Frequently Asked Questions

Chlorine with out pH asdjustment is oxidative and not very biocidal. Biofilms are burned on external layers and coliforms are protected underneath.

A small water system is less able to build and operate a conventional Fe and Mn removal plant. Sequestration therefore has several advantages over conventional treatment plants. Conventional treatment requires experienced operators and generates sludge during treatment. The cost of building a small removal plant capable of serving 200 people could cost $500,000. By contrast, to set up the equipment for sequestration at one well, it would cost less than $1400 per well and $5 per person per year. The cost for effective polyphosphate treatment ranges between $20 and $40 for each 1.0 mg/L of polyphosphate per million gallons treated, depending on the type of phosphate chosen and the suppliers cost. No waste sludge is produced. It is simple and requires very little supervision or labor.

Any product used in potable water treatment must meet the standard 60, ANSI / NSF (National Sanitation Foundation) standards. A typical project includes submitting an application for certification, product information acquisition, toxicological review, establishment of a testing program, plant audit and sample collection for testing and evaluation. Finally, the product is certified as meeting standard 60 ANSI / NSF standards. Yearly follow-up plant audits review the manufacturing process and quality assurance records as well as collecting samples for additional testing to assure that the product continues to pose no adverse health risk to consumers.

No two water systems are exactly alike; however, almost any water quality problem can be defined by chemical analysis of water in the distribution system as it compares to water at the source. There are so many variations in municipal water quality; it seems strange that some manufacturers expect a single product to be adequate to treat all water systems. Experience has shown that the specific properties of the pyros, tripolys, trimetas and hexametaphosphates allow for numerous formulations and product applications so as to achieve the desired results. It is desirable and possible to develop treatment chemicals that work on specific water quality problems. Be skeptical of any manufacturer that promotes a “one product fits all” approach.

Water Quality parameters such as pH, iron, manganese, hardness, etc. will greatly influence the final product and treatment recommendation. The following water characteristics and their affect on water quality should be part of the overall treatment evaluation.

• Alkalinity: As alkalinity increases corrosion decreases.
• Calcium: As calcium increases corrosion decreases.
• Biofilms and microbial growth: As biological activity increases corrosion increases.
• Chlorides, Sulfates and Nitrates: As part of the TDS, as these increase, corrosion increases.
• Chlorine: As chlorine increases, corrosion increases.
• Dissolved Oxygen: As dissolved oxygen increases, corrosion increases.
• Iron & Manganese: As Fe-Mn increases, discoloration increases & water quality decreases.
• Flow Velocity: Excessive flows can increase corrosion.
• Hardness: As hardness increases, corrosion decreases.
• Hydrogen Sulfide (H2S): As H2S increases, corrosion increases.
• Phosphate: Decreases corrosion by providing cathodic and anodic inhibition.
• pH: As pH increases, corrosion decreases.
• Silicates: As silicates increase, corrosion decreases.
• Temperature: As temperature increases, corrosion increases.
• Total Dissolved Solids (TDS): As TDS increases, corrosion increases.

It’s important to understand the different forms of phosphate that can be present in water and the methods used to chemically analyze them.

Ortho vs. Poly: Very simply put, ‘ortho’ phosphate in water treatment formulas is used to treat corrosive water, whereas the ‘poly’ phosphate portion is primarily used to sequester iron, manganese and hardness. Many water treatment formulas contain varying blends of both forms in an attempt to provide a multiple use product that offers sequestering and corrosion control.

Testing Methods:
Ortho Phosphate Testing Methods; Analytical tests are only able to detect ortho phosphate in water samples. The common test for ortho phosphate is called a “Reactive Phosphorus (Orthophosphate)” test, where phosphate in the water reacts with reagents to produce a blue color which is measured and reported as ______mg/L PO4. (Note, many laboratories when asked to analyze a sample for phosphate will report the sample results as phosphorus. When results are reported as mg/L of phosphorous, multiply the results by 3.06 to get results as mg/L orthophosphate, PO4.)

