Analysis of advanced process measurement parameters for a biological wastewater treatment process

This investigation attempts to show the potential of advanced process measurement parameters for the control of a biological wastewater treatment process. The research first reviews the status of instrumentation and control strategy for wastewater treatment operations, presenting recent developments in sensor technology and their applications. The problems associated with the development of a wastewater control strategy are then discussed and a problem-driven methodology is presented for developing a control strategy for a wastewater treatment plant. Advanced parameters for biological process control in wastewater treatment are identified and evaluated. By utilizing a typical biological process treating a hypothetical waste stream, an analysis is performed of the steady-state responses of these process parameters.

A two-stage Bardenpho wastewater treatment model is used in the study of the sensitivity of process measurement parameters to variations in input conditions. The first reactor zone in the Bardenpho model is for nitrate removal and the subsequent zone is designed for carbon oxidation and nitrification. The influent variables are chemical oxygen demand (COD), ammonium-nitrogen, nitrate, and hydraulic loadings. The process parameters analyzed are oxidation reduction potential (ORP), uptake rates for oxygen, nitrate, and ammonium-nitrogen (OUR, NUR, and AUR, respectively), and their specific uptake rates (SOUR, SNUR, and SAUR, respectively).

All these parameters (ORP, OUR, NUR, and AUR) are sensitive to influent changes, but to different extents. For specific uptake rates (SOUR, SNUR, and SAUR), the influent COD changes have the greatest effects, followed by the effects of influent ammonium and nitrate and the inlet flow rate. The substrate uptake rates (OUR, NUR, and AUR), however, have the greatest sensitivity to influent COD variations, following changes in inlet ammonium and nitrate and the influent flow rate. The greatest single effect on ORP values is influent nitrate concentration, followed by ammonium, COD, and the flow rate.

Monitoring of the anoxic zone in the Bardenpho model suggests that, by manipulating the recirculation rate, the SNUR and ORP are applicable as measurement parameters for monitoring the denitrification process. The two hypothesized measurement parameters are analyzed with two different mathematical models, one for SNUR and one for ORP. The responses of SNUR and ORP to input variations are used as measurement variables to the empirical model that is used to predict the required recirculation rate.Manipulation of recirculation rate is implemented based on the measurements of influentCOD, ammonium, and nitrate; the inlet flow rate; and the nitrate content in the aerobic zone outlet.