Leaching of arsenic in response to organic matter contamination in groundwater treatment practice

Journal of Water and Environment Technology, Vol. 7, No. 1, 2009

Leaching of arsenic in response to organic matter contamination in
groundwater treatment practice
Khondoker Mahbub Hassan 1) *, Kensuke Fukushi 2), Fumiyuki Nakajima 3), Kazuo Yamamoto 3)

1) Department of Urban Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656,
Japan. (e-mail: ) *Corresponding author
2) Integrated Research System for Sustainability Science (IR3S), The University of Tokyo, 7-3-1 Hongo,
Bunkyo-ku, Tokyo 113-8654, Japan. (e-mail: )
3) Environmental Science Center, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
(e-mail: ; )

ABSTRACT
A large number of drinking water treatment units have been installed in many regions adopting the technique of
arsenic removal through adsorption and co-precipitation with the naturally occurring iron in groundwater and
subsequent sand filtration. This study revealed the consequence of the organic matter inclusion on the arsenic
treatment process for drinking water. Laboratory investigation confirmed that the organic contamination in the
treatment process impeded the arsenic removal efficiency depending on the types and concentrations of the
organic matters. The impact of organic matter contamination on the arsenic removal efficiency was almost
immediate and the autoclaved examination showed similar results. Nevertheless, the bioleaching of arsenic, 93
μg/L, from the accumulated sludge in the filter bed was observed under the inoperative condition, for 7 days, of
the treatment unit. However, in the control observation (using organic matter plus antibiotic) the effluent arsenic
concentration was found to be less than 30 μg/L. The effluent iron concentration in the bioleaching process was
not worth mentioning and found to be less than 0.22 mg/L. In this study, the chemical and biological
consequences of the organic matter contamination on the arsenic removal practice is elucidated, which might
contribute in designing safe options for drinking water.

Keywords: Arsenic removal, groundwater, organic matter

INTRODUCTION

Arsenic, the world’s most hazardous chemical is found to exist within the shallow zones of
groundwater of many countries in various concentrations. Arsenic contamination in water has
posed severe health problems around the world. With newer-affected sites discovered during
the last decade, a significant change has been observed in the global scenario of arsenic
contamination, especially in Asian countries. Before 2000, Bangladesh, West Bengal in India
and sites in China were the major incidents of arsenic contamination in groundwater. Between
2000 and 2005, arsenic-related groundwater problems have emerged in different Asian
countries, including new sites in China, Mongolia, Nepal, Cambodia, Myanmar, Afghanistan,
DPR Korea, and Pakistan (Mukherjee et al., 2006). There are reports of arsenic contamination
from Kurdistan province of Western Iran and Vietnam where several million people may
have a considerable risk of chronic arsenic poisoning. During 1998, 41 of the 64 districts in
Bangladesh were identified as having concentrations of arsenic in groundwater exceeding 50
μg/L (Sengupta et al., 2003) and about 50% of the installed hand tubewells were reported to
have high arsenic concentrations (Rahman and Ishiga, 2003). It is apparent from the current
arsenic research in China that the epidemic area is still expanding. Recent updates on chronic
arsenicism in PR China (Xia and Liu, 2004) state that, up to now, chronic arsenicism via
drinking-water is found in Taiwan, Xinjiang, Inner Mongolia, Shanxi, Ningxia, Jilin, Qinghai,
Received November 21, 2008, Accepted January 27, 2009.
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Journal of Water and Environment Technology, Vol. 7, No. 1, 2009

and Anhui provinces, and in certain suburbs of Beijing. In a long-term survey on 140,150
water samples from hand-tubewells in West Bengal it was found that 48.2% had arsenic
concentrations of >10 μg/L (WHO guideline value for drinking water) and 23.9% had >50
μg/L (Mukherjee et al., 2006). Arsenic contaminations of the Red River Delta in Hanoi city
and the surrounding rural districts of Vietnam were first reported in 2001 (Berg et al., 2001).
Analysis of raw groundwater pumped from the lower aquifer for the Hanoi water supply
showed arsenic levels of 240–320 μg/L in three of eight arsenic treatment plants. In

