Brine and metal wastes valorisation to produce coagulants for wastewater treatment.

PROJECT DESCRIPTION

BACKGROUND

In reverse osmosis (RO) and ion exchange (IE) the feed water is separated into two streams, water and high-salinity brines, which are typically treated as a waste. It is estimated that there are 15 906 operating desalination plants in the world, generating around 142 million m³/day of brines. The European Union and Spain represent, respectively, 9.2 and 5.7% of the total facilities. Those brines are disposed of in the environment without treatment (discharge in water surfaces, sewers, deep-well injection, evaporation ponds and land application) or in wastewater treatment plants (WWTPs). Therefore, brine valorisation is critical. Moreover, in Spain there are more than 2 000 WWTPs, around 900 desalination plants and 1 300 drinking water treatment plants (DWTPs) that use metal salts in coagulation processes for the removal of pollutants. It is estimated that 190 000 tons/year of ferric salts are consumed in Spain and 2 150 000 tons in the EU. These coagulants are corrosive, require special equipment and hazardous substances for pH adjustment, as well as worker protection. Its manufacturing process depends on large and complex industrial processes performed worldwide, with a relevant relationship between energy production and water use for chlor-alkali chemicals, which entails constant increases of purchase prices, resulting in an increase in treatment costs. Finally, due to the increasing demand for metals there is a scarcity of resources, rising prices and environmental impacts derived from both the demand and unsustainable scrap metallic waste management. In the EU only around 3% of the raw materials necessary to maintain an increasing demand for metals are produced. Despite the historical reuse of metals, it is important to find synergies with other industrial sectors to move towards an efficient circular economy model, which promotes the valorisation of different wastes as new products.

OBJECTIVES

The LIFE Waste2Coag project aims to demonstrate a viable and cost-effective solution for brine and metal waste valorisation to produce a sustainable coagulant as an alternative to the commercial ones. The product will be used in water facilities, ensuring the use of resource efficient processes for the provision of water services. The electrolytic technology to be applied is operated with renewable energy, turning the process into a completely sustainable process based on the use of wastes as raw materials and renewable energy.

The specific objectives are to:

• Design and construct an electrolytic pilot system (ELS) to produce coagulants by recovery of brines and metal scraps instead of using virgin raw materials;
• Develop operational and maintenance protocols, and to optimise the operational parameters of the ELS considering the characteristics of both the brines and metal wastes, and the final use of the coagulant (chemical nature and concentration);
• Produce formulations of iron (Fe) and aluminium (Al)-based coagulants with neutral pH and demonstrate their effectiveness in the removal of pollutants from wastewater;
• Quantify the economic and environmental feasibility of the ELS by conducting Life Cycle Costing, Life Cycle Assessment (LCA) and social LCA (S-LCA);
• Obtain economic savings linked to in-house production and usage of coagulants, reducing operational costs in the exploitation of WWTPs;
• Determine the economic potential of the project process and products in view of future commercialisation, through a business plan;
• Develop a communication, dissemination and transfer of project;
• Promote ELS as a sustainable, autonomous and decentralised technology, proposing the inclusion of this technology as a Best Available Technology (BAT) in EU policies.

The project contributes to the implementation of the Roadmap to a Resource Efficient Europe (COM(2011) 571); European Green Deal; EU Circular Economy Action Plan (COM/2020/98); Water Framework Directive (2000/60/EC); Waste Framework Directive (2008/98/EC); Urban Wastewater Treatment Directive (91/271/EEC); Marine Strategy Framework Directive (Directive 2008/56/EC); and Directive 2009/28/EC on the promotion of the use of energy from renewable sources.

RESULTS

Expected results:

• Design, build and operation of an electrolytic pilot plant, fed with renewable energy and using wastes as secondary raw materials to produce coagulants with an estimated maximum capacity of around 60 m³/day;
• Valorisation of 75 m³/week in Gandía (100% of received brines), 400 m³/week in Wulpen (3% of discharged brines to the North Sea by the nearby drinking water facility), 1.5 m³/week in JOVIAR (100% of generated brines in their process). A total of 5 000 m³ during project duration;
• Adjustable metal concentration in the produced coagulants of 400-2 000 mg Fe/L and 250-700 mg Al/L;
• Valorisation of 0.4-2 kg Fe and 0.25-0.7 kg Al per m³ of brine processed (2-10 t Fe and 1.3-3.5 t Al during project duration). Recycling steel and Al wastes saves up to 75-95% of the non-renewable primary resources required to process Fe and Al metals for the production of commercial electrodes;
• Saving of 100% of commercial coagulants, 25-130 and 20-54 tons of ferric and Al commercial coagulants respectively during the project (€3 000-15 000 and €3 000-7 000). Equivalent to a decrease in more than 50% of current coagulant treatment costs per m³ of treated wastewater;
• Energy consumption of around 9 kWh/kg of metal in the produced coagulants. Energy consumption in coagulant production assisted at 5-100% by renewable energy (photovoltaic) depending on the demonstration site to be installed (368 KWh/year capacity);
• Demonstrated that the coagulants generated are comparable in terms of purification efficiency (COD, P, turbidity, SS reduction, pathogens and emerging contaminant) to commercial products, thus avoiding the impact associated with the manufacture of such coagulants;
• Demonstrated that the technology is applicable to the set of WWTPs in the EU where approximately 4 200 000 tons/year of coagulant are consumed (1 400 000 tons/year PAC and 2 150 000 tons/year ferric salts);
• 80% reduction of CO₂ emissions from recycling and/or primary production of Fe and Al thanks to the direct use of scrap metal as raw material;
• Avoidance of the transport of commercial coagulants thanks to their on-site generation (360 kg CO₂ equivalent);
• Possibility of modelling the concentration of coagulants based on the demand for self-consumption, supply to other WWTPs and/or commercialisation;
• Elaboration of the Best Practices & Replicability and Transferability guideline document, which will facilitate the transfer of the demonstrated technology;
• Proposal of the developed technology for EU Best Available Techniques reference document (BREF) for brine valorisation; and
  
• Exploitation and business strategy plan.