Biological Phosphorus Removal
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By: Mike Baumgartner, ARWA Wastewater Specialist
Discussion about nutrient removal is beginning to take center stage throughout the state. Many systems are in a report only status. However, many have seen mandatory limits depending on discharge location.
Eventually, everyone may have at least a minimum limit. Biological removal is the first form of removal. There may be additional need for chemical (polymer) and especially effluent filtration. In fact, I can almost guarantee the need for filtration. Phosphorus needs to be removed after being bound in the solids. It does not precipitate like nitrogen. The plant effluent will need to be very low in TSS levels. So, let's begin with Biological removal.
As mentioned, phosphorus removal depends upon the luxury uptake of orthophosphate which occurs in the activated sludge process. The microorganisms must be subjected to high dissolved oxygen levels followed by a zone (fermentation) free of dissolved oxygen or combined oxygen (free of nitrate).
This zone creates an enormous
oxygen demand and when influent
and return sludge mix with the
oxygen starved "bugs", phosphorus
is released while BOD is now being
stored. This process is repeated
using anoxic basins and reaeration
basins. Eventually, the "bugs" have
stored as much of the phosphorus
as possible and through wasting, the
phosphorus is removed. This subject
can get a bit more technical but for
now take this advice. Prepare for
biological and or chemical removal
strategies. If you are in the planning
phase of a wastewater facility, talk to
your engineer about what it is going
to take to meet the nutrient levels
that are surely going to come. Also,
you may as well begin looking into
the prospect of effluent filtration.
Sorry for the bad news but it is
always better being prepared.
Article first appeared in Waterline, Spring 2011
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