Effect of temperature on the anaerobic digestion of cardboard with waste yeast added: Dose-response kinetic assays, temperature coefficient and microbial co-metabolism

Effective co-metabolism of microbes has been reported as an available method to achieve better performance of digestion. In order to identify the optimal synergetic living conditions of microbes and obtain the highest methane production, co-digestion of cardboard and waste yeast at 15, 25 and 35 °C were investigated in batch test. The results showed that it facilitated to establish the efficient metabolism with 0.05 g yeast/g TS sludge added, which obtained the maximal biomethane production of 228.91 mL/gVS at 35 °C (C0.5). However, the addition of excessive yeast caused a serious decline in biomethane due to the accumulation of VFA. Temperature played significant roles in co-metabolism of microbes, and temperature coefficient (Q₁₀) which can reflect the effect of temperature on microbial activity showed the trend of increasing firstly, and then decreasing with the yeast added. The biggest difference was obtained after 0.2 g yeast/g TS sludge was added with the Q₁₀ of 2.67. RDA analysis showed that yeast dosage and temperature are dominant driving factors, which seriously affect microbial community structure. Syntrophic VFA-oxidizing bacteria (f_Synergistaceae) and Methanosaeta were enriched in C0.5. Energy flowing analysis revealed the energy generated in C0.5 was much greater than the others, and its net energy yield has increased by 60.1% compared with 15 °C. The results indicated that co-digestion of cardboard and yeast was beneficial to achieve the reduction and stabilization of the waste for cleaner production, and realizes highest economic benefits from energy yield at 35 °C.