Struvite Precipitation and Struvite Formation in Wastewater
Struvite in pipe and bend
Struvite in heat exchanger
Struvite on outside of centrifuge before/after treatment
Struvite Precipitation and Formation
Struvite formation is written by the following struvite formula or struvite chemical formula; Mg2+ + NH4+ PO4-3 + 6H2O → NH4MgPO4•6H2O (crystal form). The formula 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 and struvite formation.
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 feedstock of the WWTP the formation of struvite can be predicted and pre-treatment with an effective struvite control product (Struvite Preventer STSP) or struvite removal product (Struvite Remover STSR), which gives plant management tools to remove and 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
Struvite Removal offers solutions for Removal and Prevention
We typically recommend using the Remover to clear the struvite and remove any potential growth sites. From there, many customers opt to do removal maintenance or removal/cleaning as needed, or the other option is to use the Struvite Remover STSR or Struvite Preventer STSP (added polymer) and dose between 30-90 ppm (on average) to prevent struvite scale buildup by lowering the pH and dispersing/inhibiting the formation of struvite.