Evaluation of the Feasibility of Foam Glass as Filter Media in Rain Garden

Objectives:In order to recycle and resource waste glass, the feasibility of foam glass as filter media was evaluated, and column experiments using foam glass media were conducted to confirm the applicability as filter media in rain garden. Through this experiment, various design factors to be considered can be derived in application of foam glass media in the rain garden.Methods:Sieve analysis and SEM/EDS analysis were conducted to confirm the physicochemical properties of the foam glass. Column experiments filled with only foam glass and mixtures of sand and foam glass were conducted to simulate rain garden to evaluate the removal efficiency of suspended solids and turbidity using the foam glass media, head difference (Δh) and hydraulic conductivity (K) changes, and calculation of filtered suspended solids loading using both discrete and cumulative mass approach. Finally, comparison of filtration performance with various filter media used in LID facilities was performed to evaluate the feasibility of foam glass media in rain garden.Results and Discussion:Since foam glass media has a lower density than water, homogeneous particle size, and smooth surface with pores of various sizes, foam glass media effectively induces internal capture and external adsorption of suspended solids. Foam glass media has been applied to high suspended solids and turbidity removal efficiency. As the suspended solids inflow load increased, clogging occurred in the pores and the removal efficiency gradually decreased, but the foam glass media with lower density than water was continuously disturbed and rearranged due to the head difference energy, and some clogging were alleviated by rearrangement of pores and channels. The load of suspended solids in precipitated, adsorbed, and retained on the foam glass was calculated using the effluent sample (discrete) collected at regular time intervals and the continuously accumulated sample (cumulative) from the output. The filtered suspended solids load calculated using the cumulative mass approach was higher due to the estimation of the amounts of suspended solids remaining in the filtration column is lower because the samples (discrete) collected at regular time intervals from the output do not reflect the amount of suspended solids that change over time. Thus, the amounts of suspended solids removed through the filtration process can be much more accurately estimated using the cumulative samples. Finally, when comparing the removal efficiency with other filter media, foam glass can be used as excellent filter media with higher removal efficiency and greater lifespan.Conclusion:Foam glass media with smooth surface, pores of various sizes, and lower density than water can rearrange and regenerate pores to alleviate some clogging, resulting in high suspended solids and turbidity removal efficiency for a long period of time. Considering that the amount of suspended solids filtered is determined by various factors such as particle size and distribution, porosity, depth, linear velocity, and inflow load of the suspended solids, the feasibility test using foam glass media through long-term field experiments is warranted. The amounts of suspended solids removed through the filtration process can be much more accurately estimated using the cumulative samples.