Buried or recirculating sand filters can achieve an exceedingly high level of treatment of septic tank effluent before discharge to surface water or soil. Dosed recycling between sand filter and septic tank or similar devices can result in significant levels of nitrification/dentrification, equivalent to between 50 and 75 percent of overall nitrogen removal, depending on the recycling ratio. Regular buried or recirculating sand filters may require as much as 1 square foot of filter per gallon of septic tank effluent.