Recycling experts have voiced concerns over a rising number of demolition and construction projects in China's big cities, which they say is creating a growing volume of waste and is an urgent issue.

According to a Beijing municipal government plan, the city will demolish a total area of more than 40 square kilometers of illegal constructions this year, to improve the cityscape and increase space for green development.

With the relocation of noncapital functions, such as wholesale markets, to areas outside of the city and the growing trend of demolition to continue in the coming years, more construction waste will be created, according to Li Shuo, deputy general-manager of BCEG Resources Recycling Co, a State-owned company part of Beijing Construction Engineering Group.

He said during the 12th China Circular Economy Development Summit in Beijing last month that dealing with a growing volume of waste is an urgent issue, adding that dumping waste in natural environments is unacceptable.

According to data from the Ministry of Housing and Urban-Rural Development, the volume of overall construction waste in China reached 3.5 billion metric tons last year.

As cities such as Beijing and Shanghai upgrade their functions and address "big-city diseases", the waste produced by construction and demolition projects is expected to grow.

Li said Shanghai will pull down 50 sq km of buildings this year.

"In some second-tier cities, such as Zhengzhou in Henan province and Xi'an in Shaanxi province, the quantity of existing demolition waste is already huge, which brings both challenges and opportunities to companies in the recycling industry," he said.

Li's company analyzes the composition of the building waste and conducts different treatment of the waste accordingly.

"Through a series of tests, we have proved that our techniques for the treatment of demolition waste are better than natural lime soil in terms of being used for refilling," Li said.

"During large-scale demolition work, we transform construction waste into resources for refilling, which helps save energy on transporting materials and also protects the environment."

Li said the company has two such projects. One is in the Sunhe area in Beijing's northeastern Chaoyang district, and the other is in Tongzhou.

In addition to construction waste, domestic waste is also a big challenge for cities.

Pan Yonggang, vice-president of the China National Resource Recycling Association, said the recycling industry has seen a decline in profits due to global economic uncertainties in the past three years.

"Many companies and individuals have given up on the industry, which has resulted in the soaring levels of waste, because there are not enough people to collect the waste and recycle it," he said.

According to Pan, the number of people involved in China's recycling industry has fallen from 18 million at its peak to the current 12 million.

To address the problem, Beijing is working on deepening coordination between the recycling and environmental sanitation sectors, he added.