- Created by: Gina Hayley Phillips
- Created on: 04-01-12 10:29
Give some consequences of a period of extended dro
Hunger and famine: Drought often provides little water to support food crops, grass and grain (which is used to feed livestock and poultry). When drought destroys food sources people go hungry and when drought is severe famine may occur.
Thrist: People can survive for weeks without food, but only days without water.
Disease: Drought creates a lack of clean drinking water, public sanitation and personal hygiene, leading to a range of life threatening diseases.
Wildfires: Low moisture can quickly create hazardous conditions in forests and across range lands.
Social conflict and war: When water is is short supply people compete and eventually fight and kill to sucure enough water to survive.
How much salt does water have to contain to be con
Fresh water: Less than 1,000ppmm.
Slightly saline water: from 1,00 ppm to 3.000 ppm.
Moderatly saline water: from 3.000 ppm to 10,000 ppm.
Highly saline water: from 10,000 ti 35,000 ppm.
Why is saline not suitable for drinking?
Salinty outside the cells increases rapidly. So osmoregulation effects movement of water from in your cells to outside. Even when dehydrated cells will release rather than absord the water around them.
- This is a conscious decision by your body, (simple molecular physics and osmosis at work) --> during osmosis water passes from low saline concentrations to high concentrations.
What is desalination?
The removal of salt and other mineals from water.
- especially sea water
In 2002 there were 12,5000 desalination plants aro
365x24000000 = 5110000000m3
6.5%/ 100 = o.065 x 5110000000 = 332150000 m3 per year in the US.
What percentage of desalinated water does the US p
35/3-- x 100 = 11.7%
What is distillation?
The process of purifying a liquid by boiling it and condensing its vapours.
Distillation is a unit operation, or a physical separation process.
NOT A CHEMICAL REACTION
Find a diagram to show how distillation can be car
Describe the theory of osmosis.
Diffusion refers to the process by which molecules intermingle as a result of their kinetic energy of random motion.
For example to containers of gas A and B separated by a partition. The molecules of both gases are in constant motionm and make numerous collisions with the partition. If partition removed as as in the lower illistration the gases will mix because of the random velocities of their molecules.
What is the process if multi stage flash distillat
1: Feed water is pumped through the heat exchangers and is warmed up. When it reaches the brine heater it is nearly the maximum temperature.
2: After the heater the water flows back through valves to lower temperatures and pressures. The water is now called brine Each stage enters the temperature above the boiling point at the pressure of each stage and a small amount of it will boil to steam to reduce the temperature reaching an equilibrium.
3: The steam cools and condenses against heat exchanger tubes this goes towards the heating the feed water.
4: The pressure in the chamber remains constant as equal amounts of steam in formed when new warm brine enters the stage and steam is removed as it condenses on the tubes of the heat exchanger.
5: The equilibrium is stable because some point more vapor forms the pressure increases and that reduces evaporation and increases evaporation.
6: In the final stage the brine and the condensate are pumped out from the low pressure in the stage to the ambient pressure.
The brine and condensate still carry amount of heat that is lost from the system when they are let out.
As the temperature increases in the stage what pro
With increasing temperatures there are growing difficulties of scale formation and corrosion.
Why is this carried out in multiple stages instead
The reason for letting the evaporation happen in multiple stages rather then a single stage at the lowest pressure and temperature, is that in the single stage the feed water would only warm to an intermediate temperature between the condense and the stage would not maintain the lowest pressure and temperature.
What is the pressure of multiple effect evaporatio
A multiple effect evaporator is an apparatus for efficiently using the heat from steam to evaporate water. In a multiple effect evaporator water is boiled in a sequence of vessels, each held at a lower temperature than the last. Because the boiling temperature of water decreases as pressure decreases the vapor boiled off in one vessel can be used to heat the next and only the first vessel requires an external source of heat.
What is electrodialysis?
Dialysis in which the movement of ions is aided by an electric field applied across the semipermeable membrane.
Find an image to show how the process of reverse o
Compare the processes of MSF and RO in terms of en
Energy required to produce one litre together with the cost of energy makes or breaks the need for desalination and the choice of the process.
RO has a much higher yield. This means for the same output the intake of sea water only has one third in RO systems. The considerably decreases the power and other costs required for pumping sea water to the plany and disposing the spent brine.
Ro systems require considerable energy for pressurizing the water to the membrane filters. MSF require heat energy for heating the brine before vaporisation.
What percentage of people die from diarrhoeal dise
1.8 million people die each year.
1800000/1100000000 x 100 = 0.16%
What type of particles, pathogens and elements nee
Particles: Silt and debris can be removed by passing water through a 10 to 20 micron filter.
Microorganism: Bacterial agents challenge water due to their growth rate and size. Measured in colonies and killed with disinfectants.
Dissolved organic elements: Pesticides, plant and animal remains or framgments.
Large debris such as sticks, leaves, rubish and other large particles whioch may interfere with purification steps.
What are the acceptable limits of calcium and magn
Calcium: 40-80 ppm
Find a picture to show the natural water cycle.
A Scientist wanted to collect a sample of water fr
- Weather changes
- Uneven ground
- Allergic reactions to other plants in the area
After collecting a sample of water for testing, a
- Identification of the sample
- Warning symbol
-Date and time of collection
The scientists wanted to assess how the concentrat
-To be more precise they should use smaller increments of concentration of chlorine.
- Repeat same test
- Ensure clean equiptment
- Same environment
(Following graph) Fluoride is a substance that has
26. Which year was the highest level of decayed and missing teeth recorded?
27. What was the highest percentage of people drinking fluoridated water?
28. When there is 50% of people drinking the fluoridated water what is the mean number of decayed and missing teeth?
Where are the biggest desalination plants in the w
The worlds largest desalination plant in the Jebel Ali desalination plant. It produces 100,000 cubic meters of water per day, or 36.5 million cubic meters of water per year.
Water purification often uses chlorine, what shoul
- Dangerous for the environment
Low concentrations: burning in the eyes, nose, and throat, redness in the face, sneezing, and coughing.
High concentrations: tightness in throat and chest - pulmonary edema. 1000 Parts Per Million (PPM) is rapidly fatal.
What precautions should be taken when using chlori
High concentrations should be used in a fume cupboard and goggles and gloves should be worn.