Enhancing Virus Removal in Low-Cost Ceramic Pot Filters for Drinking Water Treatment

Research output: ThesisDissertation (TU Delft)

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Abstract

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.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Delft University of Technology
Supervisors/Advisors
  • van Halem, D., Supervisor
  • Medema, G.J., Supervisor
Award date7 Feb 2022
DOIs
Publication statusPublished - 2022

Funding

Delft Global Initiative

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