An Introduction to Environmental Chemistry

dihydroxynaphthalene (Fig. 4.35). Degradation then proceeds as shown for

naphthalene (Fig. 4.34).

At the Burlington Northern site the creosote-contaminated soil was sieved and

then ball milled to reduce particle size, a process that increases contaminant avail-

ability by increasing reactive surface area. The milled creosote-contaminated soil

was then slurried with water and placed in five separate (to allow comparisons)

64-litre stainless steel bioreactors, equipped with aeration, agitation and temper-

ature controls. An inoculum of PAH-degrading bacteria was then added, along

with an inorganic supplement, containing nitrogen as NH 4 , potassium,

magnesium, calcium and iron. Conditions within the reactors were controlled to

optimize degradation for 12 weeks.

Average initial concentrations in the PAH-contaminated soil and the residual

concentrations after 12 weeks in the bioreactor are shown in Table 4.12. Although

degradation was clearly greater for the lighter PAHs (98%) it was still extensive

for the heavier compounds (70%). Furthermore, these extents of degradation

were consistently achieved in the five replicated systems. Thus, while the use of

bioreactors is technically more demanding, and more expensive, biodegradation

is extensive and reliable.

4.10.4 Phytoremediation

Phytoremediation is the use of plants and trees to clean up metals, pesticides,

solvents, explosive hydrocarbons, PAHs and leachates at contaminated sites.

The Chemistry of Continental Solids 137

Naphthalene

OH Ring cleavage

OH

1,2-Dihydroxynaphthalene

HOOC OH

O

HOOC O

OH

HOOC O

OH

OH

Side-chain

Pyruvic acid removal

HOOC O

CH 3

C

Ring cleavagesee Fig. 4.33 Salicylic acid

OH

COOH

OH

OH

Catechol Salicylic aldehyde

OH

CHO

Fig. 4.34Biodegradation pathways for naphthalene.