Calvin Cycle > Factsheet > Flashcards

Factsheet Flashcards

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1
Q

What are the main constituents of domestic wastewater?

A

Physical, inorganic, organic, biological, and other (e.g. toxic gases, odors).

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2
Q

Name the main physical constituents of wastewater.

A

Suspended solids, colloidal and volatile solids, color, temperature, turbidity, and conductivity.

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3
Q

Why are suspended solids important?

A

They determine reuse potential, treatment method, and cause sludge buildup or anaerobic conditions if untreated.

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4
Q

Typical total solids concentration in domestic wastewater?

A

390–1230 mg/L.

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5
Q

Main removal methods for solids?

A

Flocculation, sedimentation, filtration, flotation.

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6
Q

What does turbidity measure?

A

Light-transmitting property; in effluent, correlates with suspended solids.

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7
Q

Why is wastewater color important?

A

Indicates freshness or septic condition.

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8
Q

Effect of temperature in wastewater treatment?

A

Affects biological reaction rates and process design.

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9
Q

What does conductivity indicate?

A

Ionic concentration; affects reuse, corrosion, and agricultural suitability.

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10
Q

How are ions removed in wastewater?

A

Electrodialysis or reverse osmosis.

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11
Q

What are the main inorganic constituents?

A

pH, alkalinity, nitrogen, phosphorus, sulfur, heavy metals, dissolved gases.

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12
Q

Why is alkalinity important?

A

It buffers pH changes and supports biological and chemical treatment.

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13
Q

Forms of nitrogen in wastewater?

A

NH3/NH4+, organic N, NO2-, NO3-, N2.

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14
Q

Why must nitrogen be removed?

A

To prevent eutrophication, groundwater pollution, and oxygen depletion.

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15
Q

How is nitrogen removed?

A

Nitrification–denitrification, anammox, algal systems.

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16
Q

Typical total N concentration?

A

20–70 mg/L.

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17
Q

Typical total P concentration?

A

4–12 mg/L.

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18
Q

Why is phosphorus removal important?

A

Prevents eutrophication and allows resource recovery (P is limited resource).

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19
Q

Common chemical methods for P removal?

A

Precipitation with Fe3+, Al3+, or Ca2+ salts.

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20
Q

Biological P removal organism?

A

Phosphorus-accumulating organisms (PAOs).

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21
Q

Main dissolved gases in wastewater?

A

H2S (toxic, odorous), CH4 (energy source), O2 (aerobic processes), NH3 (toxic), CO2 (end product).

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22
Q

Common heavy metals in wastewater?

A

As, Cd, Cr, Pb, Hg, Ni, Cu, Zn.

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23
Q

Why are heavy metals problematic?

A

Essential in small amounts but toxic in excess; interfere with microbes and reuse.

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24
Q

Main organic pollutants?

A

BOD, COD, TOC, pharmaceuticals, pesticides, surfactants.

