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)