City Meets New WW Compliance Regulations, Records Exceptionally Low Output Of Nitrates And Phosphorous With Special Activated Sludge Process

The public works manager for the City of Decatur, AR reports that replacement of their aerated pond system wastewater treatment plant (WWTP) with a special activated sludge process WWTP has provided for compliance with a more stringent National Pollutant Discharge Elimination System (NPDES) permit, while coping with a regular 90-95% weekend decrease in wastewater input, and major seasonal variations in ambient temperature.

The design 2.2 million gal./day (MGD), 1.6-1.8 MGD average usage plant was started up in 2009, following a 10-month installation, and a five-year effort to find a suitable replacement for the previous 1.375 MGD pond system, which had been installed in 1989.

While the previous system had performed adequately for biological oxygen demand (BOD) and ammonia and organic nitrogen (TKN), the replacement effort was launched in the late 1990s when new limits for nitrates were introduced. Staged reductions for phosphorous limits began in 2004.

The new plant has consistently provided 96-98% biological phosphorous reduction to help meet the new limits, and nitrates reduction to meet the drinking water standard mandated by discharge to a “losing stream”.