Arsenic Standards
In
the early 1990’s the World Health Organisation recommended that the
current drinking water standard of 50 micrograms per litre (ug/L) of
arsenic (As) should be reduced to a new standards of 10ug/L based upon
health effects testing conducted over the years. The United States EPA
enacted a new MCL standard of 10ug/L for
domestic drinking waters on October 31, 2001. The
Ministry of Science and Technology, Government of Pakistan has laid a
maximum permissible level of 10 parts per billion of arsenic in
drinking water.
Forms of Arsenic
In ground waters, arsenic is present in the inorganic form resulting
from the dissolution of solid phases such as arsenolite (As2O5) and
realgar (AsS). Arsenic is stable in four oxidation states (+V, +III,
O,-III) under different reduction/oxidation (RedOx) conditions in
water but is generally found as an ox anion in the trivalent and
pentavalent states as arsenite, AsO3-3(+III) and arsenate, AsO4-3(+V
oxidation state), respectively. The toxicity scale for arsenic is as
follows:
·
Arsine>Arsenite or
As(III)>Arsenate or As(V)>Organic arsenic.
·
Arsenite (III) is more
likely to be found in anaerobic waters while arsenate (V) is found in
more aerobic waters.
Basic Arsenic Removal Design
The EcoTech system design is based upon extensive pools of knowledge
developed by the world’s most reputed names in water technologies and
best product specifically designed for arsenic removal at the source.
At the heart of the system design is an iron-based adsorption media.
manufactured by
GEH Wasserchemie GmbH & Co. KG
Germany, and exclusively provided in Pakistan with Engineering and
after sale services by
Ecotech System International Pakistan.
The media has a high capacity for arsenic and, unlike other iron-based
media, is delivered in a dry crystalline form, is robust, easy to
handle and has NSF 61 approval. In addition to As removal, the media
will also adsorb other dissolved elements including antimony,
cadmium, hexavalent chromium, lead, manganese, phosphate, molybdenum,
selenium and vanadium. The media has a higher selectivity for As over
these other species.
Comparison of Arsenic Removal Technologies |
Technology |
Process |
Chemical Use |
Waste Generated |
Water Wasted |
GEH/GFH Media |
Simple |
Non |
Low |
<0.1% |
Reverse Osmosis |
Moderate |
Cleaning Chemicals |
Low |
10.25% |
Ion Exchange |
Complex |
Regeneration chemicals |
High |
2% |
Activated Alumina |
Complex |
Regeneration chemicals |
High |
2% |
Coagulation Microfiltration |
Complex |
Cleaning, coagulation chemicals |
Moderate |
5% |
|