Effects of particle size on the pretreatment efficiency and subsequent biogas potential of polylactic acid.

The fragmentation of bioplastics (BPs) before pretreatment and anaerobic digestion is conducted for higher efficiency; however, based on the literature, the size reduction varies widely. In this study, initially, various combinations of thermal-alkaline pretreatments were applied at different strengths to the polylactic acid (PLA) in three groups (<0.5, 0.5 < size < 1.0, and 1.0 < size < 2.0 mm). After pretreatment, the solubilization of PLA was increased to 11.5-40.0 % using alkaline dosage and temperature ranging from 50 to 200 g OH-/kg BP, 60-100 °C, respectively, in a 1-10 h timeframe. The results were statistically proved using a 3D response surface graph, where the pretreatment was more effective for smaller particle sizes. The reduction in particle size also increased the CH4 production, which was more pronounced at the strong pretreatment (24 % increment vs. 10-15 %). Computed results indicated 44-86 % conversion of pretreated PLA particles to CH4, supported by Fourier transform infrared spectroscopy analysis, especially focusing on the intensity of -OH bands.

Continuous production of high-concentrated ammonia broth through fermentation.

Being considered as a valuable resource and energy carrier, extensive research is going on to efficiently extract ammonia (NH3) from anaerobic digestate. However, due to the well-known NH3 inhibition on methanogens, the total NH3 nitrogen (TAN) concentration is typically limited to 1-4 g N/L in digestate, making the NH3 extraction process energy-consumptive. Here, NH3 fermentation, specifically targeting augmented NH3 production through biological reaction, was performed in a continuous mode. With the increase of gelatin input (10 to 150 g COD/L), NH3 concentration and volumetric productivity gradually increased, reaching 12.0 g TAN-N/L and 36.0 g NH3-N/L/d, which were the highest values ever reported. The stepwise increase in NH3 exposure prompted a shift in microbial dominance towards Hathewaya (from 1 % to 68 %), a critical factor for having high NH3 tolerance. Finally, NH3 stripping results suggested that highly concentrated broth could reduce the specific energy consumption for NH3 extraction to 1/3.