(202q) Control System Development for Integrated Biological Waste Water Treatment Process of a Paper Production Plant

A bioreactor, integrated with an anoxic reactor and a settler for waste water treatment from a paper production plant is under investigation to implement a control system for enhancing effluent quality.  In order to reveal the operation of the integrated process to achieve a specific goal, a methodology for control system development is proposed.  In this work, results of the steps of the methodology are presented, in order to address the oxygen uptake rate control. A dynamic model is developed for analysis of the conceptual design of different generated control configurations.

Biological treatment has long been the strength for waste water treatment in the paper industry.  However, in many cases, automatic control strategies have not been implemented and these types of systems have an empirical control, mainly based on rules of thumb of human operators, whose knowledge depends on a specific case, leading to errors such as lack of precise knowledge of perturbations, causing delayed or erroneous decisions.  These decisions can lead to an unstable system, excessive energy consumption, many staff, and the breach of local laws on the management of water resources.  It is by these reasons that implementation of an automatic control system become important.  Biological water treatment processes are complex, due mainly to the great variety of suspended or solubilized solids which are the nutrients or the inhibitors of the microorganisms, what make these systems be difficult for effective modeling and control system design.

In this work, a methodology for model-based control system development is proposed. This methodology is also applied to an actual case in the paper industry, whose main objective is to enhance the water quality of the effluent which is reused in paper recycling, where the oxygen uptake rate control issue is addressed.

The methodology consists of three main stages divided in a systematic sequence of steps. 

A brief description of the methodology is as follows. First, a description of the process is done (Step 1.1) in order to identify the variables (Step 1.2) and analyze the bottlenecks of the process (Step 1.3). Once this analysis is performed, the control objective can be defined (step 1.4).  After that, the development of the process dynamic model (Step 2.1) is necessary and parameter identification (Step 2.2) is mandatory to perform dynamic simulations (Step 2.3) and its corresponding analysis (Step 2.4).  Then the model validation is performed (Step 2.5). If there is not good correlation, parameter adjustment is done until we get a valid model.  Next step is the generation of the control configurations (Step 3.1) and the control laws (Step 3.2) for each configuration.  Then the control configurations are analyzed and evaluated (step 3.3).  The option that best achieves the operational objective is selected (Step 3.4).

Results of the methodology applied to an actual water treatment plant in the paper industry are presented.