Cambodia, the natural arsenic originates from the upper Mekong basin, and is widespread in
soils. Within the lower Mekong delta, 5.7% of all groundwater samples exceeded 50 μg/L,
while 12.9% exceeded 10 μg/L (Stagner et al., 2005). A small-scale health survey conducted
in Myanmar in 2002 reported that 66.6% of the water samples from wells have arsenic levels
of >50 μg/L (Tun, et al., 2002). In 1987, skin manifestations of chronic poisoning of arsenic
were first diagnosed among the residents of Ronpibool district of Thailand (Choprapawon
and Rodcline, 1992). The people of this district use water, which drains from the highlycontaminated areas of the Suan Jun and Ronna Mountains having 0.1% arsenopyrite.
Mobility of arsenic is primarily controlled by sorption onto metal oxide surfaces and the
scope of this sorption is highly influenced by the presence of organic matter. Ligand
exchange-surface complexation, between carboxyl/hydroxyl functional groups of organic
matter and metal hydroxides, was found as the dominant interaction mechanism, under
circumneutral pH conditions (Gu et al., 1994). Therefore, they tend to compete with arsenic
anions for adsorption to the solid surfaces (Xu et al., 1988). Redman et al. (2002) proposed
that aqueous organic-metal complexes may, in turn, associate strongly with dissolved arsenic
anions, presumably by metal-bridging mechanisms, diminishing the tendencies of such anions
to form surface complexes. However, organic decomposition due to microbial action may
lead to anaerobic conditions and hence anaerobic bacteria can greatly affect the mobilization
of arsenic from the associated solid phase by either an indirect or a direct mechanism (Zobrist
et al., 2000). The former is the reductive dissolution of iron hydroxide minerals, leading to the
release of associated arsenic into solution. The latter is the direct reduction of arsenate
associated with a solid phase to the less adsorptive arsenite. The reaction is energetically
favorable when coupled with the oxidation of organic matter because the arsenate/arsenite
oxidation/reduction potential is +135 mV (Oremland and Stolz, 2003). Organic matter is
ubiquitous in natural waters and typically found at TOC (total organic carbon) concentrations
between 1 and 50 mg/L (Redman et al., 2002). The water with 50 mg/L of TOC is not
appropriate for drinking water treatment. Due to lack of other options/sources, groundwater
with high organic contamination is even used in drinking water treatment in the rural areas of
Bangladesh. Moreover, the concentration of organic matter is sometimes unnoticed in the
installation process of the treatment unit.
Several techniques were reported for the removal of arsenic from groundwater including

physicochemical and biological treatments and membrane filtrations (Dang et al., 2008).
Based on the established biological iron oxidation from groundwaters (Dimitrakos et al.,
1992), arsenic removal by adsorption and co-precipitation onto the flocs of iron hydroxides
and subsequent sand filtration has become a very popular technique. Moreover, there was an
indication of arsenite oxidation by iron oxidizing bacteria, leading to improved overall
removal efficiency (Katsoyiannis and Zouboulis, 2004). Adopting this technique, different
types of arsenic and iron removal units (AIRU) were designed and installed in many regions
(Figure 1). Organic matters, present in groundwater and also from unsanitary operation and
maintenance of the AIRU might hamper the arsenic removal efficiency. The water quality in
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Journal of Water and Environment Technology, Vol. 7, No. 1, 2009

real field situation includes inorganic anions, cationic metals and both the inorganic forms of
arsenic (arsenate and arsenite) along with organic contaminants. All these constituents are
potentially important factors influencing the arsenic removal efficiency, depending on their
mutual interactions in the aquatic environments of treatment units. Many researchers have
focused on the quantitative influence of several inorganic competing ions for the removal of
arsenic from groundwater (Meng, et al., 2001, Stollenwerk, et al., 2007). However, the
harmful consequence of arsenic mobility due to the organic contamination in the AIRU
treatment process is still unrecognized and needs to be investigated properly to ensure
effective remediation strategies. In this study, the consequence of organic matter inclusion in
feed water of the AIRU on the removal performance of arsenic and iron has been elucidated.
Both the chemical and the biological phenomena related to this issue were addressed.
Stirring
Raw Water
Pump

150 cm

Raw water
(As-Fe)
Treated
water

Gravel

Pea-gravel

Sand filter

Treated
water

Sand Filter
Sand Filter

Sand filter

300 mm

Treated
water

Strainer
30 cm
Community-type AIRU
Community-

Dia, Φ = 25 mm

Household-type AIRU
Household-

Lab-scale AIRU
Lab-

Figure 1. Typical arsenic and iron removal units (AIRU)
MATERIALS AND METHODS
Field study
Preliminary minor-scale field inspection was made in Bangladesh to presume the level of
organic matter contaminations in the existing arsenic and iron removal units and their
removal performances. The collection procedure of water samples, the water quality
parameters tested and the method used for analysis are summarized in Table 1.
Table 1 Summary of the procedures and methods for sampling and analyses of selected water
quality parameters in this study
Water Quality
Parameters

Sampling
Procedure

Container

Storage time /
Temperature

Method

Trace Metals:
Fe, As

-Acidifying with HNO3
(pH <2)

Plastic

< 7 days

ICPMS

Organic Matter:
TOC

-Acidifying with HCl
(pH <2) and refrigeration

Glass

< 7 days / 4ºC

High-temperature
combustion catalyzed
oxidation

ICPMS = Inductively Coupled Plasma Mass Spectrometry; TOC = Total Organic Carbon.

