I hereby declare that this work is a product of my own research efforts, undertaken under the supervision of Mr. CHISAKUTA, and has not been presented elsewhere for the award of a diploma. All sources have been duly and appropriately acknowledged.
This is to certify that this report has been examined and approved for the award of the diploma in Water Engineering at the Natural Resources Development College.
Name: ………………………… Signature: ……………… Date: ……………………….
Name: ………………………… Signature: ……………… Date: ………………………
Head of Department
Name: ………………………… Signature: ……………… Date: ……………………….
I would like to express my intense gratitude to God for the courteous opportunity of bringing this work (project) to completion.
For the project to be productive it was the keen interest invested by the department of water engineering; the head of the department Mr. S C CHISAKUTA who also is my project supervisor, my course tutor Mr. L PHIRI and all my coursemates and friends who contributed positively to the success of this project. I wish God’s blessings to you all.
This research report is dedicated to my sibling sisters (Namioti, Mundia, Namunji, and Karen). Needless to mention every other member of my family and friends (course mates).
The Natural Resources Development College (N.R.D.C) reticulation system lacks a proper chlorination system. The ground surface water reservoir is supplied by boreholes 8 and 9, the water supply is from the underground which is less contaminated but this water gets contaminated as it is conveyed from the supply point to the consumers.
At the beginning of this project, the method of chlorine application proved to have many disadvantages than advantages in that the chlorine residual was at times too high or low and sometimes not present in the water. Pouring chlorine in form of granules into the reservoir, 300g and 200g at 06 hours and 14 hours respectively was very ineffective as indicated by the laboratory results from the water sampling that was carried out.
The mechanism of the hydraulically operated chlorine dozer can offer a better way of chlorine application in form of a solution. The concept behind the hydraulic dozer is that the flow of water in the pipe activates the dozer hence the chlorine solution is applied into the water. Chlorine granules are dissolved in a water tank which is relatively elevated to make a chlorine solution. The constant head chlorine tank which is connected to the hydraulic chlorine dozer via the chemical delivery pipe ensures a constant rate of dosage. For this reason, the flow of water in a pipe is assumed to be constant. The design mechanism of the dozer can apply the chlorine solution directly into the water supply pipe just before the surface reservoir or on top of the reservoir.
A prototype of the hydraulic chlorine dozer has been constructed using basic materials which were locally acquired. The best constructional material of the dozer is polyvinyl chloride (PVC) pipes and containers; it has been scientifically proven that chlorine doesn’t react with PVC materials. The pipe network of the dozer is constructed of the astral chlorinated polyvinyl chloride (CPVC), 20mm in diameter.
Apart from the N.R.D.C reticulation system, the dozer can be used by water utility companies for pre-treatment of the water. In the absence of electricity, the dozer can work with solar-powered pumps which are now being installed in rural areas.
In agriculture, the process of applying fertilizer to crops through irrigation is called fertigation; therefore, a fertilizer solution is made which is later added to the irrigation water before irrigating. That being the case, the hydraulically operated dozer can be used to apply fertilizer at a constant rate to the water being supplied for irrigation purposes. Operational and mechanical designs of the dozer have been clearly drawn in this report using Technical Drawing (T.D).
Chlorination is still the most practical form of disinfection of small water supplies. A wide variety of non-electrically powered chlorinators exist and some of these can be made using fairly basic materials. Technology is now available that makes the production of sodium hypochlorite in low and middle-income countries possible at regional, district, or even village levels. This removes some of the previous constraints preventing the adoption of chlorination.
- Disinfection is a process of killing micro-organisms that still remain in the water after filtration.
- The disinfection by chlorine is known as chlorination. Chlorine can be applied as a gas, liquid, or powder. It is cheap, easy to apply (high solubility of about 7000mg/l. It leaves residual in solution which provides protection against pollution in the distribution system and it is very toxic to most micro-organisms (stopping metabolic activities).
