MODIFICATION OF SLOW SAND FILTERS
CHAPTER ONE
- Introduction of the study
Slow sand filtration is a type of centralized or semi-centralized water purification system. A well-designed and properly maintained slow sand filter (SSF) effectively removes turbidity and pathogenic organisms through various biological, physical and chemical processes in a single treatment step. Only under the prevalence of a significantly high degree of turbidity or algae-contamination, pre-treatment measures (e.g. sedimentation) become necessary. Slow sand filtration systems are characterized by a high reliability and rather low lifecycle costs. Moreover, neither construction nor operation and maintenance require more than basic skills. This study intends to investigate into the Modification of slow sand filters, this chapter will specifically include; This chapter presents background of the study, the problem statement, purpose, objectives of the study, research questions, study scope, justification of the study, significance, Hypotheses, conceptual framework, as well as operational definition of key terms and concepts.
- Background of the study
Slow sand filtration was the first water treatment process introduced in 1804 in Scotland to improve the quality of surface water in Europe and North America and soon proved to provide protection against cholera and typhoid. It has remained a suitable treatment technology throughout the world and is recognised as particularly appropriate for application in developing countries by reason of the simplicity of design and construction and the ease of operation and maintenance (Freitas & Sabogal-Paz, 2019) . In areas where land is available, slow sand filtration is a low-cost water treatment process which can be operated and maintained by a trained member of the local community. No other available water treatment technology, excluding disinfection, can produce as safe a drinking water and provide as great a protection of public health (Zhao, et al., 2019).
According to the World Health Organization, slow sand filtration is simple, inexpensive, and reliable and is still chosen by some of the major cities of the world for purifying water supplies. For example, the Thames Water Authority in Iondon uses slow sand filters to provide drinking water to more than 11 million people. Slow sand filters are more widely used in European countries than in the United States (Logsdon, 2011). A recent survey of 27 slow sand filtration plants in the United States’ indicated that most are currently serving small communities (<lO,OOO persons), are more than 50 years old, and are effective and inexpensive to operate. A study comparing slow sand filtration with direct filtration” concluded that slow sand filters were superior, especially where simple operation is important (Da souza, et al., 2021).
The slow sand filtration process percolates untreated water slowly through a bed of porous sand, with the influent water introduced over the surface of the filter, and then drained from the bottom. Properly constructed, the filter consists of a tank, a bed of fine sand, a layer of gravel to support the sand, a system of underdrains to collect the filtered water, and a flow regulator to control the filtration rate. No chemicals are added to aid the filtration process (Collins, 2019).
Diagrammatic illustration of slow sand filter process
Slow sand filters require a very low application or filtration rate (0.015 to 0.15 gallons per minute per square foot of bed area, depending on the gradation of the filter medium and the quality of the raw water). The removal action includes a biological process in addition to physical and chemical ones. A sticky mat of biological matter, called a “schmutzdecke,” forms on the sand surface, where particles are trapped and organic matter is biologically degraded. Slow sand filters rely on this cake filtration at the surface of the filter for particulate straining. As the surface cake develops during the filtration cycle, the cake assumes the dominant role in filtration rather than the granular media (Liu, et al., 2019).
The move away from slow sand filtration in industrialized countries has largely been a function of rising land prices and labour costs, which increased the cost of SSF produced water. Where this is not the case, SSFs still represent a cost-effective method for water treatment (WHO, 2019). Since these conditions prevail in many developing countries, it is a very promising technique for water purification and, therefore, the development of a sustainable water system.
The simplicity of slow water filters includes contaminated freshwater flows through a layer of sand, where it not only gets physically filtered but biologically treated. Hereby, both sediments and pathogens are removed. This process is based on the ability of organisms to remove pathogens (jawaduddin, et al., 2019). This process therefore has a lot of challenges like sand filters are difficult to operate and maintain and usually required mechanical plant for backwashing and preferably air scouring as well. They do not produce a very good microbiological quality in the treated filtrate (about 1 log reduction in indicator organisms) and they usually require coagulation, which requires a reliable supply of chemicals. Inadequate water supply and poor sanitation account for approximately 30,000 deaths daily, many of them infants, and several hundreds of millions of people are suffering from water-related illnesses at any one time (Galadima, et al., 2011),
In Uganda due to poor filtration and disinfection, waterborne diseases have been found to be among the major public health problems. A number of them such as diarrheal illness, cholera and typhoid etc. are known to cause health effects. An estimated 30,000 persons die from diarrheal disease every year in Uganda and an annual average of 3000 cases of cholera are reported. The prevalence of waterborne diseases in Uganda is also attributed to poor hygiene and environmental sanitation including inadequate supply of safe water. Only 33% of the urban population in Uganda had access to adequate sanitation in 2012, a 1% rise since 1990 while 2% still practiced open defecation. Furthermore, reported that a population of 13.8 million Ugandans use unsanitary or shared latrines while 3.2 million have no latrine at all and defecate in the open, pit latrine coverage in Kampala is at 52 percent. Yet the majority of the rural populations in Kamuli municipality get their water supplies from unprotected water, underground water, streams, spring wells, ponds and lakes, this therefore indicates that Kamuli municipality is in dire need of an effective water filtration and disinfection technique that can improve the quality of water (Wolfgang, et al., 2019).
