FLOW CHARACTERISTICS OF ROCK-REED FILTERS FOR TREATMENT OF LANDFILL LEACHATE

To characterize the flow patterns of wastewater through subsurface-flo w rock-reed filters, a combination of tracer studies and specific cond uctance measurements were used. Neither the tracer study nor the speci fic conductance measurements alone provided the necessary information to understand the flow of wastewater through the system. However, the data taken together indicate that preferential flow occurred due to de nsity effects and surface flow. In gravel substrates, dense wastewater flowed beneath the less dense rainwater and influent, resulting in a decrease in the residence time. Sand-and-gravel substrates, which expe rienced a great deal of surface flow as a result of clogging, were sho wn to have very little, if any, flow through the subsurface. The resul ts of this study indicate that both preferential and overland flow sho uld be taken into account for the proper design of rock-reed filters.