Primary Treatment of Wastewater is a plain sedimentation process to remove suspended organic solids from the sewage. Chemical are sometimes used to remove finely divided and colloidal solids.
The secondary wastewater treatment is required to remove the soluble and colloidal organic matters which remain after primary treatment. As it is mostly biological process also called biological treatment.
Trickling Filter also known as percolating or sprinkling filter is like a well having depth up to about 2m and filled with some granular media. The sewage is sprinkled over the media which percolates through filter media and is collected through the under-drainage system.
Activated sludge may be define as the sludge which settled down after the sewage has been agitated freely in the presence of abundant atmospheric oxygen. Activated sludge contains a large number of aerobic bacteria and other organism and acts as a fertilizing constituent (agent)
Generally there are two types for stormwater runoff 1. Hydrograph method It is used for longer water sheds generally greater than 3km2. 2. Rational method Rational method is very handy method for the calculation of storm water in urban areas.
The process of absorbing oxygen from air is known as aeration. High amount of O2 is provided in the aeration tank because of high BOD in sewage. Three methods for aeration in activated sludge process Diffused Air Aeration, Mechanical aeration & Combine aerator
A rail is a steel bar extending horizontally between supports which is used as a track for rail road. types Double & Bull Headed & Flat Footed Rails
The separation or cutting of rail due to friction and abnormal heavy load is called wear. There are three types of wears of rail, Wear of rails at the Top, Wear of rails at the end and Wear at the side of head of rails.
The rim or flanges of the wheels are never made flat but they are in the shape of a cone with a slope of about 1 to 20. This is known as coning of wheels. The coning of wheels is manly done to maintain the vehicle in the central position with respect to the track.
The following methods are adopted for reducing wear of rails. Use of Special Alloy Steel, Good Maintenance of Track, Reduction of Expansion Gap. At places where, wear of rail is considerable, special alloy steel rails are used.