ABSTRACT
Plastics in landfills undergo a unique micronization process due to multi-factor and light-avoided conditions, but their aging process in such a typical environment remains unexplored. This study investigated the aging behavior of polyethylene plastics, representative of landfills, under simulated dynamic mechanical forces and high temperature-two prevalent environmental factors in landfills. The study explored the individual and combined contributions of these factors to the aging process. Results indicated that high temperature played a primary role in aging plastics by depolymerization and degradation through ·OH production, while mechanical forces contributed mainly to surface structure breakdown. The combined effect leads to more serious surface damage, creating holes, cracks, and scratches that provide access for free radical reactions to plastic bulk, thereby accelerating the aging and micronization process. The resulting microplastics were found to be 14.25 ± 0.53 µg L-1. Aged plastics exhibit a rapid aging rate of depolymerization and oxidation compared to virgin plastics due to their weak properties, suggesting a higher potential risk of microplastic generation. This study fills a knowledge gap regarding the aging behavior of plastics under complex and light-avoided landfill conditions, emphasizing the need for increased attention to the evolution process of microplastics from aged plastic waste in landfills.
Subject(s)
Refuse Disposal , Water Pollutants, Chemical , Refuse Disposal/methods , Plastics/chemistry , Microplastics , Waste Disposal FacilitiesABSTRACT
Pyrolysis carbonization of sewage sludge is employed to achieve carbon sequestration and access carbon resources, while the quality of the obtained sludge-based carbon (SBC) is poor due to high ash contents and volatile organic matter. Here, carbonization in KOH/Na2CO3 (K/Na) bi-molten salts was developed for SBC preparation, improvement of carbon exploitation from biomass, and to reduce the contents of ash and volatile organic matter. The results showed that the surface area and pore volume of SBC under optimized conditions reached 1631 m2 g-1 and 1.312 cm3 g-1 at 700 °C, respectively, with a K/Na bi-molten salts/sludge ratio of 2:1 (K:Na = 5:5). Moreover, over fivefold the higher surface area and 43.61% amount of carbon element could be obtained, with a decrease in the mass loss rate for sludge pyrolysis of 25%. The mechanism behind the higher surface area of the SBC was identified and divided into three stages: intense dehydration and dehydrogenation caused by molten salt-enhanced polycondensation of protein and polysaccharide (200-400 °C), strongly reduced carbon-oxygen structure after deoxygenation reactions (400-600 °C), aromatization and cyclization of long-chain fatty acids triggered by deamidation of tar catalyzed by molten salts (600-900 °C). Eventually, 14.63% carbon was sequestered for the high-surface-area SBC prepared by K/Na bi-molten salts system.
Subject(s)
Carbon , Sewage , Sewage/chemistry , Salts , Pyrolysis , Carbon Sequestration , Carbon RadioisotopesABSTRACT
The relationship between the migration process and speciation distribution of Cr is important for the risk assessment in the underground environment. In this work, soil columns were collected from the chromate production site, with a 40-year operation, in the groundwater depression cone area of North China plain. The relationship between chromium pollution features and the geochemical properties of soil was established, and the migration risk of Cr(VI) was assessed based on the Nemerow composite index and Hydrus-1D model. The maximum total Cr concentration in the chromium slag dumping site reached 907 mg/kg, and that in the chromate production workshop was more than 200 mg/kg across the depth. The migration of Cr might be accelerated in the soil with abundant Mn (236-1461 mg/kg) but scarce organic matters (< 0.45%). The Hydrus simulation indicated that Cr(VI) would reach a cumulative flux of 300-729 mg/cm2 after 50 years.
