Uncertainty in prediction of disinfection performance

Predicting the disinfection performance of a full-scale reactor in drinking water treatment is associated with considerable uncertainty. In view of quantitative risk analysis, this study assesses the uncertainty involved in predicting inactivation of Cryptosporidium parvum oocysts for an ozone reactor treating lake water. A micromodel is suggested which quantifies inactivation by stochastic sampling from density distributions of ozone exposure and lethal ozone dose. The ozone exposure distribution is computed with a tank in series model that is derived from tracer data and measurements of flow, ozone concentration and ozone decay. The distribution of lethal ozone doses is computed with a delayed Chick-Watson model which was calibrated by Sivaganesan and Marinas [2005. Development of a Ct equation taking into consideration the effect of Lot variability on the inactivation of Cryptosporidium parvum oocysts with ozone. Water Res. 39(11), 2429-2437] utilizing a large number of inactivation studies. Parameter uncertainty is propagated with Monte Carlo simulation and the probability of attaining given inactivation levels is assessed. Regional sensitivity analysis based on variance decomposition ranks the influence of parameters in determining the variance of the model result. The lethal dose model turns out to be responsible for over 90% of the output variance. The entire analysis is re-run for three exemplary scenarios to assess the robustness of the results in view of changing inputs, differing operational parameters or revised assumptions about the appropriate model. We argue that the suggested micromodel is a versatile approach for characterization of disinfection reactors. The scheme developed for uncertainty assessment is optimal for model diagnostics and effectively supports the management of uncertainty.     

Moisture, sawdust, and bleach regulate the persistence of Escherichia coli O157:H7 on floor surfaces in butcher shops

Survival of Escherichia coli O157:H7 on typical butcher shop ceramic floor tiles contaminated with meat juice was compared in the presence and absence of sawdust, and under different moisture and cleaning regimes. Floor tiles from a butcher shop were cut into 5 × 5 cm pieces, and half were cleaned with commercial bleach diluted with water at 60 °C to simulate mopping. A coating of commercial sawdust was applied to half of the tiles, while the other half were left bare. Meat juice collected from beef joints was inoculated with E. coli O157:H7 (strain #3704), and subsequently applied onto tiles at a density of 6.47 log₁₀ CFU cm⁻². Thereafter, tiles were stored at room temperature (20 ± 2 °C), with half maintained under moist conditions [relative humidity (RH) close to 100%] and the other half gradually air-dried (RH 70 ± 5%). Viable E. coli O157:H7 persisted on all tiles over 72 h, although die-off rate varied with environmental conditions. Desiccation of surfaces resulted in a more rapid decline in E. coli O157:H7 numbers, while cleaning of the tiles with bleach prior to contaminating also affected pathogen recovery. Overall, greater numbers of cells were recovered from tiles when no sawdust had been applied; however the presence of sawdust only reduced survival on tiles under dry conditions, and damp sawdust actually increased survival. This highlights the importance of regular cleaning and removal of sawdust to reduce pathogen persistence.     

Ozonation of the marine dinoflagellate alga Amphidinium sp.--implications for ballast water disinfection

Ozone has been investigated for its potential to remove marine dinoflagellate algae from ships' ballast water. Dinoflagellate algae, Amphidinium sp. isolated from the Great Barrier Reef, Townsville, Australia were used as indicators since these produce a type of cyst that is difficult to inactivate, but are relatively easy to culture. The ozonation experiments have demonstrated a high ozone demand for inactivation of the algal cultures, which increases as the culture ages. The main ozone demand in seawater is due to its reaction with bromide to form bromine compounds. The non-bromide ozone demand has been estimated by measuring the residuals produced after various doses of ozone. The Amphidinium sp. show an unexpected response to both ozonation and bromination, with an instantaneous inactivation of the organisms for all doses that produced an oxidant residual in the seawater, followed by an effect of the disinfection residual. The standard design procedure of comparing Ct will not be effective for predicting the response of the organism to varying dose, C, and contact time, t, and a plot of ozone produced oxidant residual against organism inactivation for various contact times is proposed for design purposes. High doses of ozone (5-11 mg/L) and up to 6h of residual contact were required for a 4-log inactivation of the Amphidinium sp. Ozonation is likely to be a difficult technology to implement for organisms with this ozone requirement in combination with characteristics of ballast tanks, which contain areas of sediments high in detritus and areas of corrosion.     

Haloacetic acids in drinking water in the United Kingdom

We measured concentrations of haloacetic acids (HAAs) in the water supply in regions covered by three water companies in the UK Approximately 30 samples in each region were obtained for analysis of both THMs and HAAs to assess the levels of HAAs and the relationship between HAAs and THMs, temperature, pH, free and total chlorine. We have found that there is a range of HAA levels in drinking water with the means ranging from 35-95mug/l and a maximum concentration of 244mug/l. In two out of the three regions there was a high correlation between total THMs and total HAAs, but whereas the HAA and THM levels in one of these companies were approximately equal, in another company the HAA levels were 3-4 times higher than the THM levels. In the third region there was no correlation between total THMs and total HAAs even though the average levels were approximately equal. The ratio of total THM and total HAAs levels was significantly correlated with temperature, pH, free and total chlorine. Overall total THM levels are therefore not considered to be a good indicator of HAA levels. Epidemiological studies using total THM levels should be taking this into account in the interpretation of their results, and regulatory authorities when setting water guidelines.     

