Abstract
Biochars, produced by pyrolyzing vermicompost at 300, 500, and 700°C were characterized and their ability to adsorb the dyes Congo red (CR) and Methylene blue (MB) in an aqueous solution was investigated. The physical and chemical properties of biochars varied significantly based on the pyrolysis temperatures. Analysis of the data revealed that the aromaticity, polarity, specific surface area, pH, and ash content of the biochars increased gradually with the increase in pyrolysis temperature, while the cation exchange capacity, and carbon, hydrogen, nitrogen and oxygen contents decreased. The adsorption kinetics of CR and MB were described by pseudo-second-order kinetic models. Both of Langmuir and Temkin model could be employed to describe the adsorption behaviors of CR and MB by these biochars. The biochars generated at higher pyrolysis temperature displayed higher CR adsorption capacities and lower MB adsorption capacities than those compared with the biochars generated at lower pyrolysis temperatures. The biochar generated at the higher pyrolytic temperature displayed the higher ability to adsorb CR owing to its promoted aromaticity, and the cation exchange is the key factor that positively affects adsorption of MB.
Highlights
Earthworms play an important role in the environmental ecology
Analytical-grade samples of congo red (CR), methylene blue (MB), NaOH, and HCl were procured from commercial sources
It is evident that the biochar yields from 91.56% to 71.81% as the pyrolysis temperature increased from 300°C to Biochars Yield (%) Ash content (%)
Summary
Earthworms play an important role in the environmental ecology. They are involved in the decomposition of organic matter and in nutrient cycling [1]. Earthworm farms are widely promoted for ecologically treating sludge, poultry feces, toxic organic waste, etc [2]. Vermicompost, the worm castings generated by the degradation of organic waste by earthworm [3], is characterized by a homogenous texture, well-developed porous structure, and large specific surface area. Vermicompost is widely used in farms to promote plant growth, increase crop yield, improve soil environment, and condense heavy metals [5]. The organic waste (feed) can contain heavy metals, organic pollutants, and microbial germs resulting in the vermicompost being contaminated with the incompletely
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