Figure 2 Ammonium conversion in the SHARON reactor with continuous operation. HRT and SRT were
both one day. Period 1: start up period, Period 2,4 and 6 steady state operation withot pH control, Period 3
and 5 test period to evaluate effect of reactor pH on conversion. (x: NH4-N in; o: NH4-N out; •: NO2-N out)
Water 44.1-K19 27/6/01 6:20 pm Page 155
effluent. For this control the principle of a chemostat system is used: at a constant dilution
rate the effluent substrate concentration will be constant. It has been shown that NH3 rather
then NH4
+ is the active substrate (Hellinga et al., 1999). If the pH is increased, a constant
ammonia level means a lower ammonium level. i.e. by increasing the pH the amount of
ammonium in the effluent decreases rapidly. It was shown in period 3 and 5 that indeed a
slight change in pH already leads to a large change in the effluent ammonium/nitrite ratio.
Without control already a total conversion of >90% can be obtained, it is therefore questionable
whether the extra removal by a pH control is economically worthwhile.