Total Phosphate Testing Methods; If organic phosphates, condensed inorganic or long chain linear polyphosphates are present, they must be converted to ortho phosphate before it can be measured. The sample is treated with heat and acid plus reagents to break apart the condensed or linear chain forms of poly phosphate to the basic reactive ortho phosphate before analysis. Water sample + acid + heat + reagents changes the condensed polyphosphate PO4 present to orthophosphate PO4 which can be measured by the reactive phosphorous method. Results are reported as total phosphorous PO4. Polyphosphates are thus determined indirectly by subtracting the result of the basic reactive phosphorus test from the total (acid hydrolyzable) phosphorus test. When you subtract the ortho PO4 from the total PO4 the difference is Poly phosphate, PO4.

In summary: Total phosphate as PO4 – ortho phosphate as PO4 = Poly phosphate as PO4. Always do both tests if you need to determine the polyphosphate concentration.

As discussed previously the threshold effect with these blended phosphates allows for their use at dosages far below the expected molecule to molecule level. General factors of the treated water to consider are the basic chemicals of iron, manganese and hardness, and physical concerns like temperature and pH. Most sequestering and corrosion problems can be handled by dosages less than 2 mg/L. Scale control and cleaning of the distribution system in conjunction with a thorough flushing program may require up to 5 mg/L initially but can usually be reduced and maintained at doses of 1mg/L.

Well production can drop off over time due to blockage of well casings, well screens and the adjacent water-bearing formations. These blockages or incrustations take the form of biological, chemical and /or mechanical plugging.

The well owner should keep good records of specific capacity performance so that any decline will be immediately detected. The specific capacity is the pumping rate of the well in gallons per minute divided by the total drawdown in feet, the drawdown being the difference between the static water level and the pumping water level. The new specific capacity readings taken at various times can be compared against the original specific capacity when the well was new or redeveloped. (Note: Small variations of specific capacity can be attributed to pump and bowl wear or changes in dynamic head during the testing).

Biological Incrustation occurs when wells are populated with one of several genera of iron related bacteria. These organisms form a slimy gelatinous matrix of polysaccharide polymer material that enhances the attachment to the surface, nutrient capture and protection of the cells. They feed off dissolved iron in the water that is ultimately deposited in the form of a hydroxide. The organic slime matrix combined with iron deposits can greatly reduce pumping capacity of a well in a short period of time.

Chemical Incrustation occurs when mineral scale forms around the well bore when the well is pumped. The draw down created by pumping the well causes a reduced pressure in the aquifer, which releases carbon dioxide gas (CO2), from the water. This CO2 deficiency causes a chemical imbalance forcing dissolved minerals in the water like calcium, and magnesium to form insoluble scale. In a lesser degree, iron, manganese and sulfates may also precipitate.

Mechanical Incrustation describes the plugging which occurs when silt and clay size particles in the aquifer move toward the well during pumping or describes the poor development of a well when new. This form of incrustation is rare but can occur where large amounts of these minute particles are found.

Conclusion: No mater what problem causes the yield of the well to decline, the cleaning process is always easier if the problem is diagnosed and treated early. We know from experience that well maintenance is too often performed as an emergency procedure when the well production has dropped to 50% of original pumping rates. We take a proactive approach of regular maintenance on wells before pumping rates drop more than 10-15%. We can diagnose the problem and provide the expertise and chemicals to restore a well back to near capacity.

The presence of microorganisms in wells and distribution systems is referred to as biofilm. Certain microorganisms related to Fe and Mn and sulfur have long been observed and implicated with staining problems. First noted in literature in 1833, “iron bacteria” has long been associated with problems in the delivery of quality water for domestic use.

Iron bacteria is a generalized name for a wide ranging family of organisms classified as aerobic bacteria (living in the presence of oxygen) and anaerobic bacteria (living in or active in the absence of free oxygen such as in water). Iron bacteria have the ability to extract iron and manganese from water and deposit it in their slime or thread-like sheaths or on their surfaces. These bacteria may also be able to obtain iron from the pipe itself if it is made of iron. Other similar types of sulfur organisms are also capable of using sulfate in water as an energy source and producing hydrogen sulfide “rotten egg” odor. Sulfur bacteria also can deposit objectionable dark slimes in mains.

