The result obtained after disinfection from all dug wells constructed/reconstructed:

Samples dug holes	Total Colioform	E- Coli
1	- (absent)	- (absent)
2	-	-
3	-	-
4	-	-
5	-	-
6
7	-	-
8	-	-
9	-	-
10	-	-
11	-	-
12	-	-
13	-	-
14	-	-
15	-	-
16	-	-
17	-	-
18	-	-
19	-	-
20	-	-
21	-	-
22	-	-
23	-	-
24	-	-

5. Water filtration

In very shallow aquifers, bacterial contamination is possible, and even likely if the wellhead is poorly protected. In addition to arsenic, other inorganic constituents in groundwater can cause health or aesthetic problems, notably iron, manganese, nitrate, chloride, and fluoride (WHO, 2000)

Water treatment plants typically clean water by taking it through the following processes:

1. aeration;
2. Coagulation;
3. Sedimentation;
4. Filtration;
5. Disinfection

SAND FILTER

The versatility of the sand filter is reflected in the numerous design variations that have been developed to address many different climatic and development conditions

Slow Sand

It incorporated sand with an effective size of fine sand. This very fine sand produced good quality of water of low turbidity.

Rapid Sand

Rapid sand filter might vary in effective size of coarse sand.

Mixed Media

Development of the coarse-to-fine principle of filtration has taken place in two major steps.

Basically this provides a two-layer filter in which coarse upper of coal (sp.gr. 1.4) acts as a roughing filter to reduce the load of particulates applied to the sand (sp.gr. 2.64) below. Dual media filter can retain more material removed from water than sand filter. The size of the media particles should be uniformly graded from coarse-to-fine in the direction of flow through a filter bed.

The British Geological survey (BGS, 1998) suggests that within the zone of water table fluctuation and where residence times are short, arsenic is flushed away or immobilised.

Soil Purifies Water

Santee, California, USA, a suburb of San Diego provides unusual approach to sewage treatment. Water is pumped from oxidation ponds into one or another of the basins, where it slowly soaked through soil. The water is purified variety of ways while it is contact with the soil:

• First, it is filtered; contaminants in the wastewater become lodged in the voids and spaces that exist in all soils, much as occurs in an activated carbon filter (Coffel, 1991).
• Some toxic are rendered harmless when they react with elements in the soil;
• Others become part of the soil;
• Countless microbes inhibit in most soil. Micro-organisms in soil remove nitrogen, germs, bacteria, and viruses.

State officials of Santee were far from convinced that the system would produce really clean water. They were especially concerned that viruses would find through the system. However, after extensive testing, with special attention to viral organisms, the state approved the water.

Soil is, in fact, more resilient in handling the constantly changing blends of toxic materials. The diverse community of organism present in soil are better able to react to changes in the chemistry of the wastewater to be treated. Soil filters are more effective when plants are grown on them.

Clays also adsorb arsenic because of the oxide-like character of their edges, as do carbonates. Of these components, adsorption by iron oxides is probably most important in sandy aquifers because of their greater abundance and the strong binding affinity. Nevertheless, if studies of soil phosphate are a guide, then aluminium oxides can also be expected to play a significant role when present in quantity. Experience from water treatment (Edwards, 1994) suggests that below pH 7.5 aluminium hydroxides are about as effective as iron hydroxides (on a molar basis) for adsorbing As (V) but that iron salts are more efficient at higher pH and for adsorbing As (III). Arsenic (V), like phosphate.

Surface water percolates through (4-6 meters) soil, silty sand and accumulates in fine to medium sand  (aquifer) of dug wells. If dug wells are constructed with proper care, natural biological system removes nitrogen, germs, bacteria and viruses.

Our ancestor knew this wisdom. Even now people say, “Drink crystal clear water. Don’t drink water with micro-organisms!”

6. Identification of facies change within contaminated area and locate and construct arsenic free wells

There are wells that are highly contaminated but a few wells show ground water arsenic concentration is far below Bangladesh standard. Based on an understanding of the geological origins of contamination, it may be possible to identify areas or strata that are at relatively low risk of arsenic contamination. In some areas arsenic contamination is confined to highly localized sedimentary deposits.

