Pilot-scale Study On Denitrification Technology Of Shallow Groundwater In The Lakeside Of Lake Dianchi

The lakeside of defarming and reforestation is important for the non-point source pollution control at the Lake Dianchi basin. That area is very widely, its NO₃^--N pollution in shallow groundwater is prominent, with the characteristics of low C/N, changeable groundwater level, and fluctuant NO₃^--N concentration. Therefore, It is necessary to find an economic, reasonable, and site condition adaptive pollution control technology to reduce nitrogen pollution of Dianchi Lake from lakeside. In view of the engineering measures solving this problem, we conducted a pilot-scale study on the basis of small-scale model experiment to confirm the feasibility of this technology, and to determine the design parameters guiding for the large-scale application in the future. The mainly results are as follows:Both the adding carbon source system （ACSS） and the adding sulfur source system （ASSS） were effective to purify shallow groundwater with low C/N, changeable groundwater level, and fluctuant NO₃^--N concentration. And the ASSS had a better denitrification efficiency than ACSS. Denitrification mainly occurs in the reaction pool. It can reduce NO₃^--N to a very low levels （0.08～2.30 mg/L） under the low influent concentration of NO₃^--N （0.95～7.67 mg/L）. When the average volume loading was 0.7±0.4 g/m3/d （ASSS） and 0.6±0.3 g/m3/d （ACSS） respectively, the average removal efficiency of two systems was 93.1±12.7% （ASSS） and 79.0±16.4%（ACSS） respectively. And in this case, the effluent quality of ASSS and ACSS can achieved the groundwater quality standard I class and II class, respectively. Otherwise, under the high influent concentration of NO₃^-N （9.63～26.45 mg/L）, the average volume loading was 2.1±0.7 g/m3/d （ASSS） and 1.6±0.6 g/m3/d （ACSS） respectively, and the average removal efficiency was 81.8±5.9%（ASSS） and 47.1±10.9%（ACSS） respectively. Not only to NO₃^--N, but the reaction pool also had removal efficiency to TN, NH4+-N and NO2--N. Among them, the removal rate of NO2--N decreased with the decrease of NO₃^--N removal rate. Significant negative effects were not observed in both of the systems. Specifically, the problems, including pH reducing, sulfide and sulfate accumulation had not found in the effluent water of ASSS, and the problem of COD rising had not found in the effluent water of ACSS. The restoration pool performed well in advanced water purification and recovery of water ecological function, but its sediment could released a small amount of TP into the water, and COD concentration increased at the late stage in the restoration pool due to the decomposition of plant residues.Groundwater is an important part of water resources, its repair study is of great significance for the sustainable utilization of water resources. This test has imitated the site condition of shallow groundwater in the defarming and reforestation lakeside of lake Dianchi, carried on the pilot-scale study of denitrification technology, and obtained a good benefit. Made a beneficial exploration of shallow groundwater nitrogen and phosphorus pollution control.