Methanogen and nitrifying genes dynamics in immersed membrane bioreactors during anaerobic co-digestion of different organic loading rates food waste

[Display omitted] •The variation of methanogen and nitrifying bacteria in distinct organic loading rate was studied.•The nirS, nirK and nosZ were richest in T3 of R2.•The mcrA, mcrB and mcrG genes were richest in T1 of both R1 and R2.•The nifH gene was positively correlated with Bifidobacterium, Clostridium.•The bacteria, volatile fatty acids, methanogen and nitrifying genes abundance were significantly correlated. This work was aimed to evaluate the distinctive food waste (FW) organic loading rates (OLR) on methanogen and nitrifying genes dynamics and its correlation with identified relative abundance of bacterial dynamics during the anaerobic digestion. This experiment were carried out in the digesters at high OLR of food wastes at (4 to 8 g volatile solids/liter/day reactor R1) and (6 to 10 g volatile solids/liter/day reactor R2). The results shown that the relative abundance of mcrA, mcrB and mcrG genes were richest in the first day of both R1 and R2. In addition, the most of nitrifying genes were greater in after 34 days digestion in R2, while these genes did not show the specific regularity in R1. Finally, the correlation figure shows that Clostridium and Lactobacillus genera were significantly correlated with the different organic acids and methanogen and nitrifying genes dynamics.