三种人工湿地脱氮除磷效果比较研究

对沸石潜流湿地、砾石潜流湿地和自由表面流人工湿地脱氮除磷性能进行了中试对比试验研究,结果表明在相同进水水质和水力停留时间为1 d的运行条件下,沸石潜流湿地脱氮效果最佳,总氮去除率接近60%;砾石潜流湿地除磷效果最佳,总磷去除率可达70%;自由表面流人工湿地脱氮除磷效果介于沸石和砾石潜流湿地之间.探讨了三种人工湿地脱氮除磷机理方面的差别,并对其进行了经济性、运行方式等方面的比较.     

Investigation of calcareous beach sands in the Akumal and Tulum areas for use in constructed wetlands,Eastern Yucatan Peninsula

Constructed wetlands can be a low-cost, ecologically based technology to locally treat domestic wastewater prior to discharge. Wetland systems implemented in the resort village of Akumal in the state of Quintana Roo, in the Yucatan Peninsula of Mexico have been considered moderately successful over approximately 10 years of operation. Yet the wide-scale implementation of constructed wetlands has not occurred in the region nor throughout Mexico due largely to the cost of the crushed aggregate used in these systems. Variation in the geotechnical and mineralogical properties of 29 samples of local calcareous beach sands collected from the tourist areas of Akumal and Tulum in the Yucatan, Mexico were analyzed and compared to those of crushed aggregate currently used in constructed wetland systems in Akumal. Powder X-ray diffraction on beach sand samples from Akumal and Tulum indicates that the proportion of aragonite varies from 24 to 84%, calcite varies from 7 to 38% and Mg-calcite varied from 8 to 57% compared to crushed aggregate which consists of 0–25% aragonite and 75–100% calcite. Compared to crushed aggregate beach sands are unimodal and have better uniformity coefficients, making them a better geotechnical choice than crushed sands with respect to these properties. Grain-size of the beach sands is much smaller compared to that of the crushed aggregate currently used in the constructed wetland systems in Akumal which should enhance the efficiency of the filtration of organic matter and bacteria. The average hydraulic conductivity measurements of 0.010 and 0.016 cm/s for beach sands from Akumal and Tulum, respectively are comparable or less than the average of 0.016 cm/s for crushed aggregate currently used in engineered wetland systems. Yet a combination of high bulk porosity, intragranular pores, and the presence of Mg-calcite observed in beach sands may likely result in higher dissolution rates versus the crushed aggregate. Preliminary assessment suggests that the use of local sand may be a technical, economic, and perceptual enhancement to the systems. Still a careful and thorough analysis of the potential environmental and aesthetic impacts of mining beach sands is necessary.     

人工快渗污水处理系统水力负荷周期的设计

人工快渗(CRI系统)源自快速渗滤污水土地处理系统(RI系统),并沿用了其中的干湿交替工作方式,因此, 水力负荷周期同样也成为CRI系统的重要设计参数,也是系统设计的一大难点。目前CRI系统水力负荷周期的设计,不仅需要根据已有的经验,而且还要通过一段调试运行才能确定,设计过程中缺乏理论依据和设计原则。为此,笔者研究了CRI与RI系统两者之间的差异,充分考虑水力负荷周期调整对CRI系统运行的各方面影响,分别从防止NH4 N穿透和保证系统NH4 N充分硝化两个角度,提出了水力负荷周期中淹水时间和落干时间确定新方法,并通过松岗试验实例进行了初步验证,为今后CRI系统水力负荷周期的设计提供了有效的理论依据和设计原则。     

Investigations of subsurface flow constructed wetlands and associated geomaterial resources in the Akumal and Reforma regions,Quintana Roo,Mexico

