Sunlight inactivation of somatic coliphage in the presence of natural organic matter

Effect of particulate matters on inactivation of bacteriophage MS2 under irradiation above 320 nm

The inactivation of bacteriophage MS2 under irradiation above 320 nm was investigated, focusing on different solution pH, ionic strength, and Suwannee River natural organic matter (SRNOM) concentrations when solutions contained organic or inorganic particle matters. Inorganic and organic particles were modeled using kaolinite (KAO) and Microcystis aeruginosa (MA), respectively. The results showed that the two types of particles influenced on MS2 inactivation under different conditions. The lower pH contributed to the greater MS2 aggregation within pH range of 3.0 to 8.0, leading to an increasing inactivation rate. The presence of KAO induced reactive oxygen species (ROS) under the action of irradiation above 320 nm, which promoted the inactivation of MS2. By comparison, the [Formula: see text] produced by MA after irradiation promoted the inactivation at pH < 6, whereas when the pH is ≥ 6, the inactivation effect of MS2 was lower than that of particle-free solution because MS2 was no longer aggregated and MA has a shading effect. In the presence of Na⁺ or Ca²⁺ cation, irradiation above 320 nm could not effectively inactivate the MS2 under particle-free solution. By comparison, KAO increased the inactivation efficiency as a photosensitizer. With the increase of Ca²⁺ concentration, MS2 was more easily adsorbed to MA than aggregation. Until Ca²⁺ concentration reached 20 mM, the inactivation effect in MA solution was enhanced. In the presence of SRNOM, the inactivation effect increased with the increase of SRNOM concentration. When the SRNOM was 20 mM, the inactivation increased in the particle-free solution due to the greater production of [Formula: see text]. Compared with the particle-free solution, the KAO and MA inactivation efficiency was lower.

Coliphages as a Complementary Tool to Improve the Management of Urban Wastewater Treatments and Minimize Health Risks in Receiving Waters

Even in countries with extensive sanitation systems, outbreaks of waterborne infectious diseases are being reported. Current tendencies, such as the growing concentration of populations in large urban conurbations, climate change, aging of existing infrastructures, and emerging pathogens, indicate that the management of water resources will become increasingly challenging in the near future. In this context, there is an urgent need to control the fate of fecal microorganisms in wastewater to avoid the negative health consequences of releasing treated effluents into surface waters (rivers, lakes, etc.) or marine coastal water. On the other hand, the measurement of bacterial indicators yields insufficient information to gauge the human health risk associated with viral infections. It would therefore seem advisable to include a viral indicator—for example, somatic coliphages—to monitor the functioning of wastewater treatments. As indicated in the studies reviewed herein, the concentrations of somatic coliphages in raw sewage remain consistently high throughout the year worldwide, as occurs with bacterial indicators. The removal process for bacterial indicators and coliphages in traditional sewage treatments is similar, the concentrations in secondary effluents remaining sufficiently high for enumeration, without the need for cumbersome and costly concentration procedures. Additionally, according to the available data on indicator behavior, which is still limited for sewers but abundant for surface waters, coliphages persist longer than bacterial indicators once outside the gut. Based on these data, coliphages can be recommended as indicators to assess the efficiency of wastewater management procedures with the aim of minimizing the health impact of urban wastewater release in surface waters.

Mathematical modelling of MS2 virus inactivation by Al/Fe-PILC-activated catalytic wet peroxide oxidation (CWPO)

Catalytic wet peroxide oxidation (CWPO) is a novel, alternative technology to conventional disinfection methods that are widely used to control microbial parameters in drinking water. To assess its effectiveness, new studies revealing the kinetics of MS2 coliphage inactivation by CWPO technology are required. This investigation therefore aimed to perform mathematical modelling of MS2 inactivation through CWPO technology activated by an Al/Fe-pillared clay catalyst (Al/Fe-PILC) in the presence of a synthetic surrogate of dissolved natural organic matter. The inactivation constant was obtained from two different statistical approaches, and the experimental data were better fitted to the pseudo-first-order Chick-Watson model in which the inactivation rate is constant. For this model, the maximum inactivation rate was k = 0.1648 min^-1, which was achieved in the MS2-3 catalytic test using an initial mass ratio of peroxide to active iron (Fe_act) of 1.2 mg H₂O₂/mg Fe_act. To estimate the inactivation rate due to reactive oxygen species (ROS), we supposed that the inactivation constant depends on both ROS and Fe_act. In this case, the maximum inactivation rate due to ROS was k_r = 2.4 × 10^-9 min^-1 (using 1.17 mg H₂O₂/mg Fe_act), which was achieved in the MS2-10 trial; both cases led to the conclusion that the optimal initial ratio of peroxide to active Fe in the catalyst in CWPO activated by Al/Fe-PILC was close to 1.2 mg H₂O₂/mg Fe_act. These kinetic studies showed that rapid inactivation takes place very early in the reaction, followed by slow inactivation during the remaining period of the recorded reaction time. This research revealed the strong potential of CWPO technology to improve microbiological parameters in drinking water due to the high catalytic performance in the heterogeneous Fenton reaction displayed by Fe sites incorporated in the Al/Fe-PILCs.

