Several conventional methods are used for the removal of pollutants from drinking water, such as coagulation followed by filtration, membrane processes and ion exchange.
Adsorption methods proved to be effective, economically efficient, easy to perform and
construct. Some experiments were conducted to study the efficiency of natural zeolite
clinoptilolite and of the clinoptilolite-Fe system in removal of Cu, Mn, Zn, which are
simultaneously found in water samples. A very unique property of natural zeolites is their selectivity towards cationic. The excellentresults of adsorption experiments, especially for the modified forms along with the fact that the clinoptilolite–Fe systemis inexpensive, easily synthesized and regenerated, harmless for human
beings, as well as for the environment, we
can consider it as a very promising select
ive metal adsorbent [7]. Using iron/aluminum
hydroxide to remove arsenic from water is a
proven technology. An alternative method to
enhance the performance is to use coarse-grain
ed sorbents to increase the flow rate and
throughput of the process. The removal of
arsenic from drinking water was studied by
using modified adsorbents (natural zeolite) prep
ared by the use of different iron solutions.
The arsenic sorption on the Fe-exchanged zeolite could reach up to 100 mg/kg [8,9]. The
high surface area of modified natural zeolite (clinoptilolite)-iron oxide system in strongly
basic conditions, can also enhance the removal of
cations, like Cu from drinking water. The
specific surface area of modi
fied clinoptilolite
increased up to 5-times (from 30 to 151m
2
/g)
and the maximum amount of adsorbed Cu ions was
13.6 mg/g
zeolite for natural
clinoptilolite and
37.5 mg/g
for modified clinoptilolite [10]. In spite of many scientific
evidences of the effectiveness of zeolites in
anion removal, not many of them are used on
larger scales up to date. High concentrations of fluoride ions in groundwater up to more
than 30 mg/L, occur widely, notably in the United
States of America, Africa and Asia. More
than 260 million people worldwide consume drinki
ng water with a fluoride content of >1.0
mg/L. The available techniques for the removal of F
-
-anions from drinking water are
membrane techniques, dialysis, electro-dial
ysis and finally adso
rption techniques.
Clinoptilolite-type natural zeolite was pre-conditioned with nitric acid solution before
loading with Al
3+
, La
3+
or ZrO
2+
. Aluminium-loaded low-silica zeolites as adsorbents for
fluorides showed that modified zeolites were
able to defluoridate water to below WHO’s
maximum allowable concentration (MAC) of 1.5 mg/L. The maximum fluoride adsorption
was in the pH range of 4–8 [11]. High nitrate
concentrations in drinking water sources can
lead to a potential risk to environment and public health. Removal efficiency of
NO
3
-
ions
can be increased by treatment of
the clinoptilolite samples with HDTM
+
(hexadecyltrimethylammonium cation) or cety
lpyridinium bromide (CPB) [12]. Grey water
is wastewater originated from
bathroom and laundry in households. Ammonium is one of
the most significant grey water contaminants. Natural and modified zeolites are used for
their purification and they shows good perfor
mance with up to 97% of ammonium removal
depending on contact time, zeolite loading, initial ammonium concentration and pH value.
The desorption–regeneration stud
ies demonstrated that the deso
rption of ammonium on the
zeolite is sufficiently high [13,14].