Subsurface flow constructed wetlands in the village of Akumal, Quintana Roo, Mexico were surveyed to determine the general status of the wetland systems and provide baseline information for long term monitoring and further study. Twenty subsurface flow wetlands were surveyed and common problems observed in the systems were overloading, poor plant cover, odor, and no secondary containment. Bulk mineral composition of aggregate from two subsurface flow constructed wetlands was determined to consist solely of calcite using bulk powder X-ray diffraction. Some soil structure is developed in the aggregate and aggregate levels in wetlands drop at an estimated rate between 3 and 10 cm/year for overloaded wetlands owing to dissolution. Mineral composition from fresh aggregate samples commonly is a mixture of calcite and aragonite. Trace amounts of Pb, Zn, Co, and Cr were observed in fresh aggregate. Coefficients of permeability (k) varied from 0.006 to 0.027 cm/s with an average values being 0.016 cm/s. Grain size analysis of fresh aggregate samples indicates there are unimodal and multimodal size distributions in the samples with modes in the coarse and fine sand being common. Investigations of other geologic media from the Reforma region indicate that a dolomite with minor amounts of Fe-oxide and palygorskite is abundant and may be a better aggregate source that the current materials used. A Ca-montmorillonite bed was identified in the Reforma region as well and this unit is suitable to serve as a clay liner to prevent leaks for new and existing wetland systems. These newly discovered geologic resources should aid in the improvement of subsurface flow constructed wetlands in the region. Although problems do exist in these wetlands with respect to design, these systems represent a successful implementation of constructed wetlands at a community level in developing regions.     

Adsorption of copper, nickel and lead ions from synthetic semiconductor industrial wastewater by palm shell activated carbon

Granular activated carbon produced from palm kernel shell was used as adsorbent to remove copper, nickel and lead ions from a synthesized industrial wastewater.Laboratory experimental investigation was carried out to identify the effect of pH and contact time on adsorption of lead, copper and nickel from the mixed metals solution. Equilibrium adsorption experiments at ambient room temperature were carried out and fitted to Langmuir and Freundlich models. Results showed that pH 5 was the most suitable, while the maximum adsorbent capacity was at a dosage of 1 g/L, recording a sorption capacity of 1.337 mg/g for lead, 1.581 mg/g for copper and 0.130 mg/g for nickel. The percentage metal removal approached equilibrium within 30 min for lead, 75 min for copper and nickel, with lead recording 100 %, copper 97 % and nickel 55 % removal, having a trend of Pb²⁺ > Cu²⁺ > Ni²⁺. Langmuir model had higher R² values of 0.977, 0.817 and 0.978 for copper, nickel and lead respectively, which fitted the equilibrium adsorption process more than Freundlich model for the three metals.     

Effects of plants development and pollutant loading on performance of vertical subsurface flow constructed wetlands

The influent concentration has a great effect on nutrients removal efficiency in vertical subsurface flow constructed wetland systems, but treatment performance response to different C: N: P ratios in the influent are unclear at present. At the first growing seasons, the effects of the plants present or not, season, the different C: N: P ratio in influent condition and their interaction on treatment performances were studied in the planted or the unplanted wetlands in greenhouse condition. Each set of units was operated at hydraulic loading rates of 40 L/d. Low, medium and high-strength (100, 200, 400 mg/L of chemical oxygen demand or 20, 40, 80 mg/L total nitrogen) synthetic sewage were applied as influent. According to the first growing season results, the average removal efficiencies for the unplanted and the planted wetlands were as follows: chemical oxygen demand (44–58 % and 55–61 % respectively), total nitrogen (26–49% and 31–54 %) and total phosphorus (36–64 % and 70–83 %). The both wetlands system was operated as an efficient treatment system of highest average removal rates of both chemical oxygen demand and total phosphorus when medium-strength synthetic sewage were applied. When high strength synthetic sewage was applied, the planted wetlands usually had a higher nutrients removal rates than the unplanted over the study period. The plants grew well under any high loading treatment over the study period. Anyhow, it also proved that the wetland systems have a good capacity to treat different strength wastewater in greenhouse condition.     

建立城乡统一的建设用地市场研究

建立城乡统一的建设用地市场,已被确定为中国土地制度改革的方向。要推动城乡统一的建设用地市场的建立,需要了解集体建设用地市场的现状和存在问题,分析阻碍集体建设用地入市的原因,在此基础上才能提出有建设性的改革建议和实施途径。本文对城乡建设用地市场的一些重大问题作了分析判断,认为集体建设用地市场早在改革开放前就已存在,改革开放后更为国家的工业化、城市化做出了重要贡献,这是中国亿万农民的伟大创造;1998年修订的土地管理法给这一市场带来问题,但集体建设用地市场禁而不止,仍以各种形式广泛存在;改革的难点,在于政府直接经营土地。政府不再经营土地,是建立城乡统一的建设用地市场的关键;现在最需要做的,是认真了解、总结基层的实践和群众的创造;要按照党的十八届三中全会决定的部署,稳步推进改革。提出九大方面的具体实施工作建议。     

