Conservative technologies for environmental protection based on the use of reactive polymers

Biodegradation of organic pollutants is based on 'destructive' technologies leading to the formation of low-molecular-weight compounds and carbon dioxide or methane depending on the process red-ox conditions. This is not possible for persistent pollutants (e.g., heavy metals, biorefractory organics, complex organometals) independent of the origin and structure of the chemical substrate. Reference compounds can only be recovered and eventually recycled to the production lines of origin and/or to related industrial activities. However, the quality of the recovered products must justify the recycling operation. Sorption techniques lion exchange, carbon adsorption) and membrane technology as typical 'conservative' unit operations allow for removal of pollutants to the strictest limits imposed by enforced legislation and simultaneous recovery and recycling. We discuss two examples of conservative environmental technologies, based on ion exchange and the use of reactive polymers. The first relates to metal-laden effluents from the tannery industry, and the second to the management of residues (clarifier sludge) from the drinking water industry. Both processes are aimed at the minimization of environmental impact resulting from the production lines (Cr(III)- and Al(III)-containing wastes, respectively) and the recovery of valuable by-products with the related economic revenues associated with their commercial value. (C) 2000 Elsevier Science B.V. All rights reserved.