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1、8.3 IncineratorsMany types of devices are used for incineration.The most obvious are incinerators,which are furnaces especially designed and built to burn wastes.However,wastes,especially hazardous wastes,are also burned in boilers and industrial furnaces,mainly cement and aggregate kilns.Approximat
2、ely 50%of the incinerable hazardous wastes produced in the United States in 1993 were burnt in cement kilns.Irrespective of the type of furnace used,as soon as it burns wastes,it becomes subject to all appropriate laws and regulations that govern the handling,storage,and combustion of wastes.第1页/共10
3、页Incineration is one of the most difficult applications of air pollution control systems.The gas must be cooled and multiple pollutants must be controlled with very high efficiencies.Hydrogen chloride,hydrogen fluoride,and sulfuric acid vapors can be highly corrosive if handled improperly.Particulat
4、e matter generated in the incinerators is primarily in the submicron range.Pollutants having special toxicity problems,such as metal compounds and dioxin/furan compounds,generally enter the systems at very low concentrations and must be reduced to concentrations that challenge the limits of analytic
5、al techniques.The air pollution control system typically can consist of a heat recovery boiler,a quench,a particulate removal device,and an acid gas removal device.The devices are often mounted in series.For example,the off-gas treatment system for a typical high-performance rotary kiln incinerator
6、in hazardous waste duty can include(1)a boiler to partially cool the combustion gas and recover steam;(2)a dry scrubber,also called a spray dryer,to remove some acid gas and reduce downstream caustic requirements;(3)a quench to further cool the gases;(4)a reheater to prevent condensation in the fabr
7、ic filter;(4)a fabric filter;(5)a packed column for further acid gas removal;(6)a HydroSonics scrubber that includes a steam ejector to provide the motive force for the flue gases and to act as a backup air pollution control device in case of failure of an upstream component;and(7)a stack.As can be
8、seen,the air pollution control system represents a major fraction of the total system cost.第2页/共10页8.4 Solid Waste/LandfillsThe proper management of solid waste is now,more than ever,a matter of national and international concern.As a nation,we are generating more solid waste than ever before.At the
9、 same time,we are finding that there are limitations to traditional solid waste management practices.As the generation of solid waste continues to increase,the capacity to handle it is decreasing.Many landfills and incinerators have closed,and new disposal facilities are often difficult to cite.Even
10、 though municipal solid waste(MSW)constitutes only a portion of the solid waste streams,the rate of its generation is staggering.The U.S.Environmental Protection Agencys(EPA)most recent data show that in 1988,180 million tons,or 4.0 pounds per person per day of MSW,were generated in the U.S.EPA,1990
11、a.By the year 2000,generation of MSW is projected by the EPA to reach 216 million tons,or 4.4 pounds per person per day.Based on current trends and information,EPA anticipates that 20 to 28%of MSW will be recovered annually by 1995.Exceeding this projected range will require fundamental changes in g
12、overnment programs,technology,and corporate and consumer behavior.According to EPA data EPA,1990a,recovery of MSW materials for recycling and composting was 13%in 1988,combustion was 14%of total generation,and the remaining 73%of the MSW stream was taken to landfills.第3页/共10页8.5 Water and Wastewater
13、 PlanningWaterworks,water distribution systems,sewerage,and sewage treatment works are an integrated system.The primary purpose of this system is to protect the public health and to prevent nuisances.This is achieved as follows:Waterworks produce potable waters that are free of pathogens and poisons
14、.Water distribution systems prevent the posttreatment contamination of potable water while storing it and delivering it to users upon demand.Sewerage systems efficiently and safely collect contaminated used water,thereby preventing disease transmission and nuisance,and transmit it to sewage treatmen
