The COMPACT operates on the well-known and well-proven extended aeration version of the activated sludge treatment process, incorporating a nitrification and de-nitrification stage. This type of biological treatment is generally regarded as one of the most reliable and effective methods of purifying domestic sewage. The process involves the digestion (decomposition) and oxidation of the sewage organics and nutrient matter by the influence of naturally occurring micro-organisms supported by a mechanically delivered supply of oxygen.