Based on the cross-sectional shapes the sewers may be classified as: 1. Circular Sewers 2. Non-Circular Sewers. 1. Circular Sewers: Sewers of circular section are most commonly used. These are best suitable for diameters up to 1.5 m. The various advantages of circular sewers are as indicated below: (i) A circular section gives the least perimeter for a given area, [...]
The priliminary treatment of sewage involves the use of only physical unit operations such as screening, comminution, grit removal, skimming, floatation, etc. The physical unit operations involved in preliminary treatment of seawge are accomplished by employing various units or appurtenances which include screens, comminutors, grit chambers or detritus tanks, skimming tanks, floatation units, etc. 1. Screening—Screens: Screening is the first [...]
The various considerations involved in the design of screens and screen channels are as follows: 1. Velocity of Flow: The velocity of flow ahead of and through a screen varies materially and affects its operation. The lower the velocity of flow through the screen, the greater is the amount of screenings that would be removed from sewage. However, the lower [...]
The various considerations involved in the design of grit chambers are as follows: 1. Settling Velocity 2. Surface Overflow Rate (SOR) 3. Detention Period 4. Bottom Scour and Flow through Velocity 5. Velocity Control Devices 6. Number of Units 7. Dimensions of Each Unit 8. Loss of Head. 1. Settling Velocity: Grit chamber may be designed on a rational basis [...]
For determining storm water (or rain water) flow or runoff by rational formula three factors viz., catchment area or drainage area, runoff coefficient and intensity of rainfall are required to be determined. These factors may be determined as indicated below: Factor # 1. Catchment Area or Drainage Area: The catchment area or drainage area to be served by a sewer [...]
The following article will guide you about how to estimate the quantity of sewage. Estimation of Dry Weather Flow: The dry weather flow (D.W.F) includes: (i) Domestic or sanitary sewage which is the sewage or wastewater derived from residential buildings and from commercial, institutional and similar public buildings such as offices, schools, cinemas, hotels, stations, etc.; (ii) Industrial sewage which [...]
The following points highlight the four main factors affecting the quantity of dry weather flow through the sewers. The factors are: 1. Rate of Water Supply 2. Population Growth 3. Type of Area Served 4. Infiltration and Exfiltration. Factor # 1. Rate of Water Supply: It is evident that a considerable part of the water supplied to the public through [...]
The rate of domestic or sanitary sewage produced is generally expressed in litres per capita per day (lpcd). The rate of domestic or sanitary sewage produced may be assumed to be equal to about 70 to 80% of the rate of water supply. Thus knowing the per capita rate of domestic or sanitary sewage produced and multiplying it by the [...]
The sewers are generally designed as open channels except when it is specially required to design them as conduits carrying sewage under pressure as in the case of inverted siphons. Thus various empirical formulae which are used for the design of open channels are used for the design of sewers. The following empirical hydraulic formulae are commonly used for the [...]
In this article we will discuss about the velocity of flow in sewers. Minimum Velocity of Flow in Sewers - Self Cleansing Velocity: A sewer should be so designed that the solid matter present in the sewage is not deposited at the bottom of the sewer and thus clogging of the sewer is prevented. The deposition of the solid matter [...]