Recovery of struvite via coagulation and flocculation using natural compounds

Abstract

One of the major setbacks of struvite recovery processes is the difficulty in harvesting struvite crystals. This study evaluates the use of different coagulants to improve precipitation of struvite (MgNH ₄PO₄·6H₂O) crystals. Chitosan and poly(diallyldimethyl ammonium chloride) (Poly-DADMAC) as a coagulant–flocculent and alginate and bentonite as a coagulant aid have been examined in jar tests. Also, a continuous three-phase process, i.e. struvite crystallization, coagulation/flocculation and precipitation process, was set up for real wastewater. Addition of chitosan as the coagulant and bentonite as the coagulant aid was significantly more efficient in forming struvite flocs in comparison to Poly-DADMAC alone or with coagulant aid, which did not show any positive effect. The calculated average settling velocity of struvite with chitosan–bentonite addition in synthetic and in real wastewater increased by approximately 5.3 and 2.8 folds, respectively, compared with that of no coagulant/flocculent addition. Phosphorus recovery of over 70% was achieved by the continuous process. Findings in this study clearly confirmed the possibility of using chitosan and bentonite as an efficient coagulant–flocculent to enhance the recovery of struvite crystals.

Keywords:

• struvite
• coagulation
• phosphorus recovery
• chitosan
• bentonite
• municipal wastewater