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PhD: Less expensive and more sustainable purification of groundwater

Photo: COWI

​An industrial PhD undertaken in COWI aims to uncover whether electric current can break down harmful chlorinated solvents in the groundwater. This method would be a less expensive, more efficient and more sustainable alternative to the purification method used today.

​Up until the 1970s, the use of chlorinated solvents was widespread in Denmark, e.g. for cleaning of clothes and metal working. Unfortunately, control measures were not always optimal, which is why today this group of toxic – some even carcinogenic – substances poses a threat to the Danish groundwater, which is used for drinking water.

Today, contaminated groundwater is pumped from the underground to be purified, and thereby prevent the contamination from spreading into drinking-water areas. However, this method is both slow and costly.

Scheduled to start 1 February 2016, a new industrial PhD project aims to study a method that is less expensive, more sustainable and easier to implement, because it is not possible to pump water out of the ground.

PhD student with COWI's department of Waste and Contaminated Sites, Bente Højlund Hansen, explains the practical process:

"The idea is to install electrodes in the ground, letting the electric current exercise its impact on the soil layers that the groundwater flows through. This way, the current forms chemical compounds in the groundwater that are able to chemically break down chlorinated solvents, and optimise the conditions for the bacteria that break down chlorinated solvents naturally."

Numerous advantages

The PhD project will test the method in laboratories and in a pilot scale on a contaminated site that the Capital Region of Denmark provides. In the past, electric current has been used to decontaminate contaminated soil, but this will be the first pilot project to use current to purify groundwater in the proposed way.

If the method proves valid, it will offer numerous advantages:

"In a relatively simple manner, this type of purification would be able to protect the Danish groundwater resource and reduce the health risks caused by chlorinated solvents. Because it's quite easy to install the electrodes, you can carry out purification in densely populated areas and in industrial area, which often require vast volumes of clean drinking water and hold causes of contamination," says Hansen.

Hansen also expects the field study to demonstrate that the method can meet the groundwater-quality criteria for chlorinated solvents established by the Danish Environmental Protection Agency. These criteria are strict, making it cost-intensive to maintain water treatment facilities to ensure compliance.

Sustainable purification

By using electric current, the method is also expected to be more sustainable than traditional pumping, since the electrochemical system is presumed to consume fewer resources than a pump system. 
To analyse the carbon footprint of the method, the system's power consumption will be evaluated and compared to the consumption of a traditional pump system of the same size.

Demand for alternative purification method

The PhD project's findings are expected to benefit both public authorities and plot owners, who will be able to choose a less expensive and greener solution.

The idea fuelling the development of the method came from an innovation project carried out by the Capital Region of Denmark, where COWI provided technical consultancy.

"This kind of PhD project that focuses on innovation and sustainability is completely in line with how we work in COWI. We are seeing increasing demand for methods that reduce contamination from old industrial sites and landfills as part of sustainable urban development, and we are of course excited to meet this demand," says Vice President of Waste and Contaminated Sites, Torben Kristiansen.

Figures from the Capital Region of Denmark show that the region along numbers 67 facilities that it wants to replace with an efficient, inexpensive and sustainable purification method, like the one Hansen is working on. Similar demand is evident in the other Danish regions and globally, e.g. in North America.

By Molise Windfeld-Tolsøe

Published 22.01.2016

LAST UPDATED: 10.12.2016