If these hot spots are identified through widespread arsenic testing, new wells can be preferentially installed in relatively safe areas. In areas where some geological units are arseniferous and others are not, it is important to avoid cross-contamination, which can occur in several ways. In some cases, the arsenic-rich zones may be naturally in hydraulic connection with arsenic-free zones.

By pumping water from arsenic-free zones, arsenic-rich water may be induced to flow into previously uncontaminated strata, and eventually may reach the well. In other cases, the arsenic-rich and arsenic-free zones may be separated by low-permeability materials such as clays. Drilling can disturb this natural barrier, and the borehole itself (specifically, the annular space around the well pipe) may provide a high-permeability conduit from one zone to another.

When wells are drilled with mechanical rotary rigs, it is possible to inject impermeable material such as grouting or clay into this annular space at the level of the impermeable layer, to prevent this kind of contamination. However, in many developing countries, grouting is not used, either to save money or because the drilling technologies are not compatible with grouting.

Arsenic-free wells might become contaminated over time through a third mechanism: arsenic could initially be present in a stable, solid form in aquifer sediments. If the geochemistry of the pore water, especially the pH and redox potential, should change, arsenic could become mobilized, and make its way into the abstracted groundwater.

It may sound puzzling but the aquifers are different. Local relief and rivers impact on the direction and velocity of groundwater flow and therefore on the migration of arsenic. Groundwater flow from high to low relief causes deeper penetration contaminants into the aquifer. The reverse is true in areas that are low in relief. Here upward groundwater movement would bring contaminants to shallower horizons.

A sound knowledge on underground geology, hydrology it is possible to identify arsenic free aquifer at shallow depths. This is a very cheap and highly acceptable alternative.

We have identified a channel sand facies at Khalil Pur, Faridpur

At Khailpur most of the wells are arsenic contaminated but in some areas a few wells found to be arsenic free. At Kahailpur after 12 drilling arsenic free aquifer has been identified at depths 40-55 feet within channel sand facies.

At Alipur and Vashan Char, Ambikapur, Faridpur we have identified at 40-55 channel sand facies with arsenic free aquifers.

This method can be applied to other areas for easy and cheap access of arsenic free water. This needs careful formation evaluation and routine monitoring.  Hammer drilling equipment or vibro-core is required; unfortunately it is not available in Bangladesh.

7. Rainwater collection (harvesting) and filtration

The concentrations of arsenic in the atmosphere are usually low but as noted above, are increased by inputs from smelting and other industrial operations, fossil-fuel combustion and volcanic activity. Concentrations amounting to around 10^–5–10^–3µgm^–3 have been recorded in unpolluted areas, increasing to 0.003–0.18µgm^–3 in urban areas and greater than 1µgm^–3 close to industrial plants (PCS/WHO, 2001). Much of the atmospheric arsenic is particulate. Total arsenic deposition rates have been calculated in the range <1–1000µgm^–2yr^–1 depending on the relative proportions of wet and dry deposition and proximity to contamination sources (Schroeder et al., 1987). Values in the range 38–266µgm^–2yr^–1 (29–55% as dry deposition) were estimated for the mid-Atlantic coast (Scudlark and Church, 1988).

In areas with low population density and hard rocks surfaces (rock outcrops or cement), rainwater can be collected from the ground surface by constructing microdams to channel surface runoff into underground storage tanks. In more densely populated areas, rooftop collection is more common. Corrugated iron roofs are ideally suited for this purpose, though terra cotta or wood tiles, or concrete roofs are also acceptable. Thatched roofs are not appropriate for rainwater collection, as the collected water is high in organic matter. These roofs, however, can be made suitable with the simple use of inexpensive plastic sheeting. Roofs should be cleaned thoroughly at the beginning of every rainy season, regular maintenance is also crucial.

