Water Treatment Chapter 4 - Coagulation And Flocculation

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Alkalinity

Back 1

Alkalinity is the name given to the quantitative capacity of an aqueous solution to neutralize an acid. Measuring alkalinity is important in determining a stream's ability to neutralize acidic pollution from rainfall or wastewater

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Anionic Polymer

Back 2

A polymer having a negatively charged group of ions; often used as a filter aid and for dewatering sludges

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Dewatering

Back 3

Dewatering is the removal of water from solid material or soil by wet classification, centrifugation, filtration, or similar solid-liquid separation processes

Front 4

Cationic polymer

Back 4

A polymer having positively charged group of ions; often used as an coagulant aid

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Coagulants

Back 5

Chemicals that cause very fine particles to clump (floc) together into larger particles. This makes it easier to separate the solids from the water.

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Coagulation

Back 6

The clumping together of very fine particles into larger particles (floc) caused by the use of chemicals (coagulants). The chemicals neutralize the electrical charges of the fine particles, allowing them to come closer and form larger clumps. This clumping together makes it easier to separate the solids from the water, by settling, skimming, draining or filtering.

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Colloids

Back 7

Very small, finely divided solids (particles that do not dissolve) that remain dispersed in a liquid for a long time due to their small size and electrical charge. When most of the particles in the water have negative electrical charge, they tend to repel each other. This repulsion prevents the particles from clumping together, becoming heavier, and settling out.

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Detention Time

Back 8

Important in flocculation.The theoretical (calculated) time required for a given amount of water or wastewater to pass through a tank at a given rate of flow. Formula is Detention Time (Hr.) = (Basin Volume (Gal.) X (24 Hrs) / Flow (Gal/Day))
aka Hr=(Gal X 24) / (Gal per day)

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Disinfection By-Product (DBP)

Back 9

A contaminant formed by the reaction of disinfection chemicals (such as chlorine) with other substances in the water being disinfected.

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Floc

Back 10

Clumps of bacteria and particles or coagulants and impurities that have come together and formed a cluster. Found in flocculation tanks, settling or sedimentation basins

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Flocculation

Back 11

The gathering together of fine particles after coagulation to form larger particles by a process of gentle mixing. This clumping together makes it easier to separate the solids from the water

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Head Loss

Back 12

The head, pressure, or energy (they are the same) lost by water flowing in a pipe or channel as a result of turbulence caused by the velocity of the flowing water and the roughness of the pipe, channel walls, or restrictions caused by fittings. Water flowing in a pipe loses head, pressure, or energy as a result of friction. The head loss through a filter is due to friction caused by material building up on the surface or by the water flowing through the filter media.

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Inorganic

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Chemical substances of mineral origin such as sand, salt, iron, calcium salts, and other mineral materials

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Jar Test

Back 14

A laboratory procedure that simulates coagulation/flocculation with differing chemical doses. The purpose of the procedure is to estimate the minimum coagulant dose required to achieve certain water quality goals.

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Laundering Weir

Back 15

Sedimentation basin overflow weir. A plate with V-notches along the top to ensure a uniform flow rate and avoid short-circuiting.

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Monomer (MON-o-mer)

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A molecule of low molecular weight capable of reacting with identical or different monomers to form polymers.

Front 17

Nonionic Polymer (NON-eye-ON-ick)

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A polymer that has no net electrical charge

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Net electrical charge

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Number of electrons is equal to the number of protons (which are positively charged), resulting in a net zero overall charge

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Polyanionic (poly-AN-eye-ON-ick)

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Characterized by many active negative charges especially active on the surface of particles. Makes the water have turbidity.

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Polyelectrolyte (POLY-ee-LECK-tro-lite)

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Used with other chemical coagulants to aid in binding small suspended particles to larger chemical flocs for their removal from water. Often called a POLYMER. A high-molecular-weight (relatively heavy) substance, having points of positive or negative electrical charges.

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Polymer (POLY-mer)

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A long-chain molecule formed by the union of many monomers (molecules of lower molecular weight). Polymers are used with other chemical coagulants to aid in binding small suspended particles to larger chemical flocs for their removal from water

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Short-Circuiting

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A condition that occurs in tanks or basins when some of the flowing water entering a tank or basin flows along a nearly direct pathway from the inlet to the outlet. This is usually undesirable because it may result in shorter contact, reaction, or settling times in comparison with the theoretical (calculated) or presumed detention times.

