Standards for odor pollution control in municipal solid waste landfills in China: Thoughts and suggestions

Landfilling is one of the major disposal methods for municipal solid waste (MSW) in China. Odor pollution from MSW landfills has been a social issue causing considerable public complaints. Standards related to odor pollution control are important bases of the environmental law-enforcement and management, which leads the development of related technologies, and has great significance in sustainable development. Characterization of odor emissions is the basis of establishing standards for odor pollution control in MSW landfills. There have been a large number of studies on the odor emissions in MSW landfills, and several odorants have been identified as the dominant odor contributors. In China, standards related to odor pollution control in MSW landfills, such as "Standard for pollution control on municipal solid waste landfill (GB 16889-2008)", have been established. However, there are problems and challenges for the standards. Firstly, most of the existing emission standards for odorants are universal, not specific for MSW landfills, leading to the incomplete control indexes. For example, propanethiol has been identified as a dominant odor contributor in landfills, but it is not a control index in the standards. Secondly, the lack of measurement methods for odorants with low concentrations also contributes to the incompleteness of the standards. The detection limits of existing measurement methods could be higher than the odor detection thresholds (ODTs) of odorants, resulting in the underestimation of several odorants and the lack of operability in setting emission limits. Thirdly, the odor emission data of the MSW landfill boundary and stack are insufficient, and usually limited to hydrogen sulfide, ammonia, and odor concentration, which could not effectively support for establishing the emission standard for the MSW landfill. Finally, there are uncertainties in the major odor contributors in MSW landfills, due to the changes in the function of MSW landfills and the differences in the ODTs. With the promotion of zero landfilling of raw MSW, the waste compositions in MSW landfills are changing, whose influence on odor emissions is not yet clear. In addition, the ODT data are not complete in China, and the application of foreign data could result in the misidentification of the major odor contributors. To solve these problems, several suggestions are provided. It is necessary to establish or revise the standards for measuring odorants in MSW landfills, particularly the odorants with low ODTs. The accumulation of odor emission data of the MSW landfill boundary and stack should be enhanced by extending the measuring periods (before and after the final closure) and odorants (not limited to hydrogen sulfide, ammonia, and odor concentration). The ODT data, especially for the identified dominant odor contributors, are needed to be measured by Chinese panel. Moreover, it is suggested to establish a big data platform for odorants in MSW landfills. With the monitoring data uploaded to the platform and the application of artificial intelligence, odor emission characteristics, such as the dominant odor contributors, in the MSW landfill boundary and stack could be understood, providing the basis for establishing or revising odor pollution control standards. Finally, the emission standards for odorants in the MSW landfill boundary and stack could be established or revised based on the odor intensity and health risks of the identified major odor contributors.