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Occurrence, quantification, and characterization of microplastics in sewage sludge from a university wastewater treatment system
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Researchers studying a wastewater treatment plant in India found that treated sewage sludge, often reused as fertilizer or disposed of on land, contains hundreds to over a thousand tiny plastic particles per kilogram, mostly tiny fibers and fragments from synthetic materials like nylon and plastic bags. Notably, plastic levels rose and fell along with how many people were using the campus, suggesting our daily habits directly feed plastic pollution into the environment. Since this sludge can end up in soil, water, or food systems, the findings raise concerns about how microplastics from everyday human activity may ultimately make their
Sewage sludge (SeS) produced in wastewater treatment plants (WWTPs) is increasingly recognized as a significant reservoir for microplastics (MPs). Despite this, comprehensive data on MP occurrence in advanced institutional treatment systems, particularly in developing countries, remain limited. This study provides a quantitative evaluation of MPs in SeS from an academic institution in India operating a hybrid Moving Bed Biofilm Reactor-Zero Liquid Discharge (MBBR-ZLD) system. Samples were collected fortnightly over a seven-month period (January-July) and analyzed using wet peroxide oxidation, density separation, stereomicroscopy, ATR-FTIR spectroscopy, SEM-EDX, and Nile Red fluorescence microscopy. Microplastics were detected in all samples, with concentrations ranging from 120 to 1145 particles per kilogram dry weight (n/kg dw). Particle sizes ranged from 7.02 to 4592 µm, with the 500-1000 µm size fraction being the most prevalent. Fibres dominated the morphology (43.3%), followed by fragments (39.5%) and films (11.5%). Polymer characterization identified eight types, with Nylon-PA6 (37.7%) and LDPE (16.0%) as the most abundant. Method validation using co-spiked reference materials yielded an overall recovery efficiency of 81.66 ± 2.51%, though recovery varied depending on particle type and size. Accordingly, correction factors were applied to improve data accuracy. A strong positive Spearman rank correlation was observed between campus occupancy and monthly mean MP concentration (ρ = 0.756, p = 0.049), suggesting that human activity significantly influences MP loading. This study provides a comprehensive evaluation of the temporal relationships between academic occupancy patterns and MP concentrations in SeS, along with their polymer profiles, in an Indian institutional MBBR-ZLD system. These findings highlight the role of institutional usage patterns in MP accumulation within MBBR-ZLD systems.
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