Performance of expanded polystyrene particles in deep bed filtration

The efficiency of filtration through a bed of expanded polystyrene (EPS) of different characteristics was investigated on the example of separation of iron hydroxide flocks from water. The effects studied included the EPS density, bed equivalent diameter, and bed uniformity coefficient. Studies by scanning electron microscopy showed that surface roughness of EPS particles is primarily determined by particle density. Low-density EPS particles have higher roughness than the high-density ones, and this fact has a great effect on the filtration cycle. Low-density particles yield a low head loss and long filtration cycle, which decrease with increasing particle density. As far as the bed equivalent diameter is concerned, only a small increase in particle size of the existing particle formulation decreases significantly the filtration cycle. It is very important to notice that similar bed equivalent diameter can be achieved by mixing different particle fractions, changing at the same time the uniformity coefficient. That is the reason why we investigated the effect of uniformity coefficient and showed that there exists its optimum value, yielding a maximum filtration cycle. Our investigation showed that the uniformity coefficient is of crucial importance in the optimization of EPS bed filtration.