Mặt khác, mặc dù thông thường các công nghệ loại bỏ nitơ đã chơi một vai trò quan trọng trong disposingwastewater, therearemanyproblemstobesolved, suchasuchas sự cần thiết của việc thêm nguồn cacbon trong điều trị nước thải vớilow C/N rate, demanding more energy for oxidizing ammonia intonitratethanintonitrite,andoccupyinglargerfieldandhigher investment.Soaseriesofnewtechnologiesofbio-denitrification for low C/N ratio wastewater have been developed. Firstly, as a highly effective technology, SND has been widely applied in disposing wastewater of low C/N rate. Andrade do Canto et al. using a sequencing batch biofilm reactor (SBBR) have produced the treated effluent only 0.2mg/L NO2−–N, 4.6mg/L NO3−–N and 1.0mg/L NH4−–N remained by SND [8]. Chiu et al. have reported the influence of C/N rate on the removal rate of ammonia and COD in the SBR-SND system [9]. Secondly, as it demands less carbon for removing the same amount of nitrogen, the technology of shortcut nitrification and denitrification is usually the preferential choice in disposing wastewater of low C/N ratio. Ciudad et al. have realized stably shortcut nitrification and denitrification for 170 days by partial nitrification [10]. Yu et al. have also reported that a part of ammonia in the influent should be owed to shortcut nitrification and denitrification [11]. Thirdly, as a novel technology, anaerobic ammonium axidation (ANAMMOX) has much predominance, such as needing no carbon and demanding less oxygen, thus receiving more and more attentions. Waki et al. have examined the applicability of the ANAMMOX process to three kinds of low BOD/N ratio wastewaters from animal waste treatment processes in batch mode [12]. Pathak et al. have combined ANAMMOX and denitrification and realized 80% of nitrogen removal [13]. Finally, to solve the difficulty of disposing wastewater with low C/N rate,manystudiesonimprovingthenitrogenremovingabilityof microorganism have been performed, leading to the technology offullautotrophicbiodenitrification.Roccaetal.havecombined the heterotrophic and autotrophic denitrification for disposing drinking water [14]. Sun et al. have completely realized the autotrophic nitrogen-removal in the process of wetland [15]. However, the enhancement and optimization of process designs for denitrification, especially for employing pre-denitrification, are seldom reported
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