FTIR evaluation of functional groups involved in the formation of haloacetic acids during the chlorination of raw water

This work investigated the formation potential of haloacetic acid (HAA) compounds in the raw water for the Bangkhen water treatment plant (Bangkok, Thailand). The resin adsorption technique (with three different types of resins, i.e. DAX-8, AG-MP-50 and WA-10) was employed to characterize the organic content in the raw water into six fractions, i.e. hydrophobic neutral (HPON), hydrophobic acid (HPOA), hydrophobic base (HPOB), hydrophilic neutral (HPIN), hydrophilic acid (HPIA) and hydrophilic base (HPIB). Hydrophilic species appeared to be the predominant organic species in this water source (approximately 60%) with the neutral fraction being the most abundant (approximately 40%). Hydrophobic species, on the other hand, played the most important role in the formation of haloacetic acids as they contributed to as much as approximately 56% of total HAA formation potential. Among the three hydrophobic species, the hydrophobic base exhibited the highest specific HAA formation with 208mugHAAs/mg of dissolved organic carbon (DOC). Each organic fraction was examined for its associated functional groups by Fourier transform infrared (FTIR). The investigation of the formation of HAAs was achieved by tracking the changes in the FTIR results of the same water sample before and after the chlorination reaction. Based on the results obtained from this study, carboxylic acids, ketone, amide, amino acids and aromatic characteristic organics seemed to be the main precursors to HAA formation.     

反冲洗回收水消毒对除铁锰效果影响生产性试验研究

针对高升水厂在生产运行中出现的除锰效果变差的问题进行了理论分析和生产性试验研究。发现反冲洗回收水消毒对滤池除锰效果有较大的负面作用,原因是回收水中剩余消毒药剂破坏了滤料层铁锰细菌形成的生物膜,抑制了新的铁锰细菌生长。生产性试验表明,当滤料表面铁锰细菌量达到105个/mL砂数量级后,才能获得较好的除锰效果。在除铁除锰工艺中,不宜对反冲洗回收水进行消毒处理。     

不同消毒方法在管道分质供水工程中的应用比较

管道分质供水常用的消毒方法有臭氧法、紫外(UV)法、TCAA法、二氧化氯(ClO2)法及组合工艺法等,对不同消毒方法在管道分质供水工程中的应用情况进行比较研究。结果表明,在不同消毒方法中,应用TCCA UV与ClO2 UV组合工艺法,只要控制用户终端净水中的消毒剂浓度在0.05mg/L时,对管道分质供水消毒具有较好的效果,同时可以保持水质具有良好的口感。     

给水处理消毒技术发展展望

消毒技术是给水处理工艺中的重要组成部分 ,而氯消毒是国内外最主要的消毒技术 ,但由于氯消毒产生有“三致”作用的消毒副产物等原因 ,消毒技术的优化和发展成为十分紧迫的问题。目前优化消毒主要包括优化常规的氯消毒和采用其他方式的消毒技术。详细介绍了国内外消毒技术的发展历程 ,比较了氯、二氧化氯、臭氧和紫外线消毒各自的优缺点 ,并指出了给水处理消毒技术的发展方向     

Current developments in nanostructurally engineered metal oxide for removal of contaminants in water

Clean water is one of the vital resources of every living being residing on this earth. However, rapid industrialization, growing human population, urbanization, global warming, extensive agricultural practices, and climatic change have deprived them of access to clean water. These factors convert clean water into wastewater by polluting water and making it poisonous due to heavy metals. 3.575 million deaths are observed from diseases caused by waste or polluted water every year, according to the World Health Organization report. Hence, wastewater treatment has become every country's primary concern. Although several conventional methods are available for wastewater treatment, their utilization has been restrained due to the high maintenance cost of equipment, the large surface area for installation, and a large amount of energy. Nanotechnology offers a lot of potential for improving the efficiency of water purification and disinfection. Nanomaterials can remove inorganic and organic pollutants, biological pollutants (fungi, bacteria, and microbes), and heavy metal ions from wastewater. Metal oxide nanoparticles (NPs) are the most diverse class of materials due to their unique properties such as good adsorption capacity, large surface area, improved catalysis, and enhanced reactivity. Hence, metal oxide NPs have applications in wastewater treatment. A comprehensive overview of the numerous metal oxide NPs in wastewater treatment has been presented in this review. Here, in detail, we have discussed zinc oxide, titanium oxide, silver oxide, tungsten oxide, iron oxide, and copper oxide NPs and their application in wastewater treatment.     

Visible light-responsive photocatalytic-based sustainable construction material for environmental remediation

The present study proposes a unique idea of utilizing cementitious materials incorporating iron-rich industrial waste products (IWPs) to support nano-photocatalyst like Titanium dioxide (TiO₂) to fabricate a visibly active Fe–TiO₂ composite exhibiting antibacterial property. The novelty of the present study lies in formulating a natural doping concept over the conventional techniques to facilitate the photocatalytic properties of the proposed sustainable construction material. To assess the structural performance of the prepared cementitious material, i.e., cement mortar, different physical (porosity, water absorption, and density) and mechanical (compressive strength, flexural strength, and split tensile strength) properties were performed. The results show that the cement mortar mixture FB5F having 15% (10% FA and 5% BS) proportion of conventional cement performed better in terms of workability and durability than other mix designs. Also, the stability and potency of the Fe–TiO₂ composite were analyzed using FESEM, EDS, elemental mapping, UV–vis DRS, and XRD. The characterization tests confirmed the iron-titanium (ITO) bond formation with shifting TiO₂ from UV to visible light spectrum (E_g = 2.52 eV). The Fe–TiO₂ composite was also subjected to an antibacterial check using an aliquot of E. coli bacterial suspension. The composite attained an E. Coli count of about 0.541 log reduction at the end of 45 min and thus, exhibited bacterial disinfection quality. Thus, the Fe–TiO₂ composite material proposes an eco-friendly concept which satisfies the requirement for a sustainable and low carbon footprint future which can additionally be used to treat different indoor and outdoor organic contaminants.