Small bioreactor platform capsules provide persistent digestive biomass for continuous bioreactors operated under short hydraulic retention times

Bioaugmentation treatments in general and the use of encapsulated selected microbial cultures in particular are gaining significant attention as a promising approach for the treatment of wastewater containing phenols and other organic pollutants. Thus, the purpose of this study is to investigate the biodegradation performance of a Pseudomonas putida culture encapsulated in a unique 3-D capsule known as the small bioreactor platform (SBP). Batch and continuous bioreactors, bioaugmented with two different P. putida culture states, i.e., encapsulated and free suspended cells, were operated under different phenol loadings. During the batch experiments, the biodegradation rate of the suspended culture was equal to or higher than the encapsulated culture, except for the highest phenol concentration of 1000 mg/L, where the encapsulated bacterial culture exhibited a superior biodegradation rate (45 mg/L/h) relative to the free culture (16.7 mg/L/h). In addition, in the continuous bioreactor, at a hydraulic retention time (HRT) of up to 1 h, the encapsulated P. putida completely biodegraded the phenol in the influent with 50 mg/L phenol, showing a maximal biodegradation rate of 45 mg/L/h. However, decreasing the HRT to 0.5 and 0.25 h resulted in incomplete biodegradation, despite higher biodegradation rates (90 and 70 mg/L/h, respectively). Furthermore, a sharp decrease in the biodegradation process efficiency was observed when the suspended culture was released from the SBP capsules by cutting the microfiltration membrane of the capsules. Therefore, this study demonstrates that, compared with suspended cultures, SBP culture encapsulation achieves superior performance as a bioaugmentation strategy, especially in continuous bioreactors, such that it can be applied in the treatment of phenol rich wastewater.