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Access to safe drinking-water is essential to health, a basic human right and a component of effective policy for health protection. The nature and form of drinking-water standards may vary among countries and regions. There is no single approach that is universally applicable. A number of governmental and non-governmental agencies provide guidance on safeguarding the quality of public water supplies. The documents according to which the treatment plant for disaster struck region is established are:-
- GUIDELINES FOR DRINKING WATER QUALITY by WORLD HEALTH ORGANIZATION in GENEVA’08
- GUIDANCE FOR SAFEGUARDING THE QUALITY OF PUBLIC WATER SUPPLIES by DRINKING WATER INSPECTORATE, U.K.
- SPHERE MINIMUM STANDARDS FOR HUMANITARIAN RELIEF
Here we present a brief description of what role these have in providing safe water to the public.
WHO Guidelines for drinking water: Guidelines for Drinking-water Quality explains requirements to ensure drinking-water safety, including minimum procedures and specific guideline values, and how those requirements are intended to be used. The Guidelines describe reasonable minimum requirements of safe practice to protect the health of consumers and/or derive numerical “guideline values” for constituents of water or indicators of water quality. WHO analyzes the water quality on the following aspects:-
1. Microbial aspect: – Securing the microbial safety of drinking-water supplies is based on the use of multiple barriers, from catchment to consumer, to prevent the contamination of drinking-water or to reduce contamination to levels not injurious to health. Faecally derived pathogens are the principal concerns in setting health-based targets for microbial safety. In addition to faecally borne pathogens, other microbial hazards (e.g., guinea worm [Dracunculus medinensis], toxic cyanobacteria and Legionella) may be of public health importance under specific circumstances. The parameters most commonly measured to assess microbial safety are as follows:
- E. coli: zero E. coli per 100 ml of water
- Residual chlorine: in the range of 0.2-1 mg/litre.
2. Chemical aspect: – A number of chemical contaminants have been shown to cause adverse health effects in humans as a consequence of prolonged exposure through drinking-water. The prescribed concentration of certain chemicals in purified water is as under:
3. Radiological aspects :-The health risk associated with the presence of naturally occurring radionuclides in drinking-water should also be taken into consideration, although the contribution of drinking-water to total exposure to radionuclides is very small under normal circumstances. Formal guideline values are not set for individual radionuclides in drinking-water.
4. Acceptability aspects :- Water should be free of tastes and odours that would be objectionable to the majority of consumers. Changes in the normal appearance, odour or taste of a drinking-water supply may signal changes in the quality of the raw water source or deficiencies in the treatment process and should be investigated.
Regulations according to Drinking Water Inspectorate, UK: The water quality regulations set legal standards for water, which must be met by water companies in England and . Many of the standards are based on World Health Organization guidelines and include very wide safety margins. The regulations and standards are on the DWI web site at www.dwi.gov.uk. As the ‘guardians of drinking water quality’, the main role of the Drinking Water Inspectorate is to enforce the regulations and check that water companies in England supply water that is safe to drink and meets the standards set in the regulations.
Sphere Minimum Standards For: The Sphere Project was launched in 1997 by a group of humanitarian NGOs and the Red Cross and Red Crescent movement. The main objective of water supply and sanitation programmes in disasters is to reduce the transmission of faeco-oral diseases and exposure to disease-bearing vectors through the promotion of good hygiene practices, the provision of safe drinking water and the reduction of environmental health risks and by establishing the conditions that allow people to live with good health, dignity, comfort and security.
- There are no faecal coliforms per 100ml at the point of delivery.
- Water is treated with a disinfectant so that there is a free chlorine residual at the tap of 0.5mg per litre and turbidity is below 5 NTU
- Average water use for drinking, cooking and personal hygiene in any household is at least 15 litres per person per day
- The maximum distance from any household to the nearest water point is 500 metres
Till now we have discussed the parameters and respective standards prescribed by various organizations for drinking water quality. We now turn to our problem…
OBJECTIVE: – To construct a water treatment plant for a disaster struck area in the Far east for a population of about 1500 internally displaced people that agrees with the provisions of WHO guidelines, U.K. Regulations and Sphere minimum standards and to discuss the likely microbial challenges that the plant might face and their potential impact on water quality.
Details of the water source: The only available water source is a limestone spring fed pond whose chemical analysis report is as under:-
All the other parameters are believed to be in accordance with the U.K. regulations
The desired plant supplies water to 1500 people and according to the Sphere Minimum Standards, an individual’s daily need of water is approximately 15 litres. This means that the capacity of the plant must be about 22500 litres per day (22.5 kilolitres/day)
Our prime objective in designing the treatment plant is to:
- Level the pH to about 6.5-7.5
- Bring the concentration of aluminium to below 0.2mg/l
- Benzene level below 0.01 mg/l
- Faecal coliform count to about zero per 100ml
All the above parameters are as per the WHO norms, UK regulations and Sphere standards. The rest of the parameters are in accordance with the UK Regulations and hence need not be treated. Next we design a Water
Treatment plant as per the prescribed guidelines with a capacity of 25 kilolitres per day….
