| Simple Methods for the Treatment of Drinking Water |
| Aspects of Planning and Organization |
Planning a water treatment plant requires that the best suited technology for a given site be identified, the plant designed, and an appropriate form of implementation be found. A methodology for the planning procedure is described in the following sections.
The prerequisites of sound planning are knowledge of all the possible techniques for the treatment of drinking water (Chapter 3) as well as an assessment of the technical and financial input required for suitable plants and facilities.
The selection process requires close examination of the situation at the site and the consideration of all factos which could influence the realization of the project (questionnaire, paragraph 2.2).
With this foundation, one can choose a workable procedure, or a combination of different individual methods (paragraph 2.3). It is possible that the choice of which technology to use can only be determined by a series of compromises, since the optimal solution will not be entirely compatible with the particular set of on-site circumstances.
The next step is to work out an appropriate plan for the plant, evaluating the chosen procedure with an eye towards the specific onsite situation. The individual steps are then laid out for the realization of the project, as priorities are set and necessary concomitant measures identified.
| Simple Methods for the Treatment of Drinking Water |
| Aspects of Planning and Organization |
Existing water supply and waste water disposal:
What is the health situation of the population? Are there specific frequently occurring illnesses that are connected with inadequate water supply and waste water disposal? Are there professional health care, medical counselling and advice?
What kind of technical training, or crafts skills are native to the population? Which materials, what kind of artisanry, manufacturing or small industrial operations are there?
How large are the financial resources of the single household and the community?
Describe the infrastructure in regard to energy supply, the means and routes of transportation and supply of technical goods.
How would you rate the people's consciousness of hygiene and sense of responsibility to the environment?
How does the population judge its situation regarding drinking water? Is there any interest in changing things?
Are there religious or cultural customs connected to drinking water and hygiene?
Are there traditional forms of water purification? Are there connections to traditional medicine?
Does the population have definite ideas about what constitutes "good" drinking water, i.e., clarity, color, odor, taste, temperature, etc.? Are there preferences for how a treatment plant should look and out of what material it should be built?
Who is responsible for the water supply or purification of drinking water within the family (women, children)?
Who deals with drinking water within the community? Are there special responsibilities?
What is the attitude of the people towards communal and individual water supply?
What is the annual rate of precipitation' and how is it distributed through the year?
Which organizations are responsible for water supply and waste water disposal (at the national, regional and local level)?
How is responsibility divided up in the areas of water supply, health care, education?
Are there facilities available that could be utilized for the realization of the project (laboratories, water boards, etc.)?
What kind of regulations and laws exist regarding water quality, regular monitoring, charges for water supply?
What kind of possibilities exist for financing through national or private organizations?
How large a pool of personnel is there for administration, technical support and training?
| Simple Methods for the Treatment of Drinking Water |
| Aspects of Planning and Organization |
In a first phase, a preliminary choice will be made as to which method among the various techniques suits the selected location and what is the technical level that should be sought. The following parameters are the basis for this:
- raw water quality of the existing water source(s);
- available resources;
- socio-cultural factors.
A final decision can then be reached by taking into account the geographic and climatic conditions, type of settlement and infrastructure, and the compatibility of the existing water supply system.
2. Existing Resources
3. Socio-Cultural Factors
1. Water Quality
The purpose of the treatment is to turn water of an existing source -raw water - into drinking water. The basic quality requiremeets of drinking water are that it should be free of pathogens and toxic substances. In addition, water should have a pleasant appearance, and be of a neutral smell and taste. So, the treatment process to be chosen should primarily be based on the quality of the existent water. An examination of the water will disclose its constituents and support the choice of a water source. Systematic analyses of the water should be conducted at regular intervals over an extended period of time (generally one year) so as to measure the variability of the quality. But a well equipped laboratory and experienced personnel are prerequisites for any complete analysis of all the bacteriological, viral and physical-chemical constituents of the water. Since those prerequisites are generally not given in the areas targeted by the manual, one is limited in a field study to determining the most important parameters:
- the presence of coliform bacteria and E. coli, which indicate pollution of the water through human and animal wastes;
- measuring turbidity, discoloration, odor, taste and temperature of the water;
- determination of total solid content, iron and manganese, total alkalinity, pH value.
