Unit 12

2014-10-12
• In this device, long pipes rotate slowly over a bed of stones, disturbuting the polluted water in continuous sprays. As the water trickles over and around the stones, it offers its nutrients in the presence of air to an abundance of rather unappetizing forms of life. • An alternative technique is the activated sludge process . • unappetizing • alternative • activated sludge 引不起食欲的 二者选其一的 活性污泥
• The next stage is a series of settling chambers designed to remove first the heavy grit, such as sand that rainwater brings in from road surfaces, and then, move slowly, any other suspended solidsincluding organic nutrients that can settle out in an hour or so. Up to this point the entire process, which is called primary treatment, has been relatively inexpensive but has not accomplished much. • settling chamber 沉降室 • grit n. 粗砂 • up to 直到
2014-10-12
THAபைடு நூலகம்K YOU
Unit 12： Water Purification
第二部分
Primary Treatment
• When the sewage reaches the treatment plant, it first passes though a serise of screens that remove lager obiects such as rats or grapefruits, and then through a grinding mechanism that reduces any remaining obiects to a size small enough to be handled effectively during the remaining treatment period. • screen n. 格栅 • grapefruit n. 朱栾，葡萄柚（一种植物） • grinding mechanism 磨碎装置
2014-10-12
• Here the sewage, after primary treatment, is pumped into an aeration tank, where it is mixed for several hours with air and hacteria-laden sludge.The biological action is similar to that which occurs in the trickling filter. The sludge bacteria metabolize the organic nutrients; the protozoa, as secondary consumers, feed on the bacreria.
2014-10-12
• The effluent from the biological action is still laden with bacteria and is not fit for discharge into open waters,let along for drinking.Since the microorgan-isms have done their work,they may now be killed.The final step is therefore a disinfection process,usually chlorination.Chlorine gas,injected into the effluent 15 to 30 minutes before its final discharge,can kill more than 99 percent of the harmful bacteria. • open water 地表水 • disinfection 消毒杀菌 let along 更不要说 chlorination 加氯消毒
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Secondary Treatment
• The next series of steps is designed to reduce greatly the dissolved or finely suspended organic matter by some form of accelerated biological action. What is needed for such decomposition is oxygen and organisms and an environment in which both have ready access to the nutrients.One device for accomplishing this objective is the trickling filter. • decomposition • trickling filter 物质腐烂，分解 滴滤池
• aeration tank • metabolize • protozoa
2014-10-12
曝气池 分解，代谢，新陈代谢 原生动物
• The treated waters then flow to a sendimentation tank, where the bacteria-laden solids settle out and are returned to the aerator.Some of the sludge must be removed to maintain steady-state conditions. The activated sludge process requires less land space than the trickling filters, and, since it exposes less area to the atmosphere, it dose not stink so much. • sendimentation tank • steady-state 稳态 沉淀池