Solid Wastes
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Solid Wastes
Composition of solid waste in 1993 (% by weight) Putrescibles Leather,Rubber, Wood Textiles Glass Fine Material & Miscellaneous Metals Plastic Paper
Solid Wastes in Hong Kong
An average of 2x107 kg solid waste daily in 1993. About 3.5 kg per head of population. Plastic, paper and metals occupied about 40% by weight of the domestic waste.
Disposal of solid waste
Two common disposal methods: Land filling and Incineration Incineration
Advantages:
reducing the volume by ~85% No risk of underground water pollution
Disadvantages:
polluting the atmosphere with toxic chemicals
Disposal of solid waste
Incineration
Disadvantages:
Potential environmental problems are (1) Generation of landfill gas, mainly methane. (2) Polluting the underground water
Pollution problem associated with the disposal of plastics
Plastic waste in the sea pose direct danger to fishes. Plastic waste can last for a long time, they do not undergo decomposition easily in the landfill site. Incineration produces air pollutants such as hydrogen chloride from PVC and other chlorine containing polymers.
Disposal methods of solid waste in Hong Kong Incinerated 6% Landfilled
73% Domestic 57%
Commercial
21% Industrial
Landfilled
16%
Degradable plastics
Slow degradation because enzymes in micro-organisms attack only at the ends of the polymer chains. Several types of degradable plastics: (1) Biopolymers: polymers made by living organisms. Poly(hydroxybutyrate), PHB, a natural polyester made by bacteria. Degradation completed within 9 months. 15 times more expensive than poly(ethene).
Degradable plastics (2) Photodegradable plastics: light sensitive functional groups such as carbonyl group (C=O) can in incorporated into the polymer chains. The long chains can be broken down under the action of sunlight into shorter fragments which can then be biodegradable. (3) Synthetic biodegradable plastics: made by incorporating starch or cellulose into the polymer during production.
Recycling of plastics
Direct recycling : applies only to thermoplastics. The plastics are separated, cleaned, pulverized, and remoulded into plastic items. The regenerated plastics usually have deteriorated properties due to repeated thermal and mechanical processing.
Coding symbols for sorting waste plastics Polyethylene 1 terephthalate PETE High density 2 polyethene HDPE 3 V
Polyvinyl chloride
Low density 4 polyethene LDPE Polypropene
5 PP 6 PS
Polystyrene
7 OTHER
All other resins
Recycling of plastics
Recycling of energy: energy values of plastics are quite high. The energy obtained from burning plastic waste can be used for heating or generation of electricity. Recycling of chemicals: plastic waste is pyrolysed (decomposed at high temp. in the absence of air), the products are fractionally distilled to give useful chemicals.
Composition of solid waste in 1993 (% by weight) Putrescibles Leather,Rubber, Wood Textiles Glass Fine Material & Miscellaneous Metals Plastic Paper
Solid Wastes in Hong Kong
An average of 2x107 kg solid waste daily in 1993. About 3.5 kg per head of population. Plastic, paper and metals occupied about 40% by weight of the domestic waste.
Disposal of solid waste
Two common disposal methods: Land filling and Incineration Incineration
Advantages:
reducing the volume by ~85% No risk of underground water pollution
Disadvantages:
polluting the atmosphere with toxic chemicals
Disposal of solid waste
Incineration
Disadvantages:
Potential environmental problems are (1) Generation of landfill gas, mainly methane. (2) Polluting the underground water
Pollution problem associated with the disposal of plastics
Plastic waste in the sea pose direct danger to fishes. Plastic waste can last for a long time, they do not undergo decomposition easily in the landfill site. Incineration produces air pollutants such as hydrogen chloride from PVC and other chlorine containing polymers.
Disposal methods of solid waste in Hong Kong Incinerated 6% Landfilled
73% Domestic 57%
Commercial
21% Industrial
Landfilled
16%
Degradable plastics
Slow degradation because enzymes in micro-organisms attack only at the ends of the polymer chains. Several types of degradable plastics: (1) Biopolymers: polymers made by living organisms. Poly(hydroxybutyrate), PHB, a natural polyester made by bacteria. Degradation completed within 9 months. 15 times more expensive than poly(ethene).
Degradable plastics (2) Photodegradable plastics: light sensitive functional groups such as carbonyl group (C=O) can in incorporated into the polymer chains. The long chains can be broken down under the action of sunlight into shorter fragments which can then be biodegradable. (3) Synthetic biodegradable plastics: made by incorporating starch or cellulose into the polymer during production.
Recycling of plastics
Direct recycling : applies only to thermoplastics. The plastics are separated, cleaned, pulverized, and remoulded into plastic items. The regenerated plastics usually have deteriorated properties due to repeated thermal and mechanical processing.
Coding symbols for sorting waste plastics Polyethylene 1 terephthalate PETE High density 2 polyethene HDPE 3 V
Polyvinyl chloride
Low density 4 polyethene LDPE Polypropene
5 PP 6 PS
Polystyrene
7 OTHER
All other resins
Recycling of plastics
Recycling of energy: energy values of plastics are quite high. The energy obtained from burning plastic waste can be used for heating or generation of electricity. Recycling of chemicals: plastic waste is pyrolysed (decomposed at high temp. in the absence of air), the products are fractionally distilled to give useful chemicals.
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