QFT Robust Control of Wastewater Treatment Processes

Wastewater treatment issues are extremely important for humanity. Their consideration becomes more than a necessity, a responsibility and every producer must improve their treatment processes. The efficiency increasing of these processes has been done in two ways: 1. by technological way various types of treatment were developed during the past years and this domain has almost no technological secrets; 2. by using control methods – which currently represent a real challenge for researchers. Wastewater treatment processes consist of a series of physical, chemical or biological processes that allow the separation between some particles (solid or dissolved, organic compounds, minerals etc.) and water, aiming to obtain a "clean" water able to meet certain standards for discharge or domestic/ industrial consumption. In Europe, the water purity standards are established by the Directive no. 2000/ 60/ EC. In the same time, the standards that are currently in use, defined by water law from February 3th, 1992, modified by the ordinance from February 2nd, 1998, are added to this directive. These rules define the maximum concentrations for each harmful compound from the wastewater. Generally the admissible concentrations are functions of the daily effluent flow. Currently, new rules are applied regularly to the wastewater treatment. Global indicators for treatment efficiency, such as COD (Chemical Oxygen Demand), BOD (Biochemical Oxygen Demand), TOC (Total Organic Carbon) and for nutrients removal (phosphorus, ammonia nitrogen, total nitrogen etc.), whose normative are increasingly stringent, are taken into account. New compounds such as pigments, heavy metals, organic compounds, chlorinated solvents etc. are also considered for removal. For the waters coming from different industries and to be discharged into nature, the treatment rules are not the same. They depend on the receiving water and the type of the industry from which the wastewater results. For example, in metallurgical industry the wastewater containing heavy metals dominates, unlike the food industry, where the water containing organic compounds prevails. Biological treatment processes are characterized by a number of specific features that make these processes real challenges for the specialists in control (Olsson & Newell, 1999): the daily volume of wastewater treated can be huge; the disturbances in the influent are enormous compared to most industries; the influent must be accepted and treated, there is no returning it to the supplier; the concentrations of nutrients (pollutants) are very small, even challenging sensors;