- Chlorine is the most widely used disinfection in water treatment primarily due to its low costs and relative ease of operation. Chlorine is typically used as a primary disinfectant for the inactivation of micro-organisms and as a secondary disinfectant to maintain chlorine residual levels in the distribution system to minimize biological regrowth. The amount of chlorine used in reducing these impurities, to a desirable value, is called chlorine demand. After the chlorine demand is fulfilled, chlorine appears as residual chlorine.
Residual chlorine Dissolved free chlorine is never found in natural waters, it is present in the treated water resulting from disinfection with chlorine.
A certain amount of chlorine is required for effective disinfection depending upon the quality of water. Chlorine in excess remains unused and is known as residual chlorine. The water flows in the pipelines from the treatment plants and then reaches the consumers, after traveling for some time. The residual chlorine in the water entering into the distribution system is used to kill the pathogens/micro-organisms present in the
pipeline and other components of the distribution system and thus safe potable water reaches the consumers.
To ensure this availability it is proposed that the amount of residual chlorine in the drinking water at the consumer end should be 0.1 to 0.2 mg/l.
If we add more chlorine and the residual chlorine are also more than 0.2 mg/l it is harmful and undesirable from taste point of view.
Some amount of active chlorine should be present at each stage of water treatment and distribution. The residual chlorine at the consumers end should be 0.2 mg/l.
Excessive chlorine gives bad odor and taste and is harmful also (may lead to cancer).
But, chlorination can prove to be ineffective if the chemical is not thoroughly mixed and if the contact period is less than thirty (30) minutes. The hydraulically operated doser can and will ensure thorough mixture of chlorine into the water and increase the contact period.
The chemical (chlorine) is not thoroughly and evenly distributed in the reservoir before distribution.
Health and sanitation are heavily compromised during dosing moments by the operators. The contact period is heavily reduced.
• Designing, costing, and construction of the prototype hydraulically operated chemical
(chlorine) doser for Natural Resources Development College reticulation system.
- Taking an inventory of the existing source, conveyance, and storage- distribution system for N.R.D.C.
- Conducting water sampling tests for five (5) different points, once every month for four (4) months.
- Analysis of laboratory results to ascertain if the chlorine residual is of the required standard as stipulated by ZEMA and ZABS.
- Designing and costing of the chlorinator.
- Construction and testing the operation mechanism of the prototype chlorine dozer.
2.0 LITERATURE REVIEW
The use of chlorine gas for disinfection is not considered in this paper, partly because chlorine gas is not usually readily available in many areas of low- and middle-income countries. Another reason is that chlorine is a very poisonous gas and the risks associated with safely transporting and using it in small water treatment installations mean that it is not usually appropriate for such facilities. Much is written elsewhere about disinfection using chlorine gas (e.g. White 1999) which is in use in much large treatments works.
The initial intention was to gather information from literature and to gather reported experiences from field practitioners. The widely publicized requests for information from the field did not result in a large number of responses, possibly indicating that gravity- or water-powered systems are not widely used.
The author is very thankful to those who provided the information used for preparing this report. It is hoped that this publication will increase the adoption of small-scale chlorination systems where they are appropriate, leading to an improved quality of water for many consumers. Feedback on the contents of the report will be welcomed
2.1 Chlorinators for small systems
The literature search identified only a few detailed publications relating to chlorinators suitable for operation where there is no reliable supply of electricity.
The best publication on small-scale chlorination is ‘Disinfection of rural and small-community water supplies – A manual for design and operation’ WRC (1989). This manual describes 12 different types of dozers ranging from pot-chlorinators to electrically powered dosing pumps and also includes the vacuum gas chlorinator.
The suitability of some systems will depend on whether or not the water is flowing and whether or not the flow is constant or is variable.
The devices mentioned in the following sections have been divided into three categories:
• Water-powered chlorinators – where moving water powers a mechanical device, or produces a reduced pressure, which is used to dose the chlorine solution into the water
• Gravity driven chlorinators – where the chlorine solution being dosed flows through the device naturally, as a result of the force of gravity
• Diffusion chlorinators – where the water picks up a chlorine dose by coming into contact with solid or powdered forms of a chlorine compound
Note that not all the water to be treated has to receive a dose of chlorine direct from the chlorinator. Sometimes just a proportion of the water receives a high dose of chlorine solution from the chlorinator, but this water is then thoroughly mixed with the remainder so all of it becomes chlorinated.
