Fretagsmte

1
Groundwater Governance in Theory and Practice
Managing arsenic contamination of groundwater
Managing arsenic contamination of groundwater
Part IV
Indian Institute of Technology, Roorkee, India,
November 11, 2006
2
Outline of the lecture
Management and remediation of arsenic
contaminated water

• Conventional technologies
• Coagulation
• Electro-remediation with adsorption on
  activated alumina
• Ion exchange with resins with strong base
• Reverse osmosis

3
Outline of the lecture
Management and remediation of arsenic
contaminated water

• Emerging Technologies
• Fe-oxides as adsorbent
• In-situ remediation with passive reactive
  barriers
• bioremediation with chemical precipitation
• Oxygenation of the aquifers
• Low cost technologies for developing countries
• auto-attenuation
• use of geological materials as natural
  adsorbents
• Artificial recharge
• Bacterial iron oxidation

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Management and remediation of arsenic
contaminated water
(1)

• The removal of As from water is an important
  worldwide issue.
• Incidences of elevated As concentrations in
  groundwater in developing countries with poor
  infrastructure, demands technologies that
  cost-effective for the provision of safe drinking
  water to the affected population.
• Several technologies are available to remove As
  from water, ranging from sophisticated technology
  such as ion exchange and reverse osmosis to the
  much simpler, and often highly effective
  coagulation-flocculation techniques.

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Management and remediation of arsenic
contaminated water
(2)

• The majority of the contaminated water
  remediation techniques are based on mechanisms
  that involve an initial oxidation of AsIII to AsV
  and subsequent precipitation using chemicals.
• If AsIII is present in the influent, then an
  oxidant such as chlorine (Cl2), potassium
  permanganate (KMnO4), or oxygen (O2) is typically
  used to oxidize AsIII to AsV prior to As removal.
  Coagulation, absorption to activated alumina,
  ion exchange with strong-base anion exchange
  resins, and reverse osmosis are conventional
  technologies that have been used to treat As
  contaminated water.

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Management and remediation of arsenic
contaminated water
(3)

• The use of new adsorbents, in-situ passive
  reactive barriers, bioremediation with chemical
  precipitation, and aquifer oxygenation are some
  of the emerging technologies for the insitu
  removal of As from groundwater.
• In addition, many low cost technologies for As
  removal in the developing world are also being
  researched keeping in view the sustainability and
  peoples participation in the treatment systems

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Conventional technologies for treating arsenic in
water
Coagulation

• Conventional coagulation involves the formation
  of large, non-dispersed particles from a colloid,
  such as hydrated Fe2(SO4)3, and a solute, such as
  H2AsVO4-.
• The highest removal rates were observed when
  ferric sulfate was mixed with chlorinated water
  at pH 8 or less.
• Conventional coagulation of 50 µg/L of AsV with
  30 mg/L of ferric sulfate (Fe2(SO4)3) at pH 8 or
  below removed greater than 95 percent
• Conventional coagulation of 50 µg/L of AsV with
  40 mg/L of ferric sulfate (Fe2(SO4)3) at pH 7.5
  removed 99.9 percent As while leaving less than 1
  µg/L of dissolved As after treatment.

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The effects of pH and chlorination on
arsenic removal by ferric sulfate and alum
Ex-situ processes
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Effect of pH on arsenic removal by lime softening
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Conventional technologies for treating arsenic in
water
Sorption to activated alumina

• Activated alumina (Al2O3) strongly sorbs
  arsenate (AsV). As saturated activated alumina
  can be regenerated by anion exchange with OH-.
• Activated alumina process involves removal,
  backwash, regeneration, neutralization, and steps
  of rinsing.
• The equilibrium capacities of activated alumina
  for AsV were maximized at pH values less than 7,
  while AsIII was best removed at pH values less
  than 9.
• Activated alumina and As slowly reach
  equilibrium.

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Conventional technologies for treating arsenic in
water
Ion exchange with strong-base anion exchange
resins

• Limited testing has been done with strong-base
  anion exchange resins. The initial cost of the
  resin will probably be higher than activated
  alumina, but the lower cost of regeneration with
  sodium chloride (NaCl) may make strong-base anion
  exchange resins more cost effective than
  activated alumina.

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Conventional technologies for treating arsenic in
water
Reverse osmosis

• Reverse osmosis (RO) requires external pressure
  to reverse natural osmotic flow. As pressure is
  applied to the saline solution, water flows from
  a more concetrated saline solution through the
  semipermeable membrane.
• RO membrane has a thin microporous surface that
  rejects impurities, but allows water to pass
  through.
• The membrane rejects bacteria, pyrogens, and
  85-95 of inorganic solids, especially the
  polyvalent ions such as As oxyanions are rejected
  more efficiently than the monovalent ions.
• The effectivity of the RO process depends on the
  chemistry of the inlet water. Efficacy of RO
  ranges over a wide range of pH (pH 3-11).