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Journal of Water and Environment Technology, Vol. 7, No. 1, 2009

Laboratory study
Laboratory-scale AIRU was designed and tested under variable dosages of organic matters. In
order to minimize the hazardous and toxic waste generation during the research activity in the
laboratory, a small cross-sectional area (diameter, φ = 25mm) was taken into consideration
for the development of the AIRU (Figure 1). The raw water was kept stirred to avoid any
deposition of the particles in the upper tank. Then, the raw water was fed to the sand filter
reactor using a pump and hence the concentrations of arsenic and iron were similar to the
input dose. The sand (effective size, D10 = 0.4 mm; uniformity coefficient, UC = 1.7) filter bed
having a depth of 300 mm was used. The filtration rate was kept around 0.6 ~ 0.7 m/hr, which
is the highest permissible filter loading rate for slow sand filtration (Montogomery, 1985). It
is evident from several studies that the overall arsenic removal performance in the AIRU
treatment process was mainly contributed by arsenate [As(V)] in the influent water, due to its
high adsorption capacity with iron hydroxide solid phase (Katsoyiannis and Zouboulis, 2004).
Thus, the contaminated groundwater was prepared artificially using arsenate (H3AsO4) and
ferrous sulphate (FeSO4. 7H2O) in Milli-Q water and then the pH was adjusted to 7 by using
sodium hydroxide (NaOH) reagent. Several studies identified that the organic matter
contamination in groundwater of the shallow reducing aquifer is frequently combined with
high concentrations of nitrogen and phosphorus (Bhattacharya, et al., 2001, Stollenwerk, et al.,
2007). The source of this contamination was suspected to be the wastewater from pit latrines
as well as the grey water, which was highly biodegradable. Thus, in laboratory study, the
simulated wastewater was prepared, using tryptone (T), yeast extract (Y) and glucose (G) in
pure water, following standard methods (2005) for plate count (G:Y:T ≡ 1:2.5:5 wt/wt)
excluding agar, which would give a preferable environment for the growth of bacteria.
Laboratory reagent-grade chemicals from Becton, Dickinson and Company (BD), USA were
used in the above preparation. Moreover, humic acid, constituting the major part of organic
contents in groundwater, was used separately to find its impact on the arsenic and iron
removal performances in AIRU. Humic acid reagent-grade chemicals from Aldrich, USA was

used in this study. Each organic contamination dosage was maintained for 10 bed volumes
(volume of permeate/volume of filter bed) of effluent water and within this period, the
removal efficiency was found to become almost stable. The sampling was done at the 10th bed
volume of effluent water in the AIRU. In the real field situation, the AIRU is usually operated
in both the “continuous flow” and the “intermittent flow” modes and occasionally it is kept
inoperative for a few days. The microbial decomposition of organic matter would most likely
happen in the inoperative condition of the AIRU. In the biodegradation process of organic
matter, the aerobic oxidation is preceding the other reactions, because oxygen reducers would
derive more energy from the substrate than the iron and arsenic reductions. The depletion of
dissolved oxygen due to microbial action may lead to an anaerobic condition within the
accumulated sludge in the filter bed and hence would cause the bioleaching of arsenic. Thus,
the bioleaching of arsenic, in the presence of organic matter, was observed under the
inoperative condition of the laboratory-scale AIRU. Subsequently the water samples were
collected from the outlet of the effluent pipe for the laboratory analyses. In another
observation, antibiotic (tetracycline hydrochloride, 8 mg/L) was added to control the
microbial activity in the bioleaching process.
Analytical techniques
Laboratory analyses for total arsenic and iron concentrations in water samples were carried
out by inductively coupled plasma mass spectrometry (ICP-MS, HP 4500, Yokogawa), which
allowed detection of arsenic and iron species with limits of 0.3 μg/L and 0.1 μg/L,
respectively. For the ICP-MS analysis, the water samples were digested in a closed
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Journal of Water and Environment Technology, Vol. 7, No. 1, 2009

microwave system (Multiwave 3000, Perkin-Elmer) in 10% HNO3 solution and in
temperature range of 165 ±5 ºC for 20 minutes following the standard methods (2005). After
digestion, the water samples were adjusted to 1% HNO3 concentration and filtered through
0.45 μm PTFE filter for the analysis of arsenic and iron using ICP-MS. For the isobaric

