Magnesium Hydroxide liquid dosing for odour control

Cassowary Coast Regional Council - QLD, Australia

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Replace lime and alum with Calix’s ACTI-Mag magnesium hydroxide liquid dosing system at Cassowary Coast Region, QLD, Australia.

Case Study Summary

  • Excess odour in sewage network due to high H2S generation.
  • Heavy build up of FOGs in the network leading to restricted flow.
  • Frequent need for vacuum truck cleaning leading to an increase in maintenance costs.
  • High treatment cost due to excess use of chemical agents such as lime and alum.
  • Manage H2S odour levels.
  • Eliminate fat blockages.
  • Save on chemical and maintenance costs

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Benefits of ACTI-Mag

Reduced H2S generation within the catchment.

Significant reduction of FOGs within the catchment.

Save on multiple chemical purchasing and asset maintenance costs.


Mission Beach is a mixed residential and tourist area and is home to the iconic Cassowary. A sewerage scheme was commissioned by Cassowary Coast Regional Council in 2006 to collect the wastewater from three constituent communities and pumped by two major stations, at Wongaling and North Mission Beach, to the Main Transfer Pump Station (MTPS). The MTPS then pumps 23km to the Tully Sewerage Treatment Plant (STP).

This sewer main suffered significant corrosion due to “rotten egg gas” (H2S) release in the drained sections. The Tully plant is designed for phosphate removal with liquid alum dosing for phosphate trimming and powered lime dosing for alkalinity and pH correction.

A trial of Calix’s ACTI-Mag Magnesium Hydroxide Liquid (MHL) dosing commenced in December 2017 with the primary objective to control septicity, odour and corrosion issues. Calix proposed additional objectives, i.e. the control of Fat, Oil & Grease (FOG) build-up, elimination of lime dosing at the Tully plant, and partial elimination of alum dosing for phosphate removal.

The trial eliminated odours by maintaining pH between 8.2 and 8.5. Pump station cleaning has been substantially reduced due to decreased FOG accumulation. The lime dosing system was prone to blockage and breakdowns, however dosing of ACTI-Mag has allowed suspension of lime dosing. Also, the dose rate has been reduced by more than 75% whilst still meeting phosphate effluent discharge limits.


Fats, oils and grease can build up and become what are called fatbergs.

Fatbergs are caused when oils and fats are tipped down the drain and congeal with other products, including so-called flushable wet wipes.

While each state has their own utility providers, there were at least 360 blockages caused by fatbergs in sewers serviced by QUU — which take in the Brisbane area and four other local councils.

That’s out of a total of 3,500 blockages in QUU sewer pipes that together cost $1.2 million to clear. Fatbergs also caused almost 250 sewage overflows.

But fats, oils and grease also play an important role in wastewater treatment plants, particularly those that capture biogas to generate electrical and thermal energy.


ACTI-Mag is a concentrated and stabilised suspension of magnesium hydroxide also known as milk of magnesia. An inorganic compound with the chemical formula Mg(OH)2.

Highly fluid, ACTI-Mag has proven to flow easily in most dosing systems. With a higher neutralising value per dry kilo when compared with caustic and lime and being significantly safer than other traditional alkalis, ACTI-Mag is a very cost competitive option for hydrogen sulphide gas (H2S) control in sewers and industrial waste treatment as well as for several other applications including phosphorus and nitrogen removal from wastewater.

Calix’s ACTI-Mag has several advantages over other generic MHLs.

  • Neutralises waste streams 30% faster than generic brands.
  • The pH peaks at 10.5 and buffers in the solution between 8.5 and 9.
  • The MHL dissolves slowly over time with particles remaining in suspension for as long as needed. (low “GI” alkali)


Calix’s high quality magnesite is mined and calcined in-house. Vertically integrated manufacturing means better service, reliability and performance. Calix is certified ISO 9001:2015 for process development, manufacture, delivery and application of mineral based products.

Calcination is an ancient process used to produce lime in a kiln. However, Calix’s unique, patented “Calix Flash Calcination” or “CFC” technology re-invents the kiln.

Our CFC process involves grinding magnesium carbonate to around one thousandth of a millimetre in size, and then “flash” heating the particles in a very short time at up to 800 C. As trapped gases in the mineral “bubble out” of the particles, we snap freeze the remaining magnesium oxide in a very high energy state, leaving a very porous, honey-comb-like structure.

ACTI-Mag is manufactured by hydrating Calix’s high surface area magnesium oxide. This means it has the high reactivity of nano-material, without the potential health and handling issues.

CALIX ACTI-Mag trial at Mission Beach (MB) sewerage scheme

  • 3 sub-catchments – North MB, Wongaling Beach, South MB
  • 18 pump stations
  • Pumped to Tully STP
  • Alum and Lime dosing – Alkalinity and Phosphorus removal
  • 2.5 – 3 day retention time in dry weather
  • MB ~ 40 – 45% of Tully STP flow (~800 kL/d ADWF)
  • Calix ACTI-MAG Trial Started on Dec 12th, 2017

Primary objectives and success criteria for the network

  • Controlling the odour within the catchment, H2S < 2 ppm.
  • Eliminating blockages and restricted flows by dissolving FOGs.

Secondary objectives and success criteria for the network and plant

  • Reduce corrosion within the network.
  • Demonstrating no detrimental impact on the STP.
  • Reducing or eliminating lime dosing at the STP.
  • Enhancing the removal of Phosphorus (P) and Nitrogen (N).
  • Consequently reducing Alum dose at the STP.


The Charleston Dosing Station has several benefits:

  • It is easily deployable and tamper proof.
  • It is SCADA compatible.
  • On-board load cells allow users to monitor ACTI-Mag stock levels.

The following metrics were monitored within the network:

  • pH logging
  • H2S (Odalog)
  • FOGs build-up and SPS cleaning requirements
  • The rate of corrosion (long-term assessment)


1. Reduce H2S and odours to negligible levels – Achieved

2. Eliminate blockages and restricted flows – Achieved

Observations show that ACTI-Mag;

  • Reduced H2S and odour to negligible levels within 3-4 days of dosing.
  • Eliminated FOGs within the network and allowed dirty rags to be captured by the STP.
  • Eliminated the use of costly vacuum trucks to clean out ‘fatbergs.’


  • The pH levels the STP were stable and no low pH events occurred.
  • Lime dosing was eliminated, leading to significant cost saving; the alkalinity in effluents and in the plant was stabilized.
  • Use of Alum dose was reduced by 60%, resulting in cost saving; consistent phosphorus mass content in the effluent was observed regardless of flow.


Magnesium Ammonium Phosphate (MAP), commonly known as Struvite, is a crystalline precipitate of Magnesium, Ammonia, and Phosphate.

Mg²+ + NH4+ + PO4³- + H2O = Mg.NH4.PO4.6H2O (s)

Struvite forms in pipe bends due to pressure differential in the flow. This will lead to a solid precipitate creating blockages and restricting flow.

The advantage of dosing ACTI-Mag is that it precipitates ammonia and phosphate directly in the sludge and stops struvite forming on key infrastructure.

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