MagOx: Magnesium Oxide Relationship with Magnesium Hydroxide

MagOx: Magnesium Oxide Relationship with Magnesium Hydroxide

It is very common to hear someone in the wastewater treatment industry refer to something called “MagOx” as an alkaline additive they use to control pH or low alkalinity conditions.  Often they are simply using this term as a nickname when talking about either Magnesium Hydroxide or Magnesium Oxide, which is the chemical precursor to Magnesium Hydroxide, but which has very different properties.  So, when looking to obtain an additive that will provide the most cost-effective pH control performance for your wastewater treatment application, it is important to understand the relationship between Magnesium Oxide and Magnesium Hydroxide, and how not all products are equal.

First of all, the chemistry of Magnesium Oxide (MgO) and Magnesium Hydroxide (Mg(OH)2) is based on the Magnesium di-cation (Mg2+).  Magnesium is an essential macronutrient and is the core element in chlorophyll – the stuff that makes plants green and drives photosynthesis.  While MgO and Mg(OH)2 are very similar, knowing the differences in the manufacturing processes for each will help to understand the physical and chemical differences – which is very important in the selection process of the chemical best suited for your application.

Magnesium Oxide (MgO) is typically obtained from the calcination (heating) of Magnesite ore (Magnesium Carbonate or MgCO3) in much the same way as Quicklime (CaO) is formed from Limestone (Calcium Carbonate or CaCO3).  By changing the temperature and speed of how fast the MgCO3 passes through the heat zone, one can control the structure, porosity, and reactivity of the resulting MgO particles.  You may ask why this matters?  The more porous the particulate structure, having more available surface area, the more reactive the MgO.  The ability to control structure and porosity can result in the development of a wide range of MgO products with diverse properties for numerous industrial applications.

Odor, corrosion and FOG control in sewer lines

An Inside Look at IER’s Pasco Plant

A safe and cost-effective alternative to the use of sodium hydroxide [caustic soda, NaOH]
for wastewater alkalinity and pH adjustment

AMALGAM-60 is a proprietary, concentrated aqueous suspension of magnesium hydroxide (hydrated lime of magnesia – Mg(OH)₂) produced from calcined, high purity, natural magnesite. This product is manufactured in Washington state using a proprietary blend of dispersants that result in optimum storage stability and reactivity.

AMALGAM-60 provides a highly reactive source of magnesium hydroxide (Mg(OH)2) for use in chemical processing, water treatment, and wastewater treatment applications. AMALGAM-60 offers a safe, non-hazardous means of effective acid neutralization, coagulation, H₂S and heavy metals removal in wastewater and process streams.

Magnesium Hydroxide: Environmentally-Friendly and Cost-Effective Treatment for Odor and Corrosion in Sewer Lines

As the infrastructure in the United States continues to age, it has become increasingly apparent that improved understanding, maintenance, and treatment for sewer line odor and corrosion is extremely important.

By doing a simple internet image search using the words “sewer line corrosion” or “H2S corrosion” numerous photos of gas-phase corrosion are readily accessible, showing greatly diminished life of collection system infrastructure.  The most dramatic of these photos are of concrete pipe – showing that about the only thing remaining on the top section of pipe is the rebar (see the figure below from a Dec. 11, 2019 publication of Water & Wastes Digest called “Microbiologically Induced Corrosion”).

As can be seen, the bottom of the pipe is nearly unscathed, while the top section is nearly gone. To those in the wastewater conveyance industry, this photo is not uncommon. However, it is entirely preventable using cost-effective measures that both mitigate this problem in the collection system, as well as providing beneficial treatment to the downstream water reclamation facility (WRF).

In this article we plan to cover three primary topics related to odor and corrosion in sewer lines:

  • 1. The basic chemistry of how sewer line hydrogen sulfide (H2S) odors form and how this odor is directly related to gas-phase corrosion.
  • 2. The most prevalent treatments in the marketplace for sewer line odor and corrosion.
  • 3. The benefits of Magnesium Hydroxide for this application.

