title: Microalgal TAG production strategies: why batch beats repeated-batch.
abstract: BACKGROUND
  For a commercially feasible microalgal triglyceride (TAG) production, high TAG productivities are required. The operational strategy affects TAG productivity but a systematic comparison between different strategies is lacking. For this, physiological responses of Nannochloropsis sp. to nitrogen (N) starvation and N-rich medium replenishment were studied in lab-scale batch and repeated-batch (part of the culture is periodically harvested and N-rich medium is re-supplied) cultivations under continuous light, and condensed into a mechanistic model.
  
  
  RESULTS
  The model, which successfully described both strategies, was used to identify potential improvements for both batch and repeated-batch and compare the two strategies on optimized TAG yields on light (amount of TAGs produced per mol of supplied PAR photons). TAG yields on light, for batch, from 0.12 (base case at high light) to 0.49 g molph (-1) (at low light and with improved strain) and, for repeated-batch, from 0.07 (base case at high light) to 0.39 g molph (-1) (at low light with improved strain and optimized repeated-batch settings). The base case yields are in line with the yields observed in current state-of-the-art outdoor TAG production.
  
  
  CONCLUSIONS
  For continuous light, an optimized batch process will always result in higher TAG yield on light compared to an optimized repeated-batch process. This is mainly because repeated-batch cycles start with N-starved cells. Their reduced photosynthetic capacity leads to inefficient light use during the regrowth phase which results in lower overall TAG yields compared to a batch process.
authors.affiliation: Bioprocess Engineering, AlgaePARC, Wageningen University, P.O. Box 16, 6700 AA Wageningen, The Netherlands.
authors.forename: Giulia
authors.identifier: 0000-0003-2206-5780
authors.initials: G
authors.lastname: Benvenuti
authors.affiliation: Bioprocess Engineering, AlgaePARC, Wageningen University, P.O. Box 16, 6700 AA Wageningen, The Netherlands.
authors.forename: Packo P
authors.initials: PP
authors.lastname: Lamers
authors.affiliation: Bioprocess Engineering, AlgaePARC, Wageningen University, P.O. Box 16, 6700 AA Wageningen, The Netherlands.
authors.forename: Guido
authors.initials: G
authors.lastname: Breuer
authors.affiliation: Bioprocess Engineering, AlgaePARC, Wageningen University, P.O. Box 16, 6700 AA Wageningen, The Netherlands.
authors.forename: Rouke
authors.initials: R
authors.lastname: Bosma
authors.affiliation: Microbiology, Food Science and Technology, Biotechnical Faculty, University of Ljubljana, Večna pot 111, 1000 Ljubljana, Slovenia.
authors.forename: Ana
authors.initials: A
authors.lastname: Cerar
authors.affiliation: Bioprocess Engineering, AlgaePARC, Wageningen University, P.O. Box 16, 6700 AA Wageningen, The Netherlands ; Biosciences and Aquaculture, Nordland University, 8049 Bodø, Norway.
authors.forename: René H
authors.initials: RH
authors.lastname: Wijffels
authors.affiliation: Bioprocess Engineering, AlgaePARC, Wageningen University, P.O. Box 16, 6700 AA Wageningen, The Netherlands.
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Barbosa
keywords: Batch; Mechanistic model; Microalgae; Recovery; Repeated-batch; TAG production