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M.Y.M. Soliman
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Natural organic matter (NOM) is present in water matrix that serves as a drinking water source. This study examined the effect of low and high NOM concentrations on inactivation kinetics of a model RNA virus (MS2) and a model DNA virus (PhiX 174) by copper (Cu2+) and/or silver (Ag+) ions. Cu and Ag are increasingly applied in household water treatment (HHWT) systems. However, the impact of NOM on their inactivation kinetics remains elusive despite its importance for their application. The presence of NOM in water led to faster virus inactivation by Cu2+ but slower by Ag+. The fastest inactivation kinetics of MS2 (Kobs = 4.8 h−1) were observed by Cu in water containing high NOM (20 mg C/L). Meanwhile, for PhiX 174, the fastest inactivation kinetics (av. Kobs = 3.5 h−1) were observed by Cu and Ag synergism in water containing high NOM. Altogether, it can be concluded that the combination of Cu and Ag is promising as a virus disinfectant in treatment options allowing for multiple hours of residence time such as safe water storage tanks.
...
Natural organic matter (NOM) is present in water matrix that serves as a drinking water source. This study examined the effect of low and high NOM concentrations on inactivation kinetics of a model RNA virus (MS2) and a model DNA virus (PhiX 174) by copper (Cu2+) and/or silver (Ag+) ions. Cu and Ag are increasingly applied in household water treatment (HHWT) systems. However, the impact of NOM on their inactivation kinetics remains elusive despite its importance for their application. The presence of NOM in water led to faster virus inactivation by Cu2+ but slower by Ag+. The fastest inactivation kinetics of MS2 (Kobs = 4.8 h−1) were observed by Cu in water containing high NOM (20 mg C/L). Meanwhile, for PhiX 174, the fastest inactivation kinetics (av. Kobs = 3.5 h−1) were observed by Cu and Ag synergism in water containing high NOM. Altogether, it can be concluded that the combination of Cu and Ag is promising as a virus disinfectant in treatment options allowing for multiple hours of residence time such as safe water storage tanks.
Access to safe drinking water is an essential human right and a crucial element to human survival. The quality of drinking water, has strong and direct impact on human health. Unless free of fecal contamination, water is unsafe to drink. Yet, to date, 2 billion people remain without access to safe drinking water. Consequently, the burden of waterborne disease remains a global threat to public health especially in developing countries. Fortunately, many interventions in the past decades aimed to provide safe drinking water in developing countries. Household water treatment (HHWT), provided individuals with a cheap and effective solution to treat water. Since its introduction, HHWT has dramatically improved the microbial quality of water, reduced the burden of waterborne diseases and its associated mortality. In particular, ceramic pot filters (CPFs) were described as one of the most sustainable, popular and effective HHWT systems in reducing waterborne diseases. In 2014, it was estimated that 4 million users rely on CPFs for water treatment. CPFs provide consumers with an adequate protection against bacteria and protozoa which accounts for its reported protection against waterborne diseases. However, CPFs are not highly protective against all waterborne pathogens since they fail to remove viruses. The exceptionally small size of viruses enables them to pass through the filter pores. Therefore, the objective of the thesis was to enhance virus removal in ceramic pot filters (CPFs). It was hypothesized that continued filtration of water through CPFs would lead to biofilm growth which might enhance virus removal. This hypothesis was examined using MS2 bacteriophage as ssRNA model virus. It was found that the growth of biofilm was dependent on the level of nutrients in raw water and as the subsequent virus (MS2) removal observed. The trade-off was the lower flow rates in high nutrient biofilms. Although high nutrient biofilms had better removal of virus (2.4 ± 0.5 logs), it reduced flow rates in the filters making them unusable. This limitation in virus removal and flow rate called for alternative solution. Therefore, the use of metals, namely silver (Ag) and copper (Cu), was examined as potential additives to CPFs to enhance virus removal. Ag is already being applied to CPFs in many factories but its contribution to virus removal has been controversial and only reported using model RNA virus (MS2). Cu is cheaper than Ag, hence it provided the possibility of an economical alternative or complementary addition. To that end, Cu and Ag were examined for their antiviral efficiency; separately and combined. MS2 (ssRNA) and PhiX 174 (ssDNA) bacteriophages were tested as conservative model viruses for RNA and DNA waterborne viruses. Ag (0.1 mg/L) exhibited antiviral efficiency against MS2 and PhiX 174 (≤ 2 log inactivation over 6 hours), which was reduced in the presence of 20 mg C/L of natural organic matter (NOM) in water. Overall, Cu (1 mg/L) was a more potent disinfectant than Ag (0.1 mg/L). For example, in water containing NOM (20 mg C/L), Cu inactivated ≥ 6 logs of MS2 over 3 hours, and to lesser extent PhiX 174 (≥ 1 log in 3 hours). Moreover, significant synergy of Cu and Ag in combination was observed for MS2 in the absence of NOM and to a lesser extend in presence of low NOM at pH ≥7. A synergistic effect of Cu and Ag together in disinfecting PhiX 174 was observed, but only in presence of NOM in water. Overall to achieve ≥ 3 logs of inactivation by Cu and/or Ag, hours of interaction between the metal(s) and the virus were needed. Because antiviral efficiency of Cu and Ag was observed, each was applied to ceramic filter discs (CFDs) according to the factory method (Filtron, Nicaragua) by painting metal ions solution using a hand brush. Virus removal by filtration through metal painted CFDs was examined. In addition, virus inactivation in the receptacles containing filtrate (in which there was leached Cu or Ag) was examined over 5.5 hours of storage. The contribution of Cu or Ag to enhancing virus removal by filtration was minor compared to the observed inactivation following hours of filtrate storage. This observation highlighted the value of utilizing virus inactivation as post treatment / post filtration option using Cu and/or Ag ions. Unfortunately, the rapid leaching of Cu from CFDs was an obstacle to testing Cu and Ag combination. It is therefore recommended to investigate alternative methods of Cu dosing other than painting. This thesis quantified the contribution of biofilm growth to improving virus removal in CPFs, although the effect varied. With the in-depth assessment of Cu and/ or Ag antiviral efficiency, examining the effect of water quality parameters on the achieved virus inactivation, the potential of Cu and Ag was assessed. Post treatment or safe water storage relying on Cu and Ag ions can be applied in principle to provide safe drinking water in compliance with the WHO requirements.
