Potential application of a bioreactor for removing nitrate from nursery runoff

Authors: WILSON, CHRIS - University Of Florida; Albano, Joseph

Submitted to: Southern Nursery Association Research Conference
Publication Type: Proceedings
Publication Acceptance Date: 8/10/2011
Publication Date: 9/1/2011
Citation: Wilson, C., Albano, J.P. 2011. Potential application of a bioreactor for removing nitrate from nursery runoff. Southern Nursery Association Research Conference. 52:147-149.

Interpretive Summary: Significant amounts of nitrate nitrogen may leave nursery production sites in runoff water generated during normal irrigation events. With increased pressures from state and federal regulatory agencies, nursery managers will need to reduce nutrient export from production areas to natural water bodies. Results from these studies indicate that a flow-through microbial-based bioremediation system may potentially be highly efficient at removing nitrate from drainage water within a short period of time. This type of system may be a viable option for space-limited nurseries faced with future regulation and associated financial obligations.

Technical Abstract: A bacterial-based bioreactor containing Kaldness media as a substrate for bacteria to grow on was established at a commercial nursery. During the media loading stage, redox potential was poised between +100 and +300 mv, indicating relatively aerobic conditions. Redox potential was highly variable during the denitrifier selection stage, ranging from -500 to +300 mV. Once flows were reestablished with the sucrose gravity drip system, redox stabilized between -100 to -300 mV, conditions suitable for denitrification reactions. Water pH generally ranged from 5 to 7 throughout the monitored period. During the flow-through nitrate monitoring period, removal of 85 percent of the nitrate loads entering the systems were consistently achieved when all pumps and carbon-dosing equipment were functioning properly, indicating much potential for this system. On several occasions, 100% of the nitrate load was removed during the monitored period. The reduced removal efficiencies during other periods may have resulted from several factors, including: nitrate levels exceeding the carbon-dosing levels, and inaccuracies in delivery of the sucrose using the gravity drip system due to clogging and changes in viscosity associated with temperature changes. Several operating and maintenance issues were identified that must be addressed before further enlarging the scale of the system. Because these systems will be established in, or pump from, the lowest points of the production areas, concessions must be made for reducing the inflow of sediments into the system. These sediments may clog the flow paths through the media and cause excessive wear on pumps, limiting the reliability of the bioreactors. These studies have provided valuable information needed for designing and operating these potential bioremediation systems. Current work is focused on further scaling up the system for evaluation on-site at local nurseries and adding phosphorus removal modules. In addition, research is also evaluating the possible effects of fungicides used in pest control programs on the nitrate removal ability of the microflora.