interference of ArCl+ in the arsenic analysis, the EPA recommended corrections (EPA
Method 200.8) were applied. The organic matter concentrations in stock solution and in other
water samples were determined by using a total organic carbon analyzer (TOC-VCSH,
Shimadzu), which allowed detection limit of 0.4 mg/L as TOC. The value of pH was
measured using a pH meter (HACH Co., USA). Dissolved oxygen (DO) concentrations
within the accumulated sludge in sand filter bed as well as in liquid phase of the laboratoryscale AIRU were observed using a microelectrode with a 10 μm tip diameter and a
micromanipulator having a vertical resolution of 10 μm (OX10, MM33-2, Unisense).
Standard methods (2005) were followed in all laboratory analyses of the test samples.
RESULTS AND DISCUSSION
Field inspection of the treatment units
Influent and effluent water samples from the six AIRUs (I~VI) at the field level were
collected from arsenic-contaminated groundwater areas in Bangladesh. Laboratory analyses
of the field water samples identified that most of the groundwater sources had significant
organic contamination (Table 2). In AIRUs (I~IV), in spite of having adequate iron
concentrations of 3.4~6.9 mg/L in the influent water to enable adsorption and co-precipitation
of arsenic, the effluent arsenic concentrations were beyond 50 μg/L, which is the acceptable
limit of Bangladesh standards for drinking water. In these cases, high concentration of
organic matters, 25.8~51.4 mg/L as TOC, were observed in the influent water. Several studies
reported that the dissolved organic carbon (DOC) concentrations in groundwater from
reducing aquifers in Bangladesh range from 1 to 15 mg/L (BGS and DPHE, 2001,
Bhattacharya et al., 2002, Anawar et al., 2003). The unusually high concentration of organic
matter in the studied groundwater from shallow aquifer might be due to the anthropogenic
contamination from pit latrines as well as the grey water in the rural environment. High
organic concentrations in the influent water might hamper the arsenic treatment process, and
ultimately high concentration of arsenic would appear with the effluent water.
Table 2 Effect of influent organic matter contaminations on the arsenic removal performance
through field-AIRUs in Bangladesh
Influent Water Qality
Effluent Water Quality
pH

As (μg/L) Fe (mg/L) TOC (mg/L) As (μg/L) Fe (mg/L) TOC (mg/L)
I
6.9
202
5.5
51.4
85
0.2
45.1
II
7.1
211
5
38
99
0.8
<0.4
III
7.0
199
6.9
28.1
56
1.2
<0.4
IV
7.0
182
3.4
25.8

83
0.1
<0.4
V
7.1
98
2
<0.4
39
0.1
0.7
VI
7.0
160
5
<0.4
32
0.6
<0.4
AIRU-I was a household-type unit while all other AIRUs (II~VI) were community-type units
Field-AIRUs

On the other hand, for AIRUs (V and VI) in a different locality, which were free from organic
contamination and having iron concentrations of 2 mg/L and 5 mg/L, respectively in the
influent water could satisfactorily treat the arsenic concentration less than 40 μg/L in the
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Journal of Water and Environment Technology, Vol. 7, No. 1, 2009

effluent water. The removal efficiency of TOC was found to be extraordinarily high in the
community-type AIRUs (II~IV) because of its far-extended hydraulic retention time in
comparison with the household-type AIRU-1. Another study on the AIRU treatment process
in Bangladesh, suggested that the removal efficiency was significantly influenced by the raw
water concentrations of both arsenic and iron and in this context a relationship was
established (Ahmed, 2001). Following this relationship, the removal efficiency of arsenic in
our studied AIRUs (II and VI), having the same concentration of iron in the raw water, were
estimated to be 74% and 77%, respectively. However, in our study they were found to be
53% and 80%, respectively. Considerably less arsenic removal efficiency in AIRU-II from its
estimated value might be due to the presence of high concentration of organic matter in the
raw feed water. Clear evidence was not obtained from this limited field survey. The smallscale field investigation was carried out only to presume the level of organic contamination in
the existing AIRUs and the treatment performance. A precise and large-scale spatial survey
was required to represent the real field situation of the above aspect. Considering the
requirements of resources and time related to the precise field survey and the potential human
health-risk related to the organic contamination in AIRUs, laboratory experiments were
carried out using artificially contaminated groundwater in the simulated AIRU.
Performance of the laboratory AIRU
The removal efficiency of arsenic and iron in the developed AIRU at the laboratory was
monitored in controlled condition where organic contamination was totally avoided. Arsenic
and iron concentrations in effluent water never exceeded 15μg/l and 0.1mg/l, respectively
from their influent concentrations of 500μg/l and 5mg/l, respectively indicating removal
efficiencies over 97% for arsenic and 98% for iron (Figure 2).

