Lecture 19: Wastewater Treatment

Need is the main Wastewater treatment plant in Seattle?

West Point Treatment Plant

What are 5 main things we want to REMOVE from wastewater?

environmental debris (sand, grit, etc.), suspended solids, BOD, pathogens, nutrients

what does does BOD mean?

biochemical oxygen demand

BOD is the milligrams of _____ consumed per _____ of sample during _____ days of incubation at _____ degrees celsius

oxygen; liter; 5; 20

BOD is an indicator of _____ contaminants

organic

the BOD correlates directly to the _____ present

number of microbes

what are the 2 main nutrients we want to remove from wastewater?

nitrogen and phosphorous

what are the two main types of nitrogen that we want to remove from wastewater?

ammonia and nitrate

nitrogen takes _____ and _____ and converts it to _____

ammonia; oxygen; nitrate

denitrification turns _____ into _____

nitrate; N2

what are the three mean treatment processes (in order) of wastewater treatment?

preliminary; primary; secondary

what is the main goal of preliminary treatment? why?

removing big solids → protect the equipment (that could get damaged by large items)

does preliminary treatment decrease BOD?

not by much (mainly done in other steps)

the unit operations (steps) are of preliminary treatment are doing _____ treatment

physical

what are the 3 steps of preliminary treatment?

bar screening, grit chamber, comminution

bar screening involves the removal of _____ by _____

coarse solids; interception

what are coarse solids?

rough and loose → ex. rags

the grit chamber removes _____ by _____

grit; settling

what is “grit”, give examples

heavy solids, ex. sand, broken legals, pebbles

what is comminution?

grinding of solids

the product of comminution are disposed of in the _____

landfills

bar rack screening is a _____ of the sewage at the _____ of the wastewater treatment plant

pretreatment; inlet

bar screening removes _____, _____, and _____, etc. that would _____ moving parts

rags; paper; sticks; jam

bar screening has _____, _____ bars with small _____ that _____ larger items

long, vertical; holes; snag

what are the two main types of racks used in bar screening?

trash rack and mechanically cleaned rack

which rack type has larger openings?

trash rack

parallel bars screen out _____ and the chain on the right moves the _____

large solids; rake

after bar screening, the wastewater flows into the _____ where heavy solids _____ to the _____

grit chamber; sink; bottom

how long is WW kept in the grit chamber?

minutes

solids that sink out in the grit chambers are washed to remove _____ before being deposited in the _____

organics; landfill

grit chambers tend to have a disagreeable _____ and attracts _____

odor; rodents/insects

the grit chamber removes solids that are _____ mm in diameter and have a specific gravity of _____

>0.3; >2.65

what is the main purpose of primary treatment?

remove objectionable solids

primary treatment removes solids by _____ and floating materials (particularly _____) by _____

settling; grease; skimming

the effluent of primary treatment is still _____!

offensive

what is the main step of primary treatment?

primary clarifier

how long is wastewater kept in the primary settling tank/clarifier?

2-3 hours

what are the two main steps of primary treatment?

primary clarifier and physical treatment

primary treatment was necessary to increase _____ of secondary treatment

efficiency

primary treatment removes about _____% of suspended solids and around _____% of the BOD of incoming watewater

50; 25

primary treatment places the wastewater in _____ to remove solids and floatable scum. this requires _____ conditions

circular sedimentation basins; quiescent

what does quiescent mean?

calm, inactive

flow of the primary clarifier moves the wastewater from the _____ to the _____ on the _____

center inlet; overflow trough; outside trough

what does the skimmer boom do?

skim floating scum/oil/grease out of water

_____ is the sludge collected from the primary clarifier

primary sludge

slude settling to the bottom of the primary clarifiers is collected by the _____, which carries the sludge to the _____

rotating rake; center hopper

after collection, primary sludge is transported to the _____

sludge thickener

what is the primary goal of secondary treatment?

removal of soluble BOD (and further removal of solids)

what are the 3 steps of secondary treatment?

trickling filter, activated sludge, secondary clarifier

trickling filter and activated sludge uses _____ treatment, while the secondary clarifier uses _____ treatment

biological; physical

after secondary treatment _____% of the suspended solids and _____% of the BOD have been removed

