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Introduction Solid waste is classified into five main types by making reference to the sources of waste andthe institutional arrangements for waste collection and disposal. These five types of solid waste are municipal solid waste, construction & demolition (C&D) waste, chemical waste, special waste and other solid waste. The detailed interpretations of some commonly used terms are described below.
Municipal solid waste It includes domestic waste, commercial waste and industrial waste.
Domestic waste It refers to household waste, waste generated from daily activities in institutional premises and refuse collected from public cleansing services. Public cleansing waste includes dirt and litter collected by the Food and Environmental Hygiene Department (FEHD), marine refuse collected by the Marine Department and waste from country parks collected by the Agriculture, Fisheries and Conservation Department.
Plastic Bacteria can decompose some types of the plastics. These are called biodegradable materials, and will not cause serious pollution problem after decomposition. However, non-biodegradable plastics, which cannot be decomposed, will lead to serious pollution problems.
Metal can Metal cans are not biodegradable. When they are thrown into the environment, they cause land or water pollution. Besides, these natural resources are wasted.
Commercial waste It is waste arising from commercial activities taking place in shops, restaurants, hotels, offices, markets in private housing estates, etc. It is collected mainly by private waste collectors. However, some commercial waste is mixed with domestic waste and collected by the FEHD. Some not mixed is also collected by the FEHD for historical reasons.
Industrial waste It is waste arising from industrial activities and does not include C&D waste and chemical waste. It is usually collected by private waste collectors. However, some industries may deliver their industrial waste directly to landfills for disposal
Current situation Household and other municipal waste loads have risen steadily, in line with the growth in population and wealth of the community. There is no sign of a let-up because another two million people are expected to live in the SAR by 2016.
Effect The most important of land pollution is effect on hygiene. Bacteria, and give off bad smells may decay some of the materials in the garbage. The decayed materials will create problem of hygiene. Pathogenic bacteria and other pests may also grow on the decayed materials and diseases may then be spread.
The three strategic landfills will run out of space in 10 to 15 years. Without waste reduction measures and sufficient public filling areas, SENT landfill might run out as early as 2005.
Recycling Hong Kong recycled about 35 percent of its municipal waste (mostly commercial and industrial waste) and the government wants to increase this to about 60 per cent by 2007. A number of initiatives were undertaken in 2000 with significant support from the green groups.
Some of the highlights were: • newspaper vendors were encouraged to stop distributing papers in plastic bags • the number of housing estates with waste separation bins doubled to more than 700 • the number of items recycled by hotels and the airport were increased • more recycled products were added to the government's purchasing guidelines • four new temporary sites were allocated for use by the re-cycling industry
Special waste -Clinical waste -Animal carcasses -Radioactive waste
Clinical waste Source -being produced in hospitals and government clinics E.g. contaminated sharps, infectious waste and human tissues
Deal -Segregating from ordinary refuse and being collected separately for proper disposal. -Most clinical waste will be disinfected as far as practicable and disposed at designated landfills. -Human tissues and body parts from operating theatres shall be disposed of by incineration as far as practicable
Animal carcasses Source: • Slaughterhouses • Street collections • Society for Prevention of Cruelty to Animals • Hong Kong Jockey Club Ocean Park
Deal -Land filling of animal carcasses may generate health hazards. Some animal Carcasses are infectious and spread diseases. -It is proposed to build animal carcass treatment facilities (ACTF) for proper disposal of animal carcasses to prevent the spread of diseases.
