After years of trying to improve wastewater treatment systems, urban governments are now facing a new challenge: what to do with the tons of sewage sludge the process creates.

According to figures from the Ministry of Environmental Protection, by 2010, 60 percent of all urban wastewater will be treated, which will in turn generate about 30 million tons of sludge every year.

"When it comes to treating sewage sludge, China is plagued by weak monitoring and backward technology," said Zhao Yingmin, head of the ministry's department of science, technology and standards.

"Compared with the high levels of government investment in wastewater treatment, spending on ways to deal with sludge is much lower," he said.

The ministry, in conjunction with the Beijing Environmental Protection Institute, is currently working on a sludge treatment regulation, Zhao said, without giving a timescale.

Sewage sludge is an inevitable byproduct of the wastewater treatment process, but if left untreated can become a toxic hazard, Fu Tao, director of the water policy research center of Tsinghua University, said.

"Most sewage sludge is not properly treated but rather dumped into rivers or just left to pile up, which can cause secondary pollution," he said.

It is a real threat to both the environment and people, as it usually contains heavy metals, viruses and bacteria, he said.

Sometimes, the sludge is used as landfill, is incinerated or turned into agricultural compost, but none of these methods is ideal, Fu said.

Using sludge for landfill is expensive, as it first has to be treated to remove the heavy metals and other toxic elements.

Also, incineration and composting require huge technological support, and no one wants to pay for it, he said.

In Shandong, however, the local government is hoping to cash in on sewage sludge.

In June, the province opened its first sludge-fuelled biogas plant, which is forecast to generate more than 5 million kWh of electricity per year and save the government about 4 million yuan ($585,000) annually.

Questions:

1. By 2010 it is estimated that how much urban wastewater will be treated?

2. Zhao Yingmin says China is plagued by what?

3. Though not ideal, sewage sludge can be used for what?

Answers:

1. 60 per cent.

2. Weak monitoring and backward technology.

3. Landfill or turned into agricultural compost.