Impact of microparticles on UV disinfection of indigenous aerobic spores

Numerous studies have shown that the efficacy of ultraviolet (UV) disinfection can be hindered by the presence of particles that can shield microorganisms. The main objective of this study was to determine to what extent natural particulate matter can shield indigenous spores of aerobic spore-forming bacteria (ASFB) from UV rays. The extent of the protective shielding was assessed by comparing the inactivation rates in three water fractions (untreated, dispersed and filtered on an 8 microm membrane) using a collimated beam apparatus with a low-pressure lamp emitting at 254 nm. Levels of inactivation were then related to the distribution and abundance of particles as measured by microflow imaging. Disinfection assays were completed on two source waters of different quality and particle content. A protocol was developed to break down particles and disperse aggregates (addition of 100mg/L of Zwittergent 3-12 and blending at 8000 rpm for 4 min). Particle size distribution (PSD) analysis confirmed a statistically significant decrease in the number of particles for diameter ranges above 5 microm following the dispersion protocol and 8 microm filtration. The fluence required to reach 1-log inactivation of ASFB spores was independent of particle concentration, while that required to reach 2-log inactivation or more was correlated with the concentration of particles larger than 8 microm (R(2)>0.61). Results suggest that natural particulate matter can protect indigenous organisms from UV radiation in waters with elevated particle content, while source water with low particle counts may not be subject to this interference.     

Continuous-flow solar UVB disinfection reactor for drinking water

Access to safe, reliable sources of drinking water is a long-standing problem among people in developing countries. Sustainable solutions to these problems often involve point-of-use or community-scale water treatment systems that rely on locally-available resources and expertise. This philosophy was used in the development of a continuous-flow, solar UVB disinfection system. Numerical modeling of solar UVB spectral irradiance was used to define temporal variations in spectral irradiance at several geographically-distinct locations. The results of these simulations indicated that a solar UVB system would benefit from incorporation of a device to amplify ambient UVB fluence rate. A compound parabolic collector (CPC) was selected for this purpose. Design of the CPC was based on numerical simulations that accounted for the shape of the collector and reflectance. Based on these simulations, a prototype CPC was constructed using materials that would be available and inexpensive in many developing countries. A UVB-transparent pipe was positioned in the focal area of the CPC; water was pumped through the pipe to allow exposure of waterborne microbes to germicidal solar UVB radiation. The system was demonstrated to be effective for inactivation of Escherichia coli, and DNA-weighted UV dose was shown to govern reactor performance. The design of the reactor is expected to scale linearly, and improvements in process performance (relative to results from the prototype) can be expected by use of larger CPC geometry, inclusion of better reflective materials, and application in areas with greater ambient solar UV spectral irradiance than the location of the prototype tests. The system is expected to have application for water treatment among communities in (developing) countries in near-equatorial and tropical locations. It may also have application for disaster relief or military field operations, as well as in water treatment in areas of developed countries that receive relatively intense solar UVB radiation.     

The impact of selected water quality parameters on the inactivation of Bacillus subtilis spores by monochloramine and ozone

Selected water quality parameters-pH, dissolved organic carbon, turbidity (NTU), and temperature-were tested for their potential effects on ozone and monochloramine inactivation of Bacillus subtilis spores. In oxidant demand-free phosphate-buffer, temperature had the strongest influence on inactivation kinetics when using ozone, pH had a smaller but significant impact on B. subtilis spore inactivation with both monochloramine and ozone. Where monochloramine was applied, modeling and experimental measurements confirmed that dichloramine levels were too low to produce significant inactivation effects under these experimental conditions. It was demonstrated that oxidant demand-free phosphate buffer may not be an adequate environmental analogue for inactivation responses in natural waters.     

Solar radiation disinfection of drinking water at temperate latitudes: Inactivation rates for an optimised reactor configuration

Solar radiation-driven inactivation of bacteria, virus and protozoan pathogen models was quantified in simulated drinking water at a temperate latitude (34°S). The water was seeded with Enterococcus faecalis, Clostridium sporogenes spores, and P22 bacteriophage, each at ca 1 × 10⁵ m L⁻¹, and exposed to natural sunlight in 30-L reaction vessels. Water temperature ranged from 17 to 39 °C during the experiments lasting up to 6 h. Dark controls showed little inactivation and so it was concluded that the inactivation observed was primarily driven by non-thermal processes. The optimised reactor design achieved S₉₀ values (cumulative exposure required for 90% reduction) for the test microorganisms in the range 0.63-1.82 MJ m⁻² of Global Solar Exposure (GSX) without the need for TiO₂ as a catalyst. High turbidity (840-920 NTU) only reduced the S₉₀ value by <40%. Further, when all S₉₀ means were compared this decrease was not statistically significant (prob. > 0.05). However, inactivation was significantly reduced for E. faecalis and P22 when the transmittance of UV wavelengths was attenuated by water with high colour (140 PtCo units) or a suboptimally transparent reactor lid (prob. < 0.05). S₉₀ values were consistent with those measured by other researchers (ca 1-10 MJ m⁻²) for a range of waters and microorganisms. Although temperatures required for SODIS type pasteurization were not produced, non-thermal inactivation alone appeared to offer a viable means for reliably disinfecting low colour source waters by greater than 4 orders of magnitude on sunny days at 34°S latitude.     

