Polyethylene is a flexible and very strong material that is also low in weight. Due to the seamless production, the tanks are 100% water tight. A big advantage of the material is the non-corrosive characteristic. It is not affected by waste water in any way. Due to its flexibility the material will withstand shock loads or increasing loads without cracking. A separate casting or a special filling material for protecting the enclosure is not necessary. Additionally the material is recyclable and ecological in production.

The wall construction of the NDG tank is a three layer sandwich with a wall thickness of at least 5 cm. Due to this feature the tanks are allowed in water protection areas. Beside the high stability the sandwich provides an insulation of the waste water and thus a stabilization of the treatment process in cold periods.

The basic biologic treatment step inside the NDG system is the fixed bed technology. The system operates with bacteria that are immobilized by building a coating on a supporting material. For this NDG uses special polyethylene grid like pipes, called BioBlok. The BioBlok provides a large surface in a small volume and is designed to achieve a good contact between bacteria, waste water and oxygen. The oxygen is brought in by membrane aerators installed under the fixed bed and supplied with normal air from a compressor located above the water level.

The fixed bed ensures a very economic way of treatment, because the bacteria don't have to be mixed during the treatment phase and the system needs no settlement phase for separating the bacteria from the clean water. With providing a surface for the growth specialists like nitrifying bacteria it has  the chance to develop beside the normal bacteria. The effluent results of a fixed bed system are very stable over the whole season. Problems like swimming sludge or loss of bacteria during phases of low influent are not known. The fixed bed technology has proved its success also for small units less than 16 IE.

Excess sludge will loose from the fixed bed by itself due to the flow of air through the BioBlok pipes. The excess sludge easily settles down in the secondary settlement and is pumped into the primary settlement for storage.