greater difficulty to degrade the printing and dyeing wastewater (Shaolan Ding et al.,2010). According to recent statistics, Chinas annual sewage has already reached 390 million tons, including 51% of industrial sewage, and it has been increasing with the rate of 1% every year. Each year about 70 billion tons of wastewater from textile and dyeing industry are produced and requires proper treatment before being released into the environment (State Environmental Protection Administration ,1994). Therefore, understanding and developing effective printing-dye industrial wastewater treatment technology is environmentally important.

Photodegradation of propranolol by Fe(III)-citrate complexes: kinetics, mechanism and effect of environmental media.

Photogeneration of HO was optimized in Fe(III)-citrate solution within the pH range of 3.0-9.0 to investigate its photoreactivity at neutral pH without the addition of H(2)O(2) under simulated sunlight. The generation of HO decreased with increasing pH within the range of 6.0-9.0 at the Fe(III)-to-citrate ratio of 10:50 (10(-6)M). However, when the concentration of citrate increased to 1.5 × 10(-4)M, the formation rate of HO increased in the order of pH 9.0<3.0<7.0<4.0<5.0. The pH-dependent HO production was governed by the stability of Fe(II)/Fe(II)-citrate and the amount of O(2)(-) in the solution. Propranolol can be efficiently photodegraded in Fe(III)-citrate system at pH 7.0 with pseudo-first-order constant 3.1 × 10(-4)s(-1). HO was verified to be the main reactive oxygen species (ROS) responsible for the photodegradation of propranolol. The presence of metal ions inhibited the Fe(III)-cit-induced photodegradation in the order of Mn(2+)>Cu(2+)>Ca(2+)>Mg(2+). Both humic acid (HA) and fulvic acid (FA) markedly suppressed the degradation of propranolol. Moreover, the iron in Fe(III)-citrate system was reused by a simple addition of citrate to the reaction solution. By GC-MS analysis, the photoproducts of the propranolol were identified and the degradation pathway was proposed. This work suggests that Fe(III)-citrate complexes are good alternative for the advanced treatment of organic pollutants at neutral pH in aqueous solution.

Photodegradation of selected β-blockers in aqueous fulvic acid solutions: Kinetics, mechanism, and product analysis

The photodegradation of the widely used β-blockers atenolol and metoprolol were investigated in the presence of fulvic acid (FA) under simulated sunlight. Both atenolol and metoprolol undergo indirect photodegradation in the FA solutions. The triplet excited state of FA ((3)FA(∗)) was verified to be main reactive species responsible for the photosensitized degradation of β-blockers. An electron transfer mechanism for the interaction between β-blockers and (3)FA(∗) was proposed on the basis of a series of experiments. Magnetic property of metal ions exhibited significant impact on photosensitized degradation. Diamagnetic metal ions such as Mg(2+), Ca(2+), Zn(2+), and Al(3+) negligibly affected the degradation. In contrast, paramagnetic metal ions including Mn(2+), Cu(2+), Fe(3+), and Cr(3+) markedly inhibited the reactions in the order of Cr(3+) < Fe(3+) < Cu(2+) < Mn(2+). The inhibition was related to the complexation ability with FA. By LC-ESI-MS/MS analysis, deisopropyl-atenolol (metoprolol) was identified as the main photosensitized product. The degradation pathways of β-blockers involving electron transfer processes were proposed. This finding strongly suggests that (3)FA(∗) was important reactive species for the degradation of β-blockers in natural waters.

Photodegradation of parabens by Fe(III)-citrate complexes at circumneutral pH: matrix effect and reaction mechanism.

