Contaminated Land and Bioremediation 103Figure 5.4 Biosparging
effect, the process involves superaeration of the groundwater, thereby stimulating
accelerated contaminant biodegradation. Though the primary focus of the opera-
tion is the saturated zone, the permeability of the overlying soil has a bearing 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.
Bioventing
Bioventing is a technique used to remediate contamination above the water table
boundary, and again a generalised diagram appears in Figure 5.5. This process
also involves superaeration, again with the intention of stimulating accelerated
breakdown of the pollutants present, though this time it is taking place within
the soil itself, instead of the groundwater. Bioventing is not generally suitable for
remediating sites with a water table within one metre of the surface, nor for heavy
or waterlogged soils, since air flow is compromised under these conditions.
Air is introduced from a compressor pump, via a central pipe, or set of
pipes, dependent on the size of the area to be treated, down into the region
of contamination. The extra oxygen availability thus achieved, as in the pre-
vious approach described, stimulates the resident microbes, which then treat