An innovative mixed-metal hydroxide

for pH control and wastewater microorganism activity

Joffrey Bourdareau \ May 18, 2020
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A meat packing facility and tannery in the Midwest US, processing 2.5 millions gallons per day (MGD) of wastewater, with a NPDES (National Pollutant Discharge Elimination System) permit for discharge to a river, had been using both hydrated lime and magnesium hydroxide for 10 years to try and control pH in a low rate anaerobic digester.

case study summary

Challenges
  • The plant was struggling with inadequate nitrogen removal and poor biogas production – related to poor microorganism activity.
  • Based on consulting advice to add calcium, they switched to hydrated lime (Ca(OH)2), which resulted in plugging problems and a dramatic increase in inert solids in their system.
  • They switched back to magnesium hydroxide, but with the manual addition of bags of lime, which was expensive and time consuming.
Objective
  • Optimize microorganism activity allowing the plant to achieve their NPDES permit limits
  • pH and alkalinity control
  • Save on chemical and maintenance costs
Solution

Download Success story

An innovative mixed-metal hydroxide for pH control and wastewatermicroorganism activity at a meat processing facility in the Midwest

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Benefits of AMALGAM-55

The Ca(OH)2 in AMALGAM-55 was formulated at a level sufficient for improved microorganism activity, but not enough to cause an increase in “inert” mineral solids.

AMALGAM-55 gave pH control performance at a dose comparable to the use of magnesium hydroxide on its own.

Because AMALGAM-55 is less expensive than magnesium hydroxide, the customer enjoyed a 15% chemical cost reduction, along with improved microorganism performance.

IER’s Pasco Plant, Washington, USA.

Introduction

A Midwestern meat processing facility and adjacent tannery was generating over 2.5 million gallons per day (MGD) of high strength organic wastewater. The wastewater treatment facility has a National Pollutant Discharge Elimination System (NPDES) permit for discharge to a river.

When a low-rate anaerobic digester was installed about 10 years ago, magnesium hydroxide (60% Mg(OH)2) slurry was selected for pH and alkalinity control based on its strong but gentle buffering ability.

Through the use of magnesium hydroxide, the optimal pH range for aerobic and anaerobic microorganism performance can easily be maintained, with no pH spiking. Because of its gentle buffering nature, it is virtually impossible to overfeed Mg(OH)2 above a pH of 9.

pH spikes from the use of caustic, soda ash, or lime can shock the aerobic and anaerobic populations into periods of very poor BOD (Biological Oxygen Demand) removal. Unlike caustic or soda ash, which add sodium, magnesium hydroxide adds nutrient value (magnesium) into the secondary treatment and anaerobic biological processes.

<- Owned by Calix, IER (International Environmental Resources) is a distributor of magnesium hydroxide products and other innovative environmentally-friendly process water and wastewater treatment chemicals and equipment.

Based in Spokane, Washington, IER primarily services the Pacific Northwest and Upper Midwest.

The challenge

Though the magnesium hydroxide treatment was working well for pH and alkalinity control, the facility was continually struggling to develop a diverse microorganism population for improving the overall activity of the sludge. Based on consulting advice to add more calcium to the system, they switched to the use of Hydrated Lime (Ca(OH)2).

In wastewater, lime is often used as an alkalinity supplement. But the effects of lime addition can have undesirable side impacts on the biological system, such as scaling and pH spikes.

Another significant, yet overlooked impact is the EPA documented sludge production typically associated with lime.

“The addition of treatment chemicals, especially lime, may increase volume of waste sludge up to 50% which can result in exhorting costs related to the disposal of the sludge dewatering and disposal..” EPA – wastewater technology fact sheet.

The application of lime lasted only a couple of months, as they were astounded at the increase in the inert solids loading in the anaerobic system. This was measured as the ratio of Volatile Solids (VS) to Total Solids (TS).

The ratio of Volatile Solids (VS) to Total Solids (TS) in the system was dramatically decreased from operating in the range of 75-85% with Mg(OH)2 to a range of 30-50% with Ca(OH)2.

