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
The quantity of sewage produced depends upon the quantity of water use. Generally, Average daily flow = (70 – 80) % average water consumption i.e. Average Daily Flow (ADF) of Sewage = 75% & Average Daily Demand (ADD) of water consumption = 0.75 ADD
The laying of sewer pipe consist of the following steps: 1. Locate the positions of the manhole on the ground along the longitudinal section of the sewer line. The laying of sewage pipe consist of the following steps. Locate the positions of the manhole on the ground along the longitudinal section of the sewer line.
The sewers after being laid and jointed are tested for watertight joints and also for correct straight alignment as described below 1. Test for Leakage 2. Test for Straightness of Alignment and Obstruction
Types of sewer like Asbestos Cement (AC) Sewers are manufactured from a mixture of cement and asbestos fiber. Asbestos Cement (AC) Sewers are suitable for carrying domestic sanitary sewage. Asbestos cement sewer is best as vertical pipe for carrying sullage from upper floors of multistory buildings (in two pipe system of plumbing).