## 3 Results and Discussion
### Technological Factors
The air temperature should be indicated as the main environmental factor visible primarily in relation to \(\mathrm{c_{od}}\). The strength of the correlation relationship between the odour concentration and air temperature was determined by means of [PERSON]'s rank correlation coefficient. The choice of the applied coefficient results from the type of features, number of observations and shape of the relation. The correlation coefficient \(\mathrm{r_{ho}}\) for all measurements is \(\mathrm{r_{ho}}=0.306\) and the significance level \(\alpha=0.022\). The results obtained for the source d (digestate dewatering plant) were not used for calculations. The implementation of dewatering process varies significantly between plants and is largely influenced by the technological solutions used there. However, the influence of wind cannot be ignored. The greatest wind influence was observed in the case of F biogas plant for e source (oxygen stabilisation in the open air): in the first series \(\mathrm{v_{1}}=1.5\) m/s, \(\mathrm{c_{od}}=22\) ou/m\({}^{3}\); in the second series \(\mathrm{v_{2}}=2.3\) m/s, \(\mathrm{c_{od}}=11\) ou/m\({}^{3}\). The obtained relation (an increase in wind speed results in a decrease in odour concentration) is consistent with the results of tests carried out by [PERSON] et al. [44]. This impact should be taken into account during further testing. The obtained results of air temperature and humidity impact on odour emissions are in accordance with results presented by other authors; but it should be emphasised that the scope of the research reported in the literature has not allowed for unequivocal, forecastable and obvious assessment of the discussed dependencies. Thus, this paper has contributed significantly to the subject. Knowledge of the impact of various factors (meteorological, ambient and technical) on the odour emissions and nuisance of waste treatment plants will permit to apply corrective actions to minimise them. The conducted research also shows the impact of technological processes, operating regimentation and changes in waste properties. The variability of these factors can be observed on the basis of the results of VOC and NH\({}_{3}\) concentrations, changing between separate series. In most cases, the increase in VOC or NH\({}_{3}\) concentration is accompanied by an increase in \(\mathrm{c_{od}}\) (in five out of six installations--B, C, D, E and F--at all measuring points (E and F biogas plants)) or in most of them (Table 5). It demonstrates the effect of technological factors on the odour impact of biogas facilities. The influence of technological factors takes place in both the mechanical and biological parts of the installations. Especially at B and C biogas plants (in Tychy and Promnik), the impact of technological factors on the odour effect is significant (higher \(\mathrm{c_{od}}\) at higher VOC or NH\({}_{3}\) concentration), because in these cases the research was accompanied by small differences in air temperature and humidity between individual measurement series, so their influence needs to be omitted. The increase in VOC or NH\({}_{3}\) concentration is not always accompanied by an increase in \(\mathrm{c_{od}}\). In these cases, a dominant influence of atmospheric factors is observed (according to the previously presented relationships). It is particularly evident at A biogas plant (in Jarocin), especially at the measuring points in the mechanical part of the installation. In turn, the biological part of this plant (point f: oxygen stabilisation) shows the prevailing impact of technological factors over atmospheric agents in relation to odour emissions. The highest VOC concentrations are recorded in the plants of waste storage (7740 ppb), pre-treatment (6040 ppb and 5710 ppb) and digestate dewatering (6410 ppb) at B and C biogas plant (points a, b, c, d according to Table 6).