Wastewater treatment-Lecture 20

Question 1

Objectives of a wastewater treatment plant

Answer 1

We want to remove: 
Sand, grit, debris
suspended solids
BOD-increase of biological oxygen demand, increase wastewater contaminants
- Pathogens
-Nutrients: Nitrogen, phosphorous

Question 2

Typical wastewater treatment train

Answer 2

Raw sewage->Bar screening and grit chamber->Primary Clarifier->Trickling Filter->Activated Sludge->Secondary Clarifier-> Solids Thickening->aerobic digestion->solids disposal

Question 3

Preliminary Treatment

Answer 3

Purpose: Protect WWTP equipment, does not decrease BOD much
Physical Treatment: Bar screening
Removal of Course Solids by Interception
Grit Chamber
Removal of grit(heavy solids): sand, broken glass, silt, pebbles
WW flows into chambers where heavy solids sink to the bottom
Comminution
Grinding of Solids

Question 4

Primary Treatment

Answer 4

Purpose: Remove objectionable solids, remove solids by settling, remove floating materials, particularly greases (by skimming)
Circular Sedimentation basins remove solids/floatable scum, moves from center to outside edge overflow trough, skimmer boom
- Removes about 45% to 50% of the suspended solids and 25-30% if the BD of the incoming wastewater
Primary Sludge->sludge from primary clarifier
- sludge settles to bottom and is collected by rotating rake, carries sludge to center-> sludge is transported to a sludge thickener

Question 5

Secondary Treatment

Answer 5

Purpose: removal of soluble BOD, additional removal of suspended solids
Example Unit Operations:
Biological Treatment: Trickling Filter and Activated Sludge
Physical Treatment: Secondary Clarifier
90% of suspended solids have been removed and 80-90% of BOD have been removed

Question 6

Secondary biological treatment

Answer 6

Microorganisms to convert organic wastes to CO2 and H2O
-Similar to self-purification process in streams
Organic Material+O2+nutrients->New cells +CO2+H2O
granule formation: Bacteria colonize stalks of ciliated protozoa in activated sludge

Question 7

Aerobic Biological Treatment Processes

Answer 7

1. Trickling Filter (BioFIlm process)
   - WW continuously distributed over media
   - media: rocks, plastic media
   - Space Between media allow air circulation (O2 promotes respiration)
   - no particle removal
   - - Deeper filter possible with plastic media
   - - Biofilm Bacteria: Grow on media and degrade organics as sewage trucks fiwn
2. Activated Sludge Process (Suspended growth process)
   - Aeration tank plus secondary clarifier
   - Recycles activated sludge (biomass) to maintain a sufficient concentration of biomass in aeration tank

Question 8

Important organisms in Activated sludge

Answer 8

microbes contained in flocs suspended aggregates-> decrease filament, decrease flocs

• ——– increase filament, increase SA:V, float to top, bulking
• combination of rod shaped and filamentous species

Question 9

Important Filamentous Microbe : Nocardia spp

Answer 9

Gram Positive actinomycetes
basics for flocs-> decrease BOD
- Rod-shaped-> forms filaments-> non-motile
strict aerobe that can grow over wide temperature range
Nutritionally Versatile in terms of carbon source
Can contribute to bulking-happens when FOG is high
Too much Nocardia=bad=foaming

Question 10

Zoogloea spp.

Answer 10

Gram Negative rod-shaped species, Aerobic, can dentrify, motile
Makes EPS- holds flocs together, traps toxins, nutrients
—> Can help or hurt in settling
Because of EPS, great at concentrating nutrients and scrubbing systems of organics, removing BOD
Can make Poly-hydroxybutyrate using B-ketohiolase

Question 11

Secondary Effluent, Decrease organic content

Answer 11

White bubbles
- from detergents that passed through treatment without being removed or degraded
ABS detergent not readily biodegradeabke
LAS more biodegradable

Question 12

Chlorination/Dechlorination

Answer 12

• secondary effluent is disinfected with chlorine

- water is dechlorinated before discharge, dechlorinate with NAHSO3, eliminates chlorine residual

Question 13

Sludge Treatment + Digested sludge drying bed

Answer 13

Thickening

• procedure to increase the solids content of sludge by removing a portion of water
• generally accomplished by physical means, inclusing thickening or flotation

Anaerobic Digestion

• traditional biological method of sludge processing
• anaerobic bacteria convert organics to CO2 and CH4 (methanogens)

Drying Beds: improve soil organic content, used if sludge is clean

Question 14

Anaerobic Digestors

Answer 14

Reduce Sludge volume and pathogen load

-prevent foul odors

Question 15

Wastewater Reuse

Answer 15

Direct Potable Reuse of treated WW is rare

Non potable reuse: irrigation (Agricultural and municipal), fire protection

Question 16

Protozoa, Giardia, Cryptosporidium,

Answer 16

Protozoa: Many form cysts, resting stage (dormant), develop thick wall and have low metabolic activity
Function: Protection from adverse conditions, transport to new host

Cause human disease: Malaria, amoebic dysentary, giardiasis, cryptosporiadiosis

Giardia: flagellated, forms cysts, 1st proof of waterborne pathogenic protozoan

Cryptosporidium: Nonmotile, Protozoan parasite, Causes diarrhea, abdominal pain and committing
- Thick walls provide protection from harsh environments

Question 17

The Nitrogen Cycle

Answer 17

Nitrogen Cycle: describes the routes that nitrogen atoms take through the environment
- N2 not used by organisms

Question 18

Nitrification and Denitrification

Answer 18

Nitrification: bacteria convert ammonium ions into nitrite ions then into nitrate ions

Denitrifying Bacteria: convert nitrates in soil or water to gaseous nitrogen

Question 19

Humans affect the nitrogen cycle

Answer 19

Haber-Bosch Process: production of fertilizers by combining nitrogen and hydrogen to synthesize ammonia

Fixing atmospheric Nitrogen with fertilizers:

• increase emissions of greenhouse gases and smog
• Washes calcium and potassium out of soil
• Acidifies Water and Soils
• moves nitrogen into terrestrial systems and oceans
• reducing reduces diversity of plants adapted to low- nitrogen soils
• changed estuaries and coastal ecosystems

Question 20

FISH to determine relevant metabolic groups

Answer 20

ammonia oxidizers towards periphery

flourescent probes hybridize strongly