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What is Thermal Hydrolysis?

What is thermal Hydrolysis? as used in AD Plants

What is thermal Hydrolysis? as used in AD Plants

So you want to know, what is the thermal hydrolysis process?

Thermal Hydrolysis is a chemical process in which the organic molecules (in the substrate/ feed material) are split into two parts by the addition of a molecule of water. The process forces the water molecules between the chemical bonds holding together large tissue molecules such as fats, DNA and proteins. As the name suggests thermal hydrolysis uses heat and high pressure to break the cellular tissues down to their original smaller molecular components. This also dramatically reduces viscosity, destroys all infectious agents, and above all it hugely increases biodegradability during fermentation.

Using thermal hydrolysis as a feedstock pre-treatment stage before anaerobic digestion increases the biological degradation of organic volatile solids and biogas production considerably. It makes the sludge readily available for digestion by dissolving and decomposing the sludge solids. It also makes the separation of solid and liquid phase after digestion easier.

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Up to twice the reactor throughput can be achieved compared with an AD plant without it. Thermal bio-solids hydrolysis is a proven technology and is recognized as being one of the most effective ways to enhance biogas production and solids destruction in anaerobic digestion systems.

Benefits of Thermal Hydrolysis

The benefits of hydrolysis as a carried out prior to anaerobic digestion, can be listed as

  1. Disintegration of cell structure of organic materials creates smaller molecules which dissolve
  2. The naturally occurring cell polymers which result provide a form of protein, which is easily digestible during anaerobic digestion
  3. The lower viscosity (more free flowing) sludge allows for easier pumping and digester tank mixing with up to double the normal digester dry solids loading
  4. The fermentation organisms are less stressed, which leads to more stable plant operations.
  5. The availability of so much more of the organic matter to the methanogenic organisms increases substrate (sludge, bio-waste etc) biodegradability and therefore yields more biogas
  6. Separation of liquid and solid portions of the digestate occurs more readily, with dewatering achievable up to 40% total dry solids
  7. The high pressure and temperature of hydrolysis produces a pathogen-free fertilizer, by holding the material at 165° C for 20 minutes
  8. Hydrolysation conditions meet and exceed all known national and international standards and requirements for sterilisation, including EU Animal By Products Regulation (ABPR, 1774/2002/EC) category II & III materials.

Potential for Thermal Hydrolysis as a Part of AD Systems

There is a huge potential for the introduction of thermal hydrolysis of municipal waste solids. Incorporating thermal hydrolysis in new AD Plants, and retrofitting it to existing plants. For example, it represents an opportunity for Wastewater Treatment Works operators to increase the rate of solid hydrolysis, increase the extent of volatile solids reduction, and boost biogas production. At the same time, the more complete reaction achieved brings benefits to the digestate as a fertilizer. There is an increase in nitrogen (N) and phosphorus (P) solubilization enhancing availability of these essential components of any fertilizer.

Companies Offering Thermal Hydrolysis Process Equipment

Cambi has long been well known for their Thermal Hydrolysis Sludge Pre-treatment Technology for eenhanced Anaerobic Digestion of municipal and industrial sludges. Cambi has been installing thermal hydrolysis as a pre-treatment to anaerobic digestion, around the world since 1995. However, there now seems to be a trickle-down effect for thermal hydrolysis as a pre-treatment to anaerobic digestion, to be used for smaller biogas plants, and a greater range of feed materials/ substrates.

Exelys is another company actively promoting this technology, which has a thermal hydrolysis technology that they describe as representing the next generation of bio-solids thermal hydrolysis. But, these example companies are far from being alone in having spotted a business opportunity in thermal hydrolysis within AD Plant Systems. Many companies not previously active in the AD and Biogas scene, are now also marketing their own thermal hydrolysis equipment from their previous experience of this technology from parallel applications in other closely related business sectors.

Thermal hydrolysis as a pre-treatment to anaerobic digestion is at the time of writing, very much in the news with the announcement that the UK Water Utility company, United utilities will soon start to use the world’s largest thermal hydrolysis plant as a pre-treatment stage to their anaerobic digestion plant, at a major UK Wastewater Treatment (Sewage) Works. You can read more information about that here.

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One Response to What is Thermal Hydrolysis?

  1. Stephen Last September 18, 2014 at 8:52 pm #

    Hydrolysis is not normally considered to be necessary for pre-treatment of the organic fraction of MSW, when that is digested anaerobically.

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