Water Purification Techniques

FLOCCULATION (noun): The process of flocculating, forming woolly cloudlike aggregrations.

A flocculent causes particles and dirt suspended in water to come together. The grouping of the dirt and particles creates a substance heavier than water, so the clump sinks to the bottom of the container where the water was. This creates cleaner water that rests on top of the layer of dirt and particles. In the process of flocculation, the top water is then drained off, separating clean water from dirt and particles and the bottom of the container.

Youtube video demonstrating how flocculation works on a small scale: http://www.youtube.com/watch?v=100XXIxOL9U

My Sources:
http://wordnetweb.princeton.edu/perl/webwn?s=flocculation&sub=Search+WordNet&o2=&o0=1&o8=1&o1=1&o7=&o5=&o9=&o6=&o3=&o4=&h=0
http://www.teachengineering.org/view_lesson.php?url=collection/usf_/lessons/usf_flocculant/usf_flocculant_lesson01.xml

COAGULATION
i. Coagulation is a water purification process that is used to coagulate (clump) particles together using polar charges. This happens by introducing a secondary substance, such as, in the case of clay, alum. The chemical alum produces positive charges, neutralizing any present negative charges, and making it easier for the particles to clump together on their own, this forms larger particles, which can be removed easily by other means of filtration.
ii. The process of coagulation involves the addition of a charged chemical, in the exemplary case, the chemical was alum (a positively charged chemical), followed by rapid mixing of the water to dissolve/disperse the chemical throughout the water, from there the chemicals electrical properties take over, coagulating the microscopic particles, into larger, more easily filterable particles.
iii. http://techalive.mtu.edu/meec/module03/WastewaterRegulations.htm

Coagulation:
-Add polarized chemical to water.
-Stir water vigorously until chemical is dissolved.
-wait for particles to clump up.
-filter larger particles out by other means.

Youtube Video explaining coagulation and flocculation:
http://www.youtube.com/watch?v=j_LQ7fIwjK8

FILTRATION
Drinking water filtration for the most part happens in three simple steps. First water goes into a concrete box with a layer of sand(to filter out particles) and a layer of gravel (to stop the sand from falling out). After the water is filtered through the sand and gravel it drains into a separate well to be moved on to the disinfecting process. After the filter is operated for a while it becomes clogged so water is shot through the box from the bottom up and since the particles are lighter than the sand it floats higher and it is sucked out of the filter box by a vent near the top. After the sand resettles new water is pumped in and the process restarts.

There are numerous communities of bugs that live in fresh water. When water is filtered to remove these organisms, they are not killed, but trapped in the filter, allowing the clean water to be consumed. Some filters are more efficient than others, and the pore-size efficiency determines how effective a water filter is. The pore-size efficiency is the measurement of the size of the openings in a water filter. A micron is the measurement that describes the size of the filter's openings, and is 1/1,000 of a millimeter. A filter having a micron size less than one will remove parasitic eggs and larvae in addition to protozoa from the water. However, if bacteria needs to be remove from the water, the micron size must be less than 0.4 microns. Thus, the effectiveness of a water filter depends upon what is being filtered. For example, if you wished to filter water that contains hepatitis A, and you used a filter with pores larger than the hepatitis A components, these organisms would travel directly through the pores of the filter and would be present in the "clean water." A water filter operates by having an intake hose which draws water into the filter. If you have a water bottle with a filter inside, you should place the water inside the bottle and then place the filter inside the bottle. If you have a handheld filter, you can either scoop water into a pail or directly put the intake hose in the water source. Once water is inside the intake hose, water is pressed through a filter either manually or through suction. While the water is being pressed through the filter, it traps microorganisms from the water, allowing for clean drinking water to exit through the filter outlet.

There are two main types of filters currently available. The first filter is the membrane filter, which uses thin sheets with precisely sized pores that do not allow items larger than the pore size from passing through the filter. The second type of filter is the depth filter, which uses thick porous materials (carbon or ceramic) to trap particles as water flows through the filter. With each type of filter, there are both pros and cons. While membrane filters are relatively easy to clean, they often clog much more quickly that depth filters. In addition, while depth filters have the ability to remove a gamut of organic chemicals and heavy metals, rough treatment can crack the filter, leaving the filter useless. Most water filters equipped to kill viruses often contain an iodine component, which can alter the taste of water. If  you wished to kill viruses in the water, but didn't want the water to have a bad taste, ascorbic acid can be added to improve the taste of the water, by neutralizing the iodine.

There are a few important guidelines for filtering water. First, one important guideline for filtering water, is to filter the cleanest water available. If you choose to filter extremely dirty water instead of water that is a bit cleaner, the dirty water will clog the filter much more quickly. Also, it's a good idea to pre-filter the water through something such as a bandanna, allowing the large particles to be separated from the water before the actual filter is utilized. Finally, if extremely dirty water must be filtered, it's important to let it sit out overnight so the particles are able to settle.

Although filtration is one important method by which water can be filtered, there are numerous other ways to filter water. One other method to purify water, is to boil the water. While boiling the water will remove harmful microorganisms, it takes a large amount of time, produces water with a flat taste, and a large amount of fuel must be used to boil water. In addition, chemical tablets can be used to filter water. These chemical tablets kill bacteria in the water and produce safe drinking water, but take away from water's taste by producing a bitter taste and lingering aftertaste. Chemical tablets also have a limited shelf life once they've been opened.

Sources:

http://www.princeton.edu/~oa/manual/water.shtml

http://adventure.howstuffworks.com/outdoor-activities/hiking/water-filter3.htm

http://techalive.mtu.edu/meec/module03/Sources-Groundwater.htm

Videos:
http://www.youtube.com/watch?v=ELBKBY-XY6w
         -Good overview on water purification techniques in general

http://www.youtube.com/watch?v=OMZpzcItQkc    
          -How to construct a water filter


DISINFECTION
Disinfection removes, kills, or deactivates pathogenic microorganisms physically or chemically. Chemically, disinfectants include chlorine, chlorine dioxide, and alcohols. Physically, UV light, gamma rays, and heat can disinfect water. Disinfection usually occurs due to cell wall corrosion of the microorganisms, which no longer allows the microorganisms to multiply.
                http://www.lenntech.com/processes/disinfection/what-is-water-disinfection.htm