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EFFECT OF ANAEROBIOSIS ON FILTER MEDIA POLLUTANT RETENTION
Citation:
Clark**, S., R. Pitt, AND P. Brown. EFFECT OF ANAEROBIOSIS ON FILTER MEDIA POLLUTANT RETENTION. Presented at ASCE Urban Water Resources Research Council/Engineering Foundation Conf, Snowmass, CO, 8/19-24/2001.
Description:
One of the primary problems with downflow filtration of stormwater runoff is the clogging of the filter prior to the medium's exhaustion of its chemical capacity. Upflow filtration using a siphon control may be a possibility for improving the life of the filters. However, for upflow filtration with siphon control for entering water, it would be expected that only the top of the filter would be exposed to air (unlike a gravity filter where the top and bottom are potentially exposed to air between storms), and an anaerobic environment could develop. This paper will present the results of a series of tests that were conducted to determine if four potential filter media (sand, activated carbon, peat moss, and compost) were able to retain trapped pollutants even if an anaerobic environment developed in the filter between storm events. At the end of the exposure time, the dissolved oxygen concentration and the oxidation-reduction potential (ORP) of each aerobic and anaerobic sample were taken. The samples were filtered through a 0.45 ug gel membrane filter, and the filtrates were analyzed for ammonia, nitrate, total nitrogen, phosphate, total phosphorus, and metals (calcium, magnesium, iron, copper, lead, and zinc). Results indicated that permanent retention by the filter media for the heavy metals may occur even when the filter goes anaerobic. However, retention of the nutrients may occur under anaerobic conditions. This indicates that in situations where nutrient release could be a problem for the receiving water, the filter needs to stay aerobic. Therefore, upflow filtration may nt be a suitable stormwater treatment technology for those sites. The permanent retention of the heavy metals indicates that upflow filtration may be feasible for sites where the primary concern for stormwater pollution is metals. Potential sites could include scrap metal recyclers and junkyards where the runoff metals concentrations may exceed 1 mg/L.