Bio-sorption Activated Media for Nitrogen Removal In a Rapid Infiltration Basin – Monitoring Project
The purpose of this report is to present background information for the project, data collected, analysis of data, and conclusions for the fate of nitrogen in a stormwater pond modified to discharge reclaimed water and stormwater to the ground. Funding was made possible for this project from the State Department of Environmental Protection under the FY 16-17 general appropriations act in partnership with the St John’s River Water Management District and the City of Deland.
The Bent Oak City of DeLand pond (see Appendix A for the Environmental Resource Permit #76187-5) was increased in size and permitted in March of 2016 so that it could function to discharge both excess reclaimed water and excess stormwater to the ground. It was called in the permit a reclaimed water storage and recovery modification. Because of the discharge of treated sewage, it can be referred to as a rapid infiltration basin (RIB). However, it is used for the disposal of both reclaimed water and excess stormwater. The RIB was again modified in the fall of 2016 for additional removal of nitrogen and phosphorus using Bio-sorption Activated Media (BAM) to determine if additional nitrogen can be removed. The information in this report is used to evaluate the effectiveness in the removal of nitrogen and phosphorus and to supply technical data to support the removal when BAM is used.
Two areas within the northern part of the Deland RIB were divided into two RIBs so that one RIB had two feet of BAM added to the bottom and the other RIB did not have BAM and is called the Control RIB. The Control RIB soils had about 2% clay with sand. This type of soil is believed to remove nitrogen and phosphorus, as opposed to sand which produces minor removal. Thus, it was chosen to be compared to BAM. Both the BAM RIB and the Control RIB were dosed with the same water. For two months at the end of 2016, input flow volume monitoring was conducted to balance unit volume of input flow (gallons per acre per day) to the two RIBs. Lysimeters were installed two feet under the BAM in the BAM RIB as well as two feet under the Control RIB. From January 2017 through the end of August 2017 loading was done using reclaimed water; some of which included river water augmentation. In September, Hurricane Irma provided excess stormwater to load the RIBS. Thus, two loading events and water samples from the six lysimeters were obtained to document water quality conditions during this time. In January and February 2018, loading of the RIBS continued with reclaimed water and this time in a high-water table condition. The high-water table was caused by the rain from Hurricane Irma. Thus, a total of 12 loading events of the RIBS were completed. Ten (10) events were monitored using reclaimed water from the DeLand Water Reclamation Facility (WRF) and two (2) events using excess stormwater from Hurricane Irma. City of DeLand and University of Central Florida Bio-sorption Activated Media in DeLand RIB 2.
The results show increased removal of nitrogen and phosphorus when using BAM versus the removal using on-site Taveras soil. The on-site soil is expected to remove nitrogen because of a low infiltration rate (½ - 1 inch/hr.) and the high clay composition. Natural soils normally are not consistent in clay content and thus removal is not consistent across an area. It should be noted that normally the soils beneath a RIB are primarily sand and thus little removal of nitrogen is expected.
The BAM is mixed to provide consistency in the percentage of constituents. Thus, removal across an area for nitrate and nitrite species (NOx) should be relatively more consistent than in natural soils and greater using BAM. The BAM was not formulated to remove organic and ammonia species of nitrogen but can be if needed. The history of reclaimed water quality for the Deland Water Reclamation Facility showed a high percentage of nitrates relative to total nitrogen. For this report, the term nitrate will be used as most of the reported NOx is in the form of nitrates. This also recognizes that nitrite rapidly go to nitrate in surface and surficial aquifers.
Comparisons based on measurements below detection and average removal are summarized as: Loading with Reclaimed Water: Ten loading events were sampled. There was a total of 30 lysimeter samples under the BAM RIB and 29 under the Control RIB. There was one lysimeter in the Control RIB that did not yield sufficient volume of water for analysis. For nitrate measures less than detection, the percent removal was calculated based on half the detection limit. Loading with Excess Stormwater: There were 6 lysimeter samples per RIB. The detection limit for nitrates was lowered resulting in no exceedance. Using both the excess reclaimed and excess stormwater loading, and weighting the removals by the number of samples, the removal of nitrate was 85% in the BAM RIB and 49% in the Control RIB. City of DeLand and University of Central Florida Bio-sorption Activated Media in DeLand RIB 3.
Total phosphorus removal was also calculated when loading with reclaimed as 66% and 37% for the BAM RIB and the Control RIB respectively. Other water quality measures are also listed in the report and include pH, turbidity, conductivity, chlorides, fecal coliforms, TKN, and total nitrogen. For fecal coliforms, there were 36 measurements for each of the Control and BAM lysimeters for all loading water and includes the blended river, reclaimed and stormwater. There were five measured values that were too numerous to count in the Control and none in the BAM lysimeters. The average fecal coliforms were 31 and 609 CFU/100 ml in the BAM and Control lysimeters respectively.
The nitrate removal was further supported using microbial assessment using DNA technologies. The populations of microbiological organisms demonstrated that the BAM RIB provided an environment for the cultivation of more of the appropriate bacteria compared to the Control RIB. The Control RIB itself provided potential for removal, presumably because of the 2-4% clay content, but the organisms were not as great in number and the removal was less. The micro biological analysis yielded information regarding the use of 2 feet of media as an appropriate depth and location for which the greater population were established. Further, the quantity of bacteria population can be closely related to the increased microbiological activity and consequently improved nitrate removal. The physiochemical properties of the BAM and Control RIB soil, also affected nitrate removal through the encouragement or inhibition of microbial growth aiding or preventing the removal of nitrate by the bacteria.