Progress in the development and use of refrigerants and unintended environmental consequences.

The world has entered into the "fourth-generation" of refrigerants, and it is an undeniable fact that we will continue to encounter several issues in identifying a suitable refrigerant that suits the purpose and poses no harm to the environment. The ever-changing regulations on the use of refrigerants have often posed great challenges to the refrigeration industry and there is a pressing need to develop new refrigerants and develop better equipment to use them. Theoretically, an ideal refrigerant should possess characteristics such as low-global warming potential (GWP), non-toxic, non-flammable, and zero-ozone depletion potential (ODP). In addition, the refrigerants are also expected to have excellent thermodynamic and thermophysical properties. Many new synthetic refrigerants have been reported as alternative refrigerants and have very low atmospheric life as well as low GWP and zero-ODP. However, it is irrefutable that most of the studies that reported the so-called new refrigerants are actually not new. From the invention of R-12 (Dichlorodifluoromethane) in 1930s to the invention of R-1234yf in 2000s, these substances are available for decades even before being recognized as refrigerants. This review attempts to provide chronicles on different aspects of refrigerants such as their progress since their invention in the early 1800s, classification and properties. In addition, concepts such as issues associated with the long-term use of refrigerants, barriers for the inclusion of low-GWP refrigerants, various protocols and accords that have occurred since the inception of refrigerants are also critically discussed.

A general framework and practical procedure for improving pxrf measurement accuracy with integrating moisture content and organic matter content parameters.

Rapid, accurate detection of heavy-metal content is extremely important for precise risk control and targeted remediation. Herein, a general modeling method and process based on the relationship between Pxrf measured values and site parameters are explored to construct a Pxrf correction model suitable to improve each site's measurement accuracy. Results show a significant correlation between Pb, Mn, and Zn Pxrf measured values and actual concentrations, with correlation coefficients between 0.8 and 0.93. Through the correlation analysis, the correlation coefficient between the water content and the measured value of pxrf is in the range of 0.2-0.5. Pxrf measurement of all heavy metals was weakly affected by soil organic matter content, with correlation coefficients all lower than 0.5. Model transformation effectively improved the correlation between measured Pxrf value and actual concentration, and transformation increased the correlations of Sr, Mn, and Cu by around 0.11. Model verification results showed that the Pb, Zn, Fe, and Mn models can be used to improve Pxrf method detection accuracy.

Isolation distance between municipal solid waste landfills and drinking water wells for bacteria attenuation and safe drinking.

Groundwater pollution and human health risks caused by leachate leakage have become a worldwide environmental problem, and the harm and influence of bacteria in leachate have received increased attention. Setting the isolation distance between landfill sites and groundwater isolation targets is particularly important. Firstly, the intensity model of pollutant leakage source and solute transport model were established for the isolation of pathogenic Escherichia coli. Then, the migration, removal and reduction of bacteria in the aerated zone and ground were simulated. Finally, the isolation distance was calculated based on the acceptable water quality limits, and the influence of hydrogeological arameters was analyzed based on the parameter uncertainty. The results of this study suggest that the isolation distances vary widely ranging from 106 m-5.46 km in sand aquifers, 292 m-13.5 km in gravel aquifers and 2.4-58.7 km in coarse gravel aquifers. The gradient change of groundwater from 0.001 to 0.05 resulted in the isolation distance at the highest gradient position being 2-30 times greater than that at the lowest gradient position. There was a difference in the influence of the thickness of the vadose zone. For example, under the same conditions, with the increase of the thickness of the aeration zone, the isolation distance will be reduced by 1.5-5 times, or under the same thickness of the aeration zone, the isolation distance will be significantly shortened. Accordingly, this needs to be determined based on specific safety isolation requirements. In conclusion, this research has important guiding significance for the environmental safety assessment technology of municipal solid waste landfill.

[Isolation of an excellent bio-flocculant-producing strain and its application in the treatment of cold-rolling waste oily water].

An excellent strain (designated as T-3) which produces bio-flocculants was isolated from soil samples, and identified as Klebsiella sp. species based on the analysis of morphology, physiology and biochemistry and 16S rDNA sequences measurement. The effects of culture conditions such as pH values, temperature, carbon sources and nitrogen sources on bio-flocculants production by T-3 strain were studied. The experiment results show that T-3 strain has better adaptability to carbon sources and nitrogen sources, and higher capacity of bio-flocculants was obtained when the initial pH value of culture and temperature were 9 and 25 degrees C respectively. Based on the colorimetric reactions of proteins and polysaccharide substance, ultraviolet scanning analysis and Fourier Transform Infrared Spectroscopy analysis, it is found that the bio-flocculants produced by T-3 strain contains -OH and -COO(-) groups and belongs to anionic type flocculant. Moreover, the main component is polysaccharides. The treatment of oily cold-rolling wastewater by the bio-flocculant was investigated and the better result was obtained. When the dosages of CaCl2, bio-flocculants and poly aluminium chloride were 4 g x L(-1), 10% (volume fraction) and 1 g x L(-1) respectively, and the pH value was 7.0, the oil concentration, COD and turbidity were decreased to 10 mg x L(-1), 218.4 mg x L(-1) and 1.36 from 4 819 mg x L(-1), 28 456.8 mg x L(-1) and 3 950 with the removal efficiencies of 99.79%, 92.32% and 99.97% respectively. The interaction between flocculant and oily droplets is achieved by the interaction of Van der Waals force, hydrogen bond and the bridged coordination of Ca2+, in which the bridged coordination of Ca2+ is the dominant.

[Phosphorus removal and mechanisms for advanced treatment of sewage by Spirogyra].

The novel way of advanced treatment of municipal wastewater was proposed and characterized by purifying wastewater by Spirogyra. The characteristics of nitrogen and phosphorus removal by Spirogyra were studied aiming at nitrogen and phosphorus removal in advanced treatment of sewage. Under natural light, when Spirogyra's dosage (gross mass) was more than 3.05 g/L, total phosphorus concentration, NH4+-N concentration, TN concentration and permanganate index decreased to less than 0.09, 2.82, 4.31 and 16.86 mg/L respectively, with removal efficiencies of more than 96.84%, 88.60%, 85.49% and 24.56%. During the treatment of sewage, pH value increased, while both calcium cation and magnesium cation concentration decreased, and conductivity decreased. During the growth of Spirogyra, increasing pH value induced saline minerals precipitation, and the precipitated minerals adsorbed phosphate, which were considered as the main mechanisms of phosphorus removal. Furthermore, phosphorus removal by Spirogyra followed Langmuir adsorption isotherm model, and the saturated adsorption of Spirogyra (gross mass) for phosphorus was 3.159 mg/g under this test condition. The increasing pH value made ammonia evaporate during Spirogyra-growth, which might be the main mechanism of nitrogen removal. Under suitable Spirogyra's dosage and hydraulic retention time, the treated sewage might meet the demands of water supply for landscape impoundments on nitrogen and phosphorus concentrations. The better performance of Spirogyra removing nitrogen and phosphorus might provide a novel alternative way for advanced treatment of sewage.