Solar water disinfection (SODIS) of Escherichia coli, Enterococcus spp., and MS2 coliphage: effects of additives and alternative container materials

The use of alternative container materials and added oxidants accelerated the inactivation of MS2 coliphage and Escherichia coli and Enterococcus spp. bacteria during solar water disinfection (SODIS) trials. Specifically, bottles made from polypropylene copolymer (PPCO), a partially UVB-transparent plastic, resulted in three-log inactivation of these organisms in approximately half the time required for disinfection in bottles made from PET, polycarbonate, or Tritan^®, which absorb most UVB light. Furthermore, the addition of 125 mg/L sodium percarbonate in combination with either citric acid or copper plus ascorbate tended to accelerate inactivation by factors of 1.4-19. Finally, it was observed that the inactivation of E. coli and enterococci derived from local wastewater was far slower than the inactivation of laboratory-cultured E. coli and Enterococcus spp., while the inactivation of MS2 was slowest of all. These results highlight the importance of UVB in SODIS under certain conditions, and also the greater sunlight resistance of some viruses and of bacteria of fecal origin, as compared to the laboratory-cultured bacteria commonly used to model their inactivation. Furthermore, this study illustrates promising new avenues for accelerating the inactivation of bacteria and viruses by solar disinfection.     

Inactivation of Escherichia coli by ozone under bench-scale plug flow and full-scale hydraulic conditions

To determine the disinfection efficacy of ozonation, water companies can apply several disinfection calculation methods. The goal of this study was to evaluate the use of the T10 and continuous stirred tank reactor (CSTR) method to extrapolate inactivation rates of ozone sensitive microorganisms observed in laboratory tests to full-scale ozonation in drinking water treatment. The inactivation efficacy of the ozonation at the Amsterdam water treatment works was assessed by determining Escherichia coli concentrations in large volume samples before and after ozonation over a period of 1 year. The inactivation of dosed E. coli WR1 was tested in a bench-scale dissolved ozone plug flow reactor (DOPFR) on the same feed water as the full-scale ozonation in which a concentrated ozone solution in Milli-Q water was dosed. Applying the T10 method on the inactivation rates observed in the DOPFR strongly overestimated the inactivation capacity of the full-scale ozonation. The expected inactivation based on the CSTR method (LT2ESWTR) approached the observed inactivation at full-scale. Therefore, the CSTR method should be preferred to calculate inactivation of ozone sensitive organisms such as E. coli, viruses, Giardia and Campylobacter by full-scale ozonation.     

Photocatalytic inactivation of E. coli in surface water using immobilised nanoparticle TiO2 films

Photocatalysis is a promising method for the disinfection of potable water in developing countries where solar irradiation can be employed, thus reducing the cost of treatment. In addition to microbial contamination, water normally contains suspended solids, dissolved inorganic ions and organic compounds (mainly humic substances) which may affect the efficacy of solar photocatalysis. In this work the photocatalytic and photolytic inactivation rates of Escherichia coli using immobilised nanoparticle TiO₂ films were found to be significantly lower in surface water samples in comparison to distilled water. The presence of nitrate and sulphate anions spiked into distilled water resulted in a decrease in the rate of photocatalytic disinfection. The presence of humic acid, at the concentration found in the surface water, was found to have a more pronounced affect, significantly decreasing the rate of disinfection. Adjusting the initial pH of the water did not markedly affect the photocatalytic disinfection rate, within the narrow range studied.     

