Effect of temperature, pH and reaction time on alkali-thermal pretreatment of poly(3-hydroxybutyrate): Enhancing solubilization and anaerobic CH4 production

Abstract

The effects of alkali-thermal pretreatment with operational parameters (temperature: 37–91 °C, pH: 7–13, pretreatment time: 24–120 hr) on the solubilization and the consecutive anaerobic digestion of poly(3-hydroxybutyrate), P3HB, was investigated using the tests with 3²×4 full factorial design. Near-complete solubilization of P3HB (99.6 %) was attained through the alkali-thermal pretreatment. Alkali-thermal pretreatment of P3HB significantly improved CH₄ production, resulting in 23-fold enhancement in the CH₄ production rate (73 mL CH₄/g VSS/d) and an 88 % reduction in elapsed batch time for complete anaerobic digestion, with a CH₄ yield of 380 mL CH₄/g COD. Pretreatment factors, particularly pH, exerted significant effects and showed synergistic effects with temperature. This study integrated factorial design, response surface modeling, and microbial analysis to offer a comprehensive understanding of how pretreatment conditions affected both performance and microbial dynamics in P3HB anaerobic digestion. Response surface analysis with partial cubic models successfully quantified these relationships, and strong positive correlations between solubilization and CH₄ yield were observed. Distinct bacteria and archaea communities proliferated during the anaerobic digestion of pretreated versus unpretreated P3HB. Spirochaetaceae, Syntrophomonas, Mesotoga, Christensenellaceae R-7 group, and Sedimentibacter, along with methanogens such as Methanosaeta and candidatus Methanofastidiosum, were identified as key contributors to the anaerobic digestion of P3HB. These findings support that optimized alkali-thermal pretreatment significantly enhances the anaerobic digestion of P3HB, underscoring the potential of P3HB wastes as prospective feedstocks for anaerobic digestion process.