Cpr 411

The dry (DM) and organic matter (OM) were analyzed according to Polish Standards (PN-EN 12880:2004 and PN-EN 12879:2004) [36 ,37 ]. The pH and potential redox (Eh) of the sewage sludge were measured using a multifunctional meter, CPR-411 (Elmetron), equipped with two electrodes, IJ44A and ERS-2 (Elmetron), respectively. Sample analysis involved determination of the total concentrations and chemical forms of the selected heavy metals (Cd, Cr, Cu, Ni, Pb, Zn and Hg) in the sewage sludge, collected at two stages of its processing line (S1 and S2). The total heavy metal concentrations in the obtained samples and extracts were determined using inductively coupled plasma optical spectrometry (Avio 200 ICP-OES, PerkinElmer Inc., Waltham, MA, USA). Mercury was assayed with cold vapor atomic absorption spectrometry (CV-AAS). The limits of quantifications (LOQs) were 0.015, 0.019, 0.025, 0.020, 0.027, 0.024 and 0.0005 mg·L⁻¹ for Cd, Cr, Cu, Ni, Pb, Zn and Hg, respectively. All measurements were performed in triplicate.

The pH and Eh of sewage sludge were measured using a multifunctional meter CPR-411 (Elmetron) and electrodes as in order: IJ44A (Elmetron) and ERS-2 (Elmetron). The content of DM and OM in sewage sludge was determined after drying at 105 °C and then ignition at 550 °C, according to Polish Standards, i.e., characteristics of sewage sludge, determination of dry residue and water content (PN-EN 12880:2004) [36 ] and characteristics of sewage sludge, determination of loss on ignition of dry matter (PN-EN 12879:2004) [37 ].