Disposal of Biodegradable Wastes
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Disposal of Biodegradable Wastes


Various types of waste include:
  • Household Garbage
  • Paper
  • Leaves in ponds and reflection pools
  • Oils and petroleum products
  • Insecticides
  • Herbicides
  • Detergents
    • Anionic (most common soaps and detergents)
    • Cationic (many shampoos)
    • Non-ionic (photographic rinses)

.....In each of the above categories are both biodegradable and non-biodegradable substances. ..The following piece of equipment was exhibited at the 1999 annual meeting in Chicago of the American Society for Microbiology and appeared to be an outstandingly elegant device for visualizing the biodegradation of solids such as newspaper.


A BASIC ITEM OF EQUIPMENT

Device

..... In science supply stores, a very thin and deepterrarium for ants and worms can often be found. ..Or one can be made at home out of two parallel 40 cm high by 15 cm wide sheets of clear plastic or glass, which are kept in a frame that holds them separated by about 1 or 2 cm. ..Make sure that there are several drainage holes at the bottom for excess water to escape.

..... Into the space between the plastic or glass panes is packed your experimental material - usually garden soil plus some degradable additive you want to watch degrade and disappear. ..Using Side A as the "control" side, on Side "B" you might also add something that you think might accelerate the degradation process. ..Fertilizers are a good choice; especially those that contain a mineral that is in very low concentration in the material you wish to degrade. ..Let's look at a major component in sanitary landfills. ..Newspaper often cannot be recycled but it amounts to a major fraction of the volume of a landfill. ..It has been shown that newspaper degrades so slowly in many city landfills that wording on it can still be read years later. ..Let's now look at what can be done to speed up the process. ..(Of course, it is best to send the used paper to a recycling center.)


Degradation of Paper by Soil Bacteria

..... Paper is mostly cellulose. ..(Glossy paper has a finish of finely ground clay.) Where does this cellulose come from, what is it made of, and why doesn't it break down rapidly? ..Most paper is made from cellulose pulp from tree logs. ..Cellulose is chemically very much like starch, but has only one difference, which is that the sugar molecules are coupled together in slightly different fashion (starch has "alpha" linkages between the glucoses, while cellulose has "beta" linkages - see your local biochemistry textbook about the meanings of these words and then make some tooth-pick and gum ball models). ..Anyway, since cellulose is made up of zillions of glucose sugar molecules, one expects the cellulose should degrade rapidly. ..But there is one problem, cellulose is not soluble in water and so most enzymes cannot get close enough to "chew" on it.

..... Furthermore, those few organisms that can attack cellulose find it such a great energy source that they soon overeat. ..Shredded paper is not a balanced diet as it lacks all the minerals and some other vitamins. ..Thus the paper cannot be degraded until such other growth factors slowly trickle into the paper.

..... Fill your very thin terrarium about a third full with slightly moist garden soil. ..Then make a mix of garden soil and shredded paper, and push that down into your terrarium until you have maybe 5 cm of soil and paper. ..Atop that layer and only off to one side, add a little lawn fertilizer. ..Finally fill the terrarium with more slightly moist earth. ..In this "static" exhibit you should be able to see which type of paper disappears fastest. ..A parallel study can be made to see if access to air helps speed the decay: once you have added the shredded paper stand several straws vertically upon (or slightly into) the paper layer and then fill the terrarium the rest of the way full.


Degradation of LIQUIDS by Soil Bacteria

.....You must have two set-ups that are identical in all respects but one: ..one has the experimental liquid added, and the other - the "Control" - does not. ..Each set-up must be air-tight and "loaded" in much the same way as with the newspaper, above. .. THEN both must be capped with air-tight lids through which a small rigid tube protrudes. ..To that tube a flexible one is attached that runs over to any type of gas monitoring equipment. .. A simple one that you can contruct for each set-up is an inverted graduated cylinder that is full of water and is sitting vertically in a beaker of water. ..The far end of the flexible tube is led under the immersed opening of the graduated cylinder. .. As gas is produced by the decay in the sealed terrarium, it is trapped in the graduated cylinder and easily measured as the hours and days go by. ..I will not tell you the secret for getting the upside-down cylinder full of water and standing in the beaker. ..Any young scientist worthy of this experiment ought to be able to figure that out!


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