Page 468 - Air Pollution Control Engineering

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440 Gregory T. Kleinheinz and Phillip C Wright

6. PROCESS CONTROL AND MONITORING

As these systems contain living entities, it is vital that proper process monitoring is
carried out to ensure the long-term stability of the process. For example, if the bed dries
out too much and/or high concentrations of pollutant or extremes of temperature or pH
are experienced, then this may lead to a severe decrease in performance or, in the worst
case, complete bed failure (i.e., pollutant breakthrough). The control and monitoring of
biofiltration systems is highly variable, from little, if any, monitoring to complete mon-
itoring of all operational and process parameters. Because the process at the facility
usually dictates the airflow rate, it is often not considered a controllable variable.
However, it is often important to monitor flow rates to verify that fans and the distribu-
tion system are operating properly. Generally, the more monitoring conducted, the more
the operator understands about the treatment system. More importantly, the more mon-
itoring that is conducted, the more likely that the operator will identify any upsets or
changes in the system before they become operations problems that can lead to down-
time. By identifying potential issues early, it is easier to correct them prior to serious
damage to the microbes or equipment in the system. Although extensive monitoring is
a“best case” scenario, it is often not practical or economical for some facilities. In these
cases, the operator must make changes regarding which parameters to.
Often the cost-to-need ratio dictates the level of monitoring that is performed at a site;
that is, if the biofiltration is for odor control only and the facility has a relatively small
air treatment budget, it may choose to do minimal monitoring. Conversely, if a biofilter
is being used to treat chemicals that are a regulated discharge, such as some VOCs, it
may be more important for the facility to monitor the system more stringently. When a
system used for odor control goes out of service, it often leads to some odor complaints
for the operator, but few regulatory problems. When a system treating regulated chemi-
cals goes out of service, it may mean that the facility will exceed its discharge permit and
this could cause the facility to shut down or pay fines to exceed permit discharge levels.
Table 10 lists some parameters that are often monitored and the information that the
monitoring provides the operator. If there is a need to compromise on some monitoring,
the operator should use the information that is known about the process stream to help
decide which parameters are most critical for that application. For example, if your sys-
tem were treating a significant amount of reduced-sulfur compounds, the pH would be
a critical factor to monitor because of the large amount of toxic products produced by
the oxidation of reduced-sulfur compounds. In general, for biofilter systems, moisture
and pH distributions are vital pieces of information.

7. LIMITATIONS OF THE TECHNOLOGY
As discussed previously, there are several “traditional” limitations to biofiltration
technology, such as high concentrations of chemicals, size of some units, microbial
capabilities, and process air temperatures. However, although these have been traditional
limitations, recent work in both biofilter design and operation has helped overcome
some of these problems of the past.
As mentioned earlier, operators are largely responsible (along with designers) for
successful operation of biofilters. A biofilter operator needs to be aware of the operation