The photodegradation of four parabens including methyl-, ethyl-, propyl-, and butyl-paraben in the presence of Fe(III)-citrate complexes under simulated sunlight was investigated. The degradation of parabens increased with decreasing pH within the range of 5.0-8.0 at the Fe(III)-to-citrate ratio of 10:150 (μM). The addition of low-molecular-weight carboxylic acids showed different effects on the photodegradation of methylparaben. The low-photoreactive carboxylic acids inhibited the photodegradation of methylparaben in the order of formic acid>succinic acid>acetic acid>malonic acid. In contrast, oxalic acid enhanced the photodegradation and exhibited appreciable synergistic effect with Fe(III)-citrate at concentration higher than 500 μM. Up to 99.0% of substrate was degraded after 30 min at pH6.0 in the Fe(III)-citrate-oxalate system. The various fractions of fulvic acid inhibited the photodegradation of methylparaben. The inhibition increased with increasing nominal molecular weight of fractionated fulvic acid. Moreover, the photodegradation of methylparaben was inhibited in natural waters in the order of Liangzi Lake<Donghu Lake<Changjiang River≈Seawater. The photoproducts of methylparaben were identified by GC-MS analyses and the degradation pathway was proposed.

Photoproducts of tetracycline and oxytetracycline involving self-sensitized oxidation in aqueous solutions: effects of Ca2+ and Mg2+.

Tetracyclines constitute one of the most important antibiotic families and represent a classic example of phototoxicity. The photoproducts of tetracyclines and their parent compounds have potentially adverse effects on natural ecosystem. In this study, the self-sensitized oxidation products of tetracycline (TC) and oxytetracycline (OTC) were determined and the effects of Ca2+ and Mg2+ on self-sensitized degradation were investigated. The Ca2+ and Mg2+ in the natural water sample accounted for enhancement (pH 7.3) and inhibition (pH 9.0) of photodegradation of TC and OTC due to the formation of metal-ions complexes. The formation of Mg2+ complexes was unfavorable for the photodegradation of the tetracyclines at both pH values. In contrast, the Ca2+ complexes facilitated the attack of singlet oxygen (1O2) arising from self-sensitization at pH 7.3 and enhanced TC photodegradation. For the first time, self-sensitized oxidation products of TC and OTC were verified by quenching experiments and detected by LC/ESI-DAD-MS. The products had a nominal mass 14 Da higher than the parent drugs (designated M+14), which resulted from the 1O2 attack of the dimethylamino group on the C-4 atom of the tetracyclines. The presence of Ca2+ and Mg2+ also affected the generation of M+14 due to the formation of metal-ions complexes with TC and OTC. The findings suggest that the metal-ion complexation has significant impact on the self-sensitized oxidation processes and the photoproducts of tetracyclines.

Photolysis of chlortetracycline in aqueous solution: kinetics, toxicity and products.

The aqueous photodegradation of the widely used antibiotic chlortetracycline (CTC) was investigated under simulated sunlight. The quantum yield of photodegradation increased from 3.3 x 10(-4) to 8.5 x 10(-3) within the pH range of 6.0 to 9.0. The presence of Ca2+, Fe3+, and NO(-3) enhanced the photodegradation of CTC, whereas Mg2+, Mn2+, and Zn2+ inhibited the degradation with the order Mn2+ > Zn2+ > Mg2+ at pH 7.3. The monovalent cations (Na+ and K+) had negligible effect on the photolysis of CTC. Fulvic acid (FA) decreased the photodegradation of CTC due to light screening effect. Hydrogen peroxide (H2O2) was formed concurrently with direct photodegradation of CTC. The generation rate of H2O2 increased from 0.027 to 0.086 micromol/(L x min) when the pH ranged from 6.0 to 9.0. The CTC solution was about three-fold more toxic to the Photobacterium phosphoreum bacteria after irradiation, suggesting that the photoproducts and H2O2 formed in the CTC solution exhibited high risk on the bacteria. By LC-ESI(+)-MS, the photoproducts of CTC were identified. The direct photodegradation of CTC was involved in hydroxylation and N-demethyl/dedismethyl processes. The main photoproducts included the iso-CTC analog containing hydroxyl groups (m/z 511.4 and 495.4), and the N-demethyl/dedismethyl products of the photoproduct m/z 495.4 (m/z 481.3 and 467.4). In addition, the photochemical dechlorination of CTC led to tetracycline (m/z 445.5).

