Major Issues on Atmospheric and Water Quality - Essay Example

?Q1. Describe the principal features, applications and limitations of the ‘Gaussian plume model’ for calculating the dispersion of atmospheric pollution. [25 marks] The Gaussian plume model is a method used for atmospheric dispersion modelling. Generally atmospheric pollutants are modelled through atmospheric dispersion modelling in order to discern the effects of pollutants in the air. Models previous to the Gaussian model did not assume a Gaussian distribution and also did not include the effects due to ground reflection of pollutant plumes. Sir Graham Sutton eventually came through with an air pollutant dispersion model which included the Gaussian distribution for the vertical as well as cross wind dispersion of the plume. Moreover, it also included the effects of ground reflection on the plume. (Sutton, 1947) The basis for this model and various other models is the Generalized Dispersion Equation for A Continuous Point Source Plume. (Beychok, 2005) This equation is: Where: is the cross wind dispersion parameter given as: is the vertical dispersion parameter given as: Where is the vertical dispersion with no reflection, is the vertical dispersion for reflection from the ground, is the vertical dispersion for reflection from an inversion aloft and are given as: is the concentration of emissions given in g/m3 at any given receptor that is located at meters downwind of the emission source, meters crosswind from the emission plume centreline and meters above the level of the ground. is the emission rate of the source pollutant given in g/s is the horizontal wind velocity along the plume’s centreline given in m/s is the height of the emission plume’s centreline above the ground given in m is the vertical standard deviation of the emission’s distribution given in m is the horizontal standard deviation of the emission’s distribution given in m is the height of the inversion aloft’s bottom from the ground The equation presented above compensates for upward reflection from ground as well as for downward reflection from the bottom of any inversion lids present within the atmosphere. The exponential terms in g3 converge rapidly and in most circumstances assuming m as 1, 2 and 3 provide acceptable solutions. as well as are representative functions of atmospheric stability and delineate the turbulence of the ambient atmosphere and of the downwind distance to the particular receptor. Within this arrangement, the most important variables are the degree of atmospheric turbulence and the height of the emission source. Generally dispersion is directly related to the turbulence. Q2. a. Describe the natural chemical reactions by which stratospheric ozone is created and destroyed. [10 marks] Ozone is produced in the atmosphere as the photochemical decomposition of oxygen molecules occurs. (Science Fun, 2011) As diatomic oxygen absorbs ultra violet radiation with wavelengths of less than 240 nm it tends to disintegrate as: O2 ? 2O* (reaction 1) The resulting free oxygen atoms combine with more oxygen molecules to generate ozone as below: O + O2 ? O3 Another mechanism is when ozone molecules decompose when treated with ultraviolet radiation with a wavelength of less than 290 nm. The reaction is as under: O3 ? O2 + O* (reaction 2) b. Explain the link that is believed to exist between pollution and ozone layer depletion. [10 marks] Myriad chemicals released into the air are known to react with ozone causing its depletion. The greatest danger stems from chlorofluorocarbons (CFCs) which are disintegrated by the action of ultraviolet light as below: CFCl3 + hv ? CFCl2 + Cl* (reaction 1) The activated chlorine atom now reacts with an ozone molecule to give off oxygen and chlorine oxide as under: Cl + O3 ? ClO + O2 (reaction 2) The chlorine oxide further promotes disintegration of ozone as under: ClO + O3 ? Cl* + 2O2 (reaction 3) This reaction tends to persist as reactions 2 and 3 proliferate and cause further ozone molecules to disintegrate into oxygen molecules. The net reaction for reactions 1, 2 and 3 becomes: 2O3 ? 3O2 Moreover nitrogen oxides, all forms of halides and methane are suspected ozone depletory agents. The ozone layer tends to absorb ultraviolet light emanating from the surface of the sun. Ultraviolet light tends to damage human skin causing skin cancer and is hazardous to plants and animals as well. It is expected that ozone depletion raises ultraviolet radiation levels which in turn boost the production of Vitamin D and certain form of cancers in human beings. (The Ozone Hole, 2011) c. What international agreement established the timetable for reducing emission of ozone depleting substances and what special provision was made for the needs of developing countries? [5 marks] The international agreement established for reducing ODS (Ozone Depleting Substances) is the Montreal Protocol that was signed into effect in 1987 and has been ratified by 196 countries to date. A special provision was put into place to protect the interests of developing countries. As per this developing countries will step down ODS production and usage from 1991 and 1992 such that their levels will not exceed 150% of the levels in 1986. Moreover, the ODS levels should not exceed 25% of the 1986 levels annually from 1994 and in 1996 these levels should drop to zero. (Speth, 2004) Q3. Discuss the key stages in the development of the legislative framework for atmospheric pollution control in the UK commenting where appropriate on the key air pollution problems the legislation was intended to address and the extent to which the legislation can be said to be reactive or proactive. [25 marks] The first integrated move to enact legislation for air pollution problems came in response to the Great