Water Supply Water Treatment

Vocabulary flashcards covering major concepts, equipment, chemicals, and processes discussed in the Water Supply Engineering lecture notes.

Water Treatment

Processes used to make water acceptable for its intended end use by removing or reducing contaminants.

Public-Supply Treatment Goals

Prevent health effects, improve aesthetics, and comply with regulations.

Groundwater – Advantages

Low bacteria, low turbidity, constant temperature and chemistry.

Groundwater – Disadvantages

Often hard; may contain excess iron, manganese, H₂S, radionuclides, or chemical contaminants.

Surface Water Challenges

Assumed microbiologically contaminated, usually turbid, and variable in quality.

Algae Problems

Cause taste, odor, color, toxins, filter clogging, slime, corrosion, treatment interference, and THM formation.

Aquatic Weeds – Types

Floating, submerged, and emergent weeds found in water sources.

Intake Screening

Preliminary treatment step that removes large debris to protect plant equipment.

Bar Screen

Coarse screen of parallel bars used to intercept large objects at intakes.

Wire-Mesh Screen

Fine screen using mesh fabric to remove smaller debris.

Screen Clogging

Accumulation of debris that restricts flow through intake screens.

Cyclone Degritter

Device that removes grit by centrifugal force before water enters the plant.

Microstrainer

Rotating drum with fabric that captures algae and solids and cleans via backwash jets.

Coagulation

Rapid mixing of chemicals to destabilize particles so they can agglomerate.

Flocculation

Gentle mixing that allows destabilized particles to grow into settleable floc.

Suspended Solids

Particles visible to the eye that can be removed by plain sedimentation.

Colloidal Solids

Very fine particles that remain dispersed and require coagulation to settle.

Dissolved Solids

Ions or molecules fully dissolved and not removable by settling or filtration alone.

Conventional Filtration Steps

Coagulation, flocculation, sedimentation, filtration.

Zeta Potential

Electrical repulsive force that keeps particles apart in water.

Van der Waals Force

Natural attractive force that causes particles to come together.

Floc

Aggregated particle masses formed from nonsettleable solids plus coagulant chemicals.

Alum (Aluminum Sulfate)

Most common chemical coagulant used for turbidity removal.

Ferric Chloride

Iron-based coagulant used when low-temperature or low-alkalinity water is treated.

Jar Test

Laboratory procedure to determine optimum coagulant type and dosage.

Coagulant Aid

Chemical, such as activated silica or polyelectrolyte, that enhances floc formation.

Activated Silica

Inorganic coagulant aid that adds weight and improves settling of floc.

Polyelectrolyte

Long-chain organic polymer used as a coagulant aid or filter aid.

Lime (Ca(OH)₂)

Chemical used to raise alkalinity or soften water.

Soda Ash (Na₂CO₃)

Chemical that adds carbonate alkalinity and assists lime softening.

Volumetric Feeder

Chemical feeder that delivers chemicals by measured volume per unit time.

Gravimetric Feeder

Feeder that delivers chemicals by measured weight per unit time.

Static Mixer

In-pipe device with fixed vanes that provides rapid mixing without mechanical power.

Sedimentation

Gravity settling process that removes floc to lessen filter loading.

Sedimentation Basin – Inlet Zone

Section that reduces velocity and distributes flow evenly.

Settling Zone

Calm area where particles settle out of suspension.

Outlet Zone

Provides smooth flow transition while keeping settled solids undisturbed.

Sludge Zone

Bottom area where settled solids accumulate for removal.

Detention Time

Theoretical time a water particle stays in a basin (volume ÷ flow).

Surface Loading Rate

Volume of water applied per unit surface area of basin (gpm/ft²).

Short-Circuiting

Condition where water passes through a basin faster than design detention time.

Filtration

Removal of fine suspended matter by passing water through porous media.

Turbidity

Cloudiness caused by suspended particles such as silt, floc, or microbes, measured in NTU.

Direct Filtration

Treatment using coagulation, flocculation, and filtration without sedimentation.

Disinfection

Destruction of pathogenic microorganisms in water.

Sterilization

Destruction of all microorganisms, not usually required for drinking water.

Oxidant

Chemical that accepts electrons, destroying microbes or oxidizing contaminants.

Chlorine Gas

Common disinfectant supplied in cylinders or ton containers.

Calcium Hypochlorite

Dry, 65–70 % available chlorine compound (HTH) used for disinfection.

Sodium Hypochlorite

Liquid bleach (5–15 % NaOCl) used as chlorine source.

Chloramine

Combined chlorine disinfectant formed by reacting chlorine with ammonia.

