Method B is so superior to Treatment Method A, B would be chosen. The ratio of NPV is
2.84 in favor of Method B over Method A.
Use the conventional methods of engineering economics to compare alternative treat-
ment methods. The prime consideration is that the methods compared provide equivalent
results for the remediation process.
- Develop costs for combined remediation systems
Remediation of sites always involves evaluation of a diverse set of technologies. While
biological treatment alone can be used for the treatment of many waste streams, combin-
ing bioremediation with other treatment technologies may provide a more cost-effective
remedial alternative.
Figure 23 shows the costs of a full-scale groundwater treatment system treating 120
gal/min (7.6 L/s) developed for a site contaminated with pentachlorophenol (PCP), cre-
osote, and other wood-treating chemicals at a forest-products manufacturing plant. The
site contained contaminated groundwater, soil, and sludges. Capital cost, prorated for the
life of the project, for the biological unit is twice that of an activated carbon system. How-
ever, the lower operating cost of the biological system results in a total treatment cost half
the price of its nearest competitor. Carbon polishing adds 13 percent to the base cost.
For the systems discussed in the paragraph above, the choice of alternative treatment
technologies was based on two factors: (1) Biological treatment followed by acti-
vated carbon polishing may be required to meet governmental discharge requirements.
(2) Liquid-phase activated carbon, and UV-oxidation are well established treatment meth-
ods for contaminated groundwater.
Soils and sludges in the forest-products plant discussed above are treated using a
bioslurry reactor. The contaminated material is slurried with water and placed into a
mixed, aerated biotreatment unit where suspended bacteria degrade the contaminants.
FIGURE 23. Under the right circum-
stances, biological treatment can be the
lowest-cost option for groundwater
cleanup. (Carlo, Magazine and Chemical
Engineering)