2.1.1 Water-powered chlorinators
There are several types of water-powered chlorinators. Some such as the wheel feeder is suitable where the water is flowing in a channel. Others like the float-powered system are used at a point where water is discharged from a pipe or channel. Hydraulic motor-powered systems and venturi systems require the water to be flowing in a pipe, either by gravity or because it is pressurized by a pump. Direct suction dozers make use of the reduced water pressure on the suction side of a pump that is already being used to pump the water that needs treating.
Wheel feeder dozers
This type of dozer is powered by a paddle wheel that is positioned in a channel through which the water to be treated is flowing. The flow of the water in the channel rotates the paddle, which rotates a shaft to which the chlorinator is connected. Solsona (1990 p21) makes brief mention of an ‘Archimedes wheel’. This consists of a horizontal shaft with spokes connected to it. At the end of each spoke is a small container at right angles to the spoke, facing in the direction of rotation. As the shaft rotates, each container passes through a shallow tank of chlorine solution, picking up some of the liquid. As a container approaches the top of its circular motion the liquid it contains is automatically poured out. A tray is positioned to catch the discharge and direct it into the water flowing in the channel. Since the speed of rotation of the shaft depends on the amount of water flowing in the channel the rate of dosing will be related to the rate of flow of the water to be treated. A similar device developed in Swaziland in 1966 is described in Schulz and Okun (1984, p80-83).
Float-powered chemical dozer
An interesting self-powered chemical dozer is based on a 150 liters water tank fitted with a special fast-acting siphon which rapidly empties the tank when it fills to a certain level (WRC, 1984, p15- 17), WRC (1989, p62-64) and Schulz & Okun (1984, p82-84). Ball floats, operating in vertical guides, raise and lower a small dosing cup as the water level in the tank changes. When the floats are at their lowest point the cup is submerged in a small tank containing the chlorine solution. As the floats rise, they lift the cup out of the solution and push it onto a displacement plunger, causing some of the solution to flow out of the cup, through a small weir. The weir discharges into a small hinged dispensing tube that directs it into the tank. The solution is discharged from the tube just before the siphon starts to empty the tank. The length of the displacement plunger is adjustable to vary the dose.
Wallace and Tiernan manufacture this unit. It is able to cope with flow rates of between 0.1m3/hr and 4m3/hr. The flow rate of raw water through the dozer is limited by the discharge rate of the siphon. For flows higher than 4m3/hr, the dozer can be fitted on a bypass that takes only a proportion of the flow, as long as subsequently the dosed water is thoroughly mixed with the untreated water.
Hydraulic motor/piston-driven dozers
Some enclosed dosing systems that are driven by water are available. The mode of operation of these usually ensures that the rate of dosing is reasonably proportional to the flow of water through them, such as dozers that can be of various types (e.g. reciprocating piston or diaphragm pump). Some of them use an electronic sensor system to control the dozer but this type is not considered in this publication.
Two types of water-powered mechanisms are available to operate this category of the dozer. In one type, the water to be treated drives a small motor (like a water meter) that rotates a shaft that operates the piston or diaphragm. The second type uses the water to drive a piston that moves back and forth in a valved cylinder. The reciprocating movement of the drive piston operates a displacement pump that doses the solution. These systems can raise the solution from below the pump and can inject it into a pressurized stream of water. Most types can be adjusted within a certain range, to provide a specific ratio between the volume of the dose and the volume of the water passing through the unit.
Where the flow of water to be treated is large, a smaller capacity dozer can be used on a bypass pipe through which a proportional amount of the flow is diverted. However, if the flow rate is variable, the ratio between the diverted flow and main flow should be investigated to check that it is fairly constant otherwise the incorrect dose may be applied. The bypass flow needs to be thoroughly mixed with the main flow where the two flows merge again.
