Reducing overall sludge production

Athos™ is a sludge Hydro-Thermal Oxidation (HTO) process, which turns organic sludge with low dry matter into an essentially solid mineral.


Athos™ is an innovative process, which combined with anaerobic digestion, enables sludge removal while producing a renewable energy source: biogas.


Athos™ generates 3 stable and/or recyclable by-products:

  • clean gas
  • organic liquid biodegradable by traditional water treatment
  • mineral-based inert solid


Features & Benefits

The Athos™ process complies with all regulations on the disposal of wastewater treatment sludge whilst remaining cost-effective. It benefits from the technological expertise and track-records of the Veolia Group, the world leader in municipal and industrial water treatment.


An environmentally friendly process

Athos™ is a clean technology: all the sludge components are recycled, recovered or discharged to the natural environment with no adverse effects.

  • Final result: a concentrate of mineral matter accounting for only 1% to 2% of the quantity of initial liquid sludge;
  • Possibility of recycling the technosand for building materials;
  • Stabilization of the heavy metals in the solid residue in a non-leachable form (inert waste);
  • Zero emission of polluted gases nor harmful by-products (nitrogen oxides, dioxins, furans);
  • Reduction of greenhouse gas emission (50% drop in CO2 emissions compared with incineration;
  • Destruction of toxic, malodorous (Hydrogen sulfide, mercaptan, etc.) and organic trace substances.


A cost-effective thermal process

Operating costs are reduced by:

  • Moderate operating conditions (temperature and pressure, limited O2 consumption);
  • Reducing the dewatering stage. The dewatering of oxidation residual doesn't require reagents and reaches 50% of dryness.


A flexible process

Athos™ provides high operational flexibility:

  • Treats all types of thickened sludge (7 to 8% of DS);
  • Possibility of adjusting retention time, temperature and oxygen flow, in accordance with sludge composition;
  • Equipped with advanced automation.


A compact process

Thanks to its compact design, Athos™ can be fully integrated into the wastewater treatment plant and provides continuous sludge processing, as well as by-product treatment.



Athos™ treats all types of thickened sludge :

  • Primary
  • Biological
  • Fresh
  • Digested
  • Urban
  • Industrial



P.E.: Population Equivalent


Facility Year Capacity
Trucazzanno, Italy 2004 300,000 PE
Epernay, France 2006 80,000 PE
Brussels North, Belgium 2008

1.2 Million PE

Aix-en-Provence, France 2011 175,000 PE
Rennes Beaurade, France 2012 360,000 PE


With less than one-hour retention time in the reactor, the Athos™ process results in:

  • Continuous and safe oxidation, under continuous mixing;
  • High mineralization (less than 5% organic carbon content in the solid residue);
  • Separation between liquid and mineral phases;
  • Easily biodegradable liquid sidestream.

The heat released by the oxidation reaction is recovered to pre-heat the sludge, with no external energy supply.


Hydro-Thermal oxidation prototype: Athos™