Wastewater Microbiology Flashcards

Flashcards covering key vocabulary and concepts from the Wastewater Microbiology lecture.

West Point Treatment Plant, Seattle, WA

Largest of its type on the West Coast, serving over 700,000 people. A 2017 flood resulted in the discharge of ~250 million gallons of untreated sewage into the sound.

Objectives of a Wastewater Treatment Plant

Sand, grit, debris, suspended solids, BOD, pathogens, and nutrients like nitrogen and phosphorus.

BOD (Biochemical oxygen demand)

Milligrams of oxygen consumed per L of sample during 5 days of incubation at 20 °C – indicator of organic contaminants

Nitrification

NH3 + O2 -> NO3 -

Denitrification

NO3 - -> N2

Preliminary Treatment Unit Operations

Bar screening, grit chamber, and communition (grinding of solids).

Bar Screening

Removes coarse solids (e.g., rags) by interception

Grit Chamber

Removes grit (heavy solids): sand, broken glass, silt, pebbles

Comminution

Grinding of solids

Primary Treatment Purpose

Removes objectionable solids by settling and floating materials (greases) by skimming.

Primary Treatment Process

Primary settling tank / primary clarifier (2-3 h)

Primary Treatment Efficiency

Removes about 45 to 50% of the suspended solids and 25 to 30% of the BOD of the incoming wastewater.

Primary Sludge

Sludge settling to bottom of 1o clarifiers is collected by rotating rake, which carries sludge to center hopper; then transported to a sludge thickener.

Secondary Treatment Purpose

Removal of soluble BOD and additional removal of suspended solids.

Secondary Treatment Process

Trickling filter, activated sludge, and secondary clarifier.

Secondary Treatment Efficiency

About 90% of the suspended solids and 80-90% of the BOD have been removed.

2o Biological Treatment

Use microorganisms to convert organic wastes to CO2 and H2O.

Trickling Filter (Biofilm process)

Wastewater is continuously distributed over media (rocks, plastic) with space between media for air circulation.

Activated Sludge Process

Aeration tank plus secondary clarifier; recycles activated sludge (biomass) to maintain a sufficient concentration of biomass in the aeration tank.

Biofilm bacteria in Trickling Filter

Grow on media and degrade organics as sewage trickles down.

Activated Sludge Residence Time

Hydraulic residence time: ~6-8 hr; Biomass residence time: 6-30 days.

Organisms in Activated Sludge

Microbes contained in 'flocs'-suspended aggregates; combination of rod shaped and filamentous species.

Zoogloea spp.

Gram negative rod-shaped species; aerobic, can denitrify, motile; makes EPS- exopolysaccharides- holds flocs together, traps toxins (heavy metals), nutrients. Can make Poly-hydroxybutyrate using B-ketothiolase.

White Bubbles in Secondary Effluent

From detergents that passed through treatment without being removed or degraded.

Chlorination/Dechlorination

Toxic to aquatic life, so water is dechlorinated before discharge with sodium bisulfite (NaHSO3), which eliminates chlorine residual.

Anaerobic Digestors

Reduce sludge volume and pathogen load; prevent foul odors.

Digested Sludge

Can be used as agricultural amendment if it meets standards for heavy metals, toxic non-metals, organic pollutants, and pathogens.

Where Treated Wastewater Goes

Injected into the ground or discharged to surface water.

Wastewater Reuse

Direct potable reuse is rare; indirect potable reuse is becoming more common. Non-potable reuse: irrigation, fire protection.

Protozoa Cysts

Resting stage (dormant); develop thick wall and have low metabolic activity; protection from adverse conditions; transport to new host.

Giardia

Flagellated; forms cysts; 1st proof of waterborne pathogenic protozoan

Cryptosporidium

Causes diarrhea, abdominal pain, and vomiting; resistant to chlorine, chlorine dioxide disinfection.

Haber-Bosch Process

Production of fertilizers, combining nitrogen and hydrogen to synthesize ammonia.