Questions and Answers of Retail Management

If your community is engaged in a recycling or waste reduction program, is the program voluntary or mandatory? How is the public involved—for example, are educational programs available? Which
In your home, which waste materials do you now separate? What other components could potentially be separated for eventual recycling or reuse?
How does resource recovery affect the overall cost of solid waste management? Be specific.Consider storage and collection issues, and landfill lifetime.
At your university or place of employment, what efforts have been undertaken to reduce the volume of solid waste? Describe any resource recovery or waste reduction programs in place.
The number of MRFs in the United States has increased dramatically over the past two decades. Explain the reasons for this increase based on factors such as economics, NIMBY, and environmental
Where in the MRF is human labor essential (i.e., a machine cannot adequately perform the job)?
What factors influence separation efficiency of a trommel screen?
What is the most critical parameter for efficient MSW separation by a trommel screen?
To avoid carryover of glass fines in an air classifier, what device or unit operation may wastes be first passed through?
What are the advantages in using a shredder for MSW processing in a MRF? What are the disadvantages?
Plastic wastes can be sorted optically or mechanically using “color screening” (true/false).Explain.
What is the ideal trommel rotation speed? Consider cascading, cataracting, and centrifuging of feed.
List and discuss some of the major safety hazards associated with shredding MSW.
All other factors being equal, are there any practical advantages to horizontal hammermills over vertical models? Consider efficiency of shredding, energy requirements, noise generation, and jamming
Using mechanical equipment for separation of mixed MSW, it is not possible to achieve 100% separation efficiency. Explain and provide an example.
During air classification, recovery of organics is complicated by what factors?
What factors influence the effectiveness of magnetic separation?
Calculate the waste thickness for a conveyor belt measuring 1.0 m wide with an average belt speed of 20 m/min. The waste loading rate is 25.5 MT per hour and the average density of the waste on the
A trommel screen measuring 9 m long and 3 m diameter is rotating at 2.5 rpm. The feed rate is 12 MT of raw MSW per hour. Calculate the critical speed. At the above speed, would the waste input be
If the trommel screen in Question 15 were to be adjusted to a steeper angle, how would separation efficiency be affected?
A magnetic separator is used at a MRF for ferrous recovery from commingled MSW. The feed rate to the separator is 1255 kg/h. The feed contains 4.2% ferrous. A total of 40 kg is collected in the
List the key components of the receiving area of an MSW processing facility.
In terms of separation of potentially recyclable components, what is a detrimental effect of shredding raw MSW to a fine particle size?
Contact your local waste management authority and determine the fraction of materials recovered for recycling collected via drop-off centers versus curbside pickup programs or MRFs.
Diagram a sequence of unit operations for a mechanized waste separation system. The input waste includes paper products, food waste, glass, plastic (PET, HDPE, and others), metals (ferrous and
Hazardous materials can be removed from the commingled wastes arriving at a MRF via:(a) magnetic separation, (b) manual hunt-and-pick, (c) air knife, (d) froth flotation.
Waste paper should be removed: (a) using an air classifier, (b) after ferrous removal, (c) after shredding the waste stream, (d) after trommel screening, (e) all of the above.
Suppose your community has decided to develop a waste management program with a goal of substantially greater waste recycling and materials recovery. The three major alternatives are source
It is undesirable to land-apply raw solid wastes to soil because undesirable reactions may occur, which could inhibit plant growth. Explain.
When a waste possessing a high C:N ratio (200:1) is land-applied: (a) microbial growth is relatively unchanged, (b) agricultural plants cannot compete with soil microbes for soil N, (c) N is
During the composting of MSW, a series of complex N transformations, including immobilization, nitrification, mineralization, and others occur. Explain how the C:N ratio declines during composting.
Microbial succession is important to bring the composting process to completion. Explain.
Explain how fire could be generated in an actively composting pile. How could such a scenario be prevented?
Compare the dynamics of microbial populations, oxygen levels, and temperature over time with the turned pile method of composting versus aerated static piles.
