1 STRUVITE PRECIPITATION: IMPACTS OF SEEDING MATERIALS AND MIXING STRENGTH Jun Wang 1 , Joel, G. Burken 1 , Xiaoqi (Jackie) Zhang 2 1 Department of Civil, Architectural and Environmental Engineering, Univ. of Missouri- Rolla, Rolla, MO 65401 2 Department of Civil & Environmental Engineering, Univ. of Massachusetts Lowell, Lowell, MA 01854 ABSTRACT Struvite (MgNH 4 PO 4 • 6H 2 O, or MAP) precipitation is a potential technology for removing and recovering phosphorus from municipal, industrial, or agricultural wastewater streams. Numerous researchers have investigated optimum pH values and component ratios in this process, however, studies on the seeding materials and mixing energy are lacking even though they are crucial in promoting crystal growth rates and sizes. The objectives of this study were to compare different seeding materials in facilitating struvite crystal growth and to optimize mixing strength for the process. In this study, three different seeding materials (quartz sand, granite and struvite crystals) were evaluated for potential to promote struvite crystal growth and precipitation. Results confirm that mixing strength and proper seeding materials can increase crystal size and improve settleability. Struvite crystals of 75~150 µm diameter had the best performance among seeding materials studied with respect to P removal and size distribution of individual crystals. KEYWORDS Struvite precipitation, seeding materials, phosphorus removal, mixing strength. INTRODUCTION Struvite (MgNH 4 PO 4 • 6H 2 O) is also known as magnesium ammonia phosphate or MAP, with specific gravity of 1.7. A white solid in its pure form, struvite can occur either as large single crystals, very small crystals, large curds or gelatinous mass. Struvite is highly soluble at acidic pH and highly insoluble at alkaline pH (Chirmuley 1994). Struvite precipitation was first noticed by wastewater engineers in Hyperion wastewater treatment plant in Los Angeles in the 1960s. It formed in the digested sludge lines as well as separating screens and caused operational problems by clogging pipes or freezing valves (Borgerding 1972). In wastewater treatment, precipitation can lead to the capacity loss by compromising process control and negatively affect the performance of sludge and filtrate conveyance system (Benisch et al., 2002). Struvite has also been found in anaerobic sludges from liquid animal production wastes (Booram et al., 1975). Although unintentional struvite formation has long been known to be nuisance in wastewater treatment plants (Munch and Barr, 2001), by controlling the precipitation to desired location, struvite precipitation can also serve as a process for removing and recovering phosphorus from wastewater streams. Struvite precipitation is attractive because of the following reasons: WEFTEC ® 2003 Copyright ©2003 Water Environment Federation. All Rights Reserved.