...
Access to safe drinking water is an essential human right and a crucial element to human survival. The quality of drinking water, has strong and direct impact on human health. Unless free of fecal contamination, water is unsafe to drink. Yet, to date, 2 billion people remain without access to safe drinking water. Consequently, the burden of waterborne disease remains a global threat to public health especially in developing countries. Fortunately, many interventions in the past decades aimed to provide safe drinking water in developing countries. Household water treatment (HHWT), provided individuals with a cheap and effective solution to treat water. Since its introduction, HHWT has dramatically improved the microbial quality of water, reduced the burden of waterborne diseases and its associated mortality. In particular, ceramic pot filters (CPFs) were described as one of the most sustainable, popular and effective HHWT systems in reducing waterborne diseases. In 2014, it was estimated that 4 million users rely on CPFs for water treatment. CPFs provide consumers with an adequate protection against bacteria and protozoa which accounts for its reported protection against waterborne diseases. However, CPFs are not highly protective against all waterborne pathogens since they fail to remove viruses. The exceptionally small size of viruses enables them to pass through the filter pores. Therefore, the objective of the thesis was to enhance virus removal in ceramic pot filters (CPFs). It was hypothesized that continued filtration of water through CPFs would lead to biofilm growth which might enhance virus removal. This hypothesis was examined using MS2 bacteriophage as ssRNA model virus. It was found that the growth of biofilm was dependent on the level of nutrients in raw water and as the subsequent virus (MS2) removal observed. The trade-off was the lower flow rates in high nutrient biofilms. Although high nutrient biofilms had better removal of virus (2.4 ± 0.5 logs), it reduced flow rates in the filters making them unusable. This limitation in virus removal and flow rate called for alternative solution. Therefore, the use of metals, namely silver (Ag) and copper (Cu), was examined as potential additives to CPFs to enhance virus removal. Ag is already being applied to CPFs in many factories but its contribution to virus removal has been controversial and only reported using model RNA virus (MS2). Cu is cheaper than Ag, hence it provided the possibility of an economical alternative or complementary addition. To that end, Cu and Ag were examined for their antiviral efficiency; separately and combined. MS2 (ssRNA) and PhiX 174 (ssDNA) bacteriophages were tested as conservative model viruses for RNA and DNA waterborne viruses. Ag (0.1 mg/L) exhibited antiviral efficiency against MS2 and PhiX 174 (≤ 2 log inactivation over 6 hours), which was reduced in the presence of 20 mg C/L of natural organic matter (NOM) in water. Overall, Cu (1 mg/L) was a more potent disinfectant than Ag (0.1 mg/L). For example, in water containing NOM (20 mg C/L), Cu inactivated ≥ 6 logs of MS2 over 3 hours, and to lesser extent PhiX 174 (≥ 1 log in 3 hours). Moreover, significant synergy of Cu and Ag in combination was observed for MS2 in the absence of NOM and to a lesser extend in presence of low NOM at pH ≥7. A synergistic effect of Cu and Ag together in disinfecting PhiX 174 was observed, but only in presence of NOM in water. Overall to achieve ≥ 3 logs of inactivation by Cu and/or Ag, hours of interaction between the metal(s) and the virus were needed. Because antiviral efficiency of Cu and Ag was observed, each was applied to ceramic filter discs (CFDs) according to the factory method (Filtron, Nicaragua) by painting metal ions solution using a hand brush. Virus removal by filtration through metal painted CFDs was examined. In addition, virus inactivation in the receptacles containing filtrate (in which there was leached Cu or Ag) was examined over 5.5 hours of storage. The contribution of Cu or Ag to enhancing virus removal by filtration was minor compared to the observed inactivation following hours of filtrate storage. This observation highlighted the value of utilizing virus inactivation as post treatment / post filtration option using Cu and/or Ag ions. Unfortunately, the rapid leaching of Cu from CFDs was an obstacle to testing Cu and Ag combination. It is therefore recommended to investigate alternative methods of Cu dosing other than painting. This thesis quantified the contribution of biofilm growth to improving virus removal in CPFs, although the effect varied. With the in-depth assessment of Cu and/ or Ag antiviral efficiency, examining the effect of water quality parameters on the achieved virus inactivation, the potential of Cu and Ag was assessed. Post treatment or safe water storage relying on Cu and Ag ions can be applied in principle to provide safe drinking water in compliance with the WHO requirements.
