THE INFLUENCE OF SAND AND CLOTH TERTIARY FILTRATION ON MICROPLASTIC DEBRIS

Plastic debris is ubiquitous in nature and can have adverse effects on marine and terrestrial ecosystems. Microplastic particles have many anthropogenic sources, and a common pathway for microplastics to enter the environment is through residential wastewater. Wastewater must be treated at Wastewater Treatment Plants (WWTP’s) through a series of primary, secondary, and tertiary treatment processes. Although tertiary treatment is not required, many WWTP’s incorporate processes like sand and cloth filtration in order to meet federal EPA effluent water standards. How well do sand and cloth tertiary filtration methods reduce microplastics in our wastewater effluent has not been determined.

We examined the influence of tertiary treatment on microplastic concentrations at three different urban areas in central Illinois, USA. These five WWTPs served populations ranging from 3200 to 100,000 and had either sand, cloth or no filtration. We hypothesized that cloth filtration would reduce microplastic debris the most compared to sand and no filtration. We collected microplastics using a 333μm plankton net before and after tertiary filtration and processed the samples according to established protocols. Samples were also collected within the streams where effluent was discharged into. Microplastic particles were counted (fibers, beads, fragments) to determine what filtration methods are ideal for microplastic reduction.

Results from this study shed light on how well tertiary filtration methods can reduce incoming microplastic loads in wastewater. We found microplastic concentrations to range from .73 particles/m³ to 4.87 particles/m³ in WWTP effluent. These concentrations are similar to/higher than what has been found for other WWTP effluent studies. A combination of combined sewage flows into some of the WWTP’s could account for some of the higher microplastic loads. Cloth filtration did not reduce microplastics as much as initially thought. We have seen up to 85% reduction of microplastics from pre-treated waters, but also seen an increase in microplastic debris post cloth filtration. Sand filtration has reduced up to 83% of microplastic debris. Without a reduction of plastic products, our environment and biological communities will be seriously threatened as a result of our disposable lifestyle.