Microplastics (MPs) have recently been documented as an emerging pollutant that poses a critical threat to human beings, and aquatic as well as terrestrial ecosystems. Wastewater treatment plants (WWTPs) are usually suspected of being major contributors to environmental microplastics that can rise environmental disutility in distinct ways. This study aimed to determine the removal rates and microplastic concentration of three wastewater treatment plants in Oman with different treatment processes which are conventional activated sludge (CAS), membrane bioreactor (MBR), and sequence batch reactor (SBR). Wastewater samples from different treatment stages were collected and analyzed to determine the morphology, size, color, and polymer type. The collected samples were filtered through a set of sieves ranging from 1 mm to 45 µm. Oxidation treatment was applied for all samples using Fenton's reagent followed by density separation by sodium chloride solution. 10% from each sampling point was tested utilizing Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR- FTIR) to confirm the polymer types of MPs. Risk assessment was performed using both the pollution load index (PLI) and hazard index (HI) based on the chemical toxicity and concentration of the detected particles in all examined WWTPs. The PROMETHEE method was used to rank the risk of sampling sites based on different criteria that posed potential ecological and human health risks. Overall, the results show that the average number of 0.99 MP/L, 1.38 MP/L, and 0.93 MP/L was found in the final treated effluent of Samail WWTP, Al Seeb WWTP, and Al Ansab WWTP, with overall removal efficiencies of 82.5%, 77.4%, and 79.2%, respectively. The number of MPs in sludge samples was 77.1 MP/L, 49.7 MP/L, and 80.3 MP/L found in Samail WWTP, Al Seeb WWTP, and Al Ansab WWTP, respectively. The combined load of microplastics released from all three WWTPs with discharged treated effluent totaled 187.2 ×106 per day. Most detected MPs in tertiary effluent were small (< 425 µm) and fibers in shape. Although diverse treatment stages are capable of removing a significant proportion of MPs, microfibers can effectively survive the studied treatment processes, including advanced treatment using ultrafiltration (UF). The major types of MPs in this study were polypropylene, low-density polyethylene, polyurethane, polyethylene terephthalate, and Polyvinyl chloride. Al Ansab sludge was ranked as the most hazardous sampling site. The outcomes of this study show that a considerable number of microplastics are discharged into the environment through treated effluent and sludge. The application of on-site management advanced practices for microplastic remediation such as nanotechnology shall be recommended to the wastewater management authority in Oman.