arsenic removal
TRANSCRIPT
Arsenic in water1. 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.
Need for Arsenic treatmentPresence 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
Appearance: White granulesParticle size: 0.5 – 1.5 mm Moisture content: less than 10%Bulk density: ca. 550 kg/m2
Titansorb
TitansorbTypical 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
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
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
OO
O OO
O
H
Ti
O
Ti
O
As
Ti
OTi
O
O
O O
TiO
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
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
Titansorb
Testing water
NSF/ANSI 53 Standard
Calcium 40 ppm
Magnesium 24 ppm
Sodium 10 ppm
Chloride 100 ppm
Sulfate 50 ppm
Silica (SiO2) 20 ppm
Nitrate 2 ppm
Fluoride 1 ppm
Phosphate 0.04 ppm
Titansorb Comparative Arsenic Adsorption Media Test
Flow rate 20 BV/h, pH=7.5, 300 ppb As(V), silica 10 ppm, hardness 150 mg/l
Titansorb pH influence on Arsenic adsorption
- Activated Alumina, Iron Hydroxide, Titansorb
Flow rate 60 BV/h, 50 ppb As(V), silica 20 ppm, hardness 150 mg/l
Titansorb Service Flow Rate and Arsenic Adsorption
Test water: pH=7.5, 300 ppb As(V), silica 20 ppm, hardness 150 mg/l
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
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
Questions?
Watch GmbH
Fahrlachstrasse 14
68165 Mannheim
Germany
Web: www.watchwater.de
Dr. Valentin Cimpeanu
Tel. +49-621-87951-55
Email: [email protected]