This study examines the possibility of automating the ferrous sulfate dosing at the wastewater treatment plant in Viikinmäki, Finland. The aim of the study was to optimize the biological filtration process, improve the filtration, and to reduce workload and chemical costs. The removal of phosphates from wastewater is important due to the impact on both process control and the environment to prevent eutrophication. The removal is done by coagulating the phosphates with ferrous sulfate.

Modelling and simulation were used to identify a suitable control method for automatic dosing of ferrous sulphate in wastewater treatment plant. The conclusion of the research was that the use of this type of mathematical modelling for a biological-chemical process is challenging. The created process models were not accurate enough to allow control method analysis with Simulink. Among the issues encountered during the modelling were: substantial process feedback delay, inaccuracy of the process modelling, and lack of measurable data on other variables affecting the phosphate concentration in addition to sum flow of ferrous sulphate. These additional process variables are either not measured or known at this time.

It is recommended that either an alternative approach should be considered for analysing the control method, or the control should be implemented on basis of known chemical and biological processes. This recommendation calls for better understanding of the process and measurement of all the potential variables to ensure sufficient data for both process modelling and control. This would require identifying the process feedback delay mechanism, interaction of different process variables and cooperation with the persons in charge of the process and with knowledge of the chemistry it involves.