Abstract
In Poland, the amount of municipal sewage sludge that contains both organic and inorganic pollutants increases steadily. As a result of penetration of atmospheric precipitations through sludge layers, products of biochemical decomposition of organic matter and soluble mineral compounds are washed away and form contaminated leachates (Arain, J. Hazard. Mater. 154:998–1006, 2008; Fang, J. Hazard. Mater. 310:1–10, 2016; Ignatowicz, Environ. Res. 156:19–22, 2017). Metals contained in these leachates may be particularly burdensome and dangerous, which is due to the toxic nature that disturbs the natural biological balance (Fytili and Zabaniotou, Renew. Sust. Energy Rev. 12 (1): 116–140, 2008). In order to check bio-availability of metals in sewage sludge and find out resulting risks to the environment and human health, apart from the determination of total metal content, speciation analysis is often used. It makes possible a quantitative determination of various chemical forms of metals which are bound in the sewage sludge and finding which of them poses the greatest threat to the environment (Amir, Chemosphere 59:801–810, 2005; Ciba, Waste Manage. 23:897–905, 2003; Hei, Procedia Environ Sci 31:232–240, 2016; Liu, Chemosphere 67(5):1025–1032, 2007).The degree of immobilization of selected metals in sewage sludge has been determined using one of the sequential extraction methods designed to identify groups of compounds with which the metal is bound. Such a method is the Tessier procedure (Janas, Pol J Environ Stud 26(5A):37–41, 2017). Results of this research were used to assess the threat resulting from the increase in the amount of sewage sludge; the management of which is subject to constant restrictions (storage of sewage sludge has been prohibited since January 1, 2016).As a result of the conducted research, it was found that metals in sewage sludge, which undergo various transformations, are very difficult to immobilize. The addition of calcium oxide and an agent supporting the composting process to the sludge does not affect radically the increase of leaching of the analyzed elements from the sludge.Graphical abstractThe schema of proceedings in leaching of heavy metals from sewage sludge after various modifications.
Highlights
Metals toxicity present in the environment attracts the interest of many researchers
It is important to determine the amount of metals bound with the individual components of sewage sludge
Such an assessment can be based on the sequential extraction method (Cai et al 2007; Fuentes et al 2008; Lasheen and Ammar 2009; Zhu et al 2011)
Summary
Metals toxicity present in the environment attracts the interest of many researchers. After exceeding the permissible content in the ground, metals reduce soil fertility and inhibit the enzymatic activity of plants growing on it (Arain et al 2008; Ignatowicz 2017; Lasheen and Ammar 2009). In order to determine the behavior of metals under environmental conditions and their impact on organisms living in a given ecosystem, in addition to determining their total content, their leaching rate should be assessed Such an assessment can be made by determining the amount of metals bound by individual components (fractions) of sewage sludge. The subject of the research was sewage sludge in which the mobility of metals was determined and the influence of sludge composting with the addition of calcium oxide and a commercial preparation supporting the process on the degree of leaching of metals was investigated. Dewatered sludge after composting with the addition of 30-g CaO and 3-g agent supporting the process
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