Struvite Control for Wastewater Treatment Plants
Struvite deposits and struvite obstructions in wastewater treatment plants are responsible for most of the inefficiencies found in the operations control of a wastewater treatment plant. Wastewater treatment plants are responsible for treating and disposing of our cities’ human waste, our cities’ household waste, city and industrial waste, and our dally work and household liquid by-products that we send to and through our city sewer systems from toilets, baths, showers, kitchens, sinks and industrial drains. Wastewater treatment plants (WWTP) are located in every major city in the United States and they in turn are responsible for treating our human sewage, industrial waste and agricultural wastewater (Concentrated Animal Feeding Operations: CAFO) and returning it safely to our oceans, rivers, ponds and industrial parks for useable watering. As long as these huge industrial complexes have clean and open transport pipes, they operate efficiently and cost effectively. When their pipes begin to clog up because of Struvite deposits, the WWTP operates inefficiently. When WWTP pipes are nearly shut closed by Struvite deposits, the cost of operating the plant increases quickly and their efficiency falls precipitously.
Daily struvite control is the most cost effective way to keep a WWTP free of struvite or viviante deposits. Struvite removal is mandatory when discovered to keep a plant operating efficiently and cost effectively. Every day New York City (http://www.nyc.gov/html/dep/pdf/wwsystem.pdf) delivers 1.3 billion gallons of drinking water to more than 8 million city residents. They have over 6,000 miles of sewer pipes, 93 wastewater pumping stations that bring all that water to 14 WWTPs located in their 5 boroughs. Each WWTP treats millions of gallons of water each day. They city of Los Angeles’ Hyperion WWTP treats millions of gallons of wastewater each day. No WWTP can afford to have struvite crystal rock deposits inhibit the operation of their plants.
Struvite Control through Struvite Prevention
The scientific community defines struvite as a phosphate mineral crystal whose elemental composition of magnesium, ammonia and phosphate forms in water. The chemically formula for struvite is NH4MgPO4•6H2O. Charles Jennings, Ph.D. in his article on Struvite Inhibitors also noted that Struvite is referred to as MAP by the wastewater industry, which stands for the chemical compound consisting of magnesium, ammonia, phosphate. Struvite formations will be found in varying colors from white to yellow to brown, see Wikipedia , depending upon the MAP content in the water. Charles Jennings notes that this is because struvite is not produced by strict stoichiometry calculations, i.e., struvite develops differently depending on local water conditions (see below) and local process applications at their treatment plants. Various types of struvite need different treatment regimes for struvite control and struvite removal.
The struvite chemical formation formula Mg2+ + NH4+ PO4-3 + 6H2O → NH4MgPO4•6H2O (crystal form) 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 like Jayne Products’ JS 9325, a WWTP is able to interrupt this 1:1:1 mole to mole ratio and prevent the formation of struvite.
WWTP’s wastewater temperature and its pH are also contributing factors to Struvite formation. Keep in mind that struvite manifests as a very strong crystal rock. 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 forms 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 all come together in the plant’s piping system causing struvite crystals for form; if the crystals are left untreated, they develop into rock and a special formulation like JS 9325 is then 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 like JS 9310 or struvite removal product like JS 9325 gives plant managers a tool to control Struvite.
Struvite Formation 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 elbows are especially susceptible to struvite formation
• Pumps are a prime location for struvite
• Aeration assembly
• Internal pumping components
• Plant overflow box of the anaerobic digester
• Wastewater sludge transfer line
• Plant centrifuges
• Rollers of the belt press
Struvite.info would like to remind all plant managers that rough surface areas are one of the first areas to look for struvite formation. When struvite crystal rock formations are not 100% removed from external and internal piping surfaces, the remaining struvite rough edges will form rock blocks more quickly than before.
Struvite Prevention through Struvite Control
JS 9310 is the most effective struvite prevention chemical in the wastewater treatment plant industry. The key to controlling struvite is having the ability to deal with a plant’s magnesium level, an ability to deal with its carbon dioxide release into the wastewater from degassing, and the ability to manipulate its pH. If you control the magnesium, you are able to control or prevent struvite precipitation. By using JS 9310, a plant manager is able to maintain a low pH in the water, chelate the magnesium and effectively deal with carbon dioxide. This allows the plant manager to prevent struvite crystalization and therefore, you are in control of the plant’s struvite formation.
JS 9325 is the most effective struvite removal product for WWTPs. When struvite forms, JS 9325 has the ability to break through the struvite water bond and dissolve the struvite crystal in an environmentally friendly way.
Expensive Methods of Struvite Control
Many wastewater treatment plants use iron salt or an aluminum salt to maintain a plant’s low pH and counteract the degassing of the CO2 in order to affect struvite control. Furthermore, since phosphorus and ammonia are highly sought elements for fertilizer, some WWTPs are able to use Ferric Iron (Fe+3) or aluminum (Al+3) to control the phosphorus in the wastewater by precipitating the phosphorus and remove it from the water as a solid. The same is true for the control and precipitation of ammonia.
In the Miami-Dade Water and Sewer Department's report related to struvite deposits in the solids handling process equipment at the Central District Wastewater Treatment Plant and the South District Wastewater Treatment Plant, they found no significant difference in dosage or effectiveness in using ferric chloride and ferric sulfate in controlling struvite formation. Their suggested choice was to use ferric sulfate because it is cheaper than ferric chloride, easier to handle and less corrosive to use. Nonetheless, after you create a solid precipitate to manage the struvite, you still have the cost of disposing the solid. When using a liquid product such as JS 9325 or JS 9310, the plant has no solids to deal with and no disposal costs.
Therefore, the use of iron and aluminum salts to control struvite is not a dissolve and flush treatment. These salt treatments generate a precipitate, which means that a solid is formed and has to be removed. When compared to JS 9310 or JS 9325, the cost of using a salt is more expensive than liquid products made by Jayne Products.
One of the best ways to prevent struvite from forming in a WWTP or CAFO is to use a struvite inhibitor. A struvite inhibitor conditions the surface area of equipment and infrastructure so that deposits will not form, nor will struvite crystals attach themselves to the equipment surface. This also applies to other insoluble molecules in suspension within the wastewater. In the case of struvite inhibitor JS 9310, the chelation action that JS 9310 generates towards magnesium also acts as a secondary inhibitor. In WWTP and CAFO systems where there is equipment like anaerobic digesters, heat exchangers, anaerobic lagoons, sludge transfer lines, dewatering equipment (ie belt presses, centrifuges, screw presses and rotary drum filters) without some type of inhibitor, struvite will form in low flow wastewater zones or rough surfaces on pipelines, valves and pumps. The recommended usage of JS 9310 is between 30-60 mg/l to inhibit the formation of struvite.Google+ Struvite Wastewater Struvite Removal