Jun 14, 2015
While displaying worthy aims, this project has overlooked significant design issues that threaten to compromise its potential positive outcomes. Shallow ground water in large areas of Bangladesh is contaminated with toxic levels of arsenic. The following paper from the Ministry of Public Health reviews the situation: http://users.physics.harvard.edu/~wilson/arsenic/countries/bangladesh/Minofhlth_bang.html Not all tubewells are contaminated, and efforts are underway to identify those that are. Propagation of new tube well-sourced drinking water systems must take account of the potential for spreading arsenic poisoning among the population. Thus, adequate testing must be the first step in any reformulation of this proposal. Further issues of a less dangerous nature center on the pumping, storage, and distribution aspects of this proposal. A lack of familiarity with solar electric systems and with water storage may have contributed to some misplaced assumptions in the original. The design calls for solar pumping of water from shallow tube wells, however it assumes the use of A/C motors of a high power (1 hp) with DC solar power inverted to alternating current in order to run the motors. To eliminate the need for expensive inverting equipment, 12v DC pumps should be considered. There is also some confusion around the need for battery storage, which is suggested, but if solar photovoltaic panels are hooked directly to solar pumps (through an appropriate charge controller), the water will be moved when the sun shines, so that the tank itself will become the energy storage in the system. This would reduce costs, and as the prototypical system is proposed to move only 500 liters of water per day, the solar pumps should be more than adequate. The specification of a 500 liter tank to serve 10 families of average size 5 persons and using 10 liters per person per day is naive. A capacity of at least 2-3 times this amount would be much preferred so as to ensure that a valve left inadvertently open, a broken line, or an electrical failure would not immediately leave the consumers without water. The challenge of this issue is the weight of water at 1 kg per liter, and the design of the mother tanks above ground. Attention must therefore be paid to careful construction of the RCC platform supporting the tank or tanks, which will weigh upwards of 1000 kg. Consumer tanks should also be designed to hold more than a single day's use of water, preferably 2-3 days supply. This would build RESILIENCE into the systems. Tank design is not specified, but is presumed to be of food-grade polyethylene, industrial manufacture. This material is photo-sensitive and will degrade within 5-8 years. Thus the tanks must be painted or coated with an opaque material to extend their life. Also, given the climatic conditions of coastal Bangladesh, provision should be made to shield the tanks from direct solar radiation by growing small trees and similar vegetation around them. Stored water subjected to light and heating in the tropical sun will more readily culture algae, and while not usually harmful, this can be unwelcome. Obviously, placement of the tanks in the right location near to the homes to be served is critical to limiting infrastructure costs and impacts. While the conceptual diagram shows a hub-and-spokes configuration, a more practical organization of plumbing, and one that properly mimics real urban water systems, would be a branching or dendritic pattern which limits pipe runs and uses short stubs to reach each consuming household tank from a long main. The dendritic pattern mimics nature (trees, rivers) to achieve the greatest economy of material use (length of pipe per household served). To limit the risk of a valve being left open inadvertently, and because the pipe runs are proposed to be above ground, valves to each subsidiary tank or household should be placed along main pedestrian streets or lanes and in prominent locations so that many eyes can view them. They should also be large and vividly colored so that passersby can tell at a glance when water is being drawn from the collective system. This would harness social pressure to regulate private consumption of a common resource. Because the distribution pipes are proposed to be elevated, the lines must be placed consistent with the movement of people and animals to limit the risk of traffic and work activities causing a break. Planting vertical perennials along the route of the pipelines would help to mark and protect them, as well as to provide shade against solar heating of the pipes.
Jun 16, 2015
Thank you for the insightful comment, especially the part on pumping and storage was very useful. A careful focus on these aspects will be given in a reformulated proposal. (One of the aims of this project was to keep the cost as low as possible, considering that it is a "test" project. So this project can be improved in many ways if additional funding is provided.) There is a reason we mentioned "potable water" in the proposal. We should have clearly stated that the project took into account water supply for drinking and cooking purpose, since arsenicosis is mainly caused by drinking water. Although nobody cannot guarantee a low-cost lifelong safeguard at this moment, deep tubewells (>150m) are generally safe (The Department of Public Health Engineering - Bangladesh http://www.dphe.gov.bd/index.php%3Foption%3Dcom_content%26view%3Darticle%26id%3D96%26Itemid%3D104). Arsenic testing is already a common practice in Bangladesh. So this step was assumed to be naturally included in the feasibility study. Per capita consumption per day (drinking) in a Bangladeshi village is estimated to be 2.5 litre, whereas the estimate for cooking is 9 liters (Source: http://www.iebconferences.info/356.pdf). Community awareness programs are already undertaken by different NGOs and the Government to help communities use water responsibly. So a 10liter/person estimate was considered in the proposal. The estimate may seem "naive" from a developed country perspective. However, safe drinking water is scarce in Bangladesh, and responsible water consumption is of extreme importance. However, building extra water pumping and storage systems for emergency situations should have been mentioned.
Jun 18, 2015
Taking further note on your comment, I would deliberately like to make a few more points sir. Introducing DC motor pump will be an excellent addition to the system, as it will omit the need for the costly inverter resulting in a significant reduction of the cost. But as we were planning the project, in order to make the system easily affordable, we had to emphasize on the availability of the components of the system as well as the price. All the components of the system are almost readily available in the context of Bangladesh, so is the proposed solar power system with inverter. A handful of organizations provide low cost household solar power systems with the help of government subsidy (like GrameenPower, BRAC etc.). So in the proposed design, we went for a more available option because DC pumps are not very much available in Bangladesh. But, if government makes up enough steps to make DC pumps more available and even subsidizes, it would be a very good pile for the success of the project. About the water circulation system, dendritic pattern would also be an excellent add up to the reformulation of the project. Though it would make the project a little bit more costly as bends have to be provided, I'm sure that the benefits of the pattern would be heavier in the context. About the tank design parameters, we proposed to use those units which are readily available here. In the urban areas of Bangladesh, food grade plastic tanks are ubiquitous, because of both the cost and quality. And for the record, the quality deterioration has not been that much of a problem regarding the tanks. As we planned, we think that the life duration of the motor pump will be a much bigger problem to face rather than the tank quality deterioration. Thank you.