Seasonal Variation of the Mobility and Toxicity of Metals in Beijing’s Municipal Solid Waste Incineration Fly Ash

Hang Zhao,Zhaojia Wang,Xiangfei Zeng,Rui Wang,Yang Tian,Feihua Yang,Jiancheng Shu,Mengjun Chen,Rong Wang

doi:10.3390/su13126532

Abstract

Metal mobility and toxicity of the municipal solid waste incineration (MSWI) fly ash from different seasons in Beijing were studied using leaching toxicity procedures, sequential extraction procedures, and bioavailability procedures. The X-ray diffraction results showed that MSWI fly ash contained CaSO4, CaCO3, and KCl. The Pb, Zn, and Cd contents of MSWI fly ash were high, especially during autumn, being 42, 77, and 1260 times higher than that of their soil backgrounds, respectively. Leaching toxicity experiments showed that MSWI fly ash is hazardous, since Pb exceeded the maximum threshold (5 mg/L). The main alkali metal ions and anions, heavy metals total content, leaching concentration, chemical speciation, and bioavailability varied seasonally. The Pb and Zn leaching concentrations in summer and autumn were higher than that of the other two seasons. Sequential extraction procedures indicated that Pb, Zn, and Cd showed extremely high metal mobility, i.e., the residual states of Pb and Cd in spring were 5.83% and 1.21%, respectively, and that of Zn in autumn was 10.68%. These results will help industries, governments, and the public better understand the risk of MSWI fly ash and will urge them to pay more attention to preventing harm to the ecosystem and human beings.

Highlights

Incineration has been applied for the disposal of municipal solid waste (MSW) for more than 100 years [1]
About 4.1 million tons of MSW are incinerated each year in China, leading to a large quantity of municipal solid waste incineration (MSWI) fly ash [2]
The high CaO content is caused by the excessive lime slurry that was injected to reduce the emission of acidic gases (SO2 and HCl) [30]

Summary

Introduction

Incineration has been applied for the disposal of municipal solid waste (MSW) for more than 100 years [1]. About 4.1 million tons of MSW are incinerated each year in China, leading to a large quantity of municipal solid waste incineration (MSWI) fly ash [2]. MSWI fly ash contains high levels of heavy metals (HMs) such as Zn, Pb, Cu, Cd, Cr, and Ni [3,4,5]. Their content and leaching concentration are regulated by a set of standards [6,7]. Separation/extraction [7], solidification/stabilization [4], and heat treatment [5,6]

Methods

Results

Conclusion