Salt diffusion in a temperature field: Application to salinity profiles in solar ponds

In the present investigation, the process of diffusion of salt in a vertical column of liquid, subjected to temperature variations of the types T(x) = constant, linear ( = a + bx) and parabolic ( = a + bx - cx²); with a constant concentration difference between the top and the bottom (0 and 25 per cent, respectively) is studied. It is seen that a linear temperature gradient, T(x) = a + bx, leads to a near convex parabolic salt concentration profile with maximum deviations increasing from 13.5 per cent (at 40°C) to 14.8 per cent (at 70°C) and eventually to 15.7 per cent (at 90°C) with respect to the linear concentration value of 12.5 per cent (by weight) at the midpoint. Conversely, the parabolic temperature profile as well as the modified profile due to the Soret effect leads to near cubic salt profiles which differ only by 2–3 per cent in the upper half of the pond. However, they show a point of inflexion at larger depths near the bottom around which the convex profiles change over and become concave. Subsequently, these studies have been extended to compute the salinity profiles of thermal configurations of the operational solar pond.     

Limnological characterization of interdune ponds of Curupu Island,Raposa – MA,Brazil

This study was conducted on four freshwater interdune ponds (Jacaré; Grande; Duna; Banho) located on Curupu Island within the municipality of Raposa (Maranhão State, Brazil). It focused on a diagnosis of the physical and chemical characteristics of the water and sediment in these water bodies, while at the same time obtaining basic data and information that could support the adoption of conservation strategies for the rational use of these ecosystems. Seasonal sampling of water from these ponds was conducted during the months of August, September and November 2008 and 2009 (dry period) and February, May, July 2009 and 2010 (rainy period), for the purpose of obtaining data on temperature, pH, electrical conductivity and dissolved oxygen, ammonium (NH₄), nitrite (NO₂), nitrate (NO₃) and phosphate ion (PO₄) concentrations in the pond water. Sediment sampling also was carried out to determine particle size, carbon, organic matter and phosphorus content. A large variation in most variables, especially the ammonia (NH₄), nitrate (NO₃) and phosphate (PO₄) concentrations, was observed during the study period. The pH values indicated the water in the ponds was mostly alkaline. Based on the average nitrate concentrations (137 μg L^?1 during the dry period; 123 μg L^?1 during the rainy period), the ponds exhibited primarily eutrophic conditions. The sediment samples exhibited a predominance of fine sand with low carbon and organic matter content, able to be classified by their mineral nature. Due to the fragile nature of the studied ecosystems, disciplinary control of grazing activities and tourism in the area is highly recommended, along with adoption of a basic sanitation infrastructure in the community for the purpose of rational and sustainable use of this ecosystem.     

三峡库区典型流域塘库服务功能类型及空间分布

塘库作为一种典型的人工湿地生态系统,在三峡库区分布广泛。塘库的空间分布对塘库在农业生产、居民生活以及流域生态水文过程等生态服务功能方面均有重要影响。以位于三峡库区中部的陈家沟小流域为研究区,从自然因素、社会因素、生产因素等方面建立相应指标体系,采用空间分析方法定量确定塘库分布及其服务功能类型的关联。结果表明,塘库的分布是海拔、坡度、耕地以及居民点分布等自然因素、生产因素和社会因素共同影响的结果,塘库集中分布于海拔350~550 m,坡度5°~25°以及距离农村居民点20~80 m的流域中下部区域,但其服务功能类型在空间分布上差异不显著。流域内多塘系统对流域水文调节与面源污染治理具有重要意义,塘库服务功能类型的变化则反映了农村地区经济结构与生计策略的转变。     

Full‐scale maturation ponds working below a latitude of 43°S in a semiarid area: seasonal performance and removal mechanisms

Stabilisation ponds are the most frequently used wastewater treatment technology in Argentina. This study focuses on the performance of two maturation ponds (MPs) that are part of the full‐scale sewage treatment system of Puerto Madryn. Seventy‐seven shots of surface water were analysed for organic matter, inorganic nitrogen, phytoplankton dynamics and bacterial removal. The system presented a clear evolution with respect to oxygenation and phytoplankton development. The treated wastewater reached values above 8 mg‐O₂/L, an important organic matter removal, and this was accompanied by a strong increase in pH. removal and oxidation, was active even during winter in the MPs, with average concentrations below 10 mg ‐ /L. Bacteriological removal resulted in a liquid that approached the WHO recommendations for unrestricted irrigation. These results show that is possible to generate treated wastewater in stabilisation ponds working in a semiarid and temperate region, with bacterial content and conductivity suitable for irrigation.     

