Water scarcity is an increasingly frequent and widespread phenomenon in the European Union, due to, among other things, population growth, urbanisation and climate change. The Water Framework Directive (WFD) promotes measures for water reuse from treated wastewater as one option to help avoid over exploitation of aquifers. In coastal or island areas this can be especially problematic as groundwater sources in these areas can also suffer from contamination by salt water.
As an alternative water resource, treated wastewater can be reused for agricultural and land irrigation, industrial recycling and reuse, groundwater recharge, non-drinking urban use etc. This would reduce pressure on aquifers, especially those located in coastal areas. New technological solutions, such as forward osmosis (FO) offer opportunities to improve the effectiveness of wastewater treatment systems and processes.
The main objective of the LIFE OFREA project was to increase the amount of wastewater available for reuse in areas where the salinity of fresh water is a limiting factor. This would be achieved by demonstrating the feasibility of forward osmosis (FO) technology in the production of safe and high quality water from treated wastewater for reuse, at a reasonable cost.
Specific objectives would (i) ensure that the amount of energy consumed during the treatment process was 20% lower than equivalent effluent treatment processes using reverse osmosis, and (ii) demonstrate that the treatment processes requires 15% fewer chemicals for disinfection, pre-treatment and membrane treatment than conventional (reverse osmosis) treatment processes.
Thus, the project would demonstrate a fully automated, robust and environmentally safe wastewater treatment process using forward osmosis (FO) technology. The results wold be used to promote FO as a viable option for WFD stakeholders.
The main goal of the OFREA project was to increase the percentage of reused wastewater in areas where the high salt content of treated water limits its subsequent use. At the same time, it aimed to increase the number of uses of water reused in higher value-added applications.
The OFREA project demonstrated the feasibility of forward osmosis (FO) technology to produce reclaimed water of high quality at a competitive price. Tests were carried out with five different schemes of operation, including three different draw solutions. The results showed that the FO technology could become an alternative to tertiary treatments of wastewater in order to obtain reclaimed water for irrigation purposes.
The industrial process of FO uses a high-salinity solution (Draw Solution - DS) to extract water from the feed solution through a semi-permeable membrane, using osmotic pressure. This process has the main advantage of not requiring hydraulic pressure, leading to a lower degree of irreversible membrane fouling. The main disadvantage is that the water generated by this step is mixed with the extracting solution. A system for the separation of the extracting agent is therefore needed to obtain the desired water. This separation system is nano-filtration (NF). The pilot plant therefore comprises of two steps: FO and NF, which enable the regeneration of the DS (Draw Solution) and production of desalinated water. The plant is fed with product water from the WWTP, which has a conductivity of 4-6 mS/cm and a Boron content of 1.3 ppm. In order to reuse this water for agricultural purposes, conductivity must be under 3 mS/cm and Boron content must be less than 0.5 ppm (Spanish standards for agricultural reuse).
After treatment using the OFREA solution, the resulting water has a low conductivity and a Boron content lower than 0.5 ppm, which means that it has the necessary quality for reuse.
The results yielded by tests at the pilot plant also showed that energy consumption could be reduced by 50% (from 4.4 kWh/m3 in existing desalination plants in Murcia, to 2.22 kWh/m3 using the OFREA solution at full-scale) and that chemicals could be reduced by 16.5% to 0.58 kg/m3 in FO (compared with 0.6951 kg/m3 using ultrafiltration plus reverse osmosis).
Based on projections i.e. on the basis of the LIFE OFREA technology applied to six Hm3/ (cubic hectometre)/year), the following positive socioeconomic impacts would be:
The innovation and demonstration value in this project are clear, as the OFREA plant is the first demonstration plant worldwide that uses FO technology for agricultural reuse of wastewater. The project aims to scale-up the plant in a real application. The technology is promising for other wastewater streams requiring complex pre-treatments. The project is also in line with two main environmental directives, the Water Framework Directive and Urban Wastewater Treatment Directive.
Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).