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| Flocculation with Lime |
Turbidity is a measure of the cloudiness of water- the cloudier the water, the greater the turbidity.
Turbidity in water is caused
by suspended matter such as clay, silt, and organic matter and by plankton and
other microscopic organisms that interfere with the passage of light through
the water.
Is Turbidity a health risk?
Turbidity is closely related to total suspended
solids (TSS), but also includes plankton and other organisms.
Turbidity itself is not a major health concern, but high turbidity can interfere with disinfection and provide a medium for microbial growth. It may also indicate the presence of heavy metals such as cadmium, mercury and lead or toxic organic contaminants.
Turbidity itself is not a major health concern, but high turbidity can interfere with disinfection and provide a medium for microbial growth. It may also indicate the presence of heavy metals such as cadmium, mercury and lead or toxic organic contaminants.
Causes of Turbidity:
- Flow Rate: The flow rate of a water body is a
primary factor influencing turbidity concentrations. Fast running water can
carry more particles and larger-sized sediment. Heavy rains can pick up sand,
silt, clay, and organic particles from the land and carry it to surface water.
A change in flow rate also can affect turbidity; if the speed or direction of
the water current increases, particulate matter from bottom sediments may be
resuspended.
- Soil Erosion: Soil erosion is caused by disturbance
of a land surface. Soil erosion can be caused by building and road
construction, forest fires, logging, and mining. The eroded soil particles can
be carried by stormwater to surface water. This will increase the turbidity of
the water body.
- Urban Runoff: During storm events, soil particles
and debris from streets and industrial, commercial, and residential areas can
be washed into streams. Because of the large amount of pavement in urban areas,
natural settling areas have been removed, and sediment is carried through storm
drains to creeks and rivers.
- Wastewater: The wastewater from our houses contains
food residue, human waste, and other solid material that we put down our
drains. Most of the solids and organic material are removed from the water
before being discharged to the stream, but residuals can remain..
- Decaying Plants and Animals: As plants and animals
present in a water body die and decay, suspended organic particles are released
and can contribute to turbidity.
- Bottom-Feeding Fish: Bottom-feeding fish (such as
carp) can stir up sediments as they remove vegetation. These sediments can
contribute to turbidity.
- Algal Blooms: Algal blooms can contribute to
turbidity. Algal production is enhanced when nutrients are released from bottom
sediments during seasonal turnovers and changes in water current.
Standards:
The EPA Surface Water Treatment Rule requires
systems using surface water or ground water under the direct influence of
surface water to
- (1) disinfect their water, and
- (2) filter their water or meet criteria for avoiding filtration. At no time can turbidity go above 5 nephelometric turbidity units (NTUs).
In the United States, systems that filter must ensure that the turbidity go no higher than 1 NTU in at least 95% of the daily samples in any month.
- (1) disinfect their water, and
- (2) filter their water or meet criteria for avoiding filtration. At no time can turbidity go above 5 nephelometric turbidity units (NTUs).
In the United States, systems that filter must ensure that the turbidity go no higher than 1 NTU in at least 95% of the daily samples in any month.
Filtronics systems can ensure that turbidity units
measure below the allowable standard. In most cases, Filtronics can remove
turbidity to below 0.5 NTU for high effluent turbidity samples.
The health consequences of inadequate water and sanitation services include an estimated 4 billion cases of diarrhea and 1.9 million deaths each year, mostly among young children in developing countries.
Diarrheal diseases lead to decreased food intake and nutrient absorption, malnutrition, reduced resistance to infection, and impaired physical growth and cognitive development.
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| Reverse Osmosis with Steel Tank |
However, not all of these interventions remove the turbidity that causes water to look dirty.
Although the following options are not proven to reduce diarrheal disease incidence on their own, they can be used to pre-treat water to reduce turbidity before the use of household water treatment
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| Multi-Media Filter, Highly-Activated Carbon Filter, Zeolite-Process Water Softener with Brine Tank Fiberglass-reinforced Bladder-Type Pressure Tank (fully-automatic backwash & regeneration) |
These options mechanically (through filtration) or chemically (through flocculation and settling of suspended material) remove particles and reduce turbidity.
These pretreatment methods may also increase the efficacy of household water treatment products by removing contaminants that interfere with disinfection and physical filtration processes. For more information, contact safewater@cdc.gov.
Sand Filtration
Filtration through clean sand is a fast and simple
pre-treatment option. Users pour water
from a transport container through a container of sand with gravel and a spigot
at the bottom. The water then flows into
a storage container.
The benefits of sand filtration are that it is effective at removing some bacteria, it is simple and fast for the user, and, if sand is available locally, it is inexpensive. The drawback of sand filtration is that it requires three containers and a spigot.
In laboratory studies, the use of sand filtration significantly reduced both the turbidity and the chlorine demand of turbid water.
