## 2 Materials and Methods
### Lab-Scale Odor Reduction Test  
A lab-scale experiment was conducted to reduce the NH\({}_{3}\) concentration based on surfactant foam spraying technology. This study was performed in a reactor (Styrofoam box with dimensions: length, 60 cm; width, 60 cm; height, 23 cm) containing 3 kg of NH\({}_{3}\)-contaminated soil (Figure S1), which was prepared by mixing the NH\({}_{3}\) solution with the soil (10 mL of NH\({}_{3}\)-solution/kg soil). Experiments were also conducted using swine manure. For each of the applied conditions (soil and manure), three different experiments were conducted: control test (only NH\({}_{3}\)-contaminated soil/ manure, no treatment), foam alone (surfactant foam without bacteria), and bio-foam (surfactant foam with bacteria). All lab-scale experiments were performed under two different conditions: one in the open reactor and the other in the closed reactor. A closed reactor was prepared by covering the reactor's lid. In addition to the soil in the reactor, experiments with swine manure in the reactor were also conducted in an open condition, simulating the conditions of real swine facilities. The surfactant foam (using optimal concentrations of AOS and gelatin) was then sprayed inside the box containing NH\({}_{3}\)-contaminated soil/ swine manure.  
A round-bottom flask with three necks was used to generate foam. The reagent solution was supplied from one of the necks of the flask, another neck was used for air, and the third was used for releasing the surfactant foam. The third neck was directed onto the soil/ manure stored in the reactor (15 cm above the reactor). The surfactant foam was generated by injecting air into the flask containing the foaming solution via a capillary tube tightened with a cork [25; 26]. The liquid and air flow rates were maintained at 10 and 1000 mL/min, respectively. To prepare the bio-foam, the surfactant solution was mixed with the bacterial solution in 1 (bacteria): 9 (surfactant) ratio before foam generation (the concentration of surfactant and stabilizer was constantly maintained as above). The foam quality was maintained at 99% by fixing a constant liquid and air flow rate throughout the experiment.  
Sampling was performed at five different sampling points in the reactor (four corners and the center) to measure the concentrations of malodorous gases. The gas concentration was measured using a Gastec pump and Gastec tubes (Gastec, Japan) as previously described [27; 28; 29; 30; 31; 32; 33]. Gases were sampled just above the foam after being foam-sprayed. Initially, three different gases, NH\({}_{3}\), H\({}_{2}\)S, and mercaptans (R-SH), were measured. The concentrations of H\({}_{2}\)S and R-SH were considerably low in the swine manure. In addition, the background concentration of gases emitted from the contaminated soil or manure was periodically measured during the experimental period because a small fraction of gases that were initially released before foam spraying were dispersed over the experimental area, which spread from the control box during the entire experimental period.  
A cost comparison analysis was performed by comparing the current experiment with the literature related to foam application for odor control. The estimated cost was compared based on the recipes used to prepare the foaming reagent for odor reduction. The cost of the preparation of a 1 L solution was used in the calculations. The practical assumptions were similar to those in our experimental design; that is, a study reactor with 60 cm length, 60 cm breadth, and 23 cm height was used. (82,800 cm\({}^{3}\) volume).