Contaminated Land and Bio-Remediation - Environmental Biotechnology: Theory and Application - page 104

ultimately work by modifying conditions within the soil or groundwater. There
are three major techniques commonly employed, namely, Biosparging, Biovent-
ing and Injection Recovery. In many respects, these systems represent extreme
versions of a fundamentally unified technology, perhaps best viewed individual
applications of a treatment spectrum as will, hopefully, become clearer from the
descriptions of each which follow.
As set out previously, the major benefits of in situ methods are their
low intrusion, which enables existing buildings and site features to remain
undisturbed, their relative speed of commencement and the reduced risk of
contamination spread.
Biosparging
Biosparging is a technique used to remediate contamination at, or below, the
water table boundary, a generalised diagram of which appears in Figure 5.4.
In effect, the process involves super-aeration of the groundwater, thereby stim-
ulating accelerated contaminant biodegradation. Though the primary focus of the
operation is the saturated zone, the permeability of the overlying soil has a bear-
ing on the process, since increased oxygenation of this stratum inevitably benefits
the overall efficiency of remediation.
Air is introduced via pipes sunk down into the contaminated area and forms
bubbles in the groundwater. The extra oxygen made available in this way dis-
solves into the water, also increasing the aeration of the overlying soil, stimulating
the activity of resident microbes, which leads to a speeding up of their natural
ability to metabolise the polluting substances. The method of delivery can range
from relatively simple to the more complicated, dependent on individual require-
ments. One of the major advantages of this is that the required equipment is fairly
standard and readily available, which tends to keep installation costs down. Typ-
ically the sparger control system consists of a pressure gauge and relief valve to
vent excess air pressure, with associated flow meters and filter systems to clean
particulates from the input. More sophisticated versions can also include data
loggers, telemetry equipment and remote control systems, to allow for more pre-
cise process management. It should be obvious that extensive and comprehensive
site investigation, concentrating on site geology and hydrogeology, in particular,
is absolutely essential before any work starts.
Figure5.4 Biosparging