3 - water supply options

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3. WATER SUPPLY OPTIONS

INTRODUCTION

Groundwater extracted from arsenic contaminated aquifers in worst affected areas of Bangladesh by shallow tubewells can no longer be considered safe

for drinking and cooking. Although 27 % of shallow tubewells are known to be contaminated in the national scale, in many areas more than 90% of

shallow tubewells are contaminated. The problem has been magnified due to the fact that the tubewells with high levels of arsenic are also located in the

areas where percentage of contaminated tubewells is high. In the absence of an alternative source, people in acute arsenic problem areas are drinking

arsenic contaminated water without paying much attention to possible consequences. On the other hand, people with arsenic phobia are likely to use

unprotected surface water to avoid arsenic poisoning and get sick by water borne/related diseases. Arsenic toxicity has no known effective treatment, butdrinking of arsenic free water can help the arsenic affected people to get rid of the symptoms of arsenic toxicity. Hence, provision of arsenic free water is

urgently needed to mitigate arsenic toxicity and protect health and well being of rural people living in acute arsenic problem areas of Bangladesh.

The options available for water supply in the arsenic affected areas can be brought into two major categories:

i. alternative arsenic-safe water source, and

ii. Treatment of arsenic contaminated water.

Groundwater from deep aquifers and dug wells, surface water and rain water can be potential sources of water supply to avoid arsenic ingestion through

shallow tubewell water. On the other hand, there are several treatment methods available to reduce arsenic concentration to acceptable levels for watersupply.

ALTERNATIVE ARSENIC-SAFE WATER SOURCES

Groundwater

Technological options


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The type of handpump technology suitable for a particular area depends on the groundwater level, water quality and hydrogeological conditions. Arsenic

safe groundwater is generally found in shallow aquifers in north-western region, and in pockets/strata in arsenic contaminated areas where conventional

shallow tubewells are producing arsenic-safe water. Deep aquifers separated from shallow contaminated aquifers by impermeable layers can be a

dependable source of arsenic safe water. The deeper aquifers without any separating aquiclude/clay layer may initially produce arsenic safe water but

vulnerable to contamination. The important alternative water supply technologies include:

Shallow shrouded tubewell (SST) and Very shallow shrouded tubewell (VSST)

Deep Tubewell;

Dug Well; and

Infiltration galley

Shallow Shrouded Tubewell (SST) and Very Shallow Shrouded Tubewell (VSST)

In many areas, groundwater with low arsenic content is available in shallow aquifers composed of fine sand at shallow depth. This may be due to

accumulation of rainwater in the topmost aquifer or dilution of arsenic contaminated groundwater by fresh water recharging each year by surface and rain

waters. However, the particle size of soil and the depth of the aquifer are not suitable for installing a normal tubewell. To get water through these very fine-

grained aquifers, an artificial sand packing is required around the screen of the tubewell. This artificial sand packing, called shrouding, increases the yield ofthe tubewell and prevents entry of fine sand into the screen.

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. A shallow/Very shallow tubewell is shown in Figure 3.1.

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).

Deep Tubewell

The deep aquifers in Bangladesh have been found to be relatively free from arsenic contamination. The aquifers in Bangladesh are stratified and in some

places the aquifers are separated by relatively impermeable strata as shown in Figure 2.4. 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. Deep tubewells installed in those protected deeper aquifers are producing arsenic safe water. The BGS and DPHE study has shown that

only about 1% deep tubewell having depth greater than 150 m are contaminated with arsenic higher than 50m g/L and 5% tubewell have arsenic content

above 10m g/L (BGS and DPHE, 2001). Sinking of deep tubewells in arsenic affected areas can provide safe drinking water but replacement of existing

shallow tubewells by deep tubewells involves huge cost. Some of the deep tubewells installed in acute arsenic problem areas have been found to produce

water with increasing arsenic content. Post-construction analysis shows that arsenic contaminated water could rapidly percolate through shrouded materials

to produce elevated levels of arsenic in deep tubewell water. Experimentation by sealing the borehole at the level of impermeable layer is yet to be


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conducted to draw conclusions.

Fig. 3.1 Shallow and Very Shallow Shrouded Tubewell

However, there are many areas where the separating impermeable layers are absent and aquifers are formed by stratified layers of silt and medium sand.

The deep tubewells in those areas may yield arsenic safe water initially but likely to increase arsenic content of water with time due to mixing ofcontaminated and uncontaminated waters. Again the possibility of contamination of deep aquifer by inter-layer movement of large quantity of groundwater


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cannot be ignored. If the deep aquifer is mainly recharged by vertical percolation of contaminated water from the shallow aquifer above, the deep aquifer is

likely to be soon contaminated with arsenic. However, recharge of deep aquifer by infiltration through coarse media and replenishment by horizontal

movement of water are likely to keep the aquifer arsenic free even after prolong water abstraction. Since many people in the rural area still use surface

water for cooking, installation of deep tubewell in an area can be a source of drinking water supply for a large number of people.

In general, permeability, specific storage capacity and specific yield usually increase with depth because of the increase in the size of aquifer materials.

Experience in the design and installation of tubewells shows that reddish sand produces best quality water in respect of dissolved iron and arsenic. The

reddish colour of sand is produced by oxidation of iron on sand grains to ferric form. Which will not release arsenic or iron in groundwater, rather ferriciron coated sand will adsorb arsenic from ground water. Dhaka water supply, in spite of arsenic contamination around is probably protected by its red

coloured soil. Hence, installation of tubewell in reddish sand, if available, should be safe from arsenic contamination.

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.

Dug Well

Dug well is the oldest method of groundwater withdrawal for water supplies. The water of the dug well has been found to be free from dissolved arsenic

and iron even in locations where tubewells are contaminated. The mechanism of producing water of low arsenic and other dissolved minerals concentration

by dug wells are not fully known. The following explanations may be attributed to the low arsenic content of dug well water:

The oxidation of dug well water due to its exposure to open air and agitation during water withdrawal can cause precipitation of dissolved arsenic

and iron.

Dug wells accumulates groundwater from top layer of a water table which is replenished each year by arsenic safe rain and surface waters by

percolation through aerated zone of the soil. The fresh recharges also have diluting effects on contaminated groundwater.

The presence of air and aerated water in well can oxidize the soils around dug wells and infiltration of water into wells through this oxidized soil can

significantly reduce the concentration of arsenic in well water.

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 1.2 meters in diameter. Large diameter wells may be constructed for community water supplies. The depth of the well is dependent

on the depth of the water table and its seasonal fluctuations. Wells should be at least 1m deeper than the lowest water table. 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.

