Behavior of type II methanotrophic bacteria enriched from activated sludge process while utilizing ammonium as a nitrogen source

Methanotrophs are considered one of the most important biological sinks for methane emissions mitigation. Additionally, they can be employed in various environmental biotechnologies for resources recovery from waste streams. Type II methanotrophs attracted several researchers for their unique ability for biopolymers accumulation, however, maintaining a mixed culture dominated by these microorganisms remains a challenge for long-term operation. To establish an ammonium-driven selection, this study shows the behavior of type II methanotrophs mixed culture enriched from activated sludge when subjected to different ammonium and copper concentrations under different operational conditions through a series of batch experiments. Ammonium concentrations above 20 mmol declined the growth rate and the biomass yield by 75% and 50% respectively. Adjusting the food to microorganisms ratio (F/M) and the Nitrogen to microorganisms ratio (N/M) doubled the growth rate of the enriched culture and mitigated ammonium inhibitory effects showing their great potential to be used as selection parameters for type II without losing cellular growth. Cultures grown in copper free medium were more tolerant to higher ammonium concentration. On the other hand, cultures supplemented with a copper concentration of 10 μm achieved the highest growth rates under the adjusted conditions of C/N, F/M and N/M ratios.