Wastewater Engineering 3

Vocabulary flashcards covering core terms, equipment, design parameters, settling phenomena, and biological reactors introduced in the provided wastewater engineering lecture notes.

Scum

Floatable layer in wastewater composed of grease, oil, plastics, leaves, rags, hair, and other light materials.

Primary (Raw) Sludge

The mass of settled solids collected at the bottom of a primary sedimentation tank.

Sedimentation

Gravity-driven process that removes settleable solids from wastewater; oldest and most widely used unit operation.

Primary Clarifier

Settling tank that receives raw wastewater prior to biological or chemical treatment; detention time 1–3 h (2 h typical).

Short-Circuiting

Hydraulic condition in which part of a tank has a travel time shorter than the designed flow-through time.

Septic Tank

Prefabricated combined settling, skimming, and unmixed anaerobic digestion unit; provides 6–8 h settling, suited to small facilities.

Two-Story (Imhoff) Tank

Dual-chamber unit with an upper settling compartment and lower digestion compartment plus gas vents; separates digestion from flow.

Plain Settling Tank (Clarifier)

Single-story tank optimized for settling where sludge is removed for downstream processing.

Rectangular Clarifier

Clarifier with straight-line flow; solids are scraped to one end; favored when space is limited.

Circular Clarifier

Clarifier with radial flow, typically center-feed; includes central pier, feedwell, and rotating sludge collector.

Energy Dissipating Inlet (EDI)

Device in a feedwell that distributes flow and enhances flocculation by dissipating incoming energy.

Detention Time (t)

Average time wastewater remains in a tank; primary tanks typically 1–2 h.

Overflow Rate (SOR)

Surface loading expressed in m³/m²·day; primary clarifiers: 32–48 (avg) to 80–120 (peak).

Weir Loading Rate

Flow per unit length of effluent weir; typical primary clarifier design 125–500 m³/m·day.

Discrete Settling

Settling of non-interacting particles under low solids concentration (e.g., sand removal).

Flocculant Settling

Particles initially settle independently then aggregate, increasing settling velocity as flocs form.

Tank Bottom Slope

Inclination of clarifier floor toward sludge hopper; 60–150 mm per metre (primary clarifiers).

Sludge Collector Mechanism

Rotating system of blades/scrapers that drags settled solids to the sludge sump.

Scum Skimmer Arm

Rotating device that sweeps floating material into a scum trough for removal.

Continuous-Flow Stirred Tank Reactor (CFSTR)

Completely-mixed reactor where influent and effluent flows are continuous and content is uniform.

Plug Flow Reactor (PFR)

Reactor in which wastewater moves as a piston with no back-mixing; concentration changes along the length.

Arbitrary Flow Reactor (AFR)

Reactor exhibiting partial mixing characteristics between plug-flow and complete-mix.

Packed Bed Reactor (PBR)

Reactor filled with inert media supporting attached biomass; flow can be upflow or downflow.

Fluidized Bed Reactor (FBR / FBBR)

Reactor with packing media expanded by upward flow, creating a fluidized attached-growth system.

Captor Process

FBR variant where biomass grows inside polyester foam pads that can be removed and squeezed; aerated with spargers.

Oxitron Process

FBR variant using sand as media; sand is continually cleaned and recycled; employs high-purity oxygen.

High-Rate Aeration

Activated-sludge modification emphasizing high organic loading and short detention for rapid BOD removal.

Contact Stabilization

Activated-sludge mode with separate contact (adsorption) and stabilization tanks to reduce aeration volume.

Conventional Plug-Flow (ASP)

Traditional activated-sludge configuration with sequential plug-flow aeration basin.

Step-Feed

Activated-sludge variation where influent is introduced at several points along the aeration basin.

Complete-Mix Activated Sludge

Activated-sludge process using CFSTR behavior for uniform substrate concentration throughout basin.

Extended Aeration

Low-rate activated-sludge process with long aeration time and low loading, often used for small plants.

Oxidation Ditch

Ring-shaped extended-aeration basin with horizontal mechanical aerators providing complete mix plug-flow.

Batch Decant (SBR)

Sequencing batch reactor performing fill, react, settle, and decant steps in the same basin.

Settleable Solids

Particles that will settle in an Imhoff cone in 1 h; primary removal efficiency 90–95 %.

Suspended Solids (SS)

Particles remaining suspended in wastewater; primary clarification removes 40–65 %.

Biochemical Oxygen Demand (BOD)

Amount of oxygen consumed by microbial degradation of organic matter; primary treatment removes ~20–35 %.

Short Detention Problems

Insufficient settling leading to high SS and BOD in effluent; can result from short-circuiting.

Temperature Effect (Settling)

Higher water temperature lowers viscosity, increasing settling velocity; low temperatures have the opposite effect.