Wastewater treatment plants (WWTPs) play a crucial role in mitigating microplastic (MP) release to the environment. In this paper, a WWTP of a textile manufacturing plant in Guangdong, China, was investigated to identify MP characteristics and the effectiveness of wastewater treatment within the plant. Laser Direct Infrared (LDIR) and Liquid Chromatography with Mass Spectrometry (LC-MS/MS) were applied to quantify both the number and the mass of the microplastics in the effluent of the textile manufacturing plant where most of the wastewater were from three printing and dyeing lines. The study further investigated the MP removal efficiency of each wastewater treatment process of the industry-owned WWTP and analysed the removal mechanism of each step, highlighting limitations in detecting and eliminating MPs. It is observed that (1) the results from LDIR and LC-MS/MS can be complementary to each other; (2) the MP concentration in the influent was 1730 n/L by number and 13.52 µg/L by mass; (3) the total removal efficiency of the WWTP were 99% by the number of MPs and 67.7% by the mass of MPs; (4) nine types of polymers have been identified in the influent, of which Polyamide (PA) was dominating; (5) hydrolysis acidification removed PA most; (6) aerobic tank, sand filter, and biological aerated filter (BAF) showed low removal efficiency; (7) coagulation and sedimentation tank had the highest removal efficiency to PET than any other processes.

Microplastics (MPs) removal by coagulation and sand filter was investigated in a secondary wastewater treatment plant effluent matrix. The samples were collected and treated using three typical coagulants, i.e., ferric chloride (FeCl3), polyferric sulfate (PFS) and polyaluminum chloride (PAC). Results showed that all the three tested coagulants can effectively remove MPs with applicable dosages in tertiary treatment (10-50 mg/L). The highest removal rate obtained was 61% with 40 mg/L PFS, and PFS were slightly more efficient than PAC and FeCl3. After sand filtration, about 75.7% of MPs was removed. The combined PFS (40 mg/L) +sand filter process could remove 91% of MPs, 82% of suspended solids (SS) and 85% of total phosphorus (TP). The treatment cost of coagulant was about 0.0594 Yuan/t wastewater. Therefore, it is technologically and economically feasible to use coagulation and sand filter process to remove MPs from wastewater in tertiary treatment process in wastewater treatment plant.