Modeling heterogeneous photocatalytic inactivation of E. coli using suspended and immobilized TiO2 reactors

A study was carried out to develop a kinetic model of the photocatalytic inactivation of Escherichia coli using different TiO₂ catalysts. The model developed is based on a reaction scheme that involves effectively coupling mass‐transfer fluxes between bacteria and catalyst surface on one hand and bacterial degradation reaction on the other. The photocatalytic results were derived from experiments led in a batch reactor under both dark and Ultra Violet (UV) irradiation conditions. Using a reference catalyst, the robustness of the developed model was tested under solar conditions. The experimental data validated the model as successfully able to reproduce evolutions in the viable bacteria concentration in the range of parameters studied without any further adjustment of the kinetic parameters. The model was used to simulate the bacterial degradation kinetics under different working conditions to describe the partitioning of both bacterial adhesion and photocatalytic reaction in the solution to be treated © 2015 American Institute of Chemical Engineers AIChE J, 61: 2532–2542, 2015     

智慧控制在水厂协同消毒中的应用

针对协同消毒工艺在水厂实际应用中存在的问题和难点,通过对水厂协同消毒工艺的控制进行升级改造及模拟实验,研究了传统控制与智慧控制协同消毒在多种因素影响下的实验结果。相较传统控制,智慧控制协同消毒可将消毒剂控制指标精度提高72%左右、消毒剂投加量减少16%左右、消毒副产物的生成量减少22%左右。在水厂协同消毒应用中智慧控制较传统控制具有更好的控制效果及推广价值。     

紫外线消毒技术在二次供水中的应用研究

介绍了紫外线消毒技术在二次供水中的应用情况,并进行了二次供水紫外线消毒实验。结果表明:①紫外线消毒会使二次供水中的余氯略有降低,但是仍满足我国《生活饮用水卫生标准》(GB 5749—2006)的限值要求;②紫外线消毒在80 m J/cm²辐射剂量内仅小幅改变水中部分有机物的官能团;③紫外线消毒对二次供水中消毒副产物(DBPs)的浓度和生成几乎没有影响。     

Comparison of chlorination and chloramination practices on microbial inactivation efficiencies within a scaled‐up water distribution network using central composite design

Disinfection practices reduce the incidence of water‐borne diseases but may result in formation of disinfection byproducts (DBPs) in raw water that are reported to be carcinogenic. Central composite design (CCD) was employed in the present study for optimization of disinfectant dose and contact time with the rationale to evaluate if an optimal balance could be achieved between minimal DBPs formation and effective microbial inactivation with either free or combined chlorine in treated water within a lab‐scale prototype network to simulate real water distribution network conditions. After a series of experimental runs based upon design of experiments (DoE) by CCD, dose was found to be the most significant factor (P < 0.01) in determining DBPs formation in both disinfectant’s applications. Where, contact time significantly (P < 0.01) affected bacterial inactivation in chlorination experiments, in contrast, dose was effective in chloramination experiments. Thus, it was concluded that the optimal balance may be achieved in the water networks with the help of multifactorial optimization when disinfectant dose was maintained near 3 mg/L as applied chlorine dose in both disinfection cases, while contact time was 62 and 155 min for chlorine and chloramine, respectively.     

Chlorinated Polycyclic Aromatic Hydrocarbons Associated with Drinking Water Disinfection: Synthesis,Formation under Aqueous Chlorination Conditions and Genotoxic Effects

Polycyclic aromatic hydrocarbons (PAHs) are among the most persistent and toxic organic micropollutants present in water and several of them are mutagenic and carcinogenic. Although it has been shown that chlorinated derivatives of PAHs (Cl-PAHs) may be formed during the water chlorination procedure, little is known about their potential genotoxic and carcinogenic effects. The objectives of the present work were to prepare and characterize the major chlorinated derivatives of benzo[a]pyrene (BaP) and fluoranthene (Fluo), to develop an analytical methodology for their quantification in water samples and to analyse their potential genotoxicity. Chlorinated standards were prepared by a newly developed two phase method (water/n-hexane) using sodium hypochlorite. 6-Chloro-benzo[a]pyrene was selectively obtained from BaP, while 1,3-dichloro-fluoranthene and 3-chloro-fluoranthene were obtained from Fluo. All products were isolated and characterized by nuclear magnetic resonance and mass spectrometry. The formation of BaP- and Fluo-chlorinated derivatives under aqueous chlorination conditions was observed using a SPE-HPLC-FLD methodology. In addition, the cytotoxic and genotoxic activities of the three chlorinated derivatives were analyzed in comparison to their parent compounds, in a human-derived hepatoma cell line using the neutral red uptake and comet assays, respectively. The results showed that, at the equimolar doses of 100 and 125 μM, 6-Cl-BaP was able to induce a significantly higher level of DNA damage than BaP, suggesting a more potent genotoxic effect. In contrast, neither Fluo nor its chlorinated derivatives were genotoxic in the same cell line. The identification of new and possibly hazardous water chlorination by-product from PAHs emphasizes the need to minimize total organic carbon content of raw water and the implementation of safer water disinfection methods.     

Organic acid based sanitizers and free chlorine to improve the microbial quality and shelf-life of sugar snaps

A screening in a sugar snap packaging company showed a converged build-up of aerobic psychrotrophic plate count (APC) (ca. 6.5 log CFU/100 mL), yeasts and molds (Y&M), and lactic acid bacteria (LAB) (both ca. 4.5 log CFU/100 mL) in the wash water in the absence of water sanitizer, and a low build-up of chemical oxygen demand (30 ± 5 mg O₂/L) and turbidity (5.2 ± 1.1 NTU).     

Preliminary observations of a continuous flow solar disinfection system for a rural community in Kenya

This project involves the design and installation of a continuous flow reactor which uses solar radiation, an abundant resource in most sub-Saharan countries, to disinfect water supplies. The system was installed at a rural village in Kenya to disinfect surface water collected at a recently constructed micro-dam. The solar reactor uses CPC reflectors which reflect both direct and diffuse solar radiation onto clear pipes through which the requisite water supply flows. The reaction kinetics for the full-scale design had been determined on a variety of pathogenic micro-organisms under both artificial and real sunlight in controlled conditions. The community fully participated in the planning, installation and subsequent operation of the system. The preliminary water quality results indicate that the system is providing a safe source of water for the community. The installation, commissioning and initial use of the system highlights the critical need for community involvement and approval if such interventions are going to be successful in rural areas, alongside the requirements for strategic and technical support.     

Solar disinfection of wild Salmonella sp. in natural water with a 18 L CPC photoreactor: Detrimental effect of non-sterile storage of treated water

For the first time solar disinfection of liters of water containing wild Salmonella sp. and total coliforms was carried out in a compound parabolic collector (CPC) photoreactor at temperatures of almost 50 °C. Using surface water with high turbidity, this treatment was efficient in completely inactivating Salmonella sp. without regrowth during the subsequent 72 h of dark sterile storage. However if the solar treated water is poured in a non- sterile container, bacteria regrowth occurs even if 10 mg L⁻¹ of H₂O₂ is added before the storage. On the other hand, 30 mg L⁻¹ of H₂O₂ added when the irradiation started was completely depleted within 2 h and did not prevent bacterial regrowth during post-irradiation storage in non-sterile containers, demonstrating that storage of large volumes of water treated by solar irradiation was not optimal. Finally, total coliforms (Escherichia coli included) showed a far higher sensitivity than Salmonella sp. and demonstrated to be an inappropriate indicator for monitoring bacterial contamination in water during solar disinfection processes.