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. Systems to efficiently remove nitrogen have been relatively successfully developed. However, the elimination of phosphorus components still needs to improve if the EU legislative target of 80% phosphates removal is to be met in an affordable way. Currently, several EU countries including Germany, UK, France and Spain, experience river phosphate concentration levels which reach over 500 μgP/l. Research has shown the critical levels of phosphate concentration which produce an incipient eutrophication to be much lower: 100-200 μgP/l for flowing waters and just 5-10 μgP/l for calm waters. Around 80% of phosphates production is for use as fertilisers, with agriculture still highly dependent on these products to sustain high yields. This leads to accumulation of large amounts of phosphorous in soils and landfills, and contamination of water from effluents and leaching. Furthermore, the phosphates are manufactured from phosphate-containing rock mined from deposits, a non-renewable material. The increasing scarcity of phosphate rocks is a significant environmental problem.
OBJECTIVES
The LIFE PHORWater project aimed to develop an innovative and cost-effective solution for phosphates recovery in wastewater treatment plants (WWTPs). Furthermore, it planned to show that the phosphates can be recovered in a form that can be valorised as fertiliser. It thus aimed to improve the performance of WWTPs, reduce excess phosphorous in the natural environment, and limit the demand for mining of phosphate rock. The project planned to develop a demonstration plant to recover phosphorus from wastewater at pre-industrial level, coupled to an existing WWTP. The aim was to optimise a process of precipitation to extract phosphorous in a crystallised form called struvite (magnesium ammonium phosphate), which is potentially marketable to the fertiliser industry.
RESULTS
LIFE PHORWater proved the technical and economic feasibility of an innovative and cost-effective solution for phosphates recovery in wastewater treatment plants (WWTPs). The project developed a sustainable system for the management of phosphorus in WWTPs, and identified the means of optimising phosphorus recovery from sludge. This used a reactor to crystallise phosphorus into struvite for precipitation and collection.
The feasibility of the system was demonstrated at the pilot plant scale (20.6 L continuous crystallisation reactor). To this end, the project team optimised the configuration of Calahorra WWTP, in La Rioja region of Spain, to increase (double) the phosphorus available in the pilot plant reactor. Recovery was carried out through an innovative crystallisation technology. The project produced a phosphorus management protocol as a guide for WWTPs, along with manuals and guidelines on how to maximise phosphorus recovery and for WWTP staff training, which will facilitate the replication of the technology in other WWTPs with Enhanced Biological Phosphorus Removal (EBPR).
The results obtained with the prototype were very promising. The project team obtained an average of 9.5 kg of struvite/day and around 0.6 kg of struvite/m3 of wastewater, achieving an efficiency of phosphorus recovery of nearly 92%. Furthermore, the struvite obtained complied with the parameters established by the European Sustainable Phosphorus Platform, in which the PHORWater project was involved via coordinating beneficiary DAM.
Interest in phosphorus recycling is increasing, for instance, because its removal improves the operation of WWTPs and provides environmental benefits. The uncontrolled precipitation of struvite in the anaerobic sludge treatment process for biological phosphorus removal in WWTPs causes operational problems, due to struvite deposits in pipes, which controlled struvite removal can help solve. The recovery of phosphorus in the WWTP contributes to the prevention of pollution, and minimises its adverse impacts on the environment, especially eutrophication problems in rivers, lakes and other waterbodies. Other environmental benefits arise as a result of renewable fertiliser production, reducing the depletion of phosphate rock (a non-renewable resource) and reducing energy consumption in WWTPs. The project contributes to the implementation of the EU Water Framework Directive, and policies relating to fertilisers and resource use efficiency.
Reducing the concentration of this element in sewage sludge also makes the sludge more attractive for application in agricultural soils, as phosphorus content limits the allowable rate of sludge application. The beneficiaries carried out field trials, with the struvite from the WWTP, in wheat and potato crops. The results showed that the struvite, applied alone or in combination with another standard fertiliser, is able to produce similar quality results and yields in potato and wheat to a standard fertilisation programme. Struvite is less expensive, and has a lower concentration of heavy metals, compared to phosphate rock, making its use attractive to the fertiliser industry.
The beneficiaries proved the economic feasibility of the system, through an assessment that took into account internal and external impacts. According to the project, a period of five years is needed for the full recovery of investment costs at the project scale. It is expected that this figure would be even more favourable at industrial scale. In terms of other socio-economic effects, locally-sourced recovered phosphorus will contribute to farmer fertiliser security, and hence food security. Its use substitutes for scarce phosphate rock, which can be very variable in price and potentially expensive for farmers. Recovered phosphorus can also be processed into elemental phosphorus and used in industrial applications, including food and livestock feed additives. WWTP maintenance costs and energy use can be reduced, along with greenhouse gas emissions. Economic opportunities for companies may also arise through work as providers of crystallisation reactors for WWTPs.
Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).
