Thioguard® Magnesium Hydroxide

About Thioguard®


When municipal customers hear the name THIOGUARD®, they usually think of Premier's product name for technical grade magnesium hydroxide, or milk of magnesia. However, since the creation of the first THIOGUARD® applications, the THIOGUARD® name has come to stand for so much more.

Since THIOGUARD®'s early roots as a topical coating on concrete sewers to prevent corrosion, Premier R&D and field staff invested significant money and energy into the study of the role of magnesia in wastewater from collection systems to biological treatment and biosolids processing. During the course of this evolutionary learning process, Premier has extracted the resources necessary to successfully apply THIOGUARD® to reduce odors and corrosion, improve biological treatment processes, improve effluent quality, improve digester performance and improve biosolids quality within the wastewater treatment system.

The key to the successful application of THIOGUARD® is understanding the multifaceted chemistry that it contributes to the wastewater system.


MgOH+ + OH-

Mg+2 + 2OH-

When technical grade magnesium hydroxide slurry is added to an aqueous system, the system receives 1) a high surface area, reactive, electrostatic particle, 2) a buffering cation MgOH+, 3) an acid neutralizing OH- anion and 4) a divalent cation/mineral nutrient. It can raise and buffer pH, stabilize CO2/HCO3– balance, shift the M/D ratio, and supplement mineral stores.

Direct Addition for Odor Control


Magnesia chemicals are safe. They offer environmentally responsible solutions to problems related with acid neutralization, biological treatment and biosolids disposal and handling. Premier Magnesia produces over 300,000 tons of MgO and Mg(OH)2 products annually, developing and maintaining more grades of magnesia chemicals than any other producer.

Premier Magnesia is proud to offer the THIOGUARD® family of products and services to control odor, corrosion, FOG, and enhance treatment for municipal wastewater systems.

THIOGUARD® is a safe, technical grade alkaline slurry, similar to milk of magnesia. Think of it as industrial-strength milk of magnesia for your sanitary system.

Major Advantages

- Non-Hazardous

- Safe to Handle

- Environmentally safe

- Cost-effective

- Treats Odors, Corrosion and FOG (fats, oils, and grease)

- Positive plant benefits for Nitrification, biosolids production, digestor performance and chlorination

Surface pH/Corrosion


H2S gas generated in the sewer system is converted by Thiobacillus bacteria residing on concrete and metal surfaces above the waterline to corrosive sulfuric acid. This acid attacks exposed concrete and metal surfaces.

A simple method to measure relative strength of the sulfuric acid and rate of decay of the infrastructure is surface pH testing, conducted with contact pH paper on the wetted surfaces inside wetwells, manholes and sewer lines.

The measured surface pH can then be used to correlate corrosion rate and subsequently, remaining years of useful life of a concrete structure.

The use of THIOGUARD® by direct addition has been demonstrated to elevate surface pH from a highly corrosive pH = 1-2 up to a more desirable range of pH = 5-7.

Under some circumstances, THIOGUARD® CROWN SPRAY can be applied to surfaces to provide instant neutralization and a protective, sacrificial barrier on infrastructure surfaces.

When THIOGUARD® is injected into a wastewater stream, it enters in 3 distinct phases as shown below. These phases are a result of magnesium hydroxide's unique solubility and reactivity properties and the way it reacts to other qualities of the wastewater (i.e. pH, CO2 concentration, free acid H+, biological activity, etc.).

3 Distinct Phases


Phase I (Mg(OH)2): 

Technical grade magnesium hydroxide as a particle has a solubility of 9 mg/L. While the solubility is considered relatively low, the particle, having a surface area of nearly 1 acre per gallon, is reactive and/or absorptive to acids, H2S, CO2, and some organics. The particle has a positive surface potential and is capable of improving flocculation and settling. In the collection system, it slowly dissolves as it reacts with H2S, CO2, acids, FOG, etc… At the plant, it usually enters the biosolids stream through Primary settling. That which passes through to Secondary processing is typically fully consumed by biogenic acids and CO2 produced during secondary treatment.

Phase II (MgOH+ + OH-):

This ionic phase is transitional from the particle phase to soluble phase and is indicative of technical grade magnesium hydroxide's unique abilities to "buffer" both acids and bases. This species also explains why pH's in a magnesium hydroxide supplemented stream do not accurately reflect the total amount of hydroxide present (neutralizing capability), since only the first ionized OH- contributes to the pH values. This is why pH, OH- and total alkalinity are critical measurements collectively rather than individually.

