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Home > Chemistry > Core > Chemical monitoring & management > Chemical monitoring and management: 5. Monitoring and management in water

9.4 Chemical monitoring and management: 5. Monitoring and management in water

Syllabus reference (October 2002 version)
5. Human activity also impacts on waterways. Chemical monitoring and management assists in providing safe water for human use and to protect the habitats of other organisms	Students learn to: identify that water quality can be determined by considering: concentrations of common ions total of dissolved solids hardness turbidity acidity dissolved oxygen and biochemical oxygen demand identify factors that affect the concentrations of a range of ions in solution in natural bodies of water such as rivers and oceans describe and assess the effectiveness of methods used to purify and sanitise mass water supplies describe the design and composition of microscopic membrane filters and explain how they purify contaminated water	Students: perform first-hand investigations to use qualitative and quantitative tests to analyse and compare the quality of water samples gather, process and present information on the range and chemistry of the tests used to: identify heavy metal pollution of water monitor possible eutrophication of waterways gather, process and present information on the features of the local town water supply in terms of: catchment area possible sources of contamination in this catchment chemical tests available to determine levels and types of contaminants physical and chemical processes used to purify water chemical additives in the water and the reasons for the presence of these additives

Extract from Chemistry Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW.
[Edit: 24Aug06] 

Prior Learning:Preliminary modules 8.2 (8.2.1, 8.2.2, 8.2.3) 8.3 (8.3.2, 8.3.3, 8.3.5), 8.4 (8.4.1, 8.4.3, 8.4.4), 8.5 (8.5.1, 8.5.3);HSC modules 9.2 (9.2.4), 9.3 (9.3.1,9.3.3, 9.3.4).

Background: Many environmental problems have been generated by humans and their activities. One problem is excess salinity, especially of the Murray Darling Basin. Primary production in this basin makes a major contribution to the economies of both NSW and Victoria. The chemical problems caused by excess salinity will need to have chemical solutions and will require the cooperation of all parties including farmers, the public, state and federal governments and industries that rely on water, either directly or indirectly. Management practices that ensure the sustainability of the environment and long-term viability for all parties using the environment will need to be developed and implemented.

gather, process and present information on the range and chemistry of the tests used to:

• identify heavy metal pollution of water
• monitor possible eutrophication of waterways

• Simple techniques to identify the presence of heavy metals include precipitation and flame testing. Techniques to quantitatively determine heavy metals include volumetric and gravimetric analyses, colorimetry, chromatography and spectroscopy, particularly atomic absorption spectroscopy (AAS) and mass spectroscopy.
  
  
• Tests to determine the extent of eutrophication of a waterway involve measurement of dissolved oxygen and nutrients, such as nitrates and phosphates. Gather information on the range and chemistry of tests by looking in encyclopaedia, scientific and popular journals and magazines and chemistry textbooks as well as searching the Internet under specific techniques. If you have access to CD ROMs, such as Encarta or Encyclopaedia Britannica, also search in them under specific techniques.
   
• Process your information making sure you assess its reliability by comparing information from various sources.
   
• When you present information, make sure you select and use appropriate methods to acknowledge sources of information. If a reference is from a book, provide Author(s), year, book title and publisher. If a reference is from the Internet, provide Author (if relevant), Title of item, web site owner, online (date last modified) Available at (provide URL).

Water Quality: HSC Chemistry Sydney Catchment Authority (A NEW site)

Water Quality Department of Primary Industry,Victoria, reviewed August 2004.

Animation of the process of artificial eutrophication Degradation of water quality in a lake is shown in a seven-slide presentation. Mike Docker, The Sixth Form College, Farnborough, UK.

perform first-hand investigations to use qualitative and quantitative tests to analyse and compare the quality of water samples.

• A qualitative test shows what (element, compound or ion) is present.
  
  
• A quantitative test shows how much (element, compound or ion) is present.
  
  
• Perform some investigations to determine the quality of water samples by selecting and modifying procedures like those described under the next syllabus point (below) and carrying them out carefully. Be alert to recognise where and when modifications are needed and analyse the effect of any adjustments that you make. Write descriptions of the tests used.

identify that water quality can be determined by considering:

• concentrations of common ions
• total dissolved solids
• hardness
• turbidity
• acidity
• dissolved oxygen and biochemical oxygen demand

The following tests determine water quality according to a given set of criteria supported by World Health Organisation information.

• The concentration of common ions.
  
  
• Atomic Absorption Spectrometry (AAS) is a common technique used to identify the concentration of metal ions. In testing water quality the concentration of the following cations are usually determined: sodium, magnesium, calcium and potassium.
  
  
• Gravimetric analysis can be used to determine the quantities of both cations and anions, e.g. for chloride ions precipitated and weighed as silver chloride. Common anion concentrations measured include chloride, sulfate, bicarbonate and fluoride ions.

Refer also to subsection 9.4.3 of this module, where a method for the precipitation of barium sulfate from ammonium sulfate fertilizer is described.

identify factors that affect the concentrations of a range of ions in solution in natural bodies of water such as rivers and oceans.

• Factors include:
  • the frequency of rainfall (floods and droughts),
  • water temperature
  • evaporation rates
  • soil type
  • pollution sources, such as the presence of animal faeces and fertiliser usage (leading to eutrophication)
  • land use.
     
• Farming practices such as the removal of native vegetation or irrigation can increase the salt (NaCl) concentration in rivers.

