Environmental Engineering FOURTH EDITION

292 ENVlRONMENTL ENGINEERING

Most MSW contains sufficient organisms for successful composting, and “mystery
culturesyy are not needed.
The endpoint of a composting operation is reached when the temperature drops.
The compost should have an earthy smell, similar to peat moss, and a dark brown color.
Compost is an excellent soil conditioner, but is not yet widely used by U.S. farmers.
Inorganic fertilizers are cheap and easy to apply, and most farms are located where
soil conditions are good. As yet, plentiful food supplies in developed countries does
not dictate the use of marginal cropland where compost would be of real value.

CONCLUSION

The solid waste problem must be addressed from the point of view of source control

as well as disposal. Many reuse and recycling methods are still in the exploratory

stage, but need development as land for disposal grows scarcer and more expensive,

and refuse continues to accumulate. We are still, unfortunately, years away from the

development and use of fully recyclable and biodegradable materials. The only truly

disposable package available today is the ice-cream cone.

PROBLEMS

14.1 Estimate the critical speed for a trommel screen, 2 m in diameter.

14.2 What air speed is required in an air classifier to suspend a spherical piece

of glass 1 mm in diameter? (See Eq. 9.4; assume ps = 2.65g/cm3, CD = 2.5,

/.L = 2 x lod4 P, and p = O.OOl2g/~m~.)

14.3 Refer to Fig. 14-16. By replotting the curves, estimate the Rosin-Rammler

constants n and x,. Compare these with the data in Table 14-1.

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  • 0.01 I 1111 I IIII I Ill-
    0.01 0.1 1 .o 10
    Particle size (in.)
  
  
  
  

Figure 14-16. Feed and product curves in shredding, for Problems 14.3 and 14.4.