0.20

Iron concentration
Arsenic concentration

15

0.15

10

0.10

5

0.05

0

Effluent iron concentration (mg/L)

Effluent arsenic concentration (μg/L)

20

0.00
01

20

40

60

80

100

Effluent bed volume (BV)

Figure 2. Arsenic and iron removal performances in laboratory-scale AIRU (control) which
was free from organic contamination. Arsenic and iron were spiked in influent water to
concentrations of 500 μg/L and 5 mg/L, respectively. Column values represent the average of
triplicate samples, and error bars show the range of standard deviation.
Such a high arsenic removal performance in the laboratory-scale AIRU, in comparison to the
field-AIRUs data shown in Table 2 (V and VI), was achieved due to using arsenate for the
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Journal of Water and Environment Technology, Vol. 7, No. 1, 2009

preparation of synthetically contaminated feed water. This is because, the adsorption affinity
of arsenate onto iron hydroxide solid phase is much higher than that of arsenite, which is also
an associated contaminant in most arsenic-affected groundwater. Moreover, other anions
(phosphate, sulfate, silicate, bicarbonate, nitrate etc.), influencing the sorption process of
arsenic in the AIRU treatment process, were not present in the synthetic feed water. In the
laboratory-scale AIRU, the treatment performances for both the arsenic and iron were found
to be almost stable throughout the whole observation period of 100 bed volumes of effluent
water (standard deviation < 0.6% of removal efficiency). Slightly, higher removal
performance with increased bed volume of treated water was due to deposition of iron
hydroxides within the interstices of the filter bed media which provided increased adsorption
surfaces and mechanical straining as well.
Organic matter causes chemical leaching of arsenic in AIRU
The leaching of arsenic and iron in the presence of organic matter in AIRU feed water was
investigated under dosage-response observations in multiple sets of laboratory reactors. In
case of simulated wastewater organic contaminations of 15 mg/L and 30 mg/L as TOC in the
influent water of the AIRU, arsenic concentrations of 55 μg/L and 70 μg/L, respectively were

observed in the effluent water (Figure 3). In the absence of organic contamination, however,
effluent arsenic concentration never exceeded 15 μg/L (Figure 2). The TOC removal
efficiency was found to be less than 8% in the laboratory-scale AIRU (Table 3). Thus, two
major phenomena would be related to the decrease in arsenic removal efficiency in response
to organic matter inclusion in the feed water of the AIRU. Firstly, some portion of arsenic
could not form surface complexes with the iron hydroxide solid phase due to the competitive
adsorption by organic matters and finally released in the effluent water. Secondly, some part
of the dissolved arsenic anions combined with the aqueous organic-metal complexes and
eventually came out with the effluent water.

Effluent arsenic concentration (μg/L)

100
Humic acid
Simulated wastewater
75
Sampling in 10 BV
of effluent water

50

25

0
15
30
Influent organic concentration in AIRU (mg/L TOC)

Figure 3. Effect of influent organic matter (humic acid and simulated wastewater)
contamination on the removal performance of arsenic in the laboratory-scale AIRU. Arsenic

and iron were spiked in influent water to concentrations of 500 μg/L and 5 mg/L, respectively.
Sampling was done at the 10th bed volume (BV) of effluent water.

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Journal of Water and Environment Technology, Vol. 7, No. 1, 2009

Table 3 Concentration of organic matters in the influent and effluent waters of the laboratoryscale AIRU
AIRU Influent Water
HA (mg/L as TOC) SWW (mg/L as TOC)
15
15
30
30

AIRU Effluent Water
HA (mg/L as TOC) SWW (mg/L as TOC)
13.7
13.9
28.1
28.5

HA: Humic Acid; SWW: Simulated Waste Water.

Typically, the organic contents in groundwater are mostly contributed by humic substances.
Thus, the impact of humic acid contamination on the arsenic removal performance in AIRU
was also studied. The concentration of arsenic with effluent water in this case was found to be
less in comparison to previously used simulated wastewater, possibly due to having fewer
adsorption sites in higher molecular weight humic acids. The functional groups of the organic

matter molecules deprotonate at different pH conditions. At low pH values, they are
protonated and uncharged with a tightly coiled and cross-linked conformation, but at high pH
values, they are dissociated and become negatively charged with a more open conformation.
At the neutral pH value, some functional groups were reported to become negatively charged
(Stevenson, 1982). The occurrence of negative charges and open conformation enables
organic matter to be adsorbed onto positively charged reactive sites at the surface of metal
hydroxides. Regardless of the concentration and type of the organic matter inclusion in the
AIRU feed water, the arsenic removal efficiency over 85% was achieved in the laboratory
study (Figure 3), possibly due to the partially charged functional groups of the organic matter
molecules. On the other hand, iron concentration with effluent water was found to be higher
in the case of humic acid contamination (Figure 4), possibly due to the delay in the
precipitation process of iron hydroxides.
1.00
Effluent iron concentration (mg/L)

Humic acid
0.80

0.60

Simulated wastewater

Sampling in 10 BV
of effluent water

0.40

0.20

0.00

15
30
Influent organic concentration in AIRU (mg/L TOC)

Figure 4. Effect of influent organic matter (humic acid and simulated wastewater)
contamination on the removal performance of iron in the laboratory-scale AIRU. Arsenic and
iron were spiked in influent water to concentrations of 500 μg/L and 5 mg/L, respectively.
Sampling was done at the 10th bed volume (BV) of effluent water.