A practical demonstration of water disinfection using TiO2 films and sunlight

The scope of this study is the assessment of the efficiency of solar disinfection by heterogeneous photocatalysis with sol-gel immobilized (titanium dioxide) TiO2 films over glass cylinders. The solar disinfection process known as SODIS was considered as a reference. Spring water naturally polluted with coliform bacteria was exposed to sunlight in plastic bottles with and without TiO2 over simple solar collectors and the disinfection effectiveness was measured. Total and fecal coliforms quantification was performed by means of the chromogenic substrate method in order to obtain the efficiency of each disinfection treatment. The disinfection with TiO2 was more efficient than the SODIS process, inactivating total coliforms as well as fecal coliforms. On a sunny day (more than 1000 W m(-2) irradiance), it took the disinfection with immobilized TiO2 15 min of irradiation to inactivate the fecal coliforms to make them undetectable. For inactivation of total coliforms, 30 min was required, so that in less than half the time it takes SODIS, the treated water complies with the microbial standards for drinking water in Mexico. Another important part of this study has been to determine the bacterial regrowth in water after the disinfection processes were tested. After SODIS, bacterial regrowth of coliforms was observed. In contrast, when using the TiO2 catalyst, coliforms regrowth was not detected, neither for total nor for fecal coliforms. The disinfection process using TiO2 kept treated water free of coliforms at least for seven days after sun irradiation. This demonstration opens the possibility of application of this simple method in rural areas of developing countries.     

Feasibility of the silver-UV process for drinking water disinfection

A synergistic effect between cationic silver and UV radiation (silver-UV disinfection) has been observed that can appreciably enhance inactivation of viruses. The purpose of this work was to assess the feasibility of this technique for drinking water disinfection and evaluate the effects of selected impurities, found in fresh water, and common parameters on inactivation of the coliphage MS-2 with the silver-UV process. Turbidity (kaolin), calcium hardness, carbonate alkalinity, and pH did not significantly degrade inactivation. Inactivation was reduced in the presence of chloride, at concentrations greater than 30 mg/L, and in water samples with UV-254 absorbance values greater than ca. 0.1 cm⁻¹. Inactivation of MS-2 with silver-UV disinfection was also reduced at high phosphate concentrations (above ca. 5 mM). Silver-UV inactivation of MS-2 increased with increases in temperature between 10 and 20 °C. Silver-UV inactivation of MS-2 was increased by greater than 1-log over UV alone, in two untreated fresh water sources, which indicates that silver-UV may be a viable treatment technology. An assessment of operation and management costs suggests that an increase in inactivation of MS-2 with silver-UV disinfection could be economically beneficial.     

Comparative disinfection efficiency of pulsed and continuous-wave UV irradiation technologies

Pulsed UV (PUV) is a novel UV irradiation system that is a non-mercury lamp-based alternative to currently used continuous-wave systems for water disinfection. PUV polychromatic irradiation disinfection efficiency was compared to that from continuous-wave monochromatic low-pressure (LP) and polychromatic medium-pressure (MP) UV systems, using two types of actinometry (ferrioxalate and iodide-iodate) and an absolute spectral emission method for fluence measurement. All three methods were in good agreement. Once accurate and reliable methods for fluence measurement were established, the inactivation of Escherichia coli and pathogen surrogates phage T4 and T7 were investigated under each technology. Inactivation was significantly faster using PUV irradiation compared to LP or MP UV lamps at equivalent fluence levels. A significant fraction of the enhanced PUV inactivation efficiency was due to wavelengths greater than 295 nm.     

Solar disinfection (SODIS): simulation of solar radiation for global assessment and application for point-of-use water treatment in Haiti

Haiti and other developing countries do not have sufficient meteorological data to evaluate if they meet the solar disinfection (SODIS) threshold of 3-5 h of solar radiation above 500 W/m2, which is required for adequate microbial inactivation in drinking water. We have developed a mathematical model based on satellite-derived daily total energies to simulate monthly mean, minimum, and maximum 5-h averaged peak solar radiation intensities. This model can be used to assess if SODIS technology would be applicable anywhere in the world. Field measurements were made in Haiti during January 2001 to evaluate the model and test SODIS efficacy as a point-of-use treatment option. Using the total energy from a measured solar radiation intensity profile, the model recreated the intensity profile with 99% agreement. NASA satellite data were then used to simulate the mean, minimum, and maximum 5-h averaged peak intensities for Haiti in January, which were within 98.5%, 62.5%, and 86.0% agreement with the measured values, respectively. Most of the discrepancy was attributed to the heterogeneous nature of Haiti's terrain and the spatial resolution of the NASA data. Additional model simulations suggest that SODIS should be effective year-round in Haiti. Actual SODIS efficacy in January was tested by the inactivation of total coliform, E. coli, and H2S-producing bacteria. Exposure period proved critical. One-day exposure achieved complete bacterial inactivation 52% of the time, while a 2-day exposure period achieved complete microbial inactivation 100% of the time. A practical way of providing people with cold water every morning that has undergone a 2-day exposure would be to rotate three groups of bottles every morning, so two groups are out in the sun and one is being used for consumption.     

