1 INTERNAL TREATMENT OF PROCESS WATERS IN PAPER PRODUCTION BY DISSOLVED AIR FLOTATION WITH NEW DEVELOPED CHEMICALS. PART 2: FIELD TRIALS Ruben Miranda, Carlos Negro, Angeles Blanco * Department of Chemical Engineering, Faculty of Chemistry, Complutense University of Madrid – Avda. Complutense s/n 28040 Madrid (Spain) ABSTRACT. New chemicals, based on the synergistic effect between inorganic polyaluminium salts and organic cationic polyelectrolytes, have been tested previously at lab scale and the most efficient product has been selected for an industrial trial for a dissolved air flotation unit of a paper mill based on 100% recovered paper (Part 1 of this work). A polyaluminium nitrate sulphate salt combined with a quaternary polyamine has been evaluated in a long-term industrial trial for assessing its potential benefits. Results indicate that this new chemical is able to improve the removal of contaminants by dissolved air flotation, especially when the contamination load of the waters is high, allowing a further closure of the water circuits. KEYWORDS: chemical synergistic effects, dissolved air flotation, flocculation, aluminium salts, polyamines, paper recycling, field trial. 1. INTRODUCTION Nowadays, the destabilization and removal of recalcitrant contaminants, mainly dissolved and colloidal material (DCM), is still a bottleneck for papermakers 1-2 . DCM may be removed by dissolved air flotation (DAF) units if their chemistry is optimized 3- 5 . Part 1 of this work analyzes the chemical efficiency of newly developed chemicals for treating deinking process waters by DAF 6 . The new chemicals consider the potential synergistic effect between inorganic and organic products. Three types of aluminium salts modified with three different cationic polyelectrolytes were evaluated. The aluminium salts are: polyaluminium chloride, polyaluminium chloride sulphate and polyaluminium nitrate sulphate; and the cationic polyelectrolytes are polyacrylamide, polyvinylamide and polyamine. A total of thirteen products were analyzed at lab scale: the three aluminium salts of base and ten modifications of these salts. * To whom correspondence should be addressed. Dpt. Chemical Engineering, Faculty of Chemistry, Complutense University of Madrid. Avda. Complutense s/n E-28040 Madrid (Spain). Phone: +34913944247. Fax: +34913944243. E-mail: ablanco@quim.ucm.es