锦江中氨氮污染及生物转化特征分析

The characteristics of pollution and biotransformation of ammonia nitrogen in Jin River

近年来,锦江呈现出明显的氨氮污染不断加剧的趋势.从2007～2008年度连续四个季节对流经成都市区的锦江14个断面的氨氮污染及其生物转化情况进行了初步分析,并结合COD的污染情况对影响锦江氨氮生物转化的因素进行了初步评价.通过现场调查温度、溶解氧等常规水质指标,并采集水样进行实验室无机氮和COD浓度分析.结果发现:锦江全年第2季度COD的污染情况最为严重,64%的采样点断面为劣Ⅲ类水质(>20 mg/L),第1季度仅采样点9(毛家湾)劣于Ⅲ类水质,第3和4季度COD浓度均低于20 mg/L;而锦江全年氨氮污染情况均非常严重,第1季度和第2季度锦江所有断面的氨氮浓度均为劣Ⅴ类水质(>2mg/L),除了彭山县城(采样点14)外,第3季度和第4季度中的氨氮污染均显著劣于Ⅲ类水质(1 mg/L);锦江14个主要采样点中,中和场到江安河锦江汇流处(采样点6～8)之间的断面中COD浓度均有不同程度的增加;污水处理二厂(采样点4)和一厂(采样点5)的排放口氨氮污染情况最为严重,之后呈现不断降低的趋势.另外,氨氮的生物转化主要集中在锦江下游黄佛(采样点10)到江口(采样点13)之间的河道,表现为氨氮浓度不断减少,硝酸盐浓度呈现逐渐上升的趋势.

In recent years, the Jin River has shown clear trend of continuous increase of ammonia nitrogen pollution. The ammonia nitrogen pollution and bio-transformation condition in 14 different transects of Jin River flowing through the Chengdu city was preliminarily analyzed, factors affecting the biotransformation of ammonia nitrogen were also evaluated based on the COD pollution situation in the second, third and fourth quarters of 2007 and first quarter of 2008. The conventional indexes of temperature, dissolved oxygen （DO） were in situ investigated and water samples were carried back to the lab on the same day for the concentration analysis of inorganic nitrogen and GOD. The results showed that the pol-lution condition of COD in the second quarter of a year was the most severe, in which the COD concentration at the 64% of sampling transects was the water quality of inferior standard Ⅲ （〉20 mg/L）, only the Maojia Bay （station 9） in the first quarter of 2008 was inferior to the standard Ⅲ, the COD levels of the third and fourth quarter both were below 20 mg/L; that the whole situation of ammonia nitrogen pollution in a year was very serious, the pollution of ammonia nitrogen in the first and second quarter was the water quality of inferior standard V （2〉2 mg/L） ; all the rest, except Pengshan county （station 14）, significantly were inferior to the standard Ⅲ （1 mg/L） in the third and fourth quarters. The concentration of COD increases to some degree in the transects between the Zhonghe bazar （station 6） and infall of Jiang＇an River into the Jin Rvier （station 8） ; the transects in the outfall of the second and first wastewater treatment plant （WWTP） （stations 4 and 5） of the 14 investigated transects were most serionsly polluted by the higher level of ammonia nitrogen, after them, the ammonia nitrogen gradually decreased until the last station. In addition, the biotransformation of ammonia nitrogen mainly focuses on the riverway between Huangfo （station 10） and Jiangkou （station 13） in the lower Jin River and is characterized by the trend of the continuous decrease of ammonia nitrogen and increase of nitrate.