Simulation of Water and Contaminant Transport Through Vadose Zone - Redistribution System

Movement of water in vadose zone, mainly focusing on infiltration and percolation that involves percolation of water under gravity from soil surface and redistribution which is the capillary rise of water movement upwards, is presented. In the global hydrologic cycle, 76% of the precipitating water enters the soil via percolation-infiltration, which leads to the downward movement of water (L’vovich 1974). The water used by natural processes, can move downwards due to infiltration and lift from groundwater table during natural redistribution process. The forecasting of water movement in unsaturated infiltration redistribution system is linked between soil hydraulic properties and hydrologic condition of natural surface water system. The understanding of water movement processes associated with infiltration and redistribution has a number of practical applications. One such application is to predict the fate and transport of materials through soil including nutrients, organic carbon and microbes under natural processes, which in turn will help in developing appropriate management plans for irrigation, fertilizer application and waste disposal on land

On-Site Sequencing \u27Anaerobic-Anoxic-Aerobic/Biological\u27 Process for Wastewater Reuse

The increasing scarcity of water around the world has become more evident at the beginning of this century. Management of this valuable resource is not only an environmental issue, it is also an important economic issue and its management has significant social implications. Moreover, the predicted decreases in annual rainfall around Australia, threatening the image of providing a sustainable water source for a majority of its population. The solution partly lies through the promotion of water conservation strategies involving wastewater recycling and reuse. A pilot scale 5-stage wastewater treatment system was investigated in regards to its feasibility for removing Biochemical Oxygen Demand (BOD5), Total Suspended Solids (TSS), Turbidity, Total Kjeldahl Nitrogen (TKN), Ammonia Nitrogen (NH3-N), Nitrate Nitrogen (N03-N), Organic Nitrogen (Org-N) and Total Phosphorus (TP) for the period of one year from Jan.2004 to Dec. 2004. The system readily reduced the concentration of BOD5 from average 189 mg/L to 5 mg/L (removal rate of 94%), TSS from average 216 mg/L to 3 mg/L (removal rate of 97%) and Turbidity from average 105 NTU to 2 NTU (removal rate of 96%). The removal rate for nitrogen and phosphorus was also quite satisfactory and this system was capable of reducing the Total Nitrogen (TN) from average of 41 mg/L to 5 mg/L (removal rate of 86%) and TP from average of 9 mg/L to 2 mg/L (removal rate of 81%)

Effect of dairy pond sludge/supernatant application on ryegrass dry matter yield and phosphorus fractions in soil

Pasture yield in dairy grazing systems is critical to supplying sufficient feed for milking cows and maintaining productivity. In the Australian dairy industry, ryegrass and clover are common grasses used in grazed pastures. Dairy shed effluent (DSE), the wastewater produced from washing down the dairy holding yards during and after milking, is generally managed through application to pasture as a fertilizer substitute/supplement following partial treatment in stabilization ponds. The aim of this study is to assess the benefits of applying sludge and supernatant collected from two-stage DSE pond systems to ryegrass pasture. A pot experiment was conducted which involved applying pond sludges and supernatant to soil seeded with ryegrass. The application rates of the pond by-products were set according to their labile (plant available) phosphorus content. Ryegrass yield and leachate generated from each of the pots were recorded, and samples were collected for analysis of nutrients and other parameters. The ryegrass grown in soil treated with pond sludge and supernatant yielded greater dry matter (DM) with higher nutrient content than untreated control pots. In addition, pots treated with pond sludge exhibited lower rates of phosphorus leaching from the soil compared with pots treated with supernatant. Thus, pond sludge retained more plant available phosphorus in soil than both the control and pond supernatant treatment. The potassium to calcium/magnesium ratios in the ryegrass in the pots treated with pond sludge and supernatant were below the recommended upper limit for grazing. Therefore, the application of pond sludges on the dairy paddocks was found to be superior to applying supernatant in terms of utilization and conservation of phosphorus within the dairy farm and presents low risks of groundwater pollution and grass tetany

Modeling of Contaminant Transport In on-site waste Disposal Systems

One of the most common problems of septic systems is poor drainage in the field. Septic systems release number of organic contaminants that cause groundwater pollution, especially organic substances, nutrients and pathogenic microorganisms. However, there are mechanisms that operate between soil and contaminants, which can purify the septic tank effluent. Below the drainage field, soil is separated into two zones; unsaturated and saturated zone, which provide the water movement mainly in vertical and horizontal direction, respectively. The purpose of this paper is to develop a conceptual model and to define governing equations for the transport of septic tank effluent in the vadose zone. Using the concept of mass balance and chemical kinetic equations, the governing equations have been derived

