Impact of polymer flocculants on coagulation-microfiltration of surface water

Organic polymers are widely used as flocculants in pretreatment for microfiltration. However, their impact on microfiltration system performance was not well understood. In this study, the effects of three types of polymer flocculants on microfiltration permeate water quality and membrane fouling were evaluated using a hollow fiber membrane under two different operation modes, coagulation/flocculation-sedimentation-microfiltration (CFSM) and coagulation/flocculation-microfiltration (CFM). Interestingly, the effect of polymers on membrane fouling did not appear to reflect their impact on dissolved organic matter content or floc particle properties in the membrane feed water. The addition of polymer flocculants resulted in floc particles of larger size and smaller fractal dimension and slightly enhanced the removal of dissolved organic matter, both of which were expected to reduce membrane fouling. However, it significantly aggravated membrane fouling in all cases except when the positively charged poly(diallyldimethylammonium) chloride was used in the CFSM process. In particular, all polymers greatly increased hydraulically irreversible fouling in the CFM mode. The increased fouling in the CFSM mode is attributed to the residual polymer, while that in the CFM mode is attributed to the enhanced irreversible floc particle attachment on the membrane surface. Considering the potential severe membrane fouling and the small improvement in treated water quality when polymers are used, the application of polymers in microfiltration pretreatment needs to be carefully evaluated.     

A randomized double‐blind crossover study of indoor air filtration and acute changes in cardiorespiratory health in a First Nations community

Few studies have examined indoor air quality in First Nations communities and its impact on cardiorespiratory health. To address this need, we conducted a crossover study on a First Nations reserve in Manitoba, Canada, including 37 residents in 20 homes. Each home received an electrostatic air filter and a placebo filter for 1 week in random order, and lung function, blood pressure, and endothelial function measures were collected at the beginning and end of each week. Indoor air pollutants were monitored throughout the study period. Indoor PM_2.5 decreased substantially during air filter weeks relative to placebo (mean difference: 37 μg/m³, 95% CI: 10, 64) but remained approximately five times greater than outdoor concentrations owing to a high prevalence of indoor smoking. On average, air filter use was associated with a 217‐ml (95% CI: 23, 410) increase in forced expiratory volume in 1 s, a 7.9‐mm Hg (95% CI: ?17, 0.82) decrease in systolic blood pressure, and a 4.5‐mm Hg (95% CI: ?11, 2.4) decrease in diastolic blood pressure. Consistent inverse associations were also observed between indoor PM_2.5 and lung function. In general, our findings suggest that reducing indoor PM_2.5 may contribute to improved lung function in First Nations communities.     

资源型功能磷复肥对水稻产量、养分吸收及抗折力的影响

通过2年田间试验研究了资源型功能磷复肥对晚稻生长、产量、养分吸收及抗逆性的影响。结果表明,施磷可显著促进水稻的生长发育、增加干物质积累和稻谷产量、提高水稻P、Ca、Mg的吸收量和抗折力;与高浓度磷肥处理(HP)相比,各资源型功能磷复肥处理(LP)增加稻谷产量309~689 kg/hm~2,分蘖初期P吸收量平均增加了13.1%~26.1%,收获期水稻地上部Ca、Mg的吸收量分别增加了14.3%~42.8%、20.6%~32.8%,抗折力显著增加6.8%~27.9%。各处理磷肥偏生产力无明显差异,但LP处理农学利用率显著增加21.0%~112.0%。     

Cells on biomaterials – some aspects of elemental analysis by means of electron probes

Electron probe X‐ray microanalysis enables concomitant observation of specimens and analysis of their elemental composition. The method is attractive for engineers developing tissue‐compatible biomaterials. Either changes in element composition of cells or biomaterial can be defined according to well‐established preparation and quantification procedures. However, the qualitative and quantitative elemental analysis appears more complicated when cells or thin tissue sections are deposited on biomaterials. X‐ray spectra generated at the cell/tissue–biomaterial interface are modelled using a Monte Carlo simulation of a cell deposited on borosilicate glass. Enhanced electron backscattering from borosilicate glass was noted until the thickness of the biological layer deposited on the substrate reached 1.25 μm. It resulted in significant increase in X‐ray intensities typical for the elements present in the cellular part. In this case, the mean atomic number value of the biomaterial determines the strength of this effect. When elements are present in the cells only, the positive linear relationship appears between X‐ray intensities and cell thickness. Then, spatial dimensions of X‐ray emission for the particular elements are exclusively in the range of the biological part and the intensities of X‐rays become constant. When the elements are present in both the cell and the biomaterial, X‐ray intensities are registered for the biological part and the substrate simultaneously leading to a negative linear relationship of X‐ray intensities in the function of cell thickness. In the case of the analysis of an element typical for the biomaterial, strong decrease in X‐ray emission is observed in the function of cell thickness as the effect of X‐ray absorption and the limited excitation range to biological part rather than to the substrate. Correction procedures for calculations of element concentrations in thin films and coatings deposited on substrates are well established in materials science, but little is known about factors that have to be taken into account to accurately quantify bioelements in thin and semi‐thick biological samples. Thus thorough tests of currently available quantification procedures are required to verify their applicability to cells or tissues deposited on the biomaterials.     

