Struvite is a specific scale that can form under defined conditions, normally associated with digestion processes in waste water treatment, or in anaerobic digesters using organic feedstocks. Struvite is a hard, tightly adhering scale that is based on a combination of Magnesium, Ammonium and Phosphate reacting together to form the scale in sections of the process equipment and pipework.
Like for all scale deposits, the prediction and anticipation of their formations in the process is extremely difficult. On one hand, this is related to the operating conditions and on the other hand, the water composition and the chemicals applied across these processes.
Struvite has the chemical formula: NH4MgPO4·6H2O. When Struvite formation occurs, it tends to form in specific places where flow velocity changes:
- Places where there is high kinetic energy (high turbulence) e.g. Pumps
- Pipe connections – especially elbows and T pieces
- Aeration assembly
- Internal pumping components
- Wastewater Sludge transfer line
- Plant Centrifuges
- Belt Press Rollers
- Digester Tank
Formation of Struvite in these areas leads to flow restrictions, increased pumping loads and ultimately potential hydraulic locking across the process.
How to identify Struvite formation: The tell tale signs
High pH is a warning for the potential struvite formation
Normally due to a plant upset or control issues
High conductivity increases the potential for struvite formation
The hydrolysis water contains high levels of Magnesium; the conductivity is an indication of total dissolved solids (salts) in the water.
Low temperatures foster the environment for struvite formation
Especially relevant to the Thermophilic process where sludge is cooled post pasteurisation. Higher concentrations of ammonium, phosphate and magnesium enable struvite precipitation – this is particularly difficult to control as this relates to feedstock.
Brenntag offers several solutions to this complex problem in the form of products able to prevent the formation of Struvite within the process, plus a curative product to simplify the clearing up of existing deposits before initiating a prevention program.
Struvite removal with Antiprex® MSA*
An organic acid based product that removes the deposit in place by recirculating a solution through the plant pipework.
This product removes the requirement to dismantle the plant pipework and associated equipment for pressure washing or use of concentrated hydrochloric acid and the hazards associated with handling/storage/corrosion effect of such material. Traditionally these were the commonly used methods to remove such deposits.
Struvite prevention with Antiprex® AD 1020XP*
Water soluble polymer - already proven to successfully control and prevent struvite formation in complex plant processes – dosed at a nominal rate of 10-20 ppm** into the recirculating centrate or sludge.
In addition, use of ferric salts can assist in helping control Struvite deposits in the digestor process. Although ferric salts are primarily used in these processes to control hydrogen sulphide formation, they also help to control Struvite formation by reacting with the phosphate to produce Iron phosphate salts. However, this can lead to increased sludge formation and higher polymer use in the centrifuge dewatering process for the sludge.
*Antiprex® is a registered trademark of BASF SE
**Dosage could be adjusted on site
Brenntag can support the Struvite removal and control programs through our extensive water treatment laboratory facilities based at our Bradford location.
We can provide site technical visits to identify problem specific issues and recommendations on treatment and prevention programs developed with our partners at BASF.