226. Lagoons used for purification of polluted water
227. The principal gas evolved from sludge digestion tank is
228. There are thirteen metals which are treated as pollutants. Which of the following metals is not a pollutant ?
229. The function of skimming tank in sewage treatment is to remove __________ substances.
230. The weakest sound that can be heard by a person in a quiet environment is equivalent to __________ decibel.
231. Inorganic impurities causing water pollution is
232. The main type of sludge gas evolved during sewage treatment in Imhoff tank is
233. From pollution control point of view, the maximum permissible concentration of sulphur dioxide in atmospheric air is about __________ ppm.
234. The pH value of oxidised sewage is about
235. Smog is
236. __________ is the process of killing organism in water.
237. Reingleman chart No. 2 corresponds to __________ percent black smoke.
238. Which of the following is a manmade source of air pollution ?
239. Which is the most efficient dust removal equipment for removal of sub-micronic dust particles from blast furnace gas ?
240. Insufficient washing of sand grains in a rapid sand filter causes
241. Which of the following sources is responsible for maximum air pollution ?
242. Which of the following is the most efficient for removal of very finely divided suspended solids and colloidal matter from the polluted water stream ?
243. In sewage treatment, its sedimentation is speeded up by commonly adding
244. Noise level in a quiet private business office is about __________ decibels.
245. 'Safe limit' called Threshold Limit Value (TLV) of carbon monoxide in atmospheric air is < 50 ppm. The main source of carbon monoxide pollutant in air is the
246. Inhalation of silica dust by human being causes
247. Which of the following air pollutants is not toxic to vegetation i.e., doesn't cause vegetation damage ?
248. A masonry structure built below ground level, where biochemical reaction takes place due to anaerobic bacteria is called
249. A considerable part of the harmful ultraviolet radiation of the sum does not reach the earth surface, because of the fact that, there is a layer of __________ high above earth's atmosphere, which absorbs it.
250. White smoke coming out of the chimney of a furnace indicates the use of