It is very difficult to protect the water of the dug well from bacterial contamination. Percolation of contaminated surface water is the most common route of


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pollution of well water. The upper part of the well lining and the space between the wall and soil require proper sealing. The construction of an apron

around the well can prevents entry of contaminated used water at the well site by seepage into the well. Water in a dug well is very easily contaminated if

the well is open and the water is drawn using bucket and rope. Satisfactory protection against bacteriological contamination is possible by sealing the well

top with a watertight concrete slab. Water may be withdrawn by installation of a manually operated handpump. Water in the well should be chlorinated for

disinfection after construction. Disinfecion of well water may be continued during operation by pot chlorination. A conventional dug well and a dug well

with sanitary protection sunk in most common soil strata in Bangladesh are shown in figure 3.2.


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In a completely closed dug well, the inflow of water is actuated by suction created due to withdrawal of water from the well. If aeration is controlling

process of decontamination of well water, sanitary protection may affect the quality of well water. Extensive research to understand the mechanism of

dearsination of well water and the effects of sanitary protection of well on chemical quality of water is needed. An open dug well and a closed dugwell with

a tubewell for water collection are shown in Figures 3.3 and 3.4 respectively.


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In the Chittagong hilly areas, Sylhet and northern parts of Bangladesh, construction of handpump tubewells is not always possible due to adversehydrogeological and stony soil conditions. Construction of protected dug wells can be a good option for water supply in these areas. A large number of

dug wells are found operating in those areas. Dug wells are not successful in many areas of Bangladesh having thick impermeable surface layer. In areas

with thick clayey soil, dug wells do not produce enough water to meet the requirements. Again in areas having very low water table, there may be difficulty

in construction as well as withdrawal of water. Although tubewells in Bangladesh have replaced traditional dug wells in most places, it appears from Table

2.1 that about 1.3 million people in both urban and rural areas are still dependent on dug well for drinking water supply in Bangladesh.

Infiltration Gallery / Well

Infiltration Galleries (IG) or wells can be constructed near perennial rivers or ponds to collect infiltrated surface waters for all domestic purposes. Since thewater infiltrate through a layer of soil/sand, it is significantly free from suspended impurities including microorganisms usually present in surface water.


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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 as shown in Figure 3.5.

Fig. 3.5 An Infiltration Gallery by the Side of a Surface Water Source

Experimental units constructed in the coastal area to harvest low saline surface waters show that water of the open infiltration galleries is readily

contaminated. The accumulated water requires good sanitary protection or disinfection by pot chlorination. Sedimentation of clayey soils or organic matters

near the bank of the surface water source interfere with the infiltration process and require regular cleaning by scrapping a layer of deposited materials.

Surface waters


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Protected Ponds

A protected pond in a community can provide water for drinking purpose with minimal treatment and for other domestic uses without treatment.

Traditionally, rural water supply, to a great extent, was based on protected ponds before and during early stage of installation of tubewell. Sinking of

tubewells under community water supply schemes in rural Bangladesh began in 1928. There are about 1,288,222 nos. of ponds in Bangladesh having an

area of 0.114 ha per ponds and 21.5 ponds per mauza (BBS, 1997). About 17% of these ponds are derelict and probably dry up in the dry season. The

biological quality of water of these ponds is extremely poor due to unhygienic sanitary practices and absence of any sanitary protection. Many of these

ponds are made chemically and bio-chemically contaminated for fish culture. In order to maintain good quality water, a protected ponds shall not receivesurface discharges or polluting substances and should only be replenished by rain and groundwater infiltration.

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). It is a package type slow sand filter unit developed to treat surface waters, usually low-saline pond water,

for domestic water supply in the coastal areas. 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). It has been tested and found that the treated water from a PSF is normally bacteriologically safe or within tolerable limits. Onaverage the operating period of a PSF between cleaning is usually two months, after which the sand in the bed needs to be cleaned and replaced. The

drawing of a typical PSF is shown in figure 3.6.

The program initiated by DPHE with the construction of 20 experimental units in 1984 to utilize low saline pond water for water supply in the coastal area.

Pond Sand Filters serve 200-500 people per unit. The PSF is being promoted as a option for water supply in arsenic affected areas.

The problems encountered are low discharge and difficulties in washing the filter beds. Since these are small units, community involvement in operation and

maintenance is absolutely essential to keep the system operational. A formal institutional arrangement cannot be installed for running such a unit, community

involvement in operation and maintenance is the key issue in making the system work. By June 2000, DPHE has installed 3,710 units of PSF, a significant

proportion of which remains out of operation for poor maintenance.


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Figure 3.6 Pond Sand Filter for Treatment of Surface Water

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. In such cases, the treated water may require chlorination to meet drinking water standards.

The costs of construction, advantages and limitations of Pond Sand Filters as described by different organization involved in arsenic safe water supplies are

summarized in Appendix-1. The major limitations mentioned are as follows:

Operation and maintenance are difficult;


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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.

Collection of safe water by installation of PSF on the bank of a pond is shown in Figure 3.7.

Combined Filters

A combined filter consists of roughing filters and a slow sand filter. It is introduced to overcome some of the difficulties encountered in PSF. The PSF

cannot operate effectively when the turbidity of surface water exceeds 30 mg/l. The low discharge and requirement of frequent washing of the filter beds

are common in Bangladesh. This is due to high turbidity and seasonal algal bloom in pond water. The situation can greatly be improved by design


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modifications particularly by the construction of roughing filters for pretreatment of water. The roughing filters remove turbidity and colour to acceptable

level for efficient operation of the slow sand filter installed in sequential order following roughing filters. A diagram of a combined filtration unit is shown in

Figure 3.8.

The roughing and slow sand filter units have been constructed in many parts of the world with success in reduction of very high turbidities and coliform

counts. Operation and maintenance are relatively easy and less frequent attention is needed for longer duration of operation between cleaning. A combined

unit of such filter has been constructed in Samta Village in Jessore district by Asian Arsenic Network (AAN) and it functions well in rural condition but

remains idle in dry season when there is no water in the pond (AAN, RGAG and NIPSOM, 1999).

Household Filt ers


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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 as shown in Figure 3.9. 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 as shown in figure 3.10. The container is filled with water and the filtered water is collected from the bottom. It is essential to avoid

drying up of the filter bed. Full effectiveness of the filtration process is obtained if the media remain in water all the time. The pitcher and other small


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household filters cannot completely remove micro-organisms if these are present in large numbers in raw water. Experimental units constructed in

Bangladesh and in other countries show that the residual coliform bacteria present in the filtered water may vary from a few to several hundred. However,

improvement of water quality by household filters is remarkable.

The important characteristics of household filters are:

suitable for surface water treatment;

remove turbidity, colour 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.

3.2.3 Rain Water Harves ting

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. The main advantages and disadvantages of a rainwater system are shown in Table 3.1

Table 3.1: 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 theowner/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 rainwaterharvesting.


