Immobilization of Heavy Metals in Sewage Sludge during Land Application Process in China: A Review

Abstract

Abstract:The safe disposal of sewage sludge during the process of municipal wastewater treatment has become one of the major concerns of increased production. Land application was thought of as a more economical method for sewage sludge disposal than landfill and incineration. However, the presence of heavy metals in sewage sludge restricted the use of land application. The environmental risk of heavy metals was dependent on their contents, chemical speciations, and soil characteristics. Composting and chemical immobilization were the commonly used methods to immobilize the heavy metals in sewage sludge. The immobilization mechanism and speciation transformation of heavy metals during the composting process were presented. Aluminosilicate, phosphorus-bearing materials, basic compounds, and sulfides were reviewed as the commonly used chemical immobilizing agents. The problems that occur during the immobilization process were also discussed. The combination of different methods and the modification of chemical immobilizing agents both improved the fixation effect on heavy metals.

Digestion Procedure and Determination of Heavy Metals in Sewage Sludge—An Analytical Problem

“…The pH of raw sludge was 5.3-5.7 and this range is consistent with the literature data [31]. One of the most commonly used methods of stabilizing sludge is the addition of lime [1,4]. Calcium oxide also promotes the immobilization of many heavy metals in the sludge.…”

“…In the stabilized sludge, the correlation coefficients are high or moderate and amount to R = +0.945 (Cu/Zn), R = +0.879 (Pb/Ni), R = +0.872 (Pb/Cd), R = +0.677 (Ni/Cd), R = −0.768 (Cd/Cu), R = −0.762 (Pb/Cu), R = −0.754 (Cd/Zn) R = −0.657 (Pb/Zn), R = −0.606 (Ni/Cu), R = −0.547 (Ni/Zn). Higher correlations in stabilized sludge are due to complex processes occurring in the sludge, e.g., gradual decomposition of the organic matrix, sorption of metal cations from the environment by an alkaline sludge or leaching of easily soluble metal compounds with organic substances [1,4]. The negative correlation between metals may be explained by their origin from multiple sources (e.g., commercial, micro-industrial units, domestic) and greater variation in the pollution load [27,43].…”

“…Sludge management includes the following methods e.g., landfilling, thermal processes, application to agricultural land, composting, wasteland reclamation and silviculture, use in the construction industry or recovery of rare earth metals [1,[4][5][6][7][8][9][10]. In 2014, total sewage sludge generated in Poland from industrial and municipal wastewater treatment plants was 967.4 thous.…”

Leaching Characteristics of Heavy Metals and Plant Nutrients in the Sewage Sludge Immobilized by Composite Phosphorus-Bearing Materials

“…Many kinds of chemical passivating agents have been used to immobilize heavy metals in sewage sludge and reduce the environmental risk of its land application [23]. The commonly used additives include basic compounds [24], aluminosilicates [25][26][27], phosphorus-bearing materials [28,29], and sulfides [30].…”

The Prospective Approach for the Reduction of Fluoride Ions Mobility in Industrial Waste by Creating Products of Commercial Value

“…According to literature [12,[19][20][21][22][23][24], the content of toxic ions can be reduced in two ways: by removing them from waste or by reducing their mobility in the environment-immobilization.…”