The discharge of the reactor basin through
the sludge basin in a continuous flow, intermittent discharge (CFID)
nitrification system is predicated on the assumption that there is no feed
back of ammonia from the bottom sludge deposit to the over lying water column
(See Technical Note Number 7). Such an assumption is supported by some early
research by Mortimer (1971) and Fillos and Molof (1972). They found that as
long as the dissolved oxygen in the water column is maintained at 2 to 4 mg/L,
very little, if any, ammonia escaped from the deposit. Recent investigations
conducted on an aerated lagoon by Jim Matthews of On Line Environmental, Inc.
provide additional support to the assumption. The aerated lagoon studied is a
3 mgd dual-power multicellular (DPMC) aerated lagoon system located at
Allendale, SC. The system, which is currently operating at about one-third of
its capacity, consists of one fully-suspended aerated cell (29 hp/106 gal of
volume), followed by two partially-suspended aerated cells (10 hp/106 gal of
volume) in series. Although such systems are not recommended for dependable
nitrification, some nitrification does occur in such systems, especially
during summer months in under-loaded systems such as the one in Allendale.
The monthly average
ammonia nitrogen concentration in the cell effluents are illustrated in Figure
1. The data shows that in all months (14 months), the average ammonia
concentration in the effluent of the third cell was equal to, or less than,
the ammonia found in the effluent of the first cell. The figure does not
establish that there was no feed back, but is does indicate that if feed back
does occur, nitrification in the two cells equals, or is greater than, the
ammonia feed back. As a matter of general interest, Figure 2 illustrates the
concurrent total HRT in the partially-suspended cells (cells 2 and 3) along
with the final effluent TSS and BOD5.
REFERENCES