CE 385L 2: Biological Wastewater Treatment Block 1-3.1

Conceptual Review

in a wwtp, what’s the difference between primary and secondary treatment?

primary treatment removes particulates and secondary treatments removes solubles

describe how a septic tank works

wastewater flows into a large underground tank, undergoes sedimentation and anaerobic digestion to the level of primary treatment. the treated effluent is dispensed into a drain field

list a few examples of resource recovery from wwtps

biogas

biofuel

chemical products

fertilizer

what are total solids?

H2O + solids

what does total suspended solids measure?

measures visible particles trapped by a filter

what does total dissolved solids measure?

measures invisible, dissolved minerals and salts that pass through the filter

define volatile

organic; burns into gaseous state

define non volatile

inorganic or fixed or mineral; does not burn off

how to measure suspended solids

1. filter through a membrane/filter

2. evaporate and dry the filter

3. burn at 550 degrees C to burn off organic components

how to measure total dissolved solids?

1. filter

2. evaporate water

3. burn the crucible

what makes something organic?

an organic chemical is any compound that contains carbon covalently bonded to other atoms, most commonly hydrogen, oxygen, and nitrogen

general organics formula provided in class:

Organics + O₂ → CO₂ + H₂O + other products

What are some concerns about O₂ consumption from an effluent with too much organic content?

receiving waters have many microorganisms, so degradation will occur and these organisms could drive the DO concentration to zero if the effluent concentration has too many organics. The low DO would kill fish

list the name for the following theoretical characterizations of organic chemicals:

• ThOD

• TOC’

• COD’

• COD’

• NOD

• Theoretical oxygen demand

• Total organic carbon

• chemical/carbonaceous oxygen demand

• chemical/carbonaceous oxygen demand if organic compound is biodegradable

• nitrogenous oxygen demand

list the name for the following measured characterizations of organic chemicals:

• TOD

• TOC

• COD

• BOD

• NBOD

• Total oxygen demand

• Total organic carbon

• Chemical oxygen demand

• Biological oxygen demand

• Nitrogenous biological oxygen demand

true of false: theoretical > measured and why?

true: theoretical will have higher values than the analytically measured compound

what are the overall goals of measuring solids in wastewater?

measuring solids helps operators track pollution levels, design treatment steps, and monitor biological activity (even indirectly cells in a bioreactor)

define total solids (TS)

any residue remaining after water is evaporated

define total suspended solids (TSS)

mass of solids caught on a membrane filter

define total dissolved solids (TDS)

mass of the solids not caught on the membrane filter, but are present after evaporating all the water from the sample

define volatile solids

solids that burn off when exposed to 550 degrees Celsius

define non-volatile solids

solids that do not burn off when exposed to 550 degrees Celsius

formula for tss:

(mass of filter after drying at 103 C) - (mass of filter) / sample volume

formula for volatile solids:

(mass of filter + residue after 103 C) - (mass of filter + residue after 550 C) / sample volume

why calculate ThOD?

it calculates the exact, maximum total amount of oxygen required to completely oxidize an organic compound into stable end products: CO₂, NO₃^- , H₂O,

ThOD formula

C_nH_aO_bN_c + dNH₃ + eO₂ → nCO₂ + (c+d) NO₃^- + (c+d)H + ( a + 2d - c)/ 2 H₂O

why do we calculate/measure TOC’ (total organic carbon)?

to measure the amount of organic carbon present since this helps in knowing what amount of non organic carbon needs to be removed

why do we acidify the sample to measure TOC?

acidification creates equilibrium between gas and water phase, which helps prevent the non organic carbon from being measured

TOC’ formula from notes

C_nH_aO_bN_c → nC

a student adds 100 mg/L of acetate (CH₃COO^-) to pure water. what is the TOC of the sample in mg/L C?

(100 mg/L CH₃COO ^-) (1 mmol CH₃COO^- / 59 mg CH3COO^-) (2 mmol C / 1 mmol CH3COO- ) * (12 mg C/ 1mmol C) = 40.7 mg/L TOC

why measure COD’?

it determines the amount of oxygen needed to break down organic and inorganic material in water

what is COD’ formula needed to determine how many moles of O2 are required for a particular compound?

e = n + (a-3c)/4 - b/2

why measure nitrogenous oxygen demand?

to see how much dissolved oxygen bacteria use when they turn ammonia and organic nitrogen into nitrites and nitrates

what form of oxygen demand does this expression describe?

nitrogenous oxygen demand

when collecting a BOD sample, describe the difference in content between a sample and a control bottle:

• sample:

• control

• sample: microorganisms + wastewater + dilution water

• control: microorganisms + dilution water

BOD_t Equation

if the dilution water naturally contains microorganisms or the dilution is seeded (sterile mixed with seed), what formula is appropriate to use for f?

f = (V_bottle - V_{waste sample} )/ V_bottle

if the dilution water is sterile and has a separate seed added to the bottle, then what is the formula for f?

