[Script Info]
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[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:01.41,0:00:03.93,Default,,0000,0000,0000,,- [Narrator] Coagulation is\Nthe addition of chemicals
Dialogue: 0,0:00:03.93,0:00:06.81,Default,,0000,0000,0000,,to destabilize the electrostatic forces
Dialogue: 0,0:00:06.81,0:00:09.36,Default,,0000,0000,0000,,of nonsettleable solids.
Dialogue: 0,0:00:09.36,0:00:12.66,Default,,0000,0000,0000,,Coagulant chemicals typically\Nhave a positive charge,
Dialogue: 0,0:00:12.66,0:00:16.05,Default,,0000,0000,0000,,which binds to the negatively\Ncharged particles in water,
Dialogue: 0,0:00:16.05,0:00:17.34,Default,,0000,0000,0000,,neutralizing them,
Dialogue: 0,0:00:17.34,0:00:18.93,Default,,0000,0000,0000,,and allowing them to come together
Dialogue: 0,0:00:18.93,0:00:22.59,Default,,0000,0000,0000,,to form small clumps of\Nparticles called microfloc.
Dialogue: 0,0:00:23.82,0:00:26.52,Default,,0000,0000,0000,,In most cases, the\Nchemical reaction occurs
Dialogue: 0,0:00:26.52,0:00:28.20,Default,,0000,0000,0000,,in a fraction of a second,
Dialogue: 0,0:00:28.20,0:00:30.09,Default,,0000,0000,0000,,so it's important the coagulant
Dialogue: 0,0:00:30.09,0:00:32.31,Default,,0000,0000,0000,,is dispersed quickly and evenly
Dialogue: 0,0:00:32.31,0:00:35.91,Default,,0000,0000,0000,,to encourage as many particle\Ncollisions as possible.
Dialogue: 0,0:00:35.91,0:00:39.06,Default,,0000,0000,0000,,Because this process relies\Non chemical reactions,
Dialogue: 0,0:00:39.06,0:00:41.31,Default,,0000,0000,0000,,several considerations must be made.
Dialogue: 0,0:00:42.39,0:00:44.28,Default,,0000,0000,0000,,Water temperature, for example.
Dialogue: 0,0:00:44.28,0:00:46.68,Default,,0000,0000,0000,,Colder water usually slows coagulation
Dialogue: 0,0:00:46.68,0:00:48.42,Default,,0000,0000,0000,,and flocculation reactions,
Dialogue: 0,0:00:48.42,0:00:50.04,Default,,0000,0000,0000,,which may require more time
Dialogue: 0,0:00:50.04,0:00:52.29,Default,,0000,0000,0000,,to achieve optimal floc formation.
Dialogue: 0,0:00:53.43,0:00:56.34,Default,,0000,0000,0000,,Extreme values of pH, high or low,
Dialogue: 0,0:00:56.34,0:00:59.01,Default,,0000,0000,0000,,will also interfere with the process.
Dialogue: 0,0:00:59.01,0:01:02.43,Default,,0000,0000,0000,,Coagulant effectiveness\Nis highly dependent on pH.
Dialogue: 0,0:01:03.60,0:01:06.78,Default,,0000,0000,0000,,For some coagulants,\Nalkalinity is a factor.
Dialogue: 0,0:01:06.78,0:01:09.06,Default,,0000,0000,0000,,Operators may need to raise alkalinity
Dialogue: 0,0:01:09.06,0:01:11.16,Default,,0000,0000,0000,,for coagulation to be effective
Dialogue: 0,0:01:11.16,0:01:13.71,Default,,0000,0000,0000,,when using iron or aluminum coagulants
Dialogue: 0,0:01:13.71,0:01:16.98,Default,,0000,0000,0000,,that can consume\Nalkalinity and depressed pH
Dialogue: 0,0:01:16.98,0:01:19.53,Default,,0000,0000,0000,,when they are added to\Nlow-alkalinity waters.
Dialogue: 0,0:01:20.70,0:01:23.16,Default,,0000,0000,0000,,Turbidity is also important.
Dialogue: 0,0:01:23.16,0:01:24.66,Default,,0000,0000,0000,,The lower the turbidity,
Dialogue: 0,0:01:24.66,0:01:27.33,Default,,0000,0000,0000,,the more difficult it\Nis to form proper floc.
Dialogue: 0,0:01:28.23,0:01:32.22,Default,,0000,0000,0000,,The most common coagulant\Nchemical used is aluminum sulfate,
Dialogue: 0,0:01:32.22,0:01:33.81,Default,,0000,0000,0000,,commonly called alum.
