Using the Pond as a Biofilter: Review of Theory and Practice
Intensive aquaculture systems are being used to efficiently produce fish and
shrimp. However, an intrinsic problem of these systems is the rapid accumulation
of feed residues, organic matter and toxic inorganic nitrogen species. This
cannot be avoided, since fish assimilate only 20-30% of feed nutrients. The
rest is excreted and typically accumulates in the water. Often, the culture
water is recycled through a series of special devices (mostly biofilters of
different types), investing energy and maintenance to degrade the residues.
The result is that in addition to the expense of purchasing feed, significant
additional expenses are devoted to degrade and remove two thirds of it. There
is a vital need to change this cycle. One example of an alternative approach
is active suspension pond (ASP) systems, where the water treatment is based
upon developing and controlling heterotrophic bacteria within the culture component.
Feed nutrients are recycled, doubling the utilization of protein and raising
feed utilization. Other alternatives, mostly based upon the operation of a
water treatment / feed recycling component besides the culture unit are also
relevant. Active suspension ponds are being practiced and their numbers have
increased dramatically during the last 10 years, most notably with shrimp culture.
The purpose of this paper is to raise discussion on alternative routes to the
classical recycling approach.