Danish innovations in water sector keep pollution at bay

Blue again: Once regarded as a sewer, Aarhus River is now a popular commercial and recreation area in Aarhus, Denmark’s second largest city. An intelligent drainage management system has helped clean up the river and harbour, making the city much more liveable and vibrant. Photos: TAN CHENG LI/The Star

In Denmark, tap water is as pure as spring water and the sea off city harbours are clean enough to swim in. How is that so?

WHEN it comes to good examples of managing water resources, Denmark comes to mind. The country is touted as a world leader in the water sector, and it must be doing something right – its water consumption has dropped almost 40% since 1980. Its treated water is of such high quality that everyone drinks straight from the tap; there’s even a national competition for the best-tasting tap water. And its non-revenue water is a mere 7% (Malaysia’s is over 30%).

These achievements are derived from: charging consumers the real cost of water; “save water” campaigns; and a strong focus on reducing leakage in water pipes. Also, mandatory benchmarking against best practices in the industry has driven innovative and cost-effective ways to manage water and wastewater.

Denmark’s water tariff is among the highest in Europe. The price varies between municipalities but averages €8 per cu m (RM32.30). The monthly water bill for a family of four (using 14 cu m) can easily amount to €113 (RM450). Atrocious, you say? But then, that is the true cost of water. That figure covers everything that is needed to deliver high quality drinking water to consumers, right from water abstraction and treatment to water distribution, groundwater and catchment protection, wastewater treatment, operation and maintenance of sewers, taxes and value-added tax (VAT).

“It is something people pay for to get quality water as well as security in water. The pricing policy is also an incentive for conserving water,” says Danish environment minister Kirsten Brosbol.

Safe to swim: Frequent sewer overflows meant that swimming in Copenhagen’s harbour was out of the question 15 years ago. Today, people flock there to cool down when the weather warms up. Photo: Thomas Rousing/copenhagenmediacenter.com

Denmark’s decentralised water structure sees the country having 171 municipal waterworks and 2,500 community-owned waterworks (through co-operatives) and private wells. It also adopts a “no profit-making” policy in the water business; so all profits are reinvested into the business or returned to the customers.

Tariffs are set by each utility and is the same for both consumers and industries. Of the water price, 18% is paid to the waterworks, 51.1% to the wastewater treatment company, and 30.5% to the state in the form of taxes, according to the Danish Water and Wastewater Association.

To ensure that good quality water reaches end users with little losses along the way, Denmark has developed a non-revenue water (NRW) masterplan consisting of leakage management systems and technologies such as smart meters and high-quality valves. NRW is typically caused by inaccurate billing and metering systems, leakage from deteriorating distribution infrastructures, excessive water pressure in distribution systems, and illegal siphoning of water.

More efficient ways to aerate wastewater help lower the energy bill of the Marselisborg wastewater treatment plant in Aarhus.

Safe groundwater

A year ago when Selangor was in the throes of a water shortage, talks emerged about resorting to groundwater. Should Malaysia want to exploit this resource, it can tap the expertise of Denmark, which relies solely – yes, 100% – on groundwater due to the lack of surface water supply.

“Since there is approximately 100 times more groundwater on Earth than fresh surface water, it makes sense to exploit groundwater,” says Brosbol.

Furthermore, groundwater is less exposed to pollution than surface water, so its quality is higher and it requires less treatment. “It is supplied directly to homes without treatment, just filtration. This is possible because of strong regulation on agriculture ... use of pesticides is regulated.”

Such controls are certainly needed as 66% of the land is farmed. Aquifers are mapped (through advanced airborne geophysical mapping) and not over-extracted through the use of software tools for integrated water resource modelling and monitoring.

“Through the mapping, we know where the groundwater sources are and where we need to protect,” says Brosbol.

In Aarhus, Denmark’s second largest city, water supply and wastewater treatment is handled by Aarhus Water, a public limited company fully owned by the municipality. Its nine waterworks tap 90 wells to supply 15 million cu m of potable water annually to 250,000 consumers, at €5 per cu m (RM20.20).

“The groundwater quality is so good that we can drink direct from the wells with just simple treatment of aeration and sand filtration,” says Kristian Koch Brunmark, the company communications officer.

Doing without chemical treatment (such as chlorination) calls for good filtration technology and high-quality water. They scrutinise the water quality not just at wells and waterworks but also along the 1,500km of piping lines. Within the supply system are 80 distribution wells equipped with devices that give online readings of the water pressure, flow, turbidity, pH and temperature before the water reaches customers. They help detect leakages, thus avoiding unnecessary water loss.

The real-time measurements allow for a quick response should problems arise, thus fewer people will be affected, says Brunmark. Water levels at the 30m- to 140m-deep wells are monitored to avoid over-extraction. All wells are surrounded by a 10m protection zone and a 300m hygiene zone within which there must be no percolation of wastewater. The municipality issues a groundwater plan with guidelines on distribution between waterworks, farmland and nature.

The wells are spread outside the city to relieve the impact on reserves and to minimise pollution risks. Nevertheless, the groundwater still gets contaminated.

Brunmark says of 315 test sites, 35% have pesticide residues and 18% exceeded the limits for drinking water. Some 7,200ha within groundwater-source areas are vulnerable to pesticide pollution; these are mostly sites without a protective clay layer.

