Pyrolysis is a promising thermochemical process for managing sewage sludge while simultaneously producing biochar, a valuable co-product. This study systematically investigated the effects of the pyrolysis parameters of temperature (200-800 °C), residence time (5-60 min), and inert gas flow rate (0.25-1.0 dm³/min) on the properties of biochars obtained from sewage sludge. Comprehensive characterization of the biochars was conducted, including composition analyses (ultimate, proximate, elemental, and molecular), acidity, specific surface area and pore size, and the assessment of eight heavy metals (As, Cd, Pb, Cr, Zn, Mn, Ni and Cu) in the biochars and sewage sludge. The results showed pyrolysis temperature and residence time were the most critical parameters affecting biochar quality, with negligible influence of inert gas flow rate. Higher pyrolysis temperatures (>500 °C) increased biochar pH to alkaline values (>10), ash content, and nutrient concentrations (Ca, K, Mg, P). Temperatures above 600 °C significantly increased biochar surface area, reduced pore size, and yielded H/C ratios below 0.57, improving suitability for soil remediation. Pyrolysis also facilitated volatilization of heavy metals, particularly As and Cd, which were reduced to safe levels, with Cd removal exceeding 90% at 700 °C. Metal analysis confirmed the immobilization of heavy metals in biochar, significantly reducing the environmental risk, from high (PERI=1158) in the sewage sludge feedstock to low (PERI<50) in biochar obtained at temperatures above 600 °C. Most heavy metals in biochar at these temperatures were concentrated in oxidizable and residual fractions. The results provide valuable new data to guide development of pyrolysis for the sustainable management of sewage sludge.

The large and growing volume of tire waste and sewage sludge requires disposal, for which thermochemical processes such as gasification can be used. Co-gasification of these two waste products allows the tire char to be used as a charge stabilizer and the sewage sludge to improve reactivity and efficiency. The purpose of this study was to evaluate the effect of the composition of a waste tire char and sewage sludge fuel blend on the gasification process, using steam as the gasification agent. Tests were carried out for tire char, municipal sewage sludge, and blends of the two in ratios of 90:10 and 67:33. An analysis of the materials used was carried out (ultimate and proximate analysis as well as ash composition), and isothermal measurements of steam gasification were taken using the thermal volumetric method for temperatures of 800, 850, and 900 °C at an elevated pressure of 1 MPa. On the basis of the results, the formation curves of the main gasification products (H₂, CO, CO₂, and CH₄) were created, the curves for the degree of carbon conversion were plotted, the reactivity indexes were determined for different degrees of conversion (0.25, 0.5, and 0.75), and the quantity and composition of the resulting gas were analyzed. Using the grain model, the kinetic parameters (activation energy and pre-exponential factor) of the gasification reaction were calculated. The addition of municipal sewage sludge had a positive effect on the reactivity of tire char and increased the efficiency of gasification, because it contained components that act as catalysts in the gasification process. There was a favorable effect from the addition and higher amount of sewage sludge on lowering both the activation energy (49.5 kJ/mol and 89.2 kJ/mol for 90:10 and 67:33 blends, respectively) and the pre-exponential factor. A significant improvement in reactivity, with a high degree of conversion and the best gas composition, was obtained for a 90:10 blend at 900 °C.

The aim of the study was to evaluate the content, occurrence, and leachability of arsenic (As), lead (Pb), and thallium (Tl) in wastes from coal cleaning processes with respect to the safe management of this waste. The study focused on wastes resulting from the wet gravitation and flotation processes employed for the purposes of coking coal cleaning in four coal mines situated in the Upper Silesian Coal Basin (Poland). The scope of the study included (i) determination of the content of these elements in the investigated wastes using atomic absorption spectrometry, (ii) evaluation of their mode of occurrence using electron microprobe analysis, and (iii) preliminary assessment of their leachability in deionized water. The content of the analyzed elements in the examined samples of coal waste was twice as high as the average content of these elements in the Earth’s crust. The contents of As and Pb, however, did not exceed their permissible contents in inert waste in accordance with Polish legal regulations based on EU directives. The limit on the content of Tl is not specified by these regulations, but its amount in the examined samples was similar to that occurring in the soils. Moreover, leaching tests have shown that these elements are hardly eluted from the analyzed material. Their content in the water leachates was generally lower than the detection limit of the analytical method, complying with the standards for good and very good water quality. Low leachability of these elements most probably results from their mode of occurrence in the investigated wastes. The chemical analysis using an electron microprobe and the analysis of the correlation between these elements, e.g., total and pyritic sulfur, have shown that Pb, As, and Tl are mainly found in sulfide minerals which are characterized by negligible solubility. In conclusion, the investigated hard coal processing waste does not constitute a threat to the environment and can be commercially used or safely neutralized, e.g., by landfilling.

The topic of waste combustion/co-combustion is critical, given the increasingly restrictive legal regulations regarding its environmental aspects. In this paper, the authors present the test results of selected fuels of different compositions: hard coal, coal sludge, coke waste, sewage sludge, paper waste, biomass waste and polymer waste. The authors conducted a proximate and ultimate analysis of the materials and mercury content in them and their ashes. An interesting element of the paper was the chemical analysis of the XRF of the fuels. The authors conducted the preliminary combustion research using a new research bench. The authors provide a comparative analysis of pollutant emissions—especially mercury emission—during the combustion of the material; this is an innovative element of this paper. The authors state that coke waste and sewage sludge are distinguished by their high mercury content. The value of Hg emission during the combustion depends on the initial mercury content in the waste. The results of the combustion tests showed the adequacy of mercury release compared to the emissions of other compounds considered. Small amounts of mercury were found in waste ashes. The addition of a polymer to 10% of coal fuels leads to a reduction in mercury emissions in exhaust gases.

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