World Water Crisis Looms

An investigation was undertaken to develop a robust solar water purification system for remote areas that have neither suitable potable water nor energy supplies. A study of the challenges of global water supply and existing treatment methods was made to aid the development of the design. Current world water resources are examined regarding climate change, population growth and irrigation and the likely effects are assessed for human health and mortality, potential for conflict, economics and effect on ecosystems. Solutions are posed in the form of development goals, wastewater reuse and desalination. Objectives for the design of effective desalination systems are given. Predictions are also made for various scenarios of response to the looming crisis. The most disturbing is that if there is no response, five billion people are predicted to die rapidly from 2040 on. Action is required now, a global crisis is already happening, and, if not dealt with, water pollution may dramatically decrease the global population in the 21st century with people in less developed regions paying the heaviest prices

Perspectives on solar distillation: a review

An investigation has been made to develop a robust solar water purification system for remote areas without potable water or energy. Many stills have been studied, but few are practical due to low efficiency and water yield. A study of the global water supply and existing treatment methods has been made to understand the problem and to develop the design. Further analysis should lead to an apparatus that can supply potable water in remote, water or energy-deprived areas with minimal maintenance and long-term cost. Objectives for simple still design have been identified, as well as drawbacks in current designs. Employing active techniques such as spray evaporation, baffling, vacuum distillation, forced convection, separate chambers and membrane distillation are shown as areas of potential yield improvement

Applications of hydraulic properties models on microscopic flow in unsaturated porous media

Several existing equations for solving the non-linear soil-hydraulic properties are introduced and validated to field and laboratory measured data. Models for non-linear hydraulic properties of unsaturated porous media arise from statistical and mathematical fit through the measured data and they can be expressed in forms of unsaturated permeability versus either pressure head or volumetric moisture content. This paper presents the difference models: Gardner, Knuze et al., Haverkamp et al., van Genuchten and Saxton et al. for calculation of hydraulic properties coefficients, typicallyunsaturated permeability. The accurate and computational efficiency of these five existing models are evaluated for a series of study cases simulating hydraulic properties of unsaturated porous media. The results indicate that all existing models can be applied to homogenous and heterogenous unsaturated porous media, dry and wet cycles and laboratory and field measuring data. Besides, the statistical fit model is inefficient compared to mathematical fit models. Among the mathematical fit models, van Genuchten model is the most promising model. Gardner model can be competitive with van Genuchten model and Haverkamp et al. model is less efficient than others. The mathematical fit models appear to be attractive alternatives to estimate the unsaturated permeability, although there are concerns regarding the stability behaviour of the occupied air in pores, which need to be resolved. The air movement in unsaturated porous media affected the unsaturated permeability, which gives the difference results between wet and dry cycle. Both of unsaturated permeability and volumetric water content of dry cycle were higher than ones of wet cycle. This suggests that the velocity of air-releasing during a wet process was higher than the velocity of air-entering during a dry process. The infiltration is the most important land applications. So, the wet cycle hydraulic properties test might be concerned.Moreover, most of infiltration fields locate on the mixed grain media. So too, the pore-size distribution could affect the unsaturated permeability of porous media. It was observed that the finer material, the lower unsaturated permeability

Drying of water treatment plant residuals

Drying of ferric chloride water treatment plant residuals have been studied in two experimental sand drying beds. One bed was open and the other was covered with glass to study respectively the open bed drying of residuals under normal weather conditions and passive solar energy drying. The covered bed was fabricated, with a view, to simulate the solar distillation stills. A weather station was used to monitor the dynamic weather conditions in order to study their effect on the drying process. Solids content, drainage water volumes and distillate from the covered bed were measured on a daily basis. The aim of the study was to accelerate the drying process of residuals using passive solar energy drying technique. The study showed that the residuals dry faster in the open bed. The passive solar bed design was altered several times during the study in order to improve the bed performance. However no significant improvements were found in the performance. A reduction of 33% in drying time was achieved when the solar drying bed was provided with a fan heater. The operating conditions of both beds and their effect on the drying process are studied to understand the operation of sand drying process

Simulation of water movement through unsaturated infiltration-redistribution system

This paper deals with the movement of water in a natural unsaturated zone, focusing on infiltration-redistribution system. Infiltration refers to the downward movement of water due to the gravitational force and redistribution defines the upward movement of water due to the capillary rise. Under natural conditions, the movement of water through an infiltration-redistribution depended upon the relations among water content, hydraulic conductivity and tension of soil pore. Various combinations of water balance concepts, Richards\u27 equation, soil-physics theory and capillary height concepts were applied to mathematically model the movement of water through infiltration-redistribution system. The accuracy and computational efficiency of the developed model were evaluated for the case study. Besides the laboratory scale sand/soil columns with the inner diameter of 10.4 cm were investigated in order to provide the supporting data for model calibration. Sand/soil layers were packed with a bulk density of 1.80 and 1.25 g/cm3, respectively. The infiltration was sprayed uniformly at the soil surface with the constant rate of 66.1 and 7.18 cm3/h for sand and soil columns, respectively. The redistribution process was developed by which water arriving at the column base enter to the sand/soil column due to capillary rise. The laboratory observations were simulated using the developed model. The results indicate that the developed model could well estimate the movement of water in the infiltration-redistribution system that observed in the case study and the experiments