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Use of Grey Water Footprint to determine the wastewater treatment rate

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  • Project leader: University of Architecture, Civil Engineering and Geodesy (Sofia, Bulagria)
  • Partners: the local water operators
  • Implementation time: 2 years
  • Project cost: below € 20,000; only costs for chemical analyses were financed

Context in which the project was created:

A PhD work was initiated based on some findings of EU FP7 project EcoWater. EcoWater project (2011-2014) addressed the development of meso-level eco-efficiency indicators to assess technologies and their uptake in water use sectors. The Grey Water Footprint is one of these indicators related to aquatic pollution.

The Grey Water Footprint refers to pollution and is defined as the volume of freshwater that is required to assimilate the load of pollutants given natural background concentrations and existing ambient water quality standards. The grey water footprint refers to the volume of water that is required to assimilate waste, quantified as the volume of water needed to dilute pollutants to such an extent that the quality of the ambient water remains above agreed water quality standards. 

Hoekstra, A.Y., et al., 2011. The Water Footprint Assessment Manual: Setting theGlobal Standard. Earthscan, London, UK

Strategy and objectives

The project is about how to reach consistence between the requirements of two EU Directives. Grey Water Footprint is used as a main tool for that.

The place where the WWTP (Wasterwater Treatment Plant) effluent discharges into the receiving water body is actually the physical ‘intersection point’ of two EU Directives – Directive 91/271 and Directive 2000/60/EC (Water Framework Directive, WFD). In many cases, the responsible authorities issue discharge permits, based only on the maximum allowable discharge standards for the WWTP effluent (according to Directive 91/271), without consideration of the ecological status or run off of the receiving water bodies (WFD).

The study, carried out in the University of Architecture, Civil Engineering and Geodezy in Bulgaria demonstrates the importance these two Directives to be considered together for determination of economically and environmentally sound discharge permits.

Quantitative and qualitative parameters of four rivers and six WWTP effluents were monitored in one year. This selection includes different ratio of discharge effluent to river run off (from 2 to 1,000) as well as rivers with different ecological status (moderate or good).

Grey water footprint (GWF) concept was applied to determine that effluent requirements, which will satisfy the requirements of both Directives at lowest cost.

Results and perspectives

The results of the study could be of interest for the authorities, responsible for WWTP and surface water body management, control and monitoring.

It provides competent authorities (River Basin Directorates) with a tool, enabling them to determine the necessary wastewater treatment rate in any particular case, depending of the ecological status of the river before the discharge point and the ratio between the river run off and the wastewater flowrate.

Application of this tool will contribute to the achievement of WFD requirements. It represent an innovation for policy management as well as social mediation.

How could this project be duplicated for other rivers?

It’s easy because only some data need to be collected and anaysed.

#Bulgaria #pollution #GWF #wastewater

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