Discuss the pH requirements for optimizing composting. Why, from a biochemical or microbiological perspective, is this pH range most effective?
Composting of sewage sludge poses different management concerns compared with composting of MSW. Describe how the process may differ in terms of pathogen control, odor control, leachate control, and
Explain how anaerobic reactions may occur in a compost pile that contains 15%-20%oxygen in the interstitial spaces.
What is the relationship between pile temperature and microbial growth and activity?What is an ideal compost temperature range? Why is this range considered optimal?
The city of Pristine, IL, in developing their comprehensive waste management program, will establish a composting facility adjacent to the transfer station. What attributes should be considered when
The land area of the selected compost site is smaller than optimum. Based on practical issues, the following compost method should be used: (a) turned pile, (b) static pile with forced aeration, (c)
Is there a large-scale MSW composting program operating in your community? What are the feedstock materials? Where is the facility located; for example, adjacent to the transfer station or landfill?
List and discuss the possible uses for finished compost. What are the benefits of MSW composting in a community integrated waste management program? Given the time, space requirements, energy and
For decades, the market value of compost has been quite low. However, many communities continue to support yard waste composting programs. Explain why this is so.
Bench scale tests of aerobic composting were conducted on a feedstock with the starting empirical formula C28H46O22N. Pilot tests indicated that 1000 kg dry solids of the feedstock decreased to 245
At a waste-handling facility, a mixture of approximately 70 metric tons of food waste and yard waste is to be composted. The moisture content of the feedstock measures 5.5%. It has been previously
Determine the direction of groundwater flow and draw directional arrows.
Observe the data for groundwater quality in the site wells. Are there any constituents that are in excess of maximum contaminant levels (see Table 10.1, also the Code of Federal Regulations)?
Based on groundwater data, can you suggest the plots and waste types that may be contributing to the highest levels of contamination?
Do you observe any correlation between concentrations of any of the contaminants in groundwater?
In the groundwater, does the EC correlate with data for any elements or compounds?
As mentioned above, MSW2 contained relatively higher concentrations of metals compared with other feedstocks. Why were these metals detected only at very low levels in the soil or groundwater?
If we were to assume that the soils were similar from both sites, which compost feedstock results in the lowest NO3− concentrations in groundwater? The highest concentrations?
From the data, what is the general relationship between soil data for NO3− and groundwater data for NO3−? For NH4+? For metals?
This study was not a strictly scientific one; however, conduct an Analysis of Variance(ANOVA) on soil data and determine whether any of the treatments is significantly different in terms of NO3−
Conduct an ANOVA on groundwater data and determine whether any of the treatments is significantly different in terms of NO3− contamination of groundwater.
What corrective measures would you propose in order to control the excess leaching of nutrients from any of these sites?
MSW combustion involves physical and chemical transformations in which solid materials are converted into gases and some solid residues. What factors affect the types of gases produced? What factors
Compare the operation of a mass-burn incinerator with that of a RDF-burning facility, in terms of: fuel types; waste processing operations and equipment; convenience; resource recovery; energy
What are the functions of combustion chamber overfire and underfire air? How can they be adjusted to optimize incineration?
List the engineering and design factors that serve to enhance MSW combustion in an incinerator.
Define stoichiometric air and heat value.
Discuss the major gaseous emissions from a mass-burn incinerator and how each may be effectively removed from the flue.
SO2 production may be controlled during mass-burn incineration by addition of limestone directly to the combustion chamber. What are the advantages and disadvantages of this procedure over flue gas
An incinerator operating at a sufficiently high temperature and air inflow rate may still generate PICs. Explain how such a phenomenon may occur.
How do PCDDs and PCDFs form during mass-burn incineration (given that the firebox temperature is sufficiently high, for example, >1000°C, to destroy virtually all organic compounds)? In what
Describe particulate matter as relates to MSW combustion. What are its chemical and physical properties? What size range of particulates are the most potentially damaging when inhaled? How do certain
Generation of atmospheric pollutants is directly related to MSW charge rate and combustion chamber conditions, among other factors. Explain.
