lauren@kelman.ca

TERTIARY TREATMENT TECHNOLOGIES & PRACTICES
The first step in the assessment was
microbial analysis to determine the
nature of the thick brown foam.
The microbial analysis showed the
presence of Thiothrix spp. in several
foam samples (Photograph 2). Further
investigation indicated that the high
COD utilization rate in the post anoxic
reactor combined with short HRT and
low concentration of available nitrogen
for assimilation resulted in excess
brown foam and sludge bulking.
Data collection and observation of
system response with static modeling
and simulation analysis showed the
presence of high dissolved oxygen (DO)
in the anoxic zones caused by excessive
aeration in the aerated zone from an
oversized blower with limited turndown
control. DO was also being entrained
FIGURE 1
PHOTOGRAPH 3
32 INFLUENTS Fall 2015
within the manhole splitter box that
divides flow from the anaerobic zone
into the two pre-anoxic zones. EOSi
and the plant personnel were able to
develop an operating strategy which
incorporated changes to achieve a more
steady biological process and to reduce
effluent TN from >200 mg N/L to less
than 3 mg N/L, thereby bringing the
plant into compliance. Key operational
changes included replacing the blower
with one having better turndown
control, piping changes in the influent
manholes to reduce DO entrainment,
and revised carbon feed strategy as
recommended by EOSi.
Within weeks of implementing
the process enhancements, DO
concentrations were optimized
throughout the process. Thick brown
CASE STUDY 1: Post anoxic NOx-N concentration.
CASE STUDY 1: Anoxic reactor before (left) and
after (right) EOSi implementation of key operational changes.
foam was virtually eliminated throughout
the entire plant. Photograph 3 shows the
before and after photos of the foam on
the anoxic tank. The plant achieved
full denitrification with an effluent of
NO x
-N(Nitrate+ Nitrite)