Inactivation of fungal spores by performic acid in water: Comparisons with peracetic acid.

Performic acid (PFA) has received increasing attention in water disinfection due to its high disinfection efficiency and fewer formation of disinfection by-products. However, the inactivation of fungal spores by PFA has not been investigated. In this study, the results showed that the log-linear regression plus tail model adequately described the inactivation kinetic of fungal spores with PFA. The k values of A. niger and A. flavus with PFA were 0.36 min-1 and 0.07 min-1, respectively. Compared to peracetic acid, PFA was more efficient in inactivating fungal spores and caused more serious damage on cell membrane. Compared to neutral and alkaline conditions, acidic environments demonstrated a greater inactivation efficiency for PFA. The increase of PFA dosage and temperature had a promoting effect on the inactivation efficiency of fungal spores. PFA could kill the fungal spores by damaging cell membrane and penetration of cell membranes. In real water, the inactivation efficiency declined as a result of the existence of background substances such as dissolved organic matter. Moreover, the regrowth potential of fungal spores in R2A medium were severely inhibited after inactivation. This study provides some information for PFA to control fungi pollution and explores the mechanism of PFA inactivation.

Integral evaluation of production safety and genotoxicity of recycling residual sludge for drinking water treatment plants.

Recycling residual sludge in drinking water treatment plants (DWTPs) may release excessive heavy metals and organic matter, which are substances of concern because of their toxic and carcinogenic potential. The aim of this study was to investigate potential genotoxic, cytotoxic, and mutagenic effects of recycled residual sludge in terms of quality of water in potable water works. Genotoxic effects of reusing residual sludge were evaluated using: the Ames test, sperm abnormality test in mice, micronucleus assay, comet assay, and single-cell gel electrophoresis assay. The results of the Ames assay show that the disinfected water sample displays bacteriostasis at a dose of 7 L/dish regardless of treatment styles, but mutagenicity ratio (MR) < 2 can still be judged as negative. The micronucleus rates of conventional treatment were slightly genotoxic but only at 4 and 40 L/kg·bw, whereas micronucleus rates of filtered water and disinfectant from the recycling process were negative in all of the dose groups. The levels of DNA damage that are caused by different treatment processes were equivalent. Reusing residual sludge for DWTPs did not contribute to the release of genotoxic or mutagenic compounds, but it did have a remarkable effect on saving the drug dose and increasing drinking water yield. Thus, reusing residual sludge for DWTPs should be widely recommended.

Understanding the nature of NH3-coordinated active sites and the complete reaction schemes for NH3-SCR using Cu-SAPO-34 catalysts.

Cu-SAPO-34 zeolite catalysts show excellent NH3-SCR performance at low temperature, which is due to the catalytic capacity of copper species. Isolated CuII ions and CuIIOH are active sites, but their nature and role are not fully understood. This paper reports the DFT calculations in combination with ab initio thermodynamics to investigate NH3 and H2O coordination to copper species under typical NH3-SCR reaction conditions. In the reduction part of the NH3-SCR reaction, NH2NO and NH4NO2 intermediates will form on CuII-2NH3/3NH3 and CuIIOH-2NH3 complexes, respectively. The Brønsted acid sites are crucial for the decomposition of these intermediates, rather than copper species. Furthermore, the decomposition of NH2NO is more energetically favorable than NH4NO2 which are formed on the Brønsted acid sites. In the re-oxidation part of the NH3-SCR reaction, O2 dissociation and NO2 formation occur on CuI-2NH3 complexes in the presence of NO, and the regeneration of CuIIOH-2NH3 requires the participation of H2O. The proposed complete mechanisms highlight the importance of ligand coordinated copper species for intermediate formation and O2 activation in NH3-SCR.

Efficient inactivation of bacteria in ballast water by adding potassium peroxymonosulfate alone: Role of halide ions.

