Nicole Horne ACF Abstract FY13
Removal Efficacy of Harmful Microbes and Contaminants in Biosand Filter Microcosms
4th American Society of Microbiology (ASM) Conference on Beneficial Microbes
Freshwater is a shrinking resource in large parts of the Earth, with overuse and contamination in underdeveloped countries further rendering the available supply of water unsafe. An inexpensive remedy is the use of Biosand filters of 60-100 L volume (BSFs) in every household, classroom, and hospital, delivering safe potable water – a UN Millennium goal. Whereas physical filtration of particulate impurities through graded sand is well known, there is poor understanding of the effectiveness of the microbial biofilm within BSFs in ridding water of harmful contaminants. To address this void, we investigated the efficacy of BSFs in filtering harmful contaminants: total coliforms, E. coli, arsenic, and microcystin-LR in a 3-phase study, using self-designed microcosm syringes of 60 mL volume – micro scale analogs of BSFs. Muskegon Lake, a mesotrophic urban lake in Michigan, served as the source water. In Phase I, filters exhibited significant pathogen removal from source water, upon biofilm maturity. Over a 3-day period, a reduction of total coliforms from 12.2 – 6.3 MPN/100mL in input water to 1.0 - <1 MPN/100mL in output water was observed – a 92 - 86% removal efficiency (RE). Concurrently, E. coli was reduced from 7.5 – 5.2 MPN/100mL in input water to 1.0 - <1 MPN/100mL in output water – an 87 - 83% RE. In a repeated experiment, over a 6-day period, a reduction in total coliforms from 42.0 – 8.5 MPN/100mL in input water to 2.0 - <1 MPN/100mL in output water was observed, a 95 – 89% RE. Scale-up into the full-sized Hydraid® BSF (Cascade Engineering) showed a reduction in total coliforms ranging from 104 – 21.6 MPN/100mL in input water to 3.0 – 1.0 MPN/100mL in output water over a 3-day sampling period, a 99 - 86% RE. In Phase II, addition of rusted Fe filings to microcosms resulted in reduction of arsenic (a common groundwater contaminant in many parts of Asia) from 100μg As in input water to 0μg As in output water, a 100% mean RE (n=4) in two separate experiments. Without rusted Fe fillings, mean RE was 65-75%. Phase III involved the investigation of microcystin-LR (a hepatotoxin produced by bloom-forming cyanobacteria in eutrophic lakes worldwide) removal in the absence and presence of a mature biofilm. Before biofilm maturity, mean removal efficiency was 17-30% (n=4) over a 3-day period. Following biofilm maturation, mean removal efficiency ranged from 82-95% over a 6-day period. Upon scale-up into the full-sized Hydraid® BSF, a reduction in microcystin-LR ranged from 94 - 93% mean RE (n=3) over a period of 3 days. Our study demonstrates that mature BSFs effectively remove common pathogenic microbes and harmful cyanobacteria toxins and chemical contaminants, making them a viable option for delivering safe point-of-use drinking water in undeveloped countries.
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