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The system can be located very close

to the consumption points.

A rainwater based water supply system requires determination of the capacity of storage tank and catchment area for rainwater collection in relation to

water requirement, rainfall intensity and distribution. The availability of rainwater is limited by the rainfall intensity and availability of suitable catchment area.

The mineral free rainwater may not be liked by many and the poorer section of the people may not have a roof/catchment area suitable for rainwater

harvesting.

Availabil ity of Rainwater

The mean rainfall intensity recorded in 28 stations for the period from 1987 to 1998 is shown in Figure 2.2 ( BBS, 1999). It appears that the average

yearly rainfall in the country varies from 1900 to 2900 mm. However, there are some losses in the collection system and a part of the rainwater is used for

washing of the catchment area.. The available rainwater can be estimated by the equation:

Q = C I A (1)

Where Q is the total quantity of rainwater available in m3/ year, C is coefficient of available runoff, I is the rainfall intensity in m/year and A is the catchment

area in m2. Spatial variation of rainfall in Bangladesh is quite high. Lowest rainfall less than 1500 mm occurs in the western part of the country and the

highest rainfall exceeding 4000 mm occurs in the north-east. Therefore, the requirements for rainwater harvesting would vary from place to place

depending on the total rainfall and its distribution over the whole year.

Rainwater Catchment

The catchment area for rainwater collection is usually the roof, which is connected with a gutter system to lead rainwater to the storage tank. A rainwater

collection system from roof has been shown in Figure 3.11. Rainwater can be collected from any types of roof but concrete, tiles and metal roofs givecleanest water. The C.I. sheet roofs commonly used in Bangladesh perform well as catchment areas. In Bangladesh 48% of the households have C.I sheet,

tiles and pucca roofs suitable for the collection of rainwater (BBS, 1997).

The minimum catchment area A, required for the collection of rainwater for N number of people supplied with q litres per capita per day (lpcd) of water

can derived from Equation (1) as:

A = 0.365 q N / C I (2)

About 25% of the rainwater may be assumed to be lost by evaporation and for washing the catchment area using first rain that produces inferior quality

rainwater (Ahmed, 1999). The Equation (2) can be written for an average annual rainfall of 2.46 m/yr., as indicated in Figure 2.2 and a coefficient of runoffof 0.70 in the following form :


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A = 0.212 q N (3)


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The poorer section of the people is in disadvantageous position in respect of utilization of rainwater as a source of water supply. This section of people has

smaller size thatched roof or no roof at all, to be used as catchment for rainwater collection. A thatched roof can also be used as catchment area by

covering it with polyethylene but it requires good skills to guide water to the storage tank. In coastal areas of Bangladesh, cloths fixed at four corners with a

pitcher underneath is used during rainfall for rainwater collection. A plastic sheet as shown in Figure 3.12 has been tried as a catchment for rainwater

harvesting for the people who do not have a roof suitable for rainwater collection. The use of land surface as catchment area and underground gravel/sand

packed reservoir as storage tank can be an alternative system of rainwater collection and storage. In this case, the water has to be channeled towards the

reservoir and allowed to pass through a sand bed before entering into underground reservoirs. This process is analogous to recharge of undergroundaquifer by rainwater during rainy season for utilization in the dry season.


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Storage Tank

The unequal distribution of rainfall over the year requires storage of rainwater during rainy season for use in the dry season. The minimum volume of the

storage rainwater tank V, required for rainwater can be computed by the equation:

V = O.365 f q N (4)

Where f is the fraction of water required to be stored for consumption of total available rainwater at a constant rate throughout the year. The total annualrainfall in 1996 as shown in Figure 2.2 is approximately equal to the average annual rainfall of the last 12 years. The monthly distribution of average rainfall

in 1996 shown in Figure 2.3 is assumed to represent the average condition. The rainwater availability mass curve assuming and cumulative

consumption/demand of total available rainwater at constant rate are also shown in Figure 3.13.


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Figure 3.13. Rainfall Intensity, Cumulative Rainwater Availability and Demand

The mass curve has been prepared considering the fact that 75% of the rainwater would be available. It may be observed that there is a shortfall of 0.48

m3 in the dry periods and an excess of 0.24 m3 during rainy season. For full utilization of rainwater potential, a storage tank of capacity 0.72 m3 that is

40% of the available rainwater is required for uninterrupted water supply at a constant rate throughout the year. However, if only drinking and cooking

water is harvested, the sizes of the storage tank and catchment area would be smaller and within affordable range a family. Substituting f = 0.4 in Equation

4 for representative rainfall distribution of 1996, the minimum volume of the storage tank required for rainwater becomes:

V = 0.146 q N (5)


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However, the above simple design based on average rainfall will provide about 50% reliability of year around water supply. A design with higher reliability

will require bigger catchment area and larger size of storage tank. There are several methods available for the design of a rainwater system with desired

reliability and computer programs based on these methods are also available for design.

Quality of Rainwater

The quality of rainwater is relatively good but it is not free from all impurities. Analysis of stored rainwater has shown some bacteriological contamination.

Cleanliness of roof and storage tank is critical in maintaining good quality of rainwater. The first run off from the roof should be discarded to prevent entry

of impurities from the roof. If the storage tank is clean, the bacteria or parasites carried with the flowing rainwater will tend to die off. Some devices and

good practices have been suggested to store or divert the first foul flush away from the storage tank. In case of difficulties in the rejection of first flow,

cleaning of the roof and gutter at the beginning of the rainy season and their regular maintenance are very important to ensure better quality of rainwater.

The storage tank requires cleaning and disinfection when the tank is empty or at least once in a year. The rainwater is essentially lacking in minerals, the

presence of which is considered essential in appropriate proportions. The mineral salts in natural ground and surface waters sometimes impart pleasing

taste to water.

3.2.4 Solar Distillation

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.

3.2.5Solar Disinfection

Presence of pathogenic organisms even in apparently clear arsenic safe surface water is a hindrance for use as drinking water. These organisms can be

destroyed or inactivated by solar Disinfection. This is a natural process of elimination of disease producing microorganisms using solar energy and can be

applied to disinfect small quantity of water for drinking purpose. If solar radiation allowed to penetrate in water in a thin layer. the water is disinfected by

the combined action of ultraviolet ray and temperature. It has been shown that if water in a transparent bottle is exposed to fullsunlight for about 5 hours

the water is completely disinfected (EAWAG-SANDEC. 1998). The method is not suitable for treatment of large volumes of water containing high

turbidity.


