Leachability of heavy metals from lightweight aggregates made with sewage sludge and municipal solid waste incineration fly ash.

Na Wei

doi:10.3390/ijerph120504992

Abstract

Lightweight aggregate (LWA) production with sewage sludge and municipal solid waste incineration (MSWI) fly ash is an effective approach for waste disposal. This study investigated the stability of heavy metals in LWA made from sewage sludge and MSWI fly ash. Leaching tests were conducted to find out the effects of MSWI fly ash/sewage sludge (MSWI FA/SS) ratio, sintering temperature and sintering time. It was found that with the increase of MSWI FA/SS ratio, leaching rates of all heavy metals firstly decreased and then increased, indicating the optimal ratio of MSWI fly ash/sewage sludge was 2:8. With the increase of sintering temperature and sintering time, the heavy metal solidifying efficiencies were strongly enhanced by crystallization and chemical incorporations within the aluminosilicate or silicate frameworks during the sintering process. However, taking cost-savings and lower energy consumption into account, 1100 °C and 8 min were selected as the optimal parameters for LWA sample- containing sludge production. Furthermore, heavy metal leaching concentrations under these optimal LWA production parameters were found to be in the range of China’s regulatory requirements. It is concluded that heavy metals can be properly stabilized in LWA samples containing sludge and cannot be easily released into the environment again to cause secondary pollution.

Highlights

Increasing generation of hazardous wastes is one of the main environmental problems in most countries in the world [1,2]
The main purpose of the present work is to investigate the influence of municipal solid waste incineration (MSWI) fly ash/sewage sludge (MSWI FA/SS) ratio, sintering temperatures and sintering times on the leaching characteristics of Lightweight aggregate (LWA) samples made with sewage sludge and MSWI fly ash, and to find optimal LWA production parameters
With the MSWI fly ash content increasing from 0% to 40%, the leaching rate of Cu decreased from 84% to 8% and increased to 34%

Summary

Introduction

Increasing generation of hazardous wastes is one of the main environmental problems in most countries in the world [1,2]. Most sewage sludges contain various heavy metals such as. In China, due to the rapid growth of wastewater output, sewage sludge, as an inevitable by-product of the treatment process of wastewater, is increasing very fast [3,4]. Sludge is often disposed of in open fields because of the shortage of appropriate disposal facilities, resulting in serious problems because of heavy metals leaching into groundwaters, surface waters and soils. The output of municipal solid waste incineration (MSWI) fly ash has been over 300,000 tons per year in China and is increasing year by year [5,6]. Various methods for removing or stabilizing heavy metals in sewage sludge and MSWI fly ash have been studied to minimize potential risks to human health and the environment. Heavy metal concentrations in sewage sludge can be reduced by chemical extraction [9], bioleaching [10], supercritical water technology [11]

Objectives

Methods

Results

Conclusion