Effect of tricarboxylic acid cycle regulators on the formation of humic substance during composting: The performance in labile and refractory materials

The aims of this study are to reveal the roles of tricarboxylic acid (TCA) cycle regulators in reducing CO2 emission and promoting humic substance (HS) formation during composting with different materials. The results showed that the addition of adenosine tri-phosphate (ATP) or malonic acid (MA) reduced CO2 emission during chicken manure composting. However, only the addition of MA reduced CO2 emission during lawn waste and garden waste composting. In addition, both of the two inhibitors promoted HS formation, especially for ATP. Structural equation models further confirmed that ATP and MA reduced CO2 emission by inhibiting the decomposition of amino acid by microorganisms. Meanwhile, ATP promoted the conversion of amino acid and soluble sugars to HS, while MA only promoted the conversion of soluble sugars to HS. In summary, this study provides a theoretical basis for the application of inhibitors to reduce CO2 emission and promote HS formation during composting.