Biological Clogging in Storm Water Filters

Abstract

Biological clogging of filtration and infiltration systems has been acknowledged as a significant problem in the case of wastewater systems. However, scant research has been conducted on biological clogging in storm water filtration and infiltration systems, with the main hypothesis being that biological clogging is insignificant due to the low level of organics present in storm water. This article tested that hypothesis, using a laboratory-based approach. Five replicates of each zeolite-based filter design were dosed with storm water manifesting the following forms: (1) typical storm water (base case); (2) storm water containing very high nutrient concentrations to accelerate biological clogging; (3) typical storm water that was sterilized to suppress biological clogging; and (4) typical storm water with the addition of chlorine to suppress biological activity. The hydraulic performances of these four configurations were monitored over time until the systems were fully clogged. Loss on ignition (LoI) and microscopic analysis of accumulated material within the top layers of the filters were undertaken in an attempt to assess the level of organic matter present in clogging layers of the filters. It was found that all configurations performed differently in comparison to the base case, which represents the most likely set of operational conditions in the field. For instance, the chlorinated filters treated about 30% more storm water compared with the base case. Columns dosed with sterilized storm water treated almost the same volume of storm water but removed a greater quantity of sediment with higher treatment efficiency. Columns dosed with a high level of nutrients clogged more quickly than in the base case. Results of loss on ignition partially confirmed these findings. However, results of microbial cell counts provided tenuous evidence of biological clogging being present. Although the evidence was not overpowering, the variations observed in this study suggest that biological clogging in storm water filters warrants greater attention, which is mostly ignored at present.