Should we keep DO for nitrification control? The proof is in the Ammonium Electrodes

Aeration often is the process that consumes the most energy in a wastewater plant. At the same time it is an essential process to maintain compliance for BOD and ammonia limits. It thus deserves a lot of attention.The use of dissolved oxygen measurement to control aeration is widely accepted. The literature has many examples of excellent return on investment in wastewater plants that have implemented this control. There are even theories that a concentration of 2 mg/l is the perfect value. But a DO sensor only tells how much oxygen has not been used in the process and at times this measurement may not bring the expected results. The effluent may end up out of compliance or too much energy can be spent. Examples are available.As one of the main objectives of the aeration tank is nitrification the measurement of the concentration of ammonium or ammonia can provide much better information than dissolved oxygen alone. Ion Selective Electrodes installed directly in the tank can eliminate the need for sampling lines and ensure an easier integration. Their selectivity, accuracy and lower maintenance make them an attractive solution. As demonstrated at Wheaton, IL and Colorado Springs, CO additional energy savings and compliance are possible when using either ammonia in a cascade loop with DO control or in direct control of the air flow. Direct control either in feed-forward or feed-back provide faster and better response when spikes are present.The return on investment is very good even on smaller plants and compliance is achieved.Dissolved oxygen concentration remains an important factor as it affects the quality of the sludge. The control strategy has to maintain it within limits.