Nitrogen Removal Efficiency Of The Carbon-Sulfur Coupling Surface Flow Constructed Wetland

The total nitrogen and nitrate removal efficieny of agricultural runoff was limited for its characteristics of the low C/N ratio, high nitrate proportion and organic carbon difficiency, and the water quality fluctuation of agricultural runoff further increased the difficulty to remove the total nitrogen. How economically and efficiently to remove the nitrogen from agricultural runoff is becoming one of difficult and attractive fieldAccording to the sulfur denitrification and plant-carbon denitrification process, Phragmites Australis carbon Packed Surface Flow Construct Wetland（PC-SFW） and Phragmites Australis Carbon-Sulfur Coupling Surface Flow Constructed Wetland（PS-SFW） were built to treatment of the agricultural runoff. The feasibility, nirogen removal efficieny and some influencing factors of PC-SFW and PS-SFW were studied extensively, and the results were as follows:1. The nitrogen removal efficiency of PC-SFW for long-term operation was as follows: Compared with control PSFW₀, obviously higher nitrate removal efficiency was observed in Phragmites Australis packed PSFW during 29-149 d operation. When the influent NO₃^--N and TN were 16.4±1 mg/L and 17.7±2 mg/L and the HRTs were 2d, 3d and 4d, the highest nitrogen removal efficiency was achieved under 4d HRT condition, and the NO₃^--N and TN removal efficiency in PSFW were 87.4±6% and 74.1±6%, which were 73.0% and 59.7% higher than those in PSFW₀. Slight higher denitrification efficiency was obtained in PSFW than that in PSFW₀ during 150-269 days operation. When the influent NO₃^--N and TN were 10.4±1 mg/L and 10.8±1 mg/L and the HRTs were 3d, 2d and 1d, the highest nitrogen removal efficiency was achieved under 3d HRT condition, and the NO₃^--N and TN removal efficiency in PSFW were 91.9±7% and 90.2±7%, which were 0.6% and 3.8% higher than those in PSFW₀. Slight lower denitrification efficiency was obtained in SFCW than that in SFCW0 during 270-334 d operation. When the influent NO₃^--N and TN were 5.7±0.4 mg/L and 7.2±0.8 mg/L and the HRT was 3d, the NO₃^--N and TN removal efficiency in PSFW were 88.6±10% and 82.5±7%,which were 6.0% and 5.3% lower than those of PSFW₀.2. The nitrogen removal efficiency of PS-SFW（granular sulfur was packed in the latter part of PS-SFW） for long-term operation was as follows: Under the low HRT（2d）condition, the nitrate and TN removal efficiency of PS-SFW were 62.1±2% and 62.2±5%,which was higher than those of PC-SFW, i.e.46.6±6% and 53±5%.When the HRT were high（3d, 4d）, the nitrate removal efficiency of of PS-SFW were 7.5±6%,79.2±10%,the TN removal efficiency were 63.8±6% and 62.2±5%, which was a slight lower than PC-SFW, i.e. 81±9%,87.4±6%（NO₃^--N） and 64.3±5%,74.1±6%（TN）. In general, there was not obvious difference between PC-SFW and PS-SFW under differrent HRT operation conditions.3. The ratio of sulfur to carbon（S/C） had a slight effect on the denitrification efficiency of PS-SFW, where the sulfur and soil were mixed and packed. Under the high HRT of 4d, the PS-SFW1/3.1（S/C was 1/3.1）, PS-SFW1/1.8（S/C was 1/1.8）NO₃^--N removal efficiency were 66.3±5%,90.5±4%, and TN removal were 55.5±5% and 75.4±5%.Under the low HRT（3,2days）, the PS-SFW1/3.1（S/C was 1/3.1）, PS-SFW1/1.8（S/C was 1/1.8）NO₃^--N removal efficiency were 66±10%,55.9±7%,Under different HRT operation conditions, the nitrogen removal efficiency in PS-SFW（ 1/1.8 S/C ratio） was higher than that in PS-SFW（1/3.1 S/C ratio）.