IRON CONTROL SYSTEM FOR
by Ilan Bar
Drip irrigation of 16 ha. of greenhouses, shade houses and
field grown containers was accomplished using water containing up to 6.0 mg/l of iron.
Crops were irrigated on a daily basis for three years without significant clogging
problems. The system designed and installed to control the iron problems consisted of the
1. Gas Chlorinator - To allow consistent injection of
chlorine in its most available and efficient form.
2. Hydrocyclone Containing Filtering Discs - To ensure
complete and uniform mixture of the gas in the water within a limited space.
3. Sand Media Filters - To settle the oxidized iron and
filter it from the water.
4. Back-up Disc Filters - To control filtration failures and
complete iron separation.
KEY WORDS: Drip irrigation, Filtration, Chlorination, Iron.
Iron deposit problems (ochre) in drip systems have been
reported primarily in the U.S.A., but also from other parts of the world including:
Australia, Zambia, Taiwan, and Israel. These deposits create severe clogging problems in
drip systems. Iron deposit is described as a filamentous amorphous gelatinous type of
brown-reddish slime, that precipitates from water that contains iron. The sticky iron
deposits clog the drippers and cause complete plugging of the system.
The problem exists in well water areas where the groundwater
aquifers are formed mainly of sandy soils or organic muck soils (very common in Florida)
usually with a pH of below 7.0 and in the absence of dissolved oxygen. These waters
contain ferrous iron (Fe+2) which is chemically reduced, 100% water soluble and serves as
the primary raw material for slime formation.
Iron bacteria, mainly from the filamentous genuses such as
Gallionella Sp. Leptothris and Sphaerotilus and less from the rod type, like Psendomonas
and Enterobacter, when present in the water react with the ferrous iron (Fe+2) through an
oxidation process. This changes the iron form to ferric iron (Fe+3) which is insoluble.
The insoluble ferric iron is surrounded by the filamentous bacteria colonies and creates
the sticky iron slime gel that is responsible for clogging the dripper.
Concentrations of ferrous iron as low as 0.15-0.22 mg/l are
considered as a potential hazard to drip systems (H.W. Ford 1982). Emitter clogging hazard
is moderate for concentrations between 0.2-1.5 mg/l. Concentrations above 1.5 mg/l are
described as severe (Bucks and Nakayama - 1980). Practically any water that contains
concentrations higher than 0.5 mg/l of iron cannot be used in drip systems unless they are
treated chemically or otherwise. Experiments in Florida indicate that chlorination
successfully controls iron slime when iron concentrations were less than 3.5 mg/l and the
pH below 6.5 (Nakayama and Bucks - 1986). It is also stated that long-term use of water
with a high level of iron may not be suitable for drip irrigation. The literature mentions
that water containing more than 4.0 mg/l cannot be efficiently chemically treated and it
should undergo a pond sedimentation process before pumping it back through a drip system.
Using the following system, 16 ha. of greenhouses, shade
houses and field grown containers were drip irrigated with water containing up to 6.0 mg/l
of iron. Daily irrigation for three years occurred without any significant clogging
IRON CONTROL METHODS:
There are several ways to control iron slime problems. The
common denominator of all treatments is prevention of the formation of slime.
Basically there are two preventative treatments:
1. STABILIZATION (Precipitation Inhibitors)
Stabilization treatments keep the ferrous iron in solution by
chelating it with sequestering agents. Such agents include various poly phosphates and
2. OXIDATION - SEDIMENTATION - FILTRATION
This type of treatment oxidizes the soluble
"invisible" ferrous iron into the insoluble "visible" ferric iron. It
then will precipitate, so it can be physically separated from the water by means of
The second procedure was the preferred treatment for the
severe iron problems in our supply water.
The various means to oxidize iron include aeration,
chlorination, and potassium permanganate. There are also other oxidizers.
Chlorination using gas chlorine was selected for the
1. Since the operation is located in the middle of a
residential area, there was no room for a settling basin; proper safety precautions should
be used when using gas chlorine.
2. The price per unit of chlorine derived from gas chlorine
is the least expensive among all the options of oxidizers and also a very efficient one.
SEDIMENTATION - FILTRATION:
A sand media filter is the most appropriate filter for
settling down the oxidized iron and filtering it from the water.
INSTALLED SYSTEM DESCRIPTION:
Based on these facts, three treatment stations were built
within the 16 ha. farm. The system description that deals with the heaviest load of iron,
(the components appear in their sequence order from the pump on) is as follows:
System Flow: 21 - 22 m3/hr. @ 300 -350 Kpa.
Drip System: Netafim pot drippers 2 L/H and 4 L/H operating
at 170 -180 KPa.
Gas Chlorinator: REGAL, 45.0kg cylinder with maximum
injection rate of 4.5 Kg/day using booster pump and venturi injector.
