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

Abstract

In 2011 and 2012 the new DWA Standards DWA-A 222 and DWA-M 221 for wastewater treatment plants were published, where rules for biofilm plants with submerged fixed bed and free movable biofilm carriers are included for the first time. In both technologies, the oxygen supply is usually realized by fine-bubble compressed aeration. The DWA-A 222 Standard does not adequately take into account the extensive operational experience with systems that work with submerged fixed bed. Using the specified parameters, a lack of oxygen supply can occur in the high load plant-level of carbon elimination. In this case the cleaning capability may be severely impaired.