Abstract:
Microfibers, a major category of microplastics, have been widely detected in aquatic environments
worldwide, posing threats to the natural environment. Wastewater treatment plants (WWTPs) are
considered as a major sink and a source for microfibers. They are mainly found in the industrial
wastewater derived especially from textiles. However, in Sri Lanka, the understanding of the
removal of microfibers in WWTPs is limited, and thereby, the development of effective microfiber
remediation strategies has been constrained. To address this knowledge gap, this study aims to
assess the microfiber abundance at major treatment stages of a WWTP and the stage-wise
microfiber removal efficiency, highlighting the temporal variations over four consecutive sampling
months. Sampling was conducted in a centralized industrial WWTP, in the Colombo District, Sri
Lanka, from January to April 2025, at six sampling locations, including inlet, equalization tank,
inlet and outlet of the oxidation ditch, settlement tank (secondary), and discharge point, covering
major treatment stages of the WWTP. Microfibers were visually quantified using stereomicroscopy.
Results indicated a progressive microfiber reduction along the successive treatment stages with
influent microfiber concentrations ranging from 29.11 ± 5.34 to 46.44 ± 11.47 microfibers/L. The
secondary sedimentation tank demonstrated the highest removal achieving 78.5 %, serving as the
major settling process of the WWTP, in the absence of primary settling tank. Microfiber
concentration differed significantly across treatment stages (Kruskal-Wallis, p = 0.003) and was
strongly negatively correlated with treatment stages (Spearman’s ρ = – 0.843). The final discharge
point showed < 5 microfibers/L, highlighting an effective but incomplete removal. This study
underscores the need for advanced treatment strategies for mitigating microfiber contamination in
Sri Lankan wastewater treatment systems.
