Treatment of swine manure by hydrothermal carbonization: The influential effect and preliminary mechanism of surfactants

Abstract

Treatment of swine manure by hydrothermal carbonization (HTC) with the aid of different surfactants was first explored in this study. PEG 400 (polyethylene glycol 400) and Tween 80 facilitated the formation of bio-oil. SLS (sodium lignosulfonate) and SDS (sodium dodecyl sulfate) promoted the formation of water-soluble matters/gases. Span 80 enhanced the formation of hydrochar, which resulted in a 50.19 % mass yield, 92.39 % energy yield, and a caloric value of 28.68 MJ/kg. The hydrochar obtained with Span 80 presented a similar combustion performance to raw swine manure and the best pyrolysis performance. The use of Span 80 promoted the transfer of degradation products to hydrochar, especially hydrophobic ester and ketone compounds. Notedly, Span 80 suppressed the synthesis of PAHs during the HTC process, which was reduced to 0.92 mg/kg. Furthermore, the hydrochar produced with Span 80 contained lower contents of heavy metals. On the whole, Span 80 has shown great potential in enhancing the HTC of swine manure. The acting mechanisms of surfactants in the HTC of swine manure included adsorption, dispersion, and electrostatics repulsion.