Biomedical subjects

D Cecil

Publications and source records attributed to D Cecil.

3 recordsLinked to original sources

PubMed2006

A model of the redox measurement in aerated activated sludge.

A number of investigations have shown that pH, oxygen concentration, and the organic load affect the measured redox potential in aerated activated sludge. In this investigation, a model of the redox measurement is proposed. It is a kinetic model based on the necessary balance between the number of electrons accepted by and donated to a metal electrode in the sludge. The potential changes in order to maintain this balance. The model variables are pH, oxygen concentration, temperature and the activity of reduced compounds. Data from a wastewater treatment plant is analyzed using this model and it is shown that the model can be fitted to results from other published investigations. However we cannot as yet demonstrate a correlation between the activity of reduced compounds and the organic load on the sludge. The ultimate objective of this work is to extract more information from the redox measurement. This is a practical interest because the redox measurement is inexpensive and requires little maintenance.

Electrodes↗

PubMed2003

Controlling nitrogen removal using redox and ammonium sensors.

At the Ejby Mølle WWTP (300,000 PE) operated by the Odense Water Ltd. a system of aeration control which combines ammonium concentration and redox potential has proven itself as a method of reducing nitrogen levels in the effluent. The nitrogen removal process at this plant proceeds in parallel aeration tanks that alternate between periods of aeration and denitrification. At the same time influent is redirected from one tank to the other such that influent and effluent is primarily to and from the tank where denitrification is going on. The aeration stops and the tanks open and close when the ammonium concentration reaches its set point. Aeration is restarted again when redox potential drops to its low set point or when ammonium reaches its upper set point. The average total nitrogen concentration in the effluent from the Ejby Mølle WWTP went from 4.7 down to 2.1 mgN/l after this control system was implemented. Not all of this reduction can be explained by better control. However we believe that at least 1 mgN/L of the reduction and probably more was the result of the control system based on the combination of ammonium and redox sensors.

Electrodes↗

PubMed2003

A software nitrate sensor based on ammonium and redox signals.

We have computed the nitrate concentration in the activated sludge in real-time using a model, which is a subset of ASM1. The model is in operation at two WWTPs where oxygen, ammonium and redox are measured online in the aeration tanks. The model uses these measurements to continuously adjust its values for the influent ammonium concentration, the nitrification rate, the denitrification rate and the net hydrolysis. Then it computes the nitrate concentration. This value is updated every 10 s. The model results have been compared with the output from a Dr Lange in-situ nitrate sensor at one of these WWTPs. The systematic difference between these two measurements is less than 0.2 mgN L(-1) and 90% of the differences are between -1.1 and 1.1 mgN L(-1).

Environmental Monitoring↗