Influence of environmental factors on arsenic accumulation and biotransformation using the aquatic plant species Hydrilla verticillata

Hydrilla verticillata(waterthyme) has been successfully used for phytoremediation in arsenic(As) contaminated water.To evaluate the effects of environmental factors on phytoremediation,this study conducted a series of orthogonal design experiments to determine optimal conditions,including phosphorus(P),nitrogen(N),and arsenate(As(Ⅴ))concentrations and initial pH levels,for As accumulation and biotransformation using this aquatic plant species,while also analyzing As species transformation in culture media after 96-hr exposure.Analysis of variance and the signal-to-noise ratio were used to identify both the effects of these environmental factors and their optimal conditions for this purpose.Results indicated that both N and P significantly impacted accumulation,and N was essential in As species transformation.High N and intermediate P levels were critical to As accumulation and biotransformation by H.verticillata,while high N and low P levels were beneficial to As species transformation in culture media.The highest total arsenic accumulation was(197.2±17.4) μg/g dry weight when As(V) was at level 3(375μg/L),N at level 2(4 mg/L),P at level 1(0.02 mg/L),and pH at level 2(7).Although H.verticillata is highly efficient in removing As(Ⅴ) from aquatic environments,its use could be potentially harmful to both humans and the natural environment due to its release of highly toxic arsenite.For cost-effective and ecofriendly phytoremediation of As-contaminated water,both N and P are helpful in regulating As accumulation and transformation in plants.     

Long-term effects of silver nanoparticles on performance of phosphorus removal in a laboratory-scale vertical flow constructed wetland

Silver nanoparticles(AgNPs) have been widely used in many fields,which raised concerns about potential threats to biological sewage treatment systems.In this study,the phosphorus removal performance,enzymatic activity and microbial population dynamics in constructed wetlands(CWs) were evaluated under a long-term exposure to Ag NPs(0,50,and 200 μg/L) for 450 days.Results have shown that Ag NPs inhibited the phosphorus removal efficiency in a short-term exposure,whereas caused no obviously negative effects from a long-term perspective.Moreover,in the coexisting CW system of Ag NPs and phosphorus,competition exhibited in the initial exposure phase,however,cooperation between them was observed in later phase.Enzymatic activity of acid-phosphatase at the moderate temperature(10–20°C) was visibly higher than that at the high temperature(20–30℃) and CWs with Ag NPs addition had no appreciable differences compared with the control.High-throughput sequencing results indicated that the microbial richness,diversity and composition of CWs were distinctly affected with the extension of exposure time at different Ag NPs levels.However,the phosphorus removal performance of CWs did not decline with the decrease of polyphosphate accumulating organisms(PAOs),which also confirmed that adsorption precipitation was the main way of phosphorus removal in CWs.The study suggested that Ag NPs and phosphorus could be removed synergistically in the coexistence system.This work has some reference for evaluating the influences of Ag NPs on the phosphorus removal and the interrelation between them in CWs.     

Application of CFD Methods for Modelling in Air Pollution Problems: Possibilities and Gaps

Different urban air pollution problems deal with complex structure of air flows and turbulence. For such problems the Computer Fluid Dynamics (CFD) methods become widely used. However, this approach despite a number of advantages has some problems. Experience of use of CFD tools for development of models and suggestions of their applications for a local scale air pollution over a complex terrain and stable stratification are discussed in this paper, including: Topography and complex geometry: choose of the co-ordinate system and computer grid; Turbulence closure for air pollution modelling: modified k- model for stable stratified ABL; Boundary conditions for vertical profiles of velocity for stable-stratified atmosphere; Effects of the radiation and thermal budget of inclined surfaces to dispersion of pollutants; Artificial sources of air dynamics and circulation.Some examples of CFD applications for air pollution modelling for a flat terrain, mountainous area, mining open cast and indoor ventilation are discussed. Modified k- model for stably-stratified ABL is suggested. Due to the isotropic character of the k- model a combination of it in vertical with the sub-grid turbulence closure in horizontal can be more suitable for ABL. An effective scheme of boundary conditions for velocity profiles, based on the developed similarity theory for stable-stratified ABL, is suggested. Alongside with the common studies of atmospheric dispersion, the CFD methods have also demonstrated a good potential for studying anthropogenic and artificial-ventilation sources of air dynamic and circulation in local-scale processes of air pollution.     

