PROJECT DESCRIPTION
BACKGROUND
Eutrophication can occur when a body of water acquires a high concentration of nutrients - phosphates and nitrates – from agricultural, industrial and urban effluents. The nutrients can cause excessive growth of simple organisms such as algae, blocking out light from the water and leading to the depletion of available oxygen through the decomposition of dead organic matter. These changes in water quality can eradicate more complex species of plants and animals, reduce the aesthetic and recreational value of the water body and can even create risks to human health.
Systems to efficiently remove nitrogen have been successfully developed; however the elimination of phosphorus components still needs to improve. European legislation has set a target of 80% phosphates removal and more efficient processes are needed to achieve this target in an affordable way. Currently, several EU countries including Germany, UK, France and Spain, experience river phosphate concentration levels that reach over 500 μgP/l in many cases. This is way over recommended levels. Research has shown the critical levels of phosphate concentration leading to an incipient eutrophication are 100-200 μgP/l for flowing waters and just 5-10 μgP/l for calm waters.
OBJECTIVES
The LIFE-REMPHOS project aimed to develop a more efficient and cost-effective technology for removing phosphates from wastewater that would be suitable for both industrial and urban wastewater treatments plants (WWTPs). Specifically it aimed to effectively demonstrate valorisation of a by-product of magnesite production as a precipitating agent to remove phosphates from wastewater.
The project would develop a new precipitation agent for the removal of phosphates from wastewater made of 63% magnesium oxide, a by-product of magnesite production. It hoped to demonstrate valorisation of this by-product, for which no feasible use or economic value had been found previously.
It would test the new precipitation agent in a pilot plant consisting of a Continuous Stirred-Tank Reactor (CSTR) implemented as a tertiary treatment in the WWTP after the nitrate-removal phase. It hoped to demonstrate successful reductions in phosphate concentration in the wastewater by chemical precipitation.
The project seeked to demonstrate that the technology can achieve European legislative targets on the removal of phosphates from wastewater in a way that is more cost-effective than current chemical and biological treatment solutions. Economic and other environmental benefits would arise from the use of an industrial by-product instead of freshly mined raw materials. It also hoped to find potential management solutions for the precipitate resulting from the treatment process.
RESULTS
Although at a reduced, non-industrial scale, the LIFE-REMPHOS project demonstrated a new technology for phosphate removal in WWTPs. This technology was implemented as a tertiary treatment in the Estella WWTP, improving phosphate removal. Additionally, the agronomic properties of the final precipitate were evaluated for its use as fertiliser.
The prototype developed and tested had a significantly lower purifying capacity than was originally envisaged, at just 24 m3/day instead of 480 m3/day. This affected the results achieved, which were as follows:
- Tertiary treatment implemented in Estella WWTP in Navarre;
- The precipitant agent is a by-product from the magnesia production industry;
- Reaction time is from 1 to 5 hours (depending on the precipitant agent dose);
- Phosphate removal efficiency is greater than 83% (in 1 hour); and
- The final precipitate is optimal for use as fertiliser.
Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).