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Management and remediation of arsenic
contaminated water
Emerging Technologies

• Fe-oxides as adsorbent
• In-situ remediation with passive reactive
  barriers
• bioremediation with chemical precipitation
• Oxygenation of the aquifers

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Emerging Technologies
Fe-oxide as an absorbent

• The strong affinity for As by Fe-oxide surfaces
  has also been widely used in the water
  purification processes.
• New adsorbents are developed for the removal of
  AsIII and AsV ions from synthetic and deep-well
  waters using Al2O3 and/or TiO2 coated with
  freshly precipitated FeIII(OH)3.
• Removed both AsIII and AsV ions by chemical
  reactions on the surface of the FeIII(OH)3.

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Emerging Technologies
Fe-oxide as an absorbent

• Similar to the reaction between the H2PO4- and
  Fe(OH)3 precipitates, the neutral functional
  group of FeOH reacts with H2AsO3- ions and
  surface compounds of FeAsO3H2 FeAsO3H- and
  FeAsO can be formed.
• Water treatment plants worldwide use such
  chemical fixation processes.
• However, such processes may prove expensive in
  developing countries where the effectiveness of
  the process is dependent on the local
  availability of the necessary materials.

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Emerging Technologies
In-situ remediation using passive reactive
barriers

• Arsenic can be removed from groundwater is the
  use of Fe oxide containing materials as passive
  reactive barriers.
• This type of treatment offers a low-cost
  alternative for the removal of As from pollution
  plumes.
• Experimental results from laboratory column
  experiments using a reactive barrier containing
  spodic B horizon material showed that As
  concentration was reduced from
• 1-3 mg As/L to lt 0.2 mg As/L over a period of 92
  days

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Emerging Technologies
In-situ remediation using passive reactive
barriers

• Laboratory studies at the CSIRO, Adelaide,
  Australia indicated that pyritic and oxidic
  materials sorbed between 2500 and 5000 mg/kg of
  AsV respectively, indicating that these cheap and
  easily obtained materials may be also suitable as
  alternative barrier wall materials.
• Although there has been some concern on the long
  term stability of sorbed As over time, it has
  been reported that as long as a high Fe-As ratio
  is maintained, ferric arsenates may be extremely
  insoluble and useful for the safe disposal of As.

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Emerging Technologies
Column studies of AsV sorbed by Fe and Al
containing materials
Oxisol
Pyrite
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Emerging Technologies
Bioremediation with chemical precipitation

• Another technique reported recently combines
  bioremediation and chemical precipitation
  processes to remove As.
• The potential for a biological treatment process
  to remove elemental As and arsenide under
  reducing conditions and as precipitates of iron
  hydroxides under oxic conditions.
• As contaminated groundwater was subjected to
  aerobic, aerobic-anaerobic bioreactor systems and
  through a cell containing FeCl3.

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Emerging Technologies
Bioremediation with chemical precipitation

• When the bioreactor was operated only under
  aerobic conditions, the concentration of As in
  groundwater remained unchanged.
• Under combined aerobic and anaerobic conditions,
  As concentrations in the groundwater were reduced
  by more than 70 in the first anaerobic cell and
  by another 50 in the second anaerobic cell.
• The addition of FeCl3 to the second cell was
  found to increase the total removal of As up to
  99.7.

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Emerging Technologies
Bioremediation with chemical precipitation

• The enhanced removal of As was attributed to
  precipitation of the most oxidized form of As
  (AsV) with FeIII. The optimum separation is
  controlled by pH in the anaerobic cell.
• Another process of As removal is based on
  chemical oxidation, followed by coagulation of As
  with Fe-Mn oxidation or softening plants.
• In this process soluble AsV removal efficiency
  was primarily controlled by pH during coagulation
  by FeII oxidation and Fe(OH)3 precipitation
  during Fe-Mn oxidation and by Mg(OH)2 formation
  during the softening process.

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Emerging Technologies
Aquifer oxygenation

• Arsenic has been successfully removed from
  groundwater by injecting air or oxygen into the
  aquifer to precipitate arsenate (AsV) in the
  aquifer at a Superfund site.
• This might be an attractive approach for
  treatment in certain geologies since capital and
  operational costs are relatively low.
• However, this approach requires extensive
  site-specific geological and hydrogeological
  investigations in order to confirm the
  effectiveness of the approach, and to design the
  system.