Bioaugmentation for the enhancement of hydrocarbon phytoremediation by rhizobacteria consortium in pilot horizontal subsurface flow constructed wetlands

The development of the bioaugmentation during the phytoremediation of contaminated water with diesel in pilot horizontal subsurface flow constructed wetlands was investigated for 63 days. The objective of this study was to examine the enrichment of rhizobacteria in a pilot-scale system for efficient treatment of total petroleum hydrocarbon (TPH) effluent. A consortium of three rhizobacteria strains (Bacillus aquimaris, Bacillus anthracis and Bacillus cereus), which were able to utilize hydrocarbon compounds as sole carbon sources, was injected into the constructed wetlands (batchwise operation) planted with Scirpus grossus. The TPH removals from water, without or with the addition of rhizobacteria, were found to be 72 and 84%, while from sand was found to be 59 and 77%, for each treatment, respectively. These results showed that the rhizobacteria strains could enhance S. grossus growth by decreasing diesel stress and protecting S. grossus against diesel, with 12 and 18% additional TPH removal from water and sand, respectively. Our results demonstrate that S. grossus is potential to improve the phytoremediation of hydrocarbon contaminants through inoculation with effective rhizobacterial strains.     

A review on the mechanism and affecting factors of nitrous oxide emission in constructed wetlands

Constructed wetlands (CWs) are considered important sources of nitrous oxide (N₂O). Various reports in the literature indicate that CWs have high N₂O emission rates. The release of N₂O from CWs treating wastewater emissions range from ?16.7 to 188 mg N₂O m^?2day^?1. N₂O in CWs is produced mainly by nitrification, denitrification, nitrifier denitrification, and nitrate-ammonification. Denitrification is considered the major source of N₂O under most conditions. In recent years, two main methods of sampling N₂O gas in CWs have been employed, including the headspace equilibration technique and the closed static chambers technique. N₂O emission may be affected by various operating parameters and environmental conditions. One of the main environmental factors affecting the removal of nitrogen in CWs is dissolved oxygen, which affects nitrification and denitrification processes, thus greatly influencing N₂O emission. CW gas dynamics is affected mainly by season and weather conditions, especially temperature and moisture. Aquatic plants, flow regime, oxidation–reduction potential, nitrate concentration, C/N ratio and other factors can affect N₂O emission in CWs.     

Efficiency of compost in the removal of heavy metals from the industrial wastewater

Authorities have been applying very strict regulations for the treatment of industrial wastewater recently because of the threatening level of the environmental pollution faced. Industrial wastewater containing heavy metals is a threat to the public health because of the accumulation of the heavy metals in the aquatic life which is transferred to human bodies through the food chain. Therefore, recently, researchers have been oriented toward the practical use of adsorbents for the treatment of wastewater polluted by heavy metals. The aim of this research was to determine the retention capacity of compost for copper, zinc, nickel and chromium. For this purpose, experiments in batch-mixing reactors with initial metal concentrations ranging from 100 to 1,000 mg/l were carried. It was also observed that compost could repeatedly be used in metal sorption processes. The experiments conducted indicated that compost has high retention capacities for copper, zinc and nickel, but not for chromium. Thus, compost has been approved as a potential sorbent for copper, zinc and nickel and may find place in industrial applications. Thus, solid waste which is another source of significant environmental pollution will be reduced by being converted into a beneficial product compost.     

