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The Occurrence and Risk Assessment of Microplastics: different treatment technologies for wastewater treatment plants in Oman
Summary
A study of three wastewater treatment plants in Oman — using conventional activated sludge, membrane bioreactor, and sequencing batch reactor technologies — quantified and characterized MPs at multiple treatment stages, including sludge. Membrane bioreactor technology achieved the best MP removal from effluent, but all plants concentrated MPs in sludge, highlighting an underregulated route for microplastic release back into the environment.
Microplastics (MPs) are considered an emerging pollutant and one of the greatest challenges for many states and are a significant environmental concern that requires to be addressed. Municipal wastewater treatment plants (WWTPs) are usually suspected of being major contributors to environmental MPs that can cause environmental disutility in distinct ways. The purpose of this study is to quantify and characterize MPs at different treatment technologies in major WWTPs in Oman as well as to mitigate human and environmental risks. Water samples were taken from three WWTPs; WWTP A (CAS), WWTP B (MBR), and WWTP C (SBR). Sampling points were Primary, tertiary effluent, and sludge (10L, 30L, and 2.5 L respectively). Water samples were then sieved in stainless sieves with a mesh size of 1 mm, 425 µm, 45 µm, and 1.2 µm. The samples then undergo wet peroxidation (WPO) to remove the organic matter pursued by density separation of inorganic matter. Suspected MPs were then counted under a light microscope and morphologically characterized into fibers, fragments, foams, spheres, and others. Detected MPs were then counted under a light microscope and morphologically characterized into fibers, fragments, foams, spheres, and others. Fiber MPs were dominant in all effluent types, followed by a considerable amount of fragments. Most detected MPs in tertiary effluent were small (< 425µm) and fibers in shape. Almost all shapes colors and several sizes of MPs were detected in the sludge sample which is considered the sink of microplastics. Nonetheless, diverse treatment stages are capable of removing a significant proportion of MPs, fiber MPs can effectively survive the studied treatment processes, including advanced treatment using ultrafiltration. 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..