London Smog of 1952. The Clean Air Act was passed in 1956 and held in effect up to 1964. This was followed by more stringent laws as the United Kingdom joined the European Union in 1972. EU directives were taken as benchmarks and newer legislation was implemented accordingly. However, the approach taken was highly reactive. (UKELA, 2011) Newer legislation became available in 1993 as the Clean Air Act which provided directives at setting chimney heights as well as the creation of smoke control zones. (NetRegs, 2011) Moreover, it bans the emission of dark smoke from chimneys and furnaces. The Environment Act was passed in 1995 to regulate air quality on a local level in England, Wales and Scotland. Local authorities are responsible for ensuring that their local atmosphere is compliant with national standards. Any area in violation of the recommended levels should be designated as an AQMA (Air Quality Management Area) and managed accordingly. Moreover, DEFRA (Department for Environment, Food and Rural Affairs) created the national air quality objectives in 2000 which are used as standards to compare local air quality levels. (Environment Agency UK, 2011) However the approach to dealing with air quality has largely been reactive and this is manifest with the EU’s warning to the British government that its emissions levels should be decreased in certain areas to meet standards. Failure to comply is expected to cost the nation GBP 300 million annually. Q4. a. Define disinfection and explain why it is needed in the treatment of potable water. (4 Marks) Disinfection is the process of removing unwanted substances from water. Processes may include treatment with ultraviolet light, ozone, chemicals, use of filters etc. Water plays host to a variety of pathogens that include bacteria, viruses and other such materials. Drinking water needs to be disinfected to ensure that these pathogens do not enter the human system. In case of their access to human beings myriad health problems could arise such as cholera, typhoid, diarrheal etc. b. Briefly explain the three main options used for disinfection. (8 Marks) Water can be disinfected by using chlorine and its oxides, by using ozone and by utilising ultraviolet light. Chlorine is a strong oxidant that can rapidly kill off any hazardous micro organisms that reside in water. Chlorine reacts with the dissolved oxygen in water to starve out the micro organisms. Consequently many organisms die off and the resulting water is disinfected. Ozone is an unstable form of oxygen that readily delivers an oxygen atom. This makes it a powerful oxidising agent which serves as being toxic to most microorganisms. Microorganisms die off rapidly on exposure to ozone and water is easily disinfected. Ultraviolet light is highly successful in inactivating various cysts in clear water. This effectively eliminates any microorganisms present. c. Discuss the relative advantages and disadvantages in the use of these disinfection options. (9 Marks) Chlorine is dangerous in large quantities to human beings. It tends to produce carcinogens in water if present in large quantities. Moreover, handling chlorine as a gas is dangerous so it has to be converted into sodium hypochlorite for use. Sodium hypochlorite readily dissolves in water and disinfects it. Moreover, using chlorine based disinfectants produce disinfectant residuals that can be easily removed. Ozone is simple to use and does not produce the large amount of by-products that chlorine compounds produce in water. Moreover ozone does not leave any odour or taste behind of its presence. Ozone does however produce small quantities of carcinogens of bromides. Moreover ozone does not leave any disinfectant residuals in water. Ultraviolet light can be employed effectively only if the turbidity of the water is low. The greater the turbidity of water, the lower the effectiveness of ultraviolet light becomes due to its scattering and absorption. Ultraviolet light does not produce any odours or residual compounds. There are no known carcinogens associated to the ultraviolet treatment of water. However, ultraviolet tends not to leave behind any disinfectant residuals. d. What role does disinfection play in wastewater treatment? (4 Marks) Disinfection removes pathogens from waste water. If waste water is discharged as yet, it carries a chance to proliferate pathogens in open sources of water such as rivers and oceans. This in turn reduces the quality of water and threatens living organisms within the open source of water. Moreover, if this source of water is used without treatment for example during swimming, camping etc. there are chances of getting infected easily. Q5. a. List the three main sources of water used for public supply in the UK. (3 marks) The three main sources of water in the UK are lakes, rivers and aquifers. b. Discuss the advantages and disadvantages of each of the three types of sources in (a). (7 marks) Lakes provide stored water that can be utilised for public supply. The amount of water in lakes is limited and may be subject to long term changes if water is not replenished by natural sources for too long. Moreover, water extracted from lakes is often low in turbidity levels but is rich in microorganisms. Rivers provide a continuous supply of water and flush out sewage treatment water too. However, water from rivers may contain hazardous material dumped in them upstream. Water from rivers requires less expensive treatment as they contain more suspended solids than dissolved solids. Aquifers represent underground water resources that provide water actively. However, the excessive usage of aquifers is known to deplete water levels over the longer run. Moreover, water from aquifers may require excessive treatment as they posses more dissolved