Water is collected from the roof surface in gutters, which are connected to a storage tank with a downpipe. In order to minimize the amount of contamination and organic matter in collected water, a fine mesh netting or coarse sand filter should be placed between the downpipe and the storage tank. This will also help to keep insects and small animals out of the tank, and has been shown to improve water quality, and reduce the risk of mosquito breeding.

When rain falls after a dry period, water should not be collected for the first ten to fifteen minutes, in order to clean the collection surface. This ‘first flush’ can be achieved through use of a bypass valve, or through a variety of simple designs.

Storage

A rainwater storage tank should be completely covered, and have a tap or pump for withdrawing water, to prevent contamination from users. If water is stored in open containers, or users dip cups or pitchers in a tank to retrieve water, the stored water can easily become contaminated with fecal pathogens.

The amount of storage required will depend on local rainfall patterns, especially on the extent of dry seasons. If rainfall is scarce or absent for several months, large tanks will be required, or alternate sources of drinking water used during the dry season. In rainy periods, small, inexpensive tanks are able to provide adequate storage for most household needs.

Aboveground tanks can be made of locally available materials such as brick or cement. Ferrocement (cement reinforced with iron mesh or wires) is much stronger than cement, so ferrocement tanks can be thinner and less expensive than simple cement or brick tanks. Prefabricated plastic tanks can also be used, though these are not as easy for rural users to repair, and may impart a taste to the stored water. Tanks should be cleaned at least annually, and if possible, disinfected.

Underground storage tanks can be quite large, and have smaller unit capital costs. However, underground tanks are more vulnerable to contamination from surface waters, flooding, and animal invasion, more difficult to clean, and require the use of a pump to draw water to the surface

Water Quality

The bacteriological quality of rainwater will depend on the collection and storage methods. In a well-designed system, pathogenic bacteria counts are low in collected rainwater, and the conditions (lack of light or food source) do not promote their growth. Under these conditions pathogen levels will actually decrease with storage, rather than increase. Typically, some coliform bacteria can be found in collected rainwater, but usually the bacteria are not fecal in origin (Pacey and Cullis, 1986).

Several reviews of bacteriological quality of rainwater have been made: in some cases, fecal and total coliform counts are extremely low (e.g. Dillaha and Zolan, 1985), but more commonly low levels of coliform bacteria are found. Typical fecal and total coliform counts in water collected from rooftops average 5-15 and 25-75 per 100 ml, respectively (e.g. Pinfold et al., 1993; Appan, 1997; Simmons et al., 1999a).

By examining the ratio of fecal coliforms to fecal streptococci, Appan showed that approximately 80% of the fecal contamination was of non-human origin, presumably from animal droppings on the rooftop (Appan, 1997). Simmons and others found similar coliform counts in rural New Zealand, though occasionally counts were significantly higher (maximum total and fecal coliforms were 19,000 and 840 per 100 ml). Two samples showed Cryptosporidium, but none showed Giardia, Campylobacter, or Legionella pneumophila (Simmons et al., 1999a).

Yaziz and others found moderate levels of coliform bacteria in rainwater collected from rooftops, and showed that the highest counts were in the first samples collected during a rainfall. When samples were collected after a ‘first flush’ equivalent to 35 liters per 100 square meters of roof catchment area, no fecal coliforms could be detected, and total coliforms were reduced by over 50% (Yaziz et al., 1989).

Bacterialogical studies of rain water in project area:

Samples rain water harvesting units	Total Colioform	E- Coli
1 unclean roof	+(present)	- (absent)
2 unclean roof	+	-
3 unclean roof	+	-
4 unclean roof	+	-
5 unclean roof	+	-
6 clean roof	-	-
7 clean roof	-	-
8 clean roof	-	-
9 clean roof	-	-
10 clean roof	-	-
11 clean roof	-	-
12 clean roof	-	-
13 sand filtration	-	-
14 sand filtration	-	-
15 sand filtration	-	-
16 sand filtration	-	-
17 sand filtration	-	-
18 sand filtration	-	-
19 sand filtration	-	-
20 sand filtration	-	-
21 sand filtration	-	-
22 sand filtration	-	-
23 sand filtration	-	-
24 sand filtration	-	-

If bacterial quality of stored water is unacceptable, disinfection process is followed as described. All rainwater samples after filter do not show presence of coliform bacteria.

