ERT 417 TUTORIAL – JULY 09
1. Explain the problems of waste management in the present times.
The main problems are: disposal, health, foul smell, pollution etc.
2. Define waste and explain the waste hierachy [3R’s] and ‘0’ waste’
Waste: any rejected material [garbage, chemicals, agro-material] that is unwanted,
worthless, or not usable.
Types:
Solid [leaves, wood, paper, tins, bricks, steel, plastics, tyres, packaging material, electric wires
etc.];
Liquid [Industrial effluent, municipal sewage, acids, lubricant oils];
Hazardous:[air pollutants-methane, hydrogen gases, ammonia, carbon dioxide,; chemicals
from bioprocess industries]
Waste hiearachy: Reduce, Reuse, and Recycle
Zero waste: A goal to guide people not to burn or bury waste but emulate sustainable natural
cycles by designing and managing waste products to reduce their volume and toxicity.
3. Discuss the causes of global warming.
Air-polluting gases from vehicles and factories[SO2,CO2,CH3, CO],
Agricultural practices [c.14%], deforestation,
Chloroflurocarbons [CFC’s, c.17% and ]ozone depletion,
Energy use and production through burning of fossil fuels[c.57%]
Changes in land use and industrial activities [c.12%]
4. Define and explain BOD and COD
BOD: amount of oxygen required to oxidise organic matter in water samples by microbes.
High BOD indicates water pollution
COD: A quick test to measure the overall level of of organic and inorganic contamination in
water. It is determined by measuring the equivalent amount of oxygen required to oxidise
organic and inorganic matter dissolved in the water sample using chemicals such as
dichromate, permangnate, iodate, or persulfate. High COD indicates high amount of
poolution in sample.
5. Define and explainthe significance of composting in waste management
Composting: is the biodegradation of organic matter such as agricultural and food waste by
microorganisms [bacteria, fungi, and yeast. At low temperature phases macroorganisms such
as springtails, ants, nematodes, earthworms, soldier and fruit flies can also contribute to the
biodegradation process.
Benefits of composting: improve soil structure and fertility; reduce soil erosion; provide food
for eartworms, soil insects, and beneficial microorganisms.
6. Discuss the parameters involved in composting.
i.
ii.
iii.
iv.
v.
vi.
vii.
viii.
Temperature: 25-60oC. Best to maintain between 50-55oC [122-131oF]
Aeration: 50% ideal for aerobic metabolism and controlling temperature. In sufficient
aeration promote anaerobic zones and foul odor while excess limits microbial activity
as a result of reduced moisture and cooling. Mixing or overturning the material
besides improving aeration can also prevent drying, caking, and air channeling .
pH: 5.5-8.0. Bacteria favor near neutral while fungi acidic range. Optimum 7-7.5 to
avoid loss of nitrgen. Do not exceed 8.5.
Moisture: 50-60%. It is dependent on the porosity of the material and determined by
measuring weight loss after the sample has been dried to constant weight at 100110oC.
Carbon/Nitrogen ratio: Initial ratio between 20-50 but later 25-35 is optimal. Low
ratio leads to excess NH3 formation and volatilation and increase pH. High ratio
limits nitrogen and favors composting.
Particle size: 20-70mm and high surface area for good porosity.
Blending and seeding: Adding partially decomposed solid waste such as sewage
sludge about 1-5% by weight can help in reducing composting time.
Control of pathogen: Temp. of 60-68oC [140-145oF] for 24 hr can kill many pathogens,
weeds, and seeds during composting process.
7. Exlpain the process of pyrolysis.
It is the chemical decomposition of organic material by heating [temp. above 430oC
c.500oC]in the absence of oxygen and water to produce charcoal, activated carbon, bio-oil
[methanol] and synthetic gas.
8. Describe the process of pyrolysis with the help of a diagram.
7 steps:
i.
Waste tipped into ‘holding area’
ii.
There it is pushed gradually into the incinerator
iii.
Temperture of incinerator maintained at 750oC and heat from the burning waste is
used in the boiler
iv.
The steam from burning waste is channeled to the turbine generator to create
electricity
v.
vi.
vii.
The heaviest ash residue falls into the collection point and is passed over an
electromagnet to extract metal content for recycling
Flue gases containing fine ash then pass through a Snubber reactor to treat acid
pollutants [SO2 and dioxins]
The gases then pass through a fine pasrticulate removal system and released through
the chimney stack.