Mixed culture polyhydroxyalkanoate-rich biomass assessment and quality control using thermogravimetric measurement methods

Abstract

Technology advancements for mixed culture polyhydroxyalkanoate production have been made in recent years at pilot scale, and efforts continue towards implementation of the first commercial scale production facilities. The purpose of the present work was to develop thermogravimetric analysis (TGA) methods for routine monitoring of polymer quantity and quality in PHA-rich activated sludge biomass, and for the recovered polymers. TGA quantification of the biomass PHA content correlated directly with the maximum extractable polymer (±2% gPHA/gTS). Acid pre-treatment of the biomass, prior to sample drying, significantly increased the polymer thermal stability in the biomass. This increase helps to improve the resolution of the PHA fraction of the biomass by TGA. From the TGA results, an extension to common solids analysis from Standard Methods, by including an intermediate volatile solids (IVS) assessment, was developed to quantify biomass PHA content. The IVS method entails sample volatilization and weight loss evaluation at a selected temperature between 200 and 300 °C. This intermediate temperature is in between the Standard Method sample drying (103 °C), and ashing (550 °C) oven incubations, for relative weight loss measurements that are made routinely for solids analysis. Thermogravimetric analyses were applied in isothermal polymer recovery experiments using either acetone or 2-butanol as extraction solvents. Trends in extractability as a function of extraction temperature and time correlated directly to the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) co-polymer composition in the biomass, over a 3-hydroxyvalerate in PHBV content ranging from 0 to 40 average weight percent, and a polymer weight average molecular mass between 200 and 600 kDa. Polymer type can be used to anticipate the extraction behavior, or conversely, as shown in the present work, isothermal polymer extraction trends can be used to infer the type of polymer present in the biomass.