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Water reclamation technologies for safe artificial groundwater recharge

Final Report Summary - RECLAIM WATER (Water reclamation technologies for safe artificial groundwater recharge)

The strategic objective of the RECLAIM WATER project was to develop hazard mitigation technologies for water reclamation providing safe and cost effective routes for managed aquifer recharge. The work assessed different treatment applications in terms of behaviour of key microbial and chemical contaminants. The knowledge generated in the project and the technologies developed are also suited to the needs of developing countries, which have a growing need of supplementation of freshwater resources. RECLAIM WATER integrated technological water reclamation solutions with natural attenuation processes occurring in the subsurface to achieve upgraded water quality assessed on the basis of key contaminants.

The project was structured in seven work packages (WPs):
WP1: Assessment and development of water reclamation technology
WP2: Analysis of microbial contaminants and antibiotic resistance genes
WP3: Analysis of organic compounds
WP4: Technical water reclamation and aquifer recharge case studies
WP5: Specific studies on removal and fate of microorganisms and organic compounds
WP6: Case-study related risk studies
WP7: Integrative monitoring, modelling and assessment tools for subsurface treatment and storage.

To provide a better understanding of aquifer recharge, from 2005 to 2008, eight international pilot or full scale test sites treating municipal wastewater effluent and / or stormwater for aquifer recharge have taken part in WP4 activities which included the monitoring of more than 50 basic wastewater parameters and contaminants at different location of their schemes and at least three times per year, except for the partners who joined the project in its second year (i.e. South Africa and Mexico). The main objective of this study was to assess the overall performance of these sites in recharging aquifers mainly for irrigation and potable water supply purposes by following contaminant fate throughout each scheme.

Several technical options for upgrading water quality prior to groundwater recharge are currently available consuming less than 1 Euro/m3 and 1 kWh/m3. Since comparative full scale performance is not yet available, a definitive ranking of technologies tested in pilot scale is currently not possible. Natural systems -e.g. soil passage and soil aquifer treatment (SAT)- clearly show a great upgrading potential allowing lower treatment costs and no residual streams compared with membrane systems. The final product water quality contains higher organic concentrations if compared with high pressure membrane applications. Concerning some micropollutants natural systems can only achieve a partial removal.

Different efficiencies of pathogens and antibiotic resistance genes removal were observed by natural attenuation systems at Sabadell (SAT) and Nardo (water flow in the karstic fractured subsoil) recharge sites. The results contribute to the comprehension of limits and potentialities of low costs treatments for MAR scheme that are of major importance in developing countries.

Size exclusion chromatography (SEC) and excitation emission measurements (EEM) offer the potential to identify specific fractions originating from wastewater or natural water (effluent organic matter versus natural organic matter) and can describe their fate and behaviour during water treatment. Besides single compounds that could be identified as wastewater tracers such as carbamazepine and diatrizoate the analytical combination of SEC and EEM provides evidence of specific organic fractions originating from domestic wastewaters.

The project outputs did not specifically allow drawing out some definitive conclusions on the type of pre-treatment required for a specific type of aquifer recharge site and reuse purpose or on standard residence times that should be respected for specific types of infiltrated water quality.

The aquifer barrier has proven to be an important treatment step in all the case studies, no matter the technique used to introduce the treated wastewater or stormwater into the aquifer, and the risk posed by the different hazards (microbiological, chemical and physical) is reduced. The role of the aquifer treatment is important from the health, environmental and technological points of view as well as the socio-economic one. From a marketing or acceptability perspective it can be said that water disappears from the surface which implies that treated wastewater is no longer used directly. From a legal perspective, this is of major importance since the regulations that apply to the reuse of surface and subsurface of reclaimed or reclaimed water differ considerably.

Boron isotopes reveals a valuable tracer of artificial recharge of freshwaters derived from treated sewage, both for short term tracer tests and for long term monitoring of artificial recharge, even if in aquifers with higher clay contents, sorption-linked isotope fractionation cannot be excluded.

The project results were disseminated through numerous publications.