Nitrogen Cycling in the Lagoons and Artificial Wetlands Treating the Municipal Wastewater of Logan, Utah.
Location
ECC 203
Event Website
http://water.usu.edu/
Start Date
4-5-2007 1:30 PM
End Date
4-5-2007 1:50 PM
Description
The City of Logan uses a multi-faceted, biological approach to wastewater treatment for handling of municipal wastes from Logan and the surrounding communities. The facultative lagoon system is unique because of its large size and long retention times. Over the last five years an engineered wetland has been added to provide additional treatment and nutrient reduction before water is released. Also important to this treatment program is the use of effluent water for irrigation of adjacent agricultural lands. We have been investigating the nitrogen dynamics in these linked systems with a focus on nitrification. We found that lagoon water samples generally had potential nitrification rates near or below the detection limits, much too low for effective treatment of ammonia levels in the lagoons even considering the long retention times available. Several water samples revealed nitrate accumulation and these were associated with transient nitrification. Several factors may be contributing to the weak nitrifying activity in the lagoons. These include 1) low oxygen availability 2) low surface area available for attached growth of nitrifying bacteria 3) fluctuating and transiently low NH4+ availability causing competition for NH4+ and 4) high and fluctuating pH. We observed that low NH4+ levels in lagoon cells are not due primarily from N loss from the water but rather N is being transferred from inorganic to organic forms. We believe that available NH4+ is depleted in the primary cells by the assimilation and growth of algae and heterotrophic bacteria. This starves the nitrifiers early in the process and they do not become reestablished in the lagoon system. Soil samples from the wetland root-zones showed evidence of coupled nitrification and denitrification but these processes are spatially localized and may not be sufficient to reduce overall N contents. Denitrification enzyme assays indicated that the root-zones of hard bulrushes have higher rates of N transformations overall. Efforts to enhance nitrification earlier in the lagoon system will be crucial in promoting coupled nitrification-denitrification and therefore minimizing nitrogen release to surface waters.
Nitrogen Cycling in the Lagoons and Artificial Wetlands Treating the Municipal Wastewater of Logan, Utah.
ECC 203
The City of Logan uses a multi-faceted, biological approach to wastewater treatment for handling of municipal wastes from Logan and the surrounding communities. The facultative lagoon system is unique because of its large size and long retention times. Over the last five years an engineered wetland has been added to provide additional treatment and nutrient reduction before water is released. Also important to this treatment program is the use of effluent water for irrigation of adjacent agricultural lands. We have been investigating the nitrogen dynamics in these linked systems with a focus on nitrification. We found that lagoon water samples generally had potential nitrification rates near or below the detection limits, much too low for effective treatment of ammonia levels in the lagoons even considering the long retention times available. Several water samples revealed nitrate accumulation and these were associated with transient nitrification. Several factors may be contributing to the weak nitrifying activity in the lagoons. These include 1) low oxygen availability 2) low surface area available for attached growth of nitrifying bacteria 3) fluctuating and transiently low NH4+ availability causing competition for NH4+ and 4) high and fluctuating pH. We observed that low NH4+ levels in lagoon cells are not due primarily from N loss from the water but rather N is being transferred from inorganic to organic forms. We believe that available NH4+ is depleted in the primary cells by the assimilation and growth of algae and heterotrophic bacteria. This starves the nitrifiers early in the process and they do not become reestablished in the lagoon system. Soil samples from the wetland root-zones showed evidence of coupled nitrification and denitrification but these processes are spatially localized and may not be sufficient to reduce overall N contents. Denitrification enzyme assays indicated that the root-zones of hard bulrushes have higher rates of N transformations overall. Efforts to enhance nitrification earlier in the lagoon system will be crucial in promoting coupled nitrification-denitrification and therefore minimizing nitrogen release to surface waters.
https://digitalcommons.usu.edu/runoff/2007/AllAbstracts/21