The distribution of contaminated arsenic rich water in the ground waters of Pakistan, its consequences and mitigation measures.

1. Arsenic Contamination in Ground
Water
Pakistan – A Worst Case Scenario
QA/QC Department
Infrastructure Division
Descon Engineering Limited

2. The trace element arsenic (As) is found throughout
Earth’s crust and hydrosphere.
Arsenic (As) causes health concerns due to its
significant toxicity and worldwide presence in surface
water and groundwater.
The effects of chronic As exposure have been well
documented and have provided the basis for
regulating As concentrations in drinking water.
INTRODUCTION
The U.S. and World Health Organization (WHO) have set
a limit of arsenic contamination in drinking water as 10
µg/l, while in Pakistan this limit is 50 µg/l.

3. ARSENIC CONTAMINATION
Arsenic can enter the water
through rock erosion, mining
activity, volcanic eruptions
or forest fires.
Main source of arsenic in drinking
water (usually from wells) is arsenic-
rich rocks through which the water
has been filtered.
When contaminated water is used
to irrigate fields, the element
accumulates in soil and crops,
particularly rice.
Arsenic can enter surface and sub-
surface water through run-off from
various agricultural and industrial
activities.
In communities where residents cook
with and drink from the same
contaminated well, arsenic intake
multiplies.

4. OCCURRENCE OF ARSENIC
Arsenite
Oxidation State: +3
Occurs in Reducing Environments
Cannot be removed easily by sorption techniques
Arsenate
Oxidation State: +5
Occurs in Oxidizing Environments
Can easily be removed by sorption techniques
Major Oxidation States

5. EFFECTS OF ARSENIC ON HEALTH

6. ARSENIC CONTAMINATION MAP OF PAKISTAN
Podgorski et al., Sci. Adv. 2017;3: e1700935
WHO Limit: 10 µg/l
Pakistan Limit: 50 µg/l
In Pakistan, 50–60 million
people are direct victims.

7. PERSONS AT RISK PER KM2 MAP
Podgorski et al., Sci. Adv. 2017;3: e1700935
Lahore and Hyderabad
are the HOTSPOTS.

8. COMMON ARSENIC TREATMENT TECHNIQUES
OXIDATION
CO-
PRECIPITATION
SORPTION FILTRATION ION EXCHANGE
ACTIVATED
ALUMINA
REVERSE
OSMOSIS
MEMBRANE
FILTRATION COAGULATION LIME SOFTENING
Many of these processes however, are expensive and thus not feasible for developing countries like Pakistan. In the
following slides, few cheaper treatments methods successfully applied in Vietnam, Bangladesh and India will be
presented.

9. CO-PRECIPITATION, COAGULATION AND FILTRATION
Air + Fe2+
Water Droplets
Oxidation of Fe2+ to
Hydrated Ferric
Oxide (HFO)
Adsorption of AS (III)
and AS (V) with HFO
Absorption of AS (III)
and AS (V) in
absorptive media
Treated Water
Absorbent
(e.g. Activated
Alumina)
Water Inlet
HFO HFO HFO HFO
Showering of
Contaminated Water
This system is implemented in West Bengal, India.
Since, AS-III (arsenite) is available abundantly in water and cannot be
easily precipitated, water is showered in the form of small droplets
followed by introduction of air and Fe2+ in the system. The As/Fe ratio
ranges from 16–50.
The air converts AS-III (arsenite) to AS—V (arsenate) and Fe2+ to
Hydrated Ferric Oxide (HFO) through oxidation.
Arsenate can easily be adsorbed to the particles of HFO while
remaining arsenic contaminated water is passed on to the absorbent
bed which contains activated alumina or some similar product for
further treatment.
The precipitation of HFO particles leads to the chocking of water
passage, therefore, the HFO chamber is cleaned everyday.
The average water flow from the system after treatment is 10-12
liters per minute.
Such arrangement can treat up to 10,000 bed volumes of arsenic
contaminated water.
Once the absorbent media is exhausted, it can be re-generated easily
and cheaply without disposal.

10. CO-PRECIPITATION, COAGULATION AND FILTRATION
Filtration plants in India

11. ARSENIC REMOVAL THROUGH FILTRATION
This process utilizes Mangnese Coated Sand (MCS) and Iron
Coated Sand (ICS) as filtration media for arsenic treatment through
oxidation and adsorption.
MCS not only oxidizes arsenite into arsenate but also adsorbs the
arsenate to diminish the contamination while ICS further adsorbs
the arsenate leaching from MCS.
A weight of 21.5 Kg of both MCS and ICS are poured into columns
having dimensions of 100 x 15 cm (Height x Width).
Arsenite solution introduced in the system is completely cleaned
by MCS for 18 days and ICS for 48 days. Overall, the treated water
contains the arsenic contamination level within the defined limits
of 50 µg/l for 148 days.
I Kg of MCS can oxidize 93 mg of arsenite for 61 days.

12. ARSENIC REMOVAL THROUGH FILTRATION
Filtration plant in India

13. PRECIPITATION & FILTRATION UNITS AT HOUSEHOLD SCALE
A simple precipitation and filtration model was used in several
households of Bangladesh.
The household filtration process included co-precipitation of
arsenic by adding a packet (approximately 2 g) of ferric and
hypochlorite salts to 20 L of well water and subsequent filtration
of the water through a bucket sand filter.
Ferric hydroxides were required with the Fe/As ratios of greater
than 40 (mg/mg) to reduce arsenic to less than 50 μg/l.
Experimental results obtained from the participating families
proved that the household treatment process removed arsenic
from approximately 87–313 μg/l in the well water to 1.9–21.8 μg/l in
the filtrate.
This process can be utilized in affected households in Pakistan as
well.

14. PRECIPITATION & FILTRATION UNITS AT HOUSEHOLD SCALE
Household Filters in
Bangladesh

15. ARSENIC REMOVAL BY ADSORPTION BASED TECHNOLOGIES
An iron hydroxide-doped activated carbon provides the
activated carbon an elevated active surface area for
arsenic adsorption.
It also helps to avoid the blockage of the activated carbon
pores.
The iron content of the modified samples ranged from
0.73 to 5.27%.
The smaller iron hydroxide particles exhibits an enhanced
arsenic adsorption capacity.
Other activated media successfully utilized in Bangladesh
and India for Arsenic treatment other than Carbon
includes Alumina, Layed Double Hydroxide (LDH), Natural
and Modified Zeolites & Clay and Laterite & Lemonite.

16. ARSENIC REMOVAL BY ADSORPTION BASED TECHNOLOGIES
Zeolite filter in Indian Village

17. CONCLUSION AND WAY FORWARD
According to a recent study, around 50-60 million people
of Pakistan living along the Indus Valley are consuming
arsenic contaminated water.
Since, there is little or no awareness in the local
community regarding arsenic related health problems,
people have a general belief that under-ground water is
normally safe to drink.
People must be educated and encouraged to get their
water tested in order to adopt precautionary measures in
case of arsenic contamination.
Since most of the rural filtration ideas & plants in India
and Bangladesh are developed indigenously with the
support of local donors and engineers, such practices
shall be exercised in Pakistan also.