Upstream, First of Many Treatment Plants Tackles Pollution

Three Gorges Dam is creating a reservoir that stretches from Sandouping in Hubei Province to Chongqing, approximately 630 kilometers upriver. Negative aspects include the loss of productive farmland and historical artifacts, displacement of more than 1 million people and pressure on endangered species. Many critics are equally concerned about the possible negative impacts on water quality.

As the reservoir fills, the Yangtze’s flow will slow significantly. Environmental engineers fear that water quality will decline. Some warn that unless the sluice gates work as designed, backed up silt will choke the mouths of the Yangtze’s feeder rivers in the basin. If the engineers’ sediment transport models are off, Chongqing may be looking at an extensive, expensive perpetual dredging program a few years down the road.

Another fear connected with a slower moving Yangtze is the potential for a biochemical oxygen demand buildup that would choke the life from the river. Just as the U.S. used its rivers as open sewers before the Clean Water Act was enacted, China uses its riverine networks to convey human and industrial wastes. "Eighty percent of our untreated water is discharged directly into rivers," says Suo Lisheng, vice minister of water resources.

The Chinese realize that business as usual no longer is an option as the country modernizes. Recently, the government has taken a two-pronged approach to water quality, simultaneously handing out steep fines and prison sentences to industrial polluters and also mandating an aggressive construction program of wastewater treatment plants.

There are plans to construct about 100 regional municipal plants in three stages over the next decade or so. Beijing will provide some of the funding and the remainder must come from local sources. Treatment capacity size varies from 15,000 cu m to 500,000 cu m per day. The Beijing office of U.S. multinational consultant MWH, in joint venture with locally based BODA Environmental Engineering Ltd., in 2001 won engineer-procure-construct contracts for four plants in the Three Gorges Basin.

The plants vary in size from 15,000 to 30,000 cu m. All use an oxidation ditch system, sequential batch reactors, filter-belt presses and chlorine disinfection to achieve secondary treatment.

Wan, center, inspects new plant with E-P-C team members.

The fast-tracked Zhong County plant, now in final commissioning, is designed to be a showpiece, says Wan Xu, the general manager of the regional water and sewer authority. "We will use this plant to train other operators," he says. "It is important that everything meet the highest standards."

The permitted limits for maximum biochemical oxygen demand and total suspended solids are 20 mg/l, says Zhang Chaoying, MWH operations manager. Many U.S. plants have a lower standard, with BOD and TSS limits of 30. But numbers on paper mean little without operational proof through monitoring, Zhang points out. "In the end, it’s a question of enforcement," he says. "The State Environmental Protection Agency must support the operators with a strong inspection program."

Quality engineer Xu shows off concrete column-slab underpinning.

The plant rests on seven 250-mm-thick concrete slabs cantilevered over the river and supported by 532 concrete columns. the piles typically are 800 mm in dia, says Xu Yi-Huei, a civil engineer with the quality assurance firm Chongqing Jiangxin Supervisors Co. The foundation work was labor-intensive, he says, noting that the piles were placed by hand. Using ultrasonic testing after placement, inspectors rejected two members that did not meet the specification, he adds.

The plant is designed at present to handle an average daily flow of about 8,000 cu m per day from a gravity-fed collection system serving the towns of Zhouping and Sujia. The network features 88 km of collection pipe, with a maximum diameter of 1.2 m.

The county is expanding the collection to serve a population of 120,000 and hit a goal of 74% coverage, Wan says. Hook-ups are mandatory. As the system is built out, the plant will be scaled up to handle a 30,000-cu-m-per-day flow rate, he adds.

"We hope to repeat our work all over the rest of the Three Gorges basin," Wan says.