Geostatistical analyses and fractionation of heavy metals in urban soil from industrial district in Weinan, NW China

The concentrations of metals (Pb, Cr, Ba, Zn, V, Mn, Co, Cu, Ni and As) in 38 soil samples collected from the industrial district in Weinan (NW China) were determined by wavelength dispersive X-ray fluorescence spectrometry. The magnetic parameters of soil including low-/high-frequency susceptibility and frequency-dependent susceptibility were measured. The modified three-step BCR sequential extraction procedure was used to evaluate mobility, availability and persistence of trace elements in urban soil samples. Multivariate (principal component analysis, clustering analysis and correlation analysis) and geostatistical analysis (ArcGIS tools) were applied to the obtained data to evaluate the analytical results and to identify the possible pollution sources of metals as well as geo-spatial distributions. The results revealed that the sampling area was mainly influenced by two main sources: (1) Ba, Cu, Pb, Cr and Zn were mainly derived from industrial sources, which combined with coal combustion as well as traffic factor. The mobility sequence based on the sum of the BCR sequential extraction stages was: Pb (53.79 %) > Zn (51.78 %) > Cu (50.96 %) > Ba (42.59 %) > Cr (18.47 %). Pb was the metal predominantly associated (~46.86 %) with the form bound to Fe/Mn oxides, and the highest percentage of Zn was exchangeable and carbonate-bound fraction. Cu was present mainly in organic fraction, while the residual fraction was the most dominant solid phase pool of Cr (~81.53 %) and Ba (~57.41 %). (2) Mn, V, Co, As and Ni in the study area were consistently from natural sources. The analysis of enrichment factors indicated that urban soils in Weinan City were classified as having significant enrichment by Ba, Cu, Pb, Cr and Zn. The overall results proposed the future tactics for Weinan environment quality control on a local scale that concerned not only the levels of risky, but also the industrial emission abatement techniques as well as urban setting.     

Gaseous air pollution background estimation in urban,suburban, and rural environments

There is a great demand for estimating the ambient air pollutant background concentrations in order to assess the effectiveness of different emission control strategies. In this paper, the background concentrations of four pollutants, namely sulfur dioxide (SO₂), nitrogen oxides (NOx), carbon monoxide (CO), and ozone (O₃) pollutants in urban, suburban, and rural environments were investigated using Kolmogorov–Zurbenko (KZ) filter technique. Air quality data from monitoring stations over a period of 4 years (2007–2010) was analyzed for three locations in Kuwait, namely urban, suburban, and rural. The spatial and temporal (daily, weekly, and monthly) variations of the four pollutants were analyzed. The results show that the levels of ambient air pollutant background concentrations were high in the urban site compared to suburban and rural area. The diurnal variation of SO₂ concentration showed an early morning peak, while the diurnal variation of NOx concentration constituted has two peaks, one was in the early morning hours (5 to 8 a.m.) and the second was in nighttime hours (8 to 11 p.m.). These two peaks were observed at all three locations. The monthly background NOx concentration reached a maximum in winter and minimum in summer. Diurnal variation of CO concentration showed a similar trend to SO₂ concentrations in all three locations. Because of the photochemical reactions that occur in the atmosphere, the background concentration of O₃ showed an inverse relation with respect to background concentration of NOx.     

Long-term performance of a constructed wetland/filter basin system treating wastewater,Central Florida

This study investigated the efficiency of a constructed wetland/filter basin (CW/FB) treatment system to improve the chemical composition of waste and surface waters. The system was constructed in closed phosphate mines used for clay settling and sand tailings. Monitoring was carried out for 18 months to evaluate the CW/FB performance under a variety of climatic conditions. Water samples were taken bi-monthly. To evaluate possible groundwater input into and water leaking out of the wetland 6 monitor wells were installed along the flow path and sampled monthly. In order to estimate the change of water chemistry along the wetland flow path, water samples along a transect were taken during the dry and rainy seasons. The samples were analyzed for pH, T, oxidation–reduction potential (ORP), conductivity, total dissolved solids (TDS), dissolved oxygen (DO), Fe(II), H₂S, major anions, major cations, arsenic, fecal and total coliform.The study showed the following changes in water quality between the input and output: (1) Substantial decrease of water temperature (up to 10 °C); (2) Significant change in pH from about 9 to 6.5–7; (3) Negative ORP confirming the reducing conditions of the treatment system; (4) Substantial increase of H₂S (up to 1060 µg/L); (5) Reduction of As from 5 to <2 µg/L (mostly <0.5); (6) Substantial reduction of SO₄, F, Cl, NO₃, NO₂, Br, Na, K, Ca, and Mg; (7) Reduction of fecal and total coliform from 30–730 and 1000–7000 to <2 and <100 count/100 mL, respectively. In general, the performance of the CW/FB treatment system showed great potential to improve the water quality of industrial and municipal wastewater. Despite significant seasonal variations with respect to temperature, rainfall and humidity, the chemical/microbiological composition of the wetland output remained relatively constant.     