Roof-harvested rainwater for potable purposes: Application of solar collector disinfection (SOCO-DIS)

The efficiency of solar disinfection (SODIS), recommended by the World Health Organization, has been determined for rainwater disinfection, and potential benefits and limitations discussed. The limitations of SODIS have now been overcome by the use of solar collector disinfection (SOCO-DIS), for potential use of rainwater as a small-scale potable water supply, especially in developing countries. Rainwater samples collected from the underground storage tanks of a rooftop rainwater harvesting (RWH) system were exposed to different conditions of sunlight radiation in 2-L polyethylene terephthalate bottles in a solar collector with rectangular base and reflective open wings. Total and fecal coliforms were used, together with Escherichia coli and heterotrophic plate counts, as basic microbial and indicator organisms of water quality for disinfection efficiency evaluation. In the SOCO-DIS system, disinfection improved by 20–30% compared with the SODIS system, and rainwater was fully disinfected even under moderate weather conditions, due to the effects of concentrated sunlight radiation and the synergistic effects of thermal and optical inactivation. The SOCO-DIS system was optimized based on the collector configuration and the reflective base: an inclined position led to an increased disinfection efficiency of 10–15%. Microbial inactivation increased by 10–20% simply by reducing the initial pH value of the rainwater to 5. High turbidities also affected the SOCO-DIS system; the disinfection efficiency decreased by 10–15%, which indicated that rainwater needed to be filtered before treatment. The problem of microbial regrowth was significantly reduced in the SOCO-DIS system compared with the SODIS system because of residual sunlight effects. Only total coliform regrowth was detected at higher turbidities. The SOCO-DIS system was ineffective only under poor weather conditions, when longer exposure times or other practical means of reducing the pH were required for the treatment of stored rainwater for potable purposes.     

Comparative effectiveness of solar disinfection using small-scale batch reactors with reflective, absorptive and transmissive rear surfaces

This study investigated the enhancement of solar disinfection using custom-made batch reactors with reflective (foil-backed) or absorptive (black-backed) rear surfaces, under a range of weather conditions in India. Plate counts of Escherichia coli ATCC11775 were made under aerobic conditions and under conditions where reactive oxygen species (ROS) were neutralised, i.e. in growth medium supplemented with 0.05% w/v sodium pyruvate plus incubation under anaerobic conditions. While the addition of either an absorptive or a reflective backing enhanced reactor performance under strong sunlight, the reflective reactor was the only system to show consistent enhancement under low sunlight, where the process was slowest. Counts performed under ROS-neutralised conditions were slightly higher than those in air, indicating that a fraction of the cells become sub-lethally injured during exposure to sunlight to the extent that they were unable to grow aerobically. However, the influence of this phenomenon on the dynamics of inactivation was relatively small.     

Formulation of a mathematical model to predict solar water disinfection

A mathematical model was formulated that will facilitate the prediction of solar disinfection by analyzing the effect of sunlight exposure (x(1)) and the load of bacterial contamination (x(2)), as predictor variables, on the efficiency of solar disinfection (y). Aliquots of 0.1 ml containing average numbers of E. coli, ranging between 1 and 5 x 10(3)cells/ml raw water, were introduced into each of the 96 wells of polystyrene microtitre plates. Plates, with the lid on, were exposed to sunlight for varying exposures ranging between 1.04 x 10(3) and 8.40 x 10(3)kJ m(-2). Double strength nutrient broth was then added. After 48 h incubation wells containing visible contamination were considered as containing one cell or more that survived the exposure. Data showed that disinfection is dependent both on the load of bacterial contamination and sunlight exposure. This relationship is characterized by curves having shoulders followed by a steep decline and then tailing off in an asymptotic fashion. The shoulder size increased with the increase of the contamination load, however, the slope remains the same. Statistical analysis indicates a positive correlation among the variables (R(2) = 0.893); the mathematical model, y=1-(1-e(-kx(1)))(x(2)), represents the relationship, with k being the solar inactivation constant. The exposure required to produce a given decontamination level can be predicted using the equation: x(1)=-1/kln[1-(1-y)(-1/x(2))]e(-micro/rho.m/A), where micro is the linear attenuation coefficient (m(-1)), rho is the density, m is the mass and A is the area of the exposed part of the sample. The predictor variables (x(1), x(2)) strongly influence the efficiency of solar disinfection, which can be predicted using the suggested mathematical model. The present data provides a means to predict the efficiency of solar disinfection as an approach to improve the quality of drinking water mainly in developing countries with adequate sunshine all year-round.     

