Evaluation of Speece cone performance at high MLSS concentrations in a pilot-scale MBR system

The membrane bioreactor (MBR) operated at higher than conventional mixed liquor suspended solids (MLSS) concentrations for instance above 15 g/L provide many advantages such as significant reduction in area requirement, lesser sludge production and high-quality effluent. However, applications of MBR systems operated at high MLSS ranges are limited mainly due to higher oxygen demands and extreme membrane fouling. Conventional aeration systems such as fine and coarse bubble diffusers show extremely poor oxygen transfer efficiencies at higher MLSS concentrations. However, the limitation in terms of oxygen transfer can be overcome with the help of concentrated oxygen supply technology such as Speece cone. The oxygen transfer performance of a Speece cone concentrated oxygen supply system provided for a pilot-scale MBR was evaluated at higher MLSS concentrations. The evaluation was carried out by determining the oxygen transfer parameters such as overall oxygen mass transfer rate (KLa, h-1), standard oxygen transfer rate (SOTR, kgO2 d-1), standard oxygen transfer efficiency (SOTE, %) and most importantly alpha factor (α) for MLSS concentrations of 5, 10, 20, and 28 g/L. Results showed that MLSS concentration negatively affects the KLa and alpha factor. Whereas, higher oxygen flow rates positively affect the KLa and alpha factor. SOTEs of approximately 100% were observed at 5 and10 g/L MLSS concentration, while SOTEs of approximately 50% were observed at 20 g/L MLSS concentration. On the other hand, SOTE as high as 75% was obtained at 28 g/L MLSS concentration. The alpha factors in the range of 0.6 to 1 were obtained for 5 and 10 g/L MLSS concentrations, while alpha factors from 0.2 to 0.8 were reported for MLSS concentration of 20 and 28 g/L. These alpha factors are reported as a function of oxygen flow rates. The results obtained for an evaluated range of MLSS concentrations in this research indicate that the Speece cone technology can overcome the current limitations of poor oxygen transfer exhibited by conventional aeration systems at high MLSS MBR. Thus, operating a high MLSS MBR system coupled with the Speece cone technology can ensure better oxygen transfer performance, great operational flexibility and most importantly reduce the area requirement of the system to make it an ideal innovation in the wastewater treatment field. However, it is recommended to study the fouling characteristics of membranes to further understand the limitations in terms of membrane performance