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.

A novel viewpoint to the green city concept based on vegetation area changes and contributions to healthy days: a case study of Mashhad, Iran.

One of the significant challenges in urbanization is the air pollution. This highlights the need of the green city concept with reconsideration of houses, factories, and traffic in a green viewpoint. The literature review confirms that this reconsideration for green space has a positive effect on the air quality of large cities and to reduce the air pollution. The purpose of this study is to evaluate the annual vegetation changes in the green space of Mashhad, Iran as a very populated city in the middle east to study the air pollution. To investigate the relationship between the air pollution and vegetation, the Landsat 8 satellite images for summer seasons of 2013-2019 were used to extract changes in vegetation by calculating the normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), and the optimized soil adjusted vegetation index (OSAVI). The main contribution in comparison with the relevant studies is to study the relationship between clean, healthy, and unhealthy days with the green space area for the first time in Mashhad, Iran. The results show that the implementation of green city concept in Mashhad, Iran, has been increased by 64, 81, and 53% by NDVI, EVI, and OSAVI, respectively, during the study period. The vegetation area of this city is positively correlated to clean and healthy days and has a negative correlation to unhealthy days, in which the greatest values for NDVI, EVI and OSAVI are 0.33, 0.52, and -0.53, respectively.