Nitrification and denitrification characteristics in a sequencing batch reactor treating tannery wastewater

Long-term evaluation of a SBR fed with tannery wastewater (SBRtww) was carried out to study the periods of satisfactory and unsatisfactory performance in the nitrification and denitrification properties. Another SBR fed with synthetic nitrogen medium simulating tannery wastewater (SBRsww) was used to assess separately the end points of nitritation and nitratation by online monitoring of pH and DO. Flex point in the DO and pH profiles of the SBRsww cycle corresponding to the end point of nitritation was well observed, whereas the end point of nitratation was vaguely detected. The end point of nitritation suggested that the aeration phase can be reduced considerably and denitrification via nitrite can be facilitated to minimize oxygen requirements and reduce operational costs. During the long-term operation of SBRtww, stable and unstable phases of nitrification were observed. A maximum nitrification rate of 14.1 mg/L h was obtained during the stable phase of the reactor. Inhibiting substances in tannery wastewater was found to be the possible reason for the instability in nitrification. Denitrification property, however, was not much affected as that of nitrification. The maximum denitrification rate observed was 10.7 mg/L h. Nitrogen removal in an aerobic SBR through simultaneous nitrification--denitrification could be a good option for tannery wastewater. SBR is a viable option for tannery wastewater compared to the conventional aerobic systems provided pollution control measures are conducted at the source level through the use of eco-friendly chemicals and cleaner processing methods to avoid nitrification inhibiting compounds in the effluent.