Electrolyzed water spray scrubber for removing ammonia from air

Ammonia (NH3) emissions from animal feeding operations (AFOs) are the source of a number of environmental issues. Wet spray scrubbers using non-acidic solutions might be a new approach for NH3 mitigation from AFOs. A lab-scale spray scrubber was built to clean 0.024 m3 s-1 of an NH3/air mixture with an average NH3 concentration of 20 ppmv. Three variables including contact time, nozzle type, and scrubbing solution were investigated to evaluate their effects on the ammonia removal efficiency of the scrubber. The contact times were set to 0.3, 0.6, and 0.9 s, which were achieved by changing the elevation of the spray nozzle. Two types of spray nozzles were studied. The nozzles had full-cone spray patterns with different spray angles and different droplet sizes. Reverse osmosis (RO) water and two types of electrolyzed water (50 mg L-1 of free available chlorine, FAC) with pH = 9.0 and pH = 6.5 were tested as scrubbing solutions. The parameters were evaluated in 54 experiments, which included 18 treatments with three replications, to determine the effectiveness of the treatments in scrubbing NH3 gas from air. The maximum removal efficiency of 56% was achieved with the narrow-angle nozzle, 0.9 s contact time, and electrolyzed water with pH = 6.5. Therefore, within the ranges studied, increasing the contact time, decreasing the pH of the electrolyzed water, and using the narrow-angle nozzle increased the efficiency of the scrubber. The RO water captured more of the NH3 in the form of total ammoniacal nitrogen (TAN) than did the EW, which may indicate that EW forms chloramines in the scrubbing process. TAN is a desirable by-product because it can be used as fertilizer. EW may need to be used at pH levels lower than 6.5 to maintain FAC/TAN mass ratios lower than 7.6 in order to avoid N2, Cl2, and NH3 gas losses from the scrubbing solution. © 2015 American Society of Agricultural and Biological Engineers.