**1. Introduction**

Plastics are the most used and versatile material of the modern age, and inevitably global production of plastics has increased exponentially to meet demand. Of all the plastics ever produced it is estimated that 10% has been released into the ocean [1]. Furthermore about 33% of the plastic produced every year is designed to be single use and is discarded within a year [2]. Plastic waste has become a major issue in the last century, mostly damaging marine environments, and activists have taken action to neutralize this problem. Although microplastics are yet not considered as threatening as larger plastics, they are growing in importance. It is extremely important that both plastics and microplastics are collected from rivers, oceans and waste waters to be recycled to block the environmental disaster these are causing.

Microplastics are the product of mechanical, chemical and thermal degradation of plastic objects, varying in size between 1 μm and 5 mm [3]. These particles can be found on surface waters and land, and from fresh-water to deep ocean sediments, making them susceptible to environmental factors such as heat, erosion and extreme pressures that may degrade them at rates not yet well established [4]. Through degradation they can assume many different shapes and sizes that fall into the following 5 categories [3] (**Table 1**).

The density of microplastics can vary significantly from (10–2300 kg/m3 ). The most common plastics like ABS (1030–1210 kg/m<sup>3</sup> ), PET (1300–1500 kg/m<sup>3</sup> ) and


**Table 1.**

*5 categories of degradation characteristics for microplastics found in the environment.*

PVC (1150–1700 kg/m<sup>3</sup> ) are all denser than fresh and sea waters (997–1025 kg/m<sup>3</sup> ), this allows for most of the microplastics present in water to be separated using gravity. Physical and chemical hazards related to ingestion of microplastics across a diverse range sizes and types have generated ecological concerns. Further, the impacts on human health of the chemical exposure to plastic debris from seafood consumption, and toxins that adsorb onto microplastic debris from the surrounding water, are currently unknown.

This paper proposes to use hydro cyclones to separate them from fresh and seawaters. Firstly, the paper briefly summarizes the functioning of hydro cyclones, secondly applies them to the microplastics separation, through mathematical and CFD models. And finally concludes that they could be very effective in separating up to 98% of the microplastics from the water.

## **2. Hydro cyclones**

Cyclones are used in industry as dust separators; they isolate the dust from air using differential centripetal forces generated by fast circular flow in a cylinder that allow the denser material to flow outward and downward, while the lighter material to flow inward and upward. Hydro cyclones work by using the same principles as the normal cyclone. Hydro cyclones have a cylinder-conical shape which have a tangential feed inlet into the upper cylindrical section and two outlets along the axis at the top and bottom. Hydro cyclones operate vertically: the fluid enters horizontally through an inlet, tangential to the cylinder, that creates a circular flow into the cyclone. This, in turn, produces a vortex effect, where the denser particles circulate around the outer edge of the chamber reducing their kinetic energy through friction along the cylinder and cone walls and, thus, sinking downward and leaving through the spigot. The lighter particles, due to the small area of the spigot, are taken into the inner part of the vortex that flows upward exiting at the top of the cyclone. These two downward and upward cyclonic flows are called, respectively, underflow and overflow [8]. The product of the separation is at the underflow where the denser microplastics exit as a slurry (**Figure 1**).

Theoretical Advantages of using hydro cyclones to separate microplastics are [4]:


*Performance Analysis and Modeling of Microplastic Separation through Hydro Cyclones DOI: http://dx.doi.org/10.5772/intechopen.99447*

**Figure 1.** *Diagram of the behavior and characteristics of a hydro cyclone [4].*

