Abstract: A metal stearate denitrification system utilizes insoluble and hydrophobic metal stearates as a carbon source for the bacterial substrate. The system in a long-term, low-maintenance denitrification cell is a flow-through plastic container having a replaceable porous liner filled with a porous and permeable mixture of metal stearate and volcanic scoria and a small amount of soil as a bacteria source. Oxidized effluent from an aerated home septic tank enters the container near its base and exits near its top. The insoluble and hydrophobic metal stearate remains in place as the fluid flows through the container. Over a time span of years, the metal stearate is gradually destroyed by bacteria using stearate as a metabolic food source. The aerobic bacteria first remove the dissolved oxygen in the entering fluid and then the anaerobic bacteria denitrify the nitrate.