STRUVITE REMOVAL IN THEORY AND PRACTICE

The Joint Meeting of Essex and Union Counties (JMEUC) owns and operates a water pollution control facility in Elizabeth, New Jersey which receives wastewater from seventeen communities located in both counties. The treatment plant uses the activated sludge process to treat the wastewater. Primary and waste activated sludges are combined and gravity thickened before being processed by anaerobic digestion. The digested biosolids are then dewatered using centrifuges. The JMEUC facility has experienced struvite problems since the Biosolids Dewatering Facility was placed into operation during the fall of 1991. During late 2002, the plant developed significant struvite problems that affected its ability to pump digested biosolids through the dewatering facility and, ultimately, lime stabilizationStruvite, MgNH4PO4·6H2O, is a mineral precipitate that causes problems in systems handling anaerobically digested biosolids or the supernatant derived from biosolids dewatering. Ferric chloride, FeCl3, is typically used to control struvite formation. In addition, ferric chloride can also be used to remove struvite depositsThis paper will present what went right and what went wrong with using ferric chloride to remove struvite deposits. The operational problems of struvite deposits will also be discussed. The chemistry of struvite formation and the effect of ferric chloride on struvite formation and removal will be reviewed. The results of the kinetic experiments performed will be presented, showing the effect of ferric chloride concentration on struvite removalRecommendations based on these experiences will be presented which will show what parameters should be monitored on a long-term basis to predict the existence of conditions favorable to struvite formation, and how to determine if the struvite formation is a transient situation or a long-term problem.