Nitrate is a health hazard in drinking water. We are developing a simple flow-through membrane electro-bioreactor in which immobilized enzymes catalyze the destruction of nitrate ion into harmless nitrogen gas. Three denitrifying enzymes (Nitrate Reductase, Nitrite Reductase and Nitrous Oxide Reductase) catalyze the reductions. They will be immobilized inside the pores of microporous electrically conductive membranes which serve as electrodes and as matrixes. These enzyme catalysts will be "wired" to the cathode with polymer hydrogels capable of transferring electrons from the cathode to the enzymes. In our bioreactor, nitrate solution is pumped through a sandwich of three microporous membranes: anode, insulating filter, and enzyme-immobilized cathode. A DC source powers the electrochemical reduction. During Phase I, we will prepare a microporous, electrically conductive membrane so it can receive enzymes and "wires"; prepare and ~y the enzymes; immobilize them on the membrane without denaturing; construct a filter holder with DC voltage; evaluate the bioreactor by measuring the change in nitrite concentration in the effluent stream as functions of: voltage, initial nitrate concentration, convective flux. In Phase II, we will lower the cost of the enzymes, improve its robustness through protein engineering, and control fouling.National Institute of Environmental Health Sciences (NIEHS)
