Don’t Be Blindsided by Lime’s Hidden Consequences

DON’T GET YOURSELF IN DEEP SLUDGE
It’s easy enough to do theoretical calculations and provide exact alkaline equivalents between Lime and Technical Grade Magnesium Hydroxide. However, field and trial experience tells us a more complete story. The amount of high-grade Thioguard – technical grade magnesium hydroxide required to achieve equivalent buffering / performance benefits in the biological reactors tends to be much lower than the calculations would suggest.

Often overlooked are the hidden consequences of lime use, such as softening and pH spikes, and confusion about what standard total alkalinity tests are telling us. An easy way to find out the extent of softening that is taking place in your facility is to filter your sample with a 0.45 micron filter before titration. This will remove the insoluble CaCO3 – calcium carbonate particles that are not “biologically available.” Another significant, yet overlooked impact is the EPA documented sludge production associated with Lime.

POUND FOR POUND, AND IN EVERY STEP OF YOUR PROCESS, THIOGUARD IS SUPERIOR
Compared to Lime, Thioguard is capable of supplying significantly more alkalinity in a bio-available form to a microbial waste-water system without adversely affecting pH.

AVOID A “TRIPLE” NEGATIVE CONSEQUENCE
When you add Lime to your basins, it’s likely you are creating detrimental “Hot Zones” which have the triple negative effect of:

  1. converting soluble alkalinity into an unusable form of alkalinity,
  2. creating an environment hostile to healthy bacteria, killing them off entirely or significantly reducing their ability to function efficiently
  3. converted soluble alkalinity takes up capacity in reactors and increases the inert, inorganic fraction of the operational MLSS

LIME SOFTENING = ALKALINITY REMOVAL
Lime is commonly used in potable water to “soften,”or remove hardness minerals, such as calcium and magnesium from drinking water, in an effort to minimize the effects of potential scaling in the water distribution system. However, in the softening process, calcium and magnesium are removed from water in the form of calcium carbonate (CaCO3) and magnesium carbonate (MgCO3) which are also forms of alkalinity. Removing hardness from water also removes alkalinity. In wastewater, Lime is often considered as an alkalinity supplement. However, the effects of Lime softening can have undesirable consequences to the biological system, e.g., removal of alkalinity, creation of CaCO3 – calcium carbonate sludge, and the potential for bio-upsetting pH spikes.

TRANSPORT SAVINGS
The use of Lime generates significant amounts of sludge in wastewater collections and treatment. On a chemical basis, one ton of Lime can generate as much as 11.5 to 15.5 tons of 20% sludge cake to remove or dispose. In contrast, Thioguard reactions in wastewater produce only water and water soluble products as TDS with NO added sludge. In fact, customers using Thioguard have reported reductions of 15% – 25% in total solids/sludge produced, due to a combination of improved biological performance and reduced inorganic solids loading.

The use of Lime generates significant amounts of sludge in wastewater collection systems and treatment plants. On a chemical basis, one ton of Lime can generate as much as 5 tons of 20% sludge cake to remove or dispose. In contrast, Thioguard reactions in wastewater produce only water and water-soluble products as TDS with NO added sludge. In fact, customers using Thioguard have reported reductions of 15%-25% in total solids/sludge produced, due to a combination of improved biological performance, divalent cation bridging of floc matrix, and reduced inorganic solids loading.

Most wastewater treatment plant operators understand that their wastewater treatment plants function best at some ideal pH and that a minimum amount of alkalinity is required to keep microorganisms happy. But too often, the values of pH and alkalinity are incorrectly used interchangeably, and a thorough understanding of each parameter’s true relationship to biological stability and optimal performance – gets lost in the translation.

Most often this error in terminology stems from the use of common alkaline pH modifiers and alkalinity supplements, such as hydrated Lime. It’s use may successfully meet pH targets, but will likely fall short in supplying adequate alkalinity requirements without adversely elevating pH beyond biologically healthy limits. And often, maintaining pH stability and uniformity across entire treatment basins remains a virtual impossibility.

Unfiltered testing, may cause plant operators to errantly believe there is sufficient soluble alkalinity, or true pH buffering capacity, in the aqueous system. In filtered alkalinity tests, you are removing most, if not all of the insoluble alkalinity, resulting in a much more accurate representation of pH buffering capacity. Better information leads to better decisions. Better decisions lead to improved plant performance.

THE PRACTICAL CHOICE: THIOGUARD 


HARNESS THE POWER OF THIOGUARD FOR OPTIMAL TREATMENT AND MAXIMUM RESOURCE RECOVERY
Resource Recovery is currently a primary focus in the water treatment industry across the U.S. – a key objective for plant operators, executives and municipalities. Mg-Water, Premier Magnesia’s Water Utility Group, is an innovator in helping the nation’s water industry evolve and adapt. As America’s largest supplier of magnesia products, Premier is also the water industry’s most trusted knowledge resource for magnesia and its central role in the evolving Resource Recovery Revolution.

HIDDEN COSTS: Iron use Steals Alkalinity/pH and Actually Increases Hydrogen Sulfide and Corrosion

The usual discussion of sulfide removal emphasizes iron chemistry and fails to mention other reaction products resulting from the chloride and sulfate being released when the iron combines with the sulfur to form iron sulfide, a black precipitate. Additionally, iron strips alkalinity when used inside the plant. If there is also a chronic phosphorus deficiency, the result is needless organism death and higher plant biosolids disposal costs. The focus in this write-up is on odor control complications with iron sulfate.

WHAT HAPPENS WHEN IRON SULFATE IS USED FOR ODOR
CONTROL IN WASTEWATER? 

1. The first step in the reaction produces iron sulfide as a precipitate and sulfuric acid. If this were all that happens in wastewater, iron would be fed at a stoichiometric rate of 4.5 lbs. of ferrous sulfate to remove 1 pound of H2S. This turns out not be the case and 2 to 3 times that amount is necessary for sulfide reduction. Why? There are competing reactions in wastewater that will consume iron. Phosphorus, chlorides, sulfates, hydroxide, carbonate, oxygen and other common compounds compete for the available iron.

2. Now let us examine what may happen to the H2SO4 that is produced as a reaction product. First, it is corrosive and works to lower the pH in the wastewater. Second, sulfuric acid rapidly dissociates and will allow SO4-2 to be used as an oxygen source by the sulfate reducing bacteria producing more H2S.

3. Theoretically, iron sulfate could produce as much sulfide as it removes stoichiometrically, which then must be removed with additional iron. Lowered wastewater pH will also allow more H2S to be released as gas.

COMPARISON TO THIOGUARD CHEMISTRY

In contrast, Thioguard does nothing to lower the pH of the wastewater, produces no reaction products that can lead to additional sulfide production, and produces no sludge to settle out in the system or to be dewatered at the WWTP. The reaction is as follows:

The Magnesium binds the sulfide in a similar manner to iron and it will not be released unless the pH drops to 5.5 which is not normal in wastewater. More importantly, Thioguard is preventative and controls the formation of sulfide by increasing the pH and retarding the Sulfate Reducing Bacteria activity.

CHOOSING THIOGUARD WILL: