Effects of Biochar-Derived Sewage Sludge on Heavy Metal Adsorption and Immobilization in Soils

Abstract

The object of this study was to evaluate the effect of sewage sludge biochar on adsorption and mobility of Cr, Mn, Cu, and Zn. Biochar (BC400) was produced via pyrolysis of municipal sewage sludge at 400 °C. Maximum adsorption capacities (qm) for Zn, Cr, Mn, and Cu were 5.905, 5.724, 5.681, and 5.342 mg·g−1, respectively, in the mono-metal solution and 2.475, 8.204, 1.01, and 5.415 mg·g−1, respectively, in the multi-metal solution. The adsorption capacities for Mn, Cu, and Zn decreased in the multi-metal solution due to competitive adsorption, whereas the capacity for Cr increased. Surface precipitation is an important mechanism in the sorption of these metals on BC400. The 360-day incubation experiment showed that BC400 application reduced metal mobility in contaminated soils, which was attributed to the substantial decreases in the acid-soluble fractions of Cr, Mn, Cu, and Zn (72.20%, 70.38%, 50.43%, and 29.78%, respectively). Furthermore, the leaching experiment using simulated acid rain indicated that the addition of BC400 enhanced the acid buffer capacity of contaminated soil, and the concentration of Cr, Mn, Cu, and Zn in the leachate was lower than in untreated soil. Overall, this study indicates that sewage sludge biochar application reduces the mobility of heavy metal in co-contaminated soil, and this adsorption experiment is suitable for the evaluation of biochar properties for remediation.

Sewage sludge biochars management—Ecotoxicity, mobility of heavy metals, and soil microbial biomass

“…Change in the soil Cmic reflects the processes of microbial growth and decomposition of organic matter; consequently, the simultaneous evaluation of not only biomass but also respiratory activity of microorganisms is advisable [12,17]. Micropores and mesopores could store water and dissolved substances that are needed for microbial metabolism [5,41]. Biochar macropores probably represent most of the protected microbial habitats because they are the right size to accommodate bacteria.…”

“…The amount of sewage sludge produced in Europe is slightly more than 10 million tons per year, and it is estimated that by 2020 this will increase to 13 million tons [1]. The choice of method of sewage sludge disposal is determined mainly by its quality and, in particular, the presence of pathogenic organisms and chemical contaminants posing a threat to the environment [3][4][5]. The choice of method of sewage sludge disposal is determined mainly by its quality and, in particular, the presence of pathogenic organisms and chemical contaminants posing a threat to the environment [3][4][5].…”

“…Second, liquid and gaseous products of the pyrolysis process can constitute an alternative energy source, and its solid product (biochar) is a rich source of stable carbon and nutrients for plants [7,8]. Some scientific reports describe the impact of sewage sludge biochar on the chemical properties of soil [5,11], and others describe changes in biological parameters after the application of such material [12,13]. Some scientific reports describe the impact of sewage sludge biochar on the chemical properties of soil [5,11], and others describe changes in biological parameters after the application of such material [12,13].…”

“…Directions for sewage sludge management in Europe usually depend on an indicator of economic development of the country in question [2]. The choice of method of sewage sludge disposal is determined mainly by its quality and, in particular, the presence of pathogenic organisms and chemical contaminants posing a threat to the environment [3][4][5]. Sewage sludge contains a great deal of organic matter and nutrients, which argues in favor of its reuse.…”

“…Most of studies on sewage sludge pyrolysis published so far focus on energy recovery and fuel quality [9], the effect of sewage sludge pyrolysis on the quality of the resulting biochar [10], or the application of sewage sludge biochar as a contaminant absorbent [9]. Some scientific reports describe the impact of sewage sludge biochar on the chemical properties of soil [5,11], and others describe changes in biological parameters after the application of such material [12,13].…”