  Earthmoving associated with waterfront developments can expose layers containing sulfide to air. The sulfides are oxidised by oxygen to form sulfates and sulfuric acid, which can kill fish and other living things.

  High evaporation rates in the Dead Sea have increased the dissolved salt concentration.

  Run-off of water from agricultural land in Queensland, near the Great Barrier Reef, contains ions, such as phosphate, which can affect the growth of organisms.

gather, process and present information on the features of the local town water supply in terms of:

• catchment area
• possible sources of contamination in this catchment
• chemical tests available to determine levels and types of contaminants
• physical and chemical processes used to purify
• chemical additives in the water and the reasons for the presence of these additives

• This syllabus point could efficiently be addressed by you working with other students in a group. Assign each member of the group to gather data about a part of the syllabus requirement. As a whole group, you may need to decide on the structure and components of the final group report so that relevant information is gathered. Many local regional councils and Sydney Water have web sites and some have project officers who can provide information to you on the issues listed above. Before contacting an organisation, you should conduct as much research as you can using published information from the organisation, from books in the school or local library and from the Internet. This will ensure that you are well prepared to discuss relevant chemistry and catchment issues without using an officer’s time inappropriately.
   
• Process the information gathered by comparing the information from interviews and your secondary sources. This will assist you to evaluate the validity of all information gathered.
   
• Present your information to other students. Consider using visual aids such as maps, photographs, diagrams, overhead transparencies, graphics or an extract from a video interview. A Powerpoint presentation allows each group member to develop materials individually then contribute to the final report. Keep the presentation precise, by only focusing on the information asked for in the syllabus point.

Some useful local NSW web sites:

Your water Sydney Water, Typical Drinking Water Analysis

Water quality monitoring Sydney Catchment Authority

Country towns water supply and sewerage program Local Government and Shires Association of NSW. The Country Towns Water Supply and Sewerage Program (CTWSSP) is a long standing program which supports councils in country NSW in their provision of water supply and sewerage services.

 

describe and assess the effectiveness of methods used to purify and sanitise mass water supplies.

• There are several methods used to purify mass water supplies. Most are variations on the following process:

  

• Water is collected in dams and pumped to a treatment site where the larger solids such as pieces of plastic are removed by screens.
   
• Fine particles suspended in water have electric charges on their surface that keep the particles from joining together. This stops particles from becoming large enough to settle as sediment. Separation of fine particulate matter suspended in water involves the addition of coagulants, such as iron(III) chloride, FeCl₃, to the water. The added FeCl₃ neutralises these surface charges so the particles come together. Iron(III) hydroxide is formed by reaction of FeCl₃ with water and precipitates out as a floc (flocculant). The floc collects the neutralised particles into large masses that are more easily filtered.
   
• The chloride ions added with the FeCl₃ remain in the water. They do not have a harmful impact on the water quality as determined by the Drinking water quality guidelines (1996), National Health and Medical Research Council (NHMRC).
   
• In some instances, after flocculation the particle size of suspended solids is too fine for filtration through sand beds and so membrane filters are used. They are more effective than sand filters as they can have a very small pore size. However membrane filtration is more costly than sand bed filtration.
   
• Sanitising mass water supplies involves disinfecting with chlorine gas, Cl₂, liquid sodium hypochlorite solution, NaOCl (aq), or solid calcium hypochlorite, Ca(OCl)₂. Sedimentation and filtration removes some harmful organisms, such as bacteria, viruses, cryptosporidium and giardia, but disinfection is needed to ensure concentrations are acceptably low. In some parts of the water distribution system, ammonia, NH₃, is added to form monochloramine, ClNH₂, by reaction with chlorine. This is a less reactive disinfectant, but lasts much longer in the distribution system.
   
• Assessment of the effectiveness of sanitisation methods should involve:
  • microbiological testing of water samples throughout the distribution system, in particular before and after sanitisation processes.
  • public health surveys and reporting by medical doctors of incidences of illnesses that are possibly transmitted through water supplies.
     
• A few years ago, some water supplies in NSW were contaminated by the micro-organisms, cryptosporidium and giardia. As a result, water supplies are monitored daily at water treatment plants and throughout each catchment during storms or other events that cause a rise in stream water levels and could influence water quality. This is considered effective, as the cost of treatment of all water supplies with membrane filters would make treatment very expensive.

Notes for Schools Sydney Water

describe the design and composition of microscopic membrane filters and explain how they purify contaminated water.

• Microscopic membrane filters have microscopic pores and the use of appropriate sized filters can avoid the need to chemically treat the water. The filters can be classified as microfiltration, ultrafiltration, nanofiltration or reverse osmosis membranes depending on the size of the pore.
   
• The membrane is made from synthetic polymers dissolved in a mixture of solvents. Water-soluble powders of a particular size are added. The mixture is spread out over a plate and left for the solvent to dry. The polymer membrane formed, containing particles of water-soluble powder, is then placed in water. Remaining solvent and the powder particles dissolve, leaving a very thin polymer sheet with definite sized microscopic pores where the water-soluble particles were located.
   
• Semi-permeable membranes used in reverse osmosis are either made of cellulose acetate or a layer of polyamide attached to another polymer. Under pressure these polymers allow the passage of water molecules but not that of most atoms, ions or other molecules.
   
• Water is made to flow across the membrane not through it. This reduces the blockage factor. Microfiltration removes protozoans, bacteria, colloids, some colouration and some viruses. The size of the pore determines which sized particle or organism may pass through the membrane. The finer the pore size the smaller the particles trapped and the more expensive the membrane.