Water ChemistryWater Chemistry

B. Corrosion,B. Corrosion,

C. Coagulation and flocculation C. Coagulation and flocculation

• Dissolved oxygen and carbon dioxide which Dissolved oxygen and carbon dioxide which contribute to corrosion can be removed by contribute to corrosion can be removed by de-de-aeration (aeration (e.g., through e.g., through heatingheating water). water).

• Chemical additives like sodium hydroxide and Chemical additives like sodium hydroxide and sodium hexametaphosphate (SHMP) may be sodium hexametaphosphate (SHMP) may be added to water to reduce corrosion.added to water to reduce corrosion.

• Non-corrosive materials can be used for Non-corrosive materials can be used for distribution systemsdistribution systems

• Metal pipes can be lined with non-corrosive Metal pipes can be lined with non-corrosive coveringscoverings

Controlling corrosion:Controlling corrosion:

ClarificationClarification - Three step process: - Three step process:

• Coagulation, Coagulation, accomplished by rapid accomplished by rapid mixingmixing of chemical coagulant with of chemical coagulant with “raw” (untreated) water, followed by“raw” (untreated) water, followed by

• Slow mixingSlow mixing or or flocculationflocculation, in which floc , in which floc attracts colloidal solids, andattracts colloidal solids, and

• SedimentationSedimentation, in which gravity , in which gravity settles solids out of solution. settles solids out of solution.

Coagulation:Coagulation:

• CoagulationCoagulation is the destabilization of is the destabilization of colloidal particles.colloidal particles.

• Coagulants include iron and aluminum Coagulants include iron and aluminum salts, synthetic cationic, anionic and salts, synthetic cationic, anionic and nonionic polymersnonionic polymers

• The ability of an agent to coagulate a The ability of an agent to coagulate a water is related to its charge and size of water is related to its charge and size of synthetic polymer.synthetic polymer.

Chemical Coagulants:Chemical Coagulants:

• Aluminum sulfate (alum, or AlSOAluminum sulfate (alum, or AlSO44) is the ) is the

most common chemical coagulant used in most common chemical coagulant used in drinking water treatment due to low cost.drinking water treatment due to low cost.– Insoluble aluminum hydroxide forms.Insoluble aluminum hydroxide forms.– A floc A floc forms, which forms larger particles forms, which forms larger particles

that fall out of solution (that fall out of solution (precipitationprecipitation).).– Addition of lime (calcium carbonate) or soda Addition of lime (calcium carbonate) or soda

ash (sodium carbonate) increases alkalinity ash (sodium carbonate) increases alkalinity of water to facilitate floc formation.of water to facilitate floc formation.

Other coagulants and aids:Other coagulants and aids:• Ferrous sulfate Ferrous sulfate (FeSO(FeSO44),),

• Ferric salts Ferric salts (ferric sulfate or ferric chloride),(ferric sulfate or ferric chloride),• Sodium aluminate Sodium aluminate (alumina dissolved in (alumina dissolved in

sodium hydroxide),sodium hydroxide),• Synthetic polymers Synthetic polymers (high MW charged, (high MW charged,

organic compounds)organic compounds)• Coagulant aids Coagulant aids (polymers, silica, clays, acids, (polymers, silica, clays, acids,

alkalies, etc.)alkalies, etc.)

Flocculation:Flocculation:• FlocculationFlocculation is process to promote is process to promote

aggregation and sedimentation of particles.aggregation and sedimentation of particles.• Success of the flocculation is dependent Success of the flocculation is dependent

first onfirst on– The effectiveness of the coagulation in the raw The effectiveness of the coagulation in the raw

waterwater– The flocculation process must provide The flocculation process must provide

adequate time for the desired floc size and adequate time for the desired floc size and density to formdensity to form

Measuring Treatment efficiency:Measuring Treatment efficiency:

• A A jar test jar test is often used to determine the is often used to determine the efficiency of flocculation.efficiency of flocculation.– A water sample is placed in a beaker and the pH A water sample is placed in a beaker and the pH

adjusted.adjusted.

– A coagulant is added in a variety of concentrations.A coagulant is added in a variety of concentrations.

– The sample is mixed and allowed to settle.The sample is mixed and allowed to settle.

– The amount of sediment is measured.The amount of sediment is measured.

Walking Flocculator

1. Driver Motor2. Variable Speed Device3. Gear Reducer4. Drive Linkage5. Flocculator line shafting6. Bearings7. Walking Beams8. Paddle Assemblies

Vertical flocculator

1. Driver Motor2. Variable Speed Device3. Gear Reducer4. Drive shaft coupling5. Thrust Collar6. Radical Thrust Bearing7. Drive Base8. Paddle Reel Assemblies9. Bottom Steady Bearing

Horizontal Flocculator

1. Driver Motor2. Variable Speed Device3. Gear Reducer4. Power Transfer5. Stuffing Box6. Flocculator Line Shafting7. Shaft Connections8. Bearings9. Paddle Reel Assemblies

“Alabama” flocculator

Upflow Solids Contact Clarifier

Summary:Summary:

• Corrosion is the complex electrochemical Corrosion is the complex electrochemical process that can damage water distribution process that can damage water distribution systems (pipes, tanks, etc.)systems (pipes, tanks, etc.)

• Corrosion can be controlled by using non-Corrosion can be controlled by using non-corrosive materials, coating pipes, etc.corrosive materials, coating pipes, etc.

• Coagulation, flocculation, and sedimentation Coagulation, flocculation, and sedimentation remove particulates and some bacteria as well remove particulates and some bacteria as well as organics from water with the aid of various as organics from water with the aid of various chemicals.chemicals.