Welcome

To The

Presentation

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Title Here

Presentation

Environmental Engineering-ICEN-343

Instructor

Tanaz Islam

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Group MembersName ID

1. Manik Chandra Roy 12206039

2. Md. Shariful Haque Robin 12206049

3. Md. Shifullah 12206051

4. Md. Mahmudujjaman 12206062

5. Arun Chandra Acharjee 12206066

6. Md. Oliullah Sheik 12206067

7. Rajesh Chandra Barman 12206070

8. S. M. Abrar Hossain Asif 12306001

9. Md. Monowar Hosen 13106174

10. Nur Afsar 13106175

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Our Presentation Topic: Alternative Water Supply Technologies

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CONTENTS

1. Introduction2. The important alternative water supply

technologies include:3. Shallow Shrouded Tubewell (SST) and Very

Shallow Shrouded Tubewell (VSST)4. Deep Tubewell5. Dug Well6. Pond Sand Filters7. The major limitations8. Household Filters9. The important characteristics of household filters .10.Infiltration Gallery 11.Solar desalination12.Rainwater Harvesting13.Advantages and disadvantages of rainwater

collection system

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INTRODUCTION

• The type of handpump technology suitable for a particular area depends on the groundwater level, water quality and hydrogeological conditions. There are some areas like the costal belt in the southern part of Bangladesh, where the conventional shallow and deep tubewlls technologies are not successful due to the high salinity. Alternative water supply options are needed for those areas.

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The important alternative water supply technologies include:

Shallow shrouded tubewell (SST)Very shallow shrouded tubewell (VSST)Pond sand filtersHousehold filtersInfiltration gallerySolar desalinationRainwater Harvesting

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Shallow Shrouded Tubewell (SST) and Very Shallow

Shrouded Tubewell (VSST)

These low-cost handpump tubewell technologies have been

designed and installed in the coastal areas to collect water from

very shallow aquifers formed by displacement of saline water by

fresh water. The SST/VSSTs can be convenient methods for

withdrawal of fresh water in limited quantities. Over-pumping

may yield contaminated water. Installation of low capacity

pumps may prevent over exploitation of shallow aquifers. The

systems may be considered suitable for drinking water supply for

small settlements where water demand is low. The depatment

of Public Health Engineering has sunk a total of 5,904 VSST/SST

to provide water to 0.44 million people in coastal areas (DPHE,

2000).

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Deep Tubewell

• In Bangladesh two types of deep tubewells as shown in Figure 2.4 are constructed, manually operated small diameter tubewell similar to shallow tubewells and large diameter power operated tubewells called production well. Some areas of the coastal region of Bangladesh is very suitable for construction of deep tubewell. Department of Public Health Engineering has sunk a total of 81,384 deep tubewell mainly in the coastal area to provide safe water to 8.2 million people (DPHE,2000). The identification of areas having suitable deep aquifers and a clear understanding about the mechanism of recharge of these aquifers are needed to develop deep tubewell based water supply systems in Bangladesh.

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Dug Well• Dug well is the oldest method of

groundwater withdrawal for water supplies. The mechanism of producing water of low arsenic and other dissolved minerals concentration by dug wells are not fully known. Dug wells are widely used in many countries of the world for domestic water supply. The flow in a dug wells is actuated by lowering of water table in the well due to withdrawal of water. Usually no special equipment or skill is required for the construction of dug wells. For construction by manual digging, the wells should be at least Community dug wells should be deeper to provide larger surface area for the entry of water to meet higher water demand. Private dug wells are less that 10m deep but dug wells for communal use are usually 20-30 metres deep.1.2 meters in diameter.

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Pond Sand Filters

• A prospective option for development of surface water based water supply system is the construction of community type Slow Sand Filters (SSFs) commonly known as Pond Sand Filters (PSFs). Slow sand filters are installed near or on the bank of a pond, which does not dry up in the dry season. The water from the pond is pumped by a manually operated hand tubewell to feed the filter bed, which is raised from the ground, and the treated water is collected through tap(s). The PSF is a low-cost technology with very high efficiency in turbidity and bacterial removal. It has received preference as an alternative water supply system for medium size settlements in arsenic affected areas and areas. Although PSF has a very high bacterial removal efficiency, it may not remove 100% of the pathogens from heavily contaminated surface water.