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3.3 TREATMENT OF ARSENIC CONTAMINATED WATER

3.3.1 General

Treatment of arsenic contaminated well water is an alternative option to make use of a huge number of tubewells likely to be declared abandoned for

yielding water with high arsenic content. There are several methods available for removal of arsenic from water in large conventional treatment plats. The

most commonly used technologies include oxidation, co-precipitation and adsorption onto coagulated flocs, lime treatment, adsorption onto sorptive

media, ion exchange resin and membrane techniques (Cheng et al., 1994; Hering et al., 1996, 1997; Kartinen and Martin, 1995; Shen, 1973; Joshi and

Chaudhuri, 1996). A detailed review of arsenic removal technologies is presented by Sorg and Logsdon (1978). Jackel (1994) has documented several

advances in arsenic removal technologies. In view of the lowering the drinking water standards by USEPA, a review of arsenic removal technologies wasmade to consider the economic factors involved in implementing lower drinking water standards for arsenic (Chen et al., 1999). Many of the arsenic

removal rtechnologies have been discuswses in details in AWWA reference book (Pontious, 1990). A comprehensive review of low-cost, well-water

treatment technologies for arsenic removal with the list of companies and organizations involved in arsenic removal technologies has been compiled by

Murcott (2000) with contact detail.

Some of these technologies can be reduced in scale and conveniently be applied at household and community levels for the removal of arsenic from

contaminated tubewell water. During the last 2-3 years many small scale arsenic removal technologies have been developed, field tested and used under

action research programs in Bangladesh and India. This sub-section presents a short review of these technologies with the intention to update the

technological development in arsenic removal, understand the problems, prospects and limitations of different treatment processes as alternative water

supply options for water supply.

3.3.2 Oxidation

Arsenic is present in groundwater in As(III) and AS(V) forms in different proportions. Most treatment methods are effective in removing arsenic in

pentavalent form and hence include an oxidation step as preteatment to convert arsenite to arsenate. Arsenite can be oxidized by oxygen, ozone, free

chlorine, hypochlorite, permanganate, hydrogen peroxide and fulton's reagent but Atmospheric oxygen, hypochloride and permanganate are commonly

used for oxidation in developing countries. Air oxidation of arsenic is very slow and can take weeks for oxidation (Pierce and Moore, 1982) but chemicals


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like chlorine and permanganate can rapidly oxidize arsenite to arsenate under wide range of conditions.

Passive Sedimentation

Passive sedimentation received considerable attention because of rural people's habit of drinking stored water from pitchers. Oxidation of water during

collection and subsequent storage in houses may cause a reduction in arsenic concentration in stored water(Bashi Pani). Experiments conducted in

Bangladesh showed no to high reduction in arsenic content by passive sedimentation. Arsenic reduction by plain sedimentation appears to be dependent on

water quality particularly the presence of precipitating iron in water. Ahmed et al.(2000) showed that more than 50% reduction in arsenic content ispossible by sedimentation of tubewell water containing 380-480 mg/l of alkalinity as CaCO3 and 8-12 mg/L of iron but cannot be relied to reduce arsenic

to desired level. Most studies showed a reduction of zero to 25% of the initial concentration of arsenic in groundwater. In rapid assessment of technologies

passive sedimentation failed to reduce arsenic to the desired level of 50 g/L in any well (BAMWSP, DFID, WaterAid , 2001).

In-situ Oxidation

In-situ oxidation of arsenic and iron in the aquifer has been tried under DPHE-Danida Arsenic Mitigation Pilot Project. The aerated tubewell water is

stored in a tank and released back into the aquifers through the tubewell by opening a valve in a pipe connecting the water tank to the tubewell pipe under

the pump head. The dissolved oxygen in water oxidizes arsenite to less mobile arsenate and also the ferrous iron in the aquifer to ferric iron, resulting areduction in arsenic content in tubewell water. Experimental results shows that arsenic in the tubewell water following in-situ oxidation is reduced to about

half due to underground precipitation and adsorption on ferric iron.

Solar Oxidation

SORAS is a simple method of solar oxidation of arsenic in transparent bottles to reduce arsenic content of drinking water (Wegelin et al., 2000).

Ultraviolet radiation can catalyze the process of oxidation of arsenite in presence of other oxidants like oxygen (Young, 1996). Experiments in Bangladesh

show that the process on average can reduce arsenic content of water to about one-third.

3.3.3 Co-Precipitation and Adsorption Processes

Water treatment with coagulants such as aluminium alum, Al2(SO4)3.18H2O, ferric chloride , FeCl3 and ferric sulfate Fe2(SO4)3.7H2O are effective in

removing arsenic from water. Ferric salts have been found to be more effective in removing arsenic than alum on a weight basis and effective over a wider

range of pH. In both cases pentavalent arsenic can be more effectively removed than trivalent arsenic.

In the coagulation-flocculation process aluminium sulfate, or ferric chloride, or ferric sulfate is added and dissolved in water under efficient stirring for one

to few minutes. Aluminium or ferric hydroxide micro-flocs are formed rapidly. The water is then gently stirred for few minutes for agglomeration of micro-flocs into larger easily settable flocs. During this flocculation process all kinds of micro-particles and negatively charged ions are attached to the flocs by


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electrostatic attachment. Arsenic is also adsorbed onto coagualted flocs. As trivalent arsenic occurs in non-ionized form, it is not subject to significant

removal. Oxidation of As(III) to As(V) is thus required as a pretreatment for efficient removal. This can be achieved by addition of bleaching powder

(chlorine) or potassium permanganate. Arsenic removal is dependent on pH. In alum coagulation, the removal is most effective in the pH range 7.2-7.5 and

in iron coagulation, efficient removal is achieved in a wider pH range usually between 6.0 and 8.5 (Ahmed and Rahaman, 2000).

Bucket Treatment Unit

The Bucket Treatment Unit (BTU), developed by DPHE-Danida Project is based on the principles of coagulation, co-precipitation, and adsorption

processes. The unit consists of two bucket, each 20 liter capacity, placed one above the other. Chemicals are mixed manually with arsenic contaminated

water in the upper red bucket by vigorous stirring with a wooden stick for 30 to 60 seconds and then flocculated by gentle stirring for about 90 second.

The mixed water is then allowed to settle for 1- 2 hours. The water from the top red bucket is then allowed to flow into the lower green bucket via plastic

pipe and a sand filter installed in the lower bucket. The flow is initiated by opening a valve fitted slightly above the bottom of the red bucket to avoid inflow

of settled sludge in the upper bucket. The lower green bucket is practically a treated water container.

The DPHE-Danida project in Bangladesh distributed several thousands BTU units in rural areas of Bangladesh. These unit are based on chemical doses of200 mg/L aluminum sulfate and 2 mg/L of potassium permanganate supplied in crushed powder form. The units were reported to have very good

performance in arsenic removal in both field and laboratory conditions (Sarkar et al., 2000 and Kohnhorst and Paul, 2000). Extensive study of DPHE-

Danida BTU under BAMWSP, DFID, WaterAid (2001) rapid assessment program showed mixed results. In many cases, the units under rural operating

conditions fails to remove arsenic to the desired level of 0.05 mg/L in Bangladesh. Poor mixing and variable water quality particularly pH of groundwater in

different locations of Bangladesh appeared to be the cause of poor performance in rapid assessment.

