In 2001 NDG applied for a national technical approval at the DIBt in Berlin to certify that the design, construction and effluent results of the small scale treatment plants fulfill the regulations of the German DIN 4261-T2 and the European EN 12566-3. After a one year, practical test was passed successfully the national technical approval Z-55.6-75 was issued in October 2002. In an additional subsequent half year practical test the extended nutrient removal (nitrification and denitrification) was proved and certified in the extended national technical approval Z-55.6-75 of January 2003.

Following performance was proved during the practical test including simulations of overload (150%), under load (50%), holiday and power loss situations: