It is often required to remove phosphorous content from waste water to protect waterways from nutrient pollution. However, the removal process, especially enhanced biological phosphorous removal (“EBPR”), can cause problems in a waste water treatment facility in the formation of struvite (struvite or equivalently magnesium ammonium phosphate is a phosphorus mineral with formula: NH4MgPO4.6H2O that tends to clog pipes, pumps, and tanks used in the treatment process). Waste water treatment is typically performed in stages. In a primary stage treatment waste water may be held so that heavier particles can settle and floating materials can be removed. Secondary treatment may remove dissolved and suspended biological matter.
As part of a typical secondary waste water treatment, primary treated waste water may be processed with air or pure oxygen. In this “activated sludge” process, microorganisms utilize the oxygen to metabolize the incoming waste water, forming a mixture of microorganisms and waste water known as “mixed liquor.” This mixture is moved to settling tanks for concentration, thereby forming concentrated activated sludge. A majority of this sludge is returned to the activated sludge process tankage as “return activated sludge” (RAS). A separate portion of this sludge, termed “waste activated sludge” (WAS), is removed from the activated sludge process and sent to a sludge handling system for further treatment and disposal.
From this point on a variety of subsequent processes have been employed to further process the waste water, particularly with regards to removing nutrients, such as phosphorus. These processes can be chemical or biological or a combination of the two. However in typical systems it is a challenge to remove phosphorous early in the sludge handling processes to prevent deleterious downstream struvite formation.
Accordingly it would be desirable to create a process for struvite recovery that tends to reduce or eliminate the need for the addition of magnesium, as well as removing magnesium early in the process so that clogging by struvite tends to be minimized.