Bangladesh University of Engineering and Technology (BUET) modified the BTU and obtained better results by using 100 mg/L of ferric chloride and 1.4

mg/L of potassium permanganate in modified BTU units. The arsenic contents of treated water were mostly below 20 ppb and never exceeded 37 ppb

while arsenic concentrations of tubewell water varied between 375 to 640 ppb. The BTU is a promising technology for arsenic removal at household level

at low cost. It can be build by locally available materials and is effective in removing arsenic if operated properly.

Stevens Institute Technology

This technology also uses two buckets, one to mix chemicals (reported to be iron sulphate and calcium hypochloride) supplied in packets and the other to

separate flocs by the processes of sedimentation and filtration. The second bucket has a second inner bucket with slits on the sides as shown in Figure 3.14

to help sedimentation and keeping the filter sand bed in place. The chemicals form visible large flocs on mixing by stirring with stick. Rapid assessment

showed that the technology was effective in reducing arsenic levels to less than 0.05 mg/L in case of 80 to 95% of the samples tested (BAMWSP, DFID,

WaterAid, 2001). The sand bed used for filtration is quickly clogged by flocs and requires washing at least twice a week.


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Figure 3.14 : Stevens Institute Technology

BCSIR Filt er Unit

Bangladesh Council of Scientific and Industrial Research (BCSIR) has developed an arsenic removal system, which uses the process of coagulation/co-

precipitation with a iron based chemical followed by sand filtration. The unit did not take part in a comprehensive evaluation process.

DPHE-Danida Fill and Draw Units

It is a community type treatment unit designed and installed under DPHE-Danida Arsenic Mitigation Pilot Project. It is 600L capacity (effective) tank with

/ / S O


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slightly tapered bottom for collection and withdraw of settled sludge. The tank is fitted with a manually operated mixer with flat-blade impellers. The tank is

filled with arsenic contaminated water and required quantity of oxidant and coagulant are added to the water. The water is then mixed for 30 seconds by

rotating the mixing device at the rate of 60 rpm and left overnight for sedimentation. The water takes some times to become completely still which helps

flocculation. The floc formation is caused by the hydraulic gradient of the rotating water in the tank. The settled water is then drawn through a pipe fitted at

a level few inches above the bottom of the tank and passed through a sand bed and finally collected through a tap for drinking purpose as shown in Figure

3.15. The mixing and flocculation processes in this unit are better controlled to effect higher removal of arsenic. The experimental units installed by DPHE-

Danida project are serving the clusters of families and educational institutions.

The principles of arsenic removal by alum coagulation, sedimentation and filtration have been employed in a compact unit for water treatment in the village

level in West Bengal, India. The arsenic removal plant attached to hand tubewell as shown in Figure 3.16 has been found effective in removing 90 percent

arsenic from tubewell water having initial arsenic concentration of 300 m g/l. The treatment process involves addition of sodium hypochloride (Cl2), and

aluminium alum in diluted form, mixing, flocculation, sedimentation and up flow filtration in a compact unit.

Figure 3.15 : DPHE-Danida Fill and Draw Arsenic Removal Unit Attached to Tubewell

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Fig. 3.16 Arsenic Removal Plants Attached to Tubewell

(Designed and Constructed in India)

Naturally Occurring Iron

The use of naturally occurring iron precipitates in groundwater in Bangladesh is a promising method of removing arsenic by adsorption. It has been found

that hand tubewell water in 65% of the area in Bangladesh contains iron in excess of 2 mg/l and in many acute iron problem areas, the concentration of

dissolved iron is higher than 15 mg/l. Although no good correlation between concentrations of iron and arsenic has been derived, iron and arsenic have

been found to co-exist in groundwater. Most of the Tubewell water samples satisfying Bangladesh Drinking Water Standard for Iron (1 mg/l) also satisfy

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the standard for Arsenic (50 m g/l). Only about 50% of the samples having iron content 1 - 5 mg/l satisfy the standard for arsenic while 75% of the samples

having iron content > 5 mg/l are unsafe for having high concentration of arsenic.

The iron precipitates [Fe (OH)3] formed by oxidation of dissolved iron [Fe(OH)2] present in groundwater, as discussed above, have the affinity for the

adsorption of arsenic. Only aeration and sedimentation of tubewell water rich in dissolved iron has been found to remove arsenic. The Iron Removal Plants

(IRPs) in Bangladesh constructed on the principles of aeration, sedimentation and filtration in a small units have been found to remove arsenic without any

added chemicals. The conventional community type IRPs, depending on the operating principles, more or less work as Arsenic Removal Plants (ARPs) as

well. A study suggests that As(III) is oxidized to As(V) in the IRPs to facilitate higher efficiency in arsenic removal in IRPs constructed in Noakhali (Dahiand Liang, 1998). The Fe-As removal relationship with good correlation in some operating IRPs has been plotted in Figure 3.17. Results shows that most

IRPs can lower arsenic content of tubewell water to half to one-fifth of the original concentrations. The efficiency of these community type Fe-As removal

plants can be increased by increasing the contact time between arsenic species and iron flocs. Community participation in operation and maintenance in the

local level is absolutely essential for effective use of these plants.

Fig. 3.17 Correlation between Fe and As Removal in Treatment Plants

Some medium scale Fe-As removal plants of capacities 2000-3000 m3/d have been constructed for water supplies in district towns based on the same

principle. The treatment processes involved include aeration, sedimentation and rapid sand filtration with provision for addition of chemical, if required.

These plants are working well except that treated water requirement for washing the filter beds is very high. Operations of small and medium size IRP-

cum-ARPs in Bangladesh suggest that arsenic removal by co-precipitation and adsorption on natural iron flocs has good potential.

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3.3.4 Sorptive Filtration Media

Several sorptive media have been reported to remove arsenic from water. These are activated alumina, activated carbon, iron and manganese coated sand.

kaolinite clay, hydrated ferric oxide, activated bauxite, titanium oxide, silicium oxide and many natural and synthetic media. The efficiency of all some

sorptive media depend on the use of oxidizing agent as aids to sorption of arsenic. Saturation of media by different contaminants and components of water

takes place at different times of operation depending on the specific sorption affinity of the medium to the given component.Saturation means that theefficiency in removing the desired impurities becomes zero.