Natural Photosensitizers in Constructed Unit Process Wetlands: Photochemical Characterization and Inactivation of Pathogen Indicator Organisms

Dissolved organic matter (DOM) is a natural photosensitizer that contributes to the inactivation of microbial pathogens. In constructed treatment wetlands with open water areas DOM can promote sunlight disinfection of wastewater effluent, but a better understanding of DOM spectroscopic and photochemical properties and how they are impacted by different unit process wetlands is needed to inform design. The goals of this study were: (1) to investigate whether DOM isolates realistically represent the photochemistry of the source DOM in its original water and (2) to observe how changes of DOM along a treatment wetland affect its photochemistry, including pathogen inactivation. A pilot scale unit process wetland was studied that consisted of three different cells (open water, cattail, and bulrush) fed by secondary wastewater effluent. DOM was isolated using solid-phase extraction (SPE), photochemically characterized, and compared to the original water samples and standard DOMs. For MS2 coliphage, a virus indicator, the most efficient photosensitizer was the wastewater DOM isolated from the influent of the wetland, while for the bacterial indicator Enterococcus faecalis, inactivation results were comparable across wetland isolates. SPE resulted in isolation of 47% to 59% of whole water DOM and enriched for colored DOM. Singlet oxygen precursors were efficiently isolated, while some excited triplet state precursors remained in the extraction discharge. DOM processing indicators such as SUVA₂₅₄, SUVA₂₈₀, and spectral slopes including E₂/ E₃ ratios were reflected in the isolates. Photoinactivation of MS2 was significantly lower in both the reconstituted water samples and isolates compared to the original water sample, possibly due to disturbance of the trans-molecular integrity of DOM molecules by SPE that affects distance between MS2 and DOM sites with locally higher singlet oxygen production. For E. faecalis, results were similar in original water samples and isolates. Higher sorption of DOM to E. faecalis was roughly correlated with higher photoinactivation rates. To enhance sunlight disinfection in unit process wetlands, there is no advantage to placing open water cells after vegetated cells, as passage through the vegetated cells led to increased light absorption and lower singlet oxygen and triplet-state quantum yields and steady state concentrations.

Inactivation and Loss of Infectivity of Enterovirus 70 by Solar Irradiation

Enterovirus 70 (EV70) is an emerging viral pathogen that remains viable in final treated effluent. Solar irradiation is, therefore, explored as a low-cost natural disinfection strategy to mitigate potential concerns. EV70 was exposed to simulated sunlight for 24 h at a fluence rate of 28.67 J/cm2/h in three different water matrices, namely, phosphate-buffered saline (PBS), treated wastewater effluent, and chlorinated effluent. In the presence of sunlight, EV70 decreased in infectivity by 1.7 log, 1.0 log, and 1.3 log in PBS, effluent, and chlorinated effluent, respectively. Irradiated EV70 was further introduced to host cell lines and was unable to infect the cell lines. In contrast, EV70 in dark microcosms replicated to titers 13.5, 3.3, and 4.2 times the initial inoculum. The reduction in EV70 infectivity was accompanied by a reduction in viral binding capacity to Vero cells. In addition, genome sequencing analysis revealed five nonsynonymous nucleotide substitutions in irradiated viruses after 10 days of infection in Vero cells, resulting in amino acid substitutions: Lys14Glu in the VP4 protein, Ala201Val in VP2, Gly71Ser in VP3, Glu50Gln in VP1, and Ile47Leu in 3Cpro. Overall, solar irradiation resulted in EV70 inactivation and an inhibition of viral activity in all parameters studied.

Transformation of acetaminophen in natural surface water and the change of aquatic microbes

The kinetics and transformation pathway of acetaminophen (APAP) in natural surface water (one sample from the Yangtze River and three others from different lakes), and the changes of aquatic microbes in surface water were revealed in this study. Both photochemical and microbial reactions contributed to the transformation of APAP under irradiance of 1.0-250 mW/cm². Microbial compositions were significantly different among surface water, and same microbial transformation product (1,4-bezoquinone) was detected as the predominant biotransformation intermediate in four studied surface water, but the lag phase (12-50-h) for the transformation was highly dependent on the aquatic microbial abundance and composition. The lag phase no longer existed with irradiance increased to 5.9 mW/cm². Aquatic microbial abundance and composition were influenced by the presence of APAP and radiation, and the influence extent was dependent on microbial species. The findings demonstrated that the individual contribution of biotic and abiotic process to the overall transformation of APAP and maybe other phenol in surface water varied as the background composition of surface water and the external environment changed, and biotransformation dominated (>73%) the overall transformation of APAP in surface water.