When water flows through a constriction in a pipe the velocity of the water increases and its pressure reduces. The difference between the upstream pressure and the pressure at the constriction can be used to automatically draw chlorine gas, or a chlorine solution, into the pipe. If the reduced pressure created at the constriction is less than atmospheric pressure then a single small diameter pipe connection at that point can be used to suck solution into the pipe. Such devices are variously called ejectors, injectors, eductors, aspirator feeders, or vacuum drawing systems. A sudden change in cross-section such as an orifice can be used to form the constriction. More usually, as in a venturi, the change in the section is more gradual when approaching and departing from the constriction. The pressure difference caused is proportional to the flow rate, and with a suitable arrangement, this will result in the dose automatically changing to suit the flow rate. With high flow rates, the venturi device can be fitted on a bypass that is designed to automatically take only a fixed proportion of the total flow. When the two streams are brought back together the chlorine dosed into the bypass water will be mixed with the other water.
Some venturi devices are fixed in parallel to the main pump that pumps the water into a distribution system or storage tank (Solsona, 1990 p23). In this arrangement, the inlet to the device is from a small branch connection to the outlet pipe (i.e. delivery side) of the pump and the outlet from the device is to a branch on the inlet pipe (i.e. suction side) of the pump. Valves are used to adjust the flow rate through the dozer to ensure that the water that passes through it delivers a sufficient dose for all of the water that is being pumped. This type of dozer is only appropriate if the pump main and storage provided before the distribution system give sufficient contact time.
This dozer may also be called a ‘displacement dozer’ or a ‘diaphragm displacer’ (WRC, 1989, p65-66). The latter term should not be confused with a ‘diaphragm pump’, which is a different type of dozer. With a displacement dozer, the chlorine solution is contained in a flexible bag that is held within a closed vessel. The small diameter ‘dosing pipe’ passes from inside the bag, through the lid of the vessel, and onto the discharge point. Another pipe, the ‘supply pipe’, passes only through the wall of the vessel to introduce water between the inside of the container and the outside of the bag. When the pressure of this water exceeds that of the solution in the bag, it will displace the solution out of the bag and into the dosing pipe. This differential pressure can be achieved in a number of ways. One way is to install an orifice plate on the pipe containing the water to be treated. Then the supply pipe is connected upstream of the plate and the dosing pipe is connected downstream of the plate. Alternatively, the pipes can be connected to the appropriate points on a venturi constriction on the raw water pipe. Periodically the bag is refilled from a tank containing a prepared chlorine solution whilst the water outside the bag is drained out of the vessel.
The volume of solution displaced from the dosing bag will equal the volume of water entering the vessel so a small flow-meter (e.g. a roto-meter) can be fitted on the supply pipe and a valve can be used to adjust the flow to provide the required dose. This position for the flow meter is better than placing it on the dosing pipe where it will be subject to the corrosive disinfecting solution. This dozer does not have to always be used with a venturi system. The author of this present report sees no reason why the water that is used outside the bag to displace the solution cannot gravitate from any constant-flow system. For example, a gravity-driven chlorinator could potentially be used with plain water to provide the displacement water. Such a gravity-driven device will not be subject to the effects of corrosion and scaling that it would experience when chlorine solution is flowing through it. The chlorine solution only comes into contact with pipework downstream of the bag.
2.1.2 Gravity-driven chlorinators
With all of these units, precautions need to be made to avoid sediments or scale forming since this will disrupt their performance.
The Mariotte jar is also termed a ‘constant-head aspirator’. Each version uses a large (e.g. 20- liters) sealed, a rigid bottle that contains the chlorine solution. The jar is equipped with an air inlet pipe, and an outlet pipe to discharge the chlorine solution. There are three arrangements possible for this device.
