Comparison of cobalt ferrate-based nanoparticles for promoting biomethane evolution from lactic acid anaerobic digestion

Some inhibition of biomethane (bioCH4) production system can be observed, which is due to the propionic acid generation from lactic acid degradation. In this work, the three cobalt ferrate-based nanoparticles (NPs) such as CoFe2O4, CoAl0.2Fe1.8O4 and CoCu0.2Fe1.8O4 were synthesized to promote the bioCH4 evolution from lactic acid. The CH4 yields from the CoAl0.2Fe1.8O4, CoCu0.2Fe1.8O4 and CoFe2O4 groups at 300 mg/L of NPs were 431.52, 392.12 and 396.6 mL/g lactic acid, respectively. Moreover, the highest CH4 yield was 34.15% higher than that of the control reactor (321.67 mL/g lactic acid) without NPs. The three NPs accelerated lactic acid biodegradation and propionic acid conversion, thus obtaining more CH4. Surprisingly, microbial structure revealed that CoAl0.2Fe1.8O4 increased the abundance of Bacteroidetes_vadinHA17 to 16.6%, promoting the conversion from propionic acid to acetic acid. Meanwhile, the abundance of Methanobacterium in archaeal community from CoAl0.2Fe1.8O4 group rose from 45.81% to 68.45%, which facilitated bioCH4 production.