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25
Typical BOD concentration in domestic wastewater?
110–350 mg/L.
26
Typical COD concentration?
250–800 mg/L.
27
What does BOD measure?
The oxygen demand to biologically oxidize organic matter—used to size treatment plants.
28
What does COD measure?
The oxygen needed to chemically oxidize all organics (always ≥ BOD).
29
Why remove organic matter?
Prevents oxygen depletion and septic conditions in natural waters.
30
Main removal processes for organics?
Aerobic or anaerobic biological treatment, sedimentation.
31
Define TOC.
Total Organic Carbon—indicator of total organic content.
32
What biological constituents are found in wastewater?
Bacteria, protozoa, helminths, and viruses.
33
Why are biological constituents important?
They determine health risks and treatment required for reuse.
34
Common pathogens in wastewater?
E. coli, Salmonella, Giardia, Cryptosporidium, Enterovirus.
35
Typical coliform concentration?
10^6–10^10 per 100 mL.
36
Common disinfection methods?
Chlorination, ozonation, UV, filtration, wetlands, ponds.
37
Main “other” constituents in wastewater?
Toxic compounds and odorous gases (H2S, NH3, mercaptans).
38
Main odor control methods?
Adsorption (e.g. on activated carbon or coconut coir).
39
List the main stages of wastewater treatment.
Preliminary, Primary, Secondary, Tertiary.
40
Objective of preliminary treatment?
Remove large solids, grit, oil, and grease to protect equipment.
41
Processes in preliminary treatment?
Screening, grit removal, sedimentation, flotation.
42
Objective of primary treatment?
Settle solids and remove BOD fraction to prevent downstream overload.
43
Processes in primary treatment?
Sedimentation, flotation, septic tanks.
44
Objective of secondary treatment?
Remove dissolved and colloidal organic matter biologically.
45
Examples of aerobic secondary systems?
Activated sludge, trickling filter, MBR, oxidation ditch, SBR, airlift reactor.
46
Examples of anaerobic secondary systems?
UASB, IC, EGSB reactors.
47
Objective of tertiary treatment?
Remove nutrients (N, P), pathogens, micropollutants.
48
Main tertiary N removal processes?
Nitrification–denitrification, anammox, algal bioreactors.
49
Main tertiary P removal processes?
Chemical precipitation, biological PAOs, algal uptake.
50
Other tertiary methods?
Filtration, adsorption, disinfection, advanced oxidation.
51
Difference between aerobic and anaerobic treatment?
Aerobic uses oxygen → CO2 + H2O + biomass; anaerobic lacks oxygen → CH4 + CO2.
52
Main aerobic reaction?
C6H12O6 + 6O2 → 6CO2 + 6H2O.
53
Main anaerobic reaction?
C6H12O6 → 3CO2 + 3CH4.
54
Which produces more biomass?
Aerobic (~50% biomass), anaerobic (~5% biomass).
55
Which produces energy?
Anaerobic (biogas: CH4).
56
Typical aerobic BOD removal efficiency?
90–95%.
57
Typical anaerobic BOD removal efficiency?
60–90%.
58
Energy input difference?
Aerobic needs aeration; anaerobic does not.
59
Which has shorter startup?
Aerobic (1–2 weeks) vs anaerobic (1–3 months).
60
Which has higher organic loading rate?
Anaerobic (10–40 kg COD/m³·d).
61
Examples of aerobic systems?
Activated sludge, oxidation ditch, MBR, trickling filter, RBC.
62
Examples of anaerobic systems?
UASB, EGSB, IC, anaerobic lagoon.
63
What is the sludge yield difference?
Aerobic high (0.5 kg VSS/kg COD); anaerobic low (1/5–1/10).
64
Define HRT and SRT.
HRT = time wastewater stays in reactor; SRT = time microbes stay alive in system.
65
Aerated lagoon typical sludge conc.?
0.2 g TSS/L.
66
Activated sludge conc.?
3–5 g TSS/L.
67
MBR conc.?
10–20 g TSS/L.
68
UASB conc.?
15–80 g TSS/L depending on type.
69
Why higher TSS = more efficient reactor?
More biomass → faster degradation → smaller footprint.
70
Nitrification main idea?
Oxidize NH4+ → NO2– → NO3– under aerobic conditions.
71
Denitrification main idea?
Reduce NO3– → N2 gas under anoxic conditions using organic carbon.
72
Partial nitritation + anammox idea?
NH4+ partly oxidized to NO2–, then combined with NH4+ → N2 without external carbon.
73
Algae N removal idea?
Algae assimilate N into biomass through photosynthesis.
74
Which N process needs organic carbon?
Denitrification (heterotrophic).
75
Which N process needs no organic carbon?
PN/A and algae (autotrophic).
76
Which N process saves most energy?
PN/A (60% less O2, no carbon source).
77
Main nitrifiers?
Nitrosomonas, Nitrosospira (AOB), Nitrobacter, Nitrospira (NOB).
78
Main denitrifiers?
Acinetobacter, Rhizobium, Corynebacterium.
79
Main anammox organisms?
Brocadia, Kuenenia.
80
Main algae species for N removal?
Chlorella, Scenedesmus, Phaeodactylum tricornutum.
81
Effect of nitrification on pH?
Produces H+, lowers pH.
82
Effect of denitrification on pH?
Produces OH–, raises pH.
83
Why is nitrification often rate-limiting?
Nitrifiers grow very slowly.
84
Typical anammox doubling time?
~10 days.
85
Where is N removal done?
Secondary (biological) or tertiary (polishing) stage.
86
Main P removal methods?
Chemical precipitation, biological uptake, algae assimilation.
87
Chemical P removal principle?
Add Fe3+, Al3+, or Ca2+ salts to precipitate PO4³–.
88
Bio-P removal principle?
PAOs release P anaerobically and take up P aerobically (store as polyphosphate).
89
Algae P removal principle?
Assimilate P into biomass and sometimes cause precipitation at high pH.
90
Chemical P removal advantages?
Fast, reliable, achieves <1 mg/L P.
91
Chemical disadvantages?
High cost, more sludge, pH correction needed.
92
Bio-P advantages?
Low cost, less chemical use, good biosolids quality.
93
Bio-P disadvantages?
Sensitive to load or oxygen changes, P release during storage.
94
Algal P removal advantages?
Sustainable, removes both N & P, no chemicals.
95
Algal P disadvantages?
Needs sunlight, limited uptake at night, not fully developed.
96
Main sludge treatment steps?
Dewatering → Organic mass reduction → Final disposal.
97
Main dewatering technologies?
Belt thickener, centrifuge, filter press.
98
Main organic mass reduction method?
Anaerobic digestion.
99
Main final sludge treatment options?
Composting, drying, incineration, or land use.
100
Goal of sludge treatment?
Reduce volume, stabilize organics, recover energy and nutrients.
101
At which stage is nutrient removal typically done?
Secondary treatment (biological or chemical).
102
At which stage is nutrient recovery typically done?
Tertiary or sludge treatment (post-treatment).
103
Difference between nutrient removal and recovery?
Removal = eliminate N, P from effluent; Recovery = capture them as reusable products (struvite, algal biomass).
104
Examples of nutrient recovery methods?
Struvite precipitation, ammonia stripping, algae cultivation, ash leaching.
105
Why recover nutrients?
P is limited resource, N recovery saves fertilizer energy, promotes circular economy.
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