If the pressure (or ‘head’) at an orifice or valve remains constant, then as long as there are no external physical changes, the free discharge through it into the atmosphere will remain constant. Constant-head tanks use a sensitive corrosion-resistant float valve to ensure that the level of the solution in a tank remains constant to provide a uniform pressure at a valve or orifice on a pipe connected to the tank. The orifice size is chosen to be suitable to discharge the required flow at the available head. Fine adjustment of the discharge is possible by raising or lowering the orifice in relation to the fixed level of the solution in the tank. An alternative to the orifice is to use a valve, such as a needle valve, that can be finely adjusted to achieve the required flow rate. It is best if the orifice or valve is not positioned right at the end of the pipe because contact with the air at this point may cause scale to develop. Simpler, less accurate, controls can consist of devices that squash a flexible outlet pipe to form a constriction.
One simple method of providing a constant discharge is to provide a floating inlet in the chlorine solution tank. This inlet is connected to a flexible discharge pipe that passes out of the tank near its base. Although the surface level of the liquid in the tank will change as the solution is discharged, since the float moves down with the level of the chlorine solution, the depth of liquid above the inlet to the discharge pipe will remain constant, ensuring a constant discharge.
Devices that use a ‘floating bowl’ are also promoted (USAID, 1982 a & b). In such a system a bowl containing two vertical pipes passing through its base is floated on the surface of the tank that contains the solution to be dosed. One of the pipes is quite short and it allows the solution to flow into the bowl. The other pipe, connected to a flexible pipe that passes through the side of the tank near to its base, drains out any solution that enters the bowl, and discharges it to where it is to be mixed with the raw water.
The flow into the bowl for the raised inlet type depends on the height difference between the top end of the short pipe in the bowl and the water level outside the bowl. To change the flow rate the projecting length of the short tube can be adjusted by sliding the tube through a seal in the base of the bowl. For the drowned inlet type, the flow rate depends on the difference in water level inside and outside the bowl. To change the flow rate for this type the projecting length of the outlet pipe is adjusted.
For both types, another way of changing the flow rate is to add/remove ballast to/from the bowl so that it floats higher/lower in the water. A good way of doing this is by adding/removing small stones to/from a plastic bag held in the bowl. The upper end of the short tube can be above or below the end of the tube that drains the bowl but there is less likely to be problems with encrustation if it is below the outlet. With all the float systems discussed in this section, care needs to be taken to ensure reliable performance. For example, the float needs to be kept clear of the sides of the tank that contains the solution. If it touches the side of the tank as the solution is withdrawn this may slow up its constant rate of descent. This will reduce the distance between the inlet and the surface of the solution, which will change the pressure at the inlet, and hence the discharge through it. To keep the float central, some devices use one or more nylon guide strings (USAID, 1982a), or a plastic pipe guide stem (Luff 2000 p12), that pass through a pipe sleeve in the float/bowl.
If the flexible discharge pipe below the float/bowl is too stiff it can begin to tip the float/bowl as it descends resulting in a change in the head at the inlet point. The tipping can also create sufficient friction on the float guides to cause a non-uniform rate of descent of the float. Similarly, the coiling of the pipe as the liquid level falls can also adversely affect the rate of descent. The orifice and pipes need to be kept clean of scale and sediments.
Vandos chemical feeder
Solsona (1990 p21) describes the ‘Vandos chemical feeder’, an interesting chlorinator that was developed in South Africa. It uses two identical, vertical cylindrical drums. The first drum is fixed in position and is initially filled with water that flows into the second drum at a controlled rate through a flexible pipe. The second drum is not fixed but floats in a tank that contains the chlorine solution. As the water flows into the second drum it becomes heavier, so it sinks into the solution tank, displacing an equal volume of solution. This solution flows out of a high-level outlet to the dosing point. Although during operation the water level in the first drum drops, it is falling at the same rate as the inlet to the second drum is sinking, so this maintains a constant level difference, and hence a constant flow rate. The rate of flow can be adjusted by either altering the initial height difference between the two points or by adjusting a control valve (or replacing an orifice) at the inlet to the second drum.
