Free ammonia（FA） inhibition on nitrite-oxidized bacteria（NOB） and real-time control are used to achieve nitrogen removal from landfill leachate via nitrite pathway at low temperatures in sequencing batch reactor. The inhibition of FA on NOB activity during the aerobic period was prolonged using real-time control. The degree of nitrite accumulation was monitored along with variations of the ammonia-oxidizing bacteria and NOB population using fluorescence in situ hybridization techniques. It is demonstrated that the end-point of ammonia oxidization is detected from the on-line measured dissolved oxygen,oxidization–reduction potential, and p H signals, which could avoid the loss the FA inhibition on NOB caused by excess aeration. At low temperature（13.0–17.6°C）, the level of nitrite pathway rapidly increased from 19.8% to 90%, suggesting that nitritation was successfully started up at low temperature by applying syntrophic association of the FA inhibition and real-time control, and then this high level of nitrite pathway was stably maintained for as long as 233 days. Mechanism analysis shows that the establishment of nitritation was primarily the result of predominant ammonia-oxidizing bacteria developed in the nitrifying bacteria population compared to NOB. This was mainly due to a gradual reduction of nitrite amount that is available to provide energy for the growth of NOB,eventually leading to the elimination of NOB from the bacterial clusters in sequencing batch reactor sludge system.
A novel system coupling an up-flow anaerobic sludge blanket(UASB) and sequencing batch reactor(SBR) was introduced to achieve advanced removal of organic and nitrogen from ammonium-rich landfill leachate. UASB could remove 88.1% of the influent COD at a volumetric loading rate of 6.8 kg COD·m-3·d-1. Nitritation–denitritation was responsible for removing 99.8% of NH+4-N and 25% of total nitrogen in the SBR under alternating aerobic/anoxic modes. Simultaneous denitritation and methanogenesis in the UASB enhanced COD and TN removal, and replenished alkalinity consumed in nitritation. For the activated sludge of SBR, ammonia oxidizing bacteria were preponderant in nitrifying population, indicated by fluorescence in situ hybridization(FISH) analysis. The Monod equation is appropriate to describe the kinetic behavior of heterotrophic denitrifying bacteria,with its kinetic parameters determined from batch experiments.
This study presents a biological system combined upflow anaerobic sludge bed(UASB) with sequencing batch reactor(SBR) to treat ammonium-rich landfill leachate.The start-up and operation of the nitritation at low temperatures were investigated.The synergetic interaction of free ammonia(FA) inhibition on nitriteoxidizing bacteria(NOB) and process control was used to achieve nitritation in the SBR.It is demonstrated that nitritation was successfully started up in the SBR at low temperatures(14.0 ℃-18.2 ℃) by using FA inhibition coupled with process control,and then was maintained for 482 days at normal/low temperature.Although ammonia-oxidizing bacteria(AOB) and NOB co-existed within bacterial clusters in the SBR sludge,AOB were confirmed to be dominant nitrifying population species by scanning electron microscopic(SEM) observation and fluorescence in situ hybridization(FISH) analysis.This confirmation not only emphasized that cultivating the appropriate bacteria is essential for achieving stable nitritation performance,but it also revealed that NOB activity was strongly inhibited by FA rather than being eliminated altogether from the system.