All but the last parameter should be determined immediately upon sampling at the site. Simple bacteriological test-kits (membrane filter methods) which are already manufactured in developing countries, and field analysis equipment enable semi-skilled personnel to carry out these tests.
An epidemiological survey of certain illnesses in the population, particularly those transmitted by water and fecal matter, can give a further indication of the nature of possible pollutants in the water.
WHO has established guidelines and standards for the quality of drinking water. Technically, these standards are attainable at any time. But realistically, one must realize that due to limiting factors, only a lower water quality level can be attained. A moderately effective water treatment that raises the levels of the most important quality parameters -those that affect health -without meeting al] the parameters and standards, may already mean an adequate solution.
Turbidity, pathogens and organic components of different origins reach the surface via storm run-off and through ground water discharge. The concentration of these constituents in water depends on the amount of precipitation, and can rise dramatically during the rainy season. Lakes and rivers do have their own self-cleaning processes, and when no further pollutants are involved, can return the inflowing water's quality to its original state. But that is only the case in sparsely settled areas. Surface water almost always needs to be treated. Even water from shallow ground water resources (water table between 0 and 10 meters below ground) can be contaminated by fecal matter, depending on soil conditions, the placement of wells and other factors. Generally, though, ground water, when deep enough and if lifted properly is free from pathogens and turbidity and needs no treatment.
Table 3: Effectiveness of various treatment processes with regard to the removal of water constituents
Table 4: Treatment processes and combinations as a function of turbidity and E. Coli count in the raw water. Additional aeration generally helps to increase the water's oxygen content. The turbidity values refer to the contents of settleable and nonsettleable substances. The choice of pretreatment method thus depends on the type and composition of turbidity.
Table 5: Comparisons of various treatment processes with regard to input requirments,
In Table 3, the most important quality parameters are roughly sketched, along with the effectiveness of various possible methods of treatment. The effectiveness can only be drawn in general terms, because it is in turn dependent on the design of the plants, the filter material, the proper layout and operation, etc.
Some of the processes we have presented serve only one purpose, but most can be used in different ways with varying effects. The same levels of water treatment can often be achieved in different ways.
The treatment processes described here are shown in great detail in Chapter 3, as well as possible gradations in size and equipment. We should also mention here shore filtration and groundwater recharge, both methods of water production which at the same time have a treatment component that is based on the effect of a natural sand filter. If one of these processes can be applied, it means a notable lessening of subsequent required treatment. Likewise water storage may be considered in a certain sense as a treatment process (see paragraph 3.2).
One single process is generally not enough, different treatment processes must be combined and follow one another in order to achieve the desired result. Table 4 shows possible combinations of different processes. The guides to a possible process are the amount of turbidity and E. Coli in raw water.
1. Water Quality
3. Socio-Cultural Factors
2. Existing Resources
The potential of existing resources, i.e., the availability of the
necessary materials, equipment, personnel and financial means for construction, operation
and maintenance is decisive when determining what technical level the
plant should have.
In choosing a technology, it
is wise to make use of whatever locally available materials
and skills there are in the target area. This lowers
the cost, employs native manufacturing capacities, and avoids supply problems.
The available personnel must have the skills called for by
the selected technology in order to successfully run the construction,
operation and supervision. The costs should be brought down as
low as possible, so that it is affordable for the
largest number of consumers.
For most treatment processes
it is possible to design alternatives of differing grades of
complexity. It is therefore problematic to ascribe a given process
to a specific technological niveau. The classifications in Table 5
can therefore only be regarded as guidelines.
Generally,
when there are limited resources, sedimentation or water storage and/or
coarse filtration in combination with slow sand filtration represents adequate
prior treatment. An aeration effect can also be attained easily.
On the other hand, coagulation by means of chemicals and
conventional rapid filtration call for resources which, in general, are
beyond those of the regions considered here. But using alternative
materials and simplifying the designs lower the costs significantly.
Disinfection is almost always needed, but demands a continuous
supply of chemicals and constant maintenance. Naturally, the level of
complexity rises when different procedures are combined.
1. Water Quality
2. Existing Resources
3. Socio-Cultural Factors
It is necessary to include the
user of the plant before the planning commences. The traditions
and wishes of the populace must be known and understood
in order to reach acceptable decisions. The ultimate success of
the project depends largely on an enlightened consumer who is
helped to understand the goals of the project and the
improvements anticipated.
