Constructed wetlands for wastewater treatment in cold climate — A review

Constructed wetlands (CWs) have been successfully used for treating various wastewaters for decades and have been identified as a sustainable wastewater management option worldwide. However, the application of CW for wastewater treatment in frigid climate presents special challenges. Wetland treatment of wastewater relies largely on biological processes, and reliable treatment is often a function of climate conditions. To date, the rate of adoption of wetland technology for wastewater treatment in cold regions has been slow and there are relatively few published reports on CW applications in cold climate. This paper therefore highlights the practice and applications of treatment wetlands in cold climate. A comprehensive review of the effectiveness of contaminant removal in different wetland systems including: (1) free water surface (FWS) CWs; (2) subsurface flow (SSF) CWs;and (3) hybrid wetland systems, is presented. The emphasis of this review is also placed on the influence of cold weather conditions on the removal efficacies of different contami-nants. The strategies of wetland design and operation for performance intensification, such as the presence of plant, operational mode, effluent recirculation, artificial aeration and in-series design, which are crucial to achieve the sustainable treatment performance in cold climate, are also discussed. This study is conducive to further research for the understanding of CW design and treatment performance in cold climate.     

中水回用对社区景观水体叶绿素a变化的影响

由于中水的营养盐含量较高,以中水为补水水源的社区景观水体存在较大的水华暴发风险.基于中水回用于景观水体的换水控制实验,建立了中水景观水体的富营养化模型,模拟了连续换水时和终止换水后叶绿素a的变化过程,分析了中水水质和换水周期对水体藻类生长的影响.结果表明,提高中水水质可以降低水体的叶绿素a峰值;在连续换水期,随着换水周期的缩短, 水体的叶绿素a峰值降低,并且从开始换水至达到峰值的时间增长;在连续换水期后终止换水,叶绿素a会重新达到峰值,并且原来的换水周期越短,水体的叶绿素a峰值反而越高,达到峰值所需时间越长.模型应用可为中水回用于社区景观水体的水量水质设计与维护提供依据.     

Energy and environmental applications of carbon nanotubes

Energy and environment are major global issues inducing environmental pollution problems. Energy generation from conventional fossil fuels has been identified as the main culprit of environmental quality degradation and environmental pollution. In order to address these issues, nanotechnology plays an essential role in revolutionizing the device applications for energy conversion and storage, environmental monitoring, as well as green engineering of environmental friendly materials. Carbon nanotubes and their hybrid nanocomposites have received immense research attention for their potential applications in various fields due to their unique structural, electronic and mechanical properties. Here, we review the applications of carbon nanotubes (1) in energy conversion and storage such as in solar cells, fuel cells, hydrogen storage, lithium ion batteries and electrochemical supercapacitors, (2) in environmental monitoring and wastewater treatment for the detection and removal of gas pollutants, pathogens, dyes, heavy metals and pesticides and (3) in green nanocomposite design. Integration of carbon nanotubes in solar and fuel cells has increased the energy conversion efficiency of these energy conversion applications, which serve as the future sustainable energy sources. Carbon nanotubes doped with metal hydrides show high hydrogen storage capacity of around 6?wt% as a potential hydrogen storage medium. Carbon nanotubes nanocomposites have exhibited high energy capacity in lithium ion batteries and high specific capacitance in electrochemical supercapacitors, in addition to excellent cycle stability. High sensitivity and selectivity towards the detection of environmental pollutants are demonstrated by carbon nanotubes based sensors, as well as the anticipated potentials of carbon nanotubes as adsorbent to remove environmental pollutants, which show high adsorption capacity and good regeneration capability. Carbon nanotubes are employed as reinforcement material in green nanocomposites, which is advantageous in supplying the desired properties, in addition to the biodegradability. This article presents an overview of the advantages imparted by carbon nanotubes in electrochemical devices of energy applications and green nanocomposites, as well as nanosensor and adsorbent for environmental protection.     

