Abundance, characterization, and removal of microplastics in different technology-based sewage treatment plants discharging into the middle stretch of the Ganga River, India

Tackling microplastic contamination in sewage sludge: Optimizing organic matter degradation, quantifying microplastic presence, and evaluating ecological risks for sustainable agriculture

The omnipresence of Microplastics (MPs) is a growing global concern. Using sewage sludge as fertilizer for soil amendment can be a potential source of MPs in agricultural soil if sludge contains MPs. Sludge is a complex matrix rich in organic matter, which hinders MPs separation. For maximal organic matter degradation, in this study, the application of Fenton reagents optimized for (Fe2+/H2O2) molar ratios, i.e., 1/2, 1/4, 1/6, 1/8, and 1/10. The results show that a molar ratio of 1/2 of Fe2+/H2O2 can remove 86.6 % of the organic matter in the sewage sludge. The greenness of the optimized method was assessed and compared to available methods using AGREEprep software. The method achieved a greenness score of 0.61, significantly higher than the highest score of 0.45 among the previously reported optimized methods. This optimized method was used in the analysis of MPs in sewage sludge from 14 sewage treatment plants in Ahmedabad. Also, the ecological risks due to the application of such sludge in agriculture were assessed. MPs analysis reveals variability in MPs contamination ranging from 2.43 to 22.72 × 103 units/kg of sludge. Small-sized MPs (0.05-0.25 mm) constitute the highest proportion (65 %), predominantly comprising fibers and fragments. From a chemical composition point of view, six different types of MPs are identified, among which PU, Nylon, HDPE, and PP are the most abundant. Ecological risk assessment indicated extreme hazards in terms of the potential ecological risk index being higher than 1200 for all the sludge samples due to the abundance of MPs, specifically of PU and Nylon.

Characterization of microplastic distribution, sources and potential ecological risk assessment of domestic sewage from ships

Shipboard domestic sewage, encompassing both black water and gray water, has the potential to transport significant quantities of environmentally harmful microplastics, a concern that has garnered increasing global attention. In this study, Fourier infrared (FTIR) detection was used to detect microplastics in marine domestic wastewater. The primary objective was to evaluate the abundance and characteristics of microplastics present in ship domestic sewage, investigate potential sources and influencing factors, and assess the ecological risks associated with ship sewage through analyses of microplastic abundance and hazard indices. The findings revealed that the mean abundance of microplastics in ship domestic sewage are 50.82 particles per liter(n/L), with gray water exhibiting significantly higher levels at 167 n/L compared to black water at 36.96 n/L and mixed sewage at 46.57 n/L. Fiber microplastics constituted a predominant 95% of all samples collected from ships, followed by film microplastics. In terms of color distribution, transparent and blue microplastics were the most prevalent, with the majority measuring between 100 and 1000 μm in size. Polyethylene terephthalate (PET) emerged as the most common polymer type, followed by polypropylene (PP). The risk assessment highlighted that microplastics in domestic wastewater pose significant ecological risks to aquatic organisms, with pollution load indices consistently reaching Class IV levels. Correlation analyses between microplastic abundance and the physicochemical properties of sewage demonstrated a significant relationship between microplastic levels and the concentration of suspended solids in ship sewage. This study provides essential data to inform the development of regulatory policies aimed at managing the discharge of black water and gray water discharges from both domestic and international vessels.

Extraction and analysis of microplastics in wastewater sludges of a multi-product pulp and paper mill

Pulp and paper wastewater sludges are waste streams produced in major quantities across the world. The recycling of these organic sludges, for example to soil amendments, is desired in the circular economy but carries the risk of potential pollutants to be also introduced into the environment. Pulp and paper wastewater sludges have been scarcely studied matrices in the microplastic research due to their complex composition. In this study, we optimized an extraction process for microplastics from pulp and paper wastewater sludges, and quantified and characterized microplastics down to 20 μm in primary sludge and biosludge generated at the wastewater treatment plant of a multi-product pulp and paper mill in Finland. The occurrence of microplastics was high in primary sludge, 900-1600 microplastics g-1 dry weight, while the maximum number of detected microplastics in biosludge samples remained at 210 g-1 dry weight. Biosludge samples suffered from larger amounts of remaining solids after the extraction process, thus compromising the detection of smaller microplastics (<100 μm) and increasing the uncertainty related to the interpretation of the results. The most prevalent microplastic shape in all samples was fragment, and the most recurring polymer types were polyethylene and polypropylene, while a polystyrene-based copolymer represented approximately 10% of identified microplastics in primary sludge. The present study advances the development of microplastic analysis of the challenging pulp and paper wastewater sludges and brings novel information to the progressing discussion of their circulation potential.