Activated Alumina

Activated alumina, Al2O3, having good sorptive surface is an effective medium for arsenic removal. When water passes through a packed column of

activated alumina, the impurities including arsenic present in water are adsorbed on the surfaces of activated alumina grains. Eventually the column becomes

saturated, first at its upstream zone and later the saturated zone moves downstream towards the bottom end and finally the column gets totally saturated.

Regeneration of saturated alumina is carried out by exposing the medium to 4% caustic soda, NaOH, either in batch or by flow through the column

resulting in a high arsenic contaminated caustic waste water. The residual caustic soda is then washed out and the medium is neutralized with a 2% solution

of sulfuric acid rinse. During the process about 5-10% alumina is lost and the capacity of the regenerated medium is reduced by 30-40%. The activated

alumina needs replacement after 3-4 regeneration. Like coagulation process, pre-chlorination improves the column capacity dramatically. Some of the

activated alumina based sorptive media used in Bangladesh include:

BUET Activated Alumina

Alcan Enhanced Activated Alumina

ARU of Project Earth Industries Inc.,USA

Apyron Arsenic Treatment Unit

The BUET and Alcan activated alumina have been extensively tested in field condition in different areas of Bangladesh under rapid assessment and found

very effective in arsenic removal (BAMWSP, DFID, WaterAid ,2001). The Arsenic Removal Units (ARUs) of Project Earth Industries Inc. (USA) used

hybrid aluminas and composite metal oxides as adsorption media and were able to treat 200-500 Bed Volume (BV) of water containing 550 g/L of

arsenic and 14 mg/L of iron (Ahmed et al., 2000). The Apyron Technologies Inc. (ATI) also uses inorganic granular metal oxide based media that can

selectively remove As(III) and As(V) from water. The Aqua-BindTM arsenic media used by ATI consist of non-hazardous aluminium oxide and

manganese oxide for cost-effective removal of arsenic. The proponents claimed that the units installed in India and Bangladesh consistently reduced arsenic

to less than 10g/L.

Granular Ferric Hydroxide

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M/S Pal Trockner (P) Ltd, India and Sidko Limited, Bangladesh installed several Granular Ferric Hydroxide based arrsenic removal units in India and

Bangladesh. The Granular Ferric Hydroxide (AdsorpAs) is arsenic selective abdsorbent developed by Technical University, Berlin, Germany. The unit

requires iron removal as pre-treatment to avoid clogging of filter bed. The proponents of the unit claims to have very high arsenic removal capacity and

produces non-toxic spent granular ferric hydroxide

Read-F Arsenic Removal Unit

Read-F is an adsorbent produced and promoted by Shin Nihon Salt Co. Ltd, Japan for arsenic removal in Bangladesh. Read-F displays high selectivity forarsenic ions under a broad range of conditions and effectively adsorbs both arsenite and arsenate without the need for pretreatment. The Read-F is

Ethylene-Vinyl Alcohol Copolymer (EVOH) -borne hydrous cerium oxide in which hydrous cerium oxide ( CeO 2 n H2O), is the adsorbent. The material

contains no organic solvent or other volatile substance and is not classified as hazardous material. Laboratory test at BUET and field testing of the materials

at 4 sites under the supervision of BAMWSP showed that the adsorbent is highly efficient in removing arsenic from groundwater (SNSCL, 2000).

Iron Coated Sand

BUET has constructed and tested iron coated sand based small scale unit for the removal of arsenic from groundwater. Iron coated sand has been

prepared following the procedure similar to that adopted by Joshi and Choudhuri ( 1996). The iron content of the iron coated sand was found to be 25mg/g of sand. Raw water having 300 m g/L of arsenic when filtered through iron coated sand becomes significantly arsenic-free. It was found that the

number of bed volume that can be treated satisfying the Bangladesh drinking water standard of 50 ppb arsenic was around 350. The saturated medium is

regenerated by passing 0.2N sodium hydroxide through the column or soaking the sand in 0.2N sodium hydroxide followed by washing with distilled

water. No significant change in bed volume (BV) in arsenic removal was found after 5 regeneration cycles. It was interesting to note that iron coated sand

is equally effective in removing both As(III) and As(V).

Shapla Filter

Shapla filter, a household arsenic removal unit, has been designed with iron coated brick dust as an adsorption medium and works on the same principles

as iron coated sand described above. The unit is effective in removing arsenic from drinking water.

Indigenous Filters

There are several filters available in Bangladesh that use indigenous material as arsenic adsorbent. Red soil rich in oxidized iron, clay minerals, iron ore, iron

scrap or fillings, processed cellulose materials are known to have capacity for arsenic adsorption. Some of the filters manufactured using these material

include:

Sono 3-Kolshi Filter,

Granet Home-made Filter,Chari Filter,

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Adarsha Filter,

Shafi Filter, and

Bijoypur Clay/Processed Cellulose filter.

The Sono 3-Kolshi filter uses zero valent iron fillings and coarse sand in the top Kolshi, wood coke and fine sand in the middle Kolshi while the bottom

Kolshi is the collector of the filtered water (Khan et al., 2000). Earlier Nikolaidis and Lackovic (1998) showed that 97 % arsenic can be removed by

adsorption on a mixture of zero valent iron fillings and sand and recommended that arsenic species could have been removed through formation of co-

precipitates, mixed precipitates and by adsorption onto the ferric hydroxide solids. The Sono 3-Kolshi unit has been found to be very effective in removingarsenic but the media habour growth of microorganism (BAMWSP, DFID and WaterAid, 2001). The one-time use unit becomes quickly clogged, if

groundwater contains excessive iron.

The Garnet home-made filter contains relatively inert materials like brick chips and sand as filtering media. No chemical is added to the system. Air

oxidation and adsorption on iron-rich brick chips and flocs of naturally present iron in groundwater could be the reason for arsenic removal from

groundwater. The unit produced inadequate quantity of water and did not show reliable results in different areas of Bangladesh and under different

operating conditions. The Chari filter also uses brick chips and inert aggregates in different Charis as filter media. The effectiveness of this filter in arsenic

removal is not known.

The Shafi and Adarsh filters use calyey material as filter media in the form of candle. The Shafi filter was reported to have good arsenic removal capacity

but suffered from clogging of filter media. The Adarsha filter participated in the rapid assessment program but failed to meet the technical criterion of

reducing arsenic to acceptable level (BAMWSP, DFID and WaterAid, 2000). Bijoypur clay and treated cellulose were also found to adsorb arsenic from

water (Khair, 2000).

Cartridge Filters

Filter units with cartridges filled with soptive media or ion-exchange resins are readily available in the market. These unit remove arsenic like any other

dissolved ions present in water. These units are not suitable for water having high impurities and iron in water. Presence of ions having higher affinity than

arsenic can quickly saturate the media requiring regeneration or replacement. Two household filters were tested at BUET laboratories, These are:

Chiyoda Arsenic Removal Unit, Japan

Coolmart Water Purifier, Korea.