Study on chlorine disinfection of pond effluent

Chlorine disinfection experiments were conducted to investigate the die-off patterns of the fecal coliforms when present in waste stabilization pond effluents containing from 100 to 400 mg l⁻¹ algae. The fecal coliform inactivation was observed to occur at two rates, i.e. an initial rapid kill followed by a slower kill. The magnitude of inactivation was found to be proportional to the initial chlorine dose and contact time and inversely proportional to the algal concentration. A mathematical model was developed to predict the fecal coliform survival ratio during the chlorination of the pond effluent. When compared with the experimental data, the predicted results had a correlation coefficient of 0.981.     

浅谈城市排水工程规划

结合编制宣城市排水规划,分析和研究该市城市排水系统中存在的问题和主要特征。文章提出老城区暂以截流式分流制过渡,规划改造一片,分流一片,其余各区均采用雨污分流制,雨水分片就近排放,污水收集后排入污水处理厂;充分利用内河水网服务于城市排水和排涝,同时对其进行引水换水,利用城市湖塘作为调蓄水面,将城市雨水资源化。     

废水可生化性与生物氧化塘处理效率相关性的研究

本文测定了几种工业废水可生化指标BOD_5/COD比值和相对耗氧速率,根据模拟生物塘的动态运行试验结果,提出了以耗氧速率R%作为可生化性判定指标,它比BOD_5/COD比值测定快,方法简便,更接近实际,并得出两个指标与生物塘COD去除率之间相关性的线性回归方程,为选择废水生物塘处理方案、预估其对COD去除效率提供了理论依据。     

Impact of design and operation variables on the performance of vertical-flow constructed wetlands and intermittent sand filters treating pond effluent

With the aim of improving the quality of the effluent from a waste stabilization pond (WSP) different types of vertical-flow constructed wetlands (VFCWs) and intermittent sand filters (ISFs) were tested at a pilot plant in Aurignac (France). The effectiveness of each design at upgrading the pond effluent was studied over a period of 2 years. Physicochemical parameters were monitored by taking composite samples over 24 h and grab samples every week. The hydraulic behaviour of the filters was studied using (NaCl) tracer tests and monitoring the infiltration rate. This paper describes the influence on the performance of the beds of: (a) the characteristics of the medium (type of sand, depth, and presence of Phragmites); (b) feed modes; and (c) the presence of an algae clogging layer. The study demonstrates the viability of VFCWs and ISFs as means of upgrading effluent from WSPs. For hydraulic loads (HL) of up to 80 cm/day, both technologies effectively retain algae, complete organic matter degradation, and nitrify the pond effluent. The presence of plants did not significantly affect the performance of the filters although it was important in terms of maintenance. The deeper filters presented better removals for all the parameter tested, due to higher hydraulic detention times (HDTs). The dosing regime and resting period duration all affected the hydraulic performance and purification efficiency of the filters.     

Post-Impoundment Investigation of Gravity-Driven Irrigation Ponds in Central Bolivia

Abstract

The objective of this study was to evaluate the viability of rain-fed farm ponds for sustaining agriculture in semi-arid, southeastern Cochabamba, Bolivia. Farm ponds store runoff from foothills in the study area, delivering it by gravity flow to lowlands. A typical pond has a 1,000 m³ storage capacity and serves four families. The ponds have become a common farming practice in the study area. They increase agricultural output by supplementing a sparse rainfall pattern. The ponds and complementary structures such as rock check dams have also alleviated soil erosion in the study area.     

生态塘底泥磷吸收/释放行为及作用机制

研究pH和Eh对复合生态塘系统表层底泥磷吸收/释放行为的影响,考察不同pH和Eh下各形态磷的吸收/释放潜力及其相关机制,详细探讨Eh逐渐升高对铁磷(Fe-P)形成过程影响.结果表明,不同pH下底泥对各形态磷的束缚力差异明显:铁磷和铝磷在pH=7和pH=8时结合能力最强;碱可提取有机磷(OPalk)在pH=5时结合能力最强;而钙磷在pH=9结合能力最强.Eh主要通过改变Fe(Ⅱ)和Fe(Ⅲ)的相对含量及磷的形成机制影响底泥对磷的吸收/释放.随着Eh由-650 mV升高到-50 mV,Fe(Ⅱ)逐渐氧化为Fe(Ⅲ),而Fe(Ⅲ)的还原受腐殖质络合所抑制,底泥中以P-Fe3 -O-HS-M 形式存在的Fe(Ⅲ)-P显着增加.