Influence of different Wastewater Treatment Processes on the rate and characteristics of MPs released from WWTPs in Fiji, South Pacific

Abstract The global effects of MP (MP) pollution on the environment are concerning, and they are exacerbated by the multiple sources of pollution in aquatic environments such as urban runoff, waste mismanagement, industrial pollution, and so on. South pacific islands host a large diversity of aquatic flora and fauna and given its ecological significance it is necessary to identify the sources of MP pollution in the region. To date, very little attention has been given to identify whether effluents from wastewater treatment plants (WWTP) are acting as a significant source of MP in the South Pacific region and its countries. Therefore, the present study analyzed and compared the treatment methods and fate of MPs in the country’s two main WWTPs: 1) the Kinoya WWTP (simple secondary clarifier and trickling filter) and 2) Natabua WWTP (secondary pond treatment system). Sampling locations were based on the different treatment stages, and samples were collected from each stage of treatment before effluents were released into the ocean. Kinoya WWTP had an average of 3.45 ± 0.3 particles/L in the inlet stage and released an average of 0.3 ± 0.26 particles/L of MP through the outlet with 91% removal efficiency (RE) with an output equivalent of 4500 particles per day. The initial stage of treatment from the anaerobic pond outlet at Natabua had an average of 2.9 ± 1.05 particles/L, and the maturation outlet had an average of 0.53 ± 0.42 particles/L, a removal efficiency of 81% and thus an output equivalent of 4558 particles/L of MP. Polymer analysis under FTIR confirmed that cellophane or semi-synthetic cellulose and polypropylene were common polymers in the final effluent in Kinoya WWTP, and Natabua plant has cellophane or semi-synthetic cellulose, polypropylene and polyethylene were observed as common polymers. Although there are numerous study that have compared wastewater treatment processes, this is the first study in Fiji that investigates the efficiency of the two methods of water treatment process in the context of microplastic pollution and emphasizes the effectiveness of the treatment stages in determining the concentration of MP released into the ocean.