Improving water treatment sustainability

As the world was recovering from the after-effects of World War II, there was a tremendous growth in industrial processes.

As industry was booming in the 1950s and 60s it became obvious that our business practices were causing some dramatic negative effects to the cleanliness and quality of our air, water, and soil.

In the United States the Clean Water Act of 1972 ushered in the beginning of a national coordinated effort to address water pollution by funding the construction of sewage treatment plants and regulating contaminants of industrial and municipal discharge into US waterways. One parameter critical for maintaining sustainable waters is pH. Unfortunately, the pH of industrial and municipal wastewater streams tends to drift toward an acidic value, due mostly to waterborne anaerobic microorganisms that generate acidic by-products. These acids, such as hydrogen sulfide (H2S) and small organic acids (such as acetic and butyric) emit strong odors that are simultaneously unpleasant for neighboring businesses and residents and highly corrosive to the wastewater collection system infrastructure.

Buffering the pH of industrial and municipal wastewater streams in the alkaline range is one way to reduce odor and corrosion. This is often done by dosing the wastewater with sodium hydroxide (caustic soda, NaOH), which can create more problems than it solves. Alternative treatments like sodium carbonate (soda ash) and calcium hydroxide (hydrated lime) can also be problematic.

AMALGAM Mg(OH)2: alternative to caustic soda for wastewater treatment – with Birch Bay Water & Sewer

A safe and cost-effective alternative to the use of sodium hydroxide [caustic soda, NaOH]
for wastewater alkalinity and pH adjustment

AMALGAM-60 is a proprietary, concentrated aqueous suspension of magnesium hydroxide (hydrated lime of magnesia – Mg(OH)2) produced from calcined, high purity, natural magnesite. This product is manufactured in Washington state using a proprietary blend of dispersants that result in optimum storage stability and reactivity.

AMALGAM-60 provides a highly reactive source of magnesium hydroxide (Mg(OH)2) for use in chemical processing, water treatment, and wastewater treatment applications. AMALGAM-60 offers a safe, non-hazardous means of effective acid neutralization, coagulation, H2S and heavy metals removal in wastewater and process streams.

Magnesium Hydroxide’s Role in Sludge Compaction

Trying to determine how to improve wastewater sludge dewatering and compaction can be a very complicated process. 

The root cause of the problem can be anything from an undesirable biological process to a chemical imbalance.  Biological process upsets can be varied, from an over-abundance of filamentous bacteria to the lack of a diverse microorganism population.  Chemical imbalances tend to be centered around factors that affect the charge on suspended solids, such as swings in TDS  (total dissolved solids) and conductivity, pH and alkalinity, as well as the balance of mono-, di-, and tri-valent ions in your wastewater.  Ultimately, whatever the cause, wastewater operators always strive to make improvements in coagulation of suspended solids that will lead to better sludge compaction.  In this article, we will explore the concept of how Magnesium Hydroxide can play a role in improving the valance balance of the wastewater.

Let’s first take a moment to understand the basic chemistry of mono-, di-, and tri-valent ions.  Mono-, di-, and tri- refers to the charge (valence) of the ion.  For example, the sodium cation (Na+) is a mono-valent ion, having a single positive charge on it’s nucleus.  The magnesium di-cation (Mg2+) has two positive charges, and the aluminum tri-cation (Al3+) has three positive charges.  The higher the charge (valence) on any ion, the higher the charge density of that ion.  An increase in the charge density makes the ion more like a magnet, meaning that the ion has the ability to bond strongly to negatively charged (-) particles.

The image to the right shows the effect of increasing charge density on the size of the sodium (Na+), magnesium (Mg2+), and aluminum (Al3+) ions.  While each of these metal ions weigh about the same (24 to 27 g/mole), the increased positive charge in the nucleus of the aluminum ion has a dramatic effect on pulling in the electron cloud and shrinking the ion’s size.  Therefore, the Al3+ ion is much, much smaller than the Na+ ion, making the charge density of the Al3+ ion much greater.  Due to its large size and low charge density the sodium ion (Na+) does not possess coagulation properties.