Virus removal by ceramic pot filter disks
Effect of biofilm growth and surface cleaning
Ceramic pot filters are household water treatment and safe storage (HWTS) systems designed to improve the microbial quality of drinking water. They yield high log reduction values (LRVs) for bacterial and protozoan pathogens but provide very little removal of viruses. This study investigated virus removal of ceramic filter discs (CFDs), using feed water with 3 different nutrient levels under extended continuous operation and limited cleaning frequency. The results show that filter use without cleaning resulted in biofilm growth and MS2 LRV values increased with increasing feed water nutrient content. Cleaning the filter surface by scrubbing led to a partial or total loss in improved LRVs, indicating the importance of this biological top layer to the removal of MS2. Overall, the removal capacity of a matured biofilm remained constant, regardless of its age. MS2 LRVs ranged between 0.9 ± 0.2 LRV for low nutrient (LN), 1.6 ± 0.2 LRV for medium nutrient (MN) and 2.4 ± 0.5 LRV for high nutrient (HN) biofilms. Interestingly, a change in feed conditions for the HN filters resulted in an unprecedented high LRV of >4 LRV, which supports further investigation of the mechanistic role of biofilms in virus removal.
...
Ceramic pot filters are household water treatment and safe storage (HWTS) systems designed to improve the microbial quality of drinking water. They yield high log reduction values (LRVs) for bacterial and protozoan pathogens but provide very little removal of viruses. This study investigated virus removal of ceramic filter discs (CFDs), using feed water with 3 different nutrient levels under extended continuous operation and limited cleaning frequency. The results show that filter use without cleaning resulted in biofilm growth and MS2 LRV values increased with increasing feed water nutrient content. Cleaning the filter surface by scrubbing led to a partial or total loss in improved LRVs, indicating the importance of this biological top layer to the removal of MS2. Overall, the removal capacity of a matured biofilm remained constant, regardless of its age. MS2 LRVs ranged between 0.9 ± 0.2 LRV for low nutrient (LN), 1.6 ± 0.2 LRV for medium nutrient (MN) and 2.4 ± 0.5 LRV for high nutrient (HN) biofilms. Interestingly, a change in feed conditions for the HN filters resulted in an unprecedented high LRV of >4 LRV, which supports further investigation of the mechanistic role of biofilms in virus removal.
Journal article
(2020)
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Mona Y.M. Soliman, Gertjan Medema, Boris Estrada Bonilla, Stan J.J. Brouns, Doris van Halem
Cu and Ag have been used as bactericidal agents since ancient times, yet their antiviral capacity in water remains poorly understood. This study tested the effect of copper (Cu) and silver (Ag) on model RNA and DNA viruses MS2 and PhiX 174 in solution at pH 6–8. Cu caused MS2 inactivation with similar rates at pH 6 and 7 but was inert towards PhiX 174 regardless of pH. Ag inactivated both viruses, causing denaturation of MS2 and loss of capsid spikes in PhiX 174. Ag inactivation rates were pH dependent and increased with increasing pH. At pH 8, 6.5 logs of PhiX were inactivated after 3 h and 3 logs of MS2 after only 10 min. The combined use of Cu and Ag revealed synergy in disinfecting MS2 at pH ≥ 7. Although metal concentrations used were higher than the desired values for drinking water treatment, the results prove a promising potential of Cu and Ag combinations as efficient viricidal agents.
...
Cu and Ag have been used as bactericidal agents since ancient times, yet their antiviral capacity in water remains poorly understood. This study tested the effect of copper (Cu) and silver (Ag) on model RNA and DNA viruses MS2 and PhiX 174 in solution at pH 6–8. Cu caused MS2 inactivation with similar rates at pH 6 and 7 but was inert towards PhiX 174 regardless of pH. Ag inactivated both viruses, causing denaturation of MS2 and loss of capsid spikes in PhiX 174. Ag inactivation rates were pH dependent and increased with increasing pH. At pH 8, 6.5 logs of PhiX were inactivated after 3 h and 3 logs of MS2 after only 10 min. The combined use of Cu and Ag revealed synergy in disinfecting MS2 at pH ≥ 7. Although metal concentrations used were higher than the desired values for drinking water treatment, the results prove a promising potential of Cu and Ag combinations as efficient viricidal agents.