Biological oxygen demand

This gives an idea about the water purity and quality. It is a measure of the amount of oxygen needed by bacteria and other microorganisms to oxidize the organic material present in a water sample over a period of 5 days. The biological oxygen demand (BOD) of drinking water should be less than 1. Nitrates and phosphates in water contribute to BOD. These are plant nutrients and facilitate plant and algae growth in water. When these plants die, it becomes an organic waste which gets decomposed by bacteria resulting in a high BOD level. When water temperature is increased, rate of photosynthesis increases. This enhances plant and algae growth. On death, they are decomposed and BOD level gets increased. Biological oxygen demand (BOD) can be determined experimentally by a method known as Winkler’s method. The basic idea employed here is that in alkaline medium, dissolved oxygen(DO) oxidizes manganese-2+ ions to manganese-4+ ions and in acidic medium, DO oxidizes iodine ions to free iodine.

Magnetohydrodynamic power generation

The basic principle employed here is the Faraday’s law of electromagnetic induction which involves direct conversion of kinetic energy of a flowing fluid into electricity by passing the conventional multiple conversion process. In the design of the generator, a pipe whose diameter increases from beginning to end is taken. A gas is allowed to flow through this pipe at very high temperature from left to right. A field coil is used to generate a magnetic field in a direction perpendicular to the direction of the motion of the gas. This results in the development of EMF. Gas conductivity can be increased by the addition of small amount of potassium. A two-stage cyclone furnace is used as a combustor. The electrodes used here are made of tungsten cooled with iridium and are separated from one another by beryllia insulating material. The field coil is made of a superconducting material either niobium-zirconium or niobium-tin.

Renewable sources of energy

Photovoltaic cells are renewable sources of energy. Main principle involved here is ‘photovoltaic effect’ where a photovoltaic cell converts sunlight into electricity. Electron-hole pairs are created when light strikes the photovoltaic cell. Since no materials are being wasted, it is known as a renewable process. Solar cells are composed of various semiconducting materials. Silicon is the most popular candidate since it is the second most abundant element in the earth’s crust. The other advantages of silicon are silicon wafers are thin, non-toxic etc. A large area p-n junction diode can be used as a photovoltaic cell. When sunlight strikes a photovoltaic cell, photon knocks an electron from a silicon atom. Thus electron is emitted and a hole is created in silicon.

Synthesis of nanostructured materials

Nanotechnology and nanomaterials are now interesting subjects of mankind. Generally any material whose dimension ranges 0.1 to 100 nm is called as nanomaterials. Quantum dots are zero dimensional, multilayers (Quantum wire) are one dimensional, ultrafine grained over layers or buried layers (Quantum well) are two dimensional equiaxed nanometer sized grains are three dimensional nanomaterials. There exist two steps for the synthesis of nanostructured materials- top-down and bottom-up. Examples of top-down methods are mechanical alloying or milling, lithography and erosion. Examples for bottom-up methods are chemical coprecipitation, gas phase agglomeration, sol gel, reverse micelles, physical and chemical vapour deposition, sputtering and self assembly. 

Hydroelectric power plant

Hydroelectric power plant can be used for many purposes like electrical power generation, controlling of floods, storing of irrigation water and storing of drinking water. The main advantage of hydroelectric power plant compared to other power plants is that fuel is not required here. A hydroelectric power plant remains very neat and clean always. Operational and maintenance cost is very less. Rapid load variation possible here with a longer life span. Highly skilled engineers are not an essential requirement here. There are no standby losses in hydroelectric power plants. We can easily maintain constant speed and frequency. But construction cost is very high. It takes more time for installation. Long transmission lines are required and we have to depend on monsoon. It consumes large area. The main components of a hydroelectric plant are generator, switchgear, transmission lines, catchment area, reservoir, dam and head works, sluice gate or valve, penstock, inlet valve, turbine and tail race.