Physical, chemical and spectroscopic analysis of sludge from sewage treatment plant of Mila. Algeria for its valorization

Our study focuses on the characterization of sludge from the sewage treatment plant located in Mila (Algeria) for the target to use it as fertilizer in agriculture or as a useful material for manufacturing cement and refractory materials. The reuse of sludge in building materials not only minimizes the drain problem, but also has an economic and ecological advantage. So that a several analyses were carried out using: XRF, XRD, FTIR, TG-DSC, COD, pH, NO 3 − and TOC. Analysis of X-ray fluorescence spectrometry indicates the presence of fertilizer elements such as K, P, S and Mg. A large percentage of the following elements: Fe, Ca, Si and Al as well is present. The studied sludge also contains trace metals. The mainly existing elements are the following: Cu, Cr, Zn, Ni and Pb with contents smaller than the maximum values admitted by the Algerian standard NA 17671. However, the Zn and Ni concentrations represent 85% and 75%, respectively, of the standard values. So Zn and Ni are factors that can create risks during their agricultural spreading. The measurement of the concentration of dissolved nitrate ions and the COD gave us the values of 2.4518 mg/g and 1.4 mg/g, respectively. The rate of organic matter is estimated at 48.5%. The measured pH is in vicinity to neutrality. The spectral study of the XRD and the IR indicate the presence of the important phases such as calcite, quartz, portlandite and sillimanite in the studied sludge. The results of the TG-DSC thermogravimetric analysis are very encouraging. According to the TG-DSC curve, the decarbonation takes place between 700 and 1000 °C, and it finishes with the release of lime in a particularly reactive state. The final combinations between the obtained lime are SiO 2 , Al 2 O 3 and Fe 2 O 3 which yielded a very interesting mineral in the construction field, which are the four main minerals in clinker Ca 3 SiO 5 ; Ca 2 SiO 4 ; Ca 3 Al 2 O 6 and Ca 4 Al 2 Fe 2 O 10 .