Struvite Control & Removal
Technology Overview
Struvite is an unusual chemical that can cause damage to anaerobic digestors and piping systems. Struvite
is a mineral-like compound considered to be hydrated Magnesium Ammonium Phosphate. The problem is
that harmless Magnesium Hardness in the water can cause this mineral to deposit in digestors, centrate
lines, belt presses, centrifuges and settling tanks in the anaerobic digestion system. Once struvite is formed
on pipes and tanks, the deposit is extremely tenacious.
How does Struvite get into the anaerobic system? Natural Magnesium is present in most water that we
consume. It is considered a non-toxic mineral and is present as a hardness presence in drinking
water. Normal hard water systems may have 15-50 ppm of Magnesium, which may be concentrated in
digestor systems. In digestor systems that are not specially treated to remove Ammonia there is always
Ammonia or Ammonium ions present. Urea is a waste product of Human biological systems and is broken
down to Ammonia and Carbon Dioxide in the anaerobic digestors. Phosphates are part of dishwasher and
laundry detergents and other cleaning agents and may naturally occur in the water . The conditions in the
digestors and piping systems are just right to encourage this mineral to form. Because millions of gallons
per day are processed in wastewater facilities, there is enough Magnesium and enough Phosphate to allow
formation of crystalline Struvite.
Operators of wastewater treatment systems are having to live with pipes and tanks that are continuously
becoming more and more plugged with this mineralaceous crystal that becomes pervasive to these
systems. Buildups occur over time or in some cases quite rapidly. With no present solution for Struvite
deposition, the anaerobic systems have to be replaced or cleaned. Replacement of these systems costs
millions of dollars of hard won money.
Recent suggested treatment of Struvite contaminated systems had required flushing out the system and then
treating with a high caustic solution, then a high acid solution, then a high caustic solution again, hoping
that some of the Struvite will dissolve or wash down the stream with the severe conditions it is exposed
to. Research has shown that this will not work.
Some have suggested chelating the Magnesium to remove the Struvite. EDTA may chelate Magnesium,
but it cannot easily be put in an acid format to break up the Struvite molecule or break the crystal
structure. Addition of EDTA, phosphonates or other chelating agents may aid in preventing Struvite
formation, but they do little for removal of Struvite buildups.
Struvite, being an ammonium chemical, behaves like any other ammonium salt it neutral and near neutral
solutions. In acid solutions, the ammonium salt may break down to ammonia. Ammonia is not soluble in
acid solutions. The problem is that the Struvite crystal is very stable and does not want to break down with
only the presence of an acid. The outer water molecules slow the acid reaction with the Struvite. Mineral
acids are ineffective and instead would be damaging to the piping systems.
Guard Products has developed an answer to this problem: ST 2520 is a mild cleaner which effectively
breaks the struvite deposits down at a consistent rate with general recirculation. ST 2520 is safe to apply
and easy to use. ST 2520 has been found
to be safe and non-corrosive on all substrates encountered during treatment.
Preliminary testing has shown that an 1.5 - 2 molar quantity of ST 2520 per mole of Struvite must be added
to fully break down and dissolve the Struvite . Our testing showed when this level was achieved, all the
Struvite dissolved in a few hours.
Furthermore, applications have demonstrated ST-2520 to inhibit struvite growth
with maintenance dosage rates of 10 – 30 ppm based on flow rates.
View Test Results