Iron related bacteria are generally known to:

• Pit and corrode pipe systems, attacking pipes to obtain iron.
• Lower the pH of the water
• Cause taste & odor problems (musty, metallic & rotten egg).
• Cause turbidity
• Discolor & cause staining (i.e. dark slime growths in toilet flush tanks.)
• Clog pipes and reduce water flows.

Iron related bacteria are usually associated with the generation of thick brown to black slimes. These slimes undergo a number of growth phases starting with attachment to the surface. Eventually, limited colonization over the surface ultimately produces a large polymeric “umbrella” or biofilm that protects the bacteria to some extent from adverse conditions such as chlorination. This biofilm produces finger like processes that extend into the water causing friction and ultimately a restricted flow and plugging. When left to grow without restraint, their accumulation of dead microbial bodies and other debris may lead to pipe closures and line failures due to corrosion.

Studies have shown that Coliform bacteria can grow and hide inside Biofilms on iron pipes, thus escaping disinfection by chlorine. Free chlorine doses as high as 5.0 mg/L for two weeks did not affect significant changes in viability. Application of blended phosphates having the ability to control corrosion and sequester iron and manganese has been shown to improve the efficiency of chlorine disinfection and decrease viable counts of bacteria including coliforms in biofilms. Additionally, systems with no detectable levels of phosphate often have higher rates of Coliform occurrence. This finding would dispute the idea that adding phosphate to the water may contribute to or worsen Coliform or biofilm occurrences. When chlorine is used in addition to specially blended phosphates, slimes and encrustation’s can be slowly controlled and reduced. Manufacturers of polyphosphate products suggest that the cleansing effect of special phosphates can slowly help the chlorine penetrate deeper into the slime growths and control the growth and spread of clogging cells. Polyphosphates specifically sequester soluble iron, manganese, calcium and silica and dissolve existing scale and deposits, thus eliminating food for bacterial growth. Proper sequestering is achieved when the chemical stabilization of the minerals occurs in such a way as to keep them suspended and able to be moved through the pipes without depositing on the surfaces.

Many manufacturers claim that bacteria counts in the distribution system can be lowered after extended treatment.

Since phosphate products are available in both dry and liquid form, many injection applications are possible. Liquid products can be fed at full strength or diluted from holding tanks. Electronic metering injection pumps can be used to deliver the correct doses directly to the water. Dry phosphates are mixed with water at various concentrations and added similarly. The general consensus is that phosphate should be added as far upstream before chlorine as possible so that sequestering can occur before chlorine can affect the oxidation of iron, manganese or hardness minerals.

Hydrolysis: All condensed phosphates are subject to decomposition when they are dissolved in water. The reaction is called hydrolysis because the water is an active participant in the reaction. During the reaction, bonds in both the phosphate and water are broken. The resulting hydrogen atom unites with the oxygen in the broken phosphate couple, forming P-OH. The OH portion of water reacts with the phosphorous in the broken phosphate couple, forming P-OH. The result is one molecule of condensed phosphate has reformed into two new phosphates. When the simplest condensed phosphate, pyrophosphate, undergoes hydrolysis, it is converted into two orthophosphate ions. When tripolyphosphate, the next simplest condensed phosphate, undergoes hydrolysis one orthophosphate ion and one pyrophosphate ion is formed. In both cases, the hydrolysis reaction leads directly to the formation of orthophosphate. As the phosphate chain length increases, decomposition need not always result in orthophosphate production. A six-membered linear phosphate may decompose to form two ions of tripolyphosphate. In municipal water treatment to control iron and manganese, product reversion from polyphosphate to orthophosphate is undesirable because ortho phosphate shows no sequestering or threshold effect.

