EloPhos® is a system for the recovery of phosphate from digested sewage sludge emanating from waste water treatment plants with biological phosphate (bio-P) removal in the form of Magnesium-Ammonium-Phosphate (“struvite”) fertiliser.
The EloPhos® process is based on the precipitation of dissolved phosphate from digested sewage sludge using magnesium salts, usually magnesium chloride (MgCl2).
The increased pH-value required for an efficient struvite precipitation is achieved by the EloVac® vacuum degassing.
The EloPhos® operating principle
The EloVac® vacuum degassing increases the pH in the digested sludge. This largely avoids the need for air stripping of dissolved carbon dioxide from the sludge or the addition of an alkaline solution (NaOH).
The gas extracted in the EloVac® vacuum degassing is fed directly to the gas system and cannot enter the atmosphere. Greenhouse gas emissions and odours are thus effectively prevented.
In the EloPhos® crystallisation reactor the dissolved phosphate is chemically precipitated from the digested sewage sludge as struvite by dosing magnesium salts, usually magnesium chloride (MgCl2).
If the pH increase of the digested sludge by the degassing stage is not sufficient to ensure efficient precipitation, supplementary dosing of alkaline solution into the crystallisation reactor is possible.
The MAP crystals formed in the EloPhos® crystallisation reactor are initially very small. If separation and struvite recovery are not required, these can be discharged together with the sludge. However, the retention time of the crystals in the reactor can be controlled independently of the hydraulic retention time of the sludge and crystal growth can be encouraged in a targeted manner. This process is used if a struvite fertiliser is desired with struvite crystals being recovered separately. With this option, struvite crystals of > 1 - 2 mm in diameter are separated from the sludge and collected via the automatic discharge system.
Effective and flexible process for the P recovery from digested sewage sludge
Modular concept consisting of degassing, crystallisation reactors and crystal separation
Low operational costs by avoiding an energy-intensive aeration
Environmentally friendly by avoiding methane and odour emissions into the atmosphere
Robust, wear-resistant, space-saving system design by slim and tall reactors