Optimization studies for industrial wastewater defluoridation by adsorption: application of a design of experiments

The importance of water in the human economy is growing and the supply of good quality water is becoming increasingly difficult, both because of the increase in population and living standards, as accelerated development of modern industrial techniques. The scarcity of surface drinking water forced growers to diversify supply sources, drawing increasingly further into the ground. Ground water is considered an important source for the supply of small towns. In some cases, groundwater is not directly suitable for human consumption because of certain ion concentrations exceeding the standards for the quality of drinking water, such as fluorides [1]. Industrial liquid wastes are the most significant sources of pollution to the environment. They have become a factor of pollution that should be taken into consideration for the ecosystem balance. So, it becomes clearly important to fight against this type of pollution and to take severe measures by introducing perseverant laws against untreated discharges to protect our environment.

The main sources of emissions of fluorides are presumably related to the production of phosphoric acid and phosphate fertilizers, as well as aluminum metallurgy. The fluoride ingestion by humans may be one of the main causes of acute or chronic poisoning. Thus, chronic fluoride exposure primarily affects the digestive and skeletal systems [2].

Like most industries, especially fluorine chemical industries encounter operational problems upon their water discharges (AFMW). So it is necessary to find a solution which is consistent with the requirements of releases into the environment according to recommended standards.

In this context, the use of the methodology of experimental research to optimize industrial liquid waste processing conditions would be of special importance [3]. Given the difficulty of obtaining the optimum conditions, design of experiments represent an interesting alternative. Indeed, this tool allows to model the responses of a system using empirical polynomials priori postulated order. This technique also has the advantage of structuring the experimental companion to reduce the number of tests to be performed [3].

Extraction processes or processing raw materials for the manufacture of industrial products or consumer goods are the key sources of industrial liquid discharges. Their quantity and quality vary depending on the process used by industrial sector. They often exhibit a broad spectrum of chemical polluting compounds in solid or dissolved organic and inorganic materials, metals, hydrocarbons, solvents, polymers, oils, fats or salts with varying levels of toxicity. This requires a specific approach for each type of waste [4].