# Neutralization of Toxic Malodorous Gases from Cattle Slurry
## 3 Results
### Deodorization Effect of Cattle Slurry by Microorganisms  
In this study, the scale-up of the slurry deodorization process using selected bacterial strains was conducted. The experiments included increasing the scale from flask culture to bioreactor in lab scale (2000 cm\({}^{3}\) of slurry). The bacteria were used in experiments both individually and as a bacterial consortium. Among six strains of _Bacillus_ and _Pseudomonas_ bacteria, those with the highest ammonia and hydrogen sulfide reduction were selected and a bacterial consortium was prepared. The main conditions of the experiment were chosen based on previous research. These studies were concerned primarily with the inoculum size, deodorization time, mixing, and temperature (limiting stress factors for microorganisms). The criterion for selecting the conditions for the experiment was to obtain the highest possible reduction of ammonia and hydrogen sulfide in the lowest possible time gradient. Verification of the effectiveness of odorous compound reduction from slurry using selected microorganisms and a bacterial consortium was carried out on reactors with a working volume of 2000 cm\({}^{3}\) each. Depending on the experiment, the substrate was aerated during the process by mixing the research material (200 rpm). The CS without added microorganisms was the control sample. The studies indicate that the primary malodorous gases released from the slurry were ammonia and hydrogen sulfide. As shown in Figure 2, the ammonia concentration reduced over time in CS during the deodorization process. The final NH\({}_{3}\) content at the end of the process (10 days) was 38 ppm (\"control\" in Figure 2). The addition of selected microorganisms into the slurry substantially reduced the ammonia concentration. The results showed that for _Bacillus_ bacteria, strains KKP 3899, KKP 3901, and KKP 3903 had a strong ability to remove ammonia. In our study, the highest ammonia removal rate was reported on Day 2 of the process. As shown in Figure 2 and Table 4, the KKP 3899, KKP 3901, and KKP 3903 strains showed NH\({}_{3}\) removal efficiencies of 43% (148-56 ppm), 34% (148-65 ppm), and 51% (148-48 ppm), respectively, under the closed system at ambient temperature 24 \({}^{\circ}\)C (R1-reduction compared to the control sample). \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Microorganisms**} & \multicolumn{2}{c}{**The Maximal Percentage of Volatile**} \\  & \multicolumn{2}{c}{**Compound Reduction [\%] *} \\ \cline{2-3}  & **Ammonia** & **Hydrogen Sulfide** \\ \hline _Bacillus subtilis_ KKP 3899 & 18.2 & 40.0 \\ _Bacillus subtilis_ KKP 3901 & 87.1 & 99.4 \\ _Bacillus subtilis_ KKP3903 & 8.3 & 66.7 \\ _Pseudomonas fluorescens_ KKP 3909 & 94.0 & 99.3 \\ _Pseudomonas fluorescens_ KKP 3910 & 28.6 & 83.3 \\ _Pseudomonas_ sp. KKP 3911 & 23.1 & 77.8 \\ \hline \hline \end{tabular}  
* reduction (%) compared to the initial sample.  
\end{table} 
Table 3: Reduction of volatile compounds in cultures cultivated on the CS after 72 h.  
When converting the ammonia concentration to the absolute reduction value compared to the initial sample (R2-reduction), the noted values were 62%, 56%, and 68%, respectively. After 10 days of the deodorization process, ammonia reduction for _Bacillus_ bacteria was 95% (for KKP 3899), 91% (for KKP 3901), and 99% (for KKP 9303), compared to the initial sample (R2-reduction). In the case of the _Pseudomonas_ genus, the highest decrease in ammonia emission was also observed on Day 2 of the process. The decrease in ammonia concentration for _Pseudomonas fluorescens_ KKP 3909 and KKP 3910 was 40% and 37%, respectively, while for _Pseudomonas_ sp. (KKP 3911) it was only 16%, compared to the control sample (R1-reduction). The ammonia content was noted then at the level of: 59 ppm, 62 ppm, and 83 ppm, respectively, while for the control sample, it was 98 ppm. The final residual NH\({}_{3}\) concentration in the reactor for _Pseudomonas_ bacteria ranged from 0 to 20 ppm, thereby achieving an 86-100% removal efficiency (R2-reduction) within 10 days.