A comparison of disinfection by-products found in chlorinated and chloraminated drinking waters in Scotland

Seven water treatment works were selected to compare disinfection by-products (DBPs) formed when using chlorination and chloramination. DBPs measured included trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), trihalonitromethane, iodinated THMs and nitrosamines. Generally treatment works that used chloramination were able to meet the European THM regulatory limit of 100 μg L⁻¹ whereas the chlorinated works found it significantly more difficult. There were no significant differences in the levels of nitrogenous DBPs between the treatment works using chlorination or chloramination with the exception of the nitrosamine N-nitrosodimethylamine (NDMA) which was present at one treatment works in one season.     

UV disinfection in a model distribution system:; biofilm growth and microbial community

Two model distribution systems were operated in parallel to investigate the impact of UV disinfection on water distribution system biofilms and microbial community composition. One system received an influent irradiated with UV light, whereas the control received the same influent with no treatment. The biofilm in the UV system, as compared to the control, was more responsive (i.e., had a greater increase in steady-state density of heterotrophic bacteria) to the increased nutrient availability afforded by a decrease in HRT from 12 to 2 h. However, the UV treatment did not have a consistent impact on the biofilm community, indicating the processes controlling HPC density were independent of the specific strains of bacteria forming the biofilm. There was evidence that particle shielding contributed to the survival of UV-susceptible bacteria. This hypothesis was consistent with the presence of UV-susceptible bacteria in the UV system, as well as the high similarity of the biofilm communities in the UV and control systems in one of the experiments. To simulate an intrusion event, opportunistic pathogens were added to each system after the biofilm community reached steady-state. Opportunistic pathogen attachment was not affected by the UV treatment, but was instead correlated to the biofilm density of heterotrophic bacteria.     

Impact of UV disinfection on microbially available phosphorus,organic carbon,and microbial growth in drinking water

UV irradiation at a wavelength of 253.7 nm (UV(254)) is commonly used for drinking water disinfection. UV radiation is known to convert organically combined phosphorus to orthophosphate and to degrade natural organic matter. We studied if UV disinfection increases the amount of microbially available forms of organic carbon and phosphorus in drinking waters with different characteristics, and if these changes in water chemical quality could enhance the microbial growth in drinking water. The UV(254) dose (15-50 mWs/cm(2)) used in waterworks reduced the concentration of assimilable organic carbon and the sum of the molecular size fractions. The release of microbially available phosphorus needed higher doses (204 mWs/cm(2)) of UV(254) radiation. Of bacteria in drinking water, 90% were inactivated with UV(254)-irradiation doses below 50 mWs/cm(2). A high dose (501 mWs/cm(2)) of UV(254) radiation inhibited the microbial growth in water.     

Multifaceted intra-city water system arrangements in California: Influences and implications for residents

Some cities directly provide drinking water and other utility services to their residents, whereas others contract out these responsibilities in full or in part, with considerable implications for service and non-service outcomes. There is a robust literature considering reasons for city-private provider binaries, as well as a growing number of studies assessing the rise in special district service provision, mixed service delivery arrangements, and inter-municipal service delivery within metropolitan contexts. On the other hand, there are few studies assessing city-level prevalence of these three main provider types jointly, as well as fully accounting for the diversity of institutional arrangements in drinking water service within individual cities.In this study, we construct an empirical profile of and analyze influences on diverse city-level water service provider arrangements using a dataset compiled for all 482 cities in California. Our analysis shows that 80% of cities are served by either a municipality, a private, investor-owned utility or a special district, with special districts being more common than private providers. Moreover, 20% of cities had more than one service provider, and 68% of these cities were served by more than one system type, including many where municipal and private providers co-existed. Using multivariate regression techniques, we analyze influences on different types of city-level drinking water service arrangements. We find that city incorporation date most profoundly influences the mix of water systems in cities, especially arrangements involving special districts or multiple system types. We also find that cities which run their own water system exclusively are more likely to institute conservation policies, and provide suggestive evidence that residents living in cities served by multiple water systems are exposed to wide variance in water rates. Water system fragmentation within city boundaries thus has implications for resource management policy and equity in intra-city resident essential service outcomes.     