Periodically the water in the second drum is transferred back into the first drum and the tank is refilled with a chlorine solution. This is an interesting device but no information is provided about its performance in the field. It has the potential advantage that the flow control system between the two drums does not have to be resistant to chlorine solution and will not block with precipitates or scale, something that can occur with a chlorine solution.
2.1.3 Diffusion chlorinators
In diffusion chlorinators, the chlorine is in the form of a powder or tablets which come into contact with the water that is to be dosed. Some of these chlorinators are used in fairly stationary bodies of water, such as open wells, whereas others are designed for situations where water flowing through the unit dissolves the tablets.
For treatment of drinking water, the tablets used should be of pure sodium hypochlorite or a mixture of this and an approved binding medium. Some tablets are designed to avoid water being absorbed through the tablet by capillary action. This prevents water from seeping up a stack of tablets, adversely affecting ones that are not yet in contact with the water to be chlorinated. Chemicals in some of the tablets used for chlorination of swimming pools make them unsuitable for long-term use for disinfection of drinking water. However, it may be possible to use simple swimming pool dozers with tablets designed for potable water systems.
Continuous flow diffusers (currently practiced at N.R.D.C)
Continuous flow diffusers are similar to the floating chlorinators just described but are designed so that water flows across and through a perforated section at the bottom of the vertical cylinder to slowly dissolve the tablets it contains (WRC (1989)). They are also called ‘erosion tablet feeders’. Many of the available systems use large calcium hypochlorite tablets (e.g. 75mm diameter). The dose applied to the water by these systems will usually be higher than that required for disinfection, so the unit is usually positioned on a bypass that takes only a portion of the flow of water to be treated. After the unit, the two streams are mixed together again. Some diffuser units have four separate columns of tablets, or a large diameter cylinder containing many smaller diameter tablets. The latter design can allow a large volume of water (e.g. as much as 200m3/day) to flows across the tablets to receive a fairly high dose of chlorine. If the depth of contact with the tablets is constant, then as the flow rate increases, so does the rate of dissolution of the tablets, increasing the total amount of chlorine taken into solution per minute.
Some systems use an outlet weir so that the water level in the unit rises as the flow rate increases, resulting in a greater depth of water coming into contact with the tablets and hence a higher amount of chlorine going into the solution per minute. Manual adjustment of the depth of tablet(s) submerged in the flow can be achieved on some systems. This is accomplished by either raising or lowering the cylinder. Most tablet erosion systems are un-pressurized but in at least one system the flow can be pressurized. This system uses a vertical glass cylinder to contain the tablets. At the base of the cylinder are two vertical pipe connections, one to admit water to the bottom of the cylinder and the other to let it out again. The dose can be adjusted by pumping air into the cylinder to reduce the space in the cylinder for water to flow through the tablets.
WRC (1984, p30-31 and Appendix 4.16) extensively tested one type of erosion tablet feeder. They discovered that the tablets they used tended to erode irregularly leading to a variable dose in the steady flow. This was particularly the case when an eroded tablet crumbled away and a new tablet came into use. The behavior of different types of tablets may vary depending on the binding agent (if any) used so if possible tests should be carried out with tablets from different suppliers to find which is best. However, using a large contact tank may successfully average out the effects of any short-term variations in the dosing rate.
Intermittent flow diffusers
The erosion tablet feeders just described are not suitable where the water flow is intermittent. This is because the water remaining in the unit when the flow stops will become very highly dosed with chlorine, potentially causing problems when the water begins to flow again. To avoid this problem a ‘tipping tray chlorinator’ was developed by one manufacturer (WRC, 1989, p53). In this type of chlorinator, the water to be dosed flows into a pivoted tray positioned directly below the cylinder containing the tablets. The bottom of the stack of tablets only comes into contact with the water when it fills the tray to a certain level. Shortly afterward, the continuing rise in the water level causes the tray to become unstable and it tips over, discharging its contents. The empty tray then tips back to begin to fill again. When the flow stops, if the water is not yet in contact with the tablets, it will all remain in the tray. If it is in contact with the tablets this situation does not last for very long because there is a small drainage hole in the side of the tray which soon drains water out to a level below that of the tablets.