Rainwater is much less mineralized than surface water and groundwater, which can give the water a flat taste which some may find objectionable. In parts of South America, ground tree bark is added to rainwater to improve taste; elsewhere crushed seeds, curd from sour milk, or tree leaves are used in the same way (Pacey and Cullis, 1986).

Although collected rainwater commonly contains low levels of coliform bacteria, in many cases it is of much better microbiological quality than other available water sources. Chemical parameters, especially pH and lead and zinc levels, should be monitored regularly to ensure that appropriate water quality standards are met. In most cases, however, the relative purity of rainwater makes it an attractive option in areas with uniformly high arsenic levels in other water sources. A large literature on the collection, storage, treatment, and distribution of rainwater exists, drawing on experiences from around the world. For more detailed information, the reader should consult the excellent reports produced by ENSIC (Gould, 1991), IRC (IRC, 1981; IRC, 1990), ITDG (Pacey and Cullis, 1986; Cullis and Pacey, 1991; Gould and Nissen-Petersen, 1999), and UNEP (UNEP, 1983). In recent years, several valuable websites have been set up with ready reference material on the application of rainwater collection and storage. Many such sites exist, two good introductory sites containing many links are (IRCSA, 2001) and (EU, 2001).

Studies in Thailand, India, and Sri Lanka, show that properly stored rainwater is

Safe from bacteria, and can be stored for many months. Also, research in Bangladesh by the International Centre for Diarrhoeal Disease Research, Bangladesh, (ICDDR) confirms that rainwater can be a safe drinking water source. Rainwater is very low in dissolved minerals, and as such is relatively corrosive. This lack of minerals may also cause mineral deficiency in the diets of poorly nourished consumers. Fruits like banana, mango, jackfruit etc. are advised to take regularly. The relative purity of rainwater makes it an attractive option in areas with uniformly high arsenic levels in other water sources

We have found keen interest on rainwater collection in the arsenic affected areas. We have selected all local materials and local carpenters and potters made rainwater collecting 12 units at worst affected poor rural areas. Water filter is also under construction. It is possible to collect a huge amount of rainwater. Rainwater collection makes the life of the women comfortable, as they do not require carrying water from a long distance. Advertisement in the newspaper to use rain- water does not have any affect on villagers. If simple method is shown practically, the villagers can easily repeat it.

• Rainwater collection is very popular.
• Women collects water from far distance and water at house door is a great relief for the women.
• Food tastes better like rice, lentil.
• This is possible to store rainwater for the whole year. The tank may be costly but cheaper than any other arsenic removal plants.
• Small rainwater tank for Tulagram Primary School children (650 students) has been successful. This has been constructed with coarse sand and brick chips with mix media sand filter at the top. It sweats and wind keeps the water cool.

List of Rainwater Harvesting Units:

