Implementation of Drying-Rewetting Cycles in Woodchip Bioreactors at Ground Temperature
High levels of nitrogen are present in Midwest agricultural fields due to use of fertilizer, and mineralization of soil organic matter. These fields connect to the Gulf of Mexico via the Mississippi River. Excess nitrogen in a saltwater body causes bacteria to increase their activity leading to hypoxic conditions that threaten wildlife. Bioreactors are a method for nitrate removal in water runoff from agricultural fields that involves the routing of tile drain flows through a buried trench of biomaterial. Microorganisms in bioreactors convert the nitrate to nitrogen gas to be released into the atmosphere through a process called denitrification. They can function under anaerobic conditions of a saturated underground bioreactor; however, this experiment will explore the effects on microorganism activity after introducing weekly 24 hr cycles of aeration. Three types of wood chips will be tested in a column experiment at ground temperature (10o C). Wood chips were chosen as the biomaterial because they have high carbon contents which microorganisms in bioreactors need to function. There will be two columns of each type that will be drained for a 24 hr period each week and two columns of each type receiving continuous water flow for controls. The nitrate and nitrous oxide concentrations in exit flow will be compared to the concentrations entering to determine the reduction capabilities of the woodchips. The expected outcome of this research is that introducing drying-rewetting cycles (DRW) to bioreactors at 10o C will increase nitrate removal rates above the levels occurring during continuous flow.