Microplastics in Sewage Sludge: A Known but Underrated Pathway in Wastewater Treatment Plants

Abstract

Interest in the presence of microplastics (MPs) in wastewater has grown significantly in recent years. In fact, wastewater treatment plants (WWTPs) represent the last barrier before the discharge of MPs into an aquatic ecosystem. The research has highlighted how MPs are in part effectively removed from the waters and accumulated inside the sewage sludge (SeS) produced by the WWTP, being a cause for concern, especially in the case of agricultural reuse. This work aims to analyze the existing literature on the (i) methodical procedure for MPs analysis (thermal, spectroscopic, optical analyses), (ii) qualitative and quantitative presence of MPs in SeS, (iii) effect on sludge properties, and (iv) the possible accumulation in amended soils. Based on the results already obtained in the literature, this work aims to provide critical insights to stimulate interest in the topic and direct future research on aspects that should be deepened. In particular, it emerges that there is a clear need for standardization of the collection methods and the analytical techniques for identifying and quantifying MPs, since their physico-chemical characterization and the study on aging and on the response towards acid or basic pre-treatments are fundamental for the understanding of microplastics ecotoxicological potential.

Microplastic Contamination in Human Stools, Foods, and Drinking Water Associated with Indonesian Coastal Population

“…Environments 2021, 8, 138 2 of 9 its accumulation in sewage sludge [8,12]. Due to their abundance, dura-bility, and size, microplastic can be ingested and incorporated into the tissue and organs of various aquatic and terrestrial organisms [13].…”

Removal of Polystyrene Microplastics from Aqueous Solution Using the Metal–Organic Framework Material of ZIF-67

“…Fluorescent PSMPs (with average diameter of 1.0 µm, 1% w/v) were purchased from the Tianjin Beisiline Chromtech Research Center, (Tianjin, China). The fluorescent PSMPs stock solution was diluted using deionized water, then treated with an ultrasonic device (KQ-100DE, KunShan Ultrasonic Instruments Co., Ltd., Jiangsu, China) for 10 min at 100 W and 20 kHz to obtain the desired PS concentrations (5,10,15,20,25,30,40, and 50 mg/L). The ZIF-67 used in this investigation was prepared through a high-throughput production method [47].…”

“…The PSMP adsorption rates of ZIF-67 (0.4 g/L) were then measured in response to various PSMP concentrations (5,10,15,20,25,30,40, and 50 mg/L). The contact time and temperature were 20 min and 298 K, respectively.…”

“…The effect of reaction time on PSMP adsorption performance was assessed at different contact times (1,5,10,20,30,40,50, and 60 min) at a constant 0.4 g/L ZIF-67 dose. The volume of the PSMP solution (5 mg/L) was 30 mL, with a contact temperature of 298 K.…”

“…As reported, microplastics have already been detected in wastewater in large amounts (0.05 ± 0.024 n/L), including plastic particles, fibers, fragments, films, and granules [27,28]. Microplastics will inevitably discharge into the aquatic environment, and further affect the survival of animals, plants, and microorganisms [29,30]. Several methods have been developed to remove MPs from wastewater, including filtration, coagulation, foam flotation, and magnetic separation [31][32][33][34][35].…”