# Neutralization of Toxic Malodorous Gases from Cattle Slurry
## 2 Materials and Methods
### Deodorization Experiments  
The experiments were performed in a laboratory installation, which consisted of three reactors, each with a working volume of 3000 cm\({}^{3}\). Each reactor was equipped with two spigots: for a blower connection, and exhaust air discharge (top of the cover). Reactors were filled with 2000 cm\({}^{3}\) of cattle slurry, onto which the selected microorganisms (individually or as mixed preparations of two strains in LB, BTL, Lodz, Poland) were added. The ratio between inoculum and sample volume was 1:20. All lab-scale experiments were performed in closed reactors. The deodorization process was carried out at a temperature of approx. 24 \({}^{\circ}\)C for 10 days. The pH of the slurry (i.e., 8.4) was not adjusted throughout the deodorization period.  
The reactor was placed on a magnetic stirrer with heating, thanks to which the entire sample was mixed for 2 min before each determination of NH\({}_{3}\) and H\({}_{2}\)S concentration in the exhaust air. Obtaining the set temperature in the reaction vessel was achieved through a heating plate of the magnetic stirrer. Depending on the experiment conducted, the substrate was aerated during the deodorization process, by continuous mixing of the research material (200 rpm). The deodorization process was carried out in an experimental set-up, shown in Figure 1. The studies were conducted in triplicate, using three reactors simultaneously for each experimental group.  
The deodorization efficiency of the preparations was evaluated by passing air through the reactors and measuring odorants in air generated by cattle slurry. To determine the concentrations of ammonia and hydrogen sulfide, the gas analyzer was connected to the spigot placed on the top of the chamber. The concentrations of volatile odorous compounds were determined by GfG Polytector G999 (GfG Gesellschaft fur Geratebau mbH, Dortmund, Germany), a portable gas detector with a pump, which can detect H\({}_{2}\)S gas within the range of 0-500 ppm and NH\({}_{3}\) within the range of 0-500 ppm.  
Figure 1: Experimental set-up: 1—Reactor chamber; 2—Gas detector with pump; 3—pH meter; 4—Valves; 5—Magnetic stirrer.  
The sampling was conducted at 0 h and was again recorded every 48 h for 10 days consecutively. The ammonia and hydrogen sulfide concentrations were recorded for each treatment, and the reduction was then calculated relative to the initial and control samples. The decrease in the concentration of volatile odorous compounds was calculated as  
1. the reduction R1 (%) compared to the control sample, according to the following formula: \[\text{R1}=100\%-(\text{C}\times 100\%/\text{C}_{\text{C}})\]  
where C is the concentration of investigated volatile odorous compound in the sample collected from the headspace of the chamber, and C\({}_{\text{C}}\) is the concentration of investigated volatile odorous compound in the sample collected from headspace in the control sample.
2. Here is the reduction R2 (%) compared to the initial sample, according to the following formula: \[\text{R2}=100\%-(\text{C}\times 100\%/\text{C}0)\]  
where C is the concentration of investigated volatile odorous compound collected from the headspace of the chamber, and C0 is the concentration of investigated volatile odorous compound in the sample collected from the headspace at the beginning of the deodorization process.