Sl. No.	Name	Village
1	Yunus Sk.	Tulagram, Kozuri Union
2	Nammu Sk	Tulagram, Kozuri Union
3	Dirajuddin Mollah	Tulagram, Kozuri Union
4	Latif Mollah	Tulagram, Kozuri Union
5	Mohiguddin Mollah	Tulagram, Kozuri Union
6	Razzaque Paramanik	Tulagram, Kozuri Union
7	Kusha Paramanik	Tulagram, Kozuri Union
8	Shiraj Sk.	Tulagram, Kozuri Union
9	Delwar Mollah	Tulagram, Kozuri Union
10	Mannan Mollah	Tulagram, Kozuri Union
11	Hafez Sk.	Tulagram, Kozuri Union
12	Kamal Sk.	Tulagram, Kozuri Union
13	Jabbar khan	Tulagram, Kozuri Union
14	Majid Khan	Tulagram, Kozuri Union
15	Shantu Sk.	Tulagram, Kozuri Union
16	Haroon Sk.	Tulagram, Kozuri Union
17	Zamsher Khan	Tulagram, Kozuri Union
18	Ahamed Bepari	Tulagram, Kozuri Union
19	Faju Sk.	Tulagram, Kozuri Union
20	Azad Sk.	Tulagram, Kozuri Union
21	Ishaque Sk.	Tulagram, Kozuri Union
22	Falu Dewan	Tulagram, Kozuri Union
23	Rafique Sk.	Tulagram, Kozuri Union
24	Razzaque Sk.	Tulagram, Kozuri Union
25	Jalil Sk.	Tulagram, Kozuri Union
26	Zakir Sk.	Tulagram, Kozuri Union
27	Obaidul Mollah	Tulagram, Kozuri Union
28	Abzal fakir	Tulagram, Kozuri Union
29	Ratan Pramanik	Purbogangabarti, Kojuri Union
30	Infar Mondal	Purbogangabarti
31	Mazed Sk.	Purbogangabarti
32	Billal Sk	Purbogangabarti
33	Shemala Begum	Purbogangabarti
34	Shaeed Sk.	Purbogangabarti
35	Morad Khan	Purbogangabarti
36	Amzed Khan	Purbogangabarti
37	Hashem Sk.	Purbogangabarti
38	Ismail Sk.	Purbogangabarti
39	Zahid Bepary	Purbogangabarti
40	Mannan Sk	Purbogangabarti
41	Rab Sk.	Purbogangabarti
42	Siraj Sk.	Purbogangabarti
43	Qubad Sk.	Purbogangabarti
44	Zahid mondal	Purbogangabarti
45	Ripon Mondal	Purbogangabarti
46	Shamsu Mattabar	Purbogangabarti
47	Rob Mollah	Purbogangabarti
48	Anwar Mollah	Purbogangabarti
49	Samad Mollah	Purbogangabarti
50	Ayub Ali Sk.	Purbogangabarti
51	Tara Mollah	Purbogangabarti
52	Dulal Sk.	Purbogangabarti
53	Shaheed Mondal	Purbogangabarti
54	Baten Miah	Purbogangabarti
55	Suiddique Fakir	Purbogangabarti
56	Falany Sk.	Purbogangabarti
57	Mannan Fakir	Purbogangabarti
58	Qader Mattbar	Purbogangabarti
59	Zainal Sk.	Utter Alipur, Fardpur
60	Murad Sk.	Utter Alipur, Fardpur
61	Ishaque Sk.	Utter Alipur, Fardpur
62	Yunus Sk.	Utter Alipur, Fardpur
63	Nurul Islam Mollah	Utter Alipur, Fardpur
64	Mojahar Sk.	Utter Alipur, Fardpur
65	Salam Sk.	Utter Alipur, Fardpur
66	Tayeeb Bepari	Utter Alipur, Fardpur
67	Madhi Paramanik	Utter Alipur, Fardpur
68	Jahid Sk.	Utter Alipur, Fardpur
69	Rahim Sk.	Utter Alipur, Fardpur
70	Ismail Fakir	Utter Alipur, Fardpur
71	Razzaque Sk.	Utter Alipur, Fardpur
72	Isaque Fakir	Vashan Char, Ambikapur
73	Siddique Sk.	Vashan Char, Ambikapur
74	Jalail Sk.	Vashan Char, Ambikapur
75	Ahad Mollah	Vashan Char, Ambikapur
76	Kabir Mollah	Vashan Char, Ambikapur
77	Moksud Mondal	Vashan Char, Ambikapur
78	Harun	Vashan Char, Ambikapur
79	Tasrin	Vashan Char, Ambikapur
80	Bucha	Vill. Ambikapur
81	Bisha	Vill. Ambikapur
82	Nannu	Vill. Ambikapur
83	Chunnu	Vill. Ambikapur
84	Haider	Vill. Ambikapur
85	Akkas Ali	Shovarampur Basti
86	Tota Ali	Shovarampur Basti
87	Nur Hossain Bepari	Shovarampur Basti
88	Emran sk.	Shovarampur Basti
89	Selim Bepari	Shovarampur Basti
90	Halim Sardar	Shovarampur Basti
91	Shujan Ali	Shovarampur Basti
92	Nayan Ali	Shovarampur Basti
93	Delwar Mollah	Shovarampur Basti
94	Aziz Mollah	Shovarampur Basti
95	Ranu Begum	Shovarampur Basti
96	Sham Bepari	Shovarampur Basti
97	Jani Bepari	Shovarampur Basti
98	Tazel Mollah	Shovarampur Basti
99	Mannan Khan	Klub Bazar, Koizuri Union
100	Gopal Mazumdar	Klub Bazar, Koizuri Union
101	Barek Mollah	Klub Bazar, Koizuri Union
102	Ramizuddin Mollah	Klub Bazar, Koizuri Union
103	Shanal Mollah	Klub Bazar, Koizuri Union
104	Asim Mollah	Klub Bazar, Koizuri Union
105	Nimala Khatun	Klub Bazar, Koizuri Union
106	Shamsuddin Mollah	Klub Bazar, Koizuri Union
107	Salam Mollah	Klub Bazar, Koizuri Union