Source water quality effects on monochloramine inactivation of adenovirus, coxsackievirus, echovirus, and murine norovirus

There is a need for more information regarding monochloramine disinfection efficacy for viruses in water. In this study, monochloramine disinfection efficacy was investigated for coxsackievirus B5 (CVB5), echovirus 11 (E11), murine norovirus (MNV), and human adenovirus 2 (HAdV2) in one untreated ground water and two partially treated surface waters. Duplicate disinfection experiments were completed at pH 7 and 8 in source water at concentrations of 1 and 3 mg/L monochloramine at 5 and 15 °C. The Efficiency Factor Hom (EFH) model was used to calculate CT values (mg-min/L) required to achieve 2-, 3-, and 4-log₁₀ reductions in viral titers. In all water types, monochloramine disinfection was most effective for MNV, with 3-log₁₀ CT values at 5 °C ranging from 27 to 110. Monochloramine disinfection was least effective for HAdV2 and E11, depending on water type, with 3-log₁₀ CT values at 5 °C ranging from 1200 to 3300 and 810 to 2300, respectively. Overall, disinfection proceeded faster at 15 °C and pH 7 for all water types. Inactivation of the study viruses was significantly different between water types, but there was no indication that overall disinfection efficacy was enhanced or inhibited in any one water type. CT values for HAdV2 in two types of source water exceeded federal CT value recommendations in the US. The results of this study demonstrate that water quality impacts the inactivation of viruses and should be considered when developing chloramination plans.     

Kinetics of pneumatic flocculation

A mathematical model has been established to describe the kinetics of pneumatic flocculation in terms of the process variables: energy of agitation, volume of turbid water, temperature, water viscosity, amount of synthetic turbidity, flocculating time, amount of air flow, depth of water column and size of orifice. The mathematical model tested for both normal and taper types of flocculation. The experimental data vindicated the model relationship between the concentration ratio and the rate of air flow for the air flow rate above 50 cm³ min⁻¹. Accordingly, the developed mathematical model was then linearised.     

Inactivation of indigenous coliform bacteria in unfiltered surface water by ultraviolet light

This study examined the potential for naturally occurring particles to protect indigenous coliform from ultraviolet (UV) disinfection in four surface waters. Tailing in the UV dose-response curve of the bacteria was observed in 3 of the 4 water samples after 1.3-2.6-log of log-linear inactivation, implying particle-related protection. The impact of particles was confirmed by comparing coliform UV inactivation data for parallel filtered (11 microm pore-size nylon filters) and unfiltered surface water. In samples from the Grand River (UVT: 65%/cm; 5.4 nephelometric turbidity units (NTU)) and the Rideau Canal (UVT: 60%/cm; 0.84 NTU), a limit of approximately 2.5 log inactivation was achieved in the unfiltered samples for a UV dose of 20 mJ/cm2 while both the filtered samples exhibited >3.4-log inactivation of indigenous coliform bacteria. The results suggest that particles as small as 11 microm, naturally found in surface water with low turbidity (<3NTU), are able to harbor indigenous coliform bacteria and offer protection from low-pressure UV light.     

