In conditions of high groundwater or very slowly permeable

soils,   anaerobic  soil   conditions  may  exist.    Under   these

conditions, nitrification will not occur and the nitrogen will

remain in the form of ammonium. Ammonium is readily adsorbed by

soil materials of high clay content and hence migrates much more

slowly (U.S. EPA, 1978).     As adsorption sites for ammonium are

exhausted on the soil particles, the ammonium will migrate farther

and farther from the septic system. Most of the ammonium is later

subjected to nitrification and. leaching if aerobic conditions

become reestablished (Lance, 1972).

      Because denitrification is unlikely to occur beneath soil

absorption systems and adsorption of ammonium to soil particles is

limited, dilution has been the primary mechanism for nitrate

reduction.    Because groundwater flow patterns are difficult to

predict and because many residential areas have high densities of

homes, dilution is an unacceptable part of the wastewater treatment

system. Wastewater treatment should incorporate a denitrification

system into it because this process provides the most feasible

means to reduce the nitrogen content of the effluent (Walker et.

al.,, 1973).

2.2 Nitrification and Denitrification Processes

      Nitrogen entering a conventional septic system is in the

 organic-N and ammonium-N forms. A properly functioning septic tank
 will remove approximately 10% of the influent organic nitrogen

 which is stored in the sludge (Laak et. al., 1981).  In the septic

 tank, settlement and ammonification occur, resulting in effluent