8. Arsenic Test

Most of the current field test kits are based on the Gutzeit method which involves the reduction of As(III) and As(V) by zinc to give arsine gas which is then used to produce a stain on mercuric bromide paper. Hydrogen sulphide gas is removed with zinc acetate-treated glass wool. There have been many studies of the sensitivity and reliability of these kits, particularly in India and Bangladesh. The early kits were usually good at detecting high-As waters (say greater than 100 µgl^–1) but often were found to have rather poor reliability at lower concentrations. Ideally a field test kit for arsenic should be:

• sensitive and reliable – it should be quantitative at the 5–200 µgl^–1 level and have a precision that is about the same as, or slightly better than, the short-term variability observed in the field, say ± 20 percent or ± 5 µgl^–1 for low concentrations;
• robust – it should be able to maintain a good performance for long periods under actual field conditions assuming reasonable care is taken;
• simple to use – it should be designed to be as simple as possible to use by field workers with the minimum of technical training and supervision;
• affordable – it must not be so expensive as to preclude its use either in terms of capital or recurrent costs;
• safe to use – it must not pose a hazard to the user or environment even after heavy use.

We have used test kits of Merck.

Comment: Merck Kit gives reliable result but humidity (above 90%) and temperature (above 25ºC) make the chemical inactive after two weeks use. Temperature can be regulated with cool box but not the humidity. We advise Merck to produce one hundred sealed chemicals for each test kit for use in tropical countries.

9. Analysis from selected samples

The hazardous substances used and expelled to nature by the industries are as follows:

Arsenic - agriculture, phosphate manufacture, fertilizer production, leather tanning;

Chromium - pulp and paper mills, fertilisers, leather tanning, cement works, steel works, glass works;

Copper - pulp and paper mills, fertiliser manufacture, chemical works;

Lead - paint manufacture, battery manufacture, chemical manufacture, pulp and paper mills, fertiliser manufacture, petroleum refining;

Nickel - pulp and paper mills, petroleum refining;

Most toxic trace metals occur in solution as cations (e.g. Pb²⁺, Cu²⁺, Ni²⁺, Cd²⁺, Co²⁺, Zn²⁺), which generally become increasingly insoluble as the pH increases. At the near-neutral pH typical of most ground waters, the solubility of most trace-metal cations is severely limited by precipitation as, or co precipitation with, an oxide, hydroxide, carbonate or phosphate mineral, or more likely by their strong adsorption to hydrous metal oxides, clay or organic matter.

In contrast, most oxyanions including arsenate tend to become less strongly sorbed as the pH increases (Dzombak and Morel, 1990). Under some conditions at least, these anions can persist in solution at relatively high concentrations (tens of µgl^–1) even at near-neutral pH values. Therefore the oxyanion-forming elements such as Cr, As, U and Se are some of the most common trace contaminants in ground waters.