Sunlight-mediated inactivation of health-relevant microorganisms in water: a review of mechanisms and modeling approaches

Health-relevant microorganisms present in natural surface waters and engineered treatment systems that are exposed to sunlight can be inactivated by a complex set of interacting mechanisms. The net impact of sunlight depends on the solar spectral irradiance, the susceptibility of the specific microorganism to each mechanism, and the water quality; inactivation rates can vary by orders of magnitude depending on the organism and environmental conditions. Natural organic matter (NOM) has a large influence, as it can attenuate radiation and thus decrease inactivation by endogenous mechanisms. Simultaneously NOM sensitizes the formation of reactive intermediates that can damage microorganisms via exogenous mechanisms. To accurately predict inactivation and design engineered systems that enhance solar inactivation, it is necessary to model these processes, although some details are not yet sufficiently well understood. In this critical review, we summarize the photo-physics, -chemistry, and -biology that underpin sunlight-mediated inactivation, as well as the targets of damage and cellular responses to sunlight exposure. Viruses that are not susceptible to exogenous inactivation are only inactivated if UVB wavelengths (280-320 nm) are present, such as in very clear, open waters or in containers that are transparent to UVB. Bacteria are susceptible to slightly longer wavelengths. Some viruses and bacteria (especially Gram-positive) are susceptible to exogenous inactivation, which can be initiated by visible as well as UV wavelengths. We review approaches to model sunlight-mediated inactivation and illustrate how the environmental conditions can dramatically shift the inactivation rate of organisms. The implications of this mechanistic understanding of solar inactivation are discussed for a range of applications, including recreational water quality, natural treatment systems, solar disinfection of drinking water (SODIS), and enhanced inactivation via the use of sensitizers and photocatalysts. Finally, priorities for future research are identified that will further our understanding of the key role that sunlight disinfection plays in natural systems and the potential to enhance this process in engineered systems.

Predicting attenuation of solar radiation (UV-B, UV-A and PAR) in waste stabilization ponds under Sahelian climatic conditions

Because of its importance in pathogen removal and algal productivity in waste stabilization ponds, sunlight penetration was measured in microcosms and in situ under Sahelian climatic conditions. The different wavelengths were detected using a submersible radiometer equipped with three sensors: UV-B (311 nm), UV-A (369 nm) and photosynthetically available radiation (PAR, 400-700 nm). UV-B was more attenuated than UV-A and PAR. Facultative pond was more light-attenuating than maturation pond. The mean euphotic depths for UV-B were 0.20 and 0.31 m, respectively, in the facultative and maturation ponds; PAR penetrated deeper with mean euphotic depths of 0.27 and 0.42 m, respectively. The mean Secchi depths were 0.16 and 0.10 m in the maturation and facultative ponds waters, respectively. In view of the reported results, the contribution of the deeper sections of ponds to pathogen removal mediated by sunlight seems negligible. Therefore, when designing WSPs, these findings should be considered to increase the penetration of damaging wavelengths in order to ensure efficient microbial removal. For more pathogen elimination, downstream shallow ponds could be considered. The paper also shows how suspended solids, turbidity, and Secchi depth are related to the attenuation coefficients and euphotic depths. The developed models could be used to predict light penetration and then algal growth and pathogen removal mediated by sunlight in waste stabilization ponds located in Sahelian climate.

Bacteriophages as indicators of faecal pollution and enteric virus removal

Bacteriophages are an attractive alternative to faecal indicator bacteria (FIB), particularly as surrogates of enteric virus fate and transport, due to their closer morphological and biological properties. Based on a review of published data, we summarize densities of coliphages (F+ and somatic), Bacteroides spp. and enterococci bacteriophages (phages) in individual human waste, raw wastewater, ambient fresh and marine waters and removal through wastewater treatment processes utilizing traditional treatments. We also provide comparisons with FIB and enteric viruses whenever possible. Lastly, we examine fate and transport characteristics in the aquatic environment and provide an overview of the environmental factors affecting their survival. In summary, concentrations of bacteriophages in various sources were consistently lower than FIB, but more reflective of infectious enteric virus levels. Overall, our investigation indicates that bacteriophages may be adequate viral surrogates, especially in built systems, such as wastewater treatment plants.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacteriophage are alternative fecal indicators that may be better surrogates for viral pathogens than fecal indicator bacteria (FIB). This report offers a summary of the existing literature concerning the utility of bacteriophage as indicators of viral presence (fecal sources and surface waters) and persistence (in built infrastructure and aquatic environments). Our findings indicate that bacteriophage levels in all matrices examined are consistently lower than FIB, but similar to viral pathogens. Furthermore, in built infrastructure (e.g. wastewater treatment systems) bacteriophage closely mimic viral pathogen persistence suggesting they may be adequate sentinels of enteric virus removal.