Microalgae Scenedesmus obliquus as renewable biomass feedstock for electricity generation in microbial fuel cells （MFCs）

Renewable algae biomass, Scenedesmus obliquus, was used as substrate for generating electricity in two chamber microbial fuel cells （MFCs）. From polarization test, maximum power density with pretreated algal biomass was 102mW·m^2 （951mW·m^3） at current generation of 276mA·m^-2. The individual electrode potential as a function of current generation suggested that anodic oxidation process of algae substrate had limitation for high current generation in MFC. Total chemical oxygen demand （TCOD） reduction of 74% was obtained when initial TCOD concentration was 534mg · L^-1 for 150 h of operation. The main organic compounds of algae oriented biomass were lactate and acetate, which were mainly used for electricity generation. Other byproducts such as propionate and butyrate were formed at a negligible amount. Electrochemical Impedance Spectroscopy （EIS） analysis pinpointed the charge transfer resistance （112Ω ） of anode electrode, and the exchange current density of anode electrode was 1214 nA·cm^-2.     

Stochastic analysis of radioactive waste package performance using first-order reliability method

In order to license an underground radioactive waste repository, it is important to demonstrate regulatory compliance with authoritative regulations. Also it is evidence from NRC's criteria for waste package performance that a stochastic analysis is necessary to provide that these criteria can be met with confidence. The first-order reliability method is an attractive tool to the stochastic analysis and particularly useful when statistical information is incomplete, as is common for problems occurring in the subsurface environment. The method is based on using the first-order Taylor series expansion at a specific linearization point to calculate a measure of reliability. Results from a first-order reliability analysis include an estimate of the probability of exceeding a specified performance criteria and measures of the sensitivity of the stochastic solution to the changes in input random variables and their statistical moments. The method of stochastic analysis is illustrated by analyzing the canister corrosion in a radioactive waste package.     

Effect of a seasonal diffuse pollution migration on natural organic matter behavior in a stratified dam reservoir

This article aims to describe the influence of diffuse pollution on the temporal and spatial characteristics of natural organic matter (NOM) in a stratified dam reservoir, the Daecheong Dam, on the basis of intensive observation results and the dynamic water quality simulation using CE-QUAL-W2. Turbidity is regarded as a comprehensive representation of allochothonous organic matter from diffuse sources in storm season because the turbidity concentration showed reasonable significance in a statistical correlation with the UV absorbance at 254 nm and total phosphorus. CE-QUAL-W2 simulation results showed good consistency with the observed data in terms of dissolved organic matter (DOM) including refractory dissolved organic carbon (RDOC) and labile DOC and also well explained the internal movement of constituents and stratification phenomenon in the reservoir. Instead turbidity and NOM were related well in the upper region of the reservoir according to flow distance, gradually as changing to dissolved form of organic matter, RDOM affected organic matter concentration of reservoir water quality compared to turbidity. To control the increase of soluble organic matters in the dam reservoir, appropriate dam water discharge gate operation provided effective measurement. Because of the gate operation let avoid the accumulation of organic matter within a dam reservoir by shorten of turbid regime retention time.     

Calculation of search volume on cruise-searching planktivorous fish in foraging model

Search volume of cruising planktivorous fish was calculated based on its detailed behavior Th examine the factors influencing search volume, a series of experiments were conducted by varying ambient conditions, such as structural complexity light intensity and turbidity Pseudorasbora parva were used in experiment as predator and Daphnia pulex was selected as prey The shape of scanning area of P parva showed elliptic and the search volume changed drastically depending on ambient conditions. Compared with the results of previous foraging model, the search volumes of the fish under previous study were larger (1.2 to 2.4 times) than those from our study These results on the changes in feeding rate can be useful in determining microhabitat requirement of P parva and othercyprinids with a similar foraging behavior The calculated search volume is compared with other foraging model andthe effect of zooplankton-planktivore interactions on aquatic ecosystem is discussed.     