Nearly all salts containing sodium are highly water soluble, meaning that the Na+ ion has very little strength to hold onto a (-) particle.  As a result, high levels of sodium in wastewater can cause a reduction in solids settling and compaction.  Alternatively, the aluminum ion (Al3+) has a very high charge density making it very useful as a coagulant in well-known products such as alum and poly-aluminum chloride.

The charge density of the magnesium ion (Mg2+) lies between that of Na+ and Al3+, resulting in many wastewater applications that show significant coagulation benefits from the use of Magnesium Hydroxide, resulting in improved dewatering and sludge compaction.  For this reason, the replacement of Caustic Soda for pH control with Magnesium Hydroxide, replacing Na+ with Mg2+, can have the side-benefit of improving sludge dewatering and compaction.

A key distinction of Mg2+ and Al3+ for solids compaction is that common Al3+ coagulants, such as alum or polyaluminum chloride, are acidic products (as are Fe3+ based coagulants).  Therefore, feed of these products into the wastewater system can consume alkalinity resulting in the need to feed a subsequent alkaline additive.

The feed of Mg(OH)2 does the opposite – boosting the pH and alkalinity while simultaneously releasing the Mg2+ ion to aid in solids compaction. However, just as with Al3+ and Fe3+ based coagulants, sometimes significant positive effects are observed with Magnesium Hydroxide feed and in other instances there is little to no effect.  This inability to predict Mg2+, Al3+, and Fe3+ coagulation performance likely stems from differences in microbiological diversity of the sludge or the pH, conductivity, and chemical composition of the sludge being treated.

Most suspended particles in food processing and municipal wastewater sludges are negatively charged ions, often having multiple negative charges present on each particle.  Picture a ball of string with multiple (-) sites located all along the string. The attraction of these negatively-charged (-) ions with high charge density (+) cations can result in charge neutralization and strong ionic bond formation – which is what results in the formation of strongly flocculated particles (“flocs”).

By combining and becoming mostly neutralized, these flocs continue to grow as they encounter other (+) and (-) ions in the wastewater.  As they grow, water molecules loosely bound to the ions are released, resulting in more dense flocs that are easier to dewater in a centrifuge or press.

In summary, effective charge neutralization is the primary mechanism that wastewater operators seek to exploit when trying to improve sludge compaction.  Increasing the balance of di-valent and tri-valent cations in the treated wastewater will aid in capturing and dewatering the suspended negatively charged particles that make up the great majority of the suspended solids in the system.  One simple way to improve this balance is to replace the use of Caustic Soda (NaOH) with Magnesium Hydroxide (Mg(OH)2) for wastewater pH and alkalinity control.  This reduction in Na+ and increase in Mg2+ will provide a more multi-valent ions for charge neutralization, floc formation, and sludge compaction.

Don’t be so caustic!

Treating wastewater from food processing facilities can be so much safer, more environmentally friendly and more cost-effective thanks to a benign but extremely effective ingredient.

One of the primary reasons to treat wastewater is to reduce acidity and to raise the pH level.  Balancing the pH is vital in preventing harm to the environment or to infrastructure such as pipes, storage facilities and land application systems (sprinklers), and to minimize odor.

The best way to neutralize acid in wastewater is to dose with an alkali to maintain a neutral pH level.  The traditional method to treat acidic wastewater involves the use of caustic soda, otherwise known as sodium hydroxide (NaOH).  Other widely used alkalis are soda ash (sodium carbonate) or hydrated lime (calcium hydroxide).

However, all these materials are hazardous and require high dosage rates for them to be effective. Caustic soda is often used instead of powdered alkalis like lime or soda ash because it is easier to handle and requires less maintenance.  Dosing with caustic soda is quite simple, but this dangerous substance must be handled with extreme care, abiding by chemical containment and occupational health and safety measures.

