ARS | Publication request: IMPROVED NITROGEN TREATMENT BY CONSTRUCTED WETLANDS RECEIVING PARTIALLY NITRIFIED SWINE WASTEWATER

Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 7, 2003
Publication Date: July 1, 2003
Citation: POACH, M.E., HUNT, P.G., VANOTTI, M.B., STONE, K.C., MATHENY, T.A., JOHNSON, M.H., SADLER, E.J. IMPROVED NITROGEN TREATMENT BY CONSTRUCTED WETLANDS RECEIVING PARTIALLY NITRIFIED SWINE WASTEWATER. ECOLOGICAL ENGINEERING. 2003. V. 20. P. 183-197.

Interpretive Summary: To reduce the nutrient load to the environment from current animal waste treatment, alternative forms of wastewater treatment are being examined. One promising treatment option is the use of constructed wetlands. Constructed wetlands are used because they can remove ammonia from wastewater through a two-step process. In step one, nitrification, they convert ammonia to nitrate. In step two, they convert the nitrate produced in step one to nitrogen gas. Constructed wetlands are generally limited by step one. We investigated how performing step one on wastewater prior to wetland application would affect nitrogen removal by constructed wetlands. Investigations were performed on a swine farm in North Carolina where constructed wetlands received both unaltered and partially nitrified wastewater. We found that bulrush wetlands were more effective, sometimes as high as 97%, in removal of nitrogen. Cattail wetlands were less effective even when nitrified water was added (less than 70% nitrogen removal). However, partial nitrification did lower to negligible levels the ammonia volatilization in the wetlands. These findings will assist engineers in the design and operation of more effective wetlands.

Technical Abstract: Constructed wetlands are an alternative option for animal waste treatment because they are low-cost, passive systems that provide effective nitrogen removal. In constructed wetlands receiving swine wastewater, nitrogen removal by denitrification is nitrate limited. The objective of this research was to determine the treatment potential of constructed wetlands receiving nitrified swine wastewater. Two parallel sets of constructed wetlands (3.6 x 67 meters) were loaded with swine wastewater from August 2000 through October 2001. From August 2000 through April 2001, wastewater applied to the wetland dominated by Scirpus was partially nitrified (10 to 100% nitrified). From July through October 2001, wastewater applied to the wetland dominated by Typha was partially nitrified (29 to 75% nitrified). The Scirpus wetland more effectively removed nitrogen (64 to 97% removal) than the Typha wetland (0 to 69% removal) regardless of the type of wastewater applied. However, full nitrification of wastewater should enhance wetland treatment performance because NOx-N in partially nitrified wastewater was completely removed in the first 14.4 square meters of both wetlands. Pre-wetland nitrification reduced ammonia volatilization from both wetlands.