15、t works without loss or contamination of the surrounding environment.Sewage treatment works remove contaminants from the used water prior to its return to its source,thereby preventing contamination of the source and nuisance.第4页/共10页8.6 Biological Wastewater Treatment ProcessesNational Pollutant Di
16、scharge Elimination System(NPDES)permits limit the final effluents total suspended solids(SS)and 5-day biochemical oxygen demand(BOD5).Other quality parameters and sampling requirements are included as needed.However,most biological processes produce effluents that contain only a few mg/L of soluble
17、 BOD5,or less,and the BOD5 of the final effluent is mostly biomass that has escaped capture by the final clarifier.Thus,the NPDES permits control final clarifier design and operation,not the biological process itself.Some biological processes,like completely mixed activated sludge,produce flocs that
18、 settle slowly,and this should be a consideration in their selection and operation.If effluents containing much less than 10 mg/L of SS or BOD5 are required,then additional effluent treatment like coagulation,settling,and filtration should be considered.The principal wastewater treatment scheme is t
19、he activated sludge process,which was developed by Ardern and Lockett in 1914.Its various modifications are capable of removing and oxidizing organic matter,of oxidizing ammonia to nitrate,of reducing nitrate to nitrogen gas,and of achieving high removals of phosphorus via incorporation into biomass
20、 as volutin crystals.第5页/共10页8.7 Physical Water and Wastewater Treatment ProcessesRegardless of tank configuration,mixing condition,or the number or volume of recycle flows,the average residence for water molecules in a tank is as follows,=V/Q (8.7)where=the hydraulic retention time(s)V=the active l
21、iquid volume in the tank(m3)Q=the volumetric flow rate through the tank not counting any recycle flows(m3/s)Note that Q does not include any recycle flows.The hydraulic retention time is also called the hydraulic detention time and,by chemical engineers,the space time.It is often abbreviated HRT.Mor
22、e importantly,the use of mixers generally results in very small Peclet numbers,and the reactors tend to approach completely mixed behavior,which is undesirable,because the efficiency is reduced.Thus,there is an inherent contradiction between high turbulence and ideal plug flow,both of which are want
23、ed in order to maximize tank efficiency.The usual solution to this problem is to construct the reactor as a series of completely mixed cells.This allows the use of any desired mixing power and preserves the reactor efficiency.The principal objects of mixing are(1)blending different liquid streams,(2
24、)suspending particles,and(3)mass transfer.The main mass transfer operations are treated in separate sections below.This section focuses on blending and particle suspension.第6页/共10页8.8 Chemical Water and Wastewater Treatment ProcessesSurface waters contain a variety of suspended,colloidal solids that
25、 have aesthetic,economic,or health impacts.Simple sedimentation and direct,unaided filtration are not practical in the case of clays and organic detritus,because the overflow and filtration rates required for their removal lead to facilities that are 100 to 200 times larger than those built today.Co
26、nsequently,all surface water treatment plants incorporate processes that destabilize and agglomerate colloids into larger,fastsettling particles.Sludge handling practices are also important.Water treatment sludges do not usually require processing prior to disposal.This situation arises because wate
27、r treatment sludges consist of relatively inert inorganic materials,and in the past(but no longer),plants were often permitted to dispose of their sludges by discharge to the nearest stream.Nowadays,the sludges are simply lagooned or placed in landfills.In contrast,sewage treatment sludges are putre
28、scible and require processing prior to disposal.This usually involves a dewatering step.The comparative ease and economy of dewatering iron sludges results in iron salts being the coagulant of choice in sewage treatment.Ferric iron also precipitates the sulfides found in sewage sludges,reducing their nuisance potential.第7页/共10页Problems1、朗读本章课文35遍。2、将本章英文全部翻译成汉语。3、用英文写一个900单词以内的本章梗概。4、通过阅读本章用英文谈一谈你对Environmental Engineering（环境工程学）的认识（包括口语和文字，文字字数应不少于500单词）。第8页/共10页THE END讲的不好，请大家多多提出批评！谢谢大家！第9页/共10页感谢您的观看。第10页/共10页