Three-Dimensional Numerical Simulation of Air Pollutant Dispersion in Street Canyons

The PHOENICS Computational Fluid Dynamics (CFD) software package has been used with a standard k- turbulence model to simulate the three-dimensional dispersion of air pollutants in an urban street canyon. In all cases, a vortex was formed within the street canyon, characterized by updrafts near the upwind buildings and down-drafts near the downwind buildings. Contours of pollutant concentrations over a transverse vertical plane at mid-canyon show pollutants circulating within the vortex, with higher concentrations at the leeward face than at the windward faces, and higher concentrations above downwind buildings than above upwind buildings. Longitudinal distributions of pollutant concentrations at leeward and windward faces are characterized by higher concentrations at mid-block and lower concentrations at the ends. These results agree qualitatively with previous wind tunnel findings such as those of Hoydysh and Dabberdt (1988) and Wedding et al. (1977). The results also suggest that the k- turbulence model is satisfactory for simulating the effect of turbulence on dispersion of pollutants in street canyons     

Phosphorus resources,their depletion and conservation,a review

Yearly, about 22 × 10¹² g phosphorus (P) from mined fossil phosphate resources are added to the world economy. The size of remaining fossil phosphate resources is uncertain but practically finite. Thus, fossil P resources may become depleted by ongoing mining. Despite calls for resource conservation, fossil P resources have been depleted at an increasing rate. Geographically, fossil P supply and demand are distributed in an increasingly uneven way, which has geopolitical consequences and may well affect security of supply. Current use of P gives rise to negative environmental impacts due to P losses from the economy and contaminants derived from fossil P resources. There may also be negative impacts on human health. Reducing the demand for fossil phosphorus may reduce environmental burdens and may improve the future security of supply. Technically speaking, there is much scope for the reduction of current demand for fossil P resources. Limiting consumption of P to essential uses, increased efficiency of agricultural use and increased recycling of P may substantially contribute to the reduction of demand for fossil P resources. Recycling of P has to face concerns regarding the efficiency of P recovery, pathogenic organisms and contaminating substances. Much work remains to be done to effectively address those concerns.     

Nutrients regeneration pathway, release potential, transformation pattern and algal utilization strategies jointly drove cyanobacterial growth and their succession

In order to better understand the contribution of nutrients regeneration pathway, release potential and transformation pattern to cyanobacterial growth and succession, 7 sampling sites in Lake Chaohu with different bloom degree were studied every two months from February to November 2018. The carbon, nitrogen (N) and phosphorus (P) forms or fractions in surface, interstitial water and sediments as well as extracellular enzymatic activities, P sorption, specific microbial abundance and community composition in sediments were analyzed. P regeneration pathway was dominated by iron-bound P desorption and phosphorus-solubilizing bacteria solubilization in severe-bloom and slight-bloom area respectively, which both resulted in high soluble reactive phosphorus (SRP) accumulation in interstitial water. However, in severe-bloom area, higher P release potential caused the strong P release and algal growth, compared to slight-bloom area. In spring, P limitation and N selective assimilation of Dolichospermum facilitated nitrate accumulation in surface water, which provided enough N source for the initiation of Microcystis bloom. In summer, the accumulated organic N in Dolichospermum cells during its bloom was re-mineralized as ammonium to replenish N source for the sustainable development of Microcystis bloom. Furthermore, SRP continuous release led to the replacement of Dolichospermum by Microcystis with the advantage of P quick utilization, transport and storage. Taken together, the succession from Dolichospermum to Microcystis was due to both the different forms of N and P in water column mediated by different regeneration and transformation pathways as well as release potential, and algal N and P utilization strategies.     