The author of this present report has been unable to locate details of any current manufacturer of this type of chlorinator.
3.0 STUDY AREA
The study area which is the Natural Resources Development College had its construction started in 1964, and on 27th October His Excellency the President Dr. K. D. Kaunda laid the foundation stone as part of the independence celebrations.
FIG1: The study area and the five sampling points (Google Earth and the Global Positioning System)
The college campus is located on 304 hectares of land twelve kilometers (12) from the city on the Great East Road near Chelston. This is essentially a teaching farm, with an irrigated area, and pig, poultry, and dairy cattle units.
Hydraulic Chemical Doser…WE/10/28 N.R.D.C
Small-Scale Chlorination system… 2013
Despite the presence of the Kalikiliki stream, the water used for both drinking water and irrigation water supply in the area is groundwater abstracted from six boreholes drilled to varying depths with different borehole yields. The stream experiences high pollution because it acts as a drain for the nearby settlements. A human population of approximately 1500 and 500 farm animals benefit from the abstracted groundwater. The climatic condition in this Area is average (temperature, rainfall, and humidity) while the soil type is mostly loamy clay soils and like most parts of Lusaka, NRDC is also underlain by limestone. The area is vegetative with vast under-developed land reserved mainly for pasturing animals.
The campus also encompasses a lecturer’s compound of 51 households with a population of approximately (51 x 5 people in each home) 355 people. In addition, regular and parallel students are accommodated around the campus for 3-4 months as a semester. One or two weeks after the regulars and parallels closure, the Open and Distance learning (O.D.L) students are accommodated for a period of six (6) weeks.
As soon as the O.D.L students have closed, regular and parallel students will be back on the campus and the routine repeats itself. (College handbook). (N.R.D.C)
Taking an inventory was the first task assigned to the author; this was done to determine the best possible sampling points. From this exercise, ground surface reservoir, dining hall, administration block and two different lecturer houses were identified. The houses are located on the east and west sides of the N.R.D.C institution. The points were recorded using the Global Positioning System (GPS) and have been clearly shown using Google earth map. Determining the surface reservoir volume was the second task the author undertook. This was done to calculate the required dosage at the reservoir so as to ensure 0.1-0.2mg/l chlorine residual at the consumer point. This was made possible with the help of course mates in taking measurements using a measuring tape.
Since the Natural Resources Development College reticulation system can be categorized as a small-scale water network, a small-scale chlorination system would be ideal. The author conducted a literature review on small-scale chlorination systems, specifically on water-powered liquid chlorine innovations. The author already had the operational concept of the chlorinator way before he was asked to submit a project proposal, but since it’s a designing and eventually constructional project, the sketch designs kept on changing for the better. The design could have been changing but the operational concept of the chlorinator has never been altered. During the prolonged vocational closures, the institution had the author worked with the Western Water and Sewerage Company (w.w.s.co) attached with the senanga district. With this opportunity, the author consulted extensively on factors to be considered when designing a small-scale chlorination system and had a meeting with the director of technical services for W.W.S.Co, Mr Sikoma.
