Struvite Formation and Precipitation
Struvite in pipe and bend
Struvite in heat exchanger
Struvite on outside of centrifuge before/after treatment
Struvite formation chemical formula is Mg2+ + NH4+ PO4-3 + 6H2O → NH4MgPO4•6H2O (crystal form), which tells us that struvite crystals are created when magnesium, ammonia and phosphate combine in water in a mole to mole to mole ratio of 1:1:1:. Utilizing a struvite control product one is able to interrupt this 1:1:1 mole to mole ratio and prevent struvite precipitation.
WWTP’s wastewater temperature and its pH are also contributing factors to struvite precipitation. The higher the wastewater pH the more likely the mole to mole to mole balance will be affected and the formation of struvite crystals will occur. Struvite formation occurs in wastewater treatment plants that have anaerobic digesters. Struvite forms because magnesium, which is a major ingredient and contributor of hard water, ammonia which is a byproduct of urea and urine, and phosphate, which is a major element in the organic matter processed at the plant come together in the plant’s piping system causing struvite crystals to form; if the crystals are left untreated, they develop into rock and a special formulation is required to cost effectively remove the struvite. Depending upon the wastewater feed stock of the WWTP the formation of struvite can be predicted and pre-treatment with an effective struvite control product or struvite removal product gives plant management a tool to control Struvite.
Struvite Precipitation Plant Locations
Wastewater treatment plant managers have found struvite crystal rock formations in many of the following plant areas:
- Anaerobic digesters
- Places where there is high kinetic energy (high turbulence)
- Pipe connections – especially elbows
- Pumps are a prime location
- Aeration assembly
- Internal pumping components
- Plant overflow box of the anaerobic digester
- Wastewater Sludge transfer line
- Plant Centrifuges
- Rollers of the Belt Press
Rough surface areas are one of the first areas to look for Struvite formation, when Struvite crystal rock is not 100% removed from the different surfaces, the remaining rough edges will form struvite more quickly.
Struvite Formation Tale Tell Signs
• High pH is a warning for the potential struvite formation
• High conductivity increases the potential for struvite formation
• Low temperatures foster the environment for struvite formation
• Higher concentrations of ammonium, phosphate and magnesium enable struvite precipitation