Introduction Cause of water pollution Effects of water pollution on the environment Water quality
Nowadays, our surrounding waters have been assaulted with a heavy burden of pollutants. The most obvious damage has been to coastal zones, where fouled waters and littered beaches have resulted in a reduction of resorts suitable for swimming. The longer we use our surrounding waters as a giant garbage dump the more difficult and cost the cleanup will be.
ÊLivestock waste - from pigs and poultry ËOil spillage - from ships ÌResidues of pesticides - from farms ÍDetergents in sewage - from commercial and domestic wastewater ÎIndustrial effluents - from dyeing and electroplating factories
Livestock waste À When an excessive amount of organic matter is discharge into water, the existing aquatic micro-organisms will grow and multiply rapidly. Á The oxygen dissolved in water is rapidly depleted. Because of the lack of oxygen, anaerobic micro-organisms begin to break down partially the organic matter, releasing foul- smelling and toxic gases like CH 4, NH 3 and H 2 S. Â As a result, the aquatic organisms will die.
Oil Spillage The effects of oil spillage may include the following: À Oil clogs the feathers of sea birds and prevent them from flying or swimming, oil interferes with the insulation provided by the feathers, so the birds may die of cold or pneumonia. ÁAs oil is immiscible with water and floats on water, it blocks the oxygen supply to the sea water. ÂAs oil is toxic, it kills marine life. Residues of pesticides ÀPesticides cause immediate toxic effects on aquatic life and accumulate along the food chain until a toxic level is reached.
Detergents in sewage ÀDetergents may speed up the eutrophication, because phosphates in some detergents are nutrients to algae. ÁDetergents may cause foaming in rivers and lakes, because some synthetic detergents with branched hydrophobic chains cannot be biodegraded within a short time. Industrial effluents ÀThe toxic materials present in industrial effluents vary with the industry involved. ÁThey may contain toxic metal ions of Cd, Cr, Cu, Hg, Ni, Pb and Zn; cyanides, polychlorinated hydrocarbons, organic solvents, acids and bases.
1. Dissolved Oxygen (DO) PDissolved Oxygen (DO) is an indicator of the oxygen content in water, It is measured in: a. mg of O 2 per dm of water, or b. percentage saturation of dissolved oxygen PThe maximum concentration of dissolved oxygen in water at 16°C is 10 mg dm. If a water sample contains 6mg dm of dissolved oxygen at 16,the % saturation of DO is then : 6/10 x 100 = 60 The sample is said to be 60% saturated with oxygen.
PThe amount of dissolved O 2 in water is important for aquatic life. Fishes normally require 4-6 mg dm of DO for survival. PDepletion of oxygen may be caused by biological degeneration of water matter. PThe larger the amount of organic matter in the waste water,the lower is it DO.
2. Biochemical Oxygen Demand (BOD) PBiochemical oxygen demand (BOD) is an indicator of the water pollution. It is the amount of oxygen required to break down the organic matter present in a water sample. PIf water has a high BOD, it indicates that a lot of organic waste is present and a lot of oxygen is required to break down the organic matter in the waste. PIf water has a low BOD, it indicates the presence of a small amount of organic matter and there is little organic pollution. Natural clean water has a BOD is about 1 to 4 mg dm.
PIf BOD is greater than the amount of oxygen replenished by air, then some fishes and aquatic life may die; organic debris accumulates, and anaerobic micro-organisms begin to multiply, producing unpleasant odours. PBOD is determined in the laboratory by incubating a sample of water for five days in the dark at 20 °C and measuring the amount of oxygen consumed. The BOD determined in this way is also known as five-day BOD, BOD 5. BOD 5 value is commonly used to indicate the relative oxygen requirements of treated effluents and polluted waters.
Solid Waste in Hong Kong Solid Waste in Hong Kong Disposal of Solid Waste Disposal of Solid Waste A. Incineration A. Incineration B. Landfilling B. Landfilling Pollution Problems associated with the Disposal of Plastics Pollution Problems associated with the Disposal of Plastics Solving the Plastic Pollution Problem Solving the Plastic Pollution Problem A. Development of Degradable Plastics A. Development of Degradable Plastics B. Recycling of Plastics B. Recycling of Plastics
In Hong Kong,an average of 25,000 tonnes of solid waste were disposed of daily due to human activities of domestic households, commercial and manufacturing business and construction site in the territory. This quality amounts to about 4kg of waste per head of population. Some of the waste are potentially recyclable, e.g. metals, plastic, paper and glass.
A. Incineration About 1/4 to 1/5 of solid wastes in Hong Kong is disposed by incineration. Advantages of incineration: Ê reduces the volume of the waste by approximately 85% Ë kills the disease-causing organisms at high temperature Ì makes no risk of groundwater pollution Disadvantages of incineration: Ê it may produce toxic air pollutants and increase the incidence of acid rain and photochemical smog
B. Landfilling About 4/5 to 3/4 of the solid waste is disposed by landfilling. The solid wastes are compressed and covered with soil on landfill sites. Advantage of landfilling: Êonly very small amounts of harmful air pollutants are released. Disadvantage of landfilling: the potential environmental problems associated with landfilling of waste result mainly from the generation of landfill gas and leachate.
