# The Use of Chemical Sensors to Monitor Odour Emissions at Municipal Waste Biogas Plants
## 3 Results and Discussion
(**b**) Odour activity values (based on toluene) and odour concentration at individual measurement points: 1, inside the waste storage plant; 2, mixed waste storage; 3, selectively collected waste storage; 4, mechanical treatment; 5, fermentation preparation; 6, oxygen stabilization; 7, technological wastewater pumping station; and 8, biofilter. (**c**) Range of odour activity values (based on toluene, styrene, and phenol). odour concentration than at other points of technological line. The general trend for this biogas plant was the highest OAV determined for VOCs. The larger the OAV, the more likely that compound would contribute to the overall odour of a complex odour mixture [18]. Figure 5: _Cont_. At the plant in Promnik, the sources of the highest VOC concentrations were waste storage inside the processing building (3.01 ppm), technological wastewater pumping station (2.92 ppm), and digestate dewatering (3.39 ppm). In the case of this biogas plant, there was no selective collection of biodegradable fractions in the serviced area. The fermentation process at the plant in Promnik is carried out in chambers with an automatic loading and unloading system. The highest result of ammonia concentration was obtained in the pumping station of technological wastewater (43 ppm). It was related to the decomposition processes taking place in wastewater and may be due to the faulty pumping station or a too-long storage time. In this case, the effluent comes from both the fermentation chambers and the digestate aerobic stabilization chamber. A high concentration of ammonia was also noted at the point of digestate aerobic stabilization (the second degree of the process) provided under a roofed shelter (7 ppm). Moreover, at the biogas plant in Promnik, all processes in the halls are carried out with closed gates with full-encapsulation, which undoubtedly increases the level of odorant concentrations inside the buildings and minimizes the nuisance outside. The general trend for this biogas plant was the highest OAV determined for VOCs. Analyzing Figure 5b,c, it can be observed that the OAV-VOCs were at a similar level at individual measurement points (ranging from 2.67 to 72.13, depending on the dominant component). A similar level of odor concentration was also observed at individual points of the technological line. The exception was the technological wastewater pumping station, where the highest odour concentration (187 ou/m\({}^{3}\)) and the highest odour concentration (187 ou/m\({}^{3}\)) are the highest odour concentration (187 ou/m\({}^{3}\)). The highest odour concentration (187 ou/m\({}^{3}\)) is the highest odour concentration (187 ou/m\({}^{3}\)). OAV-NH\({}_{3}\) (8.27) were recorded. In this case ammonia was more responsible for the odour concentration than at other measuring points. Figure 6: Cont. At the biogas plant located in Wolka Rokicka, the source of the highest VOC concentration was, as in the case of the biogas plant in Biala Podlaska, the aerobic stabilization of the digestate (30.58 ppm). However here, in contrast to the biogas plant in Biala Podlaska, the feedstock for the fermentation process is a biodegradable fraction separated mechanically from the mixed waste stream. In the case of the analyzed biogas plant, similarly to the one in Promnik, there is no selective collection of biodegradable fractions in the serviced area. The fermentation process at the plant in Wolka Rokicka is carried out in chambers without an automatic loading and unloading system. Moreover, no digestate dewatering is implemented there. After the fermentation process is completed, the digestate is followed by one-stage oxygen stabilization in prisms located at the technological field. The source of the highest ammonia concentration at this biogas plant was the wastewater pumping station (25 ppm). In this case, wastewater comes mainly from the processing building where the first degree of digestate oxygen stabilization is carried out.