The Ecological Risk Assessment and the Chemical Speciation of Heavy Metals in Ash after the Incineration of Municipal Sewage Sludge

Jolanta Latosińska,Przemysław Czapik

doi:10.3390/su12166517

Abstract

Popular incineration of sewage sludge results in the increase in heavy metals content in ash. The knowledge of the total content of heavy metals in sewage sludge ash does not demonstrate a potential hazard. The toxicity of heavy metals in great measure depends on the form of their occurrence. The prevailing norms do not require the ecological risk assessment of the environmental burden with heavy metals for the choice of the method of the utilization of sewage sludge ash. The paper presents the research results on the mobility of heavy metals in sewage sludge ash after its incineration. The geo-accumulation index (IGAI), the potential ecological risk index (PERI) and the risk assessment code (RAC) were used for the evaluation of the potential soil contamination with heavy metals. The authors also suggested a new formula, which took into consideration more factors influencing the risk of the contamination of a water-soil environment with heavy metals—the water and soil environment risk index (WSERI). The calculated indices for sewage sludge ash indicate the risk of soil contamination with heavy metals.

Highlights

One of the applied methods of municipal sewage sludge neutralization is a thermal treatment
The thermal treatment can be realized with the use of pyrolysis, gasification or incineration [1,2,3,4,5]
The phase composition of sewage sludge ash was determined with the Debye-Scherrer-Hull X-ray powder diffraction

Summary

Introduction

One of the applied methods of municipal sewage sludge neutralization is a thermal treatment. The incineration of sewage sludge, apart from the obvious advantages such as, among others, the application regardless of the sanitary characteristics of sludge and the possibility to recover phosphorous [11,12,13], causes an increase in the concentration of heavy metals in ash [14]. Apart from the initial concentration in sludge and the temperature of the incineration, the concentration of heavy metals in ash after the incineration of sludge is influenced by the volatility of heavy metals. The most volatile metals are mercury, cadmium and lead. Chrome and nickel are considered non-volatile metals [15]. 78–98% of cadmium, chrome, copper, nickel, lead and zinc present in sewage sludge remain in ash. 98% of mercury is removed together with the fumes [16]

Objectives

Methods

Results