WTGC

Question 1

What is the main aim of wastewater treatment?

Answer 1

To remove harmful substances from water so it’s safe for people and the environment — and to recover useful resources like water, nutrients, and energy.

Question 2

List four aims of wastewater treatment.

Answer 2

Protect public health; Avoid pollution or nuisance; Recycle or recover resources; Follow legal standards.

Question 3

Why must wastewater be treated?

Answer 3

Because it contains solids, organics, nutrients, pathogens, and micropollutants that can harm people and water bodies if discharged raw.

Question 4

Main stages in a WWTP?

Answer 4

Pre-treatment → Primary → Secondary → Tertiary → Sludge treatment.

Question 5

Difference between primary and secondary treatment?

Answer 5

Primary = physical (settling solids); Secondary = biological (microbes break down organics).

Question 6

What’s the EU Urban Wastewater Directive (2025)?

Answer 6

A law ensuring all EU towns collect and treat wastewater efficiently to protect people and the environment.

Question 7

Key goals of the EU directive?

Answer 7

Better water quality; Polluter pays; Water reuse; Climate adaptation; Sanitation for all.

Question 8

EU discharge limit for BOD and COD?

Answer 8

BOD₅ = 25 mg/L, COD = 125 mg/L.

Question 9

Why are N and P limits stricter now?

Answer 9

Because too much nitrogen and phosphorus cause eutrophication (algal blooms).

Question 10

Main constituents of wastewater?

Answer 10

Solids, organics, nutrients (N, P), pathogens, and micropollutants.

Question 11

Difference between total, volatile, and fixed solids?

Answer 11

TS = VS + FS. VS = organic part (burns off); FS = inorganic ash.

Question 12

What is BOD?

Answer 12

Biochemical Oxygen Demand – oxygen used by microbes to degrade organics (5 days).

Question 13

What is COD?

Answer 13

Chemical Oxygen Demand – total oxygen required to oxidize all organics.

Question 14

Typical COD/BOD values for domestic sewage?

Answer 14

COD ≈ 250–800 mg/L; BOD₅ ≈ 110–350 mg/L.

Question 15

Typical nutrient levels in domestic sewage?

Answer 15

N = 20–70 mg/L; P = 4–12 mg/L.

Question 16

Common pathogen indicators?

Answer 16

Coliforms, fecal coliforms, enterococci, Pseudomonas, Clostridium.

Question 17

What are micropollutants?

Answer 17

Tiny pollutants like pharmaceuticals, PFAS, pesticides, or heavy metals.

Question 18

What happens in pre-treatment?

Answer 18

Removal of large solids, grit, and oil to protect equipment.

Question 19

Units used in pre-treatment?

Answer 19

Screens, grit chambers, oil separators, equalization tanks.

Question 20

What happens in primary treatment?

Answer 20

Settling of solids in clarifiers or septic tanks; removes 30–40% BOD and 40–70% TSS.

Question 21

Purpose of secondary treatment?

Answer 21

Biologically remove dissolved organics and nutrients using microorganisms.

Question 22

Purpose of tertiary treatment?

Answer 22

Final polishing: removes nutrients, micropollutants, and pathogens before reuse/discharge.

Question 23

Types of biological conditions?

Answer 23

Aerobic (O₂), Anoxic (NO₃⁻), Anaerobic (no O₂/NO₃⁻).

Question 24

What’s aerobic oxidation?

Answer 24

Microbes use oxygen to break down organics → CO₂ + H₂O.

Question 25

What’s nitrification?

Answer 25

NH₄⁺ → NO₂⁻ → NO₃⁻ by autotrophic bacteria (Nitrosomonas, Nitrobacter).

Question 26

What’s denitrification?

Answer 26

NO₃⁻ → N₂ gas under anoxic conditions using organic carbon.

Question 27

What’s methanogenesis?

Answer 27

Anaerobic conversion of acids to CH₄ + CO₂ (biogas).

Question 28

Explain activated sludge.

Answer 28

Suspended microbes forming flocs that consume organics; settled sludge is recycled.

Question 29

Typical HRT and SRT for activated sludge?

Answer 29

HRT ≈ 1 day; SRT ≈ 5–15 days.

Question 30

What is a trickling filter?

Answer 30

Wastewater trickles over media covered with biofilm.

Question 31

Trickling filter advantages?

Answer 31

Simple, low energy, little maintenance, stable under shock loads.

Question 32

Trickling filter disadvantages?

Answer 32

Lower effluent quality, odor issues, sensitive to low temperature.

Question 33

What is MBR?

Answer 33

Membrane Bioreactor – activated sludge + membrane filtration, very clear effluent.

Question 34

MBR vs conventional?

Answer 34

MBR = higher sludge conc., better effluent, more energy use, costlier.

Question 35

What is granular sludge (Nereda)?

Answer 35

Compact microbial granules that settle fast, no clarifier needed.

Question 36

What does UASB stand for?

Answer 36

Upflow Anaerobic Sludge Blanket reactor.

Question 37

How does UASB work?

Answer 37

Wastewater flows upward through sludge granules → CH₄ + CO₂ (biogas).

Question 38

Best conditions for UASB?

Answer 38

Warm (25–37 °C), concentrated wastewater.

Question 39

Advantages of UASB?

Answer 39

Biogas production, compact, low cost.

Question 40

Disadvantages of UASB?

Answer 40

Moderate effluent quality → needs post-treatment.

Question 41

Main biological N-removal steps?

Answer 41

Nitrification (NH₄⁺→NO₃⁻) and Denitrification (NO₃⁻→N₂).

Question 42

What’s Anammox?

Answer 42

Anaerobic Ammonium Oxidation: NH₄⁺ + NO₂⁻ → N₂ gas; no O₂ or carbon source needed.

Question 43

Why is Anammox better?

Answer 43

Saves energy (less aeration), no external carbon, less sludge.

Question 44

Where is Anammox used?

Answer 44

High-NH₄ wastewater (industrial, side-stream).

Question 45

How can nitrogen be recovered?

Answer 45

Electrodialysis + membrane distillation → ammonium salts as fertilizers.

Question 46

How do microalgae clean wastewater?

Answer 46

They use CO₂, N, and P for photosynthesis, removing nutrients and producing O₂.

Question 47

Typical algae used?

Answer 47

Chlorella, Phaeodactylum tricornutum.

Question 48

Benefits of algae treatment?

Answer 48

Removes N & P, produces biomass for fuel/feed.

Question 49

Drawbacks of algae systems?

Answer 49

Need sunlight, large area, no photosynthesis at night.

Question 50

Types of algae systems?

Answer 50

Ponds, photobioreactors (suspended) or biofilm plates (attached).

Question 51

Purpose of tertiary treatment?

Answer 51

Final polishing to remove nutrients, pathogens, micropollutants before reuse/discharge.

Question 52

Examples of tertiary treatment?

Answer 52

Wetlands, sand filters, disinfection, AOPs, P-removal.

Question 53

What’s a constructed wetland?

Answer 53

A natural-like system using plants and microbes to treat water.

Question 54

Advantages of wetlands?

Answer 54

Simple, low-energy, good effluent quality.

Question 55

Disadvantages of wetlands?

Answer 55

Large footprint, weather dependent.