Phosphorus removal from sediments by Potamogeton crispus: New high-resolution in-situ evidence for rhizosphere assimilation and oxidization-induced retention

Macrophytes are usually chosen for phytoremediation tools to remove P in eutrophic aquatic ecosystems, but the lack of test methods hinders the understanding of removal mechanism and application. In this study, we used the novel technologies combined of Diffusive gradients in thin films (DGT), Planar optode (PO), and Non-invasive micro-test technology (NMT) to explore P dynamics in water-sediment continuum and rhizosphere of Potamogeton crispus over time. Results of the high-resolution in situ measurement showed that labile P(LP_DGT) fluxes at the surficial sediment significantly decreased from approximate 120, 140, and 200 pg/ (cm²?sec) via 30 days incubation period to 17, 40, and 56 pg/(cm²?sec) via that of 15 days. Obvious synchronous increase of LP_DGT was not detected in overlying water, suggesting the intense assimilation of dissolve reactive P via root over time. PO measurement indicated that O₂ concentration around the rhizosphere remarkably increased and radially diffused into deeper sediment until 100% saturation along with the root stretch downwards. NMT detection of roots showed the obvious O₂ inflow into root tissue with the uppermost flux of 30 pmol/(cm²?sec) from surroundings via aerenchyma on different treatment conditions. Different from previous reports, gradually saturating O₂ concentrations around the rhizosphere was principally driven by O₂ penetration through interspace attributing to root stretch downward rather than root O₂ leakage. Increased O₂ concentrations in deep sediment over time finally induced the oxidization of labile Fe(II) into Fe(III) bound P and local P immobilization.     

The Austrian P budget as a basis for resource optimization

Phosphorus (P) is a finite and non-substitutable resource that is essential to sustaining high levels of agricultural productivity but is also responsible for environmental problems, e.g., eutrophication. Based on the methodology of Material Flow Analysis, this study attempts to quantify all relevant flows and stocks of phosphorus (P) in Austria, with a special focus on waste and wastewater management. The system is modeled with the software STAN, which considers data uncertainty and applies data reconciliation and error propagation. The main novelty of this work lies in the high level of detail at which flows and stocks have been quantified to achieve a deeper understanding of the system and to provide a sound basis for the evaluation of various management options. The budget confirms on the one hand the dependence of mineral P fertilizer application (2 kg cap⁻¹ yr⁻¹), but it highlights on the other hand considerable unexploited potential for improvement. For example, municipal sewage sludge (0.75 kg cap⁻¹ yr⁻¹) and meat and bone meal (0.65 kg cap⁻¹ yr⁻¹) could potentially substitute 70% of the total applied mineral P fertilizers. However, recycling rates are low for several P flows (e.g., 27% of municipal sewage sludge; 3% of meat and bone meal). Therefore, Austria is building up a remarkable P stock (2.1 kg P cap⁻¹ yr⁻¹), mainly due to accumulation in landfills (1.1 kg P cap⁻¹ yr⁻¹) and agricultural soils (0.48 kg P cap⁻¹ yr⁻¹).     

Enhanced biological phosphorus removal using thermal alkaline hydrolyzed municipal wastewater biosolids

This study reports the feasibility of using municipal wastewater biosolids as an alternative carbon source for biological phosphorus removal. The biosolids were treated by a lowtemperature, thermal alkaline hydrolysis process patented by Lystek International Inc.(Cambridge, ON, Canada) to produce short-chain volatile fatty acids and other readily biodegradable organics. Two sequencing batch reactors(SBRs) were operated with synthetic volatile fatty acids(Syn VFA) and readily biodegradable organics produced from the alkaline hydrolysis of municipal wastewater biosolids(Lystek) as the carbon source, respectively.Municipal wastewaters with different strengths and COD:N:P ratios were tested in the study. The reactors' performances were compared with respect to nitrogen and phosphorus removal. It was observed that phosphorus removal efficiencies were between 98%–99% and 90%–97% and nitrogen removal efficiencies were 78%–81%, and 67% for the Syn VFA and Lystek, respectively. However, the kinetics for phosphorus release and uptake during the anaerobic and aerobic stages with Lystek were observed to be significantly lower than Syn VFA due to the presence of higher order VFAs(C4 and above) and other fermentable organics in the Lystek.     

