## 2 Materials and Methods
### Lab-Scale Equipment  
The laboratory component of the study was conducted using an automated bioreactor-fermentor equipped with a set of auxiliary sensors. The setup is based on the Yocell YC-JG reactor (Yocell Biotechnology, Qingdao, China) and includes a reactor vessel with a working volume of 11 L, made of borosilicate glass. The vessel is equipped with a controlled electromechanical stirrer featuring adjustable rotational speed, a pneumatic aeration system with adjustable aeration intensity, and a heating and cooling system through an external circuit. The setup was further equipped with a set of analytical sensors that correspond to those used in actual wastewater treatment facilities. These include the Hamilton VisiFerm DO sensor for dissolved oxygen (Hamilton Company, Reno, NV, USA), the Hamilton Polilyte Plus pH ARC sensor for pH measurement (Hamilton Company, Reno, NV, USA), the HACH A-ISE system for nitrogen compound analysis (Hach, Loveland, CO, USA), the BlueSens BlueVary system for analyzing carbon dioxide content in the outgoing air stream (BlueSens Gas Sensor GmbH, Herten, Germany), and the CarboVis 701/705 IQ system for analyzing COD and BOD (Xylem Analytics, San Diego, CA, USA).  
Control and calibration measurements were conducted using the HACH Lange DR6000 UV-Vis spectrophotometer (Hach, Loveland, CO, USA), the WTW OxiTOP-IDS system (Xylem Analytics, San Diego, CA, USA), the WTW Oxi3310 equipped with the CellOX 325 sensor (Xylem Analytics, San Diego, CA, USA), and the WTW pH 3310 analyzer (Xylem Analytics, San Diego, CA, USA). The control tests for suspended solids were performed using standard methods. Figure 1 shows a photograph of the bioreactor.  
The operation of the system was managed through an integrated controller, as well as via a personal computer using Siemens Simantic software (SIMATIC WinCC V7.5 SP2 Upd15). In addition to automating the control of the main components of the setup, the control program was configured to facilitate data collection from all analyzers. The collected data were exported to a.csv file for further analysis. For the operation of the system, wastewater from active treatment facilities was used as the substrate, along with additional substrates consisting of solutions of volatile fatty acids obtained from the acidification of the sludge and acetic acid (CH\({}_{3}\)COOH, AnalaR NORMAPUR, 99%). The volatile fatty acids were produced through the fermentation of sludge from the same treatment facilities.  
The inoculum biomass was sourced from the aeration tank of the studied treatment facilities. The operational regime of the system was aligned with the technological processes of the existing facilities.  
The bioreactor's operating conditions were optimized to achieve comparable performance characteristics of the system. The modeling was conducted in accordance with the computational principles outlined in a previous study [37]. Thus, the actual technological  
Figure 1: The lab-scale bioreactor-fermentor.  
process was replicated under controlled laboratory conditions. The data collection scheme for the laboratory setup is illustrated in Figure 2.  
The laboratory bioreactor operated in sequencing batch reactor (SBR) mode. The operational parameters of the setup are listed in Table 2.