The following factors can affect the rate of the hydrolysis reaction (Monsanto, 1995):

Temperature:

Temperature has a direct effect on reversion rate. As in any chemical reaction, as temperature increases, the rate of reaction increases.

pH:

Acids and bases catalyze the reversion reaction. As the pH of a phosphate solution becomes more acidic than pH 7 or more basic than pH 11, the hydrolysis rate increases dramatically.

Metal ions:

The presence of multivalent metal ions has been reported to catalyze reversion rates. As the concentration of Ca++ or Al++ or Fe++ increases, reversion rates increase.

Concentration:

The concentration of phosphates in solution will affect reversion rates. At the mg/L level, as concentration increases, the reversion rate decreases.

Phosphate Specie:

Reversion rates are also affected by which phosphate specie is present. It is generally accepted that pyrophosphate is the most stable phosphate. Then follows tripoly and last the glassy phosphates. (Usually the opposite is found in product literature and sales rhetoric.) During hydrolysis of the longer chained phosphates, shorter chains as well as orthophosphate are formed. Among the shorter chains formed is pyrophosphate. Research suggests that when the pyrophosphate concentration reaches a certain level due to hydrolysis of higher condensed phosphates, the rates of reversion diminish. It may be that equilibrium is set up between the higher condensed phosphate and its molecular fragments after hydrolysis. Once a certain amount of the fragments are produced, the equilibrium is satisfied and reversion rate diminishes. Manufacturers recommend adding pyrophosphate to higher condensed phosphate solutions to retard reversion.

All condensed liquid phosphates have been polymerized to the less stable longer chains of polyphosphate and therefore, over time, have a tendency to revert back to the more stable orthophosphate. Certain polyphosphates however have extremely long shelf lives’s measured in years, while others revert to orthophosphate more quickly.

• Sequesters metals & minerals to prevent staining
• Reduced flushing and flushing time
• Protects system integrity
• Maintains high system "C" factors
• Helps build particle size prior to filtration
• Removes mud balls & scale in filters
• Inhibits scale & forms a protective film
• Passivates tuberculated & new piping
• Helps with hydrogen sulfide odors and removal
• Provides corrosion control for lead, iron and copper
• Complexes metallurgy to control corrosion
• Removes biofilm
• Provides cleaner surfaces
• Penetrates scale & biofilm for more effective disinfection
• Reduced THM formation potential
• Economical to apply
• Enhanced compliance
• Removes carbonate scale
• Reduces turbidity
• Disperses loose debris
• Reduced chlorine demand as metals are sequestered
• Fewer customer complaints
• Prevents discolored water
• Protects asbestos cement pipe

In general terms they control iron and manganese staining and scale deposition, soften and remove scale and tuburculation, and control corrosion.

Sequestering:

Phosphates are often referred to as chelating or sequestering chemicals. A sequestering agent is a compound that will form a water soluble, stable metal complex without precipitation. Iron, manganese, calcium and magnesium form stoichiometric (mole to mole) relationships with the sequestrant. If the number of moles of calcium doubles, the molar amount of sequestrant required for optimum binding also doubles.

Threshold Agent:

A threshold agent is a compound that prevents the crystallization or precipitation of a normally insoluble metal like calcium or iron at levels far below that which is required in mole to mole reactions. For example, hardness at 200 mg/L as calcium carbonate would theoretically require 500-mg/L sodiumhexametaphosphate (SHMP) to sequester the calcium.

However, typically only 2 to 4 mg/L of SHMP is used to inhibit scale formation. This “threshold effect” of SHMP is not fully understood, but it may occur by interfering with early crystal growth. Most condensed phosphates can act as both sequestering agents and as threshold agents.

Dispersion and Deflocculating:

In the absence of phosphates, small particles of iron or calcium tend to attract one another due to areas of both positive and negative charges on each particle. The clumps deposit out of solution onto the surface of pipes in a process called flocculation. Threshold levels of poly phosphates coat the small particles and reduce their attraction for each other, resulting in little or no settling. This property is also key in removing (deflocculating) existing mineral oxides from pipes.

