Aluminum Hydrolysis Effects on Phosphorus Removal from Wastewaters

Abstract

<p>It is widely recognized that phosphorus removal from wastewaters by coagulation with aluminum salts is brought about not by the aluminum ion itself but by the hydrolysis products of the metal ion.</p> <p>The present work investigated the effectiveness of the aluminum polymeric species in phosphorus removal. These species were formed by partially neutralizing an aluminum chloride solution with sodium hydroxide under controlled conditions and they were given the name PBAC for Polymerized Basic Aluminum Chloride. The results were compared with those obtained using Alum, the most commonly employed aluminum coagulant. Although the removal of phosphorus from wastewaters was the main objective, the work extended to other areas such as supernatant suspended solids removal, sludge filtrability and organics removal.</p> <p>The factors that were found to influence the efficiency of the coagulants were:</p> <p>(i) The aging time of the aluminum polymers,</p> <p>(ii) The OH:Al molar ratio in the preparation of PBAC,</p> <p>(iii) The Al:P molar ratio (Aluminum dosage),</p> <p>(iv) The pH,</p> <p>(v) The presence in the wastewater of other ionic species.</p> <p>It was found that the removal of phosphorus could be adequately explained by a model involving complex formation and precipitation. It was shown, however, that the removal of organics cannot be attributed to a strictly chemical interaction and other mechanisms should be considered as well.</p>