The tremendous amount of plastic items used today creates waste disposal problems. Moreover, the use of plasticizers and CFCs in the manufacture of plastics produce ecological and environmental problems. The tremendous amount of plastic items used today creates waste disposal problems. Moreover, the use of plasticizers and CFCs in the manufacture of plastics produce ecological and environmental problems. Landfilling and incineration are two main ways to disposal of plastic wastes. Landfilling and incineration are two main ways to disposal of plastic wastes. Problems associated with the landfilling of plastics : As plastic are chemically tailored for long life, they do not generally undergo decomposition in the landfill site. Thus the plastic waste can last for a long period in the environment. The plastic wastes in landfills may delay the reuse of landfills for other purpose Problems associated with the landfilling of plastics : As plastic are chemically tailored for long life, they do not generally undergo decomposition in the landfill site. Thus the plastic waste can last for a long period in the environment. The plastic wastes in landfills may delay the reuse of landfills for other purpose.
Problems associated with the incineration of plastics: If plastics are burned away by incineration, in addition to CO 2, toxic gases may be formed, e.g. burning PVC or other chlorine-containing polymer gives HCl. HCl may contribute to the formation of acid rain. Plastics wastes in sea endanger aquatic lives, e.g. plastics bags or fragments of plastic foam may be mistakenly eaten by fishes, since plastics are not digestible, the fragments of plastic will clog their digestive tracts, the small fishes will eventually die. Sea animals have been suffocated to death by plastic bags. Plasticizers from the degradation of plastics may pollute water as they are released from landfill as leachate, e.g. PCBs are once common plasticizers that are found to be very stable in the environment and pose health hazard. Other common plasticizers such as phthalates are also found in leachate, they are safer than PCBs but are still harmful to us.
A. Development of Degradable Plastics P Biopolymers - They are polymers made by living organisms, e.g. 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 degradation of PHB in the environment is usually completed within 9 months. However, PHB is 15 times more expensive than poly(ethene). P Photodegradable plastics - Light-sensitive functional groups such as carbonyl group (C=O) can be incorporated into the polymer chains. The long polymer chains will be broken down under the action of sunlight into shorter fragments which can then be biodegraded by micro-organisms in soil.
P Synthetic biodegradable plastic - made by starch or cellulose incorporated into the polymer during production.As micro- organisms digest the starch or cellulose, the plastic is broken down into tiny pieces.The very small pieces left over have a large surface area which greatly speeds up their biodegradation. P Degradable plastics have been used for marking six-pack beverage rings, trash bags and disposable diapers. B. Recycling of plastic P Direct recycling - This apply only to thermoplastic. The plastic in the waste are separated, cleaned, pulverized, and remoulded into plastic items.
Coding system developed by the society of the Plastic Industry for sorting out plastics: PETE - Polyethylene HDPE - High density polyethylene V - Polyvinyl chloride (PVC) LDPE - Low density polyethylene PP - Polypropylene PS - Polystyrene OTHER- All other resins
Disadvantages of direct recycling: Ê the regenerated plastics usually have properties due to repeated thermal and mechanical processing,and can only be used for articles which are not subjected to high stress. Recent development on recycled plastics focuses on converting the plastic products with short service lives, such as foam, wrap and containers, to products with longer service lives, such as construction materials and plastic pipes. Ë It is not very economical to separate the plastic items from the other wastes at present. Moreover, plastic products are very difficult to be classified. Ì Plastic products contain different dyes. It is very difficult to remove them from the recycled plastics, the recycled plastics are usually black in colour.
PRecycling of energy - This applies to most plastic. The plastic wastes are burned in the incinerators. The calorific values contained in plastics are quite high. Advantages of recycling of energy: Ê The energy obtained from burning plastic waste can be used for heating or generation of electricity. Ë It is not necessary to separate the plastics. Ì Less dumping area is required. Disadvantages of recycling of energy: Ê Burning plastic produces toxic gases,e.g. PVC will give HCI. Expensive scrubber systems have to be used to remove them.
PRecycling of chemicals by pyrolysis - This applies to all plastics: n Similar to cracking, the plastic wastes can be pyrolyzed (decomposed at high temperature in the absence of air) at 600-900 °C to give useful small molecules similar to those obtained from the fractional distillation of crude oil. These small molecules are mainly hydrocarbons. n The small molecules are separated by fractional distillation. n Some of the small molecules (e.g.CH 4 ) can be used directly as fuels while other larger molecules may be employed in plastics production or used for other purposes.
Advantages of pyrolysis: ÊThe products are useful raw materials for the manufacture of plastics-reduces the use of petroleum. ËIt is not necessary to separate the plastics. ÌLess dumping area is required/saves more land for other uses. Disadvantages of pyrolysis: Burning plastics produces toxic gases, e.g.PVC will give HCI. Expensive scrubber systems have to be used to remove them. The capacity of handling plastic waste by a pyrolysis plant is also small compared to the total amount of plastic waste produced.At present, the running cost of disposal of plastic by pyrolysis is much more expensive than landfilling.