Dialogue: 0,0:01:34.77,0:01:37.95,Default,,0000,0000,0000,,When added to water, alum\Nforms jelly-like particles
Dialogue: 0,0:01:37.95,0:01:39.54,Default,,0000,0000,0000,,of aluminum hydroxide.
Dialogue: 0,0:01:40.59,0:01:43.26,Default,,0000,0000,0000,,The trivalent aluminum ions neutralize
Dialogue: 0,0:01:43.26,0:01:46.26,Default,,0000,0000,0000,,and attach to negatively\Ncharged particles in water,
Dialogue: 0,0:01:46.26,0:01:47.61,Default,,0000,0000,0000,,forming microfloc.
Dialogue: 0,0:01:48.48,0:01:52.79,Default,,0000,0000,0000,,Alum works best in a\NpH range of 5.5 to 7.5.
Dialogue: 0,0:01:54.36,0:01:56.91,Default,,0000,0000,0000,,Polyaluminum chloride and iron salts,
Dialogue: 0,0:01:56.91,0:01:59.67,Default,,0000,0000,0000,,such as ferric chloride\Nand ferric sulfate,
Dialogue: 0,0:01:59.67,0:02:01.05,Default,,0000,0000,0000,,are also used.
Dialogue: 0,0:02:01.05,0:02:03.57,Default,,0000,0000,0000,,They operate over a wider pH range.
Dialogue: 0,0:02:04.44,0:02:09.12,Default,,0000,0000,0000,,Coagulant and flocculant aids\Nare added to improved binding,
Dialogue: 0,0:02:09.12,0:02:11.46,Default,,0000,0000,0000,,build stronger, more settleable floc,
Dialogue: 0,0:02:11.46,0:02:15.39,Default,,0000,0000,0000,,and effect flocculation by\Nincreasing floc size, strength,
Dialogue: 0,0:02:15.39,0:02:17.43,Default,,0000,0000,0000,,and/or floc density.
Dialogue: 0,0:02:17.43,0:02:19.59,Default,,0000,0000,0000,,In addition, they help overcome the effect
Dialogue: 0,0:02:19.59,0:02:20.91,Default,,0000,0000,0000,,of low temperatures,
Dialogue: 0,0:02:20.91,0:02:23.19,Default,,0000,0000,0000,,reduce the amount of coagulant needed,
Dialogue: 0,0:02:23.19,0:02:25.68,Default,,0000,0000,0000,,and reduce the amount of sludge produced.
Dialogue: 0,0:02:26.55,0:02:30.57,Default,,0000,0000,0000,,Commonly used coagulant aids\Ninclude cationic polymers.
Dialogue: 0,0:02:30.57,0:02:33.81,Default,,0000,0000,0000,,Polymers are defined\Nas a synthetic compound
Dialogue: 0,0:02:33.81,0:02:35.37,Default,,0000,0000,0000,,with high molecular weight
Dialogue: 0,0:02:35.37,0:02:39.15,Default,,0000,0000,0000,,and composed of repeating\Nchemical units or monomers.
Dialogue: 0,0:02:40.20,0:02:42.99,Default,,0000,0000,0000,,Polymers may be polyelectrolytes,
Dialogue: 0,0:02:42.99,0:02:45.57,Default,,0000,0000,0000,,such as the water-soluble flocculants,
Dialogue: 0,0:02:45.57,0:02:48.81,Default,,0000,0000,0000,,water-insoluble ion-exchange resins,
Dialogue: 0,0:02:48.81,0:02:51.60,Default,,0000,0000,0000,,or insoluble uncharged materials.
Dialogue: 0,0:02:52.44,0:02:55.08,Default,,0000,0000,0000,,Polymers are long chains of molecules
Dialogue: 0,0:02:55.08,0:02:57.48,Default,,0000,0000,0000,,that produce highly charged ions
Dialogue: 0,0:02:57.48,0:02:59.67,Default,,0000,0000,0000,,and help bind microfloc together
Dialogue: 0,0:02:59.67,0:03:01.95,Default,,0000,0000,0000,,into larger floc particles.
Dialogue: 0,0:03:01.95,0:03:04.20,Default,,0000,0000,0000,,They are very popular with operators
Dialogue: 0,0:03:04.20,0:03:06.03,Default,,0000,0000,0000,,because they are very effective
Dialogue: 0,0:03:06.03,0:03:09.60,Default,,0000,0000,0000,,and can be positive, negative,\Nor neutrally charged,
Dialogue: 0,0:03:09.60,0:03:11.73,Default,,0000,0000,0000,,providing a great deal of flexibility
Dialogue: 0,0:03:11.73,0:03:13.29,Default,,0000,0000,0000,,in different circumstances.