Enhanced CBOD and Nitrogen Removal in Recirculating Sand Filter Wastewater Treatment System by Addition of Plastic Media to the Recirculation Tank.

摘要

An 8,000 gallon recirculation tank containing 5,400 gallons of wastewater is loaded with 758 pounds of Kaldnes polyethylene media to evaluate enhanced CBOD removal and dentrification in a recirculating sand filter system at the Giles Country TDOT Welcome Center on I-65 in Ardmore, Tennessee. Media that is circulated by a Flygt mixer provides a large protected surface for the growth of bacteria that consume CBOD. Media addition can mean cost savings since the sand filter is sized based on CBOD removal per square foot. If daily flows are increasing beyond design flows, the addition of media in the recirculation tank, a relatively inexpensive modification provides an environment for CBOD removal and postpones the need for increasing the sand filter size. The recirculation ratio was adjusted to provide complete nitrification. Results show that CBOD removal does occur in the recirculation tank and that nitrification occurs in the sand filter and is limited by the alkalinity of the wastewater. Denitrifying bacteria are growing on the media. The extent of denitrification is limited by the concentration of CBOD in the influent wastewater.