There are eight piped water supply systems namely: – Namwendwa, Kasambira, Bulopa, Kasolwe, Nankandulo, Kisozi, Mbulamuti and Kamuli water supply. The last three water supply schemes are under the management of National Water & Sewage Corporation (NWSC) while the first three water supply schemes are managed by Eastern Umbrella of Water and sanitation. Nankandulo and Kasolwe water supply schemes are managed by Water & Sanitation Committees, Apart from Mbulamuti water supply system that gets water from River Nile (surface water), all the other water supply systems have production wells (ground water) as their source of water. Kasolwe water supply has no distribution network i.e. it only has a Kiosk/Pump house with four taps. Rural Growth Centres (RGCs) served with piped water [(mainly Public Stand Posts (PSPs)] extended from existing schemes include: – Mukokotokwa, Kiyunga-Kisozi, Bulamuka, Namaganda-Kisozi, Lwanyama, Magogo, Bupadhengo, Nawanyago, Naibowa, Butansi. They are managed by NWSC (NWSC report, 2019).
The safe water coverage for the district is 75%, considering the projected rural population of 462,514 people, 1,163 hand-pumped water sources in use, 1237 yard taps and 47 public taps. This is the percentage population accessing safe water assuming that each hand-pumped water source serves 300 people, each yard tap serves 6 people, each PSP (or public tap) serves 150 people and the computed population served in a particular Sub-county cannot be more than the projected population of the Sub-county (NWSC report, 2019). Therefore considering the increasing population of Kamuli municipality is therefore imperative to modify the current water management system, this therefore has necessitated this study on investigating into modification of slow sand filters.
1.2 Statement of the problem
Due to the increasing population in cities it has become increasing necessary to provide an efficient water source for the population increase in the city and currently over 21 million people in Uganda are living without basic access to safe drinking water and therefore the quest to search for a better water treatment method that can improve the quality of life is imperative. According to (Terin & Sabogal-Paz, 2019) slow sand filters are more suitable for low-turbidity water or water that has been pre-filtered. They are used to remove algae and microorganisms, including protozoa, and, if preceded by micro straining or coarse filtration, to reduce turbidity (including adsorbed chemicals). Slow sand filtration is effective for the removal of some organics, including certain pesticides and also ammonia. However due to the rapid increasing prices of land slow sand filters are increasingly becoming a challenges and difficult to implement in the increasing congested cities and also expensive land , on the same note (jawaduddin, et al., 2019) notes that the process of SSF has a lot of challenges like sand filters are difficult to operate and maintain and usually required mechanical plant for backwashing and preferably air scouring as well, they are not as effective against viruses, No chlorine residual protection and therefore can lead to recontamination, Routine cleaning can harm the biolayer and decrease effectiveness.
The situation in Kamuli Municipality is one that requires urgent attention as regards to clean, safe drinking water this is because the access rates in Kamuli District vary from 36 % in Kagumba Sub-County to 95 % in Wankole Sub-County. Kamuli has 1,521 domestic water points which serve a total of 435,988 people 380,234 in rural areas. According to Kamuli District report, (2017) the Kamuli municipality currently is able to supply 500 Cubic meters of water against the Municipality requirement of 1000 Cubic meters, the report further indicates that because of the techniques of slow sand filters which limits on the capacity of water filtration therefore there is need to modify the system to enhance water capacity (Ikendi, 2019). This therefore indicates that Kamuli district is in dire need of clean safe water, (Kabwama, et al., 2017) also reports that Kamuli municipality is prone to water borne diseases like cholera, diarrhea, and typhoid. This therefore has necessitated this study on investigating into modification of slow sand filters.
- Purpose of study
The purpose of the study is to design a modification of slow sand filters.
- Objectives of the study
- To investigate the different challenges with current slow sand filters techniques.
- To design more cost effective water filtration technique
- To design an appropriate way of improving slow sand filters.
- Research Questions
- What are the different challenges with current slow sand filters techniques.
1.6 Hypothesis
- To design more cost effective water filtration technique
- What appropriate design an appropriate way of improving slow sand filters.
1.7 Significance of the study
The study will enable the management of kamuli municipality to design an appropriate water filtration techniques that can improve the quality of water.
The study will also provide information more cost effective water filtration technique and therefore this will improve the quality of life in Kamuli municipality.
Carrying out this study will enable future researchers to have a basic information on how to modify the slow sand filters for kamuli municipality.
REFERENCES
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Galadima, A. et al., 2011. Domestic water pollution among local communities in Nigeria-causes and consequences.. European Journal of Scientific Research,, Volume 52(4),, pp. pp.592-603..
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Logsdon, G. S., 2011. Water filtration practices: including slow sand filters and precoat filtration., s.l.: American Water Works Association.
Terin, U. C. & Sabogal-Paz, L. P., 2019. Microcystis aeruginosa and microcystin-LR removal by household slow sand filters operating in continuous and intermittent flows.. Water research,, Volume 150,, pp. 29-39..
Wolfgang, A. et al., 2019. Novel strategies for soil-borne diseases: exploiting the microbiome and volatile-based mechanisms toward controlling Meloidogyne-based disease complexes.. Frontiers in microbiology, ., Volume 10,, p. p.1296.
Zhao, Y. et al., 2019. Purification of harvested rainwater using slow sand filters with low-cost materials: Bacterial community structure and purifying effect.. Science of the Total Environment,, Volume 674, pp. pp.344-354..
