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A project has been launched to lay down China's biggest man-made wetland to be used for sewage treatment. Located in Bao'an District of Shenzhen in south China's Guangdong Province, the initiative represents a bid to more effectively protect the water quality in Shiyanhe reservoir which supplies the city. The project will be rolled out in two phases.

The first phase is expected to become operational in May of this year. It will cover an area of 30,000 square meters and require an investment of 8 million yuan (nearly US$1 million). It can be expected to process a daily throughput of 15,000 tons.

The second and larger phase will cover 60,000 square meters and have a capacity of 45,000 tons a day. Here the investment will be some 30 million yuan (US$3.6 million).

In the old days, human waste was widely used to fertilize the fields but it has now become a main source of environmental pollution.

"The project uses water purification technology involving a concentrated vertical flow and is specially adapted for use in an artificial wetland system," said Lei Zhihong, a senior engineer from the Shenzhen Environmental Sciences Institute and chief project designer.

As the water borne sewage percolates through the wetland, potentially harmful pollutant and nutritive elements are absorbed or broken down. The treatment process is facilitated by carefully selected and propagated wetland plant species.

The quality of treated water can match surface water "level III" standards and pollutant disposal rates exceeding 90 percent are attainable.

Compared with city based sewage treatment plants, which depend on regular biochemical technology, the man-made wetland solution offers cost benefits arising from such gains as lower transport expenses.

For example, a traditional treatment plant with a daily disposal capacity of 15,000 tons might typically requires a capital investment of 1.5 million yuan (a little over US$180,000). It would have operating costs of some 0.70-0.90 yuan (US$0.08-0.10) per ton.

In comparison the first phase of the Shiyanhe wetland project can deliver the same capacity for an investment of only eight million yuan (nearly US$1 million) and operating costs of just 0.15 yuan (US$0.02) per ton. However on the downside, the wetland project will occupy a comparatively large area, twice that of an urban sewage disposal plant of traditional design and similar capacity.

But the Shiyanhe artificial wetland will be more than just another sewage disposal facility. It will also be somewhere people can go to enjoy a broad expanse of land planted up with flowers and greenery.

(China.org.cn by Zhang Tingting, January 30, 2003)