RECOPHOS

Recovery of Phosphorus from Sewage Sludge and Sewage Sludge Ashes with the thermo-reductive RecoPhos-Process

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 Obiettivo del progetto (Objective)

'Natural phosphate sources low in heavy metals are getting scarce. Containing about 15 mass-% of P2O5, sewage sludge ash can be considered a secondary phosphorus (P-) source. The P-content in the European sewage sludge could currently replace roughly 15% of the phosphate imports into the EU. Hence already for many years, almost decades, it has been tried to recover phosphorus from sewage, sludge and ashes in various ways of which none has yet been realised at industrial scale. The reason for this failure lies firstly in the wet chemical approach, meaning complex and little efficient processes with liquids hard to handle; and secondly in the use of liquid or dewatered sludge as well as waste water, which results in a further decrease in efficiency mostly because of high mass flow and matrix effects. The RecoPhos process is a thermal process using ash from sludge mono-incineration. The principle of the used so-called InduCarb process is similar to the one of the known Woehler process; dried sludge can be added as heat source or reducing agent as an option. The phosphate (amongst other constituents) is reduced on an inductively heated coke bed to white phosphorus, which is later condensed and thus separated from other gaseous reaction products; white phosphorous is the most valuable form of phosphorous and highly asked for by the industry. Further products are an iron alloy as well as a heavy metal mixture, both usable in steel industry; a silicate slag for the use in cement ovens as well as a high calorific gas. The RecoPhos process uses an innovative reactor (InduCarb) designed for the reductive recovery of steel work dusts. By the use of ashes the material flow is minimal; if only sludge is available, it can be also used as input, adding flexibility to the concept. If additives are needed, suitable industrial wastes can be used. The innovative RecoPhos process has never been realised before. It is planned to apply it for a patent .'

Introduzione (Teaser)

European researchers are building a prototype reactor to extract phosphorus and other valuable metals from sewage sludge ash.

Descrizione progetto (Article)

Natural sources of heavy metal-free phosphorus are becoming scarce; at the same time, phosphorus content in sewage is a looming environmental concern. Previous attempts to extract phosphorus from sewage have met with little success because the processes involved are complex and inefficient.

The EU-funded http://www.recophos.org (RECOPHOS) project is addressing this by using a reactor process (called InduCarb) usually designed to recover metals from steel works dust.

Researchers started by developing a thermodynamic process model for recovering phosphorus from sewage sludge ash. They have also modelled how molten ash would flow through the InduCarb reactor.

RECOPHOS has completed a safety evaluation of the process and produced safety recommendations. User specifications and a user guide have also been compiled.

Preliminary tests of a graphite induction system for heating the ash have been positive. The reactor could maintain the high temperatures needed while remaining sealed and safe for operation.

Future project work will involve building and testing a prototype reactor and then scaling it up for industrial production. RECOPHOS will ultimately contribute to the EU strategy of waste prevention, reduction and reuse.