Effects of environmental conditions on the quality and physico-chemical properties of bio-produced polyhydroxyalkanoates (PHAs)

Jovanovski, Terezija (author), Dogša, Iztok (mentor), Werker, Alan (co-mentor)

Impacts of selected environmental conditions on the quality and quantity of polyhydroxyalkanoates (PHAs) produced with surplus activated sludge were studied. The effects on the PHA-rich biomass were measured immediately after the pH adjustments in the range from pH 2 to pH 12, and after a 48-h anaerobic incubation at 55 °C without prior PHA extraction from biomass. For comparison, two control samples at native pH, incubated at 55 °C and 25 °C, were studied. Methods applied involved quantification of the PHA by thermogravimetric analysis (TGA) together with volatile suspended solids (VSS) or chemical oxygen demand (COD) analysis. Degradation products were measured by ion chromatography (IC) or ultra-high-pressure liquid chromatography (UHPLC). PHA thermal decomposition behaviour and typical phase transitions were analysed by TGA and differential scanning calorimetry (DSC), respectively. Results show that PHA properties (quantity and quality) were best preserved at pH 2. Other conditions revealed different degrees of PHA degradation, where neutral, alkaline conditions and incubation at 25 °C were the most detrimental, especially after 48 h of incubation – a PHA concentration decrease of up to (56 ± 5)% was observed. The acidification of samples before the measurements improved their thermal stability. The observed decrease of measurable PHA mass at pH > 2 was accompanied by the changes in thermal properties (melting, crystallization, glass transition) that were indicative of decreased stability or integrity of PHA and can be explained by a decrease in the molecular weight of PHA.

• Language: English
• Keywords: polyhydroxyalkanoates, biopolymers, degradation, thermogravimetric analysis, differential scanning calorimetry
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: BF - Biotechnical Faculty
• Place of publishing: Ljubljana
• Publisher: [T. Jovanovski]
• Year: 2022
• PID: 20.500.12556/RUL-135065
• UDC: 606:628.3/.4:579.66:577.11(043.2)
• COBISS.SI-ID: 98059011
• Publication date in RUL: 19.02.2022

Secondary language

• Language: Slovenian
• Title: Vplivi okoljskih pogojev na kvaliteto in fizikalno-kemijske lastnosti biološko proizvedenih polihidroksialkanoatov (PHA)

Abstract

S polihidroksialkanoati (PHA) bogato biomaso, smo izpostavili izbranim dejavnikom okolja. Namen je bil raziskati njihov vpliv na količino in nekatere fizikalno-kemijske lastnosti PHA, proizvedenih z dohranjevanjem odpadnega aktivnega blata. Vzorce smo analizirali brez predhodne izolacije PHA iz biomase. S PHA bogato biomaso smo med 48-urno anaerobno inkubacijo izpostavili različnim pH pogojem (med pH = 2 in pH = 12) ter povišani temperaturi (55 °C). Vzorce smo analizirali takoj po spremembi pH pogojev in še po 48-urni inkubaciji. Dve kontrolni skupini, ki jim pH pogojev nismo spreminjali, inkubirani pri 25 °C in 55 °C, sta nam služili za primerjavo. Za kvantifikacijo PHA v biomasi smo uporabili termogravimetrično analizo (TGA) podprto z določanjem koncentracije organske snovi in kemijske potrebe po kisiku (KPK). Razgradni produkti v topni fazi so bili določeni z ionsko kromatografijo (IC) ali ultra visokotlačno tekočinsko kromatografijo (UHPLC). Termično razgradnjo smo analizirali s TGA, fazne prehode PHA pa z diferenčno dinamično kalorimetrijo (DSC). Količina in fizikalno-kemijske lastnosti PHA so se najmanj spremenile v kislih pogojih (pH = 2). Pri ostalih pogojih smo opazili različne stopnje razgradnje PHA. Nevtralni in alkalni pogoji ter inkubacija na 25 °C so povzročili največjo razgradnjo PHA, tj. za (56 ± 5) %. Nakisanje vzorcev pred termičnimi analizami je izboljšalo njihovo termostabilnost. Zmanjšanje koncentracije PHA pri pogojih pH > 2 smo povezali tudi s spremembami v faznih prehodih (kristalizacija, taljenje, steklasti prehod), kar nakazuje na zmanjšano stabilnost ali integriteto PHA, kar bi lahko razložili z zmanjšanjem molekulske mase PHA.

• Keywords: polihidroksialkanoati, biopolimeri, razgradnja, termogravimetrična analiza, diferenčna dinamična kalorimetrija