Wastewater Attached Growth Process

These vocabulary flashcards cover essential terms, organisms, media types, design parameters, and operational considerations for trickling filters and rotating biological contactors in wastewater engineering.

Trickling Filter

An attached-growth biological wastewater treatment unit in which wastewater is distributed over a packed media bed and flows downward while microorganisms on the media degrade organics.

Rotary Distribution Mechanism

Rotating arms that evenly sprinkle wastewater over the top of a trickling filter, ensuring uniform wetting of the media.

Underdrains

Support structures beneath trickling-filter media that collect treated effluent, remove sloughed biomass, and provide ventilation.

Filter Media

The packing inside a trickling filter that supplies surface area for microbial growth; may be rock, plastic, mesh pads, etc.

Rock & Gravel Media

Traditional trickling-filter packing made of crushed rock or slag; durable but heavy and relatively low in specific surface area.

Fiber Mesh Pad

Thin synthetic fibers formed into thick pads that offer high surface area and void space for biofilm attachment.

Brillo Pad (Ribbon Bundle)

A coarser variation of mesh pads consisting of bundled plastic ribbons used as lightweight trickling-filter packing.

Random (Dumped) Packings

Injection-molded plastic shapes (e.g., saddles, rings) dumped randomly into the filter; provide high void space and surface area.

Structured Packings

Stacked, vacuum-formed PVC sheets arranged in geometric patterns; high surface area per volume and lower cost than molded packings.

Specific Surface Area

Total media surface area per unit volume; higher values enhance biofilm contact and treatment efficiency.

Void Space

Open volume within filter media that allows air flow, prevents plugging, and accommodates biomass growth.

Slime Layer (Biofilm)

Gelatinous layer of microorganisms that coats trickling-filter media and carries out organic degradation.

Sloughings

Excess biofilm that shears off media surfaces and is carried to the secondary clarifier for settling.

Achromobacter

One of the predominant aerobic bacterial genera found in trickling-filter biofilms.

Flavobacterium

Common Gram-negative bacteria contributing to organic removal in trickling filters.

Pseudomonas

Versatile heterotrophic bacteria frequently dominating trickling-filter microbial populations.

Alcaligenes

Aerobic bacteria present in trickling-filter slime; assists in biodegradation of organics.

Sphaerotilus natans

Filamentous bacteria that form part of the slime layer; excessive growth may cause bulking.

Beggiatoa

Filamentous sulfur-oxidizing bacteria occasionally found in trickling-filter biofilms.

Nitrosomonas

Ammonia-oxidizing bacteria occurring in the lower, more aerobic zones of trickling filters.

Nitrobacter

Nitrite-oxidizing bacteria that complete the nitrification process within trickling-filter media.

Fusarium

A genus of fungi that can grow in industrial waste trickling filters and contribute to clogging.

Mucor

Filamentous fungus sometimes proliferating in trickling-filter systems treating high-strength wastes.

Penicillium

Common fungus that may colonize trickling-filter media, especially under nutrient-rich conditions.

Geotrichum

Fungal genus capable of rapid growth that can impede ventilation by clogging media voids.

Sporotrichum

Fungus noted in industrial trickling filters; excessive growth reduces filter performance.

Phormidium

Blue-green algae found on upper media surfaces where sunlight is available, supplying oxygen during daylight.

Chlorella

Green algae species contributing to oxygen production in the top zone of trickling filters.

Ulothrix

Filamentous green algae inhabiting sunlit trickling-filter surfaces.

Vorticella

Stalked protozoan that grazes on bacteria, helping to control bacterial populations in trickling filters.

Opercularia

Protozoan genus acting as predator on bacteria within biofilms, maintaining community balance.

Epistylis

Colonial protozoan aiding in regulation of bacterial numbers on trickling-filter media.

Low-Rate Trickling Filter

System loaded at 25–90 gpd/ft² hydraulically and 5–20 lb BOD/1000 ft³ organically; 75–85 % BOD removal without recirculation.

High-Rate Trickling Filter

Filter receiving 230–690 gpd/ft² and 30–60 lb BOD/1000 ft³, usually with 1:1–4:1 recirculation; 70–85 % BOD removal.

Super-Rate Trickling Filter

Plastic-media trickling filter loaded up to 3440 gpd/ft² and 50–100 lb BOD/1000 ft³; BOD removal drops to 30–70 %.

Recirculation Ratio

Volume of recycled effluent divided by influent flow, used to maintain wetting, dilute toxins, and enhance sloughing.

Rotating Biological Contactor (RBC)

Fixed-film treatment device consisting of closely spaced plastic disks mounted on a rotating shaft, alternately dipping biofilm in wastewater and exposing it to air.

Zoogleal Slime

The biofilm that develops on RBC disks, absorbing organics when submerged and re-aerating when exposed.

Hydraulic Loading Rate (RBC)

Wastewater flow (gpd) per square foot of disk surface area; typical design range is 1–3 gpd/ft².

Organic Loading Rate (RBC)

Pounds of soluble BOD applied per day per 1000 ft² of disk surface; used to assess process performance.

Soluble BOD

Biochemical oxygen demand remaining after removal of suspended solids; represents readily biodegradable dissolved organics.

K Factor

Empirical coefficient (≈0.5–0.7 for domestic wastes) used to estimate particulate BOD from suspended-solids data.

RBC Advantages

Process simplicity, operational stability, very low maintenance, and low power consumption due to slow disk speed.

RBC Limitations

Sensitivity to hydraulic/organic shocks, reduced efficiency in cold weather, and limited operational flexibility.