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Sludge

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The settleable solids separated from liquids during processing.

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(TOC)

Back 24

Total Organic Carbon (TOC), TOC is a measure of the amount of organic carbon in water.

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(THMs)

Back 25

Trihalomethanes (THMs) (tri-HAL-o-METH-hanes)
Often formed during chlorination by reactions with natural organic materials in the water. The resulting compounds (THMs) are suspected of causing cancer.

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Trihalomethanes (THMs) (tri-HAL-o-METH-hanes)

Back 26

Often formed during chlorination by reactions with natural organic materials in the water. The resulting compounds (THMs) are suspected of causing cancer.

Front 27

True Color

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Color of the water from which turbidity has been removed. The turbidity may be removed by double filtering the sample through a Whatman No. 40 filter when using the visual comparison method.

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Turbidity Meter (ter-BID-it-tee)

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An instrument for measuring and comparing the turbidity of liquids by passing light through them and determining how much light is reflected by the particles in the liquid. The normal measuring range is 0 to 100 and is expressed as nephelometric turbidity units (NTUs). Also called a turbidimeter.

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(NTUs) or simply TU

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Nephelometric (neff-el-o-MET-rick) turbidity units. a measure of the cloudiness of water or turbity.

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Turbidity (ter-BID-it-tee)

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The cloudy appearance of water caused by the presence of suspended and colloidal matter

Front 31

Weir (WEER)

Back 31

A wall or obstruction used to control flow (from settling tanks and clarifiers) to ensure a uniform flow rate and avoid short-circuiting. Formula --- Weir loading (GPM/ft) =((Flow, GPM) / (Lenght of Weir, Ft.))

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What is the purpose of coagulation and flocculation?

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To remove non settable solids aka organic (crap, dead animals) and inorganic (minerals, rocks) from water being treated.

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What happens in the coagulation process?

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Coagulation process - You add chemicals that change the negatively charged ions of organic and inorganic materials so they can start forming micro flock.

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What happens in the flocculation process?

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Flocculation process - starts to combine the micro-floc together so it becomes macro-floc and then the overall molecular weight increases and gravity can push it down into the sedimentation bin.

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What is flash mixing?

Back 35

When you quickly mix your coagulant to raw water and evenly disperse it.

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What does primary coagulants do?

Back 36

They neutralize (beat up) the electrical charges of the colloidal matter so they get together and clump.

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What are the most commonly used primary coagulants?

Back 37

Aluminum Sulfate (Alum, AL) , Ferric Sulfate, Ferris Sulfate. These are from the Metallic Salts family.
Then their cousins are the Polymers, cationic polymer, anionic polymer, nonionic polymer.

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What is the primary purpose of flash mixing?

Back 38

Is to evenly dispense the chemical coagulant into the raw water.

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What are four methods of mixing coagulant chemicals into the plant flow?

Back 39

1. Hydrological
2. Mechanical
3. Diffusers
4.. Pumped Blenders

Front 40

What is the recommended detention time in the flocculation process?

Back 40

5 to 20 minutes for direct filtration systems
30 minutes for conventional filtration systems

Front 41

How long is the typical mixing time in the coagulation process?

Back 41

Just a few seconds (That's why its called flash mixing)

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Why baffles needed in the flocculation basins?

Back 42

They help prevent short circuiting and reduce turbulence that could break apart the macro-floc

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Why is coagulation and flocculation so important to the other processes?

Back 43

It helps keep filters from failing prematurely and can help remove a large portion of colloid material before the disinfection process since those chemicals can react and cause THM's. Also bacteria can pass filters and infect the clean supply.

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What is the most important consideration in the coag-floc process?

Back 44

To make sure you add the correct type and amount of chemicals to the water being treated.

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Typical functions that an operator performs during the floc and coag process

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1. Check the quality of the water coming in and out of each process
2. Process performance
3. Adjust process controls and equipment
4. Visual inspection

Front 46

What test are used to monitor the coag and floc process?

Back 46

1. pH Levels
2.Alkalinity
3.Color
4.Chlorine demand
5. Tempearture
6. Turbidity
(Pacctt) This pact of test are used to monitor coag and floc

Front 47

Total Alkaline solution usually has these in it.

Back 47

1. Carbonate
2. Bi-Carbonate
3. Hydroxide