In recent years, ballast water disinfection has been paid much more attention due to the untreated discharged ballast water posing threaten of biological invasion and health related consequences. In this study, an effective and simple approach for ballast water disinfection by just adding potassium peroxymonosulfate (PMS) was assessed, and the role of halide ions in seawater on the enhancement of inactivation was revealed. The reactive species responsible for inactivation, the leakage of intracellular materials, and changes of cellular morphology after inactivation were evaluated to explore the inactivation mechanism. The results showed that Escherichia coli and Bacillus subtilis in ballast water could be totally inactivated within 10 min by adding 0.2 mM PMS alone. The inactivation of bacteria in ballast water fitted to the delayed Chick-Watson model. Chloride and bromide ion in seawater were found to play a crucial role in inactivating bacteria, while the effect of iodide ion could be negligible due to its relative lower concentration in seawater. Chlorine and bromine, produced by the reaction of PMS with chloride and bromide ion, were proved to be the main reactive components that were responsible for the inactivation of bacteria. The extracellular ATP and total nitrogen concentration increased after inactivation which indicated that cell membrane was destroyed by reactive oxidants produced by the reaction between PMS and halide ions. The change of cell morphology confirmed that bacteria were seriously damaged after inactivation. The results suggest that PMS is an attractive alternative disinfectant for ballast water disinfection and this application deserved further research.

Graphene oxide-polyethylene glycol incorporated PVDF nanocomposite ultrafiltration membrane with enhanced hydrophilicity, permeability, and antifouling performance.

The novel highly hydrophilic composite additive, graphene oxide-polyethylene glycol (GO-PEG, further abbreviated as P-GO), was synthesized from GO and PEG by the esterification reaction. Then, P-GO was blended into a polyvinylidene fluoride (PVDF) casting solution as an additive, and the effects of P-GO on the performance of the PVDF ultrafiltration (UF) membrane were researched. When amount of added P-GO was 0.5 wt%, the flux of the resultant modified membrane (denoted as P/0.5P-GO) reached as high as 93 L m-2·h-1, that is twice than that of the pure PVDF membrane (45 L m-2·h-1). Furthermore, water contact angle results confirmed significantly improved hydrophilicity of the P/0.5P-GO membrane. Results of antifouling tests revealed that the P/0.5P-GO membrane showed the lowest total resistance and irreversible resistance among all the membranes prepared in this study, and after physical cleaning, its flux recovery ratio was the highest-78%. These results demonstrated improved antifouling performance of the P/0.5P-GO membrane. Therefore, it can be concluded that P-GO as an additive material for the PVDF membrane has satisfactory performance in improving the membrane hydrophilicity, permeability, and antifouling performance in practical applications.

Membrane fouling control by Ca2+ during coagulation-ultrafiltration process for algal-rich water treatment.

Seasonal algal bloom, a water supply issue worldwide, can be efficiently solved by membrane technology. However, membranes typically suffer from serious fouling, which hinders the wide application of this technology. In this study, the feasibility of adding Ca2+ to control membrane fouling in coagulation-membrane treatment of algal-rich water was investigated. According to the results obtained, the normalized membrane flux decreased by a lower extent upon increasing the concentration of Ca2+ from 0 to 10 mmol/L. Simultaneously, the floc particle size increased significantly with the concentration of Ca2+, which leads to a lower hydraulic resistance. The coagulation performance is also enhanced with the concentration of Ca2+, inducing a slight osmotic pressure-induced resistance. The formation of Ca2+ coagulation flocs resulted in a looser, thin, and permeable cake layer on the membrane surface. This cake layer rejected organic pollutants and could be easily removed by physical and chemical cleaning treatments, as revealed by scanning electron microscopy images. The hydraulic irreversible membrane resistance was significantly reduced upon addition of Ca2+. All these findings suggest that the addition of Ca2+ may provide a simple-operation, cost-effective, and environmentally friendly technology for controlling membrane fouling during coagulation-membrane process for algal-rich water treatment.

Efficient pretreatment of industrial estate wastewater for biodegradability enhancement using a micro-electrolysis-circulatory system.

