One of the best-known examples of industrial ecology can be found in Kalundborg, a small industrial zone 120km west of Copenhagen in Denmark. Over time, this unplanned industrial park has evolved from a single power station into a cluster of companies that rely on each other for material inputs.

The project began in 1972 and by 1994, 16 contracts had been negotiated. The extent of the material and energy exchanges in 1995 was about 3 million tonnes a year. Estimated savings totalled  US $10 million a year, giving an average pay-back time of six years.

The core participants are:

• Asnaes, Denmark's largest coal-fired power station;
• An oil refinery owned by Statoil;
• A pharmaceuticals plant owned by Novo Nordisk;
• Gyproc, Scandinavia's largest plasterboard manufacturer;
• The municipality of Kalundborg, which distributes water, electricity and district heating to around 20,000 people.

The symbiosis has grown over the years to include partners from other districts, as well as farmers.

How does it work?

The participants exchange materials and energy for mutual benefit, on the basis that by-products from one business can be used as low-cost inputs by the others.

For example, treated wastewater from the Statoil Refinery is used as cooling water by the Asnaes power station. Meanwhile Statoil and Novo Nordisk purchase 'waste' process steam from the power station for their operations. Surplus heat from the power station is used for warming homes in the surrounding area, as well as in a local fish farm.

The power station produces other valuable by-products including 170,000 tonnes a year of fly ash, which is used in cement manufacturing and roadbuilding. The wallboard company, Gyproc, uses the power plant's fly ash to obtain gypsum, a by-product of the chemical desulphurization of flue gases. Gyproc purchases about 80,000 metric tons of this material each year, meeting almost two-thirds of its requirement.

Surplus gas from the Statoil refinery, which used to be flared off, is now delivered to the power station and to Gyproc as a low-cost energy source. Local farmers, meanwhile, make use of Novo Nordisk's by-products as fertilizers. Industrial enzymes and insulin are created through a process of fermentation, the residue from which is rich in nutrients. After lime and heat treatment, it makes an excellent fertilizer. Some 1.5 million cubic metres a year are delivered to local farmers, free of charge.

Benefits

Originally, the motivation behind the clustering of industries at Kalundborg was to reduce costs by seeking income-producing applications for unwanted by-products. Gradually, though, industry managers and local residents realized that they were generating environmental benefits as well.

This project has enabled its participants to achieve substantial cost savings and to improve their resource efficiency. Gyproc has recorded a 90-95% saving in oil consumption after switching to gas supplied by the adjacent refinery.

In addition to these reductions, the use of the excess heat from Asnaes for household heating has eliminated the need for about 3,500 oil-burning domestic heating systems.