Fecal coliform and escherichia coli in microplastic biofilms grown in wastewater and inactivation by peracetic acid and microplastic monitoring in stormwater of a city, suburban college campus, and bioretention basin

Microplastics (MP) have been proposed as a vector for pathogenic microorganisms in the freshwater environment. The objectives of the first study were (1) to compare the fecal indicator growth in biofilms on MP and material control microparticles incubated in different wastewater fractions and (2) to compare MP biofilm, natural microparticle biofilm, and planktonic cell susceptibility to disinfection by peracetic acid (PAA). Biofilms were grown on high-density polyethylene, low-density polyethylene, polypropylene MP or wood chips (as a material control) and incubated in either wastewater influent or pre-disinfection secondary effluent. Reactors were disinfected with PAA, biofilms were dislodged, and fecal coliform and E. coli were cultivated. Fecal indicators were quantifiable in both MP and wood biofilms incubated in the wastewater influent but only on the wood biofilms incubated in secondary wastewater effluent. More fecal coliform grew in the wood biofilms than MP biofilms, and the biofilms grown on MP and woodchips were more resistant to disinfection than planktonic bacteria. Thus, it may be possible to refer to the disinfection literature for fecal indicators in biofilm on other particles to predict behavior on MP. Treatments that remove particles in general would help reduce the potential for fecal indicator bypass of disinfection. The investigation detailed above was published in the March 2021 issue of WER. The second part of the thesis consists of an investigation of microplastics in stormwater:Microplastics (MP) are a commonly reported pollutant in the freshwater, marine, and soil environment. The objectives of the second study were to determine (1) the microplastic concentration, (2) polymer fingerprints and (3) inter-storm variation of MP in two stormwater outfalls and a bioretention basin. Water samples were collected during rain events over the summer and fall of 2020 and MP content analyzed with ATR-FTIR. nMDS analysis was performed on polymer fingerprints and significant differences were observed in MP composition between sites. In addition, significant differences in MP concentration existed between sites as well. A negative correlation was observed between MP concentration and cumulative rainfall. Evidence of MP accumulation in green infrastructure was noted. When designing stormwater management systems, the removal of MP and other particulate matter must be considered to optimize receiving water quality.