在硝化反应中,一般认为硝酸盐是反应的主产物,而从氨向亚硝酸盐的转化一般认为是硝化过程(Nitrification)的速度控制步骤,但是出现亚硝酸盐积累的报道也很多。 人们认为,出现亚硝酸积累是有害的。为了减少亚硝酸的积累,许多研究人员进行了控制其积累的工艺条件的研究工作,并得到了有关自由氨可抑制亚硝酸积累的结论,其结果也得到了证实并被广泛接受。随后,开始把注意力放在通过亚硝酸硝化—反硝化缩短脱氮过程上,这种工艺的潜在优势在于:①节省25%的硝化量。②节省40%的反硝化碳源。③节省50%的反硝化反应器容积。 这些对于高浓度氨氮废水的脱氮处理具有非常大的经济效益,特别是对于诸如垃圾渗滤液等碳源不足的废水更是如此。 在硝化系统中,与亚硝酸积累有关的因素包括:①自由氨的存在,②较高的pH值,③溶解氧浓度低,④温度的变化,⑤氨氮负荷高,⑥污泥龄长,⑦硝酸盐的还原。大多数研究人员认为自由氨浓度高(高pH值条件下)和溶解氧浓度低是亚硝酸盐积累的主要原因,指出亚硝酸积累的内在原因在于自由羟氨(NH2OH)的积累[1]。根据对前人试验结果的分析,表明自由羟氨不应是亚硝酸积累的最终原因,自由羟氨积累主要受溶解氧、pH的控制。 然而,实现亚硝酸反硝化的成功报道并不多见。Jetten等人利用硝酸菌和亚硝酸菌在较高温度下生长速度的显著差异,通过控制温度和污泥停留时间,将在高温下生长速度较慢的硝酸菌从反应器中冲洗出去,使亚硝酸菌在反应器中占优势,从而将氨氧化控制在亚硝化阶段,这种工艺叫作SHARON工艺(Single Reactor for High Activity Ammonia Removal Over Nitrite)[2]。但该工艺须在30~40 ℃的温度下进行,只对温度较高的污水如厌氧消化排水的脱氮处理有实际意义。对于垃圾渗滤液等废水,必须从控制溶解氧及pH值来实现稳定的亚硝酸反硝化脱氮。
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