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81.
以推拉理论为视角,分别从农村宅基地作为资源和资产属性以及拥有农村宅基地使用权的农民迁移到城市这两个角度,重新梳理影响农户宅基地退出意愿的因素,建立了农村宅基地退出影响因素的推拉分析框架。在理论分析的基础上,利用在南京市栖霞区农村实地调查得到的数据,建立二元Logistic模型归纳主要影响农户退出意愿的推力和拉力因素。研究发现,受教育水平、农户年总收入、家庭居住人口数和农户是否参加农村养老保险是宅基地退出的主要推动因素;而非农业收入占比、外出务工人口数、是否参加城镇养老保险、是否拥有城镇住所、是否有宅基地产权证书以及宅基地抵押权认知情况是影响宅基地退出的主要拉力因素。基于以上的影响因素分析,提出完善农村宅基地退出机制的政策建议。 相似文献
82.
137Cs+/90Sr2+-containing radioactive wastewater is one of the most important problems that the world has been facing with. A by-product, activated porous calcium silicate, is generated at high levels by the pre-desiliconizing and soda-lime-sintering processes for producing Al2O3 from high-alumina fly ash. In order to examine if this by-product could be used as an absorbent for removal of 137Cs+/90Sr2+ from radioactive wastewater, various parameters, such as pH, adsorbent dose, contact time, and initial concentration, were discussed. Results indicated that the equilibrium reached in about 2 hr. Activated porous calcium silicate was highly pH sensitive and able to remove Cs+/Sr2+ in a near-neutral environment. The adsorption equilibrium was best described by Freundlich isotherm equations, and the adsorption of Cs+/Sr2+ was a physical process. The adsorption kinetic data could be better fitted by the pseudo-second-order model, and the adsorption was controlled by multidiffusion. Current study showed that activated porous calcium silicate has a good adsorption of Cs+/Sr2+ for their removal. However, other characteristics, such as selectivity because of coexisting cations, elution and regeneration, thermal stability, and acid resistance, should be discussed carefully before using it in an actual field.
Implications:Removing 137Cs+/90Sr2+ from radioactive wastewater is one of the tough issues that has been attracting more and more attention world widely, which is the same as fly ash. For recycling high-alumina fly ash, in which Al is extracted to produce Al2O3, a huge amount of activated porous calcium silicate is generated year by year. In this paper, this by-product was successfully used as an absorbent to remove 137Cs+/90Sr2+ from radioactive wastewater for the first time. Factors that affect the absorbability and the mechanisms were discussed in details, providing a possible choice for disposal of 137Cs+/90Sr2+-containing radioactive wastewater. 相似文献
83.
Treatment of coking wastewater by an advanced Fenton oxidation process using iron powder and hydrogen peroxide 总被引:5,自引:0,他引:5
In this study the treatment of coking wastewater was investigated by an advanced Fenton oxidation process using iron powder and hydrogen peroxide. Particular attention was paid to the effect of initial pH, dosage of H2O2 and to improvement in biodegradation. The results showed that higher COD and total phenol removal rates were achieved with a decrease in initial pH and an increase in H2O2 dosage. At an initial pH of less than 6.5 and H2O2 concentration of 0.3 M, COD removal reached 44-50% and approximately 95% of total phenol removal was achieved at a reaction time of 1 h. The oxygen uptake rate of the effluent measured at a reaction time of 1 h increased by approximately 65% compared to that of the raw coking wastewater. This indicated that biodegradation of the coking wastewater was significantly improved. Several organic compounds, including bifuran, quinoline, resorcinol and benzofuranol were removed completely as determined by GC-MS analysis. The advanced Fenton oxidation process is an effective pretreatment method for the removal of organic pollutants from coking wastewater. This process increases biodegradation, and may be combined with a classical biological process to achieve effluent of high quality. 相似文献
84.
A comprehensive study of the degradation of monuron, one of the phenylurea herbicides, was conducted by UV-Vis/WO3 process. It was found that hydroxyl radicals played a major role in the decay of monuron while other radicals (e.g. superoxide) and hole might also contribute to the decomposition of monuron. The oxidation path likely plays a major role in the generation of hydroxyl radicals. The effects of initial pH level, initial concentration of monuron, and inorganic oxidants on the performance of UV-Vis/WO3 process were also investigated and optimized. Comparison between monuron decay pathways by UV-Vis/WO3 and UV/TiO2 was conducted. The decay mechanisms, including N-terminus demethylation, dechlorination and direct hydroxylation on benzene ring, were observed to be involved in the oxidation of monuron in these two processes. Sixteen intermediates were identified during the photodegradation of monuron and degradation pathways were proposed accordingly. 相似文献
85.
