Desarrollo de alternativas de tratamiento de aguas residuales industriales mediante el uso de tecnologías limpias dirigidas al reciclaje y/o valoración de contaminantes.

Abstract

The growing environmental concern at society is dealing with stricter wastewater limits and consumption levels. This project develops the use of clean technologies in three wastewater problems: textile, detergents and metal finishing sectors. The first case tackles several methods to treat the wastewater from a textile factory. The aim is to get a large quality effluent, enough to pour and recycle it in a RO process for final reuse. The technologies used are: biologic (trickling filter and activated sludge), chemical-physical (coagulation-flocculation and electrocoagulation) and physical (adsorption in activated carbon and microfiltration). Taking into account operating costs and treatment yield the best sequence for treatment is: trickling filter, activated sludge and coagulation-flocculation. The second case compares the electrocoagulatión-flotation, a possible clean technology, with the coagulation-flocculation and activated carbon ones in synthetic effluents with different types of detergents. Although electrocoagulation-flotation treatment provides acceptable yields (namely in effluents with anionic detergents), the costs due to high consumption of anodes and production of sludge are excessive. The third case deals with the chance to get KNO3 (a valuable fertilizer) from a pickling wastewater with nitrates, in addition to obtain a reusable effluent. The exhausted nitric acid bath is treated with KOH to precipitate the metals and thus having a concentrate solution of KNO3. After the same process the rinse water of pickling process is handled to concentration stages by electrodialysis and vacuum evaporation. In this way, it has been got crystals of KNO3 and an effluent free from metals to be reused or wasted. Rinse effluents from a pickling process with nitric-sulphuric acid mix needs a lightly different treatment. The coagulation-flocculation stage is carried out with KOH and Ca(OH)2. The vacuum evaporation step produces CaSO4 precipitation (also useful as fertilizer) jointly with a saturated solution of KNO3. Finally, cold crystallization stage provides KNO3 crystals.