Man and the environment pt. I Flashcards
How does the following process affect carbon dioxide levels in the atmosphere: photosynthesis
- CO₂: Green plants absorb atmospheric CO₂ to manufacture carbohydrates. When herbivores feed on plants, the digested carbon compounds become assimilated as part of their bodies.
How does the following process affect carbon dioxide levels in the atmosphere: dissolution
- CO₂: CO₂ dissolves in the sea water and is used by phytoplankton and algae in photosynthesis.
How does the following process affect carbon dioxide levels in the atmosphere: respiration
+ CO₂: Living organisms break down carbon compounds to release energy and CO₂.
How does the following process affect carbon dioxide levels in the atmosphere: combustion
+ CO₂: Carbon compounds in dead organisms may de deposited as fossil fuels. Fossil fuels are burned to release energy and CO₂.
How does the following process affect carbon dioxide levels in the atmosphere: decomposition
+ CO₂: Decomposers break down dead organisms and waste products into simple organic and inorganic substances, including CO₂.
Define bioaccumulation
Increase in concentration of a toxic chemical in tissues of an organism over time, from contaminated air, water, or food.
Define biomagnification / bioamplification
Increase in concentration of a toxic chemical in organisms up the trophic levels in the food chain.
State the effects of DDT
- DDT is an endocrine disruptor, affecting adults’ reproductive function and development of fetus.
- DDT causes eggshell thinning in birds. Their eggs break easily during incubation.
State the effects of the poisoning of Minamata
- Crows fall from the sky.
- Seaweed no longer grow on the sea bed.
- Dead fish floated on the sea surface.
- Mercury poisoning affects the nervous system, causing numbness, loss of motor coordination, difficulty seeing, speaking, swallowing.
- Insanity, paralysis, coma, and death after a few weeks.
- Fetus are also affected, causing birth defects.
State the sources of sewage
Wastewater from domestic and commercial sources such as households, schools, shops, hotels and office buildings (not factories)
Surface runoff from urban areas and agricultural farmland after rain. Absorbs, dissolves, leaches, suspends particles as it moves across surfaces.
State what the sewage contains and the effects of the content
- Bodily waste may contain pathogens that cause water borne diseases.
- Suspended solids and sediments, cause siltation, block sunlight, and injure gills of fish
- Fertilisers from agricultural runoff contains high nitrogen and phosphorus, causing eutrophication.
- Synthetic organic compounds found in pharmaceuticals, detergents, cosmetics, pesticides, food additives.
Describe the process of eutrophication
- Untreated sewage and agricultural runoff contains large amounts of nitrates and phosphates.
- When discharged into water bodies, it causes excessive growth of algae and floating water plants.
- Overgrowth prevents sunlight from reaching submerged algae and aquatic plants for photosynthesis, and they die.
- Dead plant matter are decomposed by aerobic bacteria, which grow rapidly, further using up oxygen in the water.
- Other aquatic organisms e.g. fish die due to lack of oxygen.
Describe the steps for sewage treatment in Singapore
Step 1: Preliminary treatment
- Wastewater is passed through bar screens to remove large coarse materials such as sand and debris.
Step 2: Primary treatment
- Water flows through large tanks called primary clarifiers very slowly. -> 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
Step 3a: Secondary treatment
- 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.
Step 3b: Secondary treatment
- 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
Step 4b: Sludge digestion
- 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.
