Remediation and Management of Contaminated Soil - Sustainable Practices in Geoenvironmental Engineering - page 424

TABLE 11.1
Comparison of Bioremediation Technologies

Parameter Windrow Composting Landfarming Biopile Composting

Applicability PAHs, explosives Fuel oil, diesel fuel, PCBs,

pesticides

Fuels, solvents

Site requirements Excavation, and special

mixing equipment

Excavation, and
earthmoving equipment,
liners

Excavation, and
earthmoving equipment,
aeration, liners

Limitations Bulking agents that increase

volume, and may need to
be removed

Permanent structures
required

Static process without
mixing

Cost $180-270/m 3 Less than < $100/m 3 $130 to 260/m 3

Sources: Adapted from Myers, T.E. and Williford, C.W., Concepts and Technologies for Bioremediation in Conined
Disposal Facilities , DOER Technical Notes Collection (ERDS TN-DOER-C11), U.S. Army Engineer
Research and Development Center, Vicksburg, MS. Available at http://el.erdc.usace.army.mil/elpubs
/pdf/doerc5.pdf, 2000; Federal Remediation Technologies Roundtable (FRTR), Remediation Technologies
Screening Matrix and Reference Guide , 4th ed., 2007.

Fertilizer was added as a nutrient and compost was used to inoculate with microorgan-
isms. Wood chips were added for support and aeration in the pile for composting. The
parameters, pH, total volatile solids, microbial count, temperature and contaminant con-
centration, were monitored over the period of ive weeks. Whereas benzene was almost
completely biodegraded, lower levels of phenol degradation were obtained (80% to 85%). It
was concluded that composting was technically feasible at lab scale.
Myers and Williford (2000) examined the bioremediation of contaminated sediments
in a CDF. Composting (windrows and biopiles), landfarming, and land treatment were
examined for PAHs, PCBs, and PCDDs/F (Table 11.1). Land treatment is similar to land
farming except that the contaminated soil or sediments interact with the surrounding
soil. Monitoring for potential leaching and volatilization of contaminants is essential.
Composting and land treatment have the potential to be cost-effective but require pilot
and demonstration studies. According to Myers et al. (2003) composting tests were not suc-
cessful for remediating PAHs but PCB degradation may be more promising.

11.5.4 Bioleaching

Bioleaching involves Thiobacillus sp. bacteria, which can reduce sulfur compounds under
aerobic and acidic conditions (pH 4) at temperatures between 15°C and 55°C, depending
on the strain. Leaching can be performed by indirect means, acidiication of sulfur com-
pounds to produce sulfuric acid, which can then desorb the metals on the soil by substitu-
tion of protons. Direct leaching solubilizes metal sulides by oxidation to metal sulfates.
In laboratory tests, Thiobacilli were able to remove 70% to 75% of heavy metals (with the
exception of lead and arsenic) from contaminated sediments (Karavaiko et al., 1988).
Options are available for bioleaching including heap leaching and bioslurry reactors.
For both heap leaching and reactors, bacteria and sulfur compounds are added. In the
reactor, mixing is used and pH can be controlled more easily; leachate is recycled during
heap leaching. Copper, zinc, uranium, and gold have been removed by Thiobacillus sp . in
biohydrometallurgical processes (Karavaiko et al., 1988).
As pyrometallurgical, and hydrometallurgical techniques are either very expensive,
energy-intensive, or detrimental to the environment, various studies have been per-
formed to develop a process to treat and microbially recover metals in low-grade oxide