Man and his environment part 2

Question 1

Pollution

Answer 1

Introduction of contaminants into the natural

environment that are harmful to living organisms.

Question 2

What cause industrial wastewater

Answer 2

Heavy metals and synthetic
organic compounds are
discharged by factories
illegally and enter rivers and oceans.

Question 3

Bioaccumulation

Answer 3

Increase in concentration of 
a toxic chemical in tissues 
of an organism over time,
from contaminated air, 
water, or food.

Question 4

Whats Bioamplification

Answer 4

Increase in concentration of
a toxic chemical in
organisms up the trophic
levels in the food chain.

Question 5

Why does bioamplification happen

Answer 5

• Ingested toxins are not excreted or broken down.
• Top consumers accumulate high concentrations of
toxin from eating affected prey.

Question 6

Why do substances bioaccumulate

Answer 6

Metals, Elements are non biodegradable

Exposed to higher concentrations than usual

Synthetic organic compounds: Organisms have not evolved specific metabolic pathways
to break them down.

Question 7

Eutrophication (5 steps)

Answer 7

1. Untreated sewage and agricultural runoff contains
   large amounts of nitrates and phosphates.
2. When discharged into water bodies, it causes
   excessive growth of algae and floating water plants.
3. Overgrowth prevents sunlight from reaching
   submerged algae and aquatic plants for
   photosynthesis, and they die.
4. Dead plant matter are decomposed by aerobic
   bacteria, which grow rapidly, further using up oxygen
   in the water.
5. Other aquatic organisms e.g. fish die due to lack of
   oxygen.

Question 8

Describe Step 1: Preliminary treatment

Answer 8

Wastewater is passed through bar screens to

remove large coarse materials e.g. sand, debris

Question 9

Describe Step 2: Primary treatment

Answer 9

• Water flows through very slowly in large tanks called
primary clarifiers → Step 3
• Solid suspensions settle to the bottom as primary
sludge → Step 4
• Light materials e.g. scum, grease float to the top,
combined with sludge → Step 4

Question 10

Describe Step 3a : Secondary treatment (aeration tank)

Answer 10

• Water enter aeration tank, mixed with aerobic
bacteria (activated sludge).
• Bacteria absorb and break down organic pollutants
in water (bio-reaction process).
• Air bubbles blown in from bottom of tank to supply
dissolved oxygen. OR
• Mechanical surface aerator stir up water and mix in
the air.

Question 11

Describe Step 3b: Secondary treatment (final clarifier)

Answer 11

• Water with bacteria enters final clarifier.
• Bacteria settle to the bottom of the tank as sludge.
• Some sludge is returned back to the aeration tank to
sustain bio-reaction process.
• Excess sludge → Step 4
• Clear water at the top discharged as final effluent

Question 12

Describe Step 4b: Sludge digestion

Answer 12

• Anaerobic bacteria decompose the sludge, produce
biogas (60-70% methane), used as biofuel to
generate electricity for water reclamation plant.
• Sludge remains in digester for 20-30 days