|CUSTOMER STORY I SEPTEMBER 2018|
CASSOWARY REGIONAL COUNCIL
Benefits of a whole-of-catchment approach
CASE STUDY SNAPSHOT
Excess odour in sewage network due to high H2S generation.
Heavy build-up of FOGs layers in the network causing severe corrosion.
Excess usage of chemical elements like lime and alum leading to higher maintenance costs.
Frequent need for vacuum truck cleaning leading to an increase in maintenance costs.
Calix ACTI-MagTM (High Surface Area) dosing to replace chemical dosing of lime and alum.
Reduced generation of H2S within the catchment, resulting in significant odour control.
No detrimental effect on sewage network and no corrosion.
Reduced the build-up of FOGs - ‘Fatberg’, thus reducing the need for frequent vacuum cleaning.
Eliminated lime dosing and reduced Alum dosing at the STP, thus saving costs.
ODOUR CONTROL – CLEANSING THE SEWER !
Dosing your Network with Calix ACTI-Mag (High Surface Area) Magnesium Hydroxide reduces the H2S in your network. This study proves that ACTI-Mag can clean Fats, Oils, and Greases (FOGs) from your Network, along with providing several other benefits.
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” (H S) 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 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 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—commonly referred to as FOG—are some of the trickiest things to treat in wastewater. 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 stabilised suspension of magnesium hydroxide, 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.
• MHL is a slurry based alkali, also known as ‘Milk of Magnesia’
• MHL particles are sparingly soluble (~ 6 mg/L, c.f. lime 1.73 g/L, Caustic 1110 g/L)
• MHL behaves like a weak alkali
• Neat MHL pH is ~10.5
• Buffers at pH ~8.5 – 9 when dosed, as compared to more soluble alkalis like Caustic (pH 14)
and Lime (pH 12.5)
• Slow alkali release by dissolution of slurry (Low ‘GI’ alkali)
• Excellent antacid
• Acid neutralization capacity similar to 50% NaOH and lime
• Totally safe to handle
ACTI-Mag is manufactured using Calix’s proprietary “mineral honeycomb” magnesium oxide (MgO).
This means it has the high reactivity of nano-material, without the potential health and handling issues.
‘Mineral Honeycomb’ – nano-pores from CO2 release during calcination
• 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-MAGTM Trial Started on Dec 12th, 2017
Primary objectives and success criteria for the network
• Controlling the odour within the catchment, H2S < 2 ppm.
• Controlling corrosion of the pumped MB to Tully main sewage line (saving costs).
Secondary objectives and success criteria for the network and plant
Odour Control – Achieved
Sewer cleansed, FOGs removed – Achieved
Baseline – Monthly cleaning of SPS by a vacuum truck
Results – Reduced cleaning across all 18 Sewer Pump Stations (SPS); thus saving costs
• Initial fatbergs were removed at the start of the trial.
• Vacuum truck cleaning was not required since the trial commenced on Dec 17.
• Initial removal of FOGs resulted in increased STP dirty rag capture in the first 2 – 3 wks of treatment.
• The slow increase in STP pH over the initial 2 – 3 weeks attributed to fat breakdown.
Acti-Mag™ slowly releases hydroxyl ions which breakdown low-density, large-chain fatty acids into glycerol and various types of soap, both of which are more readily digested by bacteria in wastewater.
Wastewater has large quantities of low-density, long-chain fatty acids.
The Carboxylate salts that are O produced further facilitate the breakdown of other fats.
TG HYDROXYL IONS CARBOXYLATE SALTS - SOAP FATTY ACID GLYCEROL
Slow pH rise – 3 weeks (vs 3 day retention) – attributed to FOG breakdown & observed associated release of ‘aged’ rags
• 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), AKA Struvite, is a crystalline precipitate of Magnesium, Ammonia & Phosphate.
Friend or Foe?
Anaerobic release of PO4+ & NH4+
Optimum conditions pH>8
Reaction Chemistry Mg2+ + NH4+ + PO43- => Mg.NH4.PO4.6H2O
Molar ratio 1 : 1 : 1
• Normally forms a nuisance scale on treatment structures.
ACTI-Mag dosing offers the following benefits:
• Facilitates controlled Struvite precipitation of (P) and (N) in the suspension.
• Can be nucleated on high surface area / high pH ACTI-MagTM particles.
• Has a potentially a low-cost method of effluent (P) removal.
• Bio-available v/s Alum (AlPO4), which is a chemically-inert sludge.
ACTI-Mag offers the following benefits:
• FOGs reduction
• Phosphate control
• No lime addition
• Reduced and potentially total elimination of alum dosing
• Reduction in sewer maintenance and cleaning costs