90; 90

secondary biological treatment uses microorganisms to convert _____ to _____ and _____

organic wastes; CO2; H20

secondary biological treatment is similar to the _____ process in _____

self-purification; streams

the conversion of organic waste to CO2 and H2O is powered by _____ and is an example of _____ metabolism

aerobic respiration; chemoorganotrophy

granule formation is when _____ colonize stalks of _____ in activated sludge

bacteria; ciliated protozoa

trickling filter uses a _____ process, while activates sludge processing uses a _____ process

biofilm; suspended growth

trickling filter _____ distributes wastewater over a _____ such as _____

continuously; media; rocks

the space between media in trickling filter allows for _____

air circulation

True or False: trickling filters remove particles by filtering them out using natural stream purification techniques

FALSE: not filtering or particle removal → uses BIOFILMS

activated sludge process starts with an _____ and is followed by a _____

aeration tank; secondary clarifier

activates sludge process _____ activated sludge to maintain a sufficient concentration of _____ in the _____ tank

recycles; biomass; aeration

activated sludge is uses as _____ to support the survival of microbes that _____

nutrients; clean the water

Trickling filter sprays sewage onto a bed of _____ that _____ bacteria can grow on and degrade the organics as the sewage _____

support media; biofilm; trickles down

activated sludge involves long rectangular _____. The hydraulic residence time is about _____, while the biomass residence time is _____

aeration basins; 6-8 hours; 6-30 days

the activated sludge basins have very HIGH _____

biomass concentrations

in the activated sludge basins, _____ is injected near the bottom of the tank through _____. This supplies the microbes with _____

air; diffusers; oxygen

the activated sludge aeration basins are controlled by _____ a portion of the microorganisms and _____ the rest

wasting; recycling

the important microbes in activated sludge are contained in _____-_____ aggregates;

flocs-suspended

the _____ of the organisms in activated sludge is critical, and is usually a combination of _____ and _____ species

composition; rod; filamentous

the ideal activated sludge flock has a _____ of filamentous and floc forming organisms and a _____ SVI

balance; SVI

why is a low SVI good?

promotes anaerobic processes in center of floc

in Filmanetous bulking activated sludge flocs, the filamentous organisms _____ and there is a _____ SVI

predominant; high

filamentous bulking activativated sludge flocs trap _____ and causing it to _____

gas; float

pin point floc has _____ levels of filamentous organisms and a _____ SVI.

low; high

why are pinpoint flocs bad?

too small, not as efficient and easier to wash away

ideal and filamentous activated sludge floc create a _____ supernatant, and pinpoint flocs have a _____ supernatant

clear; turbid

what are the 3 main components of activated sludge flocs?

bacteria, filaments, and EPS

what is the most important filamentous microbe in AS flocs?

nocardia spp.

nocardia are gram _____ and part of the _____ genus

positive; actinomycetes

actinomycetes are _____ shaped and form _____. Are they motile?

rod; filamentous; NO!

Nocardia spp. provides a _____ for the flocs to form

structural scaffold

Nocardia is a strict _____ that can grow over a wide _____ range

aerobe; temperature (environmentally robust!)

nocarida is nutritionally _____ in terms of its _____ source

versatile; carbon

Nocardia spp. can contribute to bulking when _____ is _____

FOG; high

what is FOG?

oil and grease

too much nocardia = _____ because of excess _____

bad; foaming

what is the primary rod bacteria in wastewater treatment?

Zoogloea spp.

Zoogloea is gram _____ and _____-shaped. What are its oxygen preferences, is it motile?

negative; rod; aerobic; motile

how does Zoogloea get rid of nutrients from wastewater?

does denitrification

Zoogloea spp. makes _____ that hold the flocs together and traps _____ and _____

EPS; toxins; nutrients

because of EPS, Zoogloea is great at concentrating _____ and scrubbing the system of _____, removing _____

nutrients; organics; BOD

Zoogloea can make _____ using the _____ enzyme

Poly-hydroxybutyrate; B-ketothiolase

what causes the white bubbles in secondary effluent?

detergents (that passed through without being degraded/removed)

often _____ are used to suppress foaming of secondary effluent

spray nozzles

Alkyl benzene sulfonate (ABS) is a detergent that is _____ while Linear alkyl benzene sulfonate (LAS) is _____

not biodegradable; more biodegradable

secondary effluent is _____ (often with _____)

disinfected; chlorine

why is secondary effluent disinfected with chlorine?

to destroy pathogens

because chlorine/chloramine is toxic to _____, the water is _____ before discharging

aquatic life; dechlorinated

what chemical is used to dechlorinate the wastewater?

sodium bisulfate (NaHSO3)

wen chlorine reacts with sodium bisulfate, it is turned into _____

HCl