CHAPTER 15: Waste Disposal

Municipal: difficulty: variety of materials

Open dumps
 

Sanitary landfills: layer of dayly refuse covered by layer of earth once a day.

   Uses when full: any development that does not require digging deep: golf course, park, parking lot

    gases =  CO2, SO2 (oxygen)
                  CH4, SH2 (anaerobic)

leacheate problem use impermeable top
                                                          bottom

                              CO2
Incineration          toxic gases + elements
                              very high T^o incinerators - industry

•       waste incineration for electricity

                             w/ prior incineration:ok?
Ocean Dumping  without prior incineration?: unacceptable
                             dredge spoils = not so harmless

Volume Reduction              incineration
                                           compaction     hinders recovery
                                                                 slow decay

Non Toxic organic matter    - 1st swine food
                                               - home insink garbage disposal
 

•    Composting = for plant wastes and/or animal manure
   partial decomposition of organic matter
•      improves soil structure
•      adds nutrients                                                Practiced at individual  level

U.S.             Recycling              1) Glass: does not weather             (10%)
10%             saves energy          * Oregon pioneered "bottle bill"
25%             & resources           2) Paper (newspaper - computer) (25%)
                                                   3) Plastics          biodegradable
                                                                              problem with "blends"
                                                   4) Metals

  Requires Source separation : sorting different materials, cooperation of concerned citizens is needed.
 

Wastes exchanges:                          Ind. 1                                         Ind. 2
                                                           waste         ==>                         raw material
 

Liquid Waste Disposal                  Sewage
                                                       highly toxic industrial by products

Highly toxic:   acids, bases, organic solvents
                        used motor oil   recyclable!!
Possibilities

• "Dilute & disperse": oeans - lakes

    watch for concentration by organisms
•   "Concentrate & contain"

     use adequate containers & sites

Secure Landfills                    sealed drums
                                               plastic or compacted clay layer at the bottom and at the top

Fracture of clay                                        wells & pipes to check leachate
 or                                        leakage         pump out leachate before leaking
low perm through time                              measures to contain

Deep-Well Disposal
 Characteristics of the layer? A deep permeable unit to store the waste, isolated by two impermeable layers for a long distance
                                                around the disposal well
______________________________________________________________

                     core samples
Costly           geophysics
                      geology-structure help trap waste

        More limitations than Secure landfills          geology
                                                                              earthquake  risk

                   burn (CO2)
Other          neutralize
                   waste exchange

Sewage treatment
                                                          depletion of O₂
Organic matter in H2O                      eutrophication
                                                          disease causing organisms

Septic tank systems
Settling tank     =>              porous pipes                       => leaching absorption field
solids out                           liquid & dissolved                      oxygen & org. matter
                                                                                               soil filter
 
 

•   water table must be well below level of tank
•   soil allow flow to be purified
•   soil above: 60 cm                      soil below: 150 cm          Favorable

 15 m away from any water body                                         conditions
•   scattered  => do not saturate soil

Municipal treatment                         untreated < 5%
Primary Treatment: physical processing (solids, grease, scum) byproducts that have to be landfilled or composted
Secondary Treatment :  aereation and biological decomposition (bacteria & fungi)  breakdown Org. Matter
               Chlorination added.
More  than 50 % of the sewage in the US receives only  secondary treatment .
Tertiary:         N                           Activated charcoal           =>      drinking
                       PO₄                        Distillation                                water
                       chemicals               Chlorination
 
 

Radioactive Wastes (Mc Connell site, Chapter of Energy, Nuclear Energy)
 

•   There are over 100 operating nuclear reactors in the U.S.,  approximately a quarter of all nuclear power plants worldwide.

 
•   The benefits of nuclear energy are; no air pollution, no greenhous  effect, reduces dependence on foreign oil.

 
•    The potential problems are; U.S. reactors are reaching getting old and there is no currently available site for permanent nuclear waste disposal.

 
•   High-level nuclear waste must be stored safely for thousands of years.