The benefits of sand filtration are that it is effective at removing some bacteria, it is simple and fast for the user, and, if sand is available locally, it is inexpensive. The drawback of sand filtration is that it requires three containers and a spigot.
In laboratory studies, the use of sand filtration significantly reduced both the turbidity and the chlorine demand of turbid water.
Cloth Filtration
A simple option to pre-treat turbid water is to
filter through a locally available cloth.
Users pour water from the transport container through the cloth into the
storage container.
The benefits of this option include its simplicity, the wide availability of cloth, and the fact that filtration through multiple layers of sari cloth has been shown to reduce cholera transmission in Bangladesh by removing the copepods to which the cholera bacteria are attached.
Drawbacks of this option are that the filtration capacity of cloth varies greatly, and filtering through multiple layers of cloth can be very slow.
In laboratory studies, the use of cloth filtration reduced the turbidity of water, but did not reduce its chlorine demand, the amount of chlorine that is used up by organics before disinfection can occur.
The benefits of this option include its simplicity, the wide availability of cloth, and the fact that filtration through multiple layers of sari cloth has been shown to reduce cholera transmission in Bangladesh by removing the copepods to which the cholera bacteria are attached.
Drawbacks of this option are that the filtration capacity of cloth varies greatly, and filtering through multiple layers of cloth can be very slow.
In laboratory studies, the use of cloth filtration reduced the turbidity of water, but did not reduce its chlorine demand, the amount of chlorine that is used up by organics before disinfection can occur.
Settling & Decanting
Settling and decanting is a method to reduce
turbidity by letting the
water sit for 2-24 hours so that the particulates
settle to the bottom of the container.
The clear water is then decanted off the top into a second container.
The benefit of settling and decanting is that it requires no equipment besides the containers. The drawbacks of settling and decanting are the need for multiple containers, the time it takes the water to settle, and, if the containers are opaque, the difficulty in observing the effect of settling.
The benefit of settling and decanting is that it requires no equipment besides the containers. The drawbacks of settling and decanting are the need for multiple containers, the time it takes the water to settle, and, if the containers are opaque, the difficulty in observing the effect of settling.
In laboratory studies, the use of settling and decanting significantly reduced both the turbidity and the chlorine demand of turbid waters.
Moringa Flocculation
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| Moringa Tree |
The seeds are shelled, crushed using a mortar and pestle, and about 2 grams of the seeds are added to 20 liters of water. The water is stirred for five minutes, and users let the water settle for
24 hours before decanting it off into another container.
The benefit of moringa is that it is an effective flocculant. The drawbacks are that it is time- and labor-intensive, the dosing of moringa varies for different water, two containers are required, and the moringa flavor may be objectionable.
In laboratory studies, the use of moringa significantly reduced the turbidity of water, but also significantly increased the chlorine demand of the water because of the additional organic material.
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| Ultra-Violet Bactericidal System with Pre-Filters |
The use of moringa is not recommended in conjunction with chlorine-based disinfectants.
Raket Flocculation
In Haiti, the cactus raket contains a natural flocculant. Users pick the
raket, cut it diagonally to expose the maximum flesh surface area, add the
raket to the water, stir briefly, and wait ten minutes before straining the water
through a cloth.
The benefits of raket are that it is effective at removing turbidity, and that raket is widely available in Haiti and easy to prepare. The drawbacks of raket are the need for two containers and that the threestep procedure of raket preparation, addition, and cloth
The benefits of raket are that it is effective at removing turbidity, and that raket is widely available in Haiti and easy to prepare. The drawbacks of raket are the need for two containers and that the threestep procedure of raket preparation, addition, and cloth
filtration is complicated for the user.
Alum Flocculation
Aluminum sulfate is widely used as a flocculant in
water treatment
plants in the United States and Europe. It is also widely available in developing countries, sold in naturally occurring
mineral blocks of soft white stone, and generally called ‘alum’.
There are numerous ways to use alum as a flocculant, including crushing it into a powder before adding it to water, stirring, and decanting; or, stirring the whole stone in the water for a few seconds and waiting for the solids to settle.
The benefits of alum are that it is widely available, is proven to reduce turbidity, and is inexpensive. The drawbacks of alum are that the necessary dosage varies unpredictably, it can change the pH of the treated water, and using too much leads to a salty, unpalatable taste.
In laboratory studies, the use of alum significantly reduced the turbidity of water, and also significantly reduced the chlorine demand of turbid waters.
There are numerous ways to use alum as a flocculant, including crushing it into a powder before adding it to water, stirring, and decanting; or, stirring the whole stone in the water for a few seconds and waiting for the solids to settle.
The benefits of alum are that it is widely available, is proven to reduce turbidity, and is inexpensive. The drawbacks of alum are that the necessary dosage varies unpredictably, it can change the pH of the treated water, and using too much leads to a salty, unpalatable taste.
In laboratory studies, the use of alum significantly reduced the turbidity of water, and also significantly reduced the chlorine demand of turbid waters.
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source: cdc.gov
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