Environmental Engineering Reference
In-Depth Information
require disposal. Alternative technologies are actively being researched, but
to date none appear to offer an adequate long-term solution. An up-to-date
review of treatment technologies is provided by Shaffer et al.
21
An option that offers most promise is to re-use the wastewater for sub-
sequent drilling/hydraulic fracturing operations. The benefits of re-use are
self-evident, but until recently re-use has not been seriously considered. This
is for a number of reasons, which include the detrimental effect it has on
the behaviour and performance of some of the chemical additives in the
hydraulic fracturing fluid, leading to poor operational performance of
the gas well, and the fact that freshwater is often plentiful and cheap.
Increasingly, however, recycling is being considered as regulations are in-
creasingly impacting on disposal options, freshwater resources are be-
coming limited and technology is advancing.
Evidence of this can be seen in shale gas operations exploiting the
Marcellus Shale, Pennsylvania, in the United States. As exploitation has
proceeded, wastewater has been disposed of in a range of ways (see Figure 5).
Initially there was an increase in treatment at municipal facilities, but this
has now returned to pre-exploitation levels. The reduction in use of muni-
cipal treatment facilities has been driven by a change in regulation, which
means that water can no longer be treated in municipal facilities; similarly,
limits on discharges from industrial treatment plants have also made
treatment by this method unviable for many plants. In response, there have
been sharp increases in the use of deep injection and re-use.
22
Deep disposal is not permitted in Pennsylvania, so waste water must be
transported for considerable distances to use this disposal option and,
whilst there has been an increase, there has been a much greater increase in
the volume being recycled as this is now considered to be a more practical
and cost-effective long-term option.
Figure 5 Changes in wastewater management methods for conventional wastewater
and from Marcellus shale exploitation from Lutz et al.
22
(Note differences
in vertical scales).
