Involvement of Acid-Leachable Inorganics in Pyrolysis of Pig Manure

Pig manure is a typical solid waste, which features a high content of inorganics. These inorganics might be involved in thermochemical conversion of pig manure, and this was investigated herein by pyrolysis of pig manure leached with varied concentrations of H2SO4 (0.5–6 mol L–1) at 600 °C. The removal of acid-leachable inorganics [CaCO3, Ca3(PO4)2, alkaline oxides, etc.] exposed more acidic sites derived from the oxides, like SiO2. This enhanced production of the gases at the expense of bio-oil. Furthermore, aromatization and secondary condensation reactions were also promoted, increasing not only the yield of char (from 29.6 to 39.7%, on an organic basis) but also the carbon content in char from 16.1% (blank sample) to 26.2% (leached with 6 mol L–1 H2SO4). Leaching partial inorganics rendered more sufficient contact and interaction between the organics, facilitating charring of organic matter. This further retained more carbon skeleton for generation of more micropores, which further enhanced the capability of the resulting char for adsorption of phenol. In situ infrared analysis indicated the presence of more abundant oxygen-containing functionalities and carbonaceous species after the leaching treatment, favoring the occurrence of aromatization reactions.