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Optimization of the Design of Constructed Wetlands Used for the Treatment of Municipal Wastewater in Semi-Arid Regions of the United States and the WorldEPA Grant Number: U915926
Title: Optimization of the Design of Constructed Wetlands Used for the Treatment of Municipal Wastewater in Semi-Arid Regions of the United States and the World
Investigators: Mimbela, Luz-Elena Y.
Institution: New Mexico State University - Main Campus
EPA Project Officer: Graham, Karen
Project Period: January 1, 2001 through January 1, 2004
Project Amount: $84,130
RFA: Minority Academic Institutions (MAI) Fellowships for Graduate Environmental Study (2001) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Engineering and Environmental Chemistry , Fellowship - Engineering
The objective of this research project is to develop better design procedures to improve the performance of wetlands wastewater treatment systems with an emphasis on nitrogen removal in semiarid regions of the United States and the world. Wetlands wastewater treatment systems can be either free water-surface or vegetated submerged bed (VSB) systems. VSB-constructed wetlands systems use a bed of soil, gravel, or rock as a substrate or media for growth of rooted, emergent wetland plants such as cattails (Typha) or bulrush (Scirpus). Wastewater flows horizontally through the bed media contacting a mixture of aerobic, anaerobic, and facultative microbes living in association with the substrate and plant roots (Kadlec and Knight, 1996).
There are most likely more than 10,000 operating systems in the United States covering every region and ranging in size from small home systems to large municipal facilities with daily flows of more than 3 million gallons (Zachritz, et al., 1998). In recent years, many of these systems must not only meet standards for 5-day biological oxygen demand (BOD5) and total suspended solids (TSS), which are typical secondary treatment standards, but are required to meet new, more stringent discharge standards for nutrients such as phosphorus, ammonia, nitrate, and total nitrogen (TN).
In 1998, New Mexico had more than 40 operating wetland systems of various designs, most of which were constructed in the 5 years prior to 1998. Most of these facilities do not discharge to surface waters, but to groundwater, and they are permitted by the New Mexico Environment Department’s Groundwater Bureau. Recent studies on VSB wetland systems operating in New Mexico indicated that many of these systems may not meet performance expectations for BOD5, TSS, ammonia, nitrate, and TN (Zachritz, et al., 1998). This research project will utilize data gathered from a previous experiment conducted at a VSB wetlands system located in Mesquite, New Mexico. The VSB wetlands at Mesquite treat domestic wastewater from a septic tank effluent pumping system and never complied with the groundwater discharge permit limitation of 14 mg/L TN since its construction in 1996. The experiment conducted on the Mesquite VSB wetlands consisted of installing airlift pumps to aerate the system and monitor influent. Effluent was monitored along the length of the bed parameters (i.e., ammonia, nitrate, total Kjeldahl nitrogen, BOD5, TSS, sulfate, dissolved oxygen, pH, temperature, oxidation reduction potential, conductivity, and sulfide).
The aeration of the Mesquite VSB wetlands resulted in the successful reduction of TN below the 14 mg/L groundwater discharge permit limitation in the test cell. These design procedures can be used to design wetland systems in the semiarid regions of the United States and the world that would remove nitrogen below the required permit limitation.