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

Lelum Duminda Manamperuma,Harsha Chandima Ratnaweera

doi:10.4236/jwarp.2015.717123

Lelum Duminda Manamperuma, Harsha Chandima Ratnaweera

Open Access

https://doi.org/10.4236/jwarp.2015.717123

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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.

Highlights

Over 70% of municipal wastewater in Norway is treated with a coagulation process [1] which annually consumes about 60,000 tons of inorganic coagulants consisting with 5% - 18% of aluminium or iron [2]
This paper presents results of attempts to reduce aluminium and iron content in sludge by substituting inorganic coagulants with organic coagulants, and discusses the limiting factors together with influence of coagulation mechanism
Studies show that the reduction of aluminium and iron is sludge will proportionally increase the plant availability of phosphorus in coagulated sludge

Summary

Introduction

Over 70% of municipal wastewater in Norway is treated with a coagulation process [1] which annually consumes about 60,000 tons of inorganic coagulants consisting with 5% - 18% of aluminium or iron [2]. These coagulants remove phosphorus very efficiently from wastewater solve a serious environmental problem. How to cite this paper: Manamperuma, L.D. and Ratnaweera, H.C. Wastewater sludge is no longer treated as a waste, but a resource. Over 70% of wastewater sludge in Norway is used in agriculture benefiting the high content of nitrogen and phosphorus [1]. The phosphorus prices has doubled since 2007, while there were periods with 800% price increase due to the scarcity in supplies [4]

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