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Activated Sludge Process is the biological method for treatment of wastewater. It was devised by Arden and Lockett in 1914. In this process a mixture of sewage and activated sludge is agitated and aerated in an Aeration Tank. Bacteria present in the activated sludge aerobically metabolize the organic matter present in the influent. The organic matter is oxidized to CO2, H2O, NH3 etc. and a portion of it is converted into new bacterial cells.

All rocks, when exposed for sufficient length of time to the atmosphere, undergo decay from disintegration and decomposition, together referred to as weathering. Disintegration is the break down into small particles by the action of mechanical agents of weathering such as rain, frost etc, decomposition is the breakdown of mineral particles into new compounds by the action of chemical agents such as acid in air and in rain and river water.

Rock support for tunnels and underground cavern design is a demanding and very complex task. In principle, the problem can be approached from two directions: The first way is to define the relationship between geo-mechanical properties of the rock mass and the support methods used. This is mostly based on the utilization of statistical and empirical data gathered in similar conditions. The second way is to estimate the deformation characteristics of the rock structure, and then the related effect on supporting structures.

Surface Rupture is the actual displacement and cracking of the ground surface along a fault trace. Surface rupture is confined to a narrow zone along an active fault. Rupture may happen rapidly during an earthquake or it may not occur at all. Displacement beneath a building that exceeds 1 or 2 inches can have a catastrophic effect. Some active faults undergo imperceptibly slow movement, termed fault creep.

Meridian Meridian is a reference direction with respect to which the direction of lines are mentioned. There are three types of meridian - True Meridian, Magnetic Meridian & Arbitrary Meridian 1 - True Meridian It is the reference direction of north pole of earth from a given station point. It is also called geographic meridian. 2 - Magnetic Meridian It is the direction of north pole indicated by magnetic needle. 3 - Arbitrary Meridian This is any assume direction to a well defined object. It may be useful for small areas. e.g A mosque is taken as reference and location of road will be mentioned with respect to this mosque. Direction of magnetic north with respect to true north is called magnetic direction. Bearings Bearing is the angle which a certain line make with a certain a certain meridian. Bearing with respect to true meridian is called true bearings while magnetic bearing is the angle which a line makes with respect to magnetic meridian. There are two ways to represent the bearings, Whole circle bearing (W.C.B) Reduced Bearing (R.B) 1) Whole Circle Bearing (W.C.B) It can be taken 0° to 360°. Quadrants are taken clock-wisely and angles are also determined in clockwise direction. 2) Reduced Bearing Reduced bearing or Quadrantal bearing is the angle which a line makes from North or South Pole whichever may be near. It is value is from 0° to 90°. Using the above figures you can easily convert the Whole Circle Bearing into Reduced Bearing. Some Examples are given are below. Whole Circle Bearing (W.C.B) Reduced Bearing (R.B) 135° S45E 37° N37E 65° N65E 125° S55E 215° S35W 300° N60W

Angle measurement For angle measurement with theodolite vertical hair is used. Basically there are two methods horizontal angle measurement, Repetition method (For single angle) Reiteration method (For more than one angle) 1 - By Repetition method Let suppose it is desire to measure the angle A from the following figure. We will use repetition method for this purpose. Procedure Setup the theodolite at station A. Bisect the point B with vertical hair of theodolite and move telescope in clockwise and direction to bisect at point C. Note this circle reading in the book and fix this circle reading, then again bisect the point B by keeping the circle reading fixed. Now, release the circle reading and rotate the telescope again in clockwise direction till it bisect again point C. Similarly get 3rd and 4th repetition and note the circle reading after 4th repetition in the book. Change the face of telescope and repeat the above steps, an example and method of booking observations have given below,   Inst. Station Angle Face Repetition Circle Reading (° ′ ″) Angle value(° ′ ″) Mean of faces (° ′ ″) A BAC L 1 25 20 00 25 20 10 25 20 9.5       4 101 20 40     R 1 25 20 03 25 20 09       4 101 20 36   2 - By Reiteration method This method is used if there are more than one angles to be measure from a certain station point. Consider the following fiqure, we will measure angles AOB and BOC using this method. Procedure Setup the theodolite at station O, bisect the point A with a certain circle reading with face left. Rotate the instrument in clockwise direction and bisect B, note the circle reading. Then rotate and the telescope till it bisect the point C, note this circle reading also. All these reading will book into face left position. Transit the telescope and rotate the instrument through 180°, this time bisect the point C firstly and then rotate telescope in anti clockwise direction towards B and then ultimately towards A. Put these readings in face right position. You can do more than one sets of measurements for the accurate results, i have done one set and booking method is as follows,   Inst. Station Stn. Sighted Face Circle reading(° ′ ″) Mean of faces(′ ″) Angle value(° ′ ″) O A L 10 20 05 20 06 AOB 37 10 05     R 190 20 07   B L 47 30 10 30 11     R 227 30 12 BOC 41 10 14   C L 88 40 20 40 25     R 268 40 30   One should start observation with some initial circle reading say 25°, if we start our observation with zero circle reading our calculations for computing mean will be little bit difficult.