LoDif-BioControl

The CalAgua research group formed by the staff of the Department of Chemical Engineering at the University of Valencia and the Institute of Water and Environmental Engineering (IIAMA) of the Universitat Politècnica de València, has been developing related information with the control of processes in WWTP for more than a decade. The different control algorithms developed were validated both at pilot and laboratory scale as well as on an industrial scale, through contracts with different companies. Thus, the installation of control systems in various WWTP in the Valencian Community developed by the research group allowed to transfer all the information to lines of code in the different applications installed in the WWTP. However, the specificity of each WWTP entailed the need to adapt the control algorithms through a specific application for each WWTP. This implied the need for intervention of personnel from the research group to implement the control algorithms developed in each concrete WWTP. With the intention of standardizing the developed control technology and facilitating its implementation in any WWTP by a specialized company and without the need for the participation of researchers from the CalAgua group, a basic computer tool has been developed that is totally configurable and easily adaptable to different WWTP.

The developed tool, known as “LoDif BioControl”, consists of a computer application that incorporates the control algorithms developed by the research group CalAgua during the last few years. These control algorithms, based on fuzzy logic, allow for an efficient control of both the aeration system and the biological nutrient elimination process in Wastewater Treatment Plants (WWTP), optimizing the activated sludge process, as they achieve to keep nitrogen below the discharge limits with minimum energy consumption.

The uniqueness of this tool consists of the incorporation of nutrient control algorithms based on low cost probes: oxygen, ORP (redox potential) and pH (a system protected by the patent of invention with preliminary examination titled “Control system for the biological elimination of nitrogen of wastewater by using low cost probes “, Ref. ES 2 345 090 B2). This control option offers the following advantages: a reduction in the initial investment and maintenance costs, a greater ease of operation and a reduction in the response times of the probes.

In addition, the tool incorporates the control of the aeration system, acting both on the air valves and on the blowers. This control system minimizes the required air pressure in the system and thus the energy consumption necessary to maintain the oxygen setpoints set by the plant operator. The “LoDif BioControl” tool has several configuration options so that the plant operator can choose the mode of operation of the WWTP that is most convenient. For example, in the nitrogen control system the mode of operation of the aeration system (continuous aeration or intermittent aeration) can be selected and, in both operating modes, the type of probes to be used (low cost probes or ammonium probes).

The start and stop of the blowers can also be configured by choosing either the specific order of start/stop or the operation by rotation based on the hours of operation. “LoDif BioControl” facilitates the implementation of the control system in Wastewater Treatment Plants (WWTP) by specialized companies and without the need for intervention of the research group staff. For this, the application has been programmed in Visual NET language and following an object oriented programming to obtain a basic tool totally configurable and adaptable. In addition, it is a standard application that can be installed in any WWTP, regardless of the type of SCADA existing, since the connection to the SCADA is carried out using the OPC (OLE for Process Control) standard communication protocol. The link between the SCADA/PLC variables of each WWTP and the control application is established from an OPC server (which may be the one that incorporates its own SCADA of the WWTP or another independent server).

One of the first stages in the installation of the control system in a particular WWTP is its configuration, eg. to establish the number of independent control elements or control loops. The total number of control loops depends basically on: the number of independent blower groups, the number of diffuser grids with independent control valve, the number of existing oxygen probes, etc. In order to create this control structure, to define all the necessary variables for each of the control elements and to link them with their corresponding variables in the SCADA of the plant, a configuration assistant has been developed that is executed the first time that the application “Lodif BioControl” is installed. This way, the user can establish the specific configuration of the control application for each WWTP without having to modify the application’s source code.

With this application, it is only necessary to add to the OPC server the physical variables existing in the WWTP SCASA (those coming from the probes and the final control elements), as well as the specific communication variables between “LoDif BioControl” and the SCADA. These last variables are necessary to centralize the control of the WWTP from the SCADA, that is to say, so that the plant operator can configure the operation mode of the plant from the SCADA, as usual, and not from the control application. Once the OPC server is installed and configured, the configuration wizard automatically detects the communication variables defined on the server and allows the user to link them to their corresponding variables in the control application.

Once the “LoDif BioControl” application has been configured, the parameters of each of the control loops based on fuzzy logic can be modified. The tool includes various configuration options that allow the plant manager to choose from the SCADA the mode of operation for the WWTP that is most convenient. The only parameters to configure using the “LoDif BioControl” application are the algorithms based on fuzzy logic. It should be noted that, once the control system has been calibrated, it is usually not necessary to modify these parameters.