Premium
High Removal of Effluent‐borne Nitrogen with Multiple External Electron Donors in the Engineered Drainfield of an Advanced Septic System
Author(s) -
De Mriganka,
Toor Gurpal S.
Publication year - 2016
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2016.06.0215
Subject(s) - effluent , anaerobic exercise , denitrification , suction cup , woodchips , chemistry , environmental chemistry , pulp and paper industry , environmental science , nitrogen , environmental engineering , biology , physiology , organic chemistry , fishery , engineering
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 NH 4 –N (88.8%), whereas at the sand–woodchips interface the dominant N form was NO x –N (31 mg L −1 ; 85% of total N). As the effluent passed through the aerobic–anaerobic media in the drainfield, heterotrophic denitrification reduced NO x –N to 5.4 mg L −1 . In the tank containing anaerobic media, autotrophic denitrification, facilitated by elemental sulfur, further reduced NO x –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. Core Ideas An in situ advanced septic system drainfield was designed to attenuate N. More than 90% of total N was removed within the drainfield. Heterotrophic denitrification in the drainfield removed ∼84% of total N. Autotrophic denitrification in the drainfield removed additional ∼6% of total N. Engineered drainfield was effective at preventing groundwater contamination.