Water Purification Techniques

Removing Contaminants

Easton Depp, Carly Hill, Ben Reynolds

Coagulation:

 In coagulation, chemicals are used to neutralize the electrical charge of fine particles in water. This causes the particles to drift closer and form clumps. Coagulant chemicals are used to neutralize particles. There are two types of chemicals, primary coagulants and coagulant aids. Primary coagulants neutralize the the particles so that they drift into clumps. Coagulant aids add density and toughness to the clumps, or flocs, so that they do not break apart in the next filtration steps. A common primary coagulant is called alum, or aluminum sulfate, likewise, common coagulant aids are lime and bentonite. A lot of factors affect how well coagulation works. pH is very important, and typically a low pH water works better (around 4.4 - 6). Timing is very important in coagulation, as proper mixing times affect results. Furthermore, a high temperature helps ensure that a faster and more effective reaction is performed.

Flocculation:

Flocculation is the separation of solid particles from a liquid to form soft flakes. In flocculation, a gentle mixing cycle clumps the particles together. Flocculation lasts from thirty to forty five minutes. The basin for mixing usually has separates chambers for the liquid to pass through, with gentler mixing in each chamber.  This type of mixing allows for the floc to move through the chambers without fear of the clumps being broken up by the large blades.

Video: https://www.khanacademy.org/partner-content/mit-k12/mit-k12-materials/v/flocculation


Both flocculation and coagulation are used to filter out floc from the water, and purify it. This is one step of the water purification process.


Credit to: http://water.me.vccs.edu/courses/env110/lesson4.htm

 

Filtration

 

 

Filters are designed to remove impurities of water and are made up of layers of sand and gravel. Floc (a clump of particles) along with other impurities get stuck in the sand as clean water passes through. Up to 99.5% of solid particles can be removed from the water including minerals, floc, and microorganisms.

 

The most common, everyday technique for filtration is straining. The floc cannot fit through the sand particles; therefore, leaving the floc particles behind.

 

 

Another mechanism of filtration is adsoption, which is the gathering of gas, liquid, or dissolved solids onto the surface of other material. Adsoption involves particles sticking to the sand particles.  Very small particles from water can be removed from adsoption.

 







The third mechanism of filtration is biological actions, or the process of breaking down particles such as decompositon from bacteria. In most filters, water passes through to quickly for biological action to occur.

 

Absorbtion is the final mechanism of filtration. In filters, this involves liquids being soaked up into the sand grains.
http://water.me.vccs.edu/courses/env110/lesson6.htm

Types of Filtration

 Conventional Filtration:

Conventional Filtration is the traditional method of filtration, which can provide treatment for any range of raw-water turbidity. Turbidity is the cloudiness fluid caused by individual particles, or suspended solids, that are usual unseen, similar to smoke in air. The measurement of turbidity is a test of water. The reason why conventional filtration is effective is that sedimentation, which occurs after flocculation and coagulation occurs. Sedimentation should remove most of the suspended material.


 https://www.google.com/search?q=conventional+filtration+water+treatment&source=lnms&tbm=isch&sa=X&ei=5vpOUoLRAYjA9QT6qoDYCQ&ved=0CAcQ_AUoAQ&biw=1366&bih=673&dpr=1#facrc=_&imgrc=wb_skNpgNJrC1M%3A%3B8_sCRfTAjyeLWM%3Bhttp%253A%252F%252Fpublic.health.oregon.gov%252FHealthyEnvironments%252FDrinkingWater%252FOperations%252FTreatment%252FPublishingImages%252FSchematicConvFilter.gif%3Bhttp%253A%252F%252Fpublic.health.oregon.gov%252FHealthyEnvironments%252FDrinkingWater%252FOperations%252FTreatment%252F%3B689%3B339


Direct Filtration:

In direct filtration, no sedimentation occurs after coagulation. This type of filtration is designed for filtering water with a turbidity of less than 25 NTU (Nephelometric Turbidity Units). Direct filtration is used with dual and multi-media filters to remove more suspended material per cubic foot than sand filters used in conventional filters.

 

 https://www.google.com/search?q=direct+filtration+water+treatment&source=lnms&tbm=isch&sa=X&ei=0vxOUpObH4Tg8ASa4YCoAw&ved=0CAcQ_AUoAQ&biw=1366&bih=673&dpr=1#facrc=_&imgdii=_&imgrc=Tf50L6KV7vx0uM%3A%3B8_sCRfTAjyeLWM%3Bhttp%253A%252F%252Fpublic.health.oregon.gov%252FHealthyEnvironments%252FDrinkingWater%252FOperations%252FTreatment%252FPublishingImages%252FSchematicDirFilter.gif%3Bhttp%253A%252F%252Fpublic.health.oregon.gov%252FHealthyEnvironments%252FDrinkingWater%252FOperations%252FTreatment%252F%3B702%3B377


http://www.youtube.com/watch?v=OMZpzcItQkc
http://www.mrwa.com/OP-Filtration.pdf

 

 

Disinfection

Disinfection is when pathogenic microorganisms are deactivated or removed. This causes the pathogenic microorganisms to stop their growth and development. The most common disinfection process is by boiling the water; but chemicals and UV light are also effective. A common chemical used to disinfect water is chlorine.The chlorine kills bacteria in water but can creates hazardous by products. Since it is a very good oxidizer chlorine reacts with other compounds in the water allowing it to kill pathogens. It is the most widely used chemical to disinfect water.

Another chemical used to disinfect water is ozone. Ozone or O3 is also an oxidizer. It is a very clean way to disinfect water. Ozone does not leave hazardous by products. Ozone is commonly used in Europe to disinfect their drinking water.

One way to disinfect water with out using chemicals is UV light. UV rays kill the pathogens in the water. Water is put into a chamber where a UV light is turned on. The pathogens are killed while the water goes out of the chamber.

 

http://www4.agr.gc.ca/resources/prod/img/terr/images/1241475412160_fig1_e.jpg

Sources:
http://www.cdc.gov/safewater/chlorination-byproducts.html
http://www.lenntech.com/processes/disinfection/what-is-water-disinfection.htm