Shumin Zhu

Effect of chlorine dioxide on cyanobacterial cell integrity, toxin degradation and disinfection by-product formation.

Bench scale tests were conducted to study the effect of chlorine dioxide (ClO2) oxidation on cell integrity, toxin degradation and disinfection by-product formation of Microcystis aeruginosa. The simulated cyanobacterial suspension was prepared at a concentration of 1.0×10(6)cells/mL and the cell integrity was measured with flow cytometry. Results indicated that ClO2 can inhibit the photosynthetic capacity of M. aeruginosa cells and almost no integral cells were left after oxidation at a ClO2 dose of 1.0mg/L. The total toxin was degraded more rapidly with the ClO2 dosage increasing from 0.1mg/L to 1.0mg/L. Moreover, the damage on cell structure after oxidation resulted in released intracellular organic matter, which contributed to the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) as disinfection by-products. Therefore, the use of ClO2 as an oxidant for treating algal-rich water should be carefully considered.

Degradation of carbamazepine by UV/chlorine advanced oxidation process and formation of disinfection by-products

Pharmaceuticals in water are commonly found and are not efficiently removed by current treatment processes. Degradation of antiepileptic drug carbamazepine (CBZ) by UV/chlorine advanced oxidation process was systematically investigated in this study. The results showed that the UV/chlorine process was more effective at degrading CBZ than either UV or chlorination alone. The CBZ degradation followed pseudo-first order reaction kinetics, and the degradation rate constants (kobs) were affected by the chlorine dose, solution pH, and natural organic matter concentration to different degrees. Degradation of CBZ greatly increased with increasing chlorine dose and decreasing solution pH during the UV/chlorine process. Additionally, the presence of natural organic matter in the solution inhibited the degradation of CBZ. UV photolysis, chlorination, and reactive species (hydroxyl radical •OH and chlorine atoms •Cl) were identified as responsible for CBZ degradation in the UV/chlorine process. Finally, a degradation pathway for CBZ in the UV/chlorine process was proposed and the formation potentials of carbonaceous and nitrogenous disinfection by-products were evaluated. Enhanced formation of trichloroacetic acid, dichloroacetonitrile, and trichloronitromethane precursors should be considered when applying UV/chlorine advanced oxidation process to drinking water.

Adsorption of two microcystins onto activated carbon: equilibrium, kinetic, and influential factors

AbstractMicrocystins (MCs) are very stable toxins in water bodies and can be poorly removed by traditional drinking water treatment processes. Powder-activated carbon (PAC) was employed in the present study for removal of two commonly and widely occurring algal toxins, microcystin-LR (MC-LR), and microcystin-RR (MC-RR), which were obtained from cyanobacterial blooms. Results indicated that wood PAC has better adsorption capacity on MCs compared with shell and coal PAC. The Freundlich adsorption model can better describe the adsorption behavior of MCs onto PAC. And the pseudo-second-order kinetic model can better fit the adsorption process of MCs onto PAC. Moreover, the adsorption of MCs onto wood PAC was affected by temperature, pH, and anions. The adsorption rates increased with the decreasing temperature. And the adsorption capacity of wood PAC for MCs decreased with the increasing pH. Four kinds of anion hindered the adsorption and reduced the removal rate by 14–24%. Therefore, our study provides valua...

Electrochemical inactivation of Microcystis aeruginosa using BDD electrodes: Kinetic modeling of microcystins release and degradation

Electrochemical inactivation of cyanobacteria using boron-doped diamond (BDD) electrode were comprehensively investigated in this study. The pulse amplitude modulated (PAM) fluorometry, flow cytometry, and confocal laser scanning microscopy (CLSM) were used to characterize the photosynthetic capacity and cell integrity of Microcystis aeruginosa. Persulfate is in-situ generated and activated during the process and responsible for the inactivation of M. aeruginosa. The inactivation efficiency increases along with the increase of applied currents. Additionally, a kinetic model based on a sequence of two consecutive irreversible first-order processes was developed to simulate the release and degradation of microcystins (MCLR). The model was able to successfully predict the concentration of extracellular, intracellular and total MCLR under different applied currents and extended exposure time.

Chlorination and chloramination of tetracycline antibiotics: disinfection by-products formation and influential factors.

Formation of disinfection by-products (DBPs) from chlorination and chloramination of tetracycline antibiotics (TCs) was comprehensively investigated. It was demonstrated that a connection existed between the transformation of TCs and the formation of chloroform (CHCl3), carbon tetrachloride (CCl4), dichloroacetonitrile (DCAN) and dichloroacetone (DCAce). Factors evaluated included chlorine (Cl2) and chloramine(NH2Cl) dosage, reaction time, solution pH and disinfection modes. Increased Cl2/NH2Cl dosage and reaction time improved the formation of CHCl3 and DCAce. Formation of DCAN followed an increasing and then decreasing pattern with increasing Cl2 dosage and prolonged reaction time. pH affected DBPs formation differently, with CHCl3 and DCAN decreasing in chlorination, and having maximum concentrations at pH 7 in chloramination. The total concentrations of DBPs obeyed the following order: chlorination>chloramination>pre-chlorination (0.5h)>pre-chlorination (1h)>pre-chlorination (2h).

Removal of IBMP using ozonation: role of ozone and hydroxyl radical

AbstractOzonation of a representative taste and odor compound, 2-Isobutyl-3-methoxy pyrazine (IBMP), in drinking water was systematically investigated in this study. Batch experiments were conducted to evaluate the influencing factors including initial IBMP concentration, O3 addition rate, initial pH, H2O2 dosage, and different water qualities on the degradation of IBMP in the ozonation process. Results showed that the degradation of IBMP followed pseudo-first order kinetics. The degradation rate constants increased with the increasing O3 addition rate and initial pH value, whereas it decreased with the increasing initial IBMP concentration. Degradation of IBMP is mainly dominated by direct ozone oxidation at low pH, while the free radical oxidation may become dominant at high pH levels. Moreover, appropriate H2O2 dosage can greatly increase the IBMP degradation rates, but large excess H2O2 would act as an scavenger and inhibit the degradation. In addition, lower degradation rate was observed in raw water...

Insight into carbamazepine degradation by UV/monochloramine: Reaction mechanism, oxidation products, and DBPs formation

UV/monochloramine (NH2Cl) process has attracted some attention for the elimination of contaminants of emerging concern as a novel advanced oxidation process. However, there is still much uncertainty on the performance and mechanisms of UV/NH2Cl process because of its complexity and generation of various species of radicals, including NH2•, HO•, Cl• and other reactive chlorine species (RCS). The mechanism and influence factors of degradation of carbamazepine (CBZ) in the UV/NH2Cl process were investigated, and a synergistic effect was observed. Degradation of CBZ under all investigated conditions followed pseudo-first order kinetics. The corresponding rate constant increased along with the dosage of NH2Cl, and was affected significantly by the presence of bicarbonate and natural organic matter. The process has little pH-dependency, while the specific contribution of RCS and HO• changed with solution pH, and RCS always act as a major contributor to the degradation of CBZ. Eleven byproducts of CBZ were identified and their respective evolution profiles were determined. The participation of UV in chloramination can reduce the formation of nitrogenous DBPs, but promote the formation of carbonaceous DBPs. Furthermore, when influent, sand filtered, and granular activated carbon filtered water was respectively used as background, degradation of CBZ was inhibited to different degree and more disinfection byproducts (DBPs) were generated, compared to deionized water. The electrical energy per order for degradation of CBZ in the UV/NH2Cl process was also calculated to obtain some preliminary cost information.