摘要：
Rice (Oryza sativa L.)-rapeseed (Brassica campestris L.) intercropping is a routine farming practice in Southern China, and its advantages include more efficient and productive land use as well as an improved soil environment. Field experiments were carried out on two cropping systems (rapeseed-rice rotation and rice-rice continuously) between July 2015 and October 2015. Laboratory tests were conducted to compare rapeseed-rice rotation with rice-rice continuous cropping as the control to investigate enzyme activity and the structure of bacterial communities in the soils. Two sets of soil samples were collected and tested to show that, compared to rice-rice, the catalase, urease, phosphatase and cellulase contents of the soil from rapeseedrice rotation are increased by 11.92, 24.94, 18.80 and 20.34%, respectively, and the sucrase content decreased by 17.93%. DNA from soil microbial communities was extracted for analysis of microbial diversity using the high-throughput sequencing technique. Microbial communities in the rapeseed-rice soil were significantly different in composition to those in the rice-rice soil. Crop rotation increased the size of bacterial populations and altered their proportionality in the bacterial community and decreased the population size of Chlorobi and Chloroflexi. Canonical correspondence analysis showed that there are significant differences in bacterial population size between the two cropping systems. Firmicutes, Latescibacteria, Verrucomicrobia, Gemmatimonadetes and Acidobacteria were the principal driving force microorganisms. Rape-rice soil showed more Firmicutes and Latescibacteria in the July samples and Gemmatimonadetes and Acidobacteria in the October samples whereas the rice-rice soil showed more Verrucomicrobia and Gemmatimonadetes in the July samples and Latescibacteria and Verrucomicrobia in the October samples. These results suggest that in comparison with a rice-rice planting system, long-term rapeseed-rice rotation changes the composition and structure of microbial communities, affects soil enzyme activity, supports a more abundant and diverse microbial population, and consequently maintains higher soil quality and fertility. (C) 2018 Friends Science Publishers
摘要：
In this work, to gain insight into the mechanism of p-nitrophenol (PNP) removal using the reactivity of a biochar supported nanoscale zerovalent iron composite (nZVI/biochar) and nanoscale zero valent iron (nZVI) under anaerobic or aerobic conditions, batch experiments and models were conducted. The PNP removal rate in the more acidic solutions was higher, while it was significantly suppressed at higher pH, especially at pH 9.0. The peak value of the apparent rate constants suggests that the reactivity of nZVI/biochar could be much stronger than that of nZVI under the same aeration conditions. The modified Langmuir–Hinshelwood kinetic model could successfully describe the PNP removal process using nZVI/biochar or nZVI. The reaction constants obtained through a Langmuir–Hinshelwood mechanism under different aeration conditions followed the trend nZVI/biochar (N2) > nZVI/biochar (air) > nZVI (N2) > nZVI (air), indicating that nZVI/biochar under anaerobic conditions exhibits enhanced activity for the degradation of PNP. The nZVI/biochar under anaerobic conditions has the lowest Arrhenius activation energy of PNP degradation–adsorption, suggesting that the surface interaction of eliminating PNP has a low energy barrier. In addition, TOC removal under anaerobic conditions was negligible compared with that under the aerobic system and the total number of iron ions leaching at solution pH 3.0 in the nZVI/biochar or nZVI system under air aeration conditions was much higher than that under nitrogen aeration conditions. The profiles of the intermediates formed during the PNP degradation indicated that in the anaerobic environment, reduction was the predominant step in the removal process, while the degradation of PNP could be regarded as a combination of oxidation and reduction in an aerobic environment.
摘要：
In order to improve the efficiency of water aerator,based on Venturi experimental principle in hydraulics and fluid dynamic ultrasonic generator,the inlet section,throat section,and outlet section of reed whistle ultrasonic generator were designed,and the effect of the water aerator on dissolved oxygen was preliminarily studied. Results indicate that using this water aerator,the dissolved oxygen was 7. 94 mg / L,exceeding the saturation value of dissolved oxygen( 7. 82 mg / L) at current water temperature,reaching the supersaturation. Therefore,the designed water aerator will have a bright application prospect in sewage treatment,aquaculture and aerated irrigation of plants.