Low-level Radioactive waste Source -Industry and medical and educational institutions Americium-241Smoke detector sources Promethium-147Luminous watch dials & contaminated articles Radium-226Lightning conductors and luminous watch dials Thorium-232 Rayon mantles for kerosene lanterns
Deal The wastes are properly packaged in new stainless steel standard containers
Definition • Chemical wastes are liquid, semi-solid and solid wastes which are dangerous in nature or cause a risk of pollution to the environment
Problems • Indiscriminate disposal of chemical waste • Release into coastal waters causes damage to local marine life and accumulation of toxins in seafood • Uncontrolled disposal of municipal waste facilities and into sewerage systems and sewage treatment facilities resulting in costly repairs and replacement of these facilities
Solutions • The chemical Waste Treatment Center-CWTC • Handle with 100,000 tones chemical waste per year
Main Activities of CWTC • Chemical Waste Collecting • Waste Profile Analysis • Chemical Waste Treatment • Physical/Chemical Treatment • Incinerator • The Ancillary System are designed to support the treatment processes. They are Waste Container Handling, Storage Tank Farm, Laboratory Computer System
The Waste Disposal Ordinance on Waste Management • Waste Disposal Ordinance 1987 Prohibit livestock keeping in urban areas Controls of discharge or deposit of livestock waste in control areas • Waste Disposal Ordinance 1991 Controls of chemical waste about packaging, labeling, storage, collection, disposal, import and export activities
Waste Disposal Ordinance 1994 Introduce a heavy penalty for illegal damping of waste and make it an offence to breach of the license conditions of the waste collection and disposal licenses • Waste Disposal Ordinance 1995 Control import and export of hazardous and other waste in accordance with the requirement • Waste Disposal Ordinance 1998 Expands the regulations making powers for implementation of the various waste disposal charging schemes
Development of New Waste Legislation • Control for the arrangement of clinical waste and improves control of waste import and export and illegal dumping of waste • Specifies the requirement of clinical waste producers, collectors and disposal facility operatorsAmend the schedules and prescribes fees for clinical waste collection licenses • Gives effect to the new charging scheme for clinical waste through amendment of the regulation
Gives effect to the new charging scheme for clinical waste through amendment of the regulation • Amends the schedules and clarities the definition of chemical waste in light of amendment to the Dangerous Goods Ordinance –DGO • Gives effect to the revised landfill charging scheme
Composition of domestics waste disposed of at waste facilities (% by weight)
Solutions to pollution problem of plastics • By using degradable plastics instead of the non-degradable one • Recycling plastics wastes ( remold the plastic)
Development of degradable plastics Plastics normally undergo extremely slow degradation because the enzymes in micro-organism tend to attract only the ends of the polymer chains Example????????
1.Biopolymers It is made by living micro-organism such as paracoccus, bacillus and spirullum. Poly(hydroxybutyrate) PHB, is a natural polyester made by bacteria
Advantage and disadvantage???? Advantage: Micro-organisms found in soil and natural water sources are able to break down the polymer completely within 9 months. Disadvantage: Very expensive (15 times more expensive that polyethene)
2.Photodegradable plastics As polymer consist of long chain Therefore, light sensitive functional group –c=o are incorporated in the polymer chains. As a result, the long polymer chains will be broken down into shorter fragment which will facilitate the process of biodegradation under sunlight
3.Synthetic biodegradable process By incorporating starch or cellulose into the polymer during production.
Advantage Since micro-organisms digest starch or cellulose the plastic is broken down into tiny pieces. --larger surface area for the biodegradable --speed up process
Disadvantage The products of biodegradation may cause water pollution and the rate of biodegradation is still too slow for the large quantity of plastic wastes generated.
B. Recycling of plastics • Direct recycling -----This applies only to thermoplastics. The remolded into plastic items. • Recycling of energy -----This applies to most plastics. The plastic wastes are burned in the incinerators. The calorific values contained in plastics are quite high.
Advantages: • Reduces air pollution due to the incineration of plastic • Less dumping area is required. • Reduces the use of petroleum
Disadvantages: • The regenerated plastics usually have deteriorated properties due to repeated thermal and mechanical processing and can only be used for articles which are not subjected to high stress. • It is not very economical to separate the plastic items from the other wastes at present. Moreover, plastic products may contain dyes, politicizes and fillers so that it is very difficult to classify them by observation.
2. Recycling of energy -----This applies to most plastics. The plastic wastes are burned Advantages: a.The energy obtained from burning plastic waste can be used for heating or generation of electricity b.It is not necessary to separate the plastics c.Less dumping area is required Disadvantages: Burning plastics produces toxic gases e.g. PVC will give HCl. Expensive scrubber systems have to be used to remove them.
3. Recycling of chemicals by pyrolysis------for all plastics Similar to cracking, the plastic wastes can be pyrolyzed (decomposed at high temperature in the absence of air) at 600-900 to give useful small molecules similar to those obtained from the fractional distillation of crude oil. These small molecules (mainly hydrocarbons) are separated by fractional distillation. Some of the small molecules can be used directly as fuels. Other larger molecules may be employed as raw materials in plastic production.