Pharmaceutical removal in tropical subsurface flow constructed wetlands at varying hydraulic loading rates

Determining the fate of emerging organic contaminants in an aquatic ecosystem is important for developing constructed wetlands (CWs) treatment technology. Experiments were carried out in subsurface flow CWs in Singapore to evaluate the fate and transport of eight pharmaceutical compounds. The CW system included three parallel horizontal subsurface flow CWs and three parallel unplanted beds fed continuously with synthetic wastewater at different hydraulic retention times (HRTs). The findings of the tests at 2-6 d HRTs showed that the pharmaceuticals could be categorized as (i) efficiently removed compounds with removal higher than 85% (ketoprofen and salicylic acid); (ii) moderately removed compounds with removal efficiencies between 50% and 85% (naproxen, ibuprofen and caffeine); and (iii) poorly removed compounds with efficiency rate lower than 50% (carbamazepine, diclofenac, and clofibric acid). Except for carbamazepine and salicylic acid, removal efficiencies of the selected pharmaceuticals showed significant (p<0.05) enhancement in planted beds as compared to the unplanted beds. Removal of caffeine, ketoprofen and clofibric acid were found to follow first order decay kinetics with decay constants higher in the planted beds than the unplanted beds. Correlations between pharmaceutical removal efficiencies and log K(ow) were not significant (p>0.05), implying that their removal is not well related to the compound's hydrophobicity.     

Assessment of plant-driven uptake and translocation of clofibric acid by Scirpus validus

Pharmaceutical compounds are now considered as emerging contaminants of environmental concern. The overall objective of this study was to evaluate the uptake and translocation of clofibric acid (CA) by the macrophyte Scirpus validus growing hydroponically. A set of the three replicates was established for each exposure time and for each CA concentration. Plants were grown in 4 L vessels (four plants per vessel corresponding to the three exposure period studies, i.e., 7, 14, 18, and 21 days) which contained an aerated modified Hoagland nutrient solution that was spiked with CA at concentrations of 0.5, 1.0, and 2.0 mg?L^?1. At each exposure period, CA concentration was measured in the nutrient solutions. A sea sand disruption method was employed for the extraction of CA from plant tissues. The determination of the pharmaceutical concentration was carried out using solid phase extraction (SPE) followed by chromatographic analysis. The quantification of CA concentrations in both nutrient solutions (after SPE) and plant tissues (after extraction) was conducted by chromatographic analysis. CA concentrations of 5.4–26.8 μg?g^?1 (fresh weight) were detected in the roots and 7.2–34.6 μg?g^?1 (fresh weight) in the shoots after 21 days. Mass balance calculations showed that S. validus uptake alone accounted for a significant contribution (6–13 % for the roots and 22–49 % for the shoots) of the total loss of CA. The bioaccumulation factors (BAFs) based on fresh weight for the roots ranged from 6.6 to 23.2, while values for the shoots ranged from 9.5 to 32.1. All the BAFs for the shoots were greater than those in the roots, implying that CA has greater tendency to be translocated to the shoots, rather than the roots of S. validus. All the shoot-to-root concentration ratios were more than 1, denoting that the shoots of S. validus do preferentially accumulate CA. We demonstrated that CA can be actively taken up, subsequently translocated and accumulated by aboveground tissues of S. validus. Since S. validus could account for the removal of 28–62 % of the total mass loss of CA from the system, such phytoremediation technology has great potential for the removal of pharmaceuticals such as CA from inflowing waters.     

Municipal solid waste management in China: Status,problems and challenges

This paper presents an examination of MSW generation and composition in China, providing an overview of the current state of MSW management, an analysis of existing problems in MSW collection, separation, recycling and disposal, and some suggestions for improving MSW systems in the future. In China, along with urbanization, population growth and industrialization, the quantity of municipal solid waste (MSW) generation has been increasing rapidly. The total MSW amount increased from 31.3 million tonnes in 1980 to 212 million tonnes in 2006, and the waste generation rate increased from 0.50 kg/capita/day in 1980 to 0.98 kg/capita/year in 2006. Currently, waste composition in China is dominated by a high organic and moisture content, since the concentration of kitchen waste in urban solid waste makes up the highest proportion (at approximately 60%) of the waste stream. The total amount of MSW collected and transported was 148 million tonnes in 2006, of which 91.4% was landfilled, 6.4% was incinerated and 2.2% was composted. The overall MSW treatment rate in China was approximately 62% in 2007. In 2007, there were 460 facilities, including 366 landfill sites, 17 composing plants, and 66 incineration plants. This paper also considers the challenges faced and opportunities for MSW management in China, and a number of recommendations are made aimed at improving the MSW management system.