solids than suspended solids. c. Describe the location and operation of the three main types of reservoirs used prior to water treatment works. (6 marks) Multiple types of reservoirs are used to handle water prior to water treatment. Water is flocculated first of all to remove suspended solids. This is done by adding flocculating agents that tends to combine various suspended solids into precipitates so that they can easily be removed. This helps to decrease the turbidity of water. The other kind of reservoir prior to water treatment is sedimentation ponds that tend to settle the various sediments carried by water. One end is generally deeper for these reservoirs and collected sediments are removed regularly. The third type of reservoirs is where chemical treatment of stored water is carried out using approved chemicals. d. Reservoirs may be considered to play a role in the pre-treatment of water prior to the water treatment works. Describe the "treatment" processes that may occur in a reservoir. Comment on some of the problems that may occur in reservoirs. (9 marks) During flocculation, certain flocculating agents are added to the water so that smaller particles can stick together to form larger precipitates than can be removed easily. If the flocculating agent is added excessively then its carry over is possible and there will be a need to remove it from the water. Sedimentation ponds allow water to settle easily so that it can allow sediments to drop to the bottom with relative ease. This allows the sediments to form a contiguous layer at the bottom of the pond which can be easily removed later. However, the thickness of the sediment layer should be kept as low as possible as it affects the pond’s volume and turbidity levels directly. In the chemical treatment ponds, chemicals have to be added with great care because an overdose or dearth of chemicals can both cause problems. Dearth of chemical agents will cause incomplete treatment while an overdose of chemicals will introduce toxic substances that will need to be removed later. Q6. a. What are the elements of an integrated sustainable water management system for a new estate to be developed? (10 marks) A typical sustainable water management system for a new estate is comprised of elements that manage water use, collection and reuse. Primarily water supply and consumption efficiency must be enhanced in order to utilise water as efficiently as possible. This would encourage a decrease in the net amount of water required directly. Another element is to upgrade drinking water quality as well as wastewater treatment. The economic services required to sustain operations and investment in money must be made more efficient as well. Alternative water sources such as rainwater, reclaimed water and treated water must be used to supplement already available water resources. Community involvement is another major aspect in managing water concerns. Moreover, capacity development of the personnel involved in integrated water management must be supported at all levels. (UNEP, 2009) b. What are the main differences between an integrated sustainable water management system and a standard water management scheme? (if your answer here is similar to information provided in (a) please either name again or refer to specific information already given in (a)) (6 marks) A standard water management scheme centres on the supply and treatment of raw water as well as the treatment of wastewater. Wastewater may be resupplied but in limited quantities only. Generally waste water is released to larger sources of water. Moreover, the emphasis on utilising all possible means of water collection is often low. Efficiency in use of water is not highly advocated either. c. Effluent from a sewage treatment works serving a population of 50 000 is discharged into an adjacent river. Determine the BOD, SS and DO levels in the river just downstream of the discharge given the following information: The water usage is 150 litres / person / day; The works produce Royal Commission standard effluent; The DO concentration in the effluent is 8 mg/l; The river has a flow of 0.5 m?/s; BOD of river upstream of discharge is 1.5 mg/l; SS of river upstream of discharge is 0.75 mg/l; DO deficit in river upstream of discharge is 3 mg/l; DO saturation value for water may be assumed as 10 mg/l (9 marks) flow rate of effluent = water consumed per person per day x total population flow rate of effluent = 150 x 50000 = 75,00,000 litres = 7.5 m3 water flowing in river each day = river’s flow rate x hours x minutes x seconds water flowing in river each day = 0.5 x 24 x 60 x 60 = 43,200 m3/s for BOD: For DO: For SS: Bibliography Beychok, M.R., 2005. Fundamentals Of Stack Gas Dispersion. 4th ed. author-published. Environment Agency UK, 2011. Air Quality: Position Statement. [Online] Available at: http://www.environment-agency.gov.uk/research/library/position/41241.aspx [Accessed 8 August 2011]. NetRegs, 2011. English air legislation. [Online] Available at: http://www.netregs.gov.uk/netregs/legislation/current/63598.aspx [Accessed 8 August 2011]. Science Fun, 2011. Chemical of the Week: Ozone. [Online] Available at: http://scifun.chem.wisc.edu/chemweek/ozone/ozone.html [Accessed 11 August 2011]. Speth, J.G., 2004. Red Sky at Morning: America and the Crisis of the Global Environment. New Haven: Yale University Press. Sutton, O.G., 1947. The problem of diffusion in the lower atmosphere. QJRMS, 73, p.257. The Ozone Hole, 2011. Ozone Destruction. [Online] Available at: http://www.theozonehole.com/ozonedestruction.htm [Accessed 8 August 2011]. UKELA, 2011. Environmental Law. [Online] Available at: http://www.ukela.org/rte.asp?id=14 [Accessed 8 August 2011]. UNEP, 2009. Integrated urban water management. New York: UNEP UNEP. Read More