超声预处理强化紫外线消毒效果的研究

采用超声预处理强化紫外线消毒效果,并从分子生物学的角度探讨了其强化机理.结果表明,无论是单独紫外辐照还是超声预处理/紫外辐照,紫外辐照剂量与大肠杆菌灭活率之间均具有良好的线性关系;进行超声灭活时,超声功率、作用时间及菌悬液体积对灭活率均无显著意义(P>0.05),按影响大小排序为:菌悬液体积>超声功率>作用时间;当单独超声处理200 mL大肠杆菌悬液时,超声功率为200 W、作用时间为20 S条件下的灭活率最高(0.22-1g),该条件下继续进行紫外辐照,灭活率最高达到2.75-1g,1 h光复活后灭活率仍高达1.72-1g,超声/紫外协同作用的灭活率大于二者单独作用的灭活率之和,表明该条件下超声预处理起到了强化紫外线消毒的作用;超声处理只能改变细胞的结构,不能破坏其DNA;酶敏感位点数量与大肠杆菌的灭活率具有较强的相关性,相关系数约为0.88.     

Synergistic effect of the sequential use of UV irradiation and chlorine to disinfect reclaimed water

The effectiveness of UV and chlorination, used individually and sequentially, was investigated in killing pathogenic microorganisms and inhibiting the formation of disinfection by-products in two different municipal wastewaters for the source water of reclaimed water, which were from a microfilter (W1) and membrane bioreactor (W2) respectively. Heterotrophic plate count (HPC), total bacteria count (TBC), and total coliform (TC) were selected to evaluate the efficiency of different disinfection processes. UV inactivation of the three bacteria followed first-order kinetics in W1 wastewater, but in W2 wastewater, the UV dose-response curve trailed beyond approximately 10 mJ/cm² UV. The higher number of particles in the W2 might have protected the bacteria against UV damage, as UV light alone was not effective in killing HPC in W2 wastewater with higher turbidity. However, chlorine was more effective in W2 than in W1 for the three bacteria inactivation owing to the greater formation of inorganic and organic chloramines in W1 wastewater. Complete inactivation of HPC in W1 wastewater required a chlorine dose higher than 5.5 mg/L, whereas 4.5 mg/L chlorine gave the equivalent result in W2 wastewater. In contrast, sequential UV and chlorine treatment produced a synergistic effect in both wastewater systems and was the most effective option for complete removal of all three bacteria. UV disinfection lowered the required chlorine dose in W1, but not in W2, because of the higher chlorine consumption in W2 wastewater. However, UV irradiation decreased total trihalomethane formation during chlorination in both wastewaters.     

Removal of particle-associated bacteriophages by dual-media filtration at different filter cycle stages and impacts on subsequent UV disinfection

This bench-scale study investigated the passage of particle-associated bacteriophage through a dual-media (anthracite-sand) filter over a complete filter cycle and the effect on subsequent ultraviolet (UV) disinfection. Two model viruses, bacteriophages MS2 and T4, were considered. The water matrix was de-chlorinated tap water with either kaolin or Aldrich humic acid (AHA) added and coagulated with alum to form floc before filtration. The turbidity of the influent flocculated water was 6.4+/-1.5 NTU. Influent and filter effluent turbidity and particle counts were measured as well as headloss across the filter media. Filter effluent samples were collected for phage enumeration during three filter cycle stages: (i) filter ripening; (ii) stable operation; and (iii) end of filter cycle. Stable filter operation was defined according to a filter effluent turbidity goal of <0.3 NTU. Influent and filter effluent samples were subsequently exposed to UV light (254 nm) at 40 mJ/cm(2) using a low pressure UV collimated beam. The study found statistically significant differences (alpha=0.05) in the quantity of particle-associated phage present in the filter effluent during the three stages of filtration. There was reduced UV disinfection efficiency due to the presence of particle-associated phage in the filter effluent in trials with bacteriophage MS2 and humic acid floc. Unfiltered influent water samples also resulted in reduced UV inactivation of phage relative to particle-free control conditions for both phages. Trends in filter effluent turbidity corresponded with breakthrough of particle-associated phage in the filter effluent. The results therefore suggest that maintenance of optimum filtration conditions upstream of UV disinfection is a critical barrier to particle-associated viruses.     

