Energy Conservation in Aerobic Wastewater Treatment Units - Implementing Environmental and Resource Management - page 39

that under such an aeration regime as in the experiment, the periods between air-
on and air-off was very short (1-hour), thus created post-aeration anoxic condition
in the aeration chamber. According to Ouyang et al. (1999), denitrification, or-
ganic substrate oxidation and phosphorus uptake occur at the same time in an an-
oxic condition. Also, this is probably the reason for high phosphorus removal effi-
ciency (40%) in the modification experiment. It is also believed that the aeration
regime in the modification experiment allowed for an optimum mixing of fresh
water sewage and recycled fluid from the aeration tank which according to
Bathurst Regional Council (2002), is an environment that promotes the growth of
phosphorus-hungry bacteria that in turn depend on the phosphorus for their food.
Ouyang et al. (1999) also reported that phosphate-accumulating organisms in the
aerobic chamber take up phosphorus that is released by the activated sludge in the
anaerobic chamber.
However, no ammonia nitrogen removal was observed in the modification ex-
periment ( Table 5.2 . ). This might seem strange though it may possibly be linked to
the high ammonia content of the wastewater which might have resulted in incom-
plete nitrification. In addition, it could be due to a low number of nitrifying bacte-
ria probably because of the anoxic condition. This is because nitrifying bacteria
require a higher amount of dissolve oxygen than the amount than exists in anoxic
conditions. A research by Ouyang et al. (1999) also attributes such cases to two
reasons, short sludge retention and hydraulic retention times. Not much can be ar-
gued on this line since no measurements of these parameters were made during the
experiment.
There was a positive correlation between nutrient (nitrogen and phosphorus)
removal efficiency, suspended solids and BOD. However, the significant differ-
ences in treatment performance characteristics in the various aeration regimes
could be discussed in line with sludge retention times of the experiments. A report
by Williams (1994), indicated that, variation of sludge retention time (SRT) will
modify the entire process performance, including denitrification rates, sludge pro-
duction and stability, mixed liquor concentration, oxygen uptake rates and the ex-
tent of nitrification. Improved efficiency of the BioMax system saved money,
which means that by reducing the amount of aeration required, money is saved as
less electricity is used to operate the electrical motors driving the aerators. Thus, it
is observed from the experiment that simultaneous nitrification and denitrification
is efficient and cost effective process for wastewater treatment.
5.6 Conclusions
It has long been thought that denitrification occurs only in the anaerobic chamber,
and that a better wastewater treatment performance is usually associated with long
period of aeration. From the results obtained during the two experimental studies,
it was clear that the modification experimental design is feasible for removing nu-
trients from wastewater. This is an indication that sound aeration control of the
aeration regime promotes simultaneous nitrification and denitrification in the aera-