Seed in volume dilute sample / seed volume in blank

Define L?

The amount of oxygen needed to degrade organic matter

Define L_0

Ultimate or total BOD

Define BOD5

Amount of oxygen consumed by microorganisms in five days

List important names of nitrogen forms:

• NH4+

• NH3

• TKN

• NO2-

NO3-

Ammonium ion

Ammonia gas

Total Kjeldhal Nitrogen

Nitrite

Nitrate

List general wastewater treatment levels and what they focus on removing

Primary - physical treatment to remove suspended solids and some BOD

Secondary - microbial oxidation of waste to remove BOD and TSS

Tertiary Treatment - remove particular pollutants like nitrogen and phosphorus

Sludge treatment and Energy Recovery

What are the regulation limits for flow and loading rate design?

Based on 30 day averages and must consider operation during peak and minimum flow load conditions. Do not design based on annual or monthly averages

Plotting position formula

% = (m/n+1)

Peaking Factor Formula

Peak flow rate / average long term flow rate

Mass loading

Mass loading = concentration x flow rate

Define pure culture

Lab culture containing a single type of microorganism

Microbial population

All individuals of a single living in the same habitat

Microbial community

Complex assemblage of genetically distinct populations that coexist

which analysis type can measure cells in a sample?

VSS to determine the mass of cells using the C₅H₇O₂N formula (1.42g O2/1g of cells)

define metabolism

total turnover of chemical material and energy in living cells

define catabolism

oxidation of a food source (substrate, electron donor) to obtain energy

define anabolism

energy expenditure to synthesize cellular components

heterotrophs get C from

organic C

autotrophs get C from

inorganic C

phototrophs get energy from

photosynthesis

lithotroph gets energy from

oxidation of inorganics

aerobic conditions in WWTP mean

oxygen present

anoxic conditions in WWTp mean

no oxygen, but NO3-, NO2- and other electron acceptors are present

anaerobic conditions in WWTP mean

no oxygen, NO3-, NO2-, or SO4-present

obligate anaerobos

require complete absence of oxygen because it’s toxic to them

endogenous decay

a biological and wastewater treatment process where microorganisms break down their own cellular in the absence of substrate

three reactions are critical in the design process, name them

oxidation, cell synthesis, endogenous metabolism

what is the microbial yield coefficient?

amount of cells formed per mass of substrate destroyed

what does a large Y mean?

lots of sludge, rapid response process from cells consuming substrate

define this variable: S

substrate concentration

define this variable: X

biomass concentration (usually measured as VSS, TSS, or # cells)

define this variable: K_s

half velocity of half saturation constant (mass of substrate/vol)

what does K_s mean?

it’s the amount of food or substrate needed for an organism to grow or take things in at half of its maximum speed

define this variable: K

maximum specific substrate utilization rate

a low K_s values means:

very efficient enzymes consuming food even when S availability is low; microorganisms can thrive at low food available levels

a high K_s means:

enzymes are inefficient at consuming food, so the microorganisms need a lot of food to get going

q (max specific substrate utilization rate)

the maximum capacity of cells to consume substrate

r_g=r_x

rate of growth for microbes

specific growth rate

µ’ = mass of new cells produced per time-volume / mass o cells in system per volume

what is b?

the endogenous decay coefficient

why do we want the substrate utilization rate to be as high as possible in biological reactors

Higher Product or Biomass Yield, Faster Wastewater Treatment, Reduced Residence Time, saves money

define hydraulic residence time

average amount of time a water molecule spends in the system

define solids residence time =

average amount of time that a sludge particle will spend in the system

why might we not want too many solids going to waste treatment?

financial costs

when does HRT = SRT?

is a CSTR without settling and recycling

in a CSTR with settling and recycle, endogenous metabolism depends on ____ and the more organisms per unit volume tank mean ____ substrate consumed

SRT; more

would a BOD5 measurement be sufficient in measuring )2 consumption in pure catabolic reactions?

it would be incorrect because some things require more time to degrade, so this would be an underestimate of the amount of O2 consumed beyond 5 days.

what are some advantages of this design?

consumes bod5 substrate at a higher cell concentration; useful design if space constraint is present and want to use small reactors

draw the system