水处理专业英语阅读1waterpollutionandpollutants

1 Water Pollution and Pollutants
The relationship between polluted water and disease was firmly established with the cholera epidemic of 1854 in London, England. Protection of public health, the original purpose of pollution control, continues to be the primary objective in many areas. However, preservation of water resources, protection of fishing areas, and maintenance of recreational waters are additional concerns today. Water pollution problems intensified following World War II when dramatic increases in urban density and industrialization occurred. Concern over water pollution reached a peak in the mid-seventies.
Water pollution is an imprecise term that reveals nothing about either the type of polluting material or its source. The way we deal with the waste problem depends upon whether the contaminants are oxygen demanding, algae promoting, infectious, toxic, or simply unsightly. Pollution of our water resources can occur directly from sewer outfalls or industrial discharges (point sources) or indirectly from air pollution or agricultural or urban runoff (nonpoint sources).
Chemically pure water is a collection of H2O molecules—nothing else. Such a substance is not found in nature—not in wild streams or lakes, not in clouds or rain, not in falling snow, nor in the polar ice caps. Very pure water can be prepared in the laboratory but only with considerable difficulty. Water accepts and holds foreign matter.
Municipal wastewater, also called sewage, is a complex mixture containing water (usually over 99 percent) together with organic and inorganic contaminants, both suspended and dissolved. The concentration of these contaminants is normally very low and is expressed in mg/L, that is, milligrams of contaminant per liter of the mixture. This is a weight-to-volume ratio
used to indicate concentrations of constituents in water, wastewater, industrial wastes, and other dilute solutions.
Microorganisms.Wherever there is suitable food, sufficient moisture, and an appropriate temperature, microorganisms will thrive. Sewage provides an ideal environment for a vast array of microbes, primarily bacteria, plus some viruses and protozoa. Most of these microorganisms in wastewater are harmless and can be employed in biological processes to convert organic matter to stable end products. However, sewage may also contain pathogens from the excreta of people with infectious diseases that can be transmitted by contaminated water. Waterborne bacterial diseases such as cholera, typhoid, and tuberculosis, viral diseases such as infectious hepatitis, and the protozoan-caused dysentery, while seldom a problem now in developed countries, are still a threat where properly treated water is not available for public use. Tests for the few pathogens that might be present are difficult and time consuming, and standard practice is to test for other more plentiful organiama that are always present (in the billions) in the intestines of warm-blooded animals, including humans.
Solids. The total solids (organic plus inorganic) in wastewater are, by definition, the residues after the liquid portion has been evaporated and the remainder dried to a constant weight at 103℃. Differentiation between dissolved solids and undissolved, that is, suspended, solids are accomplished by evaporating filtered and unfiltered wastewater samples. The difference in weight between the two dried samples indicates the suspended solids content. To further categorize the residues, they are held at 550℃for 15 minutes. The ash remaining is considered to represent inorganic solids and the loss of volatile matter to be a measure of the organic content Suspended solids (SS) and volatile suspended solids (VSS) are the most useful. SS and BOD
(biochemical oxygen demand) are used as measures of wastewater strength and process performance. VSS can be an indicator of the organic content of raw wastes and can also provide a measure of the active microbial population in biological processes.
Inorganic constituents. The common inorganic constituents of wastewater include:
1. Chlorides and sulphates. Normally present in water and in wastes from humans.
2. Nitrogen and phosphorous . In their various forms (organic and inorganic) in wastes from humans, with additional phosphorous from detergents.
3. Carbonates and bicarbonates. Normally present in water and wastes as calcium and magnesium salts.
4. Toxic substances. Arsenic, cyanide, and heavy metals such as Cd, Cr, Cu, Hg, Ph, and Zn are toxic inorganics which may be found in industrial wastes.
In addition to these chemical constituents, the concentration of dissolved gases, especially oxygen, and the hydrogen ion concentration expressed as pH are other parameters of interest in wastewater.
