Abstract
Sewage sludge is regarded as a potential source for soil fertilizer However, the direct utilization of sewage sludge in agricultural land is restricted since it also contains heavy metals, pathogens, and toxic compounds. Pyrolysis of the sewage sludge destroys the organic pollutants and partly volatilizes the heavy metals. In this study, pyrolysis of sewage sludge was carried out in order to determine the optimum residence time and temperature to recover the phosphorous and remove heavy metals from the resultant sewage sludge char (SSC). Pyrolysis was conducted on dried sewage sludge (DSS) by means of thermogravimetric analysis (TGA) and high-temperature oven with an N2-atmosphere. Microwave Plasma-Atomic Emission Spectroscopy (MP-AES) was used to determine the concentration of P and trace elements in the resulting solid char fraction. A combination of chemical fractionation (step-by-step leaching) of the DSS and thermodynamic equilibrium calculations were utilized to estimate the availability of phosphorous and removal of heavy metals in the SSC fraction at different temperatures. The results from the thermodynamics calculation were in line with the measured chemical composition of the SSC. Furthermore, the energy contents of the SSC obtained at different temperatures were measured. The pyrolysis evaluation results indicate that phosphorous was enriched in the char, while lead, zinc, and cadmium were significantly removed.
Highlights
Published: 8 March 2021Phosphorus (P) is a crucial element for all existing organisms and performs vital functions for nourishment, growth, and plant development
The objective of this study is to determine the effects of pyrolysis reaction parameters such as heating rate, process temperature, and residence time on the removal of heavy metals from the sewage sludge collected from the Mora wastewater treatment plant
It is evident that the heating rate has an effective influence on the decomposition of sewage sludge
Summary
Phosphorus (P) is a crucial element for all existing organisms and performs vital functions for nourishment, growth, and plant development. It is one of the fundamental parts of fertilizers and an essential element in all organic life. The shortage of P in the soil severely affects the plant metabolism and, in turn, their productions. According to scientific reports [1], the demand for P has increased considerably. Today, most of the P is obtained from phosphate rock (PR), which is non-renewable and limited [2]. Municipal sewage sludge (MSS), which is the main byproduct of wastewater treatment plants (WWTPs), has been generated in large quantities over the past few decades [3]
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