The population must be involved in
different phases:
- Investigation of the habits, rites,
traditions, precepts and prohibitions which govern the usage of water
must first be conducted to determine what measures are needed
and what possible solutions are feasible or which must, a
priori, be excluded. To this end, surveys must be taken,
particularly of the women, since they are generally in charge
of the water supply and of educating the children about
hygiene.
- The need for improvement must be
assessed, and the interest in such improvement must be stimulated
along with the preparedness for change and the willingness of
the populace to contribute to the project materially, financially and
through their labor (see also section 2.5.1). Family and village
hierarchies and property rights must be taken into consideration.
- When feasible technical solutions are worked out, they
should be presented to the population and discussed with them
in order to find an acceptable solution. A planning program
that is built upon the active participation of the populace
may be very time consuming, but experience has shown that
when the socio-cultural factors are not taken into account, little
efficiency can be expected from the project.
| Simple Methods for the Treatment of Drinking Water |
| Aspects of Planning and Organization |
After selecting the water source to be used and choosing a technology, the next step is to turn these theoretical considerations into a realistic design. The goal is to come up with a plant that will for a sufficiently long period of time withstand changes in the quality of the raw water and the water flow without changing the quality of the treated water. The design calls for decisions such as:
- selecting a site for the treatment plant;
- sizing of the plant; and
- specification of the individual elements.
In practice, the design is the basis for an accurate estimate of the necessary inputs, for seeking funding and laying out the organizational framework.
2 . Sizing
Specification of the Individual Elements
1. Selection of the Plant Site
It must be decided here as to whether the treatment facility will be incorporated into the existing water supply system or whether a new system should be built, of which treatment is just one element. The latter case is simpler since mostly geographic, topographical and settlement-related aspects determine the location of the plant.
If the existing water supply system is not to be changed, the plant must be designed in such a way that it can be incorporated into it. The first thing to decide here is whether the treatment is going to be operated by the municipality or individually.
Municipal treatment is appropriate if a central piped water supply system exists; the site of the plant lies somewhere between the water intake and the distribution system. A preliminary survey of the existing system may already suggest necessary modifications or upgrading. Potential problem areas may be: contamination of wells due to wrong location; brokendown or improperly designed water treatment plant; possible short circuiting between supply and disposal within the transmission system. The comparison of water qualities between the raw water and the water at the point of consumption may offer leads toward the detection of trouble areas.
If the supply of water occurs individually by means of village wells, public standposts or rain water collection, treatment can be incorporated either right at the point of withdrawal or in the house. These places of withdrawal should also be examined for their conditions, location and protection against pollution. A remedy for those trouble spots may yield a considerable improvement of the water quality.
1 . Selection of the Plant Site
3. Specification of the Individual Elements
2. Sizing
The size of a water treatment plant is determined by the maximum required flow rate Q, which, in turn, is given by the daily water demand and the mode of operation of the plant. In order to determine the water requirements for a given target group, information is needed about:
- the per capita domestic usage;
- the amount of water necessary for other purposes (i.e., irrigation, livestock, public buildings, industrial);
- the number of people to be supplied;
- an estimate of the annual population growth;
- the economic life of the plant.
Table 6: Typical values for domestic water consumption in litres per capita and day (1/c.d.). Source [44]
Water usage is influenced by factors such as availability and quality of the water, the income and size of a family, living standard, climate, etc. Typical per capita values for different types of water supply in rural areas of the Third World are given in Table 6. 30% should be allowed for (unaccounted for) losses. If the plant is to be built for the whole community, then the calculations must include usage for public facilities.
The required plant capacity is thus determined by the product of per capita consumption, including "unaccounted for" population growth (compounded growth) during the period for which the facility is planned (see Table 7). It is necessary to take a survey of the fluctuation in water consumption during the day, in order to correctly size the storage tank for the treated water and to determine the plant's mode of operation (for example, see 3.5.2.3).
