Rain Tank Required for Rain Water Harvesting, Water Consumption per Person, Sand Filters to Enhance Water Quality - Assignment Example

Solve the Questions Name Course Lecturer Date 1. Calculate the volume of rain tank required for Rain Water Harvesting. The area of the roof is 100 m2. Assume the average demand is =50 L/person per day. The house is occupied by four people. The monthly rainfall is summarised in the table below. Month Rainfall (Ml) Monthly Run off Volume (L) Monthly Demand (L) Balance in tank (L) Jan 103 8370 6200 2170 Feb 117 9630 5600 6200 Mar 131 10890 6200 10890 Apr 127 10530 6000 15420 May 123 10170 6200 19390 Jun 128 10620 6000 24110 Jul 98 7920 6200 25830 Aug 81 6390 6200 26020 Sep 68 5220 6000 25240 Oct 76 5940 6200 24980 Nov 83 6570 6000 25550 Dec 78 6120 6200 25470 Equations Calaculation of column 3 Monthly Runoff Volume= (Rainfall-B) *A*Roof area, where………..eqn 1 A= collection system’s efficiency, assume 9 B= rainfall loses because of the first wetting of roof surface as well as evaporation, assume 10mm/month Column 4 calculations Monthly demand= water consumption per person for each day*Number of people *Number of days in the month……………………………………………………………………………………eqn 2 Calculation of column 5 Vol end =Vol end p +(Monthly Runoff-Demand)…………………………………….eqn 3a Vol end =< Tank Volume Where Vol end-Volume remaining at the end month must be equal to or less than the tank volume Vol end p= Volume remaining in the tank at the end of the previous month From the above calculations, the volume of the tank needed for rain harvesting is 25470 litres 2. Undertake a literature review of a BMP device of your choice. Focus on the planning, modelling, design and implementation aspects of the BMP. (not more than 5 pages). Introduction In sand filters, water is let through a section containing sand. As water passes through this sand-filled section, the granules of the sand trap the dirt in the water at the top of the sand filter. In the sand at the bottom of the sand filter, there are spokes containing in them holes, which are big enough to allow water pass through, but also small enough to allow sand through. They can however let sand through if they are worn out. These spokes are called laterals. The laterals make it possible for water to get back to the pool. Following the build-up of dirt at the top of the sand filter, the water pressure used for pumping water to the sand filter builds up as well. This pressure build up slows down the efficiency of filtration of water. By the time the pressure becomes too high, there is the shutting down of the laterals at the sand filter’s bottom. When this happens, the water at the top of the sand filters is let to run directly as waste. While this water is running, it carries with it the dirt that had been trapped or that had accumulated. Upon the water running clear again, the sand filter is set back to rinse for approximately thirty seconds. Once rinsed, the sand filter can start working again. Once built, sand filters have been found to be effective when it comes to the removal of a number of common pollutants and dirt from storm water run-off. The work of sand filters generally is to control the quality of storm water. They also provide very limited control of water flow rate (Dzurik, 2002). Planning Currently, three major sand filter designs are in existence for use. The first design is called Austin sand filter. The second design is called Washington D.C. sand filter, and the last design is called Delaware sand filter. Location, for instance below or above ground, amount of water treated, the land requirements, the surface area of the filter and the drainage served, constitute the main differences among these sand filter designs. Sand filters can be modified to improve their performance and design. One way of modifying these sand filters is that of adding a peat layer in the sand filters’ filtration chamber. The peat layer addition to the sand filter may enhance the growth of microbes, which in turn improve nutrient and metals removal rates (Lindeburg, 2012). The main purpose of sand filters is to enhance water quality. Generally, sand filters are highly valued over infiltration practices like infiltration trenches, especially in situations when the groundwater is contaminated with such conventional pollutants as fecal coliform, suspended solids, or biochemical oxygen demand. This kind of contamination usually occurs in places where underlying soils alone have no capacity of treating run-off adequately. The contamination can also take place in places where there are high ground water tables. The construction of sand filters, in most cases, is done using impermeable chamber or basin bottoms. This impermeable chamber or basin bottom helps in collecting, treating, and releasing runoff water either to a storm drainage system or to surface water directly without any contact between ground water and contaminated runoff (Randolph, 2004). The selection of the right design of a sand filter depends mainly on the