Oxidation of microcystins by permanganate: reaction kinetics and implications for water treatment

A few genera of cyanobacteria produce toxins which contaminate drinking water resources. Microcystins (MC), widely reported cyanotoxins, cause acute and chronic toxicity effects in living beings including humans and warrant removal from drinking water. In the present study, unknown second-order rate constants for the reactions of microcystin-LR (MC-LR), -RR and -YR with potassium permanganate were determined at pH 6.2-8.2 and temperature 10-25 degrees C. The reaction of permanganate with MCs is second-order overall and first-order with respect to both permanganate and toxin. The second-order rate constant for the reaction of MC-LR with permanganate at pH 7 and 20 degrees C was 357.2+/-17.5M(-1)s(-1). The influence of pH on the oxidation process was not appreciable and the activation energy was 28.8 kJ mol(-1). Slightly higher reactivity with permanganate was found for MC-RR (418.0M(-1)s(-1)) and MC-YR (405.9M(-1)s(-1)). According to the results obtained, permanganate likely attacks the Adda moiety of the MC molecule. The oxidation of MCs in a natural surface water was also investigated. A permanganate dose of 1-1.25mgL(-1) was enough to reduce MCs concentration below the guideline value of 1microgL(-1). Permanganate oxidation is therefore a feasible option for microcystin removal during preoxidation processes. However, the oxidant dose must be carefully optimized in order to remove extracellular MCs without causing cell lysis (due to chemical stress) and further release of MCs.     

Disinfection by-products in ballast water treatment: An evaluation of regulatory data

To reduce the global spread of invasive aquatic species, international regulations will soon require reductions of the number of organisms in ballast water discharged by ships. For this purpose, ballast water treatment systems were developed and approved by an international procedure. These systems rely on established water treatment principles which, to different degrees, have been proven to generate disinfection by-products with hazardous properties but have only scarcely been investigated in marine environments. Our study evaluates the publicly available documentation about approved ballast water treatment systems with regard to by-product formation. The most commonly employed methods are chlorination, ozonation, and ultraviolet (UV) irradiation. Chlorination systems generate trihalomethanes, halogenated acetic acids, and bromate in substantially larger quantities than reported for other areas of application. Levels are highest in brackish water, and brominated species predominate, in particular bromoform and dibromoacetic acid. Ozonation, which is less frequently utilized, produces bromoform in lower concentrations but forms higher levels of bromate, both of which were effectively reduced by active carbon treatment. In systems based on UV radiation, medium pressure lamps are employed as well as UV-induced advanced oxidation. For all UV systems, by-product formation is reported only occasionally. The most notable observations were small increases in nitrite, hydrogen peroxide, halogenated methanes and acetic acids. The assessment of by-product formation during ballast water treatment is limited by the lacking completeness and quality of available information. This concerns the extent and statistical characterisation of chemical analysis as well as the documentation of the test water parameters.     

Comparison of the action spectra and relative DNA absorbance spectra of microorganisms: Information important for the determination of germicidal fluence (UV dose) in an ultraviolet disinfection of water

The action spectra of Bacillus subtilis spores (ATCC6633) and Salmonella typhimurium LT2 were characterized using physical radiometry for irradiance measurements and a multiple target model to interpret the inactivation kinetics. The observed action spectrum of B. subtilis spores deviated significantly from the relative absorbance spectrum of the DNA purified from the spores, but matched quite well with the relative absorbance spectrum of decoated spores. The action spectrum of B. subtilis spores determined in this study was statistically different from those reported in previous studies. On the other hand, the action spectrum of S. typhimurium bacteria matched quite well with the relative absorbance spectrum of DNA extracted from vegetative cells, except in the region below 240 nm. It is concluded that the common use of the relative DNA absorbance spectrum as a surrogate for the germicidal action spectrum can result in systematic errors when evaluating the performance of a polychromatic UV light reactors using bioassays. For example, if the weighted germicidal fluence (UV dose) calculated using the relative DNA absorbance spectrum as the germicidal weighting factor is found to be 40 mJ cm⁻² for a medium pressure lamp UV reactor, that calculated using the relative action spectrum of B. subtilis spores, as determined in this study, would be 66 mJ cm⁻².     

