Gayla Mae, in areas where the groundwater is used as the drinking water source, nitrates from septic tank effluent could become a contaminant if the concentration of septic systems is too great. The USEPA maximum contaminant level (mcl)for nitrates in drinking water is 10 parts per million (ppm), or 10 milligrams per liter (mg/l). This very low mcl for nitrates is ridiculous in my view, considering that high nitrate concentrations in drinking water affects a miniscule percentage of the general population, but that is another issue. I am unaware of the mcl for nitrates in drinking water in other countries of the world.
The traditional approach employed to control high nitrates from septic tank systems in groundwater is through dilution. Minimum densities of septic systems to attain the proper dilution of nitrates are generally half acre densities, but this area could be greater depending upon the natural background levels of nitrate in the groundwater. The sewage disposal system regulations in some jurisdictions in the USA require nitrate removal capabilities of a treatment system to produce an effluent with no more than 10 mg/l.
If the health department regulations require nitrate removal from the septic tank effluent, then the recirculating sand filter will accomplish this. If the discharge of nitrates to the groundwater is not an issue on your specific site, then perhaps another technology would be more appropriate.
It is difficult to advise you as to which technology to choose without knowledge of the regulatory constraints, and site constraints that must be considered. It is particularly difficult to make a more specific recommendation to you because you have chosen not to reveal your geographic location in the world.
Septic System Consultant