Water Resources Guidelines

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Water Resources Guidelines (Part 2 of 2): 

Water Resources Guidelines (Part 2 of 2) Prepared by Engineers Without Borders – USA Presentation compiled by EWB-UCIN Engineering Committee

Part 2 of 2 – Water Treatment & Distribution: 

Part 2 of 2 – Water Treatment & Distribution This presentation includes information regarding the treatment and distribution of potable water for the betterment of communal health. Information regarding conducting a water quantity and quality assessment can be found in part 1. Water Resources Guidelines


*Point of Use treatment techniques are designed for use at the household level, and are intended for emergency purposes until a more sustainable cost-effective community scale system can be implemented. Water Treatment Techniques Point of Use Treatment Techniques Filtration and Aeration Solar Still Water Purification Filtron – Potters for Peace Solar Water Disinfection – SODIS Ceramic Candle Filters PuR Water Treatment Packets Figure 1: Aeration Trays Figure 2: Solar Still Figure 3: Solar Water Disinfection


Community Scale Treatment Techniques Sedimentary Tanks Filtration Slow Sand Filter (SSF) Rapid Sand Filter (RSF) Disinfectants Chlorine UV Disinfection Project team is responsible for: training of operators from community working with the community to establish a sustainable operation providing maintenance fund to keep the system up and running *Community scale treatment techniques are designed to offer a sustainable long term approach to providing potable water to a community. Water Treatment Techniques


Sedimentation Tanks Purpose Remove large suspended particles by reducing velocity of incoming water and allowing gravity to settle out heavy particles Dimensions depth of tank = 1.5 m to 2.5 m surface area = flow rate / settling velocity Detention time Function of particle density and water temperature Typically 0.5 to 3.0 hours Sludge Removal Tank must be ‘out of service’ while operator removes sludge For this reason, 2-tank design is recommended Water Treatment Techniques


Filtration – Slow Sand Filter (SSF) Removes impurities through absorption, straining, sedimentation, and chemical / biological processes Three layers: Top = biologically active film Composed of bacteria, fungi, and protozoa Layer breaks down pathogens into inorganic compounds Takes 3 to 7 days to develop this layer, therefore 2 SSF are recommended Middle = sand Should be at least 1.0 m deep Max and min grain sizes are 3 mm and 0.1 mm, respectively Sands should be cleaned and sieved before use in SSF Bottom = gravel Gravel holds pipes, which collect and transport clean water Water Treatment Techniques


Filtration – Rapid Sand Filter (RSF) Similar to Slow Sand Filter Three major differences: Size of sand used Max and min grain sizes are 5 mm and 0.5 mm, respectively Operating speed Can operate up to 40 times faster, due to increased pore size Required maintenance Needs frequent cleaning due to high operating speed Backwash System Reversing flow back through the filter to flush solids Can use backwash pumps or a self backwash system of weir gates Necessary to train operators about frequent maintenance Water Treatment Techniques


Disinfection – Chlorination Most commonly used disinfectant for water supplies worldwide. Low cost Readily available Effective Things to consider: Turbidity - Low flow rate Chlorine Demand - Level of contaminants Chlorine Residual - Further contamination Chlorine Dose - Quality of water Taste and Smell - Don’t overdose Safety - Reactive and corrosive Dosing Equipment Pot Chlorinator Drip Chlorinator Floating Bowl Chlorinator Shock Chlorination Water Treatment Techniques


Disinfection – UV Disinfection Uses ultraviolet spectrum of light to disrupt the DNA of pathogenic organisms and prevent them from reproducing Has been used for years in the developed world, but Expensive Energy Intensive Some new, inexpensive units in development! May require additional chlorination if necessary Water Treatment Techniques


Pipe Materials Polyvinyl Chloride (PVC) Pipe Excellent resistance to acids, bases, salts, and oxidants Not recommended for above ground applications Due to lack of resistance to UV radiation can be coated with UV stabilizer, such as carbon black Joined using using combination of primer and cement Polyethylene (PE) Pipe Better performance in low temperatures (below 0°F) High impact strength and flexibility Bending radius, HDPE = 30*Outer Diameter Bending radius, MDPE = 20*Outer Diameter Joints may be welded, or use mechanical fittings Galvanized Steel (GI) Pipe More expensive, more rigid, and rougher than plastic pipe Generally used for high pressure and/or high stress applications Joined using tapered threaded connectors Rust may form at joints, extra care should be taken


Valves Figure 4: Ball Valve Figure 5: Butterfly Valve Figure 6: Check Valve


Distribution Delivery Rate ≈ 0.2 Liters per second (L/s) Velocity in pipeline, V  0.7 ≤ V ≤ 2.0 m/s # of taps, N  200 people/tap @ 0.2 L/s Distance from furthest dwelling ≈ 500 m


In order to effectively distribute water while maintaining adequate pressure, several factors must be considered. Primary Pipe Losses Friction from the inside walls of the pipe. Increase in elevation of pipe. Bends in the pipe system Joints in the pipe system Pipe Design Issues Secondary “Minor” Pipe Losses Pipe entry & exit Pipe diameter & direction changes Secondary losses can be neglected if the pipe diameter is sufficiently large.


Negative and Excessive Pressures: Negative Pressure… can result from excessive elevation changes. It is manifested as reduction or complete loss of fluid flow. It can be controlled by reducing friction. Excessive Pressures…can result in the flow shutting off at the distribution points. When steep elevation changes result in this condition, a small tank or a large diameter pipe can be installed to reduce the pipe pressure. Pipe Design Issues


Trenching and Installation: Place pipes at a depth to protect against Frost damage Damage from foot traffic, vehicles or hooves UV damage Use fill soil in the trench to protect from stones and to provide an even supporting surface. Expansion and contraction during temperature fluctuations should not be impeded by trench filler. It is recommended to allow the pipes to be filled with water for 24 hours before filling trench (except during rain or other adverse weather conditions). Pipe Design Issues


Pipe Anchors: Concrete “kick-blocks” should be used to anchor pipes at locations where there are changes in: Diameter Direction Elevation The “kick-blocks” will help to reduce pipe joint separation that may occur from vibration and other forces. Ravine Crossings: Many drainage crossings will require the suspension of the pipe to avoid the potential of erosion of the ravine. Plastic pipes subjected to UV rays must be protected by an outer pipe or must be replace by other UV resistant options. Pipe Design Issues


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