Critical Analysis of the DWA Standards for small Wastewater Treatment Plants (DWA-M 221 and DWA-A 222)

Abstract

In 2011 and 2012 were published the new DWA Standards DWA-A 222 and DWA-M 221 for wastewater treatment plants with a capacity up to 1000 inhabitants and for small units up to 50 inhabitants. A significant increase of mechanical plant dimensions and consequently a corresponding increase in capital and operating costs of the primary and secondary clarification result through these new rules. The discrepancies in the former dimensioning guidelines at the interface between small units up to 50 inhabitants and treatment plants with higher capacity were not removed by the new rules. There is no adequate agreement between the dimensioning by the DWA Standards and by the rules of DIBt.