A WOOD FILTER PILOT TEST: AN INNOVATIVE TREATMENT METHOD FOR ROADWAY RUNOFF POLLUTANTS

Urban water bodies receive a significant amount of pollution from stormwater runoff. The runoff pollution problem is often addressed by detention ponds or similar best management practices. But, detention ponds do not effectively remove dissolved constituents, such as heavy metals and PAHs. In our previous research we demonstrated that wood fibers significantly enhance the removal of dissolved contaminants under laboratory conditions (up to 90%). This presentation is about a pilot-scale wood filter test installed at a detention pond. The principal goal was to determine if wood fibers could effectively remove contaminants from runoff under field conditions. Four different filters were installed to determine sorption of nitrate, phosphate, copper, iron, and PAHs as a function of differences in wood mass, different residence times, and changes in temperature and pH. An average of 28% of the dissolved PAH contaminants were removed during the pilot test, but it was found that simple design chances can enhance the efficiency to 50% or more. The heavier molecular weight PAH compounds, i.e. the PAHs with higher organic carbon partitioning coefficients, sorbed more readily than the lighter molecular weight compounds. The PAH sorption effectiveness of Aspen wood was not affected by temperature or pH; however, the greater the mass of wood, the greater the sorption and effectiveness. The wood fibers appeared to promote nitrification, increasing the nitrate levels in the water, especially in the winter. More nitrate was detected in the winter than in the summer filter. The filters were 24% effective in removing phosphate from the water, but the wood leached phosphate for a few days after installation. Both copper (29%) and iron (40%) were effectively removed, especially under acidic conditions. Intense precipitation caused the filter to be less effective, and even flushed PAHs off the filter. The combined overall effectiveness of all four wood filter tests in removing phosphate, heavy metals, and 10 PAH compounds that entered the detention pond system was 31%. Laboratory tests demonstrated that Cedar wood is a very promising alternative to Aspen wood. Even after more than 50 days of continuous flushing with contaminated water, the PAH removal remained between 66% and 92%, depending on the compound studied.