Control strategies for the sludge line in wastewater treatment plants

This paper presents the implementation and evaluation of control strategies for wastewater treatment plants. The study was carried out using the platform Benchmark Simulation Model No. 2 (BSM2) and is conceived plant wide by introducing as a distinctive feature the structuring of the plant on: a water line and a sludge line, the two operating lines being interdependent but at the same time influencing simultaneously the overall functioning of the plant. For the water line only one control strategy was implemented and this strategy was used together with the five control strategies proposed for the sludge line. In evaluating the obtained results special attention has been placed on the indicators related to the percentage of time when the pollutants in the effluent are violating the quality limits for total nitrogen and ammonium. However, the effect on the overall effluent quality and operation costs have also been considered by means of the usual aggregated cost indexes. The control strategy for the sludge line that offered the best results is the one that uses the control of the total suspended solids in the fifth tank by manipulating the wastage flow rate together with the control of the storage tank volume by manipulating its flow rate.