We have found few wells containing high amount of nickel and nitrate. These are most possibly anthropogenic source.

ARSENIC IN TSP FERTILISER

Semi qualitative analysis of available TSP fertilisers in the market shows a high amount of arsenic. This was also reported in 2000 (Anwar, Arsenic Poisoning in Bangladesh). Agriculture Department should take necessary action.

10. Desinfection

Monitoring Pathogens:

Most commonly, the presence or level of abundance of colioform bacteria is used as an overall indicator of contamination of the water with faceal material. Coliform bacteria can be readily isolated, identified and counted from water sample. Despite these advantages, colioforms are by no means can be used as indicators of fact real contamination. The presence of viruses or parasites is not routinely used to indicate faecal contamination; it is advisable, for reasons of public health, to monitor water for their presence.

Isolating, identifying and counting viruses are difficult and less agreement on standard methods. In view of the difficulties of isolating, and identifying viruses from water, it would be advantageous for routine monitoring purposes to use a single, readily-indefinable virus species as an indicator of the possible presence of pathogenic viruses.

Monitoring for parasites requires skilled personnel. The most common method of identifying parasites is under direct examination, under the microscope, of water sample, the various life stages of parasitic organisms.

REMOVEBLE OF WATER-BORNE PATHOGENS

The list of potential waterborne diseases due to micro organisms is considerably larger and includes bacterial, viral, and parasitic microrganisms shown below:

Bacteria	V. cholera, Salmonella, salmonella,    Shigella
Viruses	Infectious hepatitis, Coxsackie A and B (32 types), Reoviruses (3 types), ECHO viruses (34 types), Adenoviruses (32 types) Viral gastroentertis Viral diarrhea
Parasitic	E. histolytica, Amebiasis, Giradiasis, Amoebic mening-ocephalitis, Ascariasis, Schistosomiasis

There are several outbreaks of severe waterborne diseases even from groundwater supplies in the advanced industrial countries (In the USA during 1971-78 there were 15 outbreaks of waterborne viral hepatitis and hepatitis A has been implicated in 68 outbreaks since 1946, 1965 – California salmonella outbreak,1892 cholera out break in Hamburg, Germany etc).

In Bangladesh seious outbreak of waterborne diseases is reported even drinking water from shallow groundwater (Tubewell). Drinking water from shallow groundwater has decreased waterborne diseases but it has not eliminated all diseases. Additional treatment is required namely, disinfect ion, the most important treatment process for the prevention of waterborne disease.

The following methods of disinfection is carried by the water supplies all over the world:

Physical Disinfection

Boiling can effectively kill ova, cysts, bacteria, and viruses present in water. Water should be brought to a full rolling boil, and maintained for one minute. Water boils at lower temperatures at higher altitudes, so for every 1000 meters of elevation an additional minute of boiling should be required.

Boiling is generally not recommended for several reasons:

1. It requires a large amount of fuel;
2. It may give the water a flat, unpleasant taste; there is a risk that people may heat the water without boiling, and consider the water purified.
3. Boiling in closed kettles can concentrate some volatile organic compounds.
4. Large-scale boiling is not a feasible option for drinking water in most cases because fuel costs would be prohibitive (WHO, 1997).

Desinfection By Coagulation, Settling, Filtration and adsorption processes

coagulation and filtration systems are managed properly, removal of 90 to 99% of bacteria and viruses, and over 90% of protozoa can be expected (Salvato, 1992, p. 346). However, a safety dose of chlorine should be given following filtration, to destroy any remaining pathogens, and impart a residual disinfectant to the water.

Chlorination at any stage of treatment can produce harmful disinfection by-products, depending upon the dose and composition of the treated water. The health risks posed by these by-products are smaller than the risks posed by pathogens, so disinfection should not be neglected simply to avoid by-product formation.