drainage characteristics of the area. For example, Delaware sand filter and Washington D.C. sand filter systems are very suitable for areas that are highly impervious with limited available land for structural controls because both kinds of sand filters are installed underground. These sand filters are mainly used for treating run off from storage yards, airport taxiways/ runways, garages, service stations, loading docks, driveways, and parking lots. On the other hand, the Austin sand filters are more suitable for large drainage sites with both pervious and impervious surfaces. The Austin filtration system is therefore situated at grade and is mainly used in commercial developments, in large parking areas, and at transportation facilities. Generally, it is possible to use all three kinds of sand filters as substitutes for water quality inlets. They are more often used for treating runoff water contaminated with grease and oil from drainage areas having heavy vehicle usage. In places where evaporation is more than rainfall and where a wet pond has no capacity or potential of maintaining the desired permanent pool, the best sand filter option is the Austin sand filtration system (Dzurik, 2002). Design Among the critical factors for maintaining any sand filter system’s operating life is proper design as well as maintenance of the system. Consequently, there are a number of methods, which can be used to increase the number of the filter system media. The first method involves the stabilization of the drainage area. The purpose of doing this is to minimize the sediment loadings found in the runoff. The second method involves the provision of enough or sufficient detention times for storm water. This is meant to enhance filtration and sedimentation. The last method involves the inspection and maintenance of the sand filter system frequently enough to allow for proper operation (Randolph, 2004). Modelling Sand filters Typically, a sand filter system is composed of 2 to 3 basins or chambers. The first of this is called sedimentation basin or chamber. This chamber removes heavy sediments as well as floatables. The second chamber is called the filtration chamber. This chamber gets rid of additional pollutants. It does this by filtering the water run-off via a sand bed. Last, the third chamber is called the discharge chamber. The work of this chamber is to discharge the treated or filtered water through an underground drainage system. The treated filtrate in this case is discharged either to a storm water drainage system or to the surface waters directly. Sand filters can be constructed on a very little space. They can work on highly developed sites as well as the sites having steep slopes. They can be included for retrofitting existing sites. They have the capacity of achieving high efficiencies of removal for fecal coliform bacteria, and biochemical oxygen demand, for the total metal removal, the efficiency of sand filters is however moderate. On the other hand, the sand filters’ efficiency for removal of nutrient is often low (Dzurik, 2002). Implementation All kinds of filter systems should have the capacity of providing enough access to the filter for maintenance and inspection. The inspection of the sand filters should be done after the end of a storm. This inspection is meant for verifying that the sand filters are functional as intended. Because Austin and Washington D.C. sand filter systems are constructed deep underground, it is recommended to designate them as confined spaces. Therefore, they require compliance with entry safety procedures for confined space. In most cases, sand filters start experiencing clogging issues within three to five years. In this case, accumulated debris, paper, and trash need to be removed every six months from the sand filter system. These materials can also be removed when it is necessary, even before the six months to maintain the filter clean. For all sand filters, it is important to keep a record of the dewatering times. This will help in determining whether the maintenance is necessary or not. Among the things done for the filtration chamber’s corrective maintenance is the removal of the top layers of gravel, filter fabric and sand, that has been blogged, as well as their subsequent replacement. The removed gravel, filter fabric or sand is normally disposed or placed in a landfill. It is important to test the waste media before disposing it. According to results of the test media that has been obtained so far, the media has been found to be non-toxic; hence it can be used safely in a landfill. The vegetative growth in the sand filter system also needs to be done periodically (Dzurik, 2002). References: Dzurik, A. A. (2002). Water resources planning. Lanham, Rowman & Littlefield Publishers. Lindeburg, M. R. (2012). Civil engineering reference manual for the PE Exam. Belmont, Calif, Professional Publications. Randolph, J. (2004). Environmental land use planning and management. 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