Filtração de margens para melhoria da qualidade da água num esquema de recarga gerida de aquíferos em Berlim

Responsible entity

Berlinwasser Group (Fig. 1) is the entity responsible for the Berliner’s water supply “in the most efficient and sustainably way, ensuring its quality by acting with a sense of responsibility, showing commitment and using state-of-the-art technology”.

Institutional setting

RBF was first applied in Germany’s capital, Berlin, more than 100 years ago. For the past 70 years, bank filtration has produced approximately 60% of the city’s drinking water (Gillefalk et al., 2018). Methodologies keep improving since the beginning.

Water abstraction occurs in around 650 wells and is part of a semi-closed water cycle, where effluents from waste water treatment plants reach surface water bodies subject to water extraction via RBF for water provisioning (Fig. 2). In total, 9 lakes and many reaches of the lowland rivers Spree, Dahme and Havel are affected by RBF (Gillefalk et al., 2018).

In order to be able to extract the required quantities, the groundwater is replenished with treated surface water, by impounding water into shallow earth basins or into natural ponds and ditches. The upper layers of soil act like a giant filter. The natural cleaning power of the soil improves the quality of the water physically, chemically and biologically, so that it is comparable to that of natural groundwater. On the way to the wells, percolated water also reaches the same temperature as groundwater.

Geographical setting

The Berlin water supply region has an area of 892 km2 and a population of 3.6 million. It extends 45 km at its widest point from east to west, and 38 kilometres from north to south. The River Spree flows through the city’s districts from east to west, forming a 7 kilometres wide valley, bounded by high areas in the north and south. It then flows into the valley of the River Havel near Spandau. These valleys are part of the “Warsaw-Berlin Glacial Valley” formed by the water masses which melted after the Ice Age. They are filled with sand and gravel at a depth starting at 30 metres. These gravel layers contain the groundwater resources which serve as the basis for Berlin’s drinking water supply (https://www.bwb.de/en/2164.php) (Fig. 4).

Historical overview

The effectiveness of bank filtration and artificial groundwater recharge has long been recognized in Germany. In the late 19th century, after various bacterial diseases caused by direct intake of drinking water from rivers (e.g. outbreak of epidemic cholera in Hamburg in 1892/93), direct extraction of surface water for public-water supply fell into discredit and was replaced or supplemented by artificial or natural subsoil passage of river water due to its efficiency in removing microorganisms from the infiltrating surface water (Schmidt et al., 2003).

Nowadays, approximately 16% of the drinking water in Germany is produced from bank filtrate and more than 300 water works use bank filtration, with roughly 50 plants based on artificial groundwater recharge (Fig. 8).

Berlin water supply is an emblematic example of RBF and is providing knowledge as a living lab for understanding and learning about the improvement of physical, chemical and biological water quality.

Evidence of benefits from implementation

Some of the benefits from RBF are:

• Reduces turbidity in a cost-efficient manner.
• Removes particles, biological contaminants and biodegradable compounds.
• Improves microbiological, physical and chemical water quality compared to surface water.
• Brings a more consistent water quality and temperature.
• Reduces the need/cost for disinfection.
• Decreases construction and operation costs, offering the lowest costs among water supply options (e.g. when compared with pumping from deeper aquifers).
• Generates less sludge.
• Has an easy maintenance.
• It is not susceptible to invasive plant infestation

REPLICATION POTENTIAL IN SUDOE REGION

The use of Riverbank Filtration in SUDOE areas has a strong replication potential since these are well established techniques tested in many hydrogeological setting with similar characteristics to SUDOE region. Furthermore, the specific conditions of this region (e.g. high temperatures with high evaporation; algae blooms in surface reservoirs) are naturally attenuated when using water from RBF.

The passage of water underground with a natural multiple barrier sand filter system provides several benefits for drinking water treatment. The results obtained in Berlin show that during infiltration and underground transport, processes such as filtration, sorption, and biodegradation produce significant improvements in raw water quality, therefore reducing subsequent treatment needs.

Key points of the innovative method

In Berlin, and Germany as a whole, bank filtration and artificial groundwater recharge have been used for the drinking water supply at several sites making use of different subsoil characteristics for water quality improvement, and no loss of purification capacity could be noticed (Schmidt et al., 2003).
Riverbank Filtration is an innovative method which is being continuously subject to improvements, being its main characteristics to:

• Bring a more consistent water quality (microbiological, physical and chemical) and temperature in a natural and cost-efficient manner.
• Reduce the need/cost for disinfection.
• Decrease construction and operation costs (less sludge, easy maintenance), offering the lowest costs among water supply options.