1. Chemical Desinfection
   • Chlorine
   • Iodine
   • Bromine
   • Ozone
2. Alternative Desinfectants:
   • Heat Treatment
   • Ultraviolet Irradiation
   • Metal Ions

The Swiss research centre EAWAG has shown that by storing water in clear bottles and exposing them to at least 4 hours of sunlight, over 99% pathogen removal can be achieved. The sunlight both heats and irradiates the water, and these two processes have a synergistic effect on pathogen removal. Raw water must have low turbidity (<30 NTU), for radiation to penetrate sufficiently. Bacteria, viruses, Giardia and Cryptosporidium cysts, and parasite eggs can all be effectively inactivated through the combination of ultraviolet radiation and elevated water temperature.

Studies show that pathogen inactivation was initially low, but as water temperature rose above about 50°C, the effects of radiation and elevated temperature acted synergistically, resulting in increased inactivation efficiency. This technique, called SODIS (Solar Disinfection) involves very minimal capital and operational costs, and is promising, both for use in arsenic-affected areas, and for rural water supply in general.

Disinfection By Coagulation, Settling,

Filtration and adsorption processes

The chemical coagulation process has been noted by several researchers as providing high degrees of removal of viruses.

Alum coagulation was found to remove 95 to 99 of Coxsackie virus and ferric chloride was found to be remove 92 to 94 percent of the same virus (Berg. G., 1971) Aluminium coordinates with carboxyl groups of the virus’s protein coat, followed by incorporation of complex into precipitating hydrated aluminium oxide.

Lime coagulation has demonstrated the ability to effectively remove and inactive viruses. The mechanism of inactivation under alkaline conditions is caused by denaturation of the protein coat and by disruption of the virus. In some cases, complete integrity of the virus may occur under high pH conditions.

Clear water

In the USA the plants producing very clear water also tended to secure low bacterial accounts accompanied by low incidence of viral diseases. Rural population of Bangladesh refuses to use surface water as it is not clear.  Turbidity in water can be a health hazard. In general, it interferes with

• disinfection, by creating a possible shield for disease-causing organisms,
• maintaining an effective chlorine residual, and
• bacteriological testing of water.

The modern concept of water treatment, coagulation and filtration are inseparable. Good coagulants are also efficient filter aids. The crucial direct relationship of coagulation to optimum filterability has been overlooked in the past. One is to establish the primary dosage of coagulant for maximum filterability rather than for production of the most rapid settling floc. A second approach is to add a dose of second coagulent as a filter aid to the settled water.

Coagulation

The Egyptians practiced a form of coagulation as early as 2000 B.C. Alum was known to the early Romans of 2000 B.C. By 1757 muddy water in England was treated withg 2-3 grains of

alum per qt, followed by flocculation and filtration of the supernatant. In England from about 1885, coagulation (1.5 grains per gallon) was employed ahead of sand filtration. Several inorganic salts of iron and aluminium are available commercially for coagulation:

Common Name	Formula
Alum	Al2(SO4) . 14 H2O
Lime	Ca(OH)2
Ferric Chloride	FeCl3 . 6 H2O
Ferric Sulfate	Fe2SO4. 3 H2O
Copperas	FeSo4 . 7H2O
Sodium Aluminate	Na2Al2O4

Samples dug holes	Total Colioform	E- Coli
1	- (absent)	- (absent)
2	-	-
3	-	-
4	-	-
5	-	-
6
7	-	-
8	-	-
9	-	-
10	-	-
11	-	-
12	-	-
13	-	-
14	-	-
15	-	-
16	-	-
17	-	-
18	-	-
19	-	-
20	-	-
21	-	-
22	-	-
23	-	-
24	-	-

11. Water Filter with local materials

WATER FILTRATION

Water may be treated differently in different communities depending on the quality of the water which enters the plant. Groundwater is water located under ground and typically requires less treatment than water from lakes, rivers, and streams.

BACKGROUND:

Water in lakes, rivers, and swamps often contains impurities that make it look and smell bad. The water may also contain bacteria and other microbiological organisms that can cause disease. Consequently, water from surface sources must be "cleaned" before it can be consumed by people. Water treatment plants typically clean water by taking it through the following processes: