Occurrence and distribution of microplastics in wastewater treatment plant in a tropical region of China

Wastewater Treatment Plants (WWTPs) are one of the main contributors to microplastics (MPs) in the environment. However, most of the current studies only reported the occurrence of MPs in WWTPs and rarely focused on the transfer and removal of MPs at each process unit. This work explores the MPs removal efficiency of a tropical urban WWTP during dry and rainy periods. The sewage and sludge samples were collected and analyzed to measure the MPs characteristics using a stereo-microscope and mu-FTIR techniques. Results showed the secondary treatment step eliminated most of the MPs, with an average concentration of 12.98 n/L in the effluent, indicating a 94.09% of total MPs removal rate. Throughout the sewage treatment stage, the most common MPs were black, small in size (25-380 mm), and identified as fibers. Moreover, the concentration of MPs in the effluent was higher in the rainy period compared to the dry period and some control strategies for MPs pollution in WWTPs are offered according to the results of this study.