The SBR was inoculated with seed sludge originating from a petrochemical company and subsequently fed with the wastewater from the same company. The reactor was operated for 150 days with an SBR cycle of 12 h. A standard cycle consisted of several steps, including an anaerobic feeding step, applying the anaerobic feast/aerobic famine method to induce the growth of slow-growing organisms such as GAO. The anaerobic feeding step was split into a non-mixed and mixed phase, then followed by an extended anaerobic mixing step, an aerobic period with aeration between 1 and 3 mg O2·L−1, and ultimately settling and effluent discharge steps. Throughout the operational period of the SBR, three periods or stages can be distinguished where changes to the cycle were made. During stage I (days 1–21), 1 L of influent was fed per cycle; during stage II (days 21–73), the influent volume was increased to 1.5 L per cycle; and during stage III (days 73–150) the length of the anaerobic mixing period, which follows the feeding step (1.5 L influent/cycle), was increased by 30 min to promote substrate uptake. The different times of each cycle step can be found in Table 1 for all three stages.

Table 1

Overview of SBR cycle times during different stages of operational period

Stage I (day 1–21)Stage II (day 21–73)Stage III (day 73–150)
Feeding (not mixed) 30 min 45 min 45 min 
Feeding (mixed) 30 min 45 min 45 min 
Anaerobic mixing 210 min 180 min 210 min 
Aerobic step 320 min 320 min 290 min 
Settling 120 min 120 min 120 min 
Discharge 5 min 5 min 5 min 
Total cycle time 12 h 12 h 12 h 
Stage I (day 1–21)Stage II (day 21–73)Stage III (day 73–150)
Feeding (not mixed) 30 min 45 min 45 min 
Feeding (mixed) 30 min 45 min 45 min 
Anaerobic mixing 210 min 180 min 210 min 
Aerobic step 320 min 320 min 290 min 
Settling 120 min 120 min 120 min 
Discharge 5 min 5 min 5 min 
Total cycle time 12 h 12 h 12 h 

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