The Chiyoda Arsenic Removal Unit could treat 800 BV meeting the WHO guideline value of 10 g/L and 1300 BV meeting the Bangladesh Standard of

50 g/L when the feed water arsenic concentration was 300 g/L. The coolmart Water Purifier could treat only 20L of water with a effluent arsenic content

of 25g/L (Ahmed et al., 2000). The initial and operation costs of these units are high and beyond the reach of the rural people.

3.3.5 Ion Exchange



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7/20/13 3 Water Supply Options


The process is similar to that of activated alumina, just the medium is a synthetic resin of more well defined ion exchange capacity. The process is normally

used for removal of specific undesirable cation or anion from water. As the resin becomes exhausted, it needs to be regenerated.

The arsenic removal capacity is dependent on sulfate and nitrate contents of raw water as sufate and nitrate are exchanged before arsenic. The ion

exchange process is less dependent on pH of water. The efficiency of ion exchange process is radically improved by pre-oxidation of As(III) to As(V) but

the excess of oxidant often needs to be removed before the ion exchange in order to avoid the damage of sensitive resins. Development of ion specific

resin for exclusive removal of arsenic can make the process very attractive.

Tetrahedron ion exchange resin filter tested under rapid assessment program in Bangladesh (BAMWSP, DFID and WaterAid, 2001) showed promising

results in arsenic removal. The system needs pre-oxidation of arsenite by sodium hypochloride. The residual chlorine helps to minimize bacterial growth in

the media. The saturated resin requires regeneration by recirculating NaCl solution. The liquid wastes rich in salt and arsenic produced during regeneration

require special treatment. Some other ion exchange resins were demonstrated in Bangladesh but sufficient field test results are not available on the

performance of those resins.

3.3.6 Membrane Techniques

Membrane techniques like reverse osmosis, nonofiltration and electrodialysis are capable of removing all kinds of dissolved solids including arsenic from

water. In this process water is allowed to pass through special filter media which physically retain the impurities present in water. The water, for treatment

by membrane techniques, shall be free from suspended solids and the arsenic in water shall be in pentavalent form. Most membranes, however, can not

withstand oxidizing agent.

MRT-1000 and Reid System Ltd.

Jago Corporation Limited promoted a household reverse osmosis water dispenser MRT-1000 manufactured by B & T Science Co. Limited, Taiwan. This

system was tested at BUET and showed a arsenic (III) removal efficiency more than 80%. A wider spectrum reverse osmosis system named Reid SystemLimited was also promoted in Bangladesh. Experimental results showed that the system could effectively reduce arsenic content along with other impurities

in water. The capital and operational costs of the reverse osmosis system would be relatively high.

Nanofiltration and Reverse Osmosis

The reverse osmosis (R/O) and nanofiltration (N/F) technologies can separate 95-98% of total dissolved solids including arsenic but it is relatively costly.

In recent years, a new generation of R/O and N/F membranes have been introduced by Techno-food in Bangladesh which is less expensive and is being

commercially used in industry, hotel and public water supplies. Techno-food membrane technology can remove arsenic and all other impurities present in

water including bacteria at a pressure of 50-150 psi. This method of arsenic removal does not require any chemicals and Operation and maintenancerequirements are minimum. The Techno-food water technologies section has marketed several models of R/O and N/F units of various water treatment



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7/20/13 3 Water Supply Options


capacities.

Oh et al.(2000) applied reverse osmosis and nanofiltration membrane processes for the treatment of arsenic contaminated water applying low pressure by

bicycle pump. A nanofiltration membrane process coupled with a bicycle pump could be operated under condition of low recovery and low pressure range

from 0.2 to 0.7 MPa. Arsenite was found to have lower rejection than arsenate in ionized forms and hence water containing higher arsenite requires pre-

oxidation for reduction of total arsenic acceptable level. In tubewell water in Bangladesh the average ratio of arsenite to total arsenic was found to be 0.25.

However, the reverse osmosis process coupled with a bicycle pump system operating at 4 MPa can be used for arsenic removal because of its high

arsenite rejection. The study concluded that low-pressure nanofiltration with pre-oxidation or reverse osmosis with a bicycle pump device could be usedfor the treatment of arsenic contaminated groundwater in rural areas (Oh et al., 2000).

3.3.7 Summary

A remarkable technological development in arsenic removal from rural water supply based on conventional arsenic removal processes has taken place

during last 2-3 years. A comparison of different arsenic removal processes is shown in Table 3.2.

Table 3.2 A Comparison of Main Arsenic Removal Technologies

Technologies Advantages Disadvantages

Oxidation/

Precipitation

Air Oxidation

Chemical oxidation

Relatively simple, low-

cost but slow process

Relatively simple and

rapid process

Oxidizes otherimpurities and kills

microbes

The processesremove only a part of

arsenic

Coagulation

Coprecipitation :

Alum Coagulation

Iron Coagulation

Relatively low capital

cost,

Relatively simple

operation

Common Chemicalsavailable

Produces toxic sludges

Low removal of As(III)

Preoxidation may be

required



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pp y p


Sorption Techniques

Actvated Alumina

Iron Coated Sand

Ion Exchange Resin

Other Sorbents

Relatively well known and

commercially available

Well defined technique

Plenty possibilities and

scope of development

Produces toxic solid

waste

Replacement/regeneration

required

High tech operation and

maintenanceRelatively high cost

Membrane Techniques

Nanofiltration

Reverse osmosis

Electrodialysis

Well defined and high

removal efficiency

No toxic solid wastes

produced

Capable of removal of

other contaminants

Very high capital and

running cost

High tech operation and

maintenance

Toxic wastewater

produced

A rapid assessment of 9 household level arsenic removal technologies has been completed recently (BAMWSP, DFID and Wateraid, 2000). On the basis

of this study the Technical Advisory Group (TAG) of Bangladesh Arsenic Mitigation Water Supply Project (BAWSP) has recently recommended the

following household arsenic removal technologies for experimental use in arsenic affected areas:

Alcan Enhanced Activated Alumina

BUET Activated Alumina

Sono 3-Kolshi MethodStevens Institute technology.

The widely used DPHE/Danida two bucket system and Tetrahedron ion exchange resin filters will be reviewed when more information on performance of

the systems and its revised version are available. Few more technologies in addition to technologies described in this paper are available for arsenic

removal at household and community levels. These technologies need evaluation in respect of effectiveness in arsenic removal and community acceptance.

All the technologies described in this paper have their merits and demerits and are being refined to make suitable in rural condition. The modifications

based on the pilot-scale implementation of the technologies are in progress with the objectives to:

improve effectiveness in arsenic removal,



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pp y p


reduce the capital and operation cost of the systems,

make the technology user friendly,

overcome maintenance problems, and

resolve sludge and arsenic concentrates management problems.

