Question

10.5) Contrast the three categories of solid-phase treatment.

Answer 1

Answer:

*Three categories of solid phase treatment:

Solid Phase - Solid phase treatment consists of placing the excavated materials into an above ground enclosure. Inside this enclosure, the contaminated soil is spread onto a treatment bed. This treatment bed usually has some kind of built-in aeration system. Using this system, cleanup crews are able to control the nutrients, moisture, heat, oxygen and pH. This allows them to maximize the efficiency of the bioremediation. The soil can also be tilled like farmland, helping to provide oxygen and enable additional aerobic biodegradiation of the contamination.   Solid phase treatment is especially effective if the contaminants are fuel hydrocarbons. However, it does require a lot of space and sometimes it cannot be used for that very reason.

There are three solid phase bioremediation techniques. They are: landfarming, biopiling, and composting.

1)Landfarming - Landfarming is the most

          simple of the three types of solid phase

bioremediation. It involves the

          excavation and spreading of the

          contaminated soils onto a lined bed

          (pad). The soil is usually spread so that

          it is about 18 inches thick all around.

          The bed typically has a collection

          system of some sort, designed to collect

          any leachate that may seep through the

          contaminated soil. Leachate is a solution

          containing contaminants that are picked

          up through the leaching of soil. The soil

          is then tilled and turned over repeatedly

          to allow aeration to occur. Gennerally,

          a high molecular weight, heavily

          nitrated compounds, and heavily

          chlorinated compounds tend to slow

          down the rate of contaminant

          degradation.

               Controlling the frequency of

          aeration enables the cleanup crews to

          control the amount of oxygen that is

          involved in the degradation process.

          They also control the moisture content

          of the soil by irrigation and spraying.

          They are able to control the pH of the

          soil on the bed by adding crushed

          limestone. This crushed limestone

          helps to form a buffer around neutral.

          Usually, these beds are in an enclosure.

          This prevents any inclement weather

          from affecting the degradation of the

          contaminants. It also helps to contain

          any evapourated contaminants.

2)Biopiling - This is exactly what you would

          expect from its name. The

          contaminated soil is excavated and put

          into piles. These piles are usually 2-3

         metres in height. These piles are placed

          over an aeration system. This system

          pulls air through pile of contaminated

          soil by means of a vacuum pump. This

          movement of air not only provides

          oxygen to the microorganisms, by it

          also pulls some of the contaminants out

          of the soil as it passes through soil. A

          collection system similar to the one

          used in landfarming is also

          used with soil biopiles.

               Optimal bioremediation

         conditions are maintained by the control

          of the moisture and nutrient levels.

          Another form of control is the placement

          of the piles into enclosures. This

          prevents and unwanted weather

          changes and helps to control any

         temperature changes.  Volitatile

          contaminants (evapourated

          contaminants) are minimal beacuse the

          vacuum pump pulls any evapourated

          contaminants through the pile, keeping

          them from escaping into

          the atmosphere.

               These piles do require quite a bit of

          space, but they do not need as much

          space as landfarming does.  It is a

         short term technology that usually only

          operates for a few weeks or a few

          months.

3)Composting - Composting involves first the

          excavation of the contaminated soil. A

          bulking agent of some sort is added to

          the contaminated soil, which is then

          known as compost material. Bulking

          agents include things like: hay, straw,

          and corn cobs. These things make it

          much easier for the cleanup crews to

          maintain the maximum rate of

          degradation of the contaminants. The

          bulking agents allow the cleanup crews

          to easily control the amounts of water

          and air that are available to the

          microorganisms involved in

          the degradation reaction.

               There are three methods of

         composting that are used. The first is

          called static pile composting. This

          involves the formation of piles and

          aerating them by means of a blower or a

          vacuum pump. The second is called

          mechanically agitated in-vessel

          composting, which involves the

          compost material being placed in a

          treatment vessel. Here, it undergoes

          mixing and aeration. The third is called

          windrow composting. This method

          involves placing the compost material

          into windrows (long piles as in a

          farmer's field). This windrows are then

          mixed up thoroughly by tractors and

          other such equipment.  

               Windrow composting is the most

          common method, mainly because it is

          the most cost-effective method.  

               One interesting thing about

          composting is that it not only works in

          soil but it also can be applied to

          contaminated lagoons and swampy

          areas. Another good thing about

          composting is that all of the necessary

          equipment can be commercially

          obtained.