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

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.

Recovery of phosphorus from sewage sludge ash: Influence of incineration temperature on ash mineralogy and related phosphorus and heavy metal extraction

“…Furthermore, the thermochemical calculations show that at temperatures above 800 °C, the fraction of Cu bound to ferrite decreases whereas the fraction of Cu bound in a molten slag phase increases up to 100% at temperatures above 875 °C. In contrast to the thermochemical calculations, heavy metal sequential extraction experiments for different SSA samples by Latosińska and Czapik [68], J. Li et al [64,69], Li et al [70], Pazos et al [65] and Xiao et al [66] showed only between 0.5 and 15% of total Cu bound to Fe-or Mn-oxides. In their research, they divided the heavy metal minerals into four fractions:…”

Comparison of the Possibilities of Environmental Usage of Sewage Sludge from Treatment Plants Operating with MBR and SBR Technology

“…The RAC is an indicator that takes into account the mobility of heavy metals. It analyses the contribution of the FI fraction, the most mobile fraction, to the total content of a given heavy metal [ 45 , 46 ]. The risk level is classified into five groups, which are presented in Table 5 , while the indicator itself is defined by the following formula [ 45 ]: where: F1—heavy metal content of the FI fraction, mg/kg d.m.…”

“…It takes into account the heavy metal content of soils, as for Igeo [ 40 , 42 ]. However, each metal is assigned a different toxicity level, which is defined as a toxicity factor—for Zn, 1; Cr, 2; Pb, Cu, and Ni, 5; and 30 for Cd [ 46 ]. ER is described in the following equations [ 40 , 42 ]: where:…”

Sorption of Heavy Metals by Sewage Sludge and Its Mixtures with Soil from Wastewater Treatment Plants Operating in MBR and INR Technology

“…The Igeo is used in order to assess the degree of accumulation of heavy metals. Originally, the I GAI was used for the ecological risk assessment of bottom sediments [ 32 ]. It is also used for the assessment of the contamination of soil [ 16 ], sewage sludge, and sewage sludge ash [ 32 ].…”

“…Originally, the I GAI was used for the ecological risk assessment of bottom sediments [ 32 ]. It is also used for the assessment of the contamination of soil [ 16 ], sewage sludge, and sewage sludge ash [ 32 ]. The Igeo is described in the equation [ 17 , 19 ]: where…”