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Journal of Water and Environment Technology, Vol. 7, No. 1, 2009

A physiochemical explanation for the decrease in hydration reaction has been proposed by
Ong and Bisque (1968) on the basis of the Fuoss-effect. Mutual repulsion of the negatively
charged functional groups of humic acid (carboxyls and hydroxyls) causes the polyelectrolyte
to adopt a stretched configuration. Cations like ferric ions attaching themselves to the
negatively charged groups cause a reduction in the intermolecular repulsion in the polymer
chain favoring coiling. Coiling expels a portion of the water of hydration that surrounds the
molecule, converting it from a hydrophilic to a hydrophobic colloid. Thus, the soluble
complexes of iron-humic substances were released in effluent water. Autoclaved experiment
for the inclusion of organic matter in the AIRU feed water, showed similar performance in the
removal of arsenic and iron. Moreover, in the continuous-flow mode of the AIRU (Figure 24), the dissolved oxygen concentration within the sand-filter bed was always found to be
greater than 6 mg/L. Thus, it was evident that the above leaching phenomena were chemical
rather than biological in nature.
Organic matter causes bioleaching of arsenic in AIRU
In the real field situation and especially for the household-type AIRU, sometimes it is kept
inoperative for few days when the family members go out for a trip. The bioleaching of
arsenic from the accumulated sludge in the filter bed was studied under the inoperative

condition of the laboratory-scale AIRU. Considering the favorable growth of the
microorganism, the simulated wastewater organic contamination was used. The initial
decreasing pattern of the effluent arsenic concentration (Figure 5) might be due to less stable
iron-arsenic complexes, which were driven out at the first stage. In addition to this, biological
iron oxidation (Dimitrakos et al. 1992) in aerobic condition would contribute to the greater
retention of iron-arsenic sludge.
Effluent arsenic concentration (μg/L)

200
Control (Simulated wastewater + Antibiotic)
Bioleaching (Simulated wastewater)
150

100

50

0
1

2

4

5

6

7

8

9

Inoperative time span of AIRU (days)

Figure 5. Effect of organic matter (simulated wastewater of 30 mg/L as TOC) contamination
on the bioleaching of arsenic from the accumulated sludge in filter bed under the inoperative
condition of the laboratory-scale AIRU.
However, significantly high concentration of arsenic, 93 μg/L on the 7th day of observation,
in the AIRU effluent water was noticed afterwards in the case of simulated wastewater
inclusion in feed water. In the course of the biodegradation of organic matter, aerobic
oxidation was expected to precede the other reactions because oxygen reducers would derive
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Journal of Water and Environment Technology, Vol. 7, No. 1, 2009

more energy (i.e., higher Gibbs free energy) from the substrate than the iron and arsenic
reductions. Thus, the depletion of dissolved oxygen due to microbial action led to an
anaerobic reducing environment within the accumulated sludge in the filter bed and hence
caused the bioleaching of arsenic by anaerobic bacteria. The ratio of [As (III)] / [As (V)]
concentrations in the effluent water was around 1.10 (data not shown.), indicating the
microbial reduction and dissolution of ferric hydroxide sorbing phase as well as the
dissimilatory arsenate reduction.
On the contrary, the effluent iron concentration in the bioleaching experiment was not worth
mentioning and it was always found to be less than 0.22 mg/L (data not shown). Thus, it may
be considered that the arsenic-iron sludge, retained mostly at the top portion of the sand filter
bed, caused the bioleaching of arsenate, arsenite and ferrous iron under anaerobic conditions.
While collecting the effluents, the aqueous ferrous iron, reduced in the bioleaching process,

re-oxidized to insoluble ferric form due to the intrusion of supernatant aerobic water into the
sand-filter bed and was trapped by the mechanical straining mechanism, whereas a significant
portion of arsenate and arsenite escaped due to inadequate iron hydroxide sorption sites at the
bottom part of the sand-filter bed, and they were eventually released in the effluent water. It
was also evident from other studies that arsenic release from contaminated soils and
sediments proceeds considerably faster under conditions favoring dissimilatory reduction of
ferric iron leading to the dissolution of sorbing phases (Langner and Inskeep, 2000) and the
reduction of arsenate plays a relatively minor role in the solubilization of arsenic sorbed to
iron hydroxides. In the case of the controlled microbial activity, using antibiotic in addition to
the simulated wastewater, the effluent arsenic concentrations were found to decrease
gradually. The sorption equilibrium, established in the arsenic-iron sludge, might be
interrupted due to the competing anions in the organic matter (Redman et al. 2002) and
consequently the desorbed arsenic would be released in the effluent water in the initial stage.