Variability of fecal indicator bacteria in flowing and ponded waters in southern California: implications for bacterial TMDL development and implementation

Recreational water quality is assessed by using water quality objectives for fecal indicator bacteria (FIB) including total coliform, fecal coliform (or E. coli), and/or Enterococcus. It is required under the Clean Water Act that a TMDL be developed for a bacteria-impaired water body. The development and implementation of bacterial TMDLs has proven challenging and often difficult due to unknown source(s) of FIB. This study found that FIB levels varied significantly in flowing water, ponded water, and associated sediment. FIB levels in isolated ponded water in waterways were significantly higher than in flowing water. Sediment under ponded water contained a great amount of FIB. Furthermore, FIB concentrations in ponded water tended to increase with increasing water temperature and to decrease with increasing water salinity. The result provides the field evidence of survival/growth of FIB in water and sediment under ambient conditions in southern California. A holistic approach including natural sources (e.g., a reference system) should be considered for practical and applicable purposes while developing and implementing bacterial TMDLs for pathogen-impaired waterbodies.     

Innovative method for prioritizing emerging disinfection by-products (DBPs) in drinking water on the basis of their potential impact on public health

Providing microbiologically safe drinking water is a major public health issue. However, chemical disinfection can produce unintended health hazards involving disinfection by-products (DBPs). In an attempt to clarify the potential public health concerns associated with emerging disinfection by-products (EDBPs), this study was intended to help to identify those suspected of posing potential related health effects. In view of the ever-growing list of EDBPs in drinking water and the lack of consensus about them, we have developed an innovative prioritization method that would allow us to address this issue. We first set up an exhaustive database including all the current published data relating to EDBPs in drinking water (toxicity, occurrence, epidemiology and international or local guidelines/regulations).We then developed a ranking method intended to prioritize the EDBPs. This method, which was based on a calculation matrix with different coefficients, was applied to the data regarding their potential contribution to the health risk assessment process. This procedure allowed us to identify and rank three different groups of EDBPs: Group I, consisting of the most critical EDBPs with regard to their potential health effects, has moderate occurrence but the highest toxicity. Group II has moderate to elevated occurrence and is associated with relevant toxicity, and Group III has very low occurrence and unknown or little toxicity. The EDBPs identified as posing the greatest potential risk using this method were as follows: NDMA and other nitrosamines, MX and other halofuranones, chlorate, formaldehyde and acetaldehyde, 2,4,6-trichlorophenol and pentachlorophenol, hydrazine, and two unregulated halomethanes, dichloromethane and tetrachloromethane. Our approach allowed us to define the EDBPs that it is most important to monitor in order to assess population exposure and related public health issues, and thus to improve drinking water treatment and distribution. It is also important to extend our knowledge about exposure to mixtures of emerging DBPs and possible related health effects.     

Measurement of the initial phase of ozone decomposition in water and wastewater by means of a continuous quench-flow system: application to disinfection and pharmaceutical oxidation

Due to a lack of adequate experimental techniques, the kinetics of the first 20s of ozone decomposition in natural water and wastewater is still poorly understood. Introducing a continuous quench-flow system (CQFS), measurements starting 350 ms after ozone addition are presented for the first time. Very high HO. to O3 exposures ratios (Rct=integralHO.dt/integralO3dt) reveal that the first 20s of ozonation present oxidation conditions that are similar to ozone-based advanced oxidation processes (AOP). The oxidation of carbamazepine could be accurately modeled using O3 and HO. exposures measured with CQFS during wastewater ozonation. These results demonstrate the applicability of bench scale determined second-order rate constants for wastewater ozonation. Important degrees of pharmaceutical oxidation and microbial inactivation are predicted, indicating that a significant oxidation potential is available during wastewater ozonation, even when ozone is entirely decomposed in the first 20s.     

Recognition of indigenous water values in Australia's Northern Territory: current progress and ongoing challenges for social justice in water planning

This paper details indigenous Australian water values and interests, highlights progress towards improved distributive outcomes from water planning and analyses the remaining challenges in meeting indigenous aspirations for cultural recognition. It describes the significance of water to indigenous people living in the Roper River area of Australia's Northern Territory, reports on innovations in water allocation planning processes aimed at accommodating that significance, and analyses the implications of this case study for water planning generally. We describe rich cultural and historical connections with water places, protocols governing human conduct towards water, custodial assertions regarding the need for “water for the country”, distinctive values relating to riparian vegetation, and claims of ownership and economic rights in contemporary water allocations. Current water planning objectives such as sustainable development, protection for groundwater-dependent ecosystems, and protection of indigenous values accord with contemporary indigenous perspectives in the Roper, and in a national first, the local water plan specifically proposes reserving a significant water allocation for commercial use by indigenous people. Yet that allocation is seen as unjust from a local perspective, and further analysis demonstrates a range of other limitations: the scale and boundedness of the demarcated plan area, the neglect of riparian vegetation management, insufficient resourcing of local indigenous capacity, mismatches in planning and local governance structures, and the broader question of whether a rationalist planning process can simultaneously advance indigenous claims for recognition, equity in distributions and parity in participation.     