Corrosion Inhibition:

In the late 1920’s, Dr Ralph Hall rediscovered a 100 year old report describing the use of phosphate in water treatment. He developed the first meaningful application of phosphate use in boiler feed water to precipitate and control calcium. In 1940 to 55, researchers from Calgon and MIT established the effectiveness of a 2-mg/L feed of SHMP for corrosion and scale control in municipal systems. It was shown to react with iron and calcium to form positively charged particles in the vicinity of the anodes on the pipe surface. These very small particles are then deposited on cathodic areas by a process called electro deposition. This film decreases the rate of corrosion on the pipe surface. Researchers used radioactive phosphorous in tracer tests to show the presence and amount of electrodeposited film. Once phosphate treatment stops, corrosion inhibition decreases. This suggests there is a mobile equilibrium between phosphate on the surface and in solution. Copper corrosion was thought to not improve with either orthophosphate or polyphosphate, however, long-term treatment with blended phosphates has shown that a combination of blended ortho and polyphosphates can dramatically reduce the rate of general corrosion of copper. The synergistic effect of these combinations is shown to work but has not been fully explained.

All phosphates are made from the same compound, phosphoric acid. Production of phosphoric acid or any of the various phosphates discussed here are produced by one of only two general methods:

1. The wet process
2. The furnace process

The wet process takes phosphate rock through a sulfuric acid digestion. Impurities are precipitated out and after filtering, a “green phosphoric acid” is produced. This is usually used in fertilizers. To produce phosphates by the furnace process, high quality phosphate rock is heated in an electric furnace to vaporize elemental phosphorous. The phosphorous is then burned to produce P2O5. This phosphorous pentoxide is collected and dissolved in water or dilute phosphoric acid to produce strong phosphoric acid solutions. This procedure is energy intensive but produces the highest quality phosphoric acid which is the ortho phosphate starting point for all phosphate salts used in water treatment. Under carefully controlled conditions combining sodium or potassium salts, temperature and time, ortho phosphate is converted to condensed phosphates. Condensed phosphates are sometimes called metaphosphates but are generally called polyphosphates. At 320 degrees F, ortho phosphate is condensed to pyrophosphate. At 460 degrees F and the appropriate time, pyrophosphate will condense further to form trimetaphosphate. Increasing the temperature to 1200 degrees F further condenses the trimetaphosphate followed by a rapid quench to create hexameta and higher metaphosphates.

Condensed phosphates are all phosphates comprised of multiple phosphate groups. The simplest is pyrophosphate with two groups. The term “condensed phosphates” originates from the name of the reaction forming them. Several independent phosphate groups condense into a larger group. During this phosphate condensation, water is driven off. Condensed phosphates are therefore sometimes referred to as dehydrated phosphates.

The extent of the condensation determines the physical appearance of the molecule formed. The physical appearance is sometimes used as a descriptive term. The crystalline phosphates comprise the pyro’s, tripoly’s and trimeta- phosphates. The glassy phosphates comprise the hexameta and longer chain phosphates. The commercial hexametaphosphates are mixtures of various phosphate chain lengths. Most retail suppliers of water treatment products will buy the dry powders from manufacturers and then mix various combinations of ortho, pyro, tripoly and hexametaphosphates together to make powder and liquid formulas.

Phosphates are the salts of various phosphoric acids. They are widely used in water treatment and industrial formulations because of their superior ability to soften water, control scale and corrosion, and sequester iron and manganese.

Orthophosphates are the most natural form of phosphate and are used to prevent corrosion of metals inside the water mains.

Polyphosphate ingredients in formulations generally provide scale control and the sequestering of minerals.

Blended phosphates use the ortho and poly forms of phosphate to produce products capable of corrosion control and sequestering and tend to be more stable than many single ingredient formulations. By blending various ortho and polyphosphate ingredients, it is possible to achieve a synergistic effect that produces better performance and stability over single ingredient formulations.