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Management and remediation of arsenic
contaminated water
Low cost technologies for developing countries

• auto-attenuation
• use of geological materials as natural
  adsorbents
• Artificial recharge
• Bacterial iron oxidation

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Low cost technologies for developing countries
Auto-attenuation

• The principle of auto-attenuation is one of the
  lowest costing and convenient methods to
  remediate groundwater containing high
  concentration of As and Fe.
• The method is simple to adopt at rural household
  level, and needs collected groundwater from wells
  and to stand for a few days. Most groundwater in
  the BDP are rich in dissolved iron which readily
  oxidizes upon aeration and forms ferric
  precipitates.
• The auto-oxidation of FeII to FeIII generates
  favorable substrate with surface reactive sites
  for the adsorption of both anionic AsV as well as
  uncharged AsIII species.

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Results of auto-attenuation tests on groundwater
in Bangladesh
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Low cost technologies for developing countries
Geological material as natural adsorbents

• Laterite has been tested as an adsorbent and
  proved to be a promising low-cost remedial
  technique to safeguard high-As drinking water.
• Laterite occurs as red colored vesicular clayey
  residuum abundantly in tropical regions. Laterite
  is an acidic soil with a typical pH between 4-5.
• The major components of laterite are hydrous
  oxides of Fe- and Al, with minor proportions of
  Mn and Ti.
• Both hydrous Fe and Al-oxide components in
  laterite have a pHzpc (zero point of charge) at
  8.5-8.6.

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Low cost technologies for developing countries
Geological material as natural adsorbents

• Under natural conditions they are characterized
  by net positive surface charge, and capable to
  adsorb several anionic contaminants at wide range
  of pH.
• Laterite could either be used in a filter column
  or directly mixed with water in the water-vessel
  where the soil particles would act as adsorbent
  during sedimentation.
• Adsorption batch experiments on high-As
  groundwater from West Bengal indicate a
  considerable decrease in As concentration with
  varying amounts of laterite.

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Arsenic adsorption on laterite
a Remaining As in water
using groundwater samples of
West Bengal, India
b Amount of As adsorbed on laterite
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Reduction in arsenic concentration with increased
residence time
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Behavior of As and Fe in groundwater with treated
laterite
TWT Tap water treated
DWT Distilled water treated
UT Untreated
AT Acid treated
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Low cost technologies for developing countries
Geological material as natural adsorbents

• The efficiency of As removal varied between
  50-90 for 5 g of added laterite per 100 mL
  water under a reaction time of 20 minutes.
• The maximum effective adsorption was achieved
  during the first 10 minutes and remained more or
  less constant with time.
• The fine grained laterite indicated highest
  adsorption due to available reactive surface
  area.
• Amendment or pre-treatment of laterite also
  affects the adsorption capacity due to the
  increased specific surface area.

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Low cost technologies for developing countries
Artificial recharge

• Artificial recharge has been used to augment the
  groundwater availability.
• The technique has been used to improve the
  groundwater quality to a large extent in Finland
  and in Sweden to remove iron from the
  groundwater.
• Removal of nitrate from groundwater in Denmark
  was tested by recharge through straw beds
  supplying organic matter for denitrification.
• Groundwater recharge has been used in India, to
  decrease the fluoride content of groundwater.

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Low cost technologies for developing countries
Artificial recharge

• Evidences met within the BDP reveal that the As
  is mobilized in groundwater from an adsorbed pool
  of As rich ferric oxides through reductive
  dissolution.
• The basic purpose is to elevate the redox status
  of the aquifer in order to prevent the
  transformation of FeIII to soluble FeII forms.
  Atmospheric O2, NO3-, and H2O2 (which is being
  used widely in the United States) are the 3
  practical oxidants used in aquifers.
• Oxygen has a limited solubility at high ambient
  temperature met with in the area, thus well
  infiltration of oxygenated groundwater may help
  as compared to pond recharge where growth of
  algae and their subsequent microbial degradation
  may consume oxygen rapidly.

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Schematic diagram showing the model for
artificial recharge and design of the recharge
wells
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Low cost technologies for developing countries
Bacterial iron oxidation

• The process of bacterial iron oxidation employed
  at some well sites in UK and France seem to be a
  very useful method for the removal of iron from
  groundwater.
• Naturally occurring bacterial population in the
  well environment carried to such filter beds by
  groundwater where the biogeochemical processes
  trigger the oxidation of FeII to FeIII. The
  biogenic filters rich in FeIII precipitates may
  consequently adsorb the dissolved As species.