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

Abstract

Huge amounts of sewage sludge produced globally is a substantial environmental threat and require rational handling. Application in agriculture is an economical and relatively simple method of sludge management, however, it is associated with restrictions regarding metals content. According to EU regulations, the total amounts of Cd, Cu, Cr, Pb, Ni, and Zn have to be analyzed by the AAS technique requiring effective destruction of the organic matrix. Currently used methods of sewage sludge digestion may be biased when applied without optimization. The aim of the presented work was to evaluate the efficiency of the organic substances destruction in either raw or stabilized sludge. Three mineralization procedures were evaluated, namely: (A)—drying and microwave digestion; (B)—ignition and microwave digestion; (C)—drying and conventional digestion. For matrix destruction, a mixture of concentrated HNO3 and HCl (3:1 v/v) was used. Metals were determined by flame atomic absorption spectrometry (FAAS). No limits of metal concentration were overdrawn. Generally, the method (B) was the most effective. Results obtained for Cu, Cd, and Zn after digestion by method (A) and (B) were comparable. Methods (B) and (C) yield complete decomposition of the matrix. As result, the precision of measurement substantially increases.

Effects of Food Industry Wastewater Treatment Sludge on Corn Plant Development and Soil Properties

“…In the case of limed treatment sludge, reaction (pH), electrical conductivity (EC) [17,18], and sludge organic matter content was determined by ashing at 550ºC [19]. Total N according to Kjeldahl method; ammonia (NH 4 -N) [19]; nitrate (NO 3 -N) [20]; total P, K, Na, Mg and Ca; and heavy metals (Pb, Cd, Cr, Ni, Cu, Zn, Fe, and Mn) in the solution obtained by wet digestion with HNO 3 in a microwave oven were determined by Perkin Elmer Optima 2100 DV ICP [21]. According to Table 1, the concentrations of heavy metals in this particular sludge are below the limits imposed by the European and National guidelines for the agricultural utilization of sludge (except for Zn).…”

Identification of the Chemical Forms of Heavy Metals in Municipal Sewage Sludge as a Critical Element of Ecological Risk Assessment in Terms of Its Agricultural or Natural Use

“…For many years, an increase in the amount of sewage sludge generated in municipal Wastewater Treatment Plants (WWTPs) has been observed. The main reason for this phenomenon is population growth and the increasing effectiveness of biological wastewater treatment processes used in WWTPs [ 1 , 2 ]. The disposal of sewage sludge is nowadays one of the most important issues in wastewater management, in the majority of European countries.…”

“…For these reasons, it has been successfully used in Poland and all over the world [ 9 , 11 ]. Moreover, sewage sludge contains organic matter and other substances needed by plants for growth, e.g., nitrogen, phosphorus, potassium, calcium and magnesium [ 1 , 11 , 12 , 13 , 14 , 15 ], and thus it is successfully used in agriculture as fertilizer or a regenerator for soil [ 11 , 16 ]. Unfortunately, as being the final waste material of wastewater treatment, sewage sludge also contains pathogens, poorly biodegradable organic compounds as well as heavy metals (including those toxic), etc.…”

“…Unfortunately, as being the final waste material of wastewater treatment, sewage sludge also contains pathogens, poorly biodegradable organic compounds as well as heavy metals (including those toxic), etc. Among the above-mentioned hazard factors, the content of heavy metals constitutes one of the greatest restrictions on use of sludge for agricultural or natural purposes [ 1 , 4 , 16 , 17 ]. Heavy metals in the sewage sludge originate from domestic and industrial wastewater, surface runoff, corrosion of sewerage system, pharmaceuticals, body care and cleaning products, as well as from illegal discharges, etc.…”

“…It is commonly known that knowledge of the total concentrations of heavy metals in sewage sludge allows only for an evaluation of their pollution degree, but is not conclusive, with potential ecological risk that these elements may pose to the environment and living organisms, including humans [ 2 ]. This is due to the fact that the mobility, bioavailability and toxicity of these elements depend on their speciation forms, which are influenced by their leaching and interactions with different components of the natural environment [ 1 , 2 , 14 , 22 , 23 ]. One of the most popular methods for determination of the chemical forms of heavy metals in environmental samples (sediments, soils and sewage sludge), is the three-step chemical sequential extraction procedure, proposed by the Community Bureau of Reference (BCR), now the Standards, Measurements and Testing Programme [ 24 , 25 ].…”