Wastewater Applications
Alluvial soils may also be used to purify waste-water being returned to a river after use. Treated wastewater is typically discharged into a percolation pond on the alluvial flood plain rather than flowing directly into the river. Chemical filtration will cease when all reactive sites within the flow pathway through aquifer soil have reacted. Physical filtration tends to become more effective as trapped particulates block interstitial passages between alluvial soil particles; but may ultimately limit flow rates through the soil. Particulates on the river side of the soil interface may be periodically scoured away by turbulent flow. Wastewater percolation ponds may require maintenance to break up or remove a scum layer (Schmutzdecke) forming at the bottom of the pond. Biological filtration remains effective unless organic loading causes anaerobic conditions within the riverbed alluvium.
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