Nitrate Removal From Nursery Runoff Water Using a Novel Microbial-Based Bioremediation System

Nitrate losses in surface runoff water from nursery production areas can be significant.  This study evaluated the potential use of microbial-based (denitrification), flow-through bioreactors for their nitrate-remediation ability.  Duplicate bioreactor systems were constructed at a local foliage plant nursery.  Each bioreactor system consisted of four 242 L tanks with connections alternating between bottom and top.  Each tank was filled with approximately 113 L of Kaldness media to provide surface area for attachment of native microflora.  Molasses was supplied as a carbon source for denitrification and water flow rates through the systems ranged from 5 to 16 L/min. during tests.  Automatic water samplers were used to collect composite samples every 15 minutes from both the inflow and the exit flow water.  Results from events where known amounts of potassium nitrate were injected into the systems indicate consistent removal of greater than 95% of the nitrate flowing into the systems.  Accumulation of ammoniacal and nitrite nitrogen did not occur; indicating that the nitrate-nitrogen was removed from the water, and not simply transformed into another water-soluble species.  Occasions where removal rates were less than 95% were usually traced to faulty delivery of the carbon source.  Results indicate that microbial-based bioremediation systems may be a useful tool for helping nursery managers meet stringent nitrogen water quality regulations, especially at nurseries with limited space for expansion of water retention facilities.