 
•   A potential storage site for nuclear waste is being investigated at Yucca Mountain, Nevada.

 
•   The Yucca Mountain site is isolated, has a dry climate, in rocks with low porosity and permeability, and is located far above the groundwater table. However, the area around Yucca Mountain has experienced earthquakes and volcanism.

 
•   The nuclear waste repository will not open until at least 2010.

 

 
 
 

Radioactivity:
Some isotopes have the property to decay with time, releasing radiation -

Decay rate: over a fixed period of time, the amount of atoms of a given isotope that are going to decay is a fixed % of the original - the % is specific of each isotope

Half-Life: of an isotope is the length of time required for half   of the atoms of that isotope initially present in the system to decay

•   The half life is constant Independent from: P; To, Depth, physical state -

• Radioacive decay cannot be accelerated or slowed.
• Neither can it be  eliminated by Chem. treatment.

•     Dangerous: Half-lifes: years - to 100's years
•     Poisonous: Pu239
•     Concentrated in organs = I¹³¹, Fe⁵⁹, Sr⁹⁰

• Low Level Rad. Wastes                              High Level Rad Wastes

Disposal of high level R. wastes
1) Space:   launch? Not all launchings are successful ;    expensive

2) Ice Sheet: Antarctica - Wastes melt ice
     movement of glaciers - Climate? if global warming melts ice sheet, the wastes are going to be exposed to the environment

3) Subduction zones: process too slow,  risk of containers leaks
      uncertainty: cannisters with the HLRW materials can be crushed by the pressures of the process and resurface

4) Deep Seabed: stable - far from active margins & Mn. Japan's choice.
    thick clay beds
    it leaks?   clays have the capacity to adsorb the leaks and store them in their layered structure
                    cold waters very slow circulation will render they harmless when they reach the coast
                       MAY BE A GOOD OPTION

5) Bedrock caverns - Liquid W (dilution prevents melting of container)
   Low permeability unfractured rock (granite - basalt)
   Wells have to be  monitored.
   geologic stability
 Presently cooled tanks are used -
   vitrification  of wastes (glass)=> solid=>less likely to  leak

6) Bedrock disposal of solid radioactive waste
         Granite - (Nevada test site) = Fracturation
         Basalt: (Columbia River Basalt): Vesicles - Weathering
         Tuffs: Brittle - Alteration=> zeolites => ion exchange (Yucca Mtn)
         Shales: adsorption - Interlayering - weak - ½ plastic
         Salt: does not melt - Impermeable - Plastic! - Will flow

No high level waste has been disposed yet   surface - Monitored.
Geologic stability cannot be 100% warranted - And political?
 
 

CHAPTER 15 - WASTE DISPOSAL
REVIEW QUESTIONS
1)  Distribution of wastes by category.
2)  In what different ways can municipal solid wastes be disposed of?
3)  How do sanitary landfills function? Advantages and problems. Conditions for the adequate siting and design of a landfill.
4)  Advantages and disadvantages of incineration.
5)  Ocean dumping: history and policies. Consequences of ocean dumping.
6)  Option for solid waste volume reduction. Advantages and disadvantages, requirements.
7)  Examples of waste exchanges.
8)  Which are the main types of liquid wastes that require disposal?
9)  Explain three basic methods of waste disposal for municipal wastes.
10) Describe a secure landfill. What type of wastes are sent to secure landfills?
11) Outline the required characteristics for a deep-well disposal site. What type of studies are necessary? Limitations.
12) How is sewage treated in rural homes which are not connected to a municipal sewer system?
13) Describe municipal sewage treatment. What kind of treatment is the maximum treatment given to the largest proportion of the municipal sewage in the U.S.?
14) Is it possible to change the nature or the decay rate of high level radioactive wastes? What importance does the half life of the radioactive element have? Why?.
16) Examples of low level radioactive wastes. How are they handled?
17) Advantages and disadvantages of the different proposed methods for disposal of high level radioactive waste.
18) U.S. permanent repository at Yucca Mtn., Nevada. Characteristics and concerns.