SCFI Group Limited

- Advanced Hydrothermal Oxidation (HTO) Process System


Our patented AquaCritox technology is unique. It uses an advanced hydrothermal oxidation (HTO) process to deliver a sustainable, safe and economical wet waste disposal solution - whilst also providing the potential to recover renewable energy and valuable resources.


AquaCritox technology has been developed to solve issues the water industry face when dealing with municipal biosolids and drinking water sludge. It’s the only treatment technology that ensures full organic waste destruction with real waste-to-energy potential.

Conventional issues/AquaCritox Solution

Wasted energy
As a waste-to-energy technology, AquaCritox recovers and harnesses the energy present in sludges – even the low-grade energy in processed digestate. Find out how much your waste stream could generate using our energy calculator.

Larger volumes
AquaCritox converts any organics in the waste stream into inert by-products (CO2, nitrogen and clean water) – reducing waste volume by up to 97% and mitigating the economical, socio-political and environmental issues surrounding sludge handling and disposal.

Need more capacity
By reducing the volume of the incoming waste stream, plants deploying AquaCritox can open up some or all of their anaerobic digester capacity to other gate-fee paying materials (such as food waste).

Disposal routes
With AquaCritox, there is the potential for plants to remove or greatly reduce dependence on third-party waste disposal routes, such as land spreading, landfill and incineration – so the route to disposal is fully secure.

Overworked digesters
By processing secondary (waste-activated) sludge before it reaches the digester, AquaCritox converts the solids present into inert by-products and mineralises nitrogen. This reduction in difficult-to-digest solids loading to the digesters not only cuts retention times, but also increases feed concentrations and lessens the ammonia burden – streamlining the treatment process and reducing the overall load on the plant.

Lost resources
AquaCritox allows for the recovery of valuable resources found in sludge, such as phosphorus and CO2 (and, for drinking water sludge applications, used coagulants).


Using our patented hydrothermal oxidation process, AquaCritox mineralises wet waste (such as biosolids) – converting it to carbon dioxide, elemental nitrogen, water and a small quantity of nutrient-rich, inert and odourless solid residue. AquaCritox also allows for the recovery of clean energy that would normally be lost during sludge disposal.

AquaCritox can be used to treat a variety of waste streams, including primary and secondary biosolids and drinking water sludges: providing safe, sustainable and cost-effective disposal.

Very simply, hydrothermal oxidation (HTO) combines specific temperature and pressure levels with an oxygen supply to oxidise the organic components present in wet waste. This produces carbon dioxide, nitrogen, water and a mineral residue. HTO typically reduces waste volume by up to 97%, and makes it safe for disposal through conventional routes. What’s more, it allows for the recovery of valuable resources and generates thermal energy, which can be used to produce renewable heat and/or power.

  1. The incoming waste stream is pumped up to the required pressure (221 bar (3,205 psi)) using a high-pressure pump.
  2. The pressurised feed is then passed through a heat exchanger, where it is brought up to temperature (normally 374°C (705.5°F)). Once the HTO process is underway, AquaCritox uses energy recovered from the reactor itself to heat the incoming waste stream.
  3. Raising the feed temperature and pressure to these levels causes water to behave in a completely different manner, and it becomes a perfect reaction medium. Pressurised liquid oxygen (LOX) is then introduced into the hot pressurised feed, causing an almost immediate oxidation reaction. This reaction will reach complete stoichiometric oxidation within a matter of seconds.
  4. The oxidation reaction is exothermic: by releasing the energy embedded within the waste, HTO continues to generate more thermal energy than it actually needs. This creates a steady source of steam that can be used to produce renewable electricity or hot water.
  5. AquaCritox converts any organics present in the waste stream into inert by-products (CO2, nitrogen, clean water and an odourless residue). After processing, the remaining treated effluent is safe for sewer disposal. Any inorganic materials can be easily separated and treated in a separate step to recover valuable resources.

With AquaCritox, your plant can benefit from a single-step, odour-free waste treatment solution, matched with lower costs and a much reduced carbon footprint.

Economical: Lower costs and quicker payback

With AquaCritox, the need for extensive dewatering, drying, incinerating, trucking or land spreading is dramatically reduced or eliminated. Resource recovery and renewable energy generation can also provide additional income.

Sustainable: For ass reduced carbon footprint

AquaCritox is a net energy producer - and because it’s a single-step, on-site treatment method, it reduces truck movements. The process is also odour-free and residual materials are non-hazardous.

Efficient: With a destruction rate equal to incineration and greater than conventional wet air oxidation

AquaCritox is vastly more efficient than competing technologies and does not require pre-treatment, expensive dewatering/drying or gas cleaning.

Secure: Protecting your plant for the future

With AquaCritox, there are none of the potential risks usually associated with sludge disposal, and no onerous licensing issues. By generating renewable heat/power, AquaCritox can also improve a plant’s energy performance.

Straightforward: A single-step, clean and odour-free process

AquaCritox is the smart choice for waste generators, processors and planners. Its small footprint makes for easy integration. The enclosed process is also fully automated, for minimal manpower and maintenance.

Versatile: A treatment solution for a variety of wastes and applications

AquaCritox can be used to treat municipal, sewage and drinking water sludges - as a standalone technology, or combined with other treatment methods, such as anaerobic digestion.

Bespoke: Tailored to individual applications

AquaCritox is available in four sizes, with hydraulic loads ranging from 1 to 20 tonnes per hour and footprints of between 300m² (3,229 sq ft) and 1,750m² (18,836 sq ft).

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