**3. Other propositions to purification water processes control**

An expert system for a water purification system that performs supervisory control of water quantity, and automatic filter basin control, is developed in [55]. The sand bed filters can be in four possible states: waiting for filtering, filtering, waiting for scouring, and scouring. The filter basins in a water purification system are usually divided into groups connected in parallel. Online data are gathered from distributed control systems throughout the water purification system. In [56], filter basin control is based on control of filter scouring basin and control of the number of filter basins in operation. Filter scouring occurs when the water flow falls below a preset minimum value. The number of filters in operation is controlled to match the plant processing flow to total filtering flow. A different approach is presented in [56], where the proposed chlorination control system for water treatment is a double cascade PI loop for controlling the hypochlorite dosed in the system by means of free chlorine measurements taken at two sample points of the disinfection system. Denitrification of drinking water has been also proposed in several studies. In [57], SISO and MIMO robust variable structure controls for fixed bed bioreactors are developed. A SISO variable structure control is used to control the total concentration of nitrates and nitrites by changing either the inlet flow rate or the ethanol concentration. A MIMO variable structure control is needed to optimally regulate the ethanol concentration of drinking water. In [58], drinkable water is also treated by a fixed bed bioreactor. A multiinput and multioutput sliding control law of a distributed parameter bio-filter is designed to improve the quality of the water in order to control the harmful component concentration at the outlet of the bioreactor and to optimize the addition of carbon source. However, to our knowledge, it is certainly regrettable that no specific model based on deep neural networks is performed on this type of process.
