Sorption of methylene orange on biocarbon sorbent, obtained by pyroly-sis of wastewater sludge

Abstract

Water pollution and deterioration of air and water quality is a rapidly growing problem directly related to the generation of waste water and the accumulation of significant amounts of wastewater sludge (WWS). One of the methods for recycling WWS is their pyrolytic processing into biochar adsorbents for purification from various pollutants. The type of adsorbent and its properties play a key role in the efficiency of the purification process, which explains the relevance of the search for alternative materials for water treatment processes. The purpose of the study was to create a biocarbon sorbent during the pyrolysis of wastewater sludge and determine its sorption capacity for the methylene orange dye. To obtain samples of biocarbon sorbent, dried and crushed samples of wastewater sludge were exposed to a temperature of 500 °C for 1.5 hours in a vacuum chamber with a heating rate to a given temperature of 5°C/min. Elemental analysis of the resulting sorbent allowed to establish a decrease in the content of carbon, oxygen, and sulphur: for C by 2.50 at.%, for O by 9.91 at.%, for S by 0.4 at.%, relative to WWS. Scanning electron microscopy confirmed a significant reduction in the particle size of biochar compared to the original WWS sample. In the initial WWS sample, after the sample preparation stage, the dispersion of particle sizes was 10-70 µm, and after pyrolysis of the sediment, the dispersion decreased to the range of 10-45 µm. The percentage of biochar yield was calculated, constituting 42% of the weight of the initial WWS and studies on the sorption of methylene orange were carried out. The sorption capacity of biochar for the anionic dye methylene orange after 120 min of sorption was 4.9 mg/g, the degree of solution purification reached 82%. The kinetics of dye sorption was correctly described by a pseudo-second-order equation and indicated the polymolecular nature of sorption.