Application of carbon nanotube technology for removal of contaminants in drinking water: A review

Carbon nanotube (CNT) adsorption technology has the potential to support point of use (POU) based treatment approach for removal of bacterial pathogens, natural organic matter (NOM), and cyanobacterial toxins from water systems. Unlike many microporous adsorbents, CNTs possess fibrous shape with high aspect ratio, large accessible external surface area, and well developed mesopores, all contribute to the superior removal capacities of these macromolecular biomolecules and microorganisms. This article provides a comprehensive review on application of CNTs as adsorbent media to concentrate and remove pathogens, NOM, and cyanobacterial (microcystin derivatives) toxins from water systems. The paper also surveys on consideration of CNT based adsorption filters for removal of these contaminants from cost, operational and safety standpoint. Based on the studied literature it appears that POU based CNT technology looks promising, that can possibly avoid difficulties of treating biological contaminants in conventional water treatment plants, and thereby remove the burden of maintaining the biostability of treated water in the distribution systems.     

Implications of land disturbance on drinking water treatability in a changing climate: Demonstrating the need for “source water supply and protection” strategies

Forests form the critical source water areas for downstream drinking water supplies in many parts of the world, including the Rocky Mountain regions of North America. Large scale natural disturbances from wildfire and severe insect infestation are more likely because of warming climate and can significantly impact water quality downstream of forested headwaters regions. To investigate potential implications of changing climate and wildfire on drinking water treatment, the 2003 Lost Creek Wildfire in Alberta, Canada was studied. Four years of comprehensive hydrology and water quality data from seven watersheds were evaluated and synthesized to assess the implications of wildfire and post-fire intervention (salvage-logging) on downstream drinking water treatment. The 95th percentile turbidity and DOC remained low in streams draining unburned watersheds (5.1 NTU, 3.8 mg/L), even during periods of potential treatment challenge (e.g., stormflows, spring freshet); in contrast, they were elevated in streams draining burned (15.3 NTU, 4.6 mg/L) and salvage-logged (18.8 NTU, 9.9 mg/L) watersheds. Persistent increases in these parameters and observed increases in other contaminants such as nutrients, heavy metals, and chlorophyll-a in discharge from burned and salvage-logged watersheds present important economic and operational challenges for water treatment; most notably, a potential increased dependence on solids and DOC removal processes. Many traditional source water protection strategies would fail to adequately identify and evaluate many of the significant wildfire- and post-fire management-associated implications to drinking water “treatability”; accordingly, it is proposed that “source water supply and protection strategies” should be developed to consider a suppliers’ ability to provide adequate quantities of potable water to meet demand by addressing all aspects of drinking water “supply” (i.e., quantity, timing of availability, and quality) and their relationship to “treatability” in response to land disturbance.     

Decay of intestinal enterococci concentrations in high-energy estuarine and coastal waters: towards real-time T90 values for modelling faecal indicators in recreational waters

Intestinal enterococci are the principal 'health-evidence-based' parameter recommended by WHO for the assessment of marine recreational water compliance. Understanding the survival characteristics of these organisms in nearshore waters is central to public health protection using robust modelling to effect real-time prediction of water quality at recreation sites as recently suggested by WHO and the Commission of the European Communities Previous models have more often focused on the coliform parameters and assumed two static day-time and night-time T90 values to characterise the decay process. The principal driver for enterococci survival is the received dose of irradiance from sunlight. In the water column, transmission of irradiance is determined by turbidity produced by suspended material. This paper reports the results of irradiated microcosm experiments using simulated sunlight to investigate the decay of intestinal enterococci in relatively turbid estuarine and coastal waters collected from the Severn Estuary and Bristol Channel, UK. High-turbidity estuarine waters produced a T90 value of 39.5 h. Low-turbidity coastal waters produced a much shorter T90 value of 6.6 h. In experiments receiving no irradiation, high-turbidity estuarine waters also produced a longer T90 of 65.1 h compared with corresponding low-turbidity coastal waters, T90 24.8 h. Irradiated T90 values were correlated with salinity, turbidity and suspended solids (r>0.8, p<0.001). The results suggest that enterococci decay in irradiated experiments with turbidity >200 NTU is similar to decay observed under dark conditions. Most significantly, these results suggest that modelling turbidity and or suspended solids offers a potential means of predicting T90 values in 'real-time' for discrete cells of a hydrodynamic model.