三碘树脂用于饮用水消毒的试验研究

为给研制新型便携式净水装置提供必要的技术依据，通过试验考察了三碘树脂对饮用水的消毒效果。选用颗粒状三碘树脂填充在无菌玻璃管中制成消毒柱，对添加了人工培养的纯大肠杆菌菌种的Ⅲ类地表水进行过滤消毒，以出水的细菌总数、大肠菌群数、浊度、pH值及余碘浓度等指标来衡量三碘树脂的消毒效果。结果表明：在出水流量为110mL／min的条件下，当接触时间为12．05s时，消毒后出水的细菌学指标可达到军队战时饮用水卫生标准，出水余碘浓度始终低于0.7mg／L，对人体无害。三碘树脂具有良好的消毒效果，杀菌快速、持久，可作为便携式净水装置的消毒剂使用。     

Disinfection effectiveness of organic chloramines, investigating the effect of pH

The disinfection effectiveness of three organic N-chloramines (chlorinated amino acids and peptides) on the bacteria Escherichia coli (E. coli) was investigated, including a more detailed study into the pH dependency of the disinfection effectiveness of N-chloroglycine. The organic N-chloramines were prepared by combining sodium hypochlorite with each amino acid or peptide (glycine, Ala-Ala and Arg-Gly-Asp-Ser), at a N:Cl molar ratio of 1:0.4, and then used to treat E. coli suspensions for 180 min.No evidence of inactivation was observed at pH 8.1 for any of the tested organic N-chloramines. At pH 6.0 and 6.9, E. coli inactivation with N-chloroglycine was characterized by an initial lag phase, during which little or no measurable inactivation occurred, followed by a pseudo-first-order inactivation. This is in accordance with other results in the literature and supports the two step microbial inactivation mechanism proposed by some authors. Inactivation rate coefficients (Chick-Watson and lag coefficients) were calculated by fitting the experimental data with the Rennecker-Mariñas model. pH-dependent inactivation kinetics were observed, with faster inactivation rates occurring at lower pH values, when temperature and chlorine-to-nitrogen ratio where kept constant.N-chloroglycine was determined to be the only contributor to the inactivation process in these experiments. The free chlorine contribution was considered to be negligible in all experiments due to its very low concentration. As well, given that the anionic form of N-chloroglycine is expected to be the single predominant species over the tested pH range, changes in residual N-chloroglycine speciation could not be responsible for the observed pH-dependency of E. coli inactivation. However, while pH stress was considered as a possible synergistic factor, no significant effect of pH stress on E. coli viability was observed at the tested pH levels.     

自由氯、氯胺和顺序氯化对饮用水消毒效果的试验研究

研究了自由氯、氯胺和顺序氯化三种消毒方式对大肠埃希氏菌和粪肠球菌的灭活效果.结果表明,自由氯浓度越高,对细菌的灭活速率和最终灭活率越大;氯胺浓度越高,对细菌的灭活速率和最终灭活率越大;顺序氯化消毒效果优于单独使用自由氯或氯胺时的消毒效果.同时,还探讨了pH和温度对三种消毒方式的影响.     

Kinetics of UV inactivation of wastewater bioflocs

Ultraviolet disinfection is a physical method of disinfecting secondary treated wastewaters. Bioflocs formed during secondary treatment harbor and protect microbes from exposure to ultraviolet (UV) light, and significantly decrease the efficiency of disinfection at high UV doses causing the tailing phenomena. However, the exact mechanism of tailing and the role of biofloc properties and treatment conditions are not widely understood. It is hypothesized that sludge bioflocs are composed of an easily disinfectable loose outer shell, and a physically stronger compact core inside that accounts for the tailing phenomena. Hydrodynamic shear stress was applied to the bioflocs to peel off the looser outer shell to isolate the cores. Biofloc and core samples were fractionated into narrow size distributions by sieving and their UV disinfection kinetics were determined and compared. The results showed that for bioflocs, the tailing level elevates as the biofloc size increases, showing greater resistance to disinfection. However, for the cores larger than 45 μm, it was found that the UV inactivation curves overlap, and show very close to identical inactivation kinetics. Comparing bioflocs and cores of similar size fraction, it was found that in all cases cores were harder to disinfect with UV light, and showed a higher tailing level. This study suggests that physical structure of bioflocs plays a significant role in the UV inactivation kinetics.