Chemistry

ChemistryModule 3: Industry and the environmentTopic: WaterGroup Members: Le-Jay K. Robinson Ethan Gayle Yakeine Shaw Patrick Miller

Syllabus ObjectivesDescribe the importance of the water cycleDiscuss methods of water purification Discuss the importance of dissolved oxygen to aquatic lifeDiscuss the sources of water pollutionThe Water CycleThe Water CycleIs the cycle of processes by which water circulates between the earth's oceans, atmosphere, and land, involving precipitation as rain and snow, drainage in streams and rivers, and return to the atmosphere by evaporation and transpiration.

The Water Cycle

ProcessesEvaporation- the changing of a liquid into a gas, often under the influence of heat (as in the boiling of water)

Transpiration- process by which water that is absorbed by plants is evaporated into the atmosphere from the plant surface, such as leaf pores (stomata).

Condensation- is the change of water from its gaseous form (water vapor) into liquid water.

Precipitation- rain, snow, sleet or hail that falls to or condenses on the ground.

Infiltration- is the process by which water on the ground surface enters the soil.Importance of the Water CycleRegulates the temperature of the earth by absorbing and circulating heat.

Replaces water lost by lakes, rivers oceans which are habitats for many organisms.

Provides freshwater for drinking, agriculture, industry and domestic use.

Water PurificationWater Purificationis the process of removing undesirable chemicals, biological contaminants, suspended solids and gases from contaminatedwater. The goal is to producewaterfit for a specific purpose.

Methods include:, distillation, ion exchange, filtration, chemical treatment, UV radiation and desalinisation.Distillationthe action of purifying a liquid by a process of heating and cooling.

It removes a wide range of contaminants such as bacteria, sodium chloride, heavy metals and organic compounds.

Equipment is relatively inexpensive.

Process is slow and requires large amounts of energy.Distillation Setup

Ion ExchangeIn this process, water percolates through a column of spherical resin beads. The ions in the water are exchanged for the ions fixed to the beads.

Ion-exchange methods include: softening, deionization and electro-deionization. Softening Water softeningis the removal ofcalcium,magnesium, and certain other metalcationsinhard water.

As hard water percolates through the column, the calcium and magnesium ions are exchanged for the absorbed sodium ions on the resin beads. This can be represented by the following equation: Ca2+(aq) + 2Na-resin Ca-resin + 2Na+(aq)

The resins can be regenerated by washing with concentrated aqueous sodium chloride. This can be represented by the following equation:

Ca-resin + 2NaCl(aq) 2Na-resin +CaCl2(aq)Softening Process

DeionizationRemoves dissolved minerals from water. The ion-exchange resins contain absorbed acid or alkali. The acidic resins exchange hydrogen ions for cationic contaminants while the alkaline resin exchanges the hydroxyl ions for anionic contaminants in water. The resins are regenerated by washing with alkali or acid.

Electro-deionization Electro-deionizationis a water treatment method that utilizes electricity in ion exchange membranes and resins to deionize water and separate dissolved ions (impurities) from water.

Unlike softening and deionization, this method inhibits the growth of bacteria that can attach to the resins and remove most organic compounds and microbes.Filtration Filtrationis the mechanical or physical operation which is used for the separation of solids from fluids (liquids or gases) by interposing a medium through which only the fluid can pass.

Filtration techniques include: screen filters, sand filters, carbon filters and membrane filtration.

Screen FiltersAscreen filteris a type offilterusing a rigid or flexiblescreento separate fine particles out of water for irrigation or industrial applications.

The screen is made of metal, plastic or synthetic fiber mesh.Screen Filter

Sand FiltersSand filters are layers of sand or other suitable granular material used to reduce suspended solids from water.

As the water moves vertically through the sand, suspended solids are trapped in the sand.Sand Filter

Carbon FiltersCarbon filteringis a method offilteringthat uses a bed of activatedcarbon (charcoal)to remove contaminants and impurities (VOCs/Chlorine), using chemical absorption.

It also catalyses the conversion of chlorine to chlorides and hydrogen sulphide to sulphates which reduces undesirable odours and tastes in water.

Carbon Filter

Membrane FiltrationThemembraneseparation process is based on the presence of semi permeable membranes. The principle is quite simple: the membraneacts as a very specificfilterthat will let water flow through, while it catches suspended solids and other substances.

Membrane FiltrationReverse osmosis uses an external pressure to force water through a membrane that retains the solute on one side and allows the pure water to pass through the other side. The process forces water to a region of high solute concentration to a region of low solute concentration. Membrane Filtration

UV RadiationUV light is very effective at killing pathogens and oxidizing organic compounds in water. Radiation with a wavelength of 245nm has the greatest effect on bacteria however viruses are more resistant, and cysts and worms are unaffected.

UV Radiation Apparatus

DesalinisationDesalinisation is the process of removing salt or other minerals from saline water. The two main methods used are distillation and reverse osmosis.

In this process freshwater and concentrated brine is produced. Brine is water strongly impregnated with salt. Desalinisation Apparatus

Importance of Dissolved Oxygen to Aquatic Life BackgroundOxygen is needed by aquatic life to survive because it needed for them to respire. Dissolved oxygen in water is measured in pats per million (ppm) and range from 0-18. Most natural water require 5-ppm of dissolved oxygen to support a variety of aquatic life. If dissolved oxygen falls to 3-5ppm aquatic life forms become stressed. Anything below 2ppm results in death.Factors Affecting Dissolved Oxygen ConcentrationRespiration- increase in aerobic respiration decreases oxygen concentration dissolved in water. This caused by introduction of untreated sewage which increases microbial respiration.

Temperature- as temperature increases, the amount of oxygen dissolved in water decreases.

Eutrophication- Excess nutrients in water can stimulate algal growth on the surface of water. When these plants die, bacteria use dissolved oxygen in the water for decomposition.Sources of Water PollutionMunicipal WasteThis is sewage from homes and commercial establishments.

In developing countries, an estimated 90% of wastewater is discharged directly into rivers and streams without treatment. This causes the spread of diseases such as diarrhea, cholera and tuberculosis.

Phosphates from laundering water enhances algal bloom which also causes eutrophication.

Dumping of garbage such as plastic packaging materials and synthetic fibers can entangle, injure and kill aquatic animals.AgriculturalFertilizers, herbicides and pesticides used in agriculture can be washed into waterways by the action of rainfall or irrigation. The increase in nutrient content enhances algal growth which causes eutrophication.

Herbicides and pesticides which are washed into ground water sources can remain in the water for many years. Consumption of this water can cause varying illnesses such as diarrhea, vomiting, etc.IndustrialNuclear waste- nuclear power stations produce radioactive waste which pollutes water.

Oil spills- oil spills can degrade the quality of water and suffocate marine life.

Lead- this can enter the environment from smelting, car batteries and plumbing industries. If this enters the system of a living organism it can cause varying effects.Mercury- mercury can environment as waste from burning of coal and mining. If it accumulates in an organism, it can cause nervous system damage.

Mining- this is the extraction of naturally occurring minerals from the earth. In doing this toxic heavy metals and other compounds are released into the environment.