Stockpiles - The Issues
Wet weather degrades stockpiles of
biomaterials (dewatered biosolids,
composted materials, industrial organic wastes, manures, etc.). They are
liable to slump and/or to release run-off and/or odour. This can be a water
pollution risk, and a risk to property. Whatever the site where
the biomaterial is going to be used there will be a limited time window
for application, but invariably the production facility is producing
all the time. Farmers etc. appreciate seeing the biomaterial on
site (safely contained in an ARSC) so that they know that application
Wet slumping stockpiles encroach on
the surrounding land. They
are difficult to contain and, when the time comes to spread,
application is slow, less precise, more difficult and more
costly. If you know your stockpiles might slump you should site
them where the gradient is shallow; but this is a restriction on the
land that can be treated and therefore increases costs.
Can you contain a stockpile that
starts to move? It is difficult
because the side pressures are immense. Building a wall with
large straw bales might be successful, but it is expensive in labour
and materials and there is the problem of what to do with the rotting
bales at the end of the job. If rain continues, the
stockpile can move the bales and then you need to secure them by
driving stakes into the ground; that too can fail and release the
contents. If you push up earth walls you make a lagoon, with
consequent risk of drowning, etc. unless you put up expensive fencing.
Will improving dewatering prevent
slumping? No - even digested
biosolids that had been dewatered to 25%DS have slumped during wet
Lime stabilised dewatered biosolids do
not slump. That’s true but
because stockpiles drain they lose leachate which is a water pollution
risk. An ARSC can also get over the pH>12 issue associated
with this otherwise very useful treatment process.
Does compost need ARSC?
Yes it does; when stockpiles of composted
materials become saturated with water oxygen is excluded; this sets up
anaerobic conditions which produce compounds that are malodorous and/or
Legal issues related to stockpiles.
In many countries it is an
offence to make stockpiles that are not secure and contained. In
the EU there is added obligation if the pH is 12 or greater.
Odour nuisance can be a legal offence. ARSC avoids all these
What about adding structure and
strength with bulking agent? This
can be done but it is more expensive than ARSC and it does not satisfy
the legal obligation for safe containment. Also there is the
question of finding bulking agent free from contaminants (including