Reverse Osmosis Filter Discharge Water Introduction: Estimating Volume of The Resource

Reverse Osmosis Filter Discharge Water Introduction
Reverse Osmosis (RO) filters use membrane technology to filter impurities (minerals, calcium, chloride, sodium,
chlorine, etc) from the water. The systems require periodic backwash to clean the filter. Depending on the model,
most RO filter systems* will discharge 4 to 20 gallons (15.1 L to 75.7 L) of backwash water for every gallon of filtered
water it produces. This discharge water is commonly directed to the sewer drain line. The discharge water from an
RO system is only slightly less pure than the source water entering the filter. The concentration of minerals in the
discharge water is often less than 25% greater than the source water; well within safe drinking water standards and
certainly suitable for irrigation or other alternate reuse applications.
* In recent years, some manufacturers have developed innovative RO filter systems referred to as zero-discharge;
discharging the backwash water into the water supply pipes. The zero-discharge refers to the fact that the
backwash water is not discharged into the sewer system.
Estimating Volume of the Resource

The amount of discharge water produced depends on the efficiency of the RO filter and the amount of RO water
used. Somewhat paradoxically, the less efficient the filter system, the more discharge water is available for reuse.
A typical family of four will use 2 to 5 gallons (7.57 L to 18.92 L) of RO water per day, depending on their water use
habits. Some homes use RO water just for drinking, other use it for all cooking, rinsing produce, brewing coffee and
tea, ice trays and ice makers, watering indoor plants, etc. Assuming the RO filter is 16% efficient (discharging 5
gallons (18.92 L) for every 1 gallon (3.78 L) of filtered water), a typical home will produce 3,600 to 9,000 gallons (13.6
m3 to 34.1 m3) of discharge water per year; all needlessly wasted when drained into the sewer system. An older,
less efficient RO filter might produce more than 30,000 gallons (113.5 m3) of discharge water per year.
RO water filters are also used in commercial, industrial and institutional settings; each filter producing thousands of
gallons of discharge water every day. The filtered water is used for everything from: biology and chemistry
laboratories, car washing (rinse cycle), photography processing, rinsing computer chips and hard discs, etc. In most
all applications, there are potential reuse applications on-site for the discharge water.
Potential Uses of RO Discharge Water

RO discharge water can be collected, and used similar to other alternate water sources. The discharge water has
the same sanitary qualities as the potable source water for the RO filter; the only difference is the discharge water will
haveslightly elevated concentrations of minerals and water treatment chemicals. As long as the sanitary conditions
are maintained during storage and transfer, the water can be used the same as potable water (though we never
recommend it for direct human consumption). RO discharge water is one of the few alternate water sources that can
be safely used for above surface irrigation when properly handled. If the discharge water is stored for more than a
day, it is no longer suitable for spay head type irrigation unless additionally treated.
The sanitary quality of RO discharge water suggests there are better uses for it than just irrigation. This water is
perfectly suited to use for laundry and flushing toilets in the home, when the santitation of the water is maintained.
Unlike rainwater or condensate collection, the RO filter will continually discharge a relatively constant quantity of
water; 8 to 50 gallons per day (30.3L to 189.2 L) when the home is occupied. In commercial settings, the potential
uses include: pre-rinsing, laundry, toilet and urinal flushing, irrigation, washing hardscapes, make-up water for cooling
towers and water cooled condensers, evaporative cooling, decorative fountains, swimming pools, water cooled
machinery, vehicle wash, etc.
Many of us use Reverse Osmosis Filters (RO filters) to purify Drinking Water, in areas with high
TDS (Total Dissolved Salts) content in the Water.
Around 75% of the Water fed into a RO filter, is wasted. Only 25% gets
extracted as drinking Water.
This causes a tremendous Overhead on the Water Supply as well as Sewage Treatment system of
Apartment Complexes.
So, what can you do about it?
Kannan Venkitachalam, a Resident of Shakthi Hilands in Bangalore and a Water Warrior, shares
how he re-uses the Waste Water from his Reverse Osmosis Filter, seamlessly.
" Please find my home RO system waste water reusing method for washing clothes. I am following
this for the last 6 to 7 years.
For 1 liter safe filtered drinking water in the RO tank 3 liters goes rejected as hard water. But it is
good to reuse for washing clothes, kitchen utensils cleaning, floor moping, car washing etc.
Important, the container which you use to collect the rejected water need to have bigger opening,
so that monthly once you need to clean with scotch brite for cleaning the scale. Need to have
sufficient opening to put your hand inside. The container which I have is just Rs.150/- from China
Bazaar"
In principle, yes - RO concentrate can be used for irrigation purposes and there have been some
examples of such use in places, where fresh water sources are limited - for example in South Africa.
However, in such cases water recovery (permeate produced) has to be kept at relatively low values
(~50 %) since higher water recoveries can lead to very saline RO concentrates, which may have
adverse effects on the physicochemical and microbiological properties of the irrigated soils, including
retarded growth of plants and grasses cultivated on such soils.
This is very broad question and it is dependent on RO concentrate (reject) quality and purpose of
irrigation. Often, RO concentrate contains high TDS (i.e, >2500-3000 mg/L) and other constituents
which probit use of it for irrigation purpose.
It depends on the type of salt present in the rejected streams and the concentration of salts. If
rejected stream contains heavy metal's salts such as chromium salts, then this water can not be
used for irrigation. High salinity water can not be used in irrigation. But It also depends on the type of
crop and type of soil.
Household reverse osmosis units use a lot of water because they have low back pressure. As a
result, they recover only 5 to 15% of the water entering the system. The remainder is discharged as
waste water. Because waste water carries with it the rejected contaminants, methods to recover this
water are not practical for household systems. Wastewater is typically connected to the house drains
and will add to the load on the household septic system. A reverse osmosis unit delivering five
gallons of treated water per day may discharge between 20 and 90 gallons of waste water per day
Large-scale industrial/municipal systems recover typically 75% to 80% of the feed water, or as high
as 90%, because they can generate the high pressure needed for higher recovery reverse osmosis
filtration. On the other hand, as recovery of wastewater increases in commercial operations, effective
contaminant removal rates tend to become reduced, as evidenced by product water total dissolved
solids levels.
Due to its fine membrane construction, reverse osmosis not only removes harmful contaminants
present in the water, but it also may remove many of the desirable minerals from the water. A
number of peer-reviewed studies have looked at the long-term health effects of
drinking demineralized water.[
Depending upon the desired product, either the solvent or solute stream of reverse osmosis will be
waste. For food concentration applications, the concentrated solute stream is the product and the
solvent stream is waste. For water treatment applications, the solvent stream is purified water and
the solute stream is concentrated waste.[25] The solvent waste stream from food processing may be
used as reclaimed water, but there may be fewer options for disposal of a concentrated waste solute
stream.

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Estimating Volume of the Resource

Potential Uses of RO Discharge Water

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