Dissolved oxygen concentration ( mg/L)

In the bioleaching experiment, the dissolved oxygen (DO) concentration was checked through
microelectrode studies (Figure 6) to verify the anaerobic condition within the accumulated
sludge in the filter bed of the AIRU.
10

8

6

4

2

Ai

3.
3

3.
0

2.
5

2.
0

1.
5

1.
0

0.
5

0.
1

r-s
at
ur
at
ed

Li
qu
id
ph
se

0

Depth in sand filter bed (mm)

Figure 6. Dissolved oxygen (DO) concentration profile in AIRU in the bioleaching
observation time on the 7th day.

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Journal of Water and Environment Technology, Vol. 7, No. 1, 2009

The theoretical value of the air-saturated DO concentration was 8.3 mg/L. In the course of the
biodegradation of organic matters, the oxygen was used up by bacteria and in the liquid phase
above the filter bed the DO concentration was found to be 5 mg/L. Within the sand-filter bed,
located at the bottom of the liquid phase, the reoxygenation rate was very slow through the
oxygen diffusion although the deoxygenation rate was similar. Moreover, the accumulation of
arsenic-iron sludge within the pore space of the water-saturated sand-filter bed, resulted in a
limited diffusivity of oxygen and hence shifted to an anaerobic condition within 3.3 mm
depth of the filter bed. Thus, it was evident that the bioleaching of arsenic from the
accumulated sludge in the sand-filter bed was executed through the activity of anaerobic
bacteria.
CONCLUSIONS
This study exposed the chemical and biological incidents concerning the consequence of

organic contamination on the AIRU treatment process for drinking water as outlined below:
In the continuous-flow mode of the AIRU, it was observed that the arsenic removal
efficiency was negatively impacted in response to organic matter inclusion in the feed
water. In comparison to the humic acid, the simulated wastewater organic matter was
found to be more unfavorable to the arsenic removal process. However, the effluent iron
concentration was found to be higher in the case of humic acid contamination. From the
autoclaved examination, it was evident that the related mechanism was chemical in nature.
In the course of the biodegradation process of organic matter under the inoperative
condition of the AIRU, an anaerobic condition was noticed within the accumulated sludge
in the filter bed. In anaerobic condition, high concentration of bioleached arsenic, over
100 μg/L, was observed with the effluent water. However, the effluent iron concentration
was found to be less than 0.22 mg/L. From the control observation (using organic matter
plus antibiotic), it was evident that the related mechanism was biological in nature.
Another important finding of this study is that, unusually high concentration of organic matter,
above 25 mg/L as TOC, in the feed water of the existing AIRU in Bangladesh and in this case
the effluent arsenic concentration was found to be greater than 50 μg/L.
ACKNOWLEDGEMENT
This work was supported by the Japan International Cooperation Agency (JICA), the
University of Tokyo, IR3S (through Special Coordination Funds for Promoting Science and
Technology, MEXT, Japan), and JSPS (Kakenhi) Project No: 18404011.
REFERENCES
Ahmed M.F. (2001). An overview of arsenic removal technologies in Bangladesh and India.
In: Technologies for Arsenic Removal from Drinking Water, BUET-UNU International
Workshop, Dhaka, Bangladesh.
Anawar H.M., Akai J., Komake K., Terao H., Yoshioka T. and Ishizuka T. (2003).
Geochemical occurrence of arsenic in groundwater of Bangladesh: sources and
mobilization processes. J. Geochem. Explor. 77, 109–31.
Berg M., Tran H.C., Nguyeu T.C., Pham M.V., Scherteuleib R. and Giger W. (2001). Arsenic
contamination of groundwater and drinking water in Vietnam: a human health threat.
Environ. Sci. Technol., 35, 2621-2626.

