Plastics are synthetic or semi-synthetic polymeric materials with a wide range of additives (plasticizers, acid scavengers, pigments, thermal stabilizers). Their unique properties such as lightweight, elasticity, durability, resistance to corrosion and moisture lead to a wide range of application fields. The plastic particles that are larger than 1 nm but smaller than 5 mm in size are defined as microplastic particles (MPs). Many different environments contain MPs including the air, soil, ocean, and even freshwater systems. Moreover, microplastic particles cause an increasing concern as they pose threats to aquatic species as well as human beings. This type of pollutant is ubiquitous on our planet and might cause a global hazard in terms of environmental health.
There are two types of microplastic particles: primary and secondary. Primary MPs can be produced to have a specific small size which is widely used in personal care products, cosmetics, different detergents, and cleaners. For example, researchers have found between 327 and 832 microplastic particles per gram in toothpaste and facial scrubs [1], [2]. Secondary MPs are fragmented from larger-sized pieces of plastics as a result of environmental degradation processes. Either primary or secondary MPs have different sizes, shapes, colors, and chemical compositions. The properties of MPs mentioned above are crucial for removing these particles.
Studies indicated that wastewater treatment plants (WWTPs) play an important role in the microplastic particles removal process. The majority of MPs from industrial and domestic sources are captured in wastewater treatment plants. Modern WWTPs include three main stages of treatment: primary precipitation (sand or other larger debris settling and grease removal), secondary settling (biological treatment), and tertiary treatment (advanced oxidation processes). The removal efficiency of MPs between countries is surprisingly variating from 64% in Southeast Spain to 99% in Finland [3],[4]. However, even advanced wastewater treatment technologies (such as ozonation, chlorination, physical sorption, ultrafiltration, and membrane bioreactors) are unable to completely remove microplastic particles from sewages. According to Murphy (2016), despite a 98% removal rate, over 6.5-107 MPs could enter the aquatic environment daily from a WWTP in Scotland [5]. The research on microplastic removal across WWTP might help reach significant changes in environmental improvement.
The aim of this research work is to analyze microplastic particles removal efficiency and distribution at different stages of WWTP in Lithuania. The full characteristics of MPs (size, shape, color, and chemical composition) are also fully evaluated and described.
The new insights into MPs pollution levels in influent and effluent wastewater might help create more efficient wastewater treatment systems and ensure environmental safety.