The Effect of Pretreatment of Tetraselmis subcrodiformis (Wille) Butcher and Limnospira platensis (Gomont) Ciferri et Tiboni Biomass with Solidified Carbon Dioxide on the Efficiency of Anaerobic Digestion

The aim of this study was to determine the effects of low-temperature pretreatment of microalgae (Tetraselmis subcordiformis (Wille) Butcher) and cyanobacteria (Limnospira platensis (Gomont) Ciferri et Tiboni) using solidified carbon dioxide (SCO2) on the progression of methane fermentation. The experiment was carried out under batch conditions with six process variants that differed in the volumetric ratio of SCO2 to the biomass tested. Changes in organic matter solubility, anaerobic digestion kinetics and overall CH4 production performance were analysed. The results showed that pretreatment effectively increased the solubility of organic compounds, especially in the case of L. platensis biomass, where the highest increases in soluble sTOC (up to 21.6%) and sCOD (up to 14.3%) were observed. CH4 yield in the most efficient variant (SCO2:biomass = 1:2.5) increased to 354 ± 16 mL CH4/gVS for T. subcordiformis and 403 ± 18 mL CH4/gVS for L. platensis, respectively. Despite the apparently less favourable physicochemical parameters of the biomass for anaerobic digestion, L. platensis showed a higher susceptibility to digestion and better kinetic indicators for methane fermentation. The results indicate that the efficiency of anaerobic biodegradation of biomass depends not only on the chemical composition but also on the cellular structure and physicochemical interactions during pretreatment. The use of SCO2 as a disintegrant could be an effective, energy-saving method to increase the fermentation efficiency of photosynthetic microorganisms in biowaste management.