Process & contact
RubiPhos® (TTBS)
Member of ESPP
Updated 01/2026
Input materials
Sewage sludge mono-incineration ash, from sewage works using biological and/or chemical P-removal
Low grade phosphate rock.
The process could also be adapted to intake other phosphate-containing secondary materials such as dewatered sludges, vivianite, struvite, meat and bone meals, ashes….
Minimum dry matter content of input material: 20% DM.
Output products
Phosphoric acid: ≥10 % P2O5 before concentration (recent info: 2-3%, see below)
Levels of heavy metals in the product acid are all below 1 ppm: Cd, Pb, As, Zn, Cu, Ni, and Cr, while Hg is <0.1 ppm.
Levels of iron are < 50 ppm.
Phosphoric acid can be processed to purified acid, phosphate salts, fertilisers, etc. A recent report (see below) suggests precipitation with calcium hydroxide to calcium phosphate, which can be treated with sulfuric acid to SSP.
The objective is to separately recover iron or aluminium in aqueous solution, magnesium sulphate, potassium sulphate, and use remaining residues as coagulants or as fertilizer additives. The solid residue, Rubicas, might be used e.g. in the construction industry, but no definite application has been reported as yet.
The Rubicas residue is a solid with 70% dry matter content containing 25% sulphate, 30% silicate.
Process description
Wet process based on strong acid (sulphuric acid; optionally hydrochloric acid) fast digestion of input material, followed by water addition (from process recycle streams) and the filtration of precipitated insoluble materials.
Iron is largely retained in the solid residue by selective acid digestion.
Phosphoric acid is separated from the ensuing filtrate by a diffusion dialysis (DD) membrane, leaving the bulk of other constiuents (sulfate, magnesium, iron...) of the raw acid in a reject stream. Nanofiltration is applied to this reject stream, further recovering phosphoric acid
The P recovery yield is >90% (97% in the recent pilot).
Removal of heavy metals is >95%. The Rubicas residue is largely free of heavy metals, except lead, which it collects quantitatively (current levels are reported to be above the European fertilizer limits of 120 mg/kg).
Heavy metals are precipitated from the acid residue, and concentrated as a heavy metals cake as hydroxyde or sulfide
Operating status
Successful pilot operations in TTBS's Belgian facilities and in the Netherlands at Dordrecht with 12.5 kg/h input of sewage sludge incineration ash. Pilot operated in continuous mode for up to 200 hours. 2 tonnes of fly ash have been processed to date. A STOWA commissioned pilot study (in Dutch) is available here.
A short movie is available at https://www.youtube.com/watch?v=U6swQIkazVA