Chlorine Demand

Amount of chlorine consumed by reactions with impurities before residual forms.

Chlorine Residual

Chlorine remaining in water after demand has been satisfied.

Free Available Residual

Chlorine present as HOCl/OCl⁻, strongest disinfecting form.

Combined Residual

Chlorine combined with ammonia or organics (chloramines).

C × T Concept

Product of disinfectant concentration and contact time that determines microbial kill.

Chlorine Leak Test

Ammonia vapor generates white smoke where chlorine gas is present.

Self-Contained Breathing Apparatus (SCBA)

Essential safety gear for entering chlorine storage areas during leaks.

Potassium Permanganate

Strong oxidant used to control taste, odor, and manganese; must be removed downstream.

Fluoridation

Addition of fluoride ions to drinking water to reduce dental caries.

Dental Fluorosis

Mottling of enamel from excessive fluoride ingestion during tooth development.

Sodium Fluoride

Solid fluoride compound used for water fluoridation.

Fluorosilicic Acid

Liquid (H₂SiF₆) commonly used for fluoridation.

Corrosion

Deterioration of a material (usually metal) by chemical reaction with environment.

Scaling

Deposition of mineral solids (e.g., CaCO₃) on pipe walls and equipment.

Water Stability

Tendency of water either to corrode or form scale, influenced by TDS, pH, alkalinity, etc.

Total Dissolved Solids (TDS)

Sum concentration of dissolved ions; higher levels increase conductivity and corrosion rate.

Microbiologically Influenced Corrosion (MIC)

Accelerated corrosion caused by bacterial activity producing CO₂ or H₂S.

Calcium Carbonate Scale

Most common mineral deposit formed when CaCO₃ precipitates out of water.

Alkalinity Adjustment

Process of adding chemicals to raise alkalinity and control corrosion or scale.

Corrosion Inhibitor

Chemical (e.g., orthophosphate) that forms protective film on metal surfaces.

Iron & Manganese

Metals that are colorless when dissolved but oxidize to colored precipitates.

Sequestration

Addition of polyphosphate or silicate to keep iron/manganese in solution.

Lime Softening

Process removing hardness by precipitating CaCO₃ and Mg(OH)₂ using lime and soda ash.

Hardness

Sum of calcium and magnesium ions that react with soap and form scale.

Quicklime (CaO)

Unslaked lime that must be hydrated before use in softening.

Flocculation Time – Softening

Typically 40–60 minutes for lime-soda ash process.

Ion Exchange Softening

Process where hardness ions (Ca²⁺, Mg²⁺) are exchanged for Na⁺ on resin beads.

Resin Backwash

Up-flow water rinse to loosen resin bed and remove solids before regeneration.

Salt Regeneration

Restoration of sodium form on exhausted resin using brine.

Adsorption

Removal of organic compounds by adherence to activated carbon surfaces.

Activated Carbon

Porous carbon material with high surface area used for adsorption of organics.

Powdered Activated Carbon (PAC)

Fine carbon fed into water ahead of conventional treatment processes.

Granular Activated Carbon (GAC)

Coarse carbon used in fixed beds through which water flows.

Aeration

Contacting water with air to strip gases, oxidize metals, or add oxygen.

Cascade Aerator

Step structure where water falls, contacting air for gas exchange.

Packed Tower Aerator

Column filled with packing where air flows counter-current to descending water.

Hydrogen Sulfide

Gas causing rotten-egg odor; removable by aeration or oxidation.

Excess Dissolved Oxygen

High DO that increases corrosion potential and can cause filter air binding.

Microfiltration

Pressure-driven membrane process removing particles >0.1 µm.

Ultrafiltration

Membrane process that removes macromolecules and some viruses, pores ~0.01 µm.

Nanofiltration

Membrane process that removes polyvalent ions and small organics; between UF and RO.

Reverse Osmosis (RO)

Uses pressure to overcome osmotic pressure and force pure water through semi-permeable membrane.

Osmotic Pressure

Pressure developed as solvent moves through a membrane into a more concentrated solution.

Cyclonic Flow

Spiral motion used in degritters to separate grit by centrifugal force.

Static Head Loss

Pressure drop through a filter or system due to friction and media resistance.

Trihalomethanes (THMs)

Chlorination by-products formed from reaction with natural organics; regulated carcinogens.

Taste & Odor Control

Treatment steps (e.g., PAC, permanganate, aeration) aimed at improving sensory quality.

Sedimentation Basin Sludge

Settled floc that must be removed to maintain basin efficiency.

Sludge Dewatering

Processes (drying beds, lagoons, thickeners, filters, centrifuges) that reduce sludge volume.