2. Arsenic in water
1. The main cause of Arsenic presence in ground water is believed to be the reductive
dissolution of sedimentary Arsenic-containing Iron Oxy-hydroxide by microbial driven
oxidation of organic matter. This cause the release of adsorbed Arsenic, since the
adsorbed As (V) is reduced to As (III) and leached into ground water.
2. Anthropogenic sources also contribute to Arsenic pollution.
Arsenic compounds were employed as pesticide, herbicide and in wood preservation.
Other sources of Arsenic are mining waste and glass industry.
Fertilizers are also suspected to have an important contribution to the contamination of
groundwater with Arsenic.
Coal combustion, metal smelting and refining processes release Arsenic in the
atmosphere, which eventually it is transported by rain in the surface water and
groundwater.
3. Need for Arsenic treatment
Presence of Arsenic in drinking water leads to many
proved health problems, including cancers.
Adsorbers for Arsenic removal
Passive systems – little or no user intervention
Easy to operate
Almost no waste water
In some cases, no hazardous spent material
Can achieve the best cost for treated water, especially for medium and small
systems
5. Titansorb
Typical Physical and Chemical Properties
Appearance: White granules
Particle size: 0.5 – 1,5 mm
Active surface: 400-450 m2
/g
Porosity: ca. 65%
Typical equilibrium capacity (static, 1000 ppb, pH=6.5)
Arsenic (V) 28-30 g / kg
Arsenic (III) 13-15 g / kg
Typical equilibrium capacity (static, 50 ppb, pH=7.0)
Arsenic (V) 14-16 g /kg
Arsenic (III) 5-6 g/ kg
6. Titansorb
made of Nanosized Titanium Oxyhydrate
Titanium Oxyhydrate TiO(OH)2 or Metatitanic Acid H2TiO3 - reactive material, containing
maximum number of active centers: Ti-OH groups.
Titanium Oxyhydrate is partially crystallized as Anatase nanocrystals (10 - 20 nm),
containing a high density of Ti-OH active centers on their surface:
Ti
OO
O
H
Ti
OO
O
H
Ti
O
H
Ti
OO
O
H
Ti
O
H
Ti
OO
O
H
Ti
O
H
Ti
O
O
H
Active Ti-OH groups on Anatase nanocrystals
TEM image of Anatase
7. Titansorb
The contaminants are strongly adsorbed on the active surface of nanocrystalline Anatase.
As an example, arsenate anion (As5+
) may be retained under several possible
coordinative structures:
Ti
O
Ti
O
As
Ti
O
O
O
O OO
O
H
Ti
O
Ti
O
As
Ti
O
Ti
O
O
O O
Ti
O
O
O
O
OH
Ti
O
Ti
O
As
Ti
O
O OO
O
O Chelating bidentate
Chelating
tridentate
Brigded bidentate
Chelating tridentate on a „step“
TiTi
O
As
Ti
O
OO
O OO
O
8. Titansorb
Operation conditions
High service flow rate: 15 - 35 m/h (6 – 14 gpm / ft2
) (depending on Arsenic concentration)
Backwash flow rate: 14- 24 m/h (6 - 10 gpm / ft2
)
Freeboard: 55% of bed depth
Short contact time: 30 s – 3 min (or more, depending on Arsenic concentration)
Bed depth: at least 0.8 - 1 meter
Operational pH: 4-10
12. Titansorb
Service Flow Rate and Arsenic Adsorption
Test water: pH=7.5, 300 ppb As(V), silica 20 ppm, hardness 150 mg/l
13. Titansorb
Comparative Arsenic Adsorption Media Test
- influence of pH fluctuations (pH re-set at 6.5 thereafter)
Flow rate 20 BV/h, pH=6.5, 300 ppb As(V), silica 10 ppm, hardness 150 mg/l
pH = 7.2 pH = 7.0
14. Why Titansorb?
Stronger adsorption of arsenic in comparison with alumina or iron-based media, therefore no
leaching was observed
One of the highest Arsenic adsorption capacity
Fast arsenic adsorption – less media, small footprint
Cost per liter of water treated is lower compared with other adsorbers
Wider pH tolerance (Titanium Dioxide is not soluble in acidic or basic media)
Less prone to Arsenic leaching due to pH fluctuations
Best results at pH 7 or lower
Less sensitive to ionic strength or concurrent anions (phosphate, sulfate, nitrate, etc.)
Removes other hazardous contaminants from water - such as chromate, cadmium, lead, copper,
selenium
No staining due to iron leaching
Almost no microbiological contamination (such as iron bacteria) therefore less disinfection
required and less disinfection toxic by-products (THM, chloramines, HAAs) are generated