采用气体扩散电极为阴极,钛基氧化物(Ti/SnO2-Sb2O5-IrO2)和金属铁构成组合阳极,构建了新型电化学氧化体系用于降解有机污染物。利用该氧化体系,在不同实验条件下考察了苯胺降解的效果与降解过程的相关规律。结果表明,阴极电位、铁阳极通电时间以及苯胺初始浓度均显著影响苯胺的降解效果。当阴极电位为-0.7V,pH3.0,铁阳极通电时间20min时,电化学处理200mg/L苯胺480min,TOC的去除效率达到80.4%,矿化电流效率(MCE)为8.6%,显示了该氧化体系具有良好的有机物降解能力。此外,苯胺降解过程中氨氮和硝态氮浓度的变化表明,苯胺分子中的氮主要转化为NH4和NO3^-。 相似文献
86.
Hong-Guang Guo Nai-Yun Gao Wen-Hai Chu Lei Li Yong-Ji Zhang Jin-Shan Gu Yu-Liang Gu 《Environmental science and pollution research international》2013,20(5):3202-3213
Photochemical degradation of fluoroquinolone ciprofloxacin (CIP) in water by UV and UV/H2O2 were investigated. The degradation rate of CIP was affected by pH, H2O2 dosage, as well as the presence of other inorganic components. The optimized pH value and H2O2 concentration were 7.0 and 5 mM. Carbonate and nitrate both impeded CIP degradation. According to liquid chromatography–tandem mass spectrometry analysis, four and 16 products were identified in UV and UV/H2O2 system, respectively. Proposed degradation pathways suggest that reactions including the piperazinyl substituent, quinolone moiety, and cyclopropyl group lead to the photochemical degradation of CIP. Toxicity of products assessed by Vibrio qinghaiensis demonstrated that UV/H2O2 process was more capable on controlling the toxicity of intermediates in CIP degradation than UV process. 相似文献
87.
Qinsong Xu Han Qiu Weiyue Chu Yongyang Fu Sanjuan Cai Haili Min Sha Sha 《Environmental science and pollution research international》2013,20(12):8672-8679
Laboratory experiments were conducted to investigate copper (Cu) subcellular distribution and toxicity in Hydrilla verticillata. Fronds were subjected to different concentrations (15, 75, and 150 μM) of Cu for 7 days. Cu grains were found in cell walls, plasmodesmata, and within the nuclei and chloroplasts using the autometallographic technique. Subcellular fractionation of Cu-containing tissues indicated that in leaves subjected to high Cu concentrations, 59–65 % of the element was located in the cell wall fraction, followed by cell organelles (21–30 %) and the soluble fraction (10–14 %). The levels of K, P, Zn, and Mg declined under all Cu concentrations, but Ca, Mn, and Fe contents reached their peak at 15 μM Cu and decreased thereafter. F v/F m, F 0, and F m fell significantly in line with the decrease in pigment content. Cu exposure also caused significant damage to the chloroplasts, mitochondria, and nuclei, including disintegration of the chloroplasts and vacuolization of the mitochondria and nuclei, all of which suggested that Cu hastened plant senescence. The Cu maximum permissible concentration for H. verticillata was 10 μM, which was less than the existing general water quality standard. This suggested that H. verticillata could be used to assess Cu phytotoxicity. 相似文献
88.
89.
利用IED22000A便携式微机多道能谱仪对成都市区土壤的天然放射性核素进行了直接就地测量,估算出天然环境放射性核素^238U、^232Th、^40K的比活度范围分别为10.37~77.19Bq/kg、17,85~225.74Bq/kg、284.83~892.67Bq/kg;外照射指数范围为0.16—0.8;离地面1m高的空气吸收剂量率均值为83.23nGy/h;1外照射年有效剂量当量为0.34~0.70mSv;等效镭浓度的变化范围是59.06-386.45Bq/kg,均值为164.15Bq/kg。各项指标均在容许范围之内,因而成都市属于外照射水平的安全区域,人居环境不受影响。 相似文献
90.
This study applied a method of the rotated empirical orthogonal functions to directly decompose the space-time groundwater level variations and determine the potential recharge zones by investigating the correlation between the identified groundwater signals and the observed local rainfall records. The approach is used to analyze the spatiotemporal process of piezometric heads estimated by Bayesian maximum entropy method from monthly observations of 45 wells in 1999-2007 located in the Pingtung Plain of Taiwan. From the results, the primary potential recharge area is located at the proximal fan areas where the recharge process accounts for 88% of the spatiotemporal variations of piezometric heads in the study area. The decomposition of groundwater levels associated with rainfall can provide information on the recharge process since rainfall is an important contributor to groundwater recharge in semi-arid regions. Correlation analysis shows that the identified recharge closely associates with the temporal variation of the local precipitation with a delay of 1-2 months in the study area. 相似文献