Abstract
Wastewater treatment plants treating industrial wastewater and municipal wastewater may suffer from unexpected shock loads of high ammonia concentrations,which can lead to inhibition of biological nitrification and failure to meet the wastewater discharge standards.In order to solve the problem of failure to meet the standards,the effects of high loadings of free ammonia (FA) on the nitrification process were investigated in this work using a sequencing batch reactor (SBR).For such purpose,maximum specific degradation rates of ammonia,maximum specific formation rates of nitrate,specific oxygen uptake rates and abundances of nitrifying bacteria were monitored.The results showed that FA promoted nitrification activities at low concentrations and inhibited the activities when the FA concentration exceeded a certain value.In addition,high loading concentrations of FA resulted in long recovery times.When the FA concentration increased from 3.6 mg·L-1 to 8.1 mg·L-1,the abundances of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) increased slightly,as shown by the fluorescence in situ hybridization tests.However,there were apparent decreases in the abundances of AOB and NOB when the concentration of FA was higher than 8.1 mg·L-1.The critical FA inhibitory concentrations for AOB and NOB were 8.1 mg·L-1 and 6.6 mg·L-1.It was found that the NOB flora were more sensitive than AOB to FA inhibition.
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