Table 7: Population Growth Factor
|
Time (Years) |
Annual Growth Rate | |||
|
2% |
3% |
4% |
5% |
|
|
10 |
1,22 |
1,34 |
1,48 |
1,63 |
|
15 |
1,35 |
1,50 |
1,80 |
2,08 |
|
20 |
1,49 |
1,81 |
2,19 |
2,65 |
1 . Selection of the Plant Site
2. Sizing
3. Specification of the Individual Elements
The last step entails the selection of the individual structural elements and their appurtenances, their size and materials. This selection should be made according to the following criteria:
- Choice of a design which can be implemented by local artisans and which makes the maximum use of locally available equipment and material;
- a robust type of construction for maximum durability and minimum maintenance;
- selection of the kind of outfitting that corresponds to the preferences of the consumer.
| Simple Methods for the Treatment of Drinking Water |
| Aspects of Planning and Organization |
Before beginning the implementation phase, it must be decided how the construction of the plant is to be organized, who is putting up the money for the project, and who will be responsible for operation and maintenance. Besides that, it must be determined what accompanying measures are necessary in order to successfully complete the project.
2. Institutional Factors
3. Concomitant Measures
1. Participation of the Population
The ways in which the local population
can possibly participate will have already been discussed with the
community during the phase of the choice of method. Their
contribution will consist mainly of material and labor during the
construction of the plant. It must also be ascertained as
to which local producers are able to manufacture parts for
the plant, i.e., where production or ordering can be initiated.
Personnel who shall take over the operation and maintenance of
the plant must be chosen. Collecting water charges from the
customers, necessary for cost recovery, is also part of the
task of the maintenance personnel. If the community has a
clear organizational structure of specific labor divisions along traditional lines,
then the method of the project implementation should be adapted
accordingly. Responsibilities should be assigned to accord with the existing
hierarchies (as long as they are accepted).
Training of members of the community who will be involved in
the project should be a component of the program in
order to ensure in the long run, an operation which
is self-sufficient and independent of outside support.
1. Participation of the Population
3. Concomitant Measures
2. Institutional Factors
Participation of the population alone is
not enough to ensure success of the project. The support
of national, regional, local, private or public institutions is needed,
which are to take over the management of the project
and oversee its operations on a long term basis. Those
institutions must also contribute financially to the project, since the
people in the areas under consideration generally do not have
the means for such an undertaking. The following inputs should
come forward from the various institutions:
State:
- Development of long term master plans for introduction
of water supply and disposal, health care, sanitation and hygiene
programs in underdeveloped areas:
- creation of executing agencies on regional and local levels;
- establishment
of water quality standards and regular monitoring;
- provision of financing.
Regional and Local Agencies:
- Implementation of governmental plans, meaning the provision of
management personnel who are to be responsible for the project,
technical support and training, financing and information;
- supply of material;
- setting up the necessary
local manufacturers and workshops, laboratories;
- carrying out demonstrations;
- training and employment of community workers
in the construction and operation of water supply and sanitation
facilities' hygiene, health, nutrition.
1. Participation of the Population
2. Institutional Factors
3. Concomitant Measures
As we have already mentioned, the construction of a
water treatment plant only makes sense within a larger picture.
The scarcity of clean drinking water is not the only
reason for the catastrophic health conditions of these regions. Sanitation
facilities are lacking, and existing water supply and disposal works
are not properly constructed and are insufficiently protected against contamination.
The water consumers themselves, through insufficient hygienic standards and environmental
consciousness are often the cause of the initial contamination, and
the recontamination of treated water. Frequently, cause and effect of
the contamination, transmission and spreading are not known to the
people. Accounting for these factors in preparatory and attendant measures
is indispensable to the project. Some of these measures are:
- Explanation of purpose and goal of the project;
- Communicating information to the target group through appropriate channels;
- Counselling and training in hygiene, nutrition and health care;
- Construction of disposal facilities;
- Instruction in the correct usage of the new plant;
- Technical training in construction, operation and maintenance of the plant;
- Training and employment of community workers.
Measures touching
on personal and traditional habits and customs such as hygienic
practices, are not at all easy to effectuate. The inroads
in this sensitive area must be made on a long-term
basis by people with easy access to the population -
not a foreigner. The difficulties are many, and include picking
the right ombudsman, and administering these measures adequately, since 'they
fall into various areas of responsibility, and justifying the resulting costs.