4. Conclusions
The current study revealed that thermophilic agro-food wastes could be operated at OLR of 10.2 g VS L-1 d-1 and HRT 5-8d with satisfactory stability and high methane yield. Process disturbances due to organic over loading and/or finite digestion time led to imbalance among interdepended reactions and thus digester acidification and subsequent process disturbances were experienced. The shaping in microbial profiles among stable and disturbed states suggested the occurrence of functional redundancy within AD microbiome. Conclusively, even though increasing OLR with shortening HRT is a feasible strategy for increasing process capacity at existing plants, the threshold of both parameters that guarantee the process stability should be carefully determined to avoid process disturbances. Since existence of disturbances is unavoidable in real systems, microbial community could be utilized as a pivotal bio-indicator to control AD process performance and stability.