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In this paper, a control strategy for introducing enhanced biological phosphorus removal (EBPR) in an alternating plant designed for enhanced biological nitrogen removal (EBNR) is presented. Alternating aerobic and anaerobic conditions to promote EBPR are provided by controlling the phases of the operational cycle, instead of a separate anaerobic volume. By utilising the control schemes already built in the STAR® control system for nitrogen removal, the control strategy is fully integrated in the system. The control system relies on on-line measurements of nitrogen (ammonia and/or nitrate) and orthophosphate. The control strategy has been implemented in full-scale operation at the Avedøre wastewater treatment plant in Denmark and the results show clear indications of success. The control strategy has operated robustly for several months with a 60% decrease in use of precipitation chemicals. [ABSTRACT FROM AUTHOR]

The consequences of a heavy and varying load on a BNR-WWTP (biological nitrogen removing plant) have been investigated in full scale. Theinvestigations took place at a 57,000 PE BNR plant which is operatedaccording to the BIODENITRO principle. The plant had been heavily overloaded with BOD and N, 2--3 times the designed capacity. During theoverload events, the BOD was efficiently removed to below the effluent limit. The N-removal, however, was reduced to below 50% during these events. The nitrification may be inhibited considerably after peakloadings due to a drop in pH caused by nitrification without denitrification. Full denitrification was obtained during peak loadings in spite of aeration of the total process volume. During high and varyingloads, the most efficient utilisation of the process volume can be obtained by the following; 1) The plant design should allow of a change in aeration volume from 20% to 100% of the total process volume. Changing the aeration volume is much more effective than changing the oxygen set point. 2) On-line control of the aeration time by NH4, NO3 and pH on-line meters. The historic loadings must be included in the control strategy to avoid alkalinity depletion during heavy load variations. (c) 1998 Published by Elsevier Science Ltd. [ABSTRACT FROM AUTHOR]

Three different methodologies are assessed which provide predictionsof the hydraulic load to the treatment plant one hour ahead. The three models represent three different levels of complexity ranging froma simple regression model over an adaptive grey-box model to a complex hydrological and full dynamical wave model (Chow et al., 1988). The simple regression model is estimated as a transfer function model of rainfall intensity to influent flow. It also provides a model for the base flow. The grey-box model is a state space model which incorporates adaptation to the dry weather flow as well as the rainfall runoff. The full dynamical flow model is a distributed deterministic model with many parameters, which has been calibrated based on extensive measurement campaigns in the sewer system. The three models are compared by the ability to predict the hydraulic load one hour ahead. Fiverain events in a test period are used for evaluating the three different methods. The predictions are compared to the actual measured flow at the plant one hour later. The results show that the simple regression model and the adaptive grey-box model which are identified and estimated on measured data perform significantly better than the hydrological and full dynamical flow model which is not identifiable and needs calibration by hand. For frontal rains no significant difference in the prediction performance between the simple regression model and the adaptive grey-box model is observed. This is due to a rather uniform distribution of frontal rains. A single convective rain justifies the adaptivity of the grey-box model for non-uniformly distributed rain, i.e. the predictions of the grey-box model were significantlybetter than the predictions of the simple regression model for this rain event. In general, models for model-based predictive control should be kept simple and identifiable from measured data. (c) 1998 Published by Elsevier Science Ltd. [ABSTRACT FROM AUTHOR]

This paper aims to review the development of wastewater treatment operation and control over the last two decades. Due to the authors' background and experiences there is a special emphasis on the Scandinavian perspective. Since the developments in these countries have been in the forefront in the wastewater treatment area we believe that it may give a reasonable view of the progress also in other countries. The results of regulatory, technical and economical driving forces arediscussed. A brief historical review of the progress of nutrient removal is made, and current methodologies for the operation and controlof nutrient removal systems is reviewed. (c) Published by Elsevier Science Ltd. [ABSTRACT FROM AUTHOR]

On-line measurements of pollutants in the wastewater combined with grey-box modelling are used estimate the amount of deposits in the sewer system. The pollutant mass flow at the wastewater treatment plant is found to consist of a diurnal profile minus the amount of pollutants. The diurnal profile is found to be a second order harmonic function and the pollutants deposited in the sewer are identified using first order ordinary differential equations. (c) 1998 Published by Elsevier Science Ltd. [ABSTRACT FROM AUTHOR]

The biological phosphorus removal process is often implemented at plants by the construction of an anaerobic bio-p tank in front of the traditional N removing plant configuration. However, biological phosphorus removal is also observed in plant configurations constructed only for nitrogen removal and simultaneous or post-precipitation. The operational experience with this "accidental" biological phosphorus removal is often mixed with quite a lot of frustration, as the process seems to come and go and hence behaves quite uncontrollably. The aim of this work is to develop ways of intentionally exploiting the biological phosphorus process by the use of instrumentation, control and automation to reduce the consumption of precipitants. Means to this end are first to calibrate a modified ASM2d model to a full-scale wastewater treatment plant (WWTP), including both biological and chemical phosphorus removal and a model of the sedimentation process. Second, based on the calibrated model a benchmark model is developed and various control strategies for biological phosphorus removal are tested. Experiences and knowledge gained from the strategies presented and discussed in this paper are vital inputs for the full-scale implementation of a control strategy for biological phosphorus removal at Avedøre WWTP, which is described in another paper. The two papers hence show a way to bridge the gap from model to full implementation.