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Maribor Waste Water Concession



Project number:


Business sector:

Municipal and environmental infrastructure

Notice type:


ESIA disclosed:

28 Sep 1998



Approval date:

24 Nov 1998

Purpose of the Environmental and Social Impact Assessments

Aquasystems d.o.o., Waste Water Treatment Plant for Maribor

There is a project summary document available for this project.

ESIA Summary

This Environmental Impact Assessment has been prepared by Safege and by Institut za Varstvo Okolja (Environmental Protection Institute of Maribor) for Aquasystems d.o.o. in order to comply with the European Bank for Reconstruction and Development's (EBRD) environmental policy and procedures.

1. General settings and present situation 

The City of Maribor and surrounding urban area are located along the Drava river in eastern Slovenia. Maribor has a population of about 134,000 inhabitants. Maribor is an important trade and industrial centre and has its own university. The surrounding countryside supports a range of agricultural activities including cultivation of grain, vegetables, beets and vines.

At present, most of Maribor's domestic and industrial effluent is not treated and is discharged directly into the Drava river system, polluting and seriously degrading the surface and groundwater systems downstream of the City, including specifically the aquifer downstream of Maribor from which the City gets much of its drinking water.

There is a strong local interest in improving this unacceptable situation. The Maribor Waste Water Treatment Plant (WWTP) project stems from this need to improve the environment and particularly the Drava river system.

2. Purposes of the project 

The main objective of the Maribor Waste Water Concession Project is to provide for the construction of a waste water treatment plant for the City of Maribor and its surrounding area. This will enable:

the treatment of most of the domestic and industrial waste water from the Maribor area in order to improve the area’s general environment and particularly the surface and ground water systems,

full compliance with local and EU regulations, in particular with the European Commission Directive of 21 May 1991with regard to urban waste water treatment, and with the Regulation on Emission of Discharges of Waste Water from Urban Waste Water Treatment Plants (The Official Gazette SS,n0. 4/93 and 3/96), the treatment of sludge for disposal or storage in a specially designated area (off site).

3. General description of the project 

The WWTP will extend over 6 hectares of land which is currently under agriculture. The possibility of extension over a further 4 to 5 hectares is under consideration. The site is located at a distance of around 7 km south east of Maribor City.

The closest settlement is the town of Dogose, some 1.5 km upstream of the site. The closest houses lie about 500m north of the site.

The WWTP will have the following characteristics:

  • a design capacity of 190,000 population equivalents for a complete three-stage treatment procedure

  • maximum waste water inflow rate of 5,000 m3/h for treatment levels 2 and 3

  • maximum waste water inflow rate of 7,000 m3/h for treatment level 1

  • the effluent will be discharged into the hydro-power channel in normal conditions. In extreme storm conditions (incoming sewerage water > 7,000 m3/h), the surplus waste water will be diverted into the Drava river.

The waste water treatment process will include three distinct levels; the first level will consist of mechanical cleaning, the second level will include biological processes through activated sludge to remove carbon and treat sludge, the third level will upgrade the effluents in terms of nitrogen and phosphorus removal.

The entire process, buildings and associated installations will comply with local and European regulations:

  • the whole treatment line will be constructed to ensure that it is leak free

  • treatment chemicals will be stored in specially designed areas; a significant portion of the treatment process will be automated

  • the treatment chemicals used will be to EU approved standards

  • noise and odour minimisation systems are included in the project

  • sludge will not be stored on the site for any length of time

  • health and safety measures will be taken for worker protection

  • proper training will be provided to the workers to enhance plant optimisation and security on the site.

The specific concession project does not include the construction of the sewage collector (which is being arranged by others with support from EU Phare funding). It also does not include for the long term disposal of the sewage sludge which is the subject of further studies and arrangements currently being undertaken by the Municipality of Maribor, and which will be the subject of a separate environmental impact assessment. However, sludge removal from the WWTP site will in all cases comply with EU and national legislation.

4. Phasing of the works 

The WWTP will be built in three phases corresponding to three distinct treatment levels:

  • Phase 1 
    Construction and implementation of the pre-treatment process including mechanical processes. This first phase will be implemented within the first two years.

  • Phase 2
    Construction and implementation of carbon removal and sludge treatment processes. This second phase will be completed within the first three year

  • Phase 3
    Implementation of tertiary treatment to upgrade nitrogen and phosphorus removal. This third phase will be implemented within a eight year time span.

5. Compliance with EU and local legislation 

AQUASYSTEMS d.o.o. will comply with both EU and Slovenian legislation.

The Maribor WWTP effluent quality will meet both the standards set by the 21 May 1991 European Directive and those set by local legislation, and more specifically the Regulation on Emission of Discharges of Waste Water from Urban Waste Water Treatment Plants (Environmental Protection Act - Official Gazette SS, N°4/93 and 3/96). Where uncertainty exists between the two sets of legislation, the more stringent requirements will be met.

6. Impact Assessment 

The main potential impacts of the project on the environment include:

  • impact on surface water

  • impact on soils and groundwater

  • impact on the landscape

  • impact on amenity (odours, noise, traffic)

  • impact on natural habitats, fauna and flora,

  • impact during construction

All of these potential impacts have already been taken into consideration in the design of the WWTP in order to limit their effects on the environment. As previously mentioned the plant will abide to the most stringent criteria of European and national legislation.

Impact on surface water 

Possible impacts on surface water could occur through:

  • chemical spill,

  • sludge discharge,

  • treated effluent discharge.

The risk of chemical spill affecting surface water is negligible because chemicals will either be stored as solids in specially designed and designated storage areas or as liquid chemicals in watertight containers, again in specially designed and designated storage areas, and most handling will be mechanised. Furthermore storage areas will have closed loop drainage systems.

