《专业英语》课件Unit_26.pptx
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1、Unit26Environmental EngineeringTextEnvironmental engineering is essential for development of facilities for protection of the environment and for the proper management of natural resources.The environmental engineer places special attention on the biological,chemical,and physical reactions in the ai
2、r,land,and water environments and on improved technology for integrated management systems,including reuse,recycling,and recovery measures.Environmental engineering began with societys need for safe drinking water and management of liquid and solid wastes.Urbanization and industrialization significa
3、ntly contributed to the formation of unsanitary conditions in many areas.The terms“public health”and“sanitary”were first applied to those engineers seeking solutions to the elimination of waterborne disease in the 1800s.More recently,abatement of air and land contamination became new challenges for
4、the environmental engineer.Today,management of toxic and hazardous wastes are additional focus areas.The principal environmental engineering specialties are well established:air quality control,water supply management,wastewater disposal,storm water management,solid waste management,and hazardous wa
5、ste management.Other specialties include industrial hygiene,noise control,oceanography,and radiology.TextAir quality controlAir quality control needs vary from correction of air pollution problems originating from relatively small areas,such as an industrial park impacted by one or more emission sou
6、rces,to those from large areas,such as an urban area impacted by a number of sources and a variety of contaminants.Air pollution is used to describe the presence in the atmosphere of one or more contaminants in quantities and/or characteristics that will,over a period of time be injurious to or unre
7、asonably interfere with public health and welfare or natural environmental processes.Contaminants are categorized as particulate matter and gases and their associated forms,including dust,smoke,fumes,mist,and vapor.The primary gaseous air contaminants are carbon monoxide,hydrocarbons,nitrogen oxides
8、,and sulfur oxides.Meteorological and topographical factors contribute to the creation and continuation of air pollution under specific site conditions1.Temperature inversions prevent upward diffusion,and very low wind speeds allow emissions to remain near their source.Some terrains cause emissions
9、to follow specific patterns from one area to another.TextGenerally,sources of air contaminants may be classified as stationary,mobile,or fugitive.Respectively,they are attributed to point sources,such as industrial stack emissions;transportation activities,such as automobile emissions;and uncontroll
10、ed(fugitive)sources,such as wind-blown dusts from stockpiles.The environmental engineer is instrumental in controlling particulate and gas sources of air contaminants.Source control is the first abatement method considered.For particulates,settling chambers,inertial separators,wet scrubbers,and fabr
11、ic filters are used.Gas controls include absorption,adsorption,condensation,flaring,and incineration.Other areas of practice address acid rain issues,fugitive emissions,odor control,indoor air quality,and noise abatement.Water supply managementHistorically,the environmental engineer has found ways a
12、nd means to provide ample quantities of quality drinking water for domestic use as well as quality water for commercial and industrial uses.Water supply issues include demand projections,quality requirements,surface water and groundwater source evaluations,groundwater production,surface water collec
13、tion,surface water treatment,saline water treatment,nonconventional water production,and treated water distribution2.TextThe typical surface water treatment plant uses chemicals to enhance removal of suspended solids and for disinfection.Physical treatment processes include simple settling and filtr
14、ation.In sequence,the traditional unit processes are rapid mix,coagulation,flocculation,sedimentation,filtration,and disinfection.Auxiliary systems are needed for chemical feed facilities and for sludge handling.More specialized processes include carbon adsorption,ion exchange,and softening.Treatmen
15、t of other sources generally requires site-specific determination of raw water quality.Often,the quantity of demand will influence the cost-effective selection of treatment processes.Groundwater supplies require well development and treatment,such as aeration,softening,and/or disinfection.Brackish a
16、nd saline waters also require site-specific determination of treatment processes3.Typical processes include membrane technology,such as reverse osmosis and electrodialysis.The water distribution system includes(small)service and distribution lines,(large)transmission mains,and storage facilities.Ele
17、vated storage tanks with gravity distribution and/or ground storage tanks with distribution pumping are designed to provide the quantity and pressure required to satisfy system demands.Generally,fire demands control design.Since the early 1900s,the American Water Works Association(AWWA)has been deve
18、loping standards for the drinking water industry.The standards also are designed to enhance water utility operations while addressing hundreds of products and procedures.TextWastewater DisposalWastewater is the combination of liquid and water-transported wastes from homes,commercial buildings,indust
19、rial facilities,and institutions,along with any groundwater infiltration and surface water and stormwater inflow that may enter the sewer system.At a minimum,treatment is required for suspended solids and for dissolved organics.Special processes may be necessary to achieve removal of specific pollut
20、ants,such as phosphorus from a municipal source or heavy metals from a plating facility.The minimum levels of treatment are established by regulation.For example,in the United States,85%removal of oxygen-demanding organics and suspended solids and disinfection is the minimum level of treatment for d
21、omestic wastewaters.Additional treatment,including nutrient removal,is dictated by receiving-stream assimilative capacity and downstream water uses.Physical processes are used to remove suspended solids.Screens remove debris and other large solids,and gravity or aerated grit chambers capture sandy m
22、atter,either of which may damage or interfere with subsequent pumping and treatment units4.Gravity sedimentation normally is used to remove finer(organic)suspended solids.For special applications,centrifugation,dissolved air flotation,and filtration are used to remove suspended solids.Dissolved orga
23、nics generally are treated with biological processes.The more common systems are aerobic(with oxygen)and include aerobic or facultative pond,trickling filter,and activated sludge processes.TextConcentrated wastes,such as primary sludges,or high-strength industrial wastewaters,such as meat processing
24、 or brewery wastes,are considered for anaerobic(without oxygen)treatment processes.Sludges,principally from biological processes,require special handling.The sequence of processes includes stabilization,conditioning,dewatering,drying,and residual disposal.Land application and landfilling are the mos
25、t practiced means of final disposal.Special concerns for land-applied and composted sludges arise due to the concentration of contaminants,such as heavy metals,and presence of pathogens in these sludges.Of the many other types of treatment process,increased attention is now given to natural systems,
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