Arsenic removal technologies have to compete with other technologies in which cost appears to a major determinant in the selection of a treatment option

by the users. The rural people habituated in drinking tubewell water may find arsenic removal from tubewell water as a suitable option for water supply. In

many arsenic affected areas, arsenic removal may be the only option in the absence of an alternative safe source of water supply.

3.4 PIPED WATER SUPPLY

Piped water supply is the ultimate goal of safe water supply to the consumer because:

Water can be delivered to the close proximity of the consumers

Piped water is protected from external contamination

Better quality control is possible

Water of required quantity can be collected at ease.

In respect of convenience in collection and use, only piped water can compete with existing system of tubewell water supply. But it is a very difficult and

costly option for scattered population in the rural areas.

It can be a feasible option for clustered rural settlements and urban fringes. Water can be made available through house connection, yard connection or

standpost depending on the financial condition of the consumers. The water can be produced as per demand by sinking deep tubewell in arsenic-safe

aquifer or treatment of surface or even arsenic contaminated tubewell water by community type treatment plants. A rural piped water supply system with

provision for supplying water for irrigation installed by DPHE, UNICEF, BRAC and RDA, Bogra at Pakunda in Sonargaon Upazila and inaugurated bythe Honable Minister, Ministry of Local Government, Rural Development and Cooperatives on 6 January, 2002 is shown in Figure 3.18. The system

constructed at a cost of Taka 1 944 880 provides arsenic safe water to 419 households for all domestic purposes.



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3.5 SCREENING AND MONITORING

3.5.1 Screening



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The arsenic content of water of tubewells within short distances varies widely in many palces. This is probably due to variation in the depth of tubewells

and geoenvironmental conditions of the strata of aquifers from which the tubewells abstract water. As a result, the levels of contamination in an area cannot

be accurately predicted by testing of water of sample tubewells. Screening of all tubewells in the country is needed to identify the contaminated tubewell.

Government of Bangladesh has decided to test arsenic content of water produced by all tubewells to identify the safe and unsafe tubewells. Bangladesh

Arsenic Mitigation Water Supply Project and UNICEF have so far completed screening of all tubewells of 41 Upazillas and 5 Upazilas respectively. The

estimated cost of field test kit only for the screening of estimated 7.5 million tubewells in the country is given below:

Number of Tubewell : 7.5 Million ( Estimated)

Average number of tubewels can be tested by a Kit (100 test capacity) : 80

Number of Kits Required : 7 500 000/80 = 93 750

Average Cost of an Arsenic Test Kit : Tk 2 500 ( Assumed)

Cost of Test Kit : Tk. 2 500 x 93 750 = Tk. 234 375 000 @ Tk 234 Million

The number of contaminated tubewells estimated on the basis of sample survey conducted by BGS and DPHE (2001) is 1.875 million which is 25% of thetotal estimated 7.5 million tubewells in Bangladesh. The present cost of this 1.875 million tubewells is Taka 8.44 billion. The significant deviations in

intensity of contaminated tubewells by total screening from BGS/DPHE values justify the national screening program.

2. Monitoring

The estimated 5.625 million manually operated deep and shallow tubewells still supplying water with arsenic below national standard to 83 million people in

the country are vulnerable to arsenic contamination in future. No mathematical model can correctly predict the possible or probable time of contaminationof these tubewells. In this situation, monitoring is the only way to know whether the tubewell is contaminated or not. The estimated cost of field kits for

monitoring of the safe tubewells once in a year is given below:

Monitoring Frequency : 1 Sample/year/Arsenic Safe Tubewell

Number of Uncontaminated Tubewell : 7 500 000 x 0.73 = 5 625 000

Number of Kits Required : 5 475 000/80 = 70 313

Cost of Test Kit : Tk. 70 313 x 2 500 =Tk. 175 782 500 @Tk. 176 Million



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Since estimated 87% tubewells are likely to be privately owned, testing of water for arsenic should be the responsibility of the owner. The testing of

tubewell water once in a year should be made mandatory and test facility should be available locally, preferably at the lowest level of the Local

Government body.

5. COSTS

A variety of alternative technological options as discussed in this section is available for water supply in the arsenic affected areas. The cost of arsenic

mitigation will depend on the type of alternative technologies adopted for mitigation of the arsenic problem. The costs of installation and operation of some

major technological options available from various organization involved in arsenic mitigation are summarized in Table 3.3.

Table 3.3 Costs of Installation and Operation and Manitenance of Different Options .

Alternative

Technological

options

Unit Cost,

Taka

No. of

Family (hh)

/Unit

(Family

Size = 5)

Installation

Cost

/person

Taka

O & M

Cost/Person

/Year, Taka

Total Capital Cost

for 29million

People,

BillionTaka

RainwaterHarvesting 6 200 1 1 240 20 35.90

Dug/Ring

Well

35 000 25 280 1 8.12

Deep

Tubewell

45 000 50 180 1 5.22

Pond Sand 35 000 50 140 4 -10 4.06



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Filters

Surface Water

Treatment Unit

750 000 1 000 150 95 4.35

Piped W ater

Supply

1 850 000

375 000

1808 469

1 000

100

419 (1301hh)

370

750

786

20 10.75

21.75

22.79

Arsenic

Removal

-Urban Supply

-Community

type

-Household

12 000 000

75 000

450-2 500

6 000

25

1

400

600

90-500

5 -10

40

10-60

11.60

17.40

2.61-14.50

The quality and quantity of water, reliability, cost and convenience of collection of water of the different alternative options vary widely. Among the cheaper

options providing water at a cost of 4 to 5 billion Taka to 29 million arsenic-exposed population, the deep tubewell can provide water at nominal operation

and maintenance cost. But deep tubewells are not feasible, nor able to provide arsenic free water at all places in Bangladesh. Dug/ring well is the next

option, which can provide water at moderate installation and nominal O & M cost. It is not yet fully known whether the quality of water can be maintained

at desired level and arsenic content remains at safe level under conditions of proper sanitary protection. Piped water supply can be provided at a highercost and relatively higher O & M costs but the convenience and health benefits would be enormous. Because water of adequate quantity and relatively

superior quality for all domestic purposes including sanitation will be available at residences or close proximity of the residences. The increase in the

number of household reduces costs but it would be difficult to get clustered houses in most places in rural areas. The installation costs of arsenic removal

varies from lowest to moderate but O & M costs would be a constant burden. It may be observed that cost of installation and operation of rainwater

harvesting system at household level with about only 50% reliability are very high. Installation of community rainwater harvesting system may be cheaper

but management of such a system may be difficult.

3 - water supply options

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