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Pond Sand Filter for Treatment of Surface Water

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Collection of safe water by installation of PSF on the bank of a pond

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The major limitations

Operation and maintenance are difficult;

Not suitable for heavily contaminated ponds;

People complained of foul taste in pond water and many resorted to using it for cooking only;

Conflicts with fish culture;

It is difficult to find an appropriate/reserve pond for installation of PSF;

Many ponds dry up in the dry season in some parts of the country;

Secondary contamination takes place due to lack of proper maintenance.

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Household Filters

• Surface water containing impurities can be clarified by a pitcher filter unit or a small sand filter at the household level. It is an old method of water purification, once widely used in rural areas of Bangladesh. These processes of water treatment at household level have been phased out with the introduction of tubewells for village water supply. Pitcher filters are constructed by stacking a number pitchers (Kalshis), one above the other, containing different filter media .Raw water is poured in the top Kalshi and filtered water is collected from the bottom one. In this process, water is mainly clarified by the mechanical straining and adsorption depending of the type of filter media used. Small household filters can be constructed by stacking about 300-450 mm thick well graded sand on a 150-225 mm thick coarse aggregate in a cylindrical container. The container is filled with water and the filtered water is collected from the bottom. Full effectiveness of the filtration process is obtained if the media remain in water all the time. The pitcher and other small household filters cannot completely remove micro-organisms if these are present in large numbers in raw water.

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The important characteristics of household filters are:

Suitable for surface water treatment;Remove turbidity, color and micro-

organisms;Complete removal of pathogenic micro-

organisms is not guaranteed;Not suitable for high-turbid water;Difficulty in cleaning and keeping the

system operational.

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Infiltration Gallery

• Infiltration Galleries (IG) or wells can be constructed near perennial rivers or ponds to collect infiltrated surface waters for all domestic purposes. Since the water infiltrate through a layer of soil/sand, it is significantly free from suspended impurities including microorganisms usually present in surface water. Again, surface water being the main source of water in the gallery/well, it is free from arsenic. If the soil is impermeable, well graded sand may be placed in between the gallery and surface water source for rapid flow of water.

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An Infiltration Gallery by the Side of a Surface Water Source

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Solar desalination

• Solar energy available in Bangladesh can be used for solar distillation of contaminated water in crisis areas. Experimental units based on conventional evaporation-condensation facilities have been found to produce 0.6 - 2.4 Um2/d. The water produced by solar distillation in free from all chemicals including arsenic but cannot produce enough water at a reasonable cost. The system requires further development for cost effective use in water supply in rural areas.

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Solar Distillation

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Rainwater Harvesting

• Bangladesh is a tropical country and receives heavy rainfall during the rainy season. In the coastal districts, particularly in the offshore islands of Bangladesh, rainwater harvesting for drinking purposes is a common practice in a limited scale for long time (Chowdhury et al, 1987). In some areas of the coastal region with high salinity problem, about 36 percent households have been found to practice rainwater harvesting in the rainy season for drinking purpose (Hussain and Ziauddin, 1989). In the present context, rainwater harvesting is being seriously considered as an alternative option for water supply in Bangladesh in the arsenic affected areas.

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Advantages and disadvantages of rainwater collection system

Advantages Disadvantages

The quality of rainwater is

comparatively good.

The system is independent

and therefore suitable for

scattered settlements.

Local materials and

craftsmanship can be used

in construction of rainwater

system.

No energy costs are incurred

in running the system.

Ease in maintenance by the

owner/user

The initial cost may prevent a

family from installing a

rainwater harvesting system.

The water availability is limited

by the rainfall intensity and

available roof area.

Mineral-free rainwater has a

flat taste, which may not be

liked by many.

Mineral-free water may cause

nutrition deficiencies in people

who are on mineral deficient

diets.

The poorer segment of the

population may not have a roof

suitable for rainwater

harvesting.3/23/2014 28

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