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Tracing the fate of microplastic in wastewater treatment plant: A multi-stage analysis of treatment units and sludge
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Researchers tracked microplastics through every stage of a wastewater treatment plant and found that while treatment removes many particles from the water, most end up concentrated in the leftover sludge. Fibers and fragments were the most common shapes, made primarily of polyester and polyethylene. Since treated sludge is often spread on farmland, this creates a pathway for microplastics to enter soil and potentially the food chain.
Microplastic (MP) pollution is ubiquitous in the environment presenting a global problem for both scientists and the general public. One of the major pathways of MPs entering the natural environment is through wastewater treatment plants (WWTPs). Once MPs reach the natural environment, they are posing threat to aquatic ecosystems and public health. The aim of this study is to investigate the concentration, morphology, and composition of MPs in different treatment units of a WWTP. Sampling included different points across WWTP in the water and sludge lines. Pre-treatment of the samples consists of advanced Fenton oxidation, and alkaline and enzymatic digestion followed by density separation. Once the particles were isolated, their morphology and size were studied using a stereoscopic and optical microscope followed by final confirmation with ATR-FTIR and micro-FTIR spectroscopy. Microplastic particle concentrations exhibit significant reductions as water undergoes treatment in the WWTP. For summer sampling, concentrations decreased from 351 MP/L (influent) to 35 MP/L (primary clarifier), 32 MP/L (biological reactor), and 13 MP/L (2.3 MP/L) (secondary clarifier). Similarly, winter sampling showed reductions from 403 MP/L (influent) to 159 MP/L (primary clarifier), 178 MP/L (biological reactor), and 26 MP/L (5.6 MP/L) (secondary clarifier). Removal efficiency of WWTP is high and exceeds 96%. The most abundant morphology is fibers followed by fragments and films. Polymers such as PE, synthetic cellulose, PP, PVC, PE-PP, PEEA, PA, acrylamide, and PES are widely detected in different units of WWTP. The number of MPs that are avoided from being emitted into the environment through direct water discharge was estimated to be 9.1 × 10 MP/year. Removed MPs tend to accumulate in the sludge that is used for agricultural purposes although it should be managed as waste properly, avoiding the transition of MPs pollutants to terrestrial ecosystems adding to the number of MPs that will inevitably end up in receiving water bodies through direct WWTP effluent discharge that was set in 5.1 × 10 MP/year in the studied WWTP.
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Scientists studied how tiny plastic particles called microplastics move through wastewater treatment plants and found that most of them end up trapped in the leftover sludge rather than in the treated water. This matters because that sludge is often used as fertilizer on farmland, meaning these plastics could be entering our soil, crops, and potentially our food supply. The researchers also developed better methods for detecting microplastics in messy samples like sludge, which is an important step toward understanding just how widespread this contamination really is.
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