Utilization of solar energy in sewage sludge composting: Fertilizer effect and application

Three reactors, ordinary, greenhouse, and solar, were constructed and tested to compare their impacts on the composting of municipal sewage sludge. Greenhouse and solar reactors were designed to evaluate the use of solar energy in sludge composting, including their effects on temperature and compost quality. After 40 days of composting, it was found that the solar reactor could provide more stable heat for the composting process. The average temperature of the solar reactor was higher than that of the other two systems, and only the solar reactor could maintain the temperature above 55°C for more than 3 days. Composting with the solar reactor resulted in 31.3% decrease in the total organic carbon, increased the germination index to 91%, decreased the total nitrogen loss, and produced a good effect on pot experiments.

Photodegradation of hexabromocyclododecane (HBCD) by Fe(III) complexes/H 2 O 2 under simulated sunlight

Hexabromocyclododecane (HBCD) is a globally produced brominated flame retardant used primarily as an additive flame retardant in polystyrene and textile products. Photodegradation of HBCD in the presence of Fe(III)-carboxylate complexes/H2O2 was investigated under simulated sunlight. The degradation of HBCD decreased with increasing pH in the Fe(III)-oxalate solutions. In contrast, the optimum pH was 5.0 for the Fe(III)-citrate-catalyzed photodegradation within the range of 3.0 to 7.0. For both Fe(III)-oxalate and Fe(III)-citrate complexes, the increase of carboxylate concentrations facilitated the photodegradation. The photochemical removal of HBCD was related to the photoreactivity and speciation distribution of Fe(III) complexes. The addition of H2O2 markedly accelerated the degradation of HBCD in the presence of Fe(III)-citrate complexes. The quenching experiments showed that ·OH was responsible for the photodegradation of HBCD in the Fe(III)-carboxylate complexes/H2O2 solutions. The results suggest that Fe(III) complexes/H2O2 catalysis is a potential method for the removal of HBCD in the aqueous solutions.

Photodegradation kinetics, products and mechanism of timolol under simulated sunlight

The photodegradation of β-blocker timolol in fulvic acid (FA) solution was investigated under simulated sunlight. The triplet excited state of FA ((3)FA(*)) and singlet oxygen ((1)O2) were the main reactive species responsible for the degradation of timolol in the aerated FA solutions. Both dissolved oxygen and iodide ions (I(-)) are the efficient quenchers of (3)FA(*). The photodegradation was drastically accelerated after removing the dissolved oxygen. The presence of I(-) inhibited the photosensitized degradation of timolol in the deoxygenated FA solutions, whereas the role of I(-) in the reaction was concentration-dependent in the aerated solutions. The other halide ions such as chloride (Cl(-)) and bromide (Br(-)) exhibited less effect on the photodegradation of timolol in both aerated and deoxygenated solutions. By LC-DAD/ESI-MS/MS analysis, the photoproducts of timolol in both aerated and deoxygenated FA solutions were identified. Electron transfer interaction occurred between (3)FA(*) and amine moiety of timolol, leading to the cleavage of C-O bond in the side chain and oxidation of the hexatomic ring. These findings suggest the photosensitized degradation was a significant pathway for the elimination of timolol in natural waters.

UV/persulfate preoxidation to improve coagulation efficiency of Microcystis aeruginosa

The performance of UV-activated persulfate (UV/PS) technology as preoxidation process to enhance Microcystis aeruginosa removal by subsequent coagulation-sedimentation was firstly evaluated. The results demonstrate that UV/PS preoxidation could successfully promote coagulation of algae cells through the effective neutralization of zeta potential, which was caused by the changes of cell morphology, size distribution and surface properties after simultaneous UV irradiation and formed reactive species (i.e. SO4- and HO) oxidation. Since excessive oxidation would cause cell rupture along with the release of organics, which could deteriorate coagulation efficiency, optimal PS dose (60mg/L) and UV dose (375mJ/cm2) were proposed to exist in this study. The concentrations of extracellular algal organic matter (AOM) sharply increased by 48.2% during the preoxidation period, while gradually decreased in the following coagulation and sedimentation. Most of the concerned disinfection by-products (DBPs) monotonically decreased or followed fluctuant reduction with increasing PS doses, whereas the trichloromethane, trichloroacetic acid and dichloroacetonitrile persistently increased, which was inferred to be related to the variation of AOM. This study suggests that UV/PS might be a potential pretreatment process to assist coagulation on the removal of algae.