Demonstration of Intermitttent On/Off Aeration at a Municipal Wastewater Treatment Plant for Denitrification and Energy Savings

Final Report

Introduction

Ashland wastewater treatment plant (WWTP) in the Ashland, Wisconsin, is considering an economical way of retrofitting the oxidation ditches for biological phosphorus removal (BPR). Due to nitrification and recircuration in ditches, the Ashland oxidation ditches have high concentration of nitrate (NO₃-), which has an inhibitory effect on BPR due to the consumption of readily biodegradable soluble COD by denitrifiers. Therefore, removing NO₃- in ditches is thought to be the first step to achieve BPR. Intermittent on/off aeration, which cycle the aerators on and off to provide an alternating sequence of aerobic and anoxic conditions within the same aeration tank, has been adopted by Ashland WWTP to achieve denitrification since October 1995. This report describes a study in which intermittent on/off aeration is demonstrated at the Ashland WWTP. The impact of on/off aeration operation on the removal of biological oxygen demand (BOD₅), total suspended solids (TSS), and activated sludge characteristics such as settleability are evaluated. The possible luxury phosphorus uptake from the implementing intermittent on/off aeration is also determined.

Description of Ashland Wastewater Treatment Plant

Intermittent On/Off Aeration

Determination of Denitrification Rate
Effluent Quality of Ashland WWTP Before and After On/Off Intermittent Aeration
Denitrification Efficiency of Intermittent On/Off Aeration
A 24 hour cycling monitoring
A pilot test of effluent water-level control technology

Cost Saving

Summary

Table of Figures || Table of Tables

More information on this topic: Gerry Novotny