environment Flashcards

Question

secondary air pollutants

Answer 1

- Sulphuric acid - Ozone - Formaldehydes - Peroxy-acyl-nitrate (PAN)

Answer 2

- sometimes called bell and spigot joint - are made in such a way that one of their end is enlarged, whereas the other end is normal. The enlarged end is called “socket” or “bell”, while the normal end is called “spigot”. - A few strands of jute are wrapped around the spigot before inserting it into the socket (or bell) and then, more jute is packed into the joint. The remaining space between the socket and the spigot is finally filled with molten lead - This type of joint is some what flexible and allows the pipes to be laid on flat curves without the use of any other special material. - skilled labour is required for this type of joint.

Answer 3

Imhoff tank is an improvement over septic tank, incoming sewage is not allowed to get mixed with the sludge produced and outgoing effluent is not allowed to carry large amount of organic load - detention period is less - combines the advantage of of both the septic as well as well sedimentation tank - economical to operate - dont require skilled attention - 60-65% removal of solid - 30-40% removal of BOD - no problem of sludge disposal as in case of sedimentation tank - depth is more , which makes the construction costlier - unsuitable when sewage is highly acidic - tendency to foam or boil

Answer 4

fly nuisance- flies can chock the filter, this can be avoided by DDT spray Odour Nuisance: it happen in fixed nozzels, H2S and other gases, remedy- chlorinate the water Ponding Trouble: due to heavy growth of algae and fungi , remedy - chlorine or CuSO4

Answer 5

- detention time = 24 - 48 hrs - A minimum depth of sedimentation should be 25 to 30 cm. - accumulation of sludge = 30 L/cap / year - 30 cm freeboard - 1.5 m height(assumption)

Answer 6

- to remove inorganic particles of .15-.20 mm or more - these particles could clog the channel and damage pumps - flow velocity should not be low to settle organic material - detention time 30 to 60 sec - proportional weir or sutro weir is provided at lower end of rectangular grit chamber

Answer 7

- This process uses small, plastic elements (on the order of 7 to 22 mm effective diameter) to support the growth of bio-film in the rector. - The suspended growth portion of the hybrid is designed as a complete mix reactor. - The process does not use a return sludge flow. - The media (typically polyethyle) is formed in a geometry to provide a high surface area (250-515 m2/m3). - It has a density near to that of water ( 0.96 g/cm3). - The reactors are normally filled from one-third to two-thirds of their empty volume with media. - Because of their shape, less than 15 percent of the water is displaced. - A screen across the outlet is used to prevent the media from leaving the aeration tank. - Aeration is typically by coarse bubble diffusers.

Answer 8

The LN concept: The parameter LN is a statistical measure indicating how frequently a particular sound level is exceeded. The value of LN will represent the sound pressure level that will exceed for N% of the gauging time. Say for example, the given 70 dB value of L60 will mean that the sound level will exceed 70 dB for 60% of the measuring time.

Answer 9

In sewage farming, when sewage is applied continuously on the agricultural land, the voids of soil go on clogging gradually. A time comes, when the soil voids get completely clogged, air circulation through the soil is totally stopped and sediments get deposited on the surface. An anaerobic condition is developed. At this stage, the soil is unable to absorb further sewage load. An insanitary condition is developed by liberating bad smell. Such condition is termed as sewage sickness. The following measures may be taken to prevent sewage sickness : (i) The primary treatment should be given to sewage to eliminate the suspended solids. (ii) The intermittent supply of sewage should be adopted considering the nature of soil. (iii) Crop rotation system should be followed so that the different crops may consume different fertilizing elements. (iv) The sub-soil drainage system should be provided to drain out the subsoil effluent. (v) Deep ploughing by tractor should be adopted to increase the soaking capacity of soil. (vi) Time to time, a thin layer of surface soil should be removed by scrapping.

Answer 10

[L/(Dc.f)]^(f-1) = f*[1- (f-1)*(Do/L)] can find Dc or L from that Dc =L *[10^(-kd.Tc) ] , can find Tc from here

Answer 11

Sludge Digestion: The sludge is withdrawn from sedimentation basins contains a lots of putricible organic matter that if disposed of without treatment may cause evolution of foul gases and hazardous to environment. This sludge is thus stabilized by decomposing the organic matter under controlled anaerobic conditions. This process is called sludge digestion. (ii) Various stages of sludge digestion are: (a) Acid fermentation: This is the first stage of sludge digestion in which sludge is to be acted upon by acid formers (anaerobic & facultative bacteria). These organisms solublize organic solids through hydrolysis is to form volatile acids and organic alcohols along with evolution of gases like CO2 , CH4 or SO2 etc. (b) Acid-regression stage: In this intermediate stage, the volatile organic acids and nitrogenous compounds of previous stage are converted to acid carbonates and ammonia compounds with help of bacteria. Evolution of H2S & CO2 is there but not so significant. (c) Alkaline Fermentation stage: In this final stage, more resistant materials like proteins are attacked and broken up by bacteria called methane formers. Ammonia, organic acids and gases are by-products. The liquid separates from solids and digested sludge is produced. In first two stages pH is below 7 and medium is acidic however the medium changes to alkaline in final stage.