柴油机颗粒物-氮氧化物减排系统贵金属催化剂研究进展

汽车排放的氮氧化物(NO_x)和碳烟颗粒物(PM)会对环境和人类健康造成严重的危害,但是现有的技术仅能对NO_x或PM的排放实现单独净化。与其他尾气净化技术相比,柴油机颗粒物-氮氧化物减排系统(DPNR)兼具NO_x和PM净化效果,成为下一代NO_x和PM协同净化的首选催化系统。本文综述了DPNR催化反应机理以及系统中NO_x和PM系统净化用的贵金属催化剂的研究进展;总结了Pt基催化剂在不同条件下同时消除NO_x和PM的催化活性,系统地讨论了Ba、K、Mn等元素掺杂对Pt基催化剂的影响。同时归纳比较Ag基、Ru基与Pt基催化剂在PM氧化和NO_x消除方面的区别,为研究开发同时消除NO_x和PM的高效催化剂提供参考。     

碱性氧化剂对水泥固化淤泥强度的影响研究

为消除淤泥中有机质对水泥固化淤泥的不利影响,提出了氧化降解有机质、减薄双电层厚度、维持pH值稳定等对策来提高水泥固化淤泥的强度。采用高铁酸钾和碳酸氢钠作为碱性氧化剂,配合水泥对淤泥进行固化处理。通过无侧限抗压强度试验,初步了解碱性氧化剂对水泥固化淤泥强度的影响规律,并利用有机元素试验、动电电位试验、比表面积试验和SEM等手段,进一步探究碱性氧化剂的固化机理。研究结果表明:掺碱性氧化剂的水泥固化淤泥7d无侧限抗压强度达到了1.536 MPa。碳酸氢钠通过中和有机酸,维持水泥固化淤泥为p H=9～10的碱性环境;该条件下,高铁酸钾能高效降解有机质,除去黏土颗粒表面聚合态的有机质胶膜,有利于SiO_2与Al_2O_3游离于孔隙溶液中,促进水泥水化产物的生成。同时,孔隙溶液中游离的高价阳离子与黏土颗粒表面低价阳离子交换吸附,减薄双电层厚度,引起土颗粒的絮凝团聚。     

高含水率有机质河道底泥压缩性状试验研究

河道底泥的压缩性状是影响河道底泥环保疏浚设计及处置的一个关键因素,采集了4条河道的底泥,针对4种城市河道底泥和过氧化氢处理的底泥开展了一系列物理和压缩试验,研究河道底泥的压缩性状,探讨有机质含量对河道底泥压缩性状的影响规律。试验结果表明,河道底泥的有机质含量变化范围大,河道底泥的压缩性状与底泥的物理性状密切相关,与无机质土类似,初始孔隙比和液限孔隙比是河道底泥压缩性状的两个关键控制因素。有机质对底泥压缩性状的影响可以归结于液限孔隙比的改变,有机质含量主要影响河道底泥的液限和比重,进而导致河道底泥重塑屈服应力σ_(yr)~′和压缩性状发生改变。有机质含量越高,液限孔隙比越大,压缩指数越大,呈现出的压缩性越高。     

湖北双河硒矿地质特征及成因浅析

本文介绍了双河硒矿地质特征、分布规律;阐述了成矿与碳酸盐台地海盆浅部沼泽(主要为藻沼)环境中局部出现的黑色炭质硅质岩相有关;矿质来源与火山活动有关;探讨了成矿机制;提出了该硒矿属于沉积-成岩-表生层控成因。     

四川广旺地区石煤资源开发利用研究

四川广旺含钒石煤主矿层属品位较富的钒矿资源，研究表明石煤中钒主要以Ｖ（Ⅲ）形式赋存于粘土矿物里。提钒过程中，焙烧是关键。它直接影响石煤中Ｖ（Ⅲ）向Ｖ（Ｖ）的价态转化率（ηｖ（ｖ））、Ｖ（Ｖ）进一步向可溶性的钒的转化率（η焙）及钒的浸出与沉淀。采用复合钠盐（ＮａＣｌ＋Ｎａ２ＳＯ４）焙烧比单一钠盐可提高焙烧转化率２％－５％。焙烧过程中钒的价态转化率与焙烧转化率存在着内在联系。