Water Treatment Theory Midterm Review

A comprehensive set of vocabulary flashcards covering water treatment theory, including solids measurement, colloidal stability, coagulation/flocculation, settling regimes, adsorption isotherms, and ion exchange.

Total Suspended Solids (TSS)

Solid particles suspended in water that can be trapped by a filter, typically measured by drying the retained solids at $103-105^{\circ}\text{C}$.

Total Solids

The sum of suspended solids and dissolved solids in a water sample, represented by the relationship: $\text{Total Solids} = TSS + TDS$.

Turbidity

A measure of how cloudy water is due to light scattering by particles, usually measured in NTU; it depends on particle size, shape, colour, and refractive index.

Colloids

Very small particles that often remain stable in water due to surface charges that cause repulsion and Brownian motion which keeps them suspended.

Total Organic Carbon (TOC)

All organic carbon present in a sample, consisting of both dissolved and particulate fractions ($TOC = DOC + POC$).

Dissolved Organic Carbon (DOC)

The fraction of organic carbon that passes through a filter, commonly around $0.45\,\mu\text{m}$.

Particulate Organic Carbon (POC)

Organic carbon associated with particles that are retained by a filter.

Isomorphic Substitution

A process in clay minerals where atoms in the crystal structure are replaced by others, often resulting in a negative surface charge.

$$pH_{pzc}$$

The point of zero charge; the specific pH level at which the net surface charge of a particle is zero.

Electrical Double Layer

The region surrounding a charged particle consisting of a tightly bound layer of counter-ions near the surface and a more diffuse layer farther away.

Zeta Potential

The electrical potential at the slipping plane around a particle which indicates the strength of repulsion between particles.

Ionic Strength

A measure of the concentration of ions in a solution; increasing it compresses the electrical double layer and promotes particle aggregation.

DLVO Theory

A theory explaining colloidal stability based on the balance between Van der Waals attraction and electrostatic repulsion.

Coagulation

A water treatment process used to destabilize suspended and colloidal particles, usually by reducing their surface charge.

Flocculation

A process involving gentle mixing to promote collisions between destabilized particles to form larger flocs.

Double-layer Compression

A particle destabilization mechanism where added ions reduce the thickness of the electrical double layer.

Charge Neutralization

A destabilization mechanism where coagulant ions neutralize the surface charge of particles.

Adsorption and Interparticle Bridging

A mechanism where polymers or hydrolysis products attach to multiple particles, linking them together.

Sweep Flocculation

A mechanism where metal hydroxide precipitates form and physically trap particles as they settle.

Rapid Mixing

A process that quickly disperses coagulant throughout water to ensure contact with particles before hydrolysis reactions are complete.

Velocity Gradient ($G$)

A concept used in flocculation design representing the intensity of mixing.

Detention Time ($t$)

The duration of time water remains in a treatment unit, such as a flocculation basin.

Tapered Flocculation

A design that reduces mixing intensity from one compartment to the next to allow large flocs to grow without breaking.

Discrete Settling

A settling regime where particles settle individually without changing size or shape, common in grit chambers.

Flocculent Settling

A settling regime where particles collide and grow while settling, increasing their settling velocity with depth.

Hindered Settling

A regime occurring at high particle concentrations where particles interfere with each other and settle as a zone.

Compression Settling

A regime at very high solids concentrations where particles are in contact and the solids layer compacts under its own weight.

Surface Overflow Rate (SOR)

A design parameter for sedimentation basins calculated as flow rate divided by surface area ($SOR = \frac{Q}{A}$).

Critical Settling Velocity ($v_c$)

The minimum settling velocity needed for a particle entering at the top of a basin to be completely removed under ideal conditions; it equals the SOR.

Adsorption

The attachment of molecules or ions onto the surface of a solid.

Absorption

A process where a substance enters into the bulk interior of another material.

Desorption

The reverse process of adsorption, where an adsorbed substance leaves the surface and returns to the liquid phase.

Intraparticle Diffusion

The movement of adsorbate molecules through the internal pores of an adsorbent particle.

Adsorption Isotherm

The relationship between the amount of substance adsorbed on a solid and the equilibrium concentration in solution at a constant temperature.

Linear Adsorption Isotherm

An isotherm model defined by $q_e = K_d C_e$, used when adsorption is directly proportional to concentration, typically at low concentrations.

Distribution Coefficient ($K_d$)

The ratio of adsorbate on the solid to the adsorbate in solution in a linear isotherm, often measured in $L/g$ or $L/kg$.

Langmuir Isotherm

A model assuming adsorption occurs on a fixed number of identical sites forming a monolayer with a maximum capacity ($q_{max}$).

Freundlich Isotherm

An empirical model for adsorption on heterogeneous surfaces where capacity increases nonlinearly ($q_e = K_F C_e^{1/n}$).

Breakthrough Curve

A plot of effluent concentration divided by influent concentration ($C/C_0$) versus time or treated volume in a column experiment.

Mass Transfer Zone (MTZ)

The specific region in a fixed-bed adsorption column where adsorption is actively occurring.

Empty Bed Contact Time (EBCT)

The ratio of the adsorbent bed volume to the flow rate ($EBCT = \frac{\text{bed volume}}{Q}$).

Ion Exchange

A process that removes target ions from water by exchanging them stoichiometrically with other ions attached to a resin.

Leakage (Ion Exchange)

The appearance of target ions in treated water before the resin bed is fully exhausted.

Bypass Flow

The practice of allowing a portion of influent water to skip a treatment unit and blend with treated water to control final water quality.