Phase III (Mg+2 + 2OH-):

This ionic phase is the result of complete dissolution of the Mg(OH)2 molecule. Complete dissolution occurs as a result of free proton (H+) acid neutralization or the formation of bicarbonate (HCO3-) from the reaction of OH- with CO2. Once dissociated, the divalent magnesium cation (Mg+2) aids wastewater treatment by 1) being utilized as a bridging particle for improved flocculation, settling and clarification in both Primaries and Secondaries and improved dewatering and densification in bio-solids processing 2) facilitating the transport and stabilization of P during ADP/ATP conversion and ATP hydrolysis, and 3) supplementing biological nutrients.

Residual OH- is reflected in pH readings. Since the reactive pH is 9, it "buffers" strongly in the pH range between pH 8 and 9, and most preferably near 8.4. As pH rises, magnesium shifts back towards Phases I and II. This is how magnesium hydroxide is extracted from brines and seawater for commercial production.

Thioguard Benefits WWTPs


Direct addition of THIOGUARD® to a collection system provides the following benefits at the Treatment Plant:

- Odor Control

- Corrosion Control

- Nutrient Addition — Essential Element for Cell Metabolism

- Alkalinity Supplementation

- pH Control

THIOGUARD® improves secondary wastewater treatment for BOD (Biological Oxygen Demand), TSS, Turbidity, ammonia and phosphorus, while enhancing sludge growth and settling characteristics, and improving biosolids treatment, dewatering and disposal.

Nitrogen compounds are the primary cause of pH/alkalinity degradation in treatment plants, with pH depletion being the major cause of activated sludge bulking, high SVI (Sludge Volume Index), and disinfection problems.

Digestion, Nitrification, Alkalinity and pH Control

Aerobic digestion and nitrification in the activated sludge process depletes natural alkalinity and can cause pH depression. A drop in pH can arrest second-stage nitrification and cause major upset conditions in the secondary clarifiers, resulting in effluent violations for BOD, TSS (Total Suspended Solids), ammonia, etc...Likewise, adequate alkalinity insures biological process stability and improves methane gas production of anaerobic digesters. THIOGUARD® provides both alkalinity and pH stability for biological processes.

Secondary Clarifiers and SVI

Periodic pH problems interfere with the growth of floc-forming activated sludge. When this happens, sludge bulking and unwanted denitrification may cause SVI levels to increase. THIOGUARD® provides both pH stability and divalent cations, which improve the Monovalent/Divalent (M/D) Cation Ratio.


These divalent cations and pH stability provided by THIOGUARD® also improves dewatering/drying performance, polymer use and odor reduction, whether using drying beds, filters, or centrifuges.

Chlorine Disinfection

Incomplete nitrification allows nitrite (NO2-N) to pass through the clarifiers and into the chlorine contact tank, consuming chlorine at accelerated rates. Moreover, low pH and inadequate alkalinity can hinder rapid hydrolysis of Cl2 gas, reducing disinfection efficiency. THIOGUARD® facilitates complete nitrification and provides pH stability for efficient chlorination.

pH Control

Technical grade magnesium hydroxide slurry has long been used to maintain pH during nitrification. Because alkalinity is released slowly, there are no hot spots to kill Nitrosomonas or Nitrobacter bacteria.

And since the by-products of technical grade magnesium hydroxide reactions are soluble salts, THIOGUARD® does not increase the amount of sludge produce in the plant. In fact, studies have shown THIOGUARD® may actually reduce sludge production by 10-20%.

Thioguard® vs Nitrates


In a recent head-to head trial, THIOGUARD® outperformed Nitrate. With Nitrate feeding at 80 gallons per day and $1.90/gallon, THIOGUARD® outperformed Nitrate by feeding < 40 gallons per day at $2.05/gallon, saving 40% in dollar savings and achieving 97% improvement in reduction of H2S gas levels.

Concentration Symptoms

0-10 ppm 

Irritation of eyes, nose, and throat

2 ppm

Bronchial constriction in asthmatic individuals, spontaneous abortion

5 -9.3 ppm

Increased blood lactate concentration, decreased skeletal muscle citrate synthase activity

10-50 ppm 

Headache, dizziness, nausea, vomiting, coughing, difficulty breathing

150 - 250 ppm

Olfactory paralysis

50 - 200 ppm

Severe respiratory tract irritation, eye irritation/ acute conjuntivitis, shock, convulsions, coma and death in severe cases

Thioguard® product literature

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Thioguard® Video

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