- 39 -


Journal of Water and Environment Technology, Vol. 7, No. 1, 2009

BGS [British Geological Survey] and DPHE [Department of Public Health Engineering,
Bangladesh] (2001). Arsenic contamination of groundwater in Bangladesh. In:
Kinniburgh D.G., Smedley P.L., editors. BGS Technical Report WC/00/19.
Bhattacharya P. and Mukherjee A.B. (2001). Arsenic in groundwater in the Bengal Delta
Plain: slow poisoning in Bangladesh. Environ. Rev., 9, 189-220.
Bhattacharya P., Jacks G., Ahmed K.M., Routh J. and Khan A.A. (2002). Arsenic in
groundwater of the Bengal delta plain aquifers in Bangladesh. Bull. Environ. Contam.
Toxicol., 69, 538–545.
Choprapawon C. and Rodcline A. (1992). Chronic arsenic poisoning in Ronpibool Nakhon
Sri Thammarat, the southern province of Thailand. In: Arsenic exposure and health effects,
C.O. Abernathy, R.L. Calderon and W.R. Chappell (eds). New York, Chapman-Hall, 6977.
Dang S.V., Kawasaki J., Abella L.C., Auresenia J., Habaki H., Gaspillo P.D. and Kosuge H.
(2008). Removal of arsenic from synthetic groundwater by adsorption using the
combination of laterite and iron-modified activated carbon. J. Water and Environ.
Technol., 6(1), 43-54.
Dimitrakos G., Martinez N.J., Vayenas D. and Lyberatos G. (1992). Removal of iron from
potable water using a trickling filter. Water Res., 31(5), 991-996.
Gu B., Schmitt J., Chen Z., Liang L. and McCarthy J.F. (1994). Adsorption and desorption of
natural organic matter on iron oxide: mechanisms and models. Environ. Sci. Technol., 28,
38–46.
Katsoyiannis I.A. and Zouboulis A.I. (2004). Application of biological processes for the
removal of arsenic from groundwaters. Water Res., 38, 17-26.
Langner H.W. and Inskeep W.P. (2000). Microbial reduction of arsenate in the presence of
ferrihydrite. Environ. Sci. Technol., 34, 3131–3136.

Meng X., Korfiatis G.P., Christodoulatos C. and Bang S. (2001). Treatment of arsenic in
Bangladesh well water using a household co-precipitation and filtration system. Water
Res., 35(12), 2805-2810.
Montogomery J.M. (1985). Water Treatment Principles and Design, John Willy & Sons.
Mukherjee A., Sengupta M.K., Hossain M.A., Ahamed S., Das B., Nayak B., Lodh D.,
Rahman M.M. and Chakraborti D. (2006). Arsenic Contamination in Groundwater: A
Global Perspective with Emphasis on the Asian Scenario. J. Health. Popul. Nutr., 24 (2),
142-163.
Ong H.L. and Bisque R.E. (1968). Coagulation of humic colloids by metal ions., Soil Science,
106, 220-224.
Ormland R.S. and Stolz J. F. (2003). The ecology of arsenic. Science, 300, 939-944.
Rahman M.H. and Ishiga H. (2003). Arsenic pollution in soil and groundwater of Bangladesh.
J. Water and Environ. Technol., 1, 125-131.
Redman A.D., Macalady D.L. and Ahmann D. (2002). Natural organic matter affects arsenic
speciation and sorption onto hematite. Environ. Sci. Technol., 36, 2889-2896.
Sengupta M.K., Mukherjee A., Hossian M.A., Ahamed S., Rahman M.M. and Lodh D.
(2003). Groundwater arsenic contamination in the Ganga-Padma-Meghna-Brahmaputra
plain of India and Bangladesh. Arch. Environ. Health, 58, 701-712.
Stagner G., VanTroung T., Le Thi My Ngoc K.S., Luyen T.V. and Thanh T.T. (2005).
Arsenic in groundwaters of the Lower Mekong. Environ. Geochem. Health, 27, 341-357.
Standard Methods for Examination of Water and Wastewater (2005). 21st edn, American
Public Health Association/American Water Works Association/Water Environment
Federation, Washington DC, USA.

- 40 -


Journal of Water and Environment Technology, Vol. 7, No. 1, 2009

Stevenson F.J. (1982). Humus Chemistry; Genesis, Composition, Reactions. New York,

Wiley-Inter-science.
Stollenwerk K.G., Breit G.N., Welch A.H., Yount J.C., Whitney J.W., Foster A.L., Uddin
M.N., Majumder R.K. and Ahmed N. (2007). Arsenic attenuation by oxidized aquifer
sediments in Bangladesh. Sci. Total Environ., 379, 133-150.
Tun M.K. (2002). A report on assessment of arsenic content in groundwater and the
prevalence of arsenicosis in Thabaung and Kyonpyaw townships, Ayeyarwaddy division,
Yangoon: Clinical Research Division, Department of Medical Research, 9-19.
Xia H. and Y, Liu J. (2004). An overview on chronic arsenicism via drinking water in PR
China. Toxicology, 198, 25–29.
Xu H., Allard B. and Grimvall A. (1988). Influence of pH and organic substance on the
adsorption of As(V) on geological materials. Water Air Soil Pollut., 40, 293–305.
Zobrist J., Dowdle P. R., Davis J. A. and Oremland R. S. (2000). Mobilization of arsenite by
dissimilatory reduction of adsorbed arsenate. Environ. Sci. Technol., 34, 4747-4753.

- 41 -