[Analysis of Microbial Community Characteristics and Function Prediction of MBBR with Magnetic Biocarriers at Low Temperature].

In order to clarify effect of magnetic biocarriers on the performance of MBBR at low temperatures, the microbial diversity, community structure, functional characteristics, and nitrogen metabolism of biofilm in the reaction system were investigated. The results indicated that MBBR with magnetic biocarriers had a better pollutant removal efficiency, with the average removal rates of NH4+-N and TN being 16.2% and 12.1% higher than those in the control group (commercial biocarriers), respectively. Illumina high-throughput sequencing analysis showed that higher diversity and richness of the bacterial community was established in the biofilm of magnetic biocarriers. There were obvious differences in microbial community structure of biofilm between the two biocarrier duos to bacterial magnetic susceptibility. The relative abundances of nitrifying bacteria (e.g., Nitrosomonas and Nitrospira) and denitrifying bacteria (e.g., Sphaerotilus and Zoogloea) were increased in the magnetic biocarriers. Functional prediction analysis with PICRUSt2 showed that the microorganism of magnetic biocarriers had a better total gene function expression level, which was significantly more increased than commercial biocarriers in gene-representing signal transduction mechanisms and intracellular trafficking, secretion, and vesicular transport. Furthermore, most of the abundances of nitrogen metabolism genes were raised in the biofilm of magnetic biocarriers (e.g., genes amo and hao, were responsible for nitrification, and genes nap and nor, which were responsible for denitrification). Magnetic biocarriers increased biofilm potential for denitrification at low temperatures. Our results explained the difference in performance between the two reactors from microbiology and provided the theoretical basis for magnetic biocarrier-enhanced performances of MBBR at low temperatures.

Effects of microplastics on the water characteristic curve of soils with different textures.

Microplastic (MP) pollution in the soil severely damages the soil structure and affects the soil water-holding property, thereby affecting the soil water characteristic curve (SWCC). After polyethylene MP (PE-MP) addition at three concentrations (0.5%, 1%, and 2%) under three particle sizes (150 µm, 550 µm, and 950 µm) and two soil textures (sandy soil and loamy soil), SWCCs were measured and fitted with the van Genuchten model. The soil pore structure characteristics were obtained based on CT scanning combined with soil pore three-dimensional reconstruction to quantitatively analyze the relationships between MP properties and soil structure and the SWCC. Low concentrations (0.5%) of PE-MPs did not significantly affect the soil water content, while the accumulation of PE-MPs at a high concentration (2%) strongly affected the soil water-holding property, with small PE-MPs (150 µm) exerting significantly positive effects on the water-holding capacity of loamy soil and 950-µm MPs reducing the soil water content more strongly in sandy soil. The contributions of MP properties and soil textures to the SWCCs differed, and the impact of soil texture on the SWCCs was significantly higher than those of MP concentrations and particle sizes. Differences in MP occurrence characteristics and soil textures also led to variations in the fitted hydraulic parameters of the SWCCs. The addition of 2% 150-µm PE-MPs to loamy soil increased the soil porosity and surface area, while the addition of a higher concentration of large PE-MPs (2%, 950 µm) to sandy soil reduced soil porosity and circularity. This is related to the addition of a large number of small MPs, which may adsorb and bind many smaller soil particles to form larger, water-stable agglomerated structures, while the addition of high concentrations of large MPs in sandy soils may be related to the destruction of the original capillary pore structure of sandy soils and the weakening of soil capillarity. This study provides a theoretical basis for agroecological risk assessments.