Microfiber Removal in Wastewater Treatment: A Stage-wise Analysis from Sri Lanka

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.