To protect these crucial water sources, the company has signed agreements with farmers to stop using pesticides for 2,400ha. The farmers are compensated for reduced yields. Another 4,800ha remain unprotected and it will be up to the municipality to evoke a bylaw requiring pesticide-free cultivation.

The company has also spent 20mil kroner (RM11mil) to buy over 240ha of farmland in vulnerable water catchment areas for afforestation.

NEXT: Energy from waste

Beneath this car park and lawn in Aarhus is a 10m-deep tank with a capacity of 18,000 cu m. During downpours, excess wastewater is stored here so as not to overwhelm city sewers and sewage treatment plants.

Energy from waste

Collecting and treating wastewater is an energy-intensive process; 3% of Denmark’s energy consumption is used just for that. This prompts increased focus on energy efficiency and energy recovery in these facilities. Today, most Danish wastewater treatment plants have online measuring equipment to optimise treatment processes and plant hydraulics, and Aarhus Water is no exception.

Its four wastewater treatment plants treat 30 million cu m of effluent annually. By switching from traditional surface aeration (the energy guzzler in most plants) to bottom diffused aeration in the activated sludge tanks (to remove organic matter, nitrogen and phosphorus), it saves 2GWh a year, which is the power used by 300 typical households. This also curbs carbon dioxide emissions of over 1,600 tonnes a year.

Its Marselisborg treatment plant generates power as it treats sewage. Methane from anaerobic digestion of the sludge is tapped to run turbines to produce energy and heat.

Last year, the plant generated 40% more energy than it used and also sold 2.5GWh of heat to the district heating system.

Key in achieving these figures is the use of energy-efficient components and advanced process controls. Frequency converters (supplied by Danfoss Power Electronics) are used to control equipment such as blowers, pumps and mixers, enabling the plant to adapt to the considerable variation in the daily load of wastewater, and using less energy while at it.

“A wastewater treatment plant is typically energy-intensive but now, it can produce energy. In future, it will no longer be called a wastewater treatment plant but a biorefinery because it is not a pain anymore but a resource,” says Mads Warming, a director at Danfoss.

Once viewed as a waste to be disposed of, municipal wastewater (a mix of sewage and stormwater) is increasingly being seen as a resource: its organic content can be used to produce energy and heat; phosphorus can be extracted for fertiliser; and after treatment, the resulting water is usually clean enough for non-potable uses such as irrigation and general cleaning purposes.

Scientists at the Technical University of Denmark are researching into recovering resources from wastewater. One project is cultivating algae in wastewater to extract the nutrient content.

“Nitrogen and phosphorus in wastewater occur as chemical compounds. Now, we concentrate the nutrients in biological cells (in the form of algae). When you put algae on land, it will be a slow-release fertiliser. If you just put treated wastewater on land, it will run through and you lose most of the nutrients,” explains Prof Barth F Smets.

They are in the midst of getting funding for a pilot plant at the Lynetten wastewater treatment plant in Copenhagen. Another research is on using nanoparticles to purify contaminated groundwater.

Another promising research is on growing microbes responsible for wastewater cleansing, in granular form and in dense clusters. “This way, we can get 10 times more microbes per reactor volume and make the removal of nitrogen (from wastewater) more efficient and cheaper,” says Smets.

Technical University of Denmark scientist Borja Valverde Perez is researching into growing algae in wastewater to recover the nutrients found within. 

Holding back stormwater

For over 60 years, Aarhus River was covered up and a road was even built atop it. When the city council decided to develop the riverfront and also restore the old harbour into residential and recreational areas, it first had to clean up the river and sea which were polluted by sewer overflows.

This happens because of old, combined sewer systems where a single pipeline channels both rain water and wastewater to treatment plants. During heavy rains, increased stormwater overwhelms the sewerage system, causing discharges of untreated wastewater.

To resolve this, the combined sewers were replaced with a separate sewer system where rain water is not mixed with sewage, so treatment plants will not be burdened with an influx of stormwater. Excess wastewater is stored in underground retention tanks and released only when the sewer network and treatment plants have the capacity to handle it.

With extreme weather events predicted for the future and bringing with it the risk of flooding, the underground storage has become a solution for the city to adapt to climate change.

Water technology company DHI helped set up the intelligent control system of the sewerage infrastructure, in operation since 2013. A radar forecasts rainfall in different areas an hour ahead. Computers which monitor the entire wastewater system process the rainfall data, then direct the water flows, either to the treatment plant or to retention tanks.

“So we are having some kind of traffic rules for how we divert the water, how we fill the storage tanks and empty them, to avoid combined sewer overflows,” says DHI head of innovation (urban water) Anders Lynggaard-Jensen.

Also, an early warning system tells people when they cannot swim in the river or harbour because of pollution. “This is because there will always be a bigger rain, causing sewer overflows. That cannot be avoided ... we cannot build sewers big enough,” says Lynggaard-Jensen.

With the project, river and coastal water quality has improved. Retail shops and restaurants now front the river instead of backyards and eventually, artificial beaches will be created at the harbour.

A similar wastewater and drainage management system is already in place in Copenhagen. By modernising the sewage system and diverting runoffs to retention basins (one is a skating rink when not used to store water), the water quality in the harbour improved so much that a public harbour bath opened in 2002. The port area is now a vibrant cultural and recreational centre today.

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