Differences in organic and inorganic components of poplar, spirulina and pig manure form biochar of very distinct properties

Abstract

Poplar, spirulina and pig manure are representatives of woody biomass, algae, and biowastes in poultry breeding. They are all carbonaceous, but their distinct composition in both organic and inorganic fractions could impact properties/compositions of pyrolytic products. The detailed impacts were investigated herein by conducting pyrolysis of poplar, spirulina and pig manure at 500 °C and systematic analysis of resulting products. The results showed that bio-oil yield from poplar or spirulina was roughly 2 times of that from pig manure, due to their abundant organic components. However, the yield of biochar from poplar or spirulina was less than half of that from pig manure, but, on organic basis (excluding ash in biochar), the biochar yield was the highest from pyrolysis of poplar. Abundant inorganic components in pig manure formed ash-rich biochar (73.2 %), which was much higher than the ash content in spirulina-biochar (23.9 %) or poplar-biochar (9.0 %). This led to remarkably lower heating value (5.3 versus 26.3 MJ/kg for poplar-biochar) and much lower overall combustion index. Additionally, more intensive cracking induced by low thermal stability of organics in spirulina and pig manure, together with their abundant inorganics (i.e. SiO₂, CaCO₃ and KCl), resulted in remarkably lower carbon yields than that from pyrolysis of poplar. This, however, reduced the activation energy in pyrolysis of spirulina. Biological fibrous structures of poplar could be inherited by poplar-biochar, while morphology of pig manure-char was very irregular. Melting/agglomeration of proteins and lipids in spirulina formed spirulina-biochar of densified structures with smooth surface.