5 cm Super Hydrocyclone Plastic Disc Filter: Netafim - Arkal
Sand Media Filters Battery: Netafim - Odis Model 2 x 50 cm
5 cm In-Line Plastic Disc Filters (Backup): Netafim - Arkal
RESULTS AND DISCUSSION:
Since water quality, iron content, zone size and free
chlorine change slightly with time, the following table represents several measurements at
TABLE 1: The levels of free chlorine and iron in different
spots during irrigation-chlorination cycle.
Head of System
At the Dripper
| IRON (mg/1)
3.5 - 6.0
3 - 5
3 - 5
30 - 45*
| CHLORINE (mg/1)
10 - 15
2 - 2.5
0.4 - 0.5
0.4 - 0.5
*Estimated and calculated through dilution.
As shown in Table 1, there is a very slight change in the
iron content because the field kit is measuring both ferrous and ferric. The very dramatic
chlorine consumption indicates that most of the ferrous was converted to ferric. The free
residual chlorine at the dripper indicates that the oxidation process was brought to
completion - the bacteria was inhibited by the presence of chlorine and iron slime was
avoided so that the system could function without clogging.
The reasons for chlorination were:
- a) to oxidize the soluble ferrous iron to insoluble ferric
iron which can be removed by filtration, and
- b) to control bacterial growth in the system which helps
control iron slime.
The following criteria determine the type of chlorine
- 1. Water quality.
- 2. Size and type of the irrigation system.
- 3. The time between the chlorine injection and the moment the
water is being filtered, and from filtration, the time it takes to reach the drippers.
- 4. Crop type.
- 5. Soil type.
- 6. Fertilizer type.
Since the iron levels were so high we decided to use
continuous injection of chlorine. This was the best way to ensure no build-up of iron
slime. It is important to remember that the drip system that is being used irrigates
individual containers, which means that one plugged dripper results in losing the plant
because there is no compensation between the drippers. High levels of iron also dictate
high concentration of chlorine. Since we are dealing with herbaceous plants which are
relatively insensitive to chlorine, and the soil-less mixture which is being used is rich
in organic material, allowed the use of water with initial levels of up to 15 mg/l
chlorine. Therefore, we decided to use gas chlorine, which is the least expensive chlorine
unit on the market, in addition to the fact that it does not lose its availability (which
is 100%) over time. Another advantage of gas is its ability to acidify the water, which
helps to maintain high efficiency of chlorination. Other chlorine sources tend to raise
the pH of the water and reduce chlorination efficiency. The gas reacts with the water
according to the following equation: H2O + CL2 ® HOCl + H++Cl-. The next step is:
HOCl H+ + OCl-. HOCl and OCl- are both considered as free chlorine but HOCl is 40 to 80
times more efficient. For pH less than 6, most of the free chlorine will be in the HOCl
form. On pH greater than 7.5, the predominate form will be OCl-. Another advantage of the
gas chlorinator is simplicity, reliability and dependability of the system.
The efficiency of the chlorination also depends on contact
time. Since the existing conditions dictated a relatively small and compact system.
Contact time and distribution uniformity of the chlorine in water was improved by
installing a hydrocyclone downstream from the chlorine injection point in order to assure
a proper mixture of gas and water. This also helps spread the water in very thin layers
via the discs which also improves the contact and uniformity of the mixture. The disc
backup filters are used as an additional safety factor to separate any iron deposits that
were able to pass the media filters.
Working under the conditions of very high iron levels,
limited space, high cash crop (tropical foliage) and individual drippers system, a system
was designed, installed and maintained that drip irrigated and fertigated a 16 ha. farm
since 1991 without any significant clogging problems by using either plastic or ten stage
epoxy coated filters (media) to avoid corrosion, backflushing the system automatically
every 1.0 hr. for 3 minutes, changing the media every two months and rinsing the discs
with weak hydrochloric acid at the same time. The system was kept in excellent condition.
Replacement was needed on some small rubber parts on the hydraulic relay valves, solenoids
and some plain steel bolts.
The author would like to express his thankfulness and
appreciation to Mr. Kevin Kraft and Mr. Bob Chavez from Kraft Gardens and to Mr. Brian
Shade from Netafim Irrigation, Inc.
1. Clark, G.A. and A.G. Smajstrla (1992) Treating Irrigation
Systems With Chlorine. Circular 1039 Florida Cooperative Extension Service, I.F.A.S,
University of Florida, Gainesville.
2. Ford, H.W., (1982) Iron Ochre and related sludge deposits
in subsurface drain lines. Circular 671 Florida Cooperative Extension Service , I.F.A.S,
University of Florida, Gainesville.
3. Malchi, I. 1986a. Iron In Irrigation Water
"Hassadeh", Vol. 66 (12) September 1986 (Israel). Malchi, I. 1986b. Personal and
Internal Information, (Netafim Irrigation Inc. U.S.A.)
4. Nakayama, F.S. and D.A. Bucks (1986) Trickle Irrigation
for Crop Production, Elsevier Science Publishers B.V. 1986 (383 p.)