Recently, the research in biological denitrification applied to low nitrate concentration municipal wastewater and polluted groundwater has gained considerable attention. There is, however, much less research on high-strength nitrate industrial wastewater treatment by biological denitrification. The present investigation hence aims towards studying biological treatment of high nitrate concentration wastewater for removal of nitrogen components and understanding its operational characteristics. Three different types of bioreactors, viz.: an activated sludge reactor (ASR), a biologically mediated activated carbon fluidized bed reactor (BAFBR), and an upflow immobilized cell reactor (UICR) were used. Results revealed that the start-up period of UICR was the shortest, followed by BAFBR, while it was longest for ASR. Thus higher volumetric load appears to lead to a shorter start-up period. From long periods of operation, it was observed that the volumetric load of BAFBR was the highest (30 kg N/m3-d), followed by UICR (8.9 kg N/m3-d) and the lowest (1.0 kg N/m3-d) was ASR. The influence of power outage or system shutdown was found to be the most significant for BAFBR, the second most affected was UICR, and ASR was the least affected. The ability to acclimate to shock loading was observed to be best for UICR, the next was BAFBR, while the worst was ASR.

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