Performance of experimental bioreactors developed for removing nitrate from nursery runoff water

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

Submitted to: Southern Nursery Association Research Conference
Publication Type: Proceedings
Publication Acceptance Date: 8/8/2011
Publication Date: 9/1/2011
Citation: Wilson, C., Albano, J.P. 2011. Performance of experimental bioreactors developed for removing nitrate from nursery runoff water. Southern Nursery Association Research Conference. 53:524-526.

Interpretive Summary: Nutrient enrichment of public surface water bodies throughout the United States is becoming a major issue as the US Environmental Protection Agency (EPA) and state governments begin developing and enforcing Total Maximum Daily Loads (TMDLs) for nutrient-impaired water bodies. Previous work has indicated that significant amounts of nutrients can be leached from pots and production areas during normal irrigation and fertigation operations. Nitrate concentrations in nursery runoff or drainage water reported by others has ranged from 1.6 ppm to 304 ppm. In a zero-discharge situation, nutrient enrichment is not likely an issue. However, not all nurseries have the drainage infrastructure to insure zero-discharge conditions. For those nurseries, nutrient enrichment of drainage water can be reduced by only applying what the plant needs, careful irrigation management, and/or by employing runoff retention and remediation techniques. Constructed wetlands and retention ponds are effective nutrient removal and retention strategies for nurseries with the capacity to dedicate land area to non-production uses. However, this may not be practical, for smaller nurseries and those in areas where land is limited or too expensive. For those situations, the ideal water treatment system would be one that could be incorporated into the nursery production landscape without sacrificing production area. This system could collect and treat drainage water close to the individual production areas, rather than on a whole nursery scale. It could be constructed beneath roadways, plant holding areas, or other areas used for production purposes.

Technical Abstract: A bacterial-based bioreactor containing Kaldness media as a substrate for bacteria to grow on was established at a commercial nursery. Data from approximately 90 sampling events are reported. Results indicate that the system, when properly managed, offers much potential for removing nitrate from surface water quickly and with great efficiency. Inflow nitrate concentrations ranged from 0.7 to 1512 mg/L, and outflow concentrations ranged from undetectable-1012 mg/L. Percentage nitrate-N removal during each sampling event is shown in Figure 1. Routine removal of greater than 90% of the nitrate load was achievable when the system was operating under optimal conditions. The depression in removal efficiency seen from months January through April were due to air pockets developing in the molasses delivery line, resulting in insufficient carbon supply for the microflora. However, once this problem was discovered and management improved, greater than 95% nitrate removal has been consistently achieved. The average amount of nitrate-N pumped into the bioreactor systems was 2.3 kg during each 24-hr period. Thus, conceptually this system seems to offer much promise for removing nitrate efficiently and quickly from drainage water using very little actual production space.