联合脱氮法用于硝酸盐污染地下水修复的机理研究

地下水硝酸盐已经成为了世界性环境和健康问题。目前针对硝酸盐的化学还原脱氮、自养脱氮、异养脱氮等单一脱氮方法研究较多;联合脱氮体系包括化学还原、自养脱氮和异养脱氮三种脱氮途径,综合了单一脱氮法的优点,但研究甚少。本研究通过静态批试验,采用零价铁、甲醇和混合菌液研究了联合脱氮法的脱氮能力、脱氮产物、脱氮途径及脱氮机理。结果表明,5 d后单一的零价铁化学还原、自养脱氮和异养脱氮的去除率分别为5.79%、14.30%和63.03%;而联合脱氮的去除率接近100%,去除效果显著优于单一的化学还原脱氮、自养脱氮或异养脱氮。在联合脱氮法体系中,零价铁化学还原、自养脱氮未引起亚硝酸盐积累,而异养脱氮造成了亚硝酸盐积累;化学还原、自养脱氮和异养脱氮引起的铵盐增量均<0.6 mg/L,绝大部分硝酸盐未被还原成铵盐,进而省去了后续除铵工艺;零价铁化学还原、自养脱氮、异氧脱氮三者发生协同作用,表现于在厌氧环境下,零价铁发生腐蚀,产生阴极氢和二价铁,为自养脱氮菌提供了电子供体,从而促进了自养脱氮;异养脱氮不仅占主导地位,而且还会产生CO2,CO2被自养脱氮菌作为无机碳源加以利用,从而提高了体系中自养脱氮能力。这种协同作用表现为联合脱氮法的去除率增加,而在单一的异养脱氮或自养脱氮体系中则无法形成这一良性过程。实验表明联合脱氮法是一种潜在的有效可行的地下水原位修复方法。

Mechanism Study on a Combined Denitrification Approach for Nitrate-Contaminated Groundwater Remediation

Nitrate in groundwater has become a worldwide environmental and public health issue. Nitrate can cause methaemoglobinaemia, septicemia, hepatopathy, and even cancers. Currently, single chemical reduction (CR), autotrophic denitrification (AD) and heterotrophic denitrification (HD) have been reported worldwide, however their combined denitrification approaches are rarely studied. In this paper the denitrification capacities, by products, pathways and mechanisms of a combined denitrification approach via batch experiments are explored, which are supported by zero valent iron, methanol and mixed bacteria. The results indicate that the elimination rates of 5.79%, 14.30% and 63.03% were achieved by single zero valent iron-based CR, AD and HD respectively after 5 days, whereas close to 100% was attained by the combined approach. The combined approach is superior to single CR, AD or HD. Nitrite accumulation did not occur in the single CR or AD, but did take place in the single HD. Ammonium variations of <0.6 mg/L were respectively found in CR, AD and HD. Nitrate was reduced to nitrogenous gas by CR, AD and HD. The combined system, in which HD played a dominant role, included three denitrification pathways, those of CR, AD and HD. Anaerobic zero valent iron corrosion provided cathodic hydrogen and ferrous iron for autotrophic denitrifiers. HD provided carbon dioxide for autotrophic denitrifiers. The combined system improved the elimination rate, which was not achieved by single AD and HD system. This combined approach was a potential, feasible and effective approach for groundwater in situ remediation.