Microplastics in a University Wastewater Treatment Plant and a Small Community Aerated Wastewater Stabilization Pond

Analyzing Microplastics in the Environment: Striving to Better Assess Occurrence, Fate and Effects
Oral Presentation

Prepared by Z. Gao
University of Mississippi, 101 Creekmore Blvd, Apt 3222, OXFORD, MS, 38655, United States


Contact Information: zgao2@go.olemiss.edu; 662-715-9806


ABSTRACT

Microplastics (MPs), including synthetic fibers, fragments, and beads, enter wastewater streams. While the role wastewater treatment plants (WWTPs) play in the transport and release of MPs to the environment has been studied, our study is one of the first to examine MPs in wastewater stabilization ponds (WSPs). We characterized MPs in an oxidation ditch (OD) WWTP at the University of Mississippi and an aerated WSP in a small community in Oxford, Mississippi. For wastewater, each sample consisted of MPs >45 µm from 50 L of water, except for the WWTP influent which was from 1 L. Samples were subject to a wet peroxide digestion, density separation, and filtering before examination by stereomicroscopy. For the WWTP, we found higher abundances of MPs in both the influent and OD when students were on campus (fall) compared to off-campus (summer). MPs (particles/L ± 1SD, n=3) increased from 13±5 to 28±9 in the influent and from 2.9±0.7 and 4.1±0.7 in the OD. Concentrations also increased (p=0.073) in the effluent during the fall (0.65±0.17 vs. 0.78±0.13). There was a significant (p<0.005) decrease in MP concentrations from the influent (averaging >20 particles/L) to the effluent (averaging <0.8 particles/L), with many of the MPs entering the sludge stream. For the WSP, concentrations were similar between the pond water (4.1±0.6, n=6) and effluent (3.9±0.5, n=6), suggesting that WSPs may not be effective in MP removal. Surface sediment from the pond had lower MPs concentrations (11±2 particles/g) compared to the WWTP sludge. However, there was relatively high concentrations in surface algae (75±22 particles/g), suggesting that the surface scum harbors MPs. Total discharges of MPs (particles >45µm/day) from WWTP and WSP were estimated to be 8.9×108 and 6.5×108, respectively. Overall, our findings suggest that WWTPs and WSPs should not be ignored as a source of MP pollution.