The wastewater treatment sector discharges a significant amount of re-usable nutrients into the environment (e.g. rivers, dewatered sludge and the atmosphere). One such nutrient is phosphorus, which is essential for agriculture. Modern agriculture is dependent on phosphorus mining, derived from high-grade phosphate rock, which is a non-renewable resource. The present consumption of rock phosphorus as fertiliser is over 1 million tonnes per year (Rahman et al., 2011). The phosphate rock is unevenly distributed around the world, with more than 70% of reserves located in Morocco. Due to the relevance of this material for the strategic agriculture sector, the EU has included phosphate rock as a critical raw material in the framework of the EU Raw Materials Initiative. Additionally, manufacturing fertiliser from phosphate rock is highly complex and environmentally unfriendly.
Nitrogen is another nutrient present in effluent from wastewater treatment plants (WTTPs) that poses a threat to the quality of water (via eutrophication) and air (through ammonia emissions). In this case, the presence of nitrogen in wastewater also affects the carbon footprint of the plant as the biological nitrogen removal processes emit nitrous oxide (N2O), a strong greenhouse gas. The integration of alternative processes for nitrogen recovery could therefore have a positive impact on WWTPs’ environmental footprint, and help achieve the objectives of the Water Framework Directive, the Urban Waste Water Treatment Directive and the 2020 EU Climate and Energy Package.
The production of dry sludge from WWTPs in the EU-27 amounted to 10.13 million tonnes in 2013. The Sewage Sludge Directive and the Urban Waste Water Treatment Directive encourage the use of sludge in agriculture, as long as it is not a threat to the environment and human health. In Spain, WWTPs generate about 1.2 million tonnes of sludge. Up to 82.6% of the sludge generated is used as fertiliser, although its direct use in agriculture poses several environmental problems for soil and water quality due to the presence of pollutants such as heavy metals.
LIFE ENRICH will demonstrate a cost-efficient and highly replicable recovery system for nitrogen and phosphorus from WWTPs and its valorisation in agriculture (either via direct use on crops or through the fertiliser industry). To this end, the project will design and build a new sludge line configuration in Murcia Este’s WWTP that aims to extract and concentrate phosphorus in the liquid phase with a later full recovery via crystallisation. The nitrogen recovery unit will be based on ammonium adsorption into zeolites combined with membrane contactors. The products obtained will be combined in order to find optimal mixtures and their agronomic properties will be validated at full-scale through field tests, in order to ensure the products' viability.
Specific objectives are to:
In addition to the benefits relating to water and climate policy, the project will help implement the new EU Circular Economy Action Plan through the recovery of phosphorus, a critical raw material. Such materials are a priority area of the plan.