科研之友
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摘要
Septic systems can be a major source of nitrogen (N) in shallow groundwater. We designed an in situ engineered drainfield with aerobic-anaerobic (sand-woodchips) and anaerobic (elemental sulfur-oyster shell) media to remove N in the vadose zone and reduce N transport to groundwater. Effluent was dispersed on top of the engineered drainfield (3.72 m(2) infiltrative surface) and then infiltrated through the aerobic-anaerobic and anaerobic media before reaching natural soil. Water samples were collected over 64 sampling events (May 2012-December 2013) from three parts of the drainfield: (i) a suction cup lysimeter installed at the sand-woodchips interface, (ii) a pipe after effluent passed through the aerobic-anaerobic media, and (iii) a tank containing anaerobic media. In the effluent, most of the total N (66 mg L-1) was present as NH4-N (88.8%), whereas at the sand-woodchips interface the dominant N form was NOx-N (31 mg L-1; 85% of total N). As the effluent passed through the aerobic-anaerobic media in the drainfield, heterotrophic denitrification reduced NOx-N to 5.4 mg L-1. In the tank containing anaerobic media, autotrophic denitrification, facilitated by elemental sulfur, further reduced NOx-N to 1 mg L-1. Overall, 90% of total added N was removed as the effluent passed through the aerobic-anaerobic and anaerobic media within the engineered drainfield. We conclude that the use of multiple electron donors from external media (sand-woodchips and elemental sulfur-oyster shell) was effective at removing N in the engineered drainfield and will reduce the risk of groundwater N contamination from septic systems in areas with shallow groundwater.
- 出版日期2016-12