Explain how the following air pollutants can be removed from stack gases: SO2, particulates, mercury, and PCDDs.
Explain why the majority of MSW incinerators in the United States are mass-burn rather than RDF-fired.
How do electrostatic precipitators and cyclone separators differ in terms of efficiency of removal of particulate matter, SO2, and PCDDs.
Cd occurring in raw MSW can become significantly more soluble (and hence more leachable)following MSW combustion in a mass-burn incinerator. Explain.
Discuss the major concern(s) with RDF storage, both indoors and outdoors.
Which of the following is a significant concern when considering RDF production and utilization with coal: (a) dust production; (b) odor production; (c) separation of RDF and coal during handling;
For RDF to produce the same amount of heat as coal, more ash will probably be produced.Explain.
Compare and contrast RDF and raw MSW in terms of fuel properties. How do they differ in heat content, moisture content, density, and ash content?
How do RDF and coal differ regarding emissions of SO2, NOx, and HCl? How do they differ in ash composition?
A materials recovery facility is being installed in Pristine, IL (pop. 110,000). The MRF will be receiving mixed MSW. RDF will be produced. For maximum efficiency and ease of mixing with coal, what
How will the RDF be stored: (a) in the customers’ yard for easy utilization; (b) in a covered pole barn; (c) no need to store the RDF as it will be immediately sent to market; (d) in 50:50 mixtures
An incinerator burns 120 MT/h of MSW with the formula C285H455O235N4S. How much air is needed to completely combust this waste? A rate of 35% excess air is used during combustion.
Calculate the heating value for the waste discussed in Question 23.
List and discuss the passive approaches to landfill gas removal.
What is the minimum landfill CH4 concentration that poses an explosion hazard? At what concentration is methane of possible commercial (heating) value?
Under RCRA, new landfills cannot be located in seismic zones unless the operator can demonstrate that all containment structures (e.g., liners) are designed to resist the maximum horizontal shifting
Landfill bird hazards to airports can be limited to a certain extent by shredding and baling MSW prior to disposal. Explain.
Landfill sizing is affected by the desired landfill lifetime, population served, and shape and height of the landfill, among other factors. Explain.
What chemical changes occur during earliest anaerobic stage of decomposition in a sanitary landfill? Discuss in terms of pH, BOD, and transformations of metals.
Methanogenic microorganisms prefer what specific environmental conditions? How do they respond to pH?
What factors influence methane gas migration below the land surface? Consider soil texture, soil temperature, soil moisture, and barometric pressure.
What waste types are restricted from sanitary landfills under current federal regulations?Be specific.
What is the significance of saturated hydraulic conductivity (Ks) in assessing soil for landfill liners and caps, and as landfill foundation? How is Ks influenced by soil texture and engineering
RCRA calls for stringent controls in MSWLF operation for air quality, explosive gases, stormwater runoff, wetlands protection, cover material, and vectors. Discuss the specific requirements for each.
Geomembrane installation practices may influence future losses of leachate. List and discuss the factors that must be considered for successful geomembrane installation.
Explain the various phases of MSW decomposition in a closed landfill cell. How do leachate quality and gas composition differ between each phase?
Under what conditions is passive landfill gas control acceptable? When is active gas control a requirement?
How does landfill gas differ from utility-grade natural gas in terms of chemical composition?How must landfill gas be processed to render it suitable for sale to an energy utility?
If stormwater enters a landfill unit and contacts waste, how does its regulatory designation change (i.e., according to RCRA)—is it considered nonhazardous, hazardous, special waste, or another
RCRA regulations require that bulk or noncontainerized liquid wastes are not to be placed in MSWLFs, with two exceptions. What are they?
Landfill leachates vary in terms of physical characteristics, inorganic and organic composition, microbial populations, and toxicity. How are the above variables affected by waste type and by age in
Subtitle D requires, at the time of landfill closure, the installation of a final cover (cap)system. What are the primary purposes of the cover? Consider erosion, subsidence, and limiting leachate
What are the subtitle D requirements for proper landfill cover design and construction?

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