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Has Caustic Soda Become the New Unobtanium?

Brian Jones
by Brian Jones
14 October 2022
4 minutes read

    Brian Jones, Business Development Manager, discusses the shortages of caustic chemicals  and why reducing a reliance on them can lower a site’s expenditure and its impact on the environment. 

    One very important chemical that we tend to take for granted is Sodium Hydroxide, or as it is commonly known, caustic soda. The UK is currently experiencing unprecedented pricing pressure on caustic soda due to its localised availability, increased demand, and soaring energy costs due to the war in the Ukraine. 

    Caustic soda is used in a large number of different products and processes. One of its key uses is in the treatment of wastewater. Predominantly in pH correction - to enable effective treatment and to ensure water being discharged meets local regulatory requirements.

    A recent market analysis that monitors the global caustic soda market stated that it is poised to grow by 18469.89 Thousand Tonnes during 2022-2026, accelerating at a CAGR of 4.22% during the forecast period. 1

    What we once considered  a basic commodity chemical is currently a much sought after and expensive ingredient to a wastewater treatment process.  

    Why use Caustic?

    Traditional wastewater treatments tend to rely heavily on pH correction using caustic soda to counteract the drop in pH when using ferric or aluminium based coagulants. Without this the chemistry simply will not work. So without caustic, consent breaches and compliance issues are more likely. 

    These metal based coagulants rely on iron or aluminium being dissolved in hydrochloric acid. This results in a strongly acidic hazardous product that is corrosive. The process also involves large inputs of energy and as a result these products have increased significantly in price too.

    Who is at risk from the lack of caustic soda?

    If we were to focus on one particular market, it would be  the Food and Beverage industry. The wastewater profile of many companies in this sector tends to be more acidic, particularly for confectionary, dessert, and ready meal production. The use of caustic soda to pH adjust the wastewater stream is unavoidable to ensure there are no breaches as the minimum pH for any wastewater process is typically pH 6.

    What else could be considered?

    Veolia Water Technologies' ‘Hydrex 6861’ is an organic metal free coagulant, it has the capacity to work effectively at far lower pH ranges than the conventional metal coagulants such as ferric chloride and PAC. Hydrex 6861 will not reduce the pH of the wastewater once added  in the same way metal based coagulants do,  because it is not strongly acidic.  This dramatically reduces the need to pH correct using caustic soda. Due to the chemistry not relying on pH correction it is possible to eliminate the use of caustic soda completely. 

    How to transition from metal coagulant to organic coagulant

    The change over is a simple three step process:

    1. A site audit by a Veolia Waste Water Specialist to fully understand the wastewater profile and chemistry.
    2. Jar testing of the wastewater using Hydrex 6861 followed up with a trial proposal supported with costs, benefits and potential savings.
    3. Full scale on site trial which would be supported by Veolia Waste Water Specialist. 

    Each of the three stages will be carefully managed by a Veolia Business Development Manager.

    Case Study

    A ready meal production site in the North West of England produces Asian themed dishes. The wash water from the process contained acidic components including onions, citreous elements and vinegar.  Due to the low pH of the wastewater stream (pH 5) - Hydrex 6861 was used to achieve coagulation without any need to pH adjust upwards. A DAF unit effectively removes the sludge and the clean water runs through a V notch.  A small amount of 32% caustic soda is added prior to the final discharge to raise the pH to just over pH 6 to ensure compliance. This method of control ensures the lowest dose rate of caustic soda ensuring costs are managed well, the chemistry still is very effective to achieve the lowest MOGDEN results and finally the pH is controlled to a tight consent limit.

    If this site was using traditional metal based coagulants the pH profile of 5 would be too low and a metal based coagulant would not work alone. The pH would need to be raised to at least 7 to 8 prior to coagulant addition to achieve the same results.

    Sodium Hydroxide usage from a recent Effluent treatment trial where PAC was replaced with Veolia Hydrex 6861 organic coagulant. The daily flow was 413 m3/day and the pH profile of the influent was between 6 and 7. The client was a ready meals manufacturer. 

    The cost of the sodium hydroxide 32% per day gives a real insight into how much this single product can impact on the treatment operational cost.  In this example the potential saving would be £35,800 per year. The use of caustic soda would also result in increased sludge volume from the process as a byproduct too.

    Chat to one of our experts about tackling issues surrounding caustic soda and transitioning from metal-based coagulants to organics, here: 


    1. Reportlinker (August 2022)


    Brian Jones

    Author | Brian Jones

    Brian has over 30 years experience in the chemical and water purification industry. The first 18 years were spent working for Hays Chemical Distribution in senior roles, working in quality, safety and process management. His problem solving approach and chemical background made going into wastewater treatment a good fit. He has spent the last 14 years working in sales in this industry having bought a wealth of knowledge to the role, proving to be a valuable asset.

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