What is a sustainable city?

Hammarby Sjostad in Stockholm, Sweden, is one of the city's major urban development projects, an environmentally friendly, sustainable city for a new age. Originally intended as the site of the 2004 Summer Olympics, the area is based around Lake Hammarby Sjo and draws much of its inspiration from the water.

Integrated planning -- the introduction of a new concept

The aim is to create a natural cycle in which waste water is treated and reused or discharged into the lake. Solid waste is used for heating and producing biogas while solar energy is used for offices and hotels. Public transport is preferred over private cars and everything is easily accessible. There is a wetland close to the city to promote oxygen and wildlife, which all helps to create a good picture of the city.

"This approach to handling energy, waste and water is called the Hammarby Model," says Mr Freudenthal. "It's the water that inspired the inception of the whole project."

The original plan was conceived in 1990. The goal is for 30,000 people to live and work in the city while a total of 10 thousand residential units will be built. Today, almost 10 thousand people live in the area. The sustainable city will be completed by 2015.

Implementation--innovative solutions and new technology

This is a showcase project for technical solutions developed cooperatively by Project Hammarby Sjostad, Stockholm Water, the Department of Sanitation and energy company Fortum.

"From day one, the city has imposed tough environmental requirements on buildings, infrastructure and traffic," said Freudenthal. To achieve these goals, integrated planning, innovative solutions and new technology were necessary.

First they cleared up the old industrial garbage so that the soil met environmental requirements. They then decided that all construction materials should be environmentally friendly ЁC neither copper nor PVC is used. To transport construction materials, they made careful calculations and built a logistics center to ensure traffic will not be blocked or interrupted by construction. Although this increased the cost of the project by approximately 3 percent, they also calculated that if they did not do this, waste for the whole project would be approximately 6 percent.

Coming out of the information office in GlashusEtt, there is a row of cars parked out front.

"This is the car pool," explained Freudenthal.

Approximately one third of the town's residents are members of the car pool. They can book a place in advance on the internet. Most people use the car pool to shop in the supermarket over the weekend. Usually two or three people share a car to go shopping. There is also the option of the tram, which is specially built for the people here to go to work in the Stockholm center which is about 15 to 20 minutes away by all means of transport. Water taxies are also ready among the many private boats on the lake. The water taxi is free between the city and the subway stop Slussen, a transfer stop near the center. There are also several buses coming through the city.

There are also cleverly designed water channels in front of each building. These channels collect rainwater from houses and gardens where it is directed into the lake. Rainwater from the streets is also collected and purified by sand filters or in artificially established wetlands in the area and then released into the lake. This way, the burden on the waste water treatment plant is reduced and rainwater pollution is avoided.

The main footpath, the carefully preserved oak forest, the green surfaces and all the other trees that have been planted help to collect rain water locally before it drains into the sewage system. The vegetation also ensures cleaner air and provides a counterbalance to the dense urban landscape. The stonecrop or sedum plants covering the roofs of buildings are not just an attractive detail. The plants also absorb rain water that would otherwise drain into the sewers.

For convenience, road lights were installed underground, while on the top of the poles, a special material is used to reflect the light. The light energy of the sun is harnessed and transformed into electrical energy in solar cells. The energy from a single solar cell module covering one square meter provides around 100 kilowatts an hour per year, which is equivalent to the household energy needed for three square meters of housing. Freudenthal said scientists calculated that two days of sunshine would be sufficient to supply the earth with energy for a year. The question is how to store such energy.

Solar panels also absorb the sun's warmth which is then used to heat water. The solar panels generate sufficient energy to meet half the building's annual hot water requirements.

From waste to energy

Biogas is a byproduct produced in the waste water treatment plant from the digestion of organic waste or sludge from the waste water. The waste water from a single household produces enough biogas for the household's gas cooker. Most of the biogas is currently used as fuel in eco-friendly cars and buses. The heaviest and bulkiest waste fractions are sorted and collected via an underground waste collection system. The waste is sucked through pipes into a central room, one fraction at a time. The containers are collected from the room by refuse collection lorries, thereby reducing vehicle traffic in the area.

Of course all the necessary facilities such as kindergartens, schools and clinics are in the area. The city is also friendly to the physically impaired, with ramps and easy access for wheelchairs. In winter, locals can go skiing on the nearby hills.

"The Hammarby Sjostad Model shows the environmental impact of urbanization and normal houses or apartments can be halved," Freudenthal said. "The most important idea is that the entire plan is integrated ЁC everything is built into the one system so that people can take advantage of it immediately. This is also a way to balance money, environment and happiness."

Glashouse. Sjostaden's environmental information center disseminates knowledge via study trips, exhibitions and demonstrations of new environmental technology, including fuel cells and the building's double-glazed facade. The center can organize a trip almost every day if it is booked in advance.

By Chen Xuefei, People's Daily Online correspondent in Stockholm.