Abstract: The present invention describes a powder mixture and delivery method for the treatment of wastewater and water streams for the removal of phosphorus-containing compounds. The solid mixture is comprised of an aluminum-based coagulant mixed with a magnesium-containing compound and, optionally, additional compounds to aid in the control of pH, alkalinity, sludge production, settling rate, and other factors. This solid mixture is delivered to a wastewater stream or unit process where the aluminum-based coagulant works to react with, flocculate, and/or coagulate phosphorus compounds prior to their removal.