Arsenic Removal in Water Treatment

A poisonous and carcinogenic metalloid, arsenic is found in the environment through natural and human-made sources. The gravest danger emanates from dissolved arsenic in our drinking water. Having an effective “arsenic filter” is therefore essential for ensuring a safe supply of drinking water.

In the early 1990s, new studies revealed that, aside from its acute toxicity, even a tiny concentration of arsenic is harmful, given its cancer-causing effect. It was for this reason that a threshold limit value of 10 μg/l was set for arsenic in drinking water. At that time, no simple, technical solution existed for small and medium-sized waterworks to reliably remove arsenic and meet the newly-defined limit value. This gave rise, in the early 1990s, to the development of the granular adsorbent known as GEH®. Since arsenic is commonly found in water as a dissolved substance, such as arsenate (As(V)) or arsenite (As(III)), conventional filter materials have reached their bounds of possibilities. The following methods are, in principle, suitable for removing arsenic:

Adsorption

Arsenentfernung durch Adsorption

During the adsorption process, arsenic binds to the surface of a solid adsorptive media, or adsorbent. Prior to iron-based adsorbents being developed, activated alumina were primarily used to remove arsenic. Due to the low capacity and hazardous nature of dissolved aluminium, this no longer has any active role to play these days.
Iron-hydroxide adsorbents are the best demonstrated available technology for removing arsenic during drinking water production. Their most significant benefits lie in how simple and safe it is to operate adsorption filters and remove arsenic to a level that is below the detection limit. Moreover, no wastewater streams or contaminated sludges are generated during operation. The removal of arsenic using granular ferric hydroxide occurs selectively – leaving the water’s natural composition unchanged. Both arsenate and arsenite are removed during this process.

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Pro

  • Simple plant configuration and uncomplicated operation
  • Very high capacity due to high arsenic selectivity
  • High plant availability and low maintenance requirements
  • Established technology used globally in over 2000 locations
  • Easy removal without sludge treatment

Contra

  • Residence time depends on water matrix
  • Adsorbent needs to be replaced at regular intervals
Adsorber unitsAdsorber units fillingAdsorber units installation backwash

You have questions or want to get to know us? We are looking forward to your message!

Simon Kellmann

Your contact person:

M.Sc. Simon Kellmann
Tel. +49 541 1220-09

info@geh-wasserchemie.de

Flocculation/Filtration

Arsenentfernung durch Flockung/Filtration

Flocculation typically involves the use of iron or aluminium salts. These are precipitated in the raw water and filtered out. The dissolved arsenic binds to the surface of the filtratable flocs and is thus removed from the water. A certain amount of flocculant is required depending on the arsenic concentration. Periodic analyses must be performed to determine this. The filtered sludge needs to be subsequently treated and is ultimately disposed of, in accordance with the local regulations, as residual or special waste depending on the arsenic content. Given the high, technical input involved in this process, it is an especially interesting option for very large treatment plants.

Pro

  • Standard drinking water treatment process
  • Several impurities, e.g. turbidity, can be removed at the same time
  • Relatively low chemical costs

Contra

  • Efficiency of the arsenic removal depends on the flocculant dosage
  • Requires treatment and disposal of arseniferous sludge
  • High investment costs
  • Complex plant technology; requires skilled personnel
  • Not suitable for small plants

Ion exchange

Arsenentfernung durch Ionenaustauscher

Depending on the type of material involved, ion exchangers can remove anions or cations while also releasing other ions of the same charge to the water. As long as arsenic is present in the water in the shape of arsenate, it is charged and can, in principle, be removed using ion exchangers; by contrast, arsenite cannot be removed, however. With only limited selectivity for arsenate, however, capacities are relatively low in practice. To achieve a practicable residence time, these therefore need to be regenerated. During this process, toxic regenerate solutions accumulate which need to be subsequently treated. In practice, this renders ion exchangers unimportant in the removal of arsenic.

Pro

  • Parallel removal of different ions possible
  • Ion exchangers can typically be regenerated
  • Frequently exhibit high reaction kinetics

Contra

  • Minimal selectivity for arsenic --> high interference from other ions such as sulphate
  • Arsenite (As(III)) cannot be removed
  • Frequent regeneration cycles due to low capacity
  • Regeneration requires use of chemicals and produces arseniferous solutions that need to be subsequently treated
  • High material costs

Membrane processes

Arsenentfernung durch Membranverfahren

Using high pressure, membrane processes remove substances in the water through size exclusion as well as through interaction with the membrane material. To remove arsenic safely, the employment of dense membranes like nanofiltration or reverse osmosis are required. Here, the arsenic, along with other compounds in the water that are unable to pass through the membrane, is retained and discharged in a sewage flow. The untreated water is completely or partially desalinated by this process. The highly arseniferous sewage flow then undergoes subsequent treatment. This non-selective removal process changes not only the arsenic content but also the mineral composition of the water, which, depending on how the water is to be used, may be desired or detrimental.

Pro

  • Established water treatment technology
  • No selective process; other contaminants are removed at the same time
  • Modular design, readily scalable

Contra

  • Non-selective; removes all compounds in the water --> demineralised water
  • Typically requires pre-treatment
  • Concentrate stream requires subsequent treatment
  • High energy requirement
  • Extensive plant technology with high investment costs
  • Operating facility needs specially trained personnel

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Did you know... ?

170 Mio m³
of water are treated annually using GEH®
2900 kg
of pure arsenic are removed from our environment annually thanks to GEH®
830 t CO₂
saved since 2013 by optimizing GEH® production
34 %
increase in energy efficiency thanks to optimization of GEH® production
60
countries where GEH projects have been completed
170 Mio m³
of water are treated annually using GEH®
2900 kg
of pure arsenic are removed from our environment annually thanks to GEH®
830 t CO₂
saved since 2013 by optimizing GEH® production
34 %
increase in energy efficiency thanks to optimization of GEH® production
60
countries where GEH projects have been completed