Solid Waste

Amount of solid waste Over tonnes daily in 1997 About 6.5 kg daily per head of the population Between 1983 and 1993, there is a two-fold increase Exert tremendous pressure on waste disposal facilities.

In USA 45% of paper produced, 15% of aluminium produced, 75% of glass produced, 30% of plastics packaging==> went into packaging

Composition of domestic waste In % by weight is plastic, paper and metals.

Methods of solid waste disposal Landfill Incineration Dumping at sea Recycling

Landfill

SENT LANDFILL

Environmental problems generate landfill gas (mostly methane) generate leachate (groundwater from landfills)

Burning of landfill gas

Restoration of landfill For recreational purposes after emissions have ceased, the land has settled will take about 30 years!

Incineration

Complete combustion of oxidizable material will occur at o C ash, glass, metal and other materials remain.

Incineration Volume of solid waste is reduced by 85% high temp. kills pathogens no risk of groundwater pollution heat produced can be used as a source of energy recover valuable metals like Fe, Al from the incinerator waste in USA

Incineration Polluting the atmosphere: incinerating cans, jar lids and batteries give fly ash containing toxic metals e.g. Cr, Pb, Hg. Some plastics including Teflon produce irritating or toxic gases (e.g. HCl) as they burn. large amount of CO 2 adds to problem of ‘Greenhouse Effect’.

Dumping at sea Much of waste from construction is dumped areas chosen are far from the coast and in deep sea.

Dumping at sea Increase in the suspended solids and turbidity of water will occur pelagic species of fish will avoid such areas => a reduced diversity of species will occur coral which are sensitive to high turbidity will be destroyed.

Recycling Conserves Earth’s reserves and saves energy Used aluminium is as good as new. The cost of re-using scrap aluminium is only 1/20 of the cost of making the pure metal. In Hong Kong 50% of glass beverage bottles are collected for reuse or recycling.

Recycling Pulping and recycling used paper is a simple matter. The recycled paper is softer and less strong. The collection, sorting and recycling of metals has become an important industry.

Disposal of plastics Plastics are non-biodegradable do not generally undergo decomposition in the landfill site plastic waste can last for a long period in the environment.

Disposal of plastics If the waste is burnt with the plastics included, potentially useful energy is generated. Some plastics, however, burn with the formation of toxic gases, e.g. hydrogen chloride from PVC, and hydrogen cyanide from poly(propenenitrile).

Degradable plastics Biopolymers photodegradable plastics synthetic biodegradable plastics

Biopolymers Poly(hydroxybutyrate), PHB, is a natural polyester made by certain bacteria. Micro-organisms found in soil and natural water sources are able to break down the polymer. The properties of the polymer can be tailored by incorporating copolymers to make it suitable for a range of articles.

photodegradable plastics a carbonyl group(>C=O) can be incorporated into the polymer chain, the carbonyl group will absorb light and use the energy to break chemical bonds in the polymer. The long polymer chains will be broken down into shorter fragments which can then be biodegraded.

synthetic biodegradable plastics incorporating starch or cellulose into the polymer during production. The polyethene chains and starch chains interweave to form a material which is strong enough for shopping bags. As micro-organisms digest the starch or cellulose, the plastic is broken down into tiny pieces.

Recycling of plastics Direct recycling – this applies only to thermoplastics. In 1988, the Society of the Plastics Industry (SPI) developed a uniform coding system that makes it possible to sort waste plastics. The plastics in the waste are separated, cleaned, pulverized, and remoulded into plastic items.

Recycling of plastics Recycling of energy – the energy obtained from burning plastic waste in incinerators can be used for heating or generation of electricity.

Materials polystyrene polyethene heating oil fats leather PVC paper wood Calorific values / kJ kg Calorific values of plastics and various materials

Recycling of plastics Recycling of chemicals – the plastic waste is pyrolysed (decomposed at high temperature in the absence of air), the product fractionally distilled to give useful chemicals.

pyrolysis product ethene propene methane butadiene benzene Chemical manufactured polyethene polypropene town gas rubber various plastics (e.g. polystyrene) Chemicals manufactured from pyrolysis products

Pollution control in HK The Hong Kong Government has since 1990 been actively promoting the 3Rs concept (Reduce, Reuse, Recycle) to increase public environmental awareness and participation in waste minimization and recycling activities. This not only helps in saving resources but also in reducing the demand of valuable landfilling space.

Pollution control in HK Some publicity programmes such as the ‘Reusable Bag’ campaign and the ‘Bring Your Own Bag’ (BYOB) campaign have been launched to educate the public to minimize the use of plastic bags. Within 6 months from the start of the scheme a 10% reduction in plastic bags had been achieved.

Pollution control in HK The Hong Kong Environmental Resource Centre in Wan Chai is dedicated to inform people about their environment, show the community what is being done to improve their environment and encouraging people to play their part.