Recycling Matters

As a result of this oversupply, scrap values for many recyclable materials have fallen noticeably over the past few years. Further complicating matters are new efforts from regulators and environmental activists to mandate the reuse of certain materials (rates and dates) and that products be made with specified amounts of recycled material (product content laws). Such demand-side measures distort market forces and do not appear to be justified on either economic or environmental grounds. 

In AFBC units, heat is removed from the flue gas by a convection-pass tube bank. The particulates leaving the boiler with the flue gas consist of unreacted and spent sorbent, unburned carbon, and ash. Multiclones after the convection pass remove much of the particulate matter and recvcle it to the combustor, increasing the in-furnace residence time an improving combustion efficiency and sulfur retention performance. Bubbling PFBC units do not have convection-pass tube banks and do not recycle solids to the boiler. 

Control technologies employed for the handling of air emissions normally include the capture and recycling or combustion of emissions from vents, product transfer points, storage tanks, and other handling equipment. Boilers, heaters, other combustion devices, cokers, and catalytic units may require paniculate matter controls. Use of a carbon monoxide boiler is normally a standard practice... 

Composting is another way to recycle nutrients and organic matter in sludge. The benefits from using sludge composts include increased water and nutrient holding... 

As a matter of fact, the main advantage in comparison with HPLC is the reduction of solvent consumption, which is limited to the organic modifiers, and that will be nonexistent when no modifier is used. Usually, one of the drawbacks of HPLC applied at large scale is that the product must be recovered from dilute solution and the solvent recycled in order to make the process less expensive. In that sense, SFC can be advantageous because it requires fewer manipulations of the sample after the chromatographic process. This facilitates recovery of the products after the separation. Although SFC is usually superior to HPLC with respect to enantioselectivity, efficiency and time of analysis [136], its use is limited to compounds which are soluble in nonpolar solvents (carbon dioxide, CO,). This represents a major drawback, as many of the chemical and pharmaceutical products of interest are relatively polar. 

Besides nitrogen fixation, the only other major source of reduced nitrogen is the decomposition of soil or aquatic organic matter. This process is called ammonification. Heterotrophic bacteria are principally responsible for this. These organisms utilize organic compounds from dead plant or animal matter as a carbon source, and leave behind NH3 and NHJ, which can then be recycled by the biosphere. In some instances heterotrophic bacteria may incorporate a complete organic molecule into their own biomass. The majority of the NH3 produced in this way stays within the biosphere however, a small portion of it will be volatilized. In addition to this source, the breakdown of animal excreta also contributes to atmospheric... 

As shown in Figure 6.1, the separation step has been assumed to give clean splits, with pure A being recycled back to the reactor. As a practical matter, the B and C streams must be clean enough to sell. Any C in the recycle stream will act as an inert (or it may react to component D). Any B in the recycle stream invites the production of undesired C. A realistic analysis would probably have the recovery system costs vary as a function of purity of the recycle stream, but we will avoid this complication for now. 

It is claimed that only by fully considering all stages of the life cycle is it possible to arrive at a meaningful evaluation of a product. Thus the feasibilities and limitations of recycling are important, but are not the only aspects of the matter. Also discussed are the utilisation of plastics scrap as a raw material and energy carrier, and techniques under development. 11 refs. 

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