Characteristics and source origin analysis of halogenated hydrocarbons in Hong Kong.

Despite being regulated globally for almost three decades, halocarbon continues to play a vital role in climate change and ozone layer because of its long lifetime in the ambient air. In recent years, unexpected halocarbon emissions have been found in Asia, raising concerns about ozone recovery. As a number of studies focused on halocarbon variations and source profiles, there is an increasing need to identify halocarbon source origins. In this study, an eight-month regular air sampling was conducted at a coastal site in Hong Kong from November 2020 to June 2021, and seventeen halocarbon species were selected for extensive investigation after advanced sample analysis in our laboratory. The temporal variations of halocarbon mixing ratio enhancements were analyzed, and the spatial variations of source origins were investigated by wind sectors and backward trajectory statistics. Our results indicate lower enhancements beyond the background values for major regulated CFCs and CCl4 than later controlled HCFCs and HFCs, suggesting the greater progress of Montreal Protocol implementation for the former species. The notable high enhancement values of non-regulated halocarbons from the north direction indicate their widespread usage in China. The source apportionment analysis estimates the contributions from six emission sectors on measured halocarbons, including solvent usage (43.57 ± 4.08 %), refrigerant residues (17.05 ± 5.71 %), cleaning agent/chemical production (13.18 ± 4.76 %), refrigerant replacements (13.06 ± 2.13 %), solvent residues (8.65 ± 3.28 %), and foaming agent (4.49 ± 1.08 %). Trajectories statistical analysis suggests that industrial solvent was mainly contributed by eastern China (i.e., Shandong and YRD), cleaning agent/chemical production was spread over southeast China (i.e., YRD and Fujian), and refrigeration replacements were dominant in Hong Kong surrounding regions. This work provides insight into the progress made in implementing the Montreal Protocol in Hong Kong and the surrounding region and the importance of continuous emission control.

Revealing the correlation of biomethane generation, DOM fluorescence, and microbial community in the mesophilic co-digestion of chicken manure and sheep manure at different mixture ratio.

Batch co-digestion tests of chicken manure (CM) and sheep manure (SM) at different ratio (Rs/c) were conducted under mesophilic condition (35 °C). Batch kinetic analysis of bioCH4 production, excitation-emission matrix (EEM) fluorescence of dissolved organic matter (DOM), and microbial community were investigated. The well-fitted modified Gompertz model (R2, 0.98-0.99) resulted that the co-digestion markedly improved the methane production rate and shortened the lag phase time. The highest bioCH4 yield of 219.67 mL/gVSadd and maximum production rate of 0.378 mL/gVSadd/h were obtained at an optimum Rs/c of 0.4. Additionally, a significant variation of DOM was detected at the Rs/c of 0.4 with a consistent degradation of soluble microbial byproduct-like and protein-like organics. The positive synergy effects of co-digestion conspicuously enhanced the bioCH4 production efficiency. FI370 and NADH were significantly correlated to Rs/c (p < 0.05). Moreover, the correlations among process indicator, EEM-peaks and different environmental parameters were evaluated by Pearson correlation analysis. The high diversity of acetoclastic methanogens and hydrogenotrophic methanogens in the co-digestion improved the stability of process. Graphical Abstract.

Optimizing biomethane production of mesophilic chicken manure and sheep manure digestion: Mono-digestion and co-digestion kinetic investigation, autofluorescence analysis and microbial community assessment.

Optimization of mesophilic methane production from Chicken manure (CM) and Sheep manure (SM) at total solid (TS) of 8% and 1.6% were obtained by sequence tests in mono-digestion. However, the positive synergy of co-digestion with an optimum CM/SM of 2.5 (310 mLCH4/gVSadded) resulted in a high hydrolytic capacity and methane production. The modified Gompertz model (R2 > 0.98) and modified Aiba model (R2 > 0.88) illustrated co-digestion significantly improved the methane generation rate with strong ammonia tolerance. Dissolved Organic Matter (DOM) variation in response to the metabolic rate of microbial community illustrated that the SMP-like and protein-like components half-split by EEM-PARAFAC were significantly negative corresponded to bio-methane production. Moreover, the canonical correlation analysis (CCA) resulted a significant difference between the substrate and DOM composition. Potential functional metabolic illustrated statistically significance difference between mono and co-digestion, however, Methanosaeta and Syntrophobacter predominated the syntrophic methanogenesis. The constructed complex metabolic cooperation caused the co-digestion stable and high efficiency.