and consequently the amount of free
ammonia (NH3) available in the medium (beyond its consumption).
While this effect can be counterbalanced by applying
external pH control, the principal inhibitory metabolite,
nitrite, continues to accumulate, inhibiting growth and limiting
cell concentration (Tan et al. 2008). Fed-batch and continuous
cultures of N. europaea, with or without biomass
recycling, were also reported (Tappe et al. 1999; Güven and
Schmidt 2009; Yingling and Zhengfang 2013). The highest
cell concentrations reported to date—using systems retaining
the biomass—were about 400 mg/L dry cell mass (DCW