Fortunately, there is an alternative.  An increasing number of food processing companies have switched to magnesium hydroxide to control their wastewater pH levels.  This non-hazardous compound provides an extremely strong buffer to control pH and is more friendly to the environment…

Safety of common alkalis for wastewater treatment

Safety of common alkalis for wastewater treatment

Wastewater treatment presents a multitude of hazards, such as drowning; confined spaces; and exposure to hazardous chemicals or gases.

↑ Caustic skin burn caused by sodium hydroxide (caustic soda)

Hazardous chemicals can pose a significant risk to health and safety if not managed correctly. Municipal and industrial plant managers have specific duties under

increasingly stringent health and safety regulations to manage risks associated with using, handling and storing hazardous chemicals.

Being a plant manager at a wastewater treatment plant is an enormous responsibility with the need to answer to many high authorities such as the Environmental Protection Agency (EPA) or Occupational Health and Safety Administration (OSHA).

In this article, we have compared three common alkalis for wastewater treatment, and explained why IER magnesium hydroxide products are the safest and most-cost-effective options.

  1. Ca(OH)2 -> calcium hydroxide, lime slurry, hydrated lime
  2. NaOH -> sodium hydroxide, caustic soda
  3. Mg(OH)2 -> magnesium hydroxide, milk of magnesia

There are laws in each state or territory that set out the requirements for handling and transporting dangerous goods. Switching to safer chemical products means you are not only protecting the health and safety of your people, but you are also making cost savings for years to come.

AMALGAM-60

Magnesium Hydroxide (Mg(OH)2) is a safe, environmentally-friendly, and cost-effective alternative to the use of Sodium Hydroxide (Caustic Soda, NaOH) for wastewater pH and alkalinity control.  Inland Environmental Resources, Inc. (IER) is the Pacific Northwest manufacturer of this chemistry in a 60% Mg(OH)2 product called AMALGAM-60, with plant locations in Pasco and Centralia.

 

Cost:  Every 1.0 lb of 50% NaOH can be replaced with 0.60 lbs of 60% Mg(OH)2 to provide the same number of moles of hydroxide (OH-).  This 40% reduction in daily usage rate translates into a dramatic cost savings – for something that is “green” and safe!

Safety:  Though Mg(OH)2 is much stronger for supplying OH- buffering, it is dramatically safer for operators to handle and for treating wastewater microorganisms.  Mg(OH)2 dissolves only when it encounters acidity, unlike NaOH which immediately releases OH- to burn operator’s skin and eyes.  This is why the pH can rapidly spike to > 12 if Caustic is overfed, while the overfeed of Mg(OH)2 will safely buffer the pH up to 8 or 9.  This controlled release” trait of Mg(OH)2 is a primary driver for its acceptance as an ideal buffering agent for nitrification and anaerobic digestion processes.

“Green”:  Magnesium is the core element of chlorophyll (what makes plants green), while salinity from Sodium is detrimental, especially for land reuse applications.

Freezing:  50% NaOH freezes at 60oF, so in winter 25% NaOH is commonly used.  60% Mg(OH)2 freezes at 32oF, just like water, greatly minimizing freeze concerns.

Solids Settling:  Mg(OH)2 can provide improved solids settling and sludge compaction benefits that NaOH does not.  When Mg(OH)2 dissolves, the Mg2+ cation can coagulate suspended solids to improve both microorganism activity and solids removal efficiency – often reducing polymer usage.

Trial Equipment:  IER supplies agitated storage tanks (from 100 to 1500 gallons) to allow real-time measurement of cost savings while confirming performance, safety, and feed reliability – allowing a clear understanding about how Mg(OH)2 will improve your overall system before deciding to make a permanent transition.  IER supplies AMALGAM-60 in full tanker or small volume quantities using dedicated, in-house delivery specialists and equipment.

Please call if you would like to learn more about IER’s safe, “green”, and cost-effective Magnesium Hydroxide product for your operation.