10 Questions
Manholes are constructed for inspection, cleaning ,mantanence of sewerage drainage system
Location of manholes
1- every bend
2- every junction
3- change of sewer diameter
4- change of gradient
Primary pollutant are emitted directly from either natural events or human activities
list of primary pollutant ; carbon mono oxide, carbondioxide, oxide of nitrogen, sulphur dioxide, particulate matter, suspended particulate matters
secondary pollutant form due to reaction of primary pollutant with each other or with air components
list of secondary pollutant :- Ozone o3, Sulphuric Acid H2SO4, Nitric Acid, Nitrogen dioxide, peroxyacil nitrate PAN
Concept:
1- BOD, COD, TOC and TOD all are associated with organic content of water.
2- COD is related to both organic and inorganic content of water
3- COD is also known as Di- chromate demand
COD is the amount of oxygen required by the biodegradable and non biodegradable organic matter in waste water
BOD is the biological oxygen demand required by the biodegradable organic matter in water water
TOD the through chemical reaction equations the exact amount of oxygen is calculated
Two pipe system is the most improved method of plumbing
Manning equation V = R^2/3. S^1/2/N, where N is roughness coefficient or manning coefficient
R hydraulic mean depth= A/P, where A cross section area, P is wetted perimeter
S slope of bed
value of N for cement is 0.011, wood planed = 0.015
concrete 0.012
Design period is defined as the time period for which the component remains functional
examples;- design period of some components
land acquisition less than or equal to 30years
Main sewer 30 years
Non conventional sewers 15 years
pumping mains 30 years
pumping station 30 years
pumping machinery 15 years
sewage treatment plant 15 years
effluent disposal 30 years
effluent utilisation 15 years
Saprophytic bacteria devour dead organic substances, which helps to break down waste into inorganic and organic products. These bacteria play critical role in the treatment of sewage, without this bacteria decomposition may not occur
Pathogenic bacteria is a form of parasitic bacteria manufacture toxins that cause disease in the host organism. source of this bacteria is the excreta of people suffer from dysentery, cholera , typhoid
types of sewer
circular brick sewer is used under culverts and at such places where big diameter is required for short lengths. this sections are plastered from inside. In olden days these were common, but now a days these are not used due to their much wear and difficult centring
semi elliptical sewer is suitable for sewers carrying large discharges throughout the year, These ara usually constructed with RCC
horse shoe sewer is constructed with RCC and is used in case of heavy discharges, the height is less than its width
egg shaped sewer is the sewer having depth one and half time their width. best for self cleansing
Self cleansing velocity = V = {(8kgd(G-1)/f}½,
where k is constant depend upon type of solid in the sewage
f = friction factor
d= diameter of particle
g= acceleration due to gravity
G= specific gravity of solid
Note;-
v= 0.45m/sec for 1mm Inorganic particles and for 5mm organic particles
v should be greater than 0.8 -0.9m/sec if sewer designed for design flow condition and velocity at design depth of flow
Types of traps
1- intercepting traps generally used between manhole outlet and public sewer, so that the sewer doesnot enter the house sewer line through manhole. water seal is about 100mm
2- p trap name after its shape ,water seal 25mm to 75mm
3- gully trap used in horizontal sewer line , placed in already built masonry chamber , made upof stone ware cover with cast iron grating, water seal 60mmto 70mm
4- floor trap generally used in kitchen bathroom sink, made up of pvc or cast iron , water seal depth 50mm