In a nutshell, the author spent more time designing and redesigning the hydraulic chlorine dozer to ensure that not only can it work for N.R.D.C but for any other small-scale chlorination system. Time spent in the designing chamber was to ensure that the dozer met the standards of an efficient chlorinator;
• • •
Simple in design and operation Portable and robust
Basic constructional materials Easy to maintain and operational by unskilled personnelRelatively cheap The author has used Geometrical and Mechanical Drawing (G.M.D) which is one of the courses undertaken in first and second year for Water Engineers. With this knowledge, any design structure can be portrayed in a 3dimension free-hand sketch. Apart from the isometric drawings, the design of the hydraulic dozer has also been drawn in autographic projection. With this projection, the designs have been viewed from different angles i.e. the plan, front view, and the end elevation. After being satisfied with the chlorinator designs (autographic and isometric) as having attained the factors of a chlorinator, the author proceeded to purchase the materials for the prototype construction according to the dimensions and specifications. The total cost of the materials has been attached in the later pages of this report. During the construction period, the author worked with a plumber by profession man named, Felix. He (Felix) has a hardware shop from which the author purchased each and every CPVC material. Apart from the supplier of the dozer materials, Mr Felix also helped with technical experience pertaining to CPVC material construction. The construction period took one (1) week after which the author conducted operational tests on the chlorinator. Theory and practical’s are two different stages, theoretically, the dozer worked but practically, a few alterations were considered on the chlorinator. More than five (5) operational tests were undertaken just to make sure that the chlorinator worked efficiently. Checking the operational aspects of the dozer did not mean the actual connection of the dozer to the main supply pipe, but a hosepipe was connected to the dozer water inlet chlorinated polyvinyl chloride pipe (CPVC). This demonstrated how water entered, mixed with the chemical and left the prototype; it also demonstrated the ball valve mechanism once water entered the water delivery cylinder. Water samples were taken from the five (5) selected water sampling points; this was done to determine the efficiency of the chlorination method that was currently practiced at the surface reservoir. The water samples were tested for faecal-total coliforms and chlorine residual. Sample collection was done at N.R.D.C while testing was done at the University of Zambia (UNZA) great east road campus. Sample collection and testing was done once every month for three months starting on the 27 Th February 2013.
5.0 ANALYSIS AND RESULTS
THE FOLOWING WHERE THE FINDINGS FROM THE INVENTORY THAT WAS CARRIED OUT ON 4THJANUARY 2013
N.R.D.C Surface Reservoir (square)
Height of overflow pipe: 2.8m
Materials used: measuring tape, scale and the water treatment schedule/monitoring book. TABLE 1: Application time / quantity.
|Time(hours)-everyday at||Quantity in grams|
TABLE 2: Pump (Boreholes) Supplying the Reservoir
|Borehole number||Discharge (l/s)||Diameter(inches)|
|Booster pump at the reservoir||18||–|
MAXIMUM VOLUME OF THE RESERVOIR Assumption: No overflow or seepage
• Subtracting the wall thickness from the total length.
Length=9.15m-2(0.254m) =8.642m Height=2.8m
Volume=surface area x height
i.e. V=L2 X H
V=8.642m X 8.642m X 2.8m = 209.1156592m3 App… 209000.00 liters of water.
Chlorine concentration when reservoir is full in the morning. Assumption: no overflow and concentration is constant in the reservoir.
Concentration = ????(?????) ??????(??????)
= 300? 209000?
How long it takes to empty the chlorinated water
Assumptions: no replenishing the reservoir, booster pump of 18l/s is efficient and maintained and no water losses are suffered.
18 liters 1 sec,
209000 liters x sec, x =11611.11111 sec`s, App…3 hrs 13minutes.
Therefore, it takes 3hr 13minutes for the 18l/s booster pump to drain the 209000 liters of water from the reservoir.
5.1 Mechanism behind the hydraulically operated dozer
Given: 300g of chlorine, 2 (two) supply pumps of borehole 8 and 9.Chlorine tank of 160 liters
and the hydraulically operated dozer.
Assumption: no over flow, supply pumps working at full capacity.
A concentrated chlorine solution of 300g/160 liters will be formed in the chlorine tank. Therefore, chlorine tank concentration will be 1875mg/l
Since the reservoir is being supplied by the two boreholes 8 and 9, the combined inflow into the reservoir is 32l/s
32 l 1 sec
209000 l x seconds, x =6531.25 seconds, = 1hr 48 minutes
Therefore, it takes approximately 1hr 48 minutes for the two supply pumps to fill the surface reservoir to the overflow pipe.
Note: In 1hr 48 minutes, the reservoir is filled to capacity (209000liters), the 160 liters chlorine tank with a concentration of 1875mg/l should be added to this water within 1hr 56 minutes.