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Format:
Print
Author:
Tharp, Rebecca
Dept./Program:
Natural Resources
Year:
2011
Degree:
MS
Abstract:
Nearly a billion people worldwide lack access to safe drinking water, leading to nearly 2 million deaths per year (UN20I0, WHO 2010, Vorosmarty 2011). The most affected are those living in developing countries where access to improved services is lacking and infrastructural limitations inhibit reliable material transport that could improve water quality.
Sand filtration provides exceptional primary disinfection via ecological processes in the active uppermost layers ofsand (schmutzdecke) in a ripened filter. Secondary, or residual, disinfection is most often achieved by chlorine application. Though effective at providing protection for stored and transported water, its toxicity, expense and difficult dosing requirements make its use in developing communities a concern.
This research aims to determine if Mentha aquatica, an aquatic mint species, can work in conjunction with intermittently operated biosand filter (BSF) units as a living secondary disinfectant to eliminate the apparent concerns with chlorine for application in developing regions.
Four BSF units were built and analyzed for their ability to reduce bacterial counts as a factor of flow rate and influent colony forming unit (cfu) density. The data support evidence of a relationship between filter flow rate and bacterial reduction and a connection between increased influent bacterial counts and reduction in filter accuracy. Normally operating filters exhibited fewer bacterial colonies in effluent (p=0.01) when flow rates averaged under 300 mL/minute. Filters spiked with high E. coli counts (15,000-40,000 cfu/mL) responded similarly.
Capacity for mint to reduce pathogenic bacteria in its growth water was investigated with two types of experiments: one utilized K-12 E. coli in high (>2,000 cfu/mL) concentrations and the second used unadulterated surface water. All experiments operated as batch reactors and tested bacteria counts at regular intervals, up to 48 hours. K-12 trials indicated overall reduction in bacteria between 0 and 48 hours, but in a time frame not in keeping with published research. Surface water trials exhibited a general trend of more rapid increase in coliform counts in test units from 0 to 24 hours. Test unit counts exceeded controls at 24 hours (p<0.05) followed by a rapid reduction culminating in fewer colonies in test units than controls (p<0.05) at 48 hours.
Disinfectants capable of providing a residual effect for drinking water sources are uncommon but important for improving water quality for those who are in the greatest need. The action of M. aquatica may not work fast enough in the arrangement tested here. However, the significant difference in measurements between tests and controls indicate a need for further study, perhaps using this species with greater root density or as partofacomplexstand of plants. Additional potential exists for the use of extracted compounds rather than relying on living root exudation which would more easily allow dosing standardization.