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What are the various constituents of dom...

What are the various constituents of domestic sewage ? Discuss the effects of sewage discharge on a river. 

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Domestic sewage contains four kind of impurities :
(i) Suspended solids : They are soil particles such as sand and silt.
(ii) Colloidal particles : They are inorganic and organic materials such as faecal matter, bacteria, paper and cloth.
(iii) Dissolved solids : They are nitrates, phosphates, ammonia, sodium, calcium and other nutrients.
(iv) Pathogens: Domestic sewage has pathogens of various diseases such as typhoid, cholera, dysentery, diarrhoea, etc. Effect of sewage discharge on river are :
(a) Eutrophication. (b) Growth of pathogenic bacteria. (c) Ageing of river where silt and decaying
matters start accumulating and filling river. (d) Increase in BOD. (e) Destruction of flora and fauna of that river.
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Knowledge Check

  • What happens during the first stage of sewage treatment plant?

    A
    Aeration is done
    B
    Bacterial activity is allowed
    C
    Physical particles are removed
    D
    All the above

  • Statement .A.: Sewage water contains large amount of organic matter and microbes. Statement .B.: Sewage water is treated through heterotrophic bacteria and the effluents is released to rivers. (A) Statement A and statement B are true and statement B is the correct explanation of A (B) Statement A is false and B is true. (C) Statement A is true and B is false. (D) Both statement A and B are false.

    A
    Statement A and statement B are true and statement B is the correct explanation of A
    B
    Statement A is false and B is true.
    C
    Statement A is true and B is false.
    D
    Both statement A and B are false.

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    Thin films, including soap bubbles and oil slicks, show patterns of alternating dark and bright regions resulting from interference among the reflected light waves. If two waves are in phase their crest and troughs will coincide. The interference will be constructive and the aplitude of the resultant wave will be greater than the amplitude of either constituent wave. if the two waves are out of phase, the crests of one wave will coincide with the troughs of the other wave. The interference will be destructive and the amplitude of the resultant wave will be less than that of either constituent wave. at the interface between two transparent media some light is reflected and some light is refracted. * When incident light, reaches the surface at point a, some of the light is reflected as ray R_(a) and and some is refracted following the path ab to the back of the film. *At point b some of the light is refracted out of the film and part is reflected back refracted out of the fiml as ray R_(c) . R_(a) and R_(c) are parallel. However, R_(c) has travelled the extra distance within the film of abc. if the angle of incidence is small then abc is approximately twice the film's thickness. if R_(a) and R_(c) are in phase they will undergo constructive interference and the region ac will be bright if R_(a) and R_(c) are out of phase, they will undergo destructive interference. * Refraction at an interface never changes the phase of the wave. * For reflection at the interface between two media 1 and 2, if n_(1)ltn_(2) the reflected wave will change phase by pi . if n_(1)gtn_(2) the reflected wave will not undergo a phase change. for reference n_(air)=1.00 * if the waves are in phase after refection at all interfaces, then the effects of path length in the film are Constructive interference occur when (n= refractive index) 2t=mlamda//n" "m=0,1,2,3... .. Destructive interference occurs when 2t=(m+1//2)lamda//n" "m=0,1,2,3... Q. The average human eye sees colors with wavelengths between 430 nm to 680 nm. For what visible wavelength will a 350 nm thick n=1.35 soap film produce maximum destructive interference?

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