Underestimation of phosphorus fraction change in the supernatant after phosphorus adsorption onto iron oxides and iron oxide–natural organic matter complexes

The phosphorus(P) fraction distribution and formation mechanism in the supernatant after P adsorption onto iron oxides and iron oxide-humic acid(HA) complexes were analyzed using the ultrafiltration method in this study.With an initial P concentration of 20 mg/L(I =0.01 mol/L and pH = 7),it was shown that the colloid(1 kDa-0.45 μm) component of P accounted for 10.6%,11.6%,6.5%,and 4.0%of remaining total P concentration in the supernatant after P adsorption onto ferrihydrite(FH),goethite(GE),ferrihydrite-humic acid complex(FH-HA),goethite-humic acid complex(GE-HA),respectively.The 1 kDa component of P was still the predominant fraction in the supernatant,and underestimated colloidal P accounted for 2.2%,55.1%,45.5%,and 38.7%of P adsorption onto the solid surface of FH,FH-HA,GE and GE-HA,respectively.Thus,the colloid P could not be neglected.Notably,it could be interpreted that Fe~(3+) hydrolysis from the adsorbents followed by the formation of colloidal hydrous ferric oxide aggregates was the main mechanism for the formation of the colloid P in the supernatant.And colloidal adsorbent particles co-existing in the supernatant were another important reason for it.Additionally,dissolve organic matter dissolved from iron oxide-HA complexes could occupy large adsorption sites of colloidal iron causing less colloid P in the supernatant.Ultimately,we believe that the findings can provide a new way to deeply interpret the geochemical cycling of P,even when considering other contaminants such as organic pollutants,heavy metal ions,and arsenate at the sediment/soil-water interface in the real environment.     

活性污泥胞外聚合物的组成与结构特点及环境行为

在活性污泥处理系统中,微生物大多以污泥絮体的形式悬浮在水中。胞外聚合物(EPS)作为污泥絮体的重要组成部分,以其独特的聚合结构和化学组成,在污水生物处理系统中起到重要作用。为了更好的描述EPS的环境行为,文章综合了近年来国内外相关的研究成果,首先分析了EPS的来源、化学组成及结构分布,得出EPS中包含蛋白质、多糖、腐殖酸、核酸、糖醛酸及脂类大分子等化学物质,其中蛋白质和多糖之和占总有机物含量的70%~80%;在结构上,EPS分为SB-EPS、LB-EPS和TB-EPS,三者与细胞结合的紧密程度递增,其中所含化学成分比例的不同将使其具有不同的理化特性。其次,文章对EPS的理化特征对污水处理系统的影响,如对系统中微生物降解特性的影响、磷和重金属的吸附等进行了讨论,并总结了EPS中相关的官能团对上述环境行为的贡献。同时,文章还论述了EPS中官能团的亲疏水特性及化学成分对污泥絮体的脱水性、絮凝沉降性能的影响。     

黄磷储罐火灾临界安全距离理论分析与数值模拟

基于建筑防火隔离带的设计理念,研究了黄磷储罐临界安全距离的计算方法,将黄磷储罐火灾简化为罐内池火模型,通过理论计算和数值模拟黄磷储罐火灾周边热辐射分布,根据目标可燃物接受到的临界辐射通量是否大于或等于10 kW/m2来确定临界安全距离。研究表明：临界安全距离可通过火焰对目标可燃物接受到的临界辐射通量求得,且理论计算和数值模拟计算获得的临界安全距离基本一致。对于黄磷储罐火灾的防治具有一定的参考价值。     

Assessing effects of aerobic and anaerobic conditions on phosphorus sorption and retention capacity of water treatment residuals

Water treatment residuals (WTRs) are the by-products of drinking water clarification processes, whereby chemical flocculants such as alum or ferric chloride are added to raw water to remove suspended clay particles, organic matter and other materials and impurities. Previous studies have identified a strong phosphorus (P) fixing capacity of WTRs which has led to experimentation with their use as P-sorbing materials for controlling P discharges from agricultural and forestry land. However, the P-fixing capacity of WTRs and its capacity to retain sorbed P under anaerobic conditions have yet to be fully demonstrated, which is an issue that must be addressed for WTR field applications. This study therefore examined the capacity of WTRs to retain sorbed P and sorb further additional P from aqueous solution under both aerobic and anaerobic conditions. An innovative, low cost apparatus was constructed and successfully used to rapidly establish anoxic conditions in anaerobic treatments. The results showed that even in treatments with initial solution P concentrations set at 100 mg l(-1), soluble reactive P concentrations rapidly fell to negligible levels (due to sorption by WTRs), while total P (i.e. dissolved + particulate and colloidal P) was less than 3 mg l(-1). This equated to an added P retention rate of >98% regardless of anaerobic or aerobic status, indicating that WTRs are able to sorb and retain P in both aerobic and anaerobic conditions.