2017年滇池外海水质异常下降原因及对策

The cause for abnormal water quality deterioration of Waihai of Dianchi Lake in 2017 and the countermeasures

2017年滇池外海水质由GB 3838—2002《地表水环境质量标准》Ⅴ类降为劣Ⅴ类,特别是6—8月主要水质指标总磷(TP)、总氮(TN)、化学需氧量(CODCr)及叶绿素a(Chla)浓度异常上升。引起滇池外海水质异常下降的根本原因:首先,2017年6—8月流域降水量较上年同期增加81%,为1999年以来同期降水量之最,异常降水使外海北部3条主要入湖河流宝象河、盘龙江、金汁河输入TN、TP污染负荷量较上年同期分别增加50%和59%,导致外海北部水质指标异常升高。其次,因为截污体系雨季混合污水溢流严重,造成污水处理厂污水收集率下降,昆明市第二、第三、第四、第九污水处理厂雨季进水CODCr、TN及TP平均浓度分别比旱季降低15%、15%和20%;第十污水处理厂雨季进水CODCr、TN和TP平均浓度分别降低16%、19%和8%。此外,2017年牛栏江补水量较上年减少50%,而补水水质NH3-N、TP、TN浓度分别上升75.2%、51.1%、40.2%,补水对外海水质改善作用降低。由此提出滇池外海水质稳定提升的对策:推进截污系统效能核查,进一步完善污水收集系统,着力提高污水收集效率;优化流域已建调蓄池的运行,提高对雨污混合水的调蓄作用;通过优化运行、加强监管及雨季联合调度,提高污水厂处理效率,促进污染负荷削减与减排;加强牛栏江补水水源区的保护与治理,提升补水的环境效率。

The water quality of Waihai of Dianchi Lake abnormally deteriorated from Ⅴclass to worse than Ⅴclass（ Environmental Quality Standards for Surface Water（ GB 3838-2002）） in 2017. Particularly, the concentration of water quality indicators, TP, TN, CODCrand Chla, abnormally rose during June to August. The roots causing the water quality deterioration are as following： compared with the same period of the last year, the precipitation increased by 81% during June to August in 2017, and it is the highest since 1999. Because of the abnormal precipitation, the pollution loads of TN, TP carried by Baoxiang River, Panlong River and Jinzhi River which arethe main inflows of Waihai increased by 50% and 59%, respectively, directly leading to the water deterioration of the north of Waihai. In addition, the combined sewage interception system was overflow during the rainstorm,leading to the low collection rate of waste water treatment plants（ WWTPs）. Compared with the dry season, the average influent concentration of CODCr, TN, TP of the WWTPs of No. 2, No. 3, No. 4 and No. 9 decreased by15%, 15% and 20% in rainy season, and the average influent concentration of CODCr, TN, TP of the WWTPs of No. 10 decreased by 16%,19% and 8%, respectively. Meanwhile, compared with the year of 2016, the water supply by Niulanjiang water transfer project decreased by 50%, the concentration of NH3-N, TP, TN increased by75. 2%, 51. 1%, 40. 2%, and therefore the effect of water quality improvement was reduced. Four strategies to improve the water quality of Waihai of Dianchi Lake were proposed, including improving the sewage collection system and enhancing the efficiency of wastewater collection by advancing the check of pollution interception system; improving the regulation of the combined sewage by optimizing the operation of the built storage pools;improving the purifying rate of sewage treatment plant by optimizing operation, enhancing supervision and joint operation in rainy season; improving the environment efficiency of water supplement project by enhancing the protection and governance of water source area of Niulanjiang River.