A novel strategy for improving ammonia resistance of acidogenesis using domesticated sludge combined with nZVI addition in an ambient anaerobic digestion system

High ammonia stress, which inhibited the performance and stability of anaerobic digestion (AD) systems, is considered a bottleneck problem. To improve the performance of ambient acidogenic AD system under high ammonia stress, three different strategies were developed, including native sludge with nano zero valent iron (nZVI) addition (SnZVI), domesticated sludge enriched with homoacetogens with no additive (SDomesticated) and domesticated sludge with nZVI addition (SDomesticated+nZVI). All groups were operated at ambient temperature (24 +/- 1 degrees C). Results showed that ammonia stress restricted the acidogenic rate in ambient acidogenic system significantly. Under ammonia stress, both SDomesticated and SDomesticated+nZVI showed positive impact on acidogenesis to resist, while the nZVI solely of SnZVI couldn't relieve the ammonia stress effectively. Compared to nZVI or domesticated sludge solely added system, SDomesticated+nZVI showed highest acidogenic rate under high ammonia stress. The SDomesticated treatment increased acetic acid and ethanol production under high ammonia stress compared to the SControl. The SDomesticated+nZVI further increased the production of formic acid and H2 and reduced the generation of CO2. Microbial community analysis indicated that the relative abundances of main acidogens Bifidobacterium, Solobacterium and ethanol producing bacteria Ethanoligenens, increased in the SDomesticated and SDomesticated+nZVI groups. Moreover, SDomesticated+nZVI increased the relative abundance of relevant functional enzyme-encoding genes involved in the generation of acetic acid, formic acid and ethanol and reduced the relative abundance of key functional enzyme-encoding genes related to butyric acid production. This work could provide a novel practical strategy to improve the performance of ambient acidogenic AD system under ammonia stress.