Monitoring pilot-scale polyhydroxyalkanoate production from fruit pulp waste using near-infrared spectroscopy

Given the current plastic disposal global crisis, biodegradable polymers may have an important role in leading the way towards a more sustainable plastic industry. Polyhydroxyalkanoates (PHA) are biobased and biodegradable aliphatic polyesters synthesized by bacteria and stored as intracellular granules. In this study, PHA was produced at pilot scale by a mixed microbial culture (MMC) fed with fermented fruit pulp waste. The PHA accumulation reactor was monitored at line by near-infrared (NIR) spectroscopy to develop and optimize partial least squares (PLS) calibration models for predicting bulk PHA concentration and intracellular PHA content. The PLS models were subjected to internal cross-validation (62 spectra) and the ones with best performance were validated with an external test set (12 spectra). For bulk PHA concentration, a root mean squared error of prediction (RMSEP) of 0.69 g/L and a coefficient of determination (R²) of 0.89 were attained, while intracellular PHA content was predicted with a RMSEP of 14.6% and a R² of 0.86. These NIR-based calibration models demonstrated a great potential for the real-time monitoring of the MMC pilot-scale PHA production from a complex fruit pulp waste substrate. This approach can be used for in situ control of the pulse-wise feeding strategy of the PHA accumulation stage, minimizing PHA consumption triggered by carbon source depletion and contributing for an improved global process efficiency and productivity.