Hexamine adsorption study on activated carbon from aqueous solutions for application in treatment of hexamine industrial wastewater

The adsorption of hexamine onto powdered activated carbon from aqueous solutions was studied in a fixed bed system. Langmuir, Freundlich, Redlich–Peterson and Toth isotherm models were used to fit the experimental data and isotherm parameters were determined. The results revealed that the adsorption isotherm models fitted the data in the order of Langmuir > Toth > Redlich–Peterson > Freundlich. Lagergren pseudo-first order kinetic model was found to correlate well with the experimental data. The effects of solution pH, temperature, initial hexamine concentration and added salts concentration on the adsorption capacity and the rate of adsorption were studied. The results indicate that the rate of adsorption increases and then decreases as temperature of the hexamine solution increases, however, the adsorption capacity decreases. The addition of low concentration of salt significantly increases the adsorption capacity of activated carbon. The results showed that the activated carbon has potential for the adsorption of hexamine from industrial hexamine wastewater.     

城乡统筹发展中的土地利用问题探讨

城乡统筹中的土地开发利用,应当体现整体化、融合化、动态化的配置原则。要调整传统的城市规划化、土地国有化、农民市民化的城市化发展演进模式,改变目前城乡社会资源要素不均,衡配置和土地开发利用的双轨制,应当在发展思路、发展方式和发展机制上予以完善、改革和创新,可将统筹“两规”、统筹基础设施和公共服务用地,统筹农村低效土地利用作为切入口。     

Eutrophication and salinization of urban and rural kettle lakes in Kalamazoo and Barry Counties,Michigan, USA

Salinization and eutrophication caused by runoff of road salt and nutrients was assessed in three kettle lakes, two (Woods and Asylum Lakes) located in urban Kalamazoo, MI, and one (Brewster Lake) in rural Hastings, MI. Profiles of dissolved O₂, conductivity, pH, and temperature were measured in situ, at half meter intervals. Water samples were collected at discrete depth intervals of 1 m and analyzed for Fe(II), Mn(II), ammonium, alkalinity, Cl^?, Na, Mg, K and Ca. Results of this study indicate that all three lakes are eutrophic with anoxic bottom waters. Conductivity was much greater, and Cl^? levels were more than 100 times greater, in the two urban lakes compared to the rural lake, demonstrating the significant impact of road salt deicers on urban lake water chemistry.     

Differences in pathogen indicators between proximal urban and rural karst springs,Central Kentucky,USA

Because of their architecture, karst aquifers are susceptible to contamination by fecal-derived pathogens. Previous studies have examined the behavior of bacterial indicators such as total coliforms (TC) and fecal coliforms (FC) in karst aquifers, but simple techniques for discriminating between human and non-human inputs are still needed. This study examines concentrations of TC, FC, atypical colonies (AC, which grow on the same media as TC), male-specific coliphage virus (MSP, an indicator of human feces), and nitrate at two springs in the Inner Bluegrass region of Kentucky (USA). Blue Hole Spring primarily drains the city of Versailles, whereas spring SP-2 drains pasture. Baseflow was monitored, usually biweekly, from December 2002 to March 2004, while storm flow was monitored in September 2003 and March 2004. At each spring, bacterial concentrations were highest in storm flow and lowest in “normal” baseflow (for which 72-h antecedent precipitation was negligible). Concentrations in baseflow tended to be highest during late spring and summer and lowest during autumn and winter. FC concentrations exceeded regulatory (contact) standards in storm-flow samples. For both storm flow and baseflow, AC concentrations were greater than TC, which in turn were greater than FC. Median AC and TC concentrations were greater in baseflow at Blue Hole than at SP-2. MSP was detected in most samples from Blue Hole but never at SP-2. The AC/TC ratio was typically <15 except for normal baseflow samples at Blue Hole, which is probably impacted by leakage from sanitary sewers, as suggested by MSP and nitrate results. Mobilization of sessile bacteria appears to reduce the AC/TC ratio during storm flow. Consequently, this ratio shows promise as a screening tool to identify sewage inputs in karst groundwater basins under baseflow conditions.