Simultaneous nitrification and denitrification in microbial community-based polyhydroxyalkanoate production

•Dissolved oxygen (DO) control on nitrifying and PHA-storing bacteria was evaluated.•Low DO levels can limit nitrifying activity without slowing PHA production.•Concomitant anoxic PHA production was evaluated at low DO concentrations.•An optimum DO level exists where SND is exploited for effective PHA production. Microbial community-based polyhydroxyalkanoate (PHA) production has been demonstrated repeatedly at pilot scale. Ammonium, normally present in waste streams, might be oxidized by nitrifying bacteria resulting in additional aeration energy demand. The use of low dissolved oxygen (DO) concentrations allowed to reduce nitrifying rates by up to 70% compared to non-oxygen limiting conditions. At lower DO concentrations nitrate was used as alternative electron acceptor for PHA production and therefore, a constant PHA production rate could only be maintained if nitrate was sufficiently available. An optimum DO concentration (0.9 mgO2/L) was found for which nitrification was mitigated but also exploited to supply requisite heterotrophic nitrate requirements that maintained maximum PHA production rates. PHA accumulations with such DO control was estimated to reduce oxygen demand by about 18%. This work contributes to establish fundamental insight towards viable industrial practice with the control and exploitation of nitrifying bacteria in microbial community-based PHA production.