Adler, IJ; (2014) Application of filtration and silver-ion based disinfection to purify rainwater for potable uses in rural communities of Mexico. Doctoral thesis , UCL (University College London).

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Abstract

With growing pressures on water supplies worldwide, rainwater harvesting (RWH) is increasingly seen as a viable option to provide drinking water to an expanding population. However, rooftop runoff is not without quality issues. Microbiological and chemical contamination have been detected in several studies, posing a health risk for consumers. This research explores the use of silver ions, combined with conventional filtration and settling mechanisms, as a safe and affordable treatment method that can be applied at a small scale. The systems were installed and tested in rural communities of San Miguel de Allende, a Mexican semi-arid region, throughout two different periods of fieldwork analyses. Lab-scale models were also implemented at UCL, in order to further refine the technology. Silver has been known for centuries to be a powerful disinfectant, with no known harmful effects to humans if applied in appropriate doses. However, implementation in small-scale rainwater harvesting systems has received little attention, possibly due to a general perception that it is complicated and/or expensive. The devices studied in this thesis are able to dose silver ions at a relatively low cost, avoiding the use of complex nano-materials. System performance is seen to be highly linked to source water conductivity and ionic strength, highlighting the importance of adapting the technology for the specific case of RWH. Total coliform elimination efficiencies of up to 99.9% are achieved in the field, with a marked exception where cross-contamination from external seepage occurs. Sites with relatively clean rooftops show an absence of total coliforms in the untreated runoff, compared with others where values as high as 1650 CFU/100 ml are recorded. Disinfection using an emerging technique for bacteriophage detection is investigated in the laboratory, indicating a capacity to inactivate viral particles. Technology adoption issues are also explored, particularly where increased contamination occurs due to insufficient stakeholder participation. Observations show that the silver ion dispensers themselves require little maintenance, while the other components of the system tend to pose more of a challenge.

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