Methanogenic treatment of dairy product wastewater by thermophilic anaerobic membrane bioreactor: Ammonia inhibition and microbial community

[Display omitted] •Protein-rich dairy product wastewater was treated by an anaerobic membrane reactor.•Ammonia self-detoxification effect and washout dynamic by dilution were analysed.•Syntrophic oxidising of organic acid processes were inhibited by ammonia.•Acetic acid and H2/CO2 production was a major metabolic process after inhibition. Dairy product wastewater contains high-strength organic matter suitable for anaerobic treatment, but excessive protein degradation may lead to an ammonia inhibition problem. This work studied protein-rich dairy product wastewater treatment in the anaerobic membrane bioreactor. The results showed that a temporary self-detoxification phase of ammonia inhibition from the change of pH buffer system was vital for rapid reactor recovery by substrate dilution. The ammonia washout from the reactor was simulated by a kinetic model. After ammonia inhibition, the relative abundance of syntrophic lactic and propionic acids oxidising bacteria significantly reduced along with fermentative bacteria involved in mixed organic acids production. Nevertheless, the relative abundance of the protein degradation bacteria producing acetic acid and H2/CO2 increased. A potential metabolic process change was proposed by profiling the functional community. To conclude, substrate dilution is essential for overcoming ammonia inhibition in the anaerobic treatment of protein-rich dairy product wastewater.