Volatile fatty acids productivity by anaerobic co-digesting waste activated sludge and corn straw: Effect of feedstock proportion

• SCFAs yield was enhanced by co-digesting waste activated sludge and corn stover.
• Corn stover proportion in feedstock determined the acidification product spectrum.
• Corn stover addition improved the hydrolysis and acidification of particulate organics.
• Optimal feedstock proportion was 65%WAS:35%CS from carbon balance and cost estimation.

Volatile fatty acids (VFAs) are the most suitable and biodegradable carbon substrates for many bioprocesses. This study explored a new approach to improve the VFAs production from anaerobic co-digesting waste activated sludge (WAS) with corn straw (CS). The effect of feedstock proportion on the acidification efficiency was investigated. The maximum VFAs yield (corresponding fermentation time) was substantially increased 69% (96 h), 45% (72 h), 13% (120 h) and 12% (120 h) with 50%, 35%, 25% and 20% CS proportion of feedstock, respectively. HAc (acetic acid) was consistently the most abundant, followed by HPr (propionic acid) and n-HBu (butyric acid) in the co-digesting tests. The increase of CS in feedstock led to more production of HAc and HPr. Moreover, the consumption of protein and carbohydrate were also improved remarkably from 2955 and 249 mg COD/L (individual WAS fermentation) to 6575 and 815 mg COD/L (50%WAS:50%CS co-digestion) from 120 onward, respectively. The highest contribution of CS to additional VFAs production was1113 mg VFAs (as COD)/g CS/L in the 65%WAS:35%CS co-digesting test. Our study indicated a valuable method to improve VFAs production from anaerobic co-digesting WAS and CS.