Monitoring of Microalgal Processes

Abstract

Process monitoring, which can be defined as the measurement of process variables with the smallest possible delay, is combined with process models to form the basis for successful process control. Minimizing the measurement delay leads inevitably to employing online, in situ sensors where possible, preferably using noninvasive measurement methods with stable, low-cost sensors. Microalgal processes have similarities to traditional bioprocesses but also have unique monitoring requirements. In general, variables to be monitored in microalgal processes can be categorized as physical, chemical, and biological, and they are measured in gaseous, liquid, and solid (biological) phases. Physical and chemical process variables can be usually monitored online using standard industrial sensors. The monitoring of biological process variables, however, relies mostly on sensors developed and validated using laboratory-scale systems or uses offline methods because of difficulties in developing suitable online sensors. Here, we review current technologies for online, in situ monitoring of all types of process parameters of microalgal cultivations, with a focus on monitoring of biological parameters. We discuss newly introduced methods for measuring biological parameters that could be possibly adapted for routine online use, should be preferably noninvasive, and are based on approaches that have been proven in other bioprocesses. New sensor types for measuring physicochemical parameters using optical methods or ion-specific field effect transistor (ISFET) sensors are also discussed. Reviewed methods with online implementation or online potential include measurement of irradiance, biomass concentration by optical density and image analysis, cell count, chlorophyll fluorescence, growth rate, lipid concentration by infrared spectrophotometry, dielectric scattering, and nuclear magnetic resonance. Future perspectives are discussed, especially in the field of image analysis using in situ microscopy, infrared spectrophotometry, and software sensor systems.

Microalgae, old sustainable food and fashion nutraceuticals

“…On the other hand, scale-up methodologies have to be improved for achieving efficient light provisions, minimal carbon dioxide losses, and efficient mixing and removal of generated oxygen (Gupta et al, 2015). Microalgal processes have similarities to traditional bioprocesses but demand unique monitoring requirements (Havlik et al, 2016). Modularization and computational fluid dynamics have been used to optimize the structural configurations of PBRs for scale-up (Xu et al, 2009).…”

Microalgae cultivation and metabolites production: a comprehensive review

“…The pH is crucial for the metabolism and uptake of ions associated with the growth of microalgae. In particular, the pH regulates enzymatic activity, phosphorus availability, ammonia toxicity, and the availability of inorganic carbon . Equation was proposed by Mayo to evaluate the growth rate (μ) in function of the pH …”

Peer Review #1 of "Off-line and on-line optical monitoring of microalgal growth (v0.1)"

“…All these are valuable contributors to the balance and growth of human activity on a global scale (Gupta et al, 2015). Havlik and colleagues compiled a wide review of on-line and off-line technologies to monitor physicochemical and biological parameters of microalgae (Havlik et al, 2016). There are also several photobioreactor models to predict growth (Pulz, 2001;Carvalho et al, 2006;Xu et al, 2009).…”