Sludge discharge into the surface water system will not occur because sludge will not be stored on site for any length of time. Nevertheless, the sludge handling area will be watertight and equipped with a closed loop drainage system with a possibility of recirculation through the treatment line.

The liquid effluent will be discharged into the hydro-power channel. Calculations have shown that even in the best natural water quality conditions (upstream from Maribor), the effluent will have a negligible impact on the surface water system both in terms of quality and quantity. In fact the treatment process and diversion of treated effluent into the hydro-power channel will have a major positive impact on the environment as it will prevent uncontrolled direct discharges of untreated municipal and industrial effluents into the Drava river system, as is now the case.

Impact on soils and groundwater 

The project could potentially affect soils and groundwater through:

  • Chemical spill,

  • Sludge percolation,

  • Sewage water and effluent percolation,

  • Building work,

  • Surface water quality.

The risk of chemical spill and sludge percolation will be negligible for the reasons already explained above.

The entire treatment system from the plant inlet to the plant outlet will be watertight; the risk of waste water percolation into the ground is therefore negligible.

Building deep foundations will require groundwater pumping: the lack of data prevents an assessment of the pumping effect on the aquifer. It is reasonable to assume however that the effects of pumping will be moderate to negligible. They will in any case be temporary.

Flow exchanges between surface water and groundwater will contribute to improve groundwater downstream from Maribor as surface water quality will improve.

Impact on landscape 

The WWTP will not have any significant impact on landscape as the plant itself will not be visible from any housing units, nor from most of the neighbouring areas.

Great care have been given to the Plant’s general aesthetics: essentially it will be hidden from view by green vegetation, which will be kept neat and clean.

Impact on amenity 

Containment of noise emitting engines or activities in sound-proofed areas prevent any will result in no additional noise impacts away from the site, and in particular in the vicinity of the nearest existing housing units.

Odour removal systems included in the project design will prevent olfactory nuisances.

Traffic will not significantly increase in the area of the WWTP, except on a temporary basis during the construction phase.

For reasons mentioned above the WWTP is expected to improve surface and groundwater quality. As such it will contribute to remove odours arising from the Drava river’s poor quality water.

Impact on natural habitats, fauna and flora 

There are no sensitive, nor any unusual species of fauna or flora in the site area ; this area is indeed primarily devoted to agriculture. The WWTP site is in an area which is likely to be designated as the Drava Nature Park, a "landscape park". According to available information, the park status is currently under consideration (non official). For reasons explained above the WWTP will have a positive impact on the Park.

Impact during construction 

These are essentially restricted to additional traffic and noise generation by construction equipment and machinery during the construction phase. Nuisances generated will be negligible for the local population.

7. Overall assessment and mitigation measures 

The Maribor WWTP will include modern technology for operation and control. It will comply with the most stringent requirements of both the EU and Slovenian legislation. Environmental aspects have been taken into account from the start of the design of the project.

Due to all the control, fail-safe and protection measures and steps included in its design, the WWTP will have only minor negative impacts on the environment, some of which will be restricted to the periods of construction activity.

Once operational, it will have a major positive impact on the environment as it will allow a great improvement in surface water quality and possibly groundwater quality. This improvement will be gradual through time and will extend over a 8 year time span according to the project’s three phase implementation.

To secure this advantage, the following recommendations are made:

  • monitor the detailed design and construction of the WWTP to ensure that work is carried out to high standards and that the treatment works are likely to remain watertight throughout the design life;

  • monitor the aquifer pumping during the construction phase;

  • impose good working practices on all contractors to minimise noise emission, minimise traffic and keep the site as clean as possible during the construction phases;

  • set up a monitoring system to check that all parts of the plant continue to meet Slovenian and EU requirements;

  • explain the WWTP benefits to the public;

  • install a piezometer system to monitor the shallow groundwater aquifer downstream of the WWTP site.

8. Public information and consultation 

The concept of the Maribor WWTP project originated in the late 1980s. At this time a number of sites were under consideration, including the one currently selected. Since this time extensive public consultation has taken place both to select the site and to find ways in which to mitigate the environmental impact of the construction and operation of the plant itself.

Key meetings of the Executive Committee, the Municipal Assembly, the City Council and other associated bodies in Maribor took place in 1993, 1994 and 1995. The Concession Act which was the key decision required to commence the formal process of implementing and financing of the WWTP was passed by both the Assembly of the Municipality of Maribor and by the Assembly of the Local Communities on 30 June 1994 and by the Labour Assembly on 7 July 1994.

Both before and after that time, an extensive public consultation process, including public meetings and discussions, has taken place, in full compliance with the Slovenian legal requirements. This process has been supervised by the Ministry of Environment and Physical Planning, who is responsible for the regulation of the physical planning process. Following a formal consultation process and the answering of a number of questions raised the government approved the Land Use Plan on 18 July 1994.

Most recently public meetings have taken place as recently as September 1998 to discuss details of the WWTP project with the local population. The consultation process is on-going.

Full ESIA availability

Full ESIA documentation is available locally at:
EBRD Headquarters in London,


This document was prepared at an early stage of project development, before consideration by the EBRD Board of Directors. Details of a project may change following disclosure.

Environmental and Social Impact Assessments and ESIA summaries are produced by project sponsors, and the EBRD makes them available without any comment or implied endorsement. Any views expressed or statements made in the Environmental and Social Impact Assessment or the ESIA Summary do not necessarily reflect the views or opinions of the EBRD.

Last updated 25 June 2014

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