I would like to add a cautionary note concerning aerobic and anaerobic
digesters. As I am sure you can appreciate being in the farming related
business, digesters are biological systems that require careful monitoring
and operation in order to be successful. When one of these systems crashes,
it can take weeks to return the system to a healthy steady state operating
condition. Microorganisms can be quick to multiply under good conditions,
slow to multiply under sub-optimal conditions, but are even quicker to die
under poor operating conditions.
Digesters work best under reasonably constant flows (if continuous) and
loading. Intermittent operation is not easy to achieve. Significant changes
in the make up of the inputs can lead to significant changes in the operation
and outputs. It takes considerable experience to run a digester efficiently.
Performance data will be very much dependent on the expertise of the
operator, environmental factors (such as temperature), and the quality and
mix of inputs.
A break down of a tractor or other farm implement is generally not going to
result in a catastrophic failure of the crop. A break down in a component of
a digester can result in a rapid failure of the system.
Having stated these cautions, I would al;so like to add that digesters are a
proven technology. However, they require careful scrutiny and maintenance of
the operating parameters and a TRAINED operator to maintain the system and
detect problems BEFORE the system crashes. In the event where you are
dependent on the digester for disposing of waste materials, what will you do
with this waste if your system crashes for several weeks? Do you have a
storage option or contingency plan? These are additional considerations to
include in evaluating digesters.
Alan Ismond, P.Eng.
Aqua-Terra Consultants
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