In an ideal system, the percentage of VS is greater than 90%, meaning that most of the solids in the system are “bug bodies” or other organic matter. The lower the percentage of VS, the higher the percentage of “inert” or mineral solids in the system.

By significantly dropping the ratio of Volatile Solids (VS) to Total Solids (TS), lime Ca(OH)2 can increase operational and maintenance costs related to scaling and sludge disposal.

 

 

The reduced percentage of VS during the period of lime usage is consistent with the formation of insoluble calcium minerals, such as gypsum (CaSO4) and limestone (CaCO3) from complexation of calcium with the high levels of sulfate (SO42-) and carbonate (CO32-) present in the meat processing and tannery wastewater streams.

The added costs resulting from the need to remove waste sludge at a much more rapid rate (increased sludge disposal costs / hauling fees) as well as a dramatic increase in pumping and plugging problems, resulted in the facility switching back to magnesium hydroxide.

With magnesium hydroxide use, the resulting salts of magnesium sulphate (epsom salt, MgSO4) and magnesium carbonate (magnesite) are thousands-fold more soluble than the corresponding calcium salts (gypsum and limestone). Hence these ions remain in solution and do not become a part of the solids fraction, resulting in a much higher VS-to-TS ratio.

Increased inert solids => extra sludge disposal costs*

Sludge is an expensive and problematic byproduct of the wastewater treatment process.

*Sludge disposal costs = pumping + energy use + hauling

Hydrated lime Ca(OH)2 can increase operational and maintenance costs related to formation of scale and accumulated solids/sludge.

High quality technical service played a critical part in this customer success story. By working along side the plant managers and understanding their specific requirements, IER was able to offer an innovative customised solution, specifically aimed at solving the plant’s challenges.

The Solution

IER takes pride in being a technically credible wastewater treatment company, not simply a magnesium hydroxide supplier.

For over 20 years, IER has worked with plant engineers and operators to offer the most cost effective solutions for their specific needs.

This results driven approach is what allows us to work with plant management to determine a minimum amount of calcium required as a feed supplement into the system. With this information, a proprietary blended product was formulated to contain predominantly magnesium hydroxide, with a minor component of calcium hydroxide. In this case, the Ca(OH)2 was formulated at a level sufficient for improved microorganism metabolism and not in an excess to cause an increase in the “inert” solids as was observed with straight lime feed.

This results driven approach is what brought us together with plant management to understand that the incoming wastewater was low in divalent cations (Mg2+ and Ca2+) due to softening of incoming hard water, as well as brine discharge into the wastewater stream (both high in sodium, Na+).  As we were already feeding magnesium hydroxide, we were able to determine a minimum amount of calcium required as a feed supplement in order to optimize the microbiological system.

The feed of this blended product, called AMALGAM-55, resulted in improved microorganism activity while not impacting the ratio of Volatile Solids to Total Solids.

The plant has been using AMALGAM-55 for the past 12 years while maintaining the percentage of Volatile Solids in the range of 75-85%, identical to that observed with the use of straight magnesium hydroxide.

In addition, though formulated to contain only 55% total solids, the required dose for AMALGAM-55 to maintain the desired pH and alkalinity was equal to or less than that required for 60% Mg(OH)2.

By combining the lower cost raw material of hydrated lime into the formula, the overall product price for AMALGAM-55 was less per lb than that for straight magnesium hydroxide.

 

We pride ourselves in being a wastewater treatment partner:

Technically credible

High quality products

Proactive customer service

 

Conclusion

The results of this study demonstrated that significant performance benefits can be observed by formulating alkalinity supplements into blended products to address the needs of the wastewater microorganism population.

AMALGAM-55, an innovative blend of magnesium hydroxide and calcium hydroxide, was found to provide comparable pH and alkalinity control to that of straight 60% magnesium hydroxide, while also providing a nutritional supplement of calcium for improved microorganism diversity and activity.

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AMALGAM

AMALGAM has a higher neutralizing value per pound than any other alkaline additive.  This translates into a 40% reduction in chemical usage when compared with caustic soda, while being significantly safer for operators to handle and more nutritive for the microorganisms being maintained – making it the most cost-effective option.

Find more about AMALGAM

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