废水反硝化除氮

反硝化是ＮＯ３＾－在反硝化细菌作用下，经ＮＯ２＾－、ＮＯ、Ｎ２Ｏ被还原为Ｎ２。反硝化对ＮＯ３＾－及有机基质呈零级动力学反应。文章还介绍了生物反硝化的生化反应，反硝化细菌以及基质、温度、溶解氧、ＰＨ对反硝化作用的影响。     

A/O和A2/O法除磷脱氮工艺影响因素及除磷动力学的研究

重点介绍A/O除磷工艺和A~2/O除磷脱氮工艺,以及影响除磷脱氮工艺因素和除磷动力学的研究。工艺研究采用了动态与静态实验方法,采用色质联机研究了有毒有机物的降解情况。试验结果表明,A/O、A~2/O工艺的BOD_5去除率近于二级污水处理厂,A~2/O法TP去除率近于三级污水处理厂,且去除难降解有毒有机物的效率高于传统的活性污泥法。动力学公式的修正使之更适于低碳源的情况。八种影响因素的研究为工艺的设计与运行提供了依据。     

活性污泥外循环SBR系统循环污泥释磷能力研究

本试验以HAc作为厌氧释磷的碳源有机物，以SBR系统外循环污泥作为研究对象，探索外循环活性污泥的厌氧释磷能力和获取高浓度富磷污水的途径，试验表明：厌氧过程中聚磷菌吸收HAc和释放PO4^3 的分子比为1：1。即吸收2．06mgHAc-COD将诱导1mgP释放，单位时段比污泥的平均释磷速率Vp=6.54.t^0.76，理想的厌氧时间为60－180min，减少循环污泥释磷系统的反应容积可以提高富磷污水磷酸盐的浓度。     

反硝化聚磷一体化设备生产性实验研究

反硝化聚磷一体化设备主要特点是在利用含反硝化聚磷菌的活性污泥在缺氧状态过量聚磷，在完成磷去除的同时进行反硝化。通过实验得出缺氧释磷在前30min内大量释放，60min以后甚微；反硝化吸磷在最初10几分钟内速率极大；吸磷与反硝化紧密相关；聚磷菌在释、聚磷时利用一定量的有机物。     

化学沉淀法除磷和生物法除磷的比较

对化学沉淀法除磷和生物法除磷的机理作了较详细的阐述，并就两者在除磷效果，污泥产量，污泥处置，除磷费用方面进行了比较。结果表明，两种方法磷的去除率比较接近，总费用没有明显差别，其优点是，生物法除磷污泥产量少，而化学沉淀法除磷操作简便。     

The dynamics of artisanal and small-scale mining reform

Artisanal and small‐scale mining are activities that have long been established in many developing countries, employing millions of people globally, either directly or in affiliated industries. Also, such activities are deplored for their adverse environmental impacts and their general avoidance of governments, tax collectors and other regulators. Decades of work have gone into addressing these problems, but with limited overall progress in evidence. Going back to some of the key dynamic relationships involved in artisanal mining and small‐scale mining, the need for policy reform that gives consistent and effective incentives is argued to be the foundation on which other discussions about environmental protection, sustainability and livelihoods can be built.     

Phosphorus recovery from municipal and fertilizer wastewater: China's potential and perspective

Phosphorus (P) is a limited resource, which can neither be synthesized nor substituted in its essential functions as nutrient. Currently explored and economically feasible global reserves may be depleted within generations. China is the largest phosphate fertilizer producing and consuming country in the world. China''s municipal wastewater contains up to 293,163 Mg year of phosphorus, which equals approximately 5.5% of the chemical fertilizer phosphorus consumed in China. Phosphorus in wastewater can be seen not only as a source of pollution to be reduced, but also as a limited resource to be recovered. Based upon existing phosphorus-recovery technologies and the current wastewater infrastructure in China, three options for phosphorus recovery from sewage sludge, sludge ash and the fertilizer industry were analyzed according to the specific conditions in China.