LAYOUT OF THE TREATMENT PLANT
We now present an elaborate overview of the plant and the methods incorporated in it…
Water leaves the limestone spring fed pond and is pumped into the two raw water reservoirs each of capacity 25kilolitres. The purpose of having two reservoirs is that when one needs to be cleaned the plant can still operate continuously.
Pre-chlorination is done at this stage in the two raw water reservoirs. It is done by using a dosing pump that supplies sodium hypochlorite. As a result disinfection begins.
Water from the raw water reservoir enters the Flash Mixer where a coagulant Poly Aluminum Chloride (PAC) is added to bind any small particles. Sodium carbonate is also added to control the pH and also to remove the hardness caused by limestone. The ‘dosed water’ is now retained for a short period to enable the ‘binding process’ to start before the water passes to the ‘Clarification Stage’.
The water dosed with coagulant is discharged into the bottom of the clarifier and as the water flows upwards so the particles bound together by the PAC form a sludge blanket just below the surface of the water. The sludge blanket traps more particles as the water flows through it to the outlet channels which span the clarifier at the water surface. From time to time some of the sludge blanket is ‘drawn off’ and discharged to the sludge processing plant.
The ‘clarified supernatant water’ is then sent to therapid gravity filters, containing a gravel base and a bed of granular activated carbon which removes any remaining fine particles. The granular activated carbon is also extremely useful in removing organic compounds such as benzene which can cause taste problems in the supply.
To provide an effective barrier againstfaecal coliforms, the filtered water is then passed through amembrane filtration system. It also retains the flocculants of aluminium hydroxide that are formed due to excess concentration (concentration greater than 2mg/litre) of aluminium in water.
In this microfiltration plant the water is allowed to pass through six different compartments each containing a mesh (or screen) of pore size 0.2 microns (1 micron = one thousandth of a millimeter), readily available in the market. Feed water passes through the walls of this membrane producing a filtrate free of faecal coliform and other suspended solids.
Following filtration the ‘filtered water’ is further dosed with chlorine to ensure adequate disinfection. It remains in contact with a high dose of chlorine for a minimum of six hours in a covered contact tank. Chlorine disinfects the water by killing bacteria and viruses.
After leaving the contact tank, the final water is dosed with Sulphur Dioxide to reduce the chlorine residual to its set point before being sent for distribution.
This way we obtain clean and safe water for supply to the customers.
A major problem we encountered in the limestone spring fed pond was the grazing of farm animals particularly goats that led to microbial contamination of the pond. Grazing animals can negatively affect water quality through erosion and sediment transport into surface waters, through nutrients from urine and feces dropped by the animals. The two nutrients of primary concern relating to animal production are N and P. Nitrogen is of concern because high concentrations in drinking water in the NO3 form cause methemoglobinemia (blue baby disease), whereas other forms of N (primarily nitrite, NO2) are considered to be potentially carcinogenic. Phosphorus in the PO4 form is of concern because it causes eutrophication of surface water bodies.
The next major problem is of the migratory aquatic birds that arrive during a three week period in November. During migratory movements, birds carry pathogens that can be transmitted between species at breeding, wintering, and stopover places where numerous birds of various species are concentrated. During these yearly migrations, birds have the potential of dispersing microorganisms that can be dangerous for public as well as animal health. Birds are believed to be responsible for the wide geographic distribution of various pathogens, including viruses (e.g., West Nile, Sindbis, influenza A, Newcastle), bacteria (e.g., borrelia, mycobacteria, salmonellae), and protozoa (e.g., cryptosporidia). Bacteria, viruses, and protozoa when ingested in drinking water can cause a number of infectious waterborne diseases such as cholera, typhoid, hepatitis, and infectious gastrointestinal diseases like cryptosporidiosis and giardiasis.
Some microbial contaminants can be removed by water treatment coagulation and filtration processes. Disinfection has been proven effective against bacteria and viruses, and the method of Membrane Filtration is sufficient to remove the Cryptosporidium.
A very essential condition of an effective treatment plant is to establish a well developed watershed or a wellhead protection program. Controlling or eliminating microbial sources before they contaminate a water supply will go a long way toward simplifying treatment and reducing costs associated with a contaminated supply.
This is the proposed plant for the treatment of water which the community can operate and which provides a healthy and safe drinking water. Apart from this the people should be aware enough to utilize optimum amount of water and the people should consider it as their moral responsibility to prevent contamination of water by their activities.
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