A self-made micro-electrolysis-circulatory system with the mixture regime of an upflow bed and reactor was tested for the pretreatment of industrial estate wastewater with a low ratio of biological to chemical oxygen demand (BOD5/COD) at room temperature, 1:1 vol ratio of sponge iron (SFe)/granular activated carbon (GAC), and an intermittent process in aeration and discharge. The system efficiency was evaluated in view of the effects of various processes (hydraulic retention time (HRT), fillers/wastewater ratio (S/L) and aeration). COD reduction of about 51% was obtained for industrial estate wastewater at an S/L ratio of 25%, refluence rate of 16 L/h, HRT of 24 h, and aeration of 60 L/h as the optimal conditions. The considerable change in the calculated BOD5/COD ratio, from 0.07 to 0.49, showed favorable application of the micro-electrolysis-circulatory system for the reductive and oxidative degradation of organic pollutants to enhance wastewater biodegradability. The reusability of the SFe was also investigated after three successive runs. On the basis of the results of Fe leaching, HRT, S/L ratio, scanning electron microscopy observation, and X-ray photoelectron spectroscopic analysis, the corrosion products facilitated by the inherent porosity of SFe played a significant role due to different oxygen conditions in the surface and internal layers. One result from the removal of organic pollutants dominated by the galvanic cell reactions between SFe and GAC was observed, and the integration coagulation in the bulk solution was mainly attributed to the leaching of Fe. The innovative approach described in this study provides a promising and economical technology for pretreatment of industrial wastewater prior to a biological process.

[Effect of various factors on ozone inactivating Giardia in water].

In order to study the effect of O3 inactivating Giardia in water, different factors (CT value, pH, temperature, turbidity, organic content and inorganic ions) which might influence the inactivation were investigated by using fluorescence staining method. The results indicated that the whole process of O3 inactivating Giardia could be divided into two periods, the inactivated rate in log phase was significantly faster than it in the slow phase [k1 = (5.64 +/- 0.023) x 10(-1) mg x min, k2 = (2.72 +/- 0.002) x 10(-2) mg x min, k1 >> k2]. When the turbidity was 0.1 to 20. 0NTU, temperature was 5 to 35 degrees C, pH was 6.0 to 9.0, HA content was 0.5 to 10.0 mg/L, the turbidity was lower, the higher inactivating ratio could be received. With the increasing of temperature, the inactivating effect was decreased. The ability of O3 inactivating Giardia was stronger under acidic condition than it was in alkali circumstance. When the reaction system contained higher concentration of organics, the competition reaction might take place between Giardia and organics with O3, which might reduce inactivation ratio. The sequence of affecting disinfectant ability of O3 was NO3- > None > SO4(2-) > HCO3-, while inorganic cations (Ca2+, Mg2+ and Cu2+) promoted the inactive reaction to a certain extent. If the CT value of O3 was more than 15.0 min x mg/L, the ratio of inactivation could exceed 99.0% during disinfecting drinking water.

Inactivation of Cryptosporidium by ozone and cell ultrastructures.

The fluorescence staining method and scanning electron microscopy (SEM) were used to study the effect of ozone (O3) inactivating Cryptosporidium in water and cell ultrastructures variation to shed light on the mechanism of inactivation preliminarily. Results indicated that O3 had a stronger inactivating capability. When the concentration of O3 was above 3.0 mg/L and the contact time was up to 7 min, a significant inactivating effect could be achieved. The turbidity on inactivation effects was also found to be statistically significant in artificial water. With increases in turbidity, the inactivating effect decreased. Inactivation rate improved with a temperature increase from 5 to 25 degrees C, but decreased beyond this. The inactivating capability of O3 was found to be stronger under acidic than that under alkalic conditions. When the concentration of organic matter in the reaction system was increased, the competition between Cryptosporidium and organics with O3 probably took place, thereby reducing the inactivation rate. In addition, the cellular morphology of Cryptosporidium varied with different contact times. At zero contact time, cells were rotundity and sphericity, at 60 sec they became folded, underwent emboly, and burst at 480 sec, the cell membrane of Cryptosporidium shrinked and collapsed completely.