exam 3 cheat sheet solid waste engineering

8/10/2019 Exam 3 Cheat Sheet Solid Waste Engineering

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a. Determine the amount of oxygen that will be consumed if 70% of the dry organic

material is degraded on a daily basis.

b. Determine the mass of mater ial remaining after degradation (dry weightbasis) on a daily and annual basis.

c. Finished compost ready for use has a moisture content of about 35%. Determine the amount ofwater that must be removed fr/this process over all 2create a finished compost product on daily basis.



ANAEROBIC DIGESTION



UNDESIRABLE EFFECTS OF COMBUSTION**Waste Heat**Ash Power plants produce both bottom ash and fly ash. Bottom ash is recovered from the combustion chamber and consists of the inorganic material as well as some unburned organics, while fly ash is the particulates removed from the gaseous emis-

sions. The major problem with ash from MSW combustion is the presence of heavy metals. Some of the uses of ashInclude • Road base material, • Structural fill, • Gravel drainage ditches, • Capping strip mines • Mixing with cement to mak e building blocks. In addition, ash from MSW combustion contains metals that can be reclaimed, especially steel and aluminum.

Air PollutantsThe air pollutants of concern in municipal-waste incineration can be classified as gases or particulates.The sulfuric acid, in combination with the hydrochloric acid produced in the reaction of chlorine compounds and the nitric acid produced from nitrogen oxides, produces acid rain

The microorganisms responsible foranaerobic decomposition can be dividedinto two broad categories:1. Acid formers that ferment the complexorganic compounds to more simple o rganicforms, such as acetic and propionic acids.These hardy organisms can be either fa cul-tative or strict anaerobes.2. Methane formers that convert the organicacids to methane. These organisms arestrict anaerobes and have very slow growthrates—two characteristics that cause con-siderable problems in anaerobic processesin wastewater treatment and will similarlyplague anaerobic decomposition of refuse.

Mass Burn vs Refuse Derived Fuel (RDF)

Combustion systems are characterized as either mass burn units or refuse-derivedfuel (RDF) units. A mass burn unit has no pre-processing of the solid waste prior tobeing fed into the combustion unit. The solid waste is loaded into a feed chute,which leads to the grates: the solid waste in the chute provides an air lock, whichallows the amount of combustion air to be controlled. From the chute, the solidwaste moves directly onto the combustion grate.16In an RDF system, the solid waste is processed prior to combustion toremove noncombustible items and to reduce the size of the combustible fraction,thus producing a more uniform fuel at a higher heat value. The RDF is fedthrough a rotary feeder and injected into the combustion unit above the grate.Some combustion takes place above the grate with the remaining combustionoccurring on the grate. This is referred to as semi-suspension firing . If no grateexists and all combustion occurs in the air, this would be called suspensionfiring . Suspension firing is common when burning pulverized coal but is notgenerally applicable to RDF.The advantage of an RDF plant is that the heat value of the fuel is more uniform,and thus, the amount of excess air required for combustion is reduced.The amount of combustion air used is important, because if there is insufficientoxygen in the combustion chamber, a reducing atmosphere is created, which

leads to corrosion problems. For RDF systems, the excess air (abovestoichiometric requirements) is about 50%, while in mass burn plants(because of the large variation in fuel value between items) about100% excess air is needed. For the same amount of fuel, a mass burnplant requires more air and larger airpollution control devices. Inaddition, by pre-processing the solid waste, some of the potentialproblem items—such as batteries that contain mercury—can beremoved. While there appear to be several theoretical advantages ofRDF over mass burn plants, they have had their share of operatingproblems. Processing solid waste is not easy, and RDF plants haveencountered corrosion and erosion problems. But with RDF, the totalamount of combustion air needed is sharply reduced, and the cost ofemission controls (which could be as much as 100% of the operatingcost of the combustion process) is considerably reduced. Whetherthere is an advantage to incurring the additional cost related to theproduction of RDF over mass burn is still unclear.What is clear is that, if the RDF is produced from mixed paper that hasbeensorted as part of the recycling effort, the fuel is a valuable resource. The character-istics of shredded mixed paper as a fuel are shown in Table 7-9. The data in thistable are the average values obtained from 12 different communities



1. A combined organic garbage and sewage sludge mixture from Cape Cordial, FL has amoisture content of 50% by weight. This mixture will be composted. The chemical formula ofthe dry weight portion of the mixture is C40H90O30N. Cape Cordial has a pop of 100,000that generates 2 Kg of combined mixture/person per day. Remember that aerobic degrada-tion on a dry weight basis follows the formula:

CaH bOc Nd + ((4a+b-2C-3d)/4) O2 = aC0 2 + ((b-3d)/2) H 2 0 + dN H 3

Part c)



a. (6) Determine the moisturecontent of the collected wastetipped at the landfill.

EXAM 1 Stuff

b. (10) Currently, the waste is simply placed in the landfill and buried without further compact-ing. If the waste were compacted in place in the landfill to a density of 1200 Ib/yd3, how muchlandfill volume would be saved per year?

3. An abandoned landfill in Mississippi has a bottom liner composed of 2.6m of clay. You arewor r ied that leachate will contaminate the groundwater table. Regulations prohibit leachatedischarge at greater than a rate of 40 L/25,000 m2/day (10 gal/acre/day in US units). Overtime, leachate has accumulated to a depth of 0.8 m above the clay liner .

a) Determine the hydraulic conductivity the clay liner must possess to limit the leakage rateof leachate to the legal standard.

Assume the value of (alpha) is 0. 3.

1. Florida generates 10 tons of Municipal Solid Waste (MSW) per collection day. MSW is

collected 4 days per week, 52 weeks per year, in compaction trucks. The collected MSW

tipped from the trucks at the landfill has a compacted composite density of 500 Ib/yd 3average values for the waste at the landfill tipping site are shown in the table below:

c. Because remaining LF space is limited, the City decides to implement a new2pronged approach 2 manage their waste: incineration in waste-to-energy plant andvoluntary curbside recycling. The projected recycling goals, expressed as percent-ages of the original waste component to be recycled are shown in the table below.



b) If the clay liner has an area of 10 hectares (1 hectare = 10^4m) and the actual value of K =5X10^-6 cm/sec, how much leachate leak from the entire landfill/yr into groundwater?Q=KA*dH/dL

c) Two employees of a local Mississippi waste hauling firm (Sopranos R Us, Inc.) are caught

illegally pumping liquid hazardous waste into the abandoned landfill. In a worse-case sce-nario (the liquid haz. waste is pumped directly into the leachate collecting above the liner).how quickly will the hazardous material reach the ground water? Use the K value of part (b).

exam 3 cheat sheet solid waste engineering

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