Significant effects of rural wastewater treatment plants in reducing microplastic pollution: A perspective from China's southwest area

Sewage systems are a major source for microplastics in riverine exports to oceans. Urban areas are generally considered hotspots for microplastic discharge, whereas emissions from rural areas remain largely understudied. Hence, this study investigated the abundance, characteristics, and polymer types of microplastics in rural wastewater treatment plants (WWTPs) in Guiyang and estimated the annual microplastic emissions of China based on sewage discharge. The influent abundance of microplastics was 3.8-8.2 items/L, the effluent abundance was 3.1-5.9 items/L, with a lower removal rate of 14.4 %-54.6 %, which might be influenced by lower operating loads and influent concentrations. Raman spectroscopy analysis revealed that polyvinyl alcohol (PVA) was the predominant polymer type. Rural WWTPs were more effective at removing large-sized particles (> 0.1 mm) and films, resulting in higher removal effectiveness by weight (49.1 %) compared to urban WWTPs (30.8 %). Based on the abundance of microplastics in WWTPs within the study area and China's annual sewage discharge, this study estimated the microplastic emissions released through sewage in China in 2022. The annual microplastic emissions through sewage in China were estimated to be 2995.7 tons, with rural and urban areas contributing 25.1 % and 74.9 %, respectively. Approximately 724.8 tons and 1001.6 tons of microplastics were removed from rural and urban WWTPs, respectively. This work indicates the unignorable emissions of microplastics from rural sewage and highlights the crucial role of rural WWTPs in reducing microplastic pollution.

Microplastics and Endocrine Disruptors in Typical Wastewater Treatment Plants in Megacity Shanghai

The fast development of China's urbanization has led to a notable release of emerging pollutants, including microplastics (MPs) and endocrine disruptors (EDCs). Generally, these pollutants enter the coastal environment through the discharge of wastewater treatment plants (WWTPs) and finally threaten the organisms in the receiving waterbody. The study investigated the environmental behavior of MPs and EDCs in two typical WWTPs in one of the megacities in China, Shanghai. The abundance of MPs in the influent ranged from 321 to 976 items/L. Four shapes (films, fragments, fibers, and microbead) were found, while fibers and films dominated. Transparent (31-63%) and white (20-47%) MPs were more frequently observed, while polyethylene terephthalate, cellulose, and cellophane were the main polymetric materials. The size of the MPs fell between 15.8 μm and 2220 μm, and the smaller one (<500 μm) dominated. The removal efficiencies of the two WWTPs for MPs ranged from 64% to 92%, and both WWTPs performed better for large pieces of MPs (>500 μm). For EDCs, total concentrations in the influent were detected, ranging from 113 to 2780 ng/L. Two groups, including phenolic estrogens (PEs) and steroid estrogens (SEs), were detected, and PEs, especially bisphenol A (BPA), were the predominant individuals among the studied EDCs. Specifically, PEs ranged from 82.8 to 2637 ng/L, while SEs ranged from 27.3 to 143 ng/L. The removal efficiencies of the WWTPs for EDCs varied (82.8-100%) as well, possibly due to the different treatment compartments and contamination load in the influent. Seasonal variations for both MPs and EDCs were observed. Specifically, concentrations of MPs and EDCs in WWTPs influent were higher in the wet season, as well as the removal efficiency. Furthermore, there was a correlation observed between the concentrations of MPs and EDCs, suggesting that MPs and EDCs may originate from the same source and that EDCs released by MPs cannot be ignored during treatment. Finally, the study evaluated the environmental risk of the effluents. MPs led to a minor risk (Level I), while EDCs might lead to an adverse impact on algae (RQs = 0.0014-0.024) and fish (RQs = 3.4-30.2). In summary, WWTPs received considerable amounts of MPs and EDCs. Although the WWTPs removed the contaminants efficiently, the environmental risk of the effluent needs to be noted.

Coagulative removal of polystyrene microplastics from aqueous matrices using FeCl3-chitosan system: Experimental and artificial neural network modeling

Effluent from sewage treatment plants (STPs) is a significant source of microplastics (MPs) re-entry into the environment. Coagulation-flocculation-sedimentation (CFS) process as an initial tertiary treatment step requires investigation for coagulative MPs removal from secondary-treated sewage effluents. In this study, experiments were conducted on synthetic water containing 25 mg/L polystyrene (PS) MPs using varying dosages of FeCl3 (1-10 mg/L) and chitosan (0.25-9 mg/L) to assess the effect of process parameters, such as pH (4-8), stirring speed (0-200 rpm), and settling time (10-40 min). Results revealed that ∼89.3% and 21.4% of PS removal were achieved by FeCl3 and chitosan, respectively. Further, their combination resulted in a maximum of 99.8% removal at favorable conditions: FeCl3: 2 mg/L, chitosan: 7 mg/L, pH: 6.3, stirring speed: 100 rpm, and settling time: 30 min, with a statistically significant (p < 0.05) effect. Artificial neural network (ANN) validated the experimental results with RMSE = 1.0643 and R2 = 0.9997. Charge neutralization, confirmed by zeta potential, and adsorption, ascertained by field-emission scanning electron microscope (FESEM) and Fourier-transform infrared spectroscopy (FTIR), were primary mechanisms for efficient PS removal. For practical considerations, the application of the FeCl3-chitosan system on the effluents from moving bed biofilm reactor (MBBR) and sequencing batch reactor (SBR)-based STPs, spiked with PS microbeads, showed > 98% removal at favorable conditions.