The urban environment is based on the use of pyrolysis technology to safely treat printing and dyeing sludge.

With the rapid progress of industrialization, the amount of printing and dyeing sludge is increasing year by year. According to the China Environmental Statistics Yearbook, the production of printing and dyeing sludge in China was 4.65 million tons in 2016. Printing and dyeing sludge is very complex, rich in polycyclic aromatic hydrocarbons, heavy metals, surfactants, dyes, solvents, detergents and other compounds. Among them, nitro and amino compounds and heavy metal elements in dyes are hazardous wastes and have strong biological toxicity. Therefore, once the printing and dyeing sludge is improperly handled, it will cause serious damage to the ecological environment and human health. At present, the treatment and disposal of printing and dyeing sludge at home and abroad mainly draws on the treatment and disposal methods of municipal sludge (land use, landfill and incineration). These treatment and disposal methods have their own shortcomings, and it is easy to cause secondary pollution. It can be seen that there is still a lack of safe and reliable printing and dyeing sludge treatment and disposal technology.

The Research Institute of Clean Energy Technology and Carbon Materials of the Institute of Urban Environment of the Chinese Academy of Sciences (Wang Yin team) has developed a printing and dyeing project based on the complex and high-toxicity of printing and dyeing sludge and high pollutant content. The study on migration and transformation of heavy metals and chemical morphological transformation during sludge pyrolysis process clarified the migration and transformation of heavy metals and the mechanism of chemical morphological transformation in printing and dyeing sludge. The study found that printing and dyeing sludge pyrolysis technology can cause most heavy metals to change from unstable bioavailable state to stable residual state. Heavy metals enriched in biochar are mainly solidified in biochar matrix, resulting in printing and dyeing sludge. The environmental risk of biochar is greatly reduced. In addition, as the pyrolysis temperature increases, the quality of the prepared printing and dyeing sludge biochar is also significantly improved. The research results provide a theoretical basis for the recycling and harmless disposal of printing and dyeing sludge, and also provide some reference for the subsequent safety application of the dyed sludge biochar.

The research results are published on Ecotoxicology and environmental safety under the topic of Effect of pyrolysis temperature on characteristics, chemical speciation and risk evaluation of heavy metals in biochar derived from textile dyeing sludge. The research was supported by the Sino-Japanese International Science and Technology Innovation Cooperation Key Project (2016YFE0118000), the National Natural Science Foundation of China (41373092), the Tianjin Key R&D Program (16YFXTSF00420), and the Chinese Academy of Sciences Young Talents Frontier Key Project (IUEQN201501).