Greening Greywater: Testing Filtration Systems to Protect Earthworm Food Supply

2013 Fairfax County Regional Science and Engineering Fair

The abstract below was written by the student. The Northern Virginia Soil and Water Conservation District made no editorial changes.

Greening Greywater: Testing Filtration Systems to Protect Earthworm Food Supply

By: Valentina Lohr, Thomas Jefferson High School for Science and Technology



The growing popularity of residential greywater irrigation threatens earthworm food supply. Last year’s project linked greywater containing triclosan, a common antibacterial in household products, to significantly lower earthworm weight gain and reduce soil microbial food supply than tap or creek water. Existing greywater filters may not remove triclosan. This experiment tested the ability of filtration systems to protect earthworm food supply. The hypothesis were that an activated charcoal and slow sand filter would result in significantly higher earthworm weigh gain and more diverse soil microbes than a slow sand filter alone. 

Three filtration systems-no filter, slow sand filter, and slow sand filter with activated charcoal filter-were tested in planters simulating lawn irrigation conditions. Worm weight was measured before and after the 17-day treatment period. Optical density readings of soil bacteria in a 31 substrate BioLog® Ecoplate were measured daily from post-treatment samples. Average well color development (AWCD), measuring carbon utilization, and Shannon-Weaver Diversity Indexes were calculated and significance across treatments was tested with Analysis of Variance (ANOVA) and t-tests.

There was no significant difference in earthworm biomass across treatments. At 72 hours after inoculation, the activated charcoal filter exhibited significantly high Shannon-Weaver Index values, indicating a more diverse soil microbial community, than the slow sand filter and no filter. Though worms were not affected in this experiment, a reduction in diversity of food supply can have long term consequences for resilience. A cost-effective charcoal filter can “green” household greywater irrigation.

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