A Strategy for Controlling Deposition of Struvite in Municipal Wastewater Treatment Plants

Abstract

This paper presents strategies to reduce the risk of struvite deposition by controlling its location of formation. Two technical routes were investigated: (1) to fix the phosphate into the dewatered sludge cake, and (2) to remove phosphate from centrate or filtrate. Chemicals used include magnesium hydroxide [Mg(OH)2], both of reagent grade and reclaimed from a flue gas desulfurization system, magnesium chloride (MgCl2), calcium hydroxide [Ca(OH)2], ferric chloride (FeCl3) and aluminum sulfate [Al2(SO4)3]. Research results indicate that (1) for anaerobically well-digested sludge, Mg(OH)2 is effective in fixing phosphate into sludge cake and improving sludge dewaterability, and (2) adding Mg(OH)2 into a reactor, located between the sludge dewatering facilities and the centrate or filtrate discharge line, and using air for mixing and carbon dioxide stripping, proves feasible in reducing struvite deposition in centrate or filtrate discharge lines and can generate a potentially valuable plant fertilizer--struvite.