Organic matter.Proteins and carbohydrate constitute 90 percent of the organic matter in domestic sewage. The sources of these biodegradable contaminants include excreta and urine from humans; food wastes from sinks; soil and dirt from bathing; washing, and laundering; plus various soaps, detergents, and other cleaning products.
Various parameters are used as a measure of the organic strength of wastewater. One method is based on the amount of organic carbon (total organic carbon, or TOC) present in the waste. TOC is determined by measuring the amount of CO2 produced when the organic carbon in the sample is oxidized by a strong oxidizer and comparing it with the amount in a standard of known
TOC.
Most of the other common methods are based on the amount of oxygen required to convert the oxidizable material to stable end products. Since the oxygen used is proportional to the oxidizable material present, it serves as a relative measure of wastewater strength. The two methods used most frequently to determine the oxygen requirements of wastewater are the COD and BOD tests. The COD. or chemical oxygen demand, of the wastewater is the measured amount of oxygen needed to chemically oxidize the organics present; the BOD. or biochemical oxygen demand, is the measured amount of oxygen required by acclimated microorganisms to biologically degrade the organic matter in the wastewater.
BOD is the most important parameter in water pollution control. It is used as a measure of organic pollution, as a basis for estimating the oxygen needed for biological processes, and as an indicator of process performance.
The amount of organic matter in water or wastewater can be measured directly (as TOC, for example), hut this doesn’ t tell us whether the organic s are biodegradable or not. To measure the amount of biodegradable organics, we use an indirect method in which we measure the amount of oxygen used by a growing microbial population to convert (oxidize) organic matter to CO2 and H2O in a closed system. The oxygen consumed. or biochemical oxygen demand (BOD). is proportional to the organic matter converted, and therefore BOD is a relative measure of the biologically degradable organic matter present in the system. Because biological oxidation continues indefinitely, the test for ultimate BOD has been arbitrarily limited to 20 days, when perhaps 95 percent or more of the oxygen requirement has been met. Even this period, however,
is too long to make measurement of BOD useful, so a five-day test, BOD5, carried out at 20℃, has become standard. The rate of the BOD reaction depends on the type of waste present and the temperature and is assumed to vary directly with the amount of organic matter (organic carbon) present.
单词表
cholera n.霍乱evaporate v 蒸发
epidemic n.流行，传染differentiation n.区分
recreational a 娱乐性的filter v 过滤
imprecise a.不精确的evaporate v.挥发
alga, algae n. 海藻，藻类20℃20 degree centigrade contaminant n 污染物categorize vt 分类
contaminate vt.污染residue n 残渣
infectious a.传染性的volatile a 挥发性的
unsightly a. 难看的content n 含量
sewer n.下水道chloride n.氯化物
outfall n. 排放口sulphate n.硫化物
runoff n.排水，流放口nitrogen n 氮
laboratory n 实验室phosphorous n 磷
sewage n.污水，废水detergent n.清洁剂
organic a 有机的carbonate n.碳酸盐
inorganic a 无机的bicarbonate n.重碳酸盐
suspend v.悬浮calcium n.钙盐
concentration n 浓度magnesium n.镁盐
milligram n.毫克arsenic n.砷
constituent n.组成物cyanide n.氰
dilute a 稀释的cadmium n 镉
suitable a. 适当的chrome n 铬
moisture n.潮湿水分copper n 铜
microbe n.微生物mercury n 汞
virus n.病毒lead n 铅
protozoa n.原生动物zinc n 锌microorganism n 微生物hydrogen ion n 氢离子pathogen n.病菌病原体parameter n.参数
excreta n.排泄物粪便carbohydrate n.碳水化合物waterborne a.水传播的biodegradable a 可生物降解的typhoid n.伤寒sink n.下沉污水坑tuberculosis n.肺结核launder v 洗涤，洗熨viral a.滤过型病毒的oxygen n 氧气hepatitis n.肝炎oxidize v 氧化dysentery n.痢疾acclimate v. 适应环境organism n 有机体生物体微生物degrade v 降解intestine a.内部的. n.肠ultimate a 最终的根本的definition n.定义arbitrarily a.专横的residule n.剩余残渣co2carbon dioxide。