Coagulation Mechanisms during the Substitution of Inorganic Salts with Cationic Polymers to Increase the Sludge Value

Lelum Duminda Manamperuma^*, Harsha Chandima Ratnaweera

Department of Mathematical Sciences and Technology, Norwegian University of Life Sciences, Aas, Norway.

DOI: 10.4236/jwarp.2015.717123                

Abstract

Phosphorus in wastewater sludge is a valuable resource although coagulated sludge reported to give only 10% of plant availability of phosphates. Since all Al and Fe added as coagulants end up in sludge, the potential to substitute them with cationic coagulants was studied. During combined coagulation, substitution possibilities up to 44% were observed with low coagulant-to-particle ratio where the adsorption-charge neutralisation (ACN) anticipated being the predominant mechanism. Comparatively high coagulant-to-particle ratio preferred Sweep-floc mechanism giving <20% substitution possibilities, though even lower values anticipated at higher phosphate removals. The cationic polymers’ ability to compete with positively charged Al- and Fe-hydrolysis products was argued as the explanation for higher substitution possibilities during ACN mechanism. Sub-stitutions can be enhanced with dual coagulation with intermediate sludge separation by avoiding competition between two coagulants.

Keywords

Organic Polymers, Inorganic Coagulants, Plant Availability of Phosphorus, Phosphorus Removal, Coagulation Mechanisms

Conflicts of Interest

The authors declare no conflicts of interest.

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