Evaluation of a pilot MBR system operated at high MLSS provided with a speece cone aeration system as an alternative for sanitation provision in emergencies

A size (volume) reduction for membrane bioreactor systems (MBR)s is constrained by the maximum amount of biomass that can be accommodated in the aerobic basin. The maximum achievable biomass concentration in the aerobic basin, known as the mixed liquor suspended solids (MLSS), is limited mainly by the extremely low oxygen transfer efficiency observed at MLSS concentrations higher than 20 g/L. Another limitation for achieving such high MLSS concentration in MBRs is the membrane permeability; causing limitation of the performance by membrane fouling. A pilot MBR system with a hydraulic treatment capacity of approximately 1 m³/d was located at the Harnaschpolder wastewater treatment plant in Delft, The Netherlands. The pilot MBR was operated at high MLSS concentrations (up to approximately 25 g/L). The MBR system was provided with an alternative source of oxygen supply (Speece cone system) to overcome the oxygen transfer limitations exhibited by conventional bubble diffuser systems. The MBR system showed very high COD removal efficiencies (>90%) even at hydraulic retention times (HRT) as low as 3.4 hours. The MBR performance was evaluated by monitoring the influent and effluent water quality, the membrane permeability, the sludge filterability, and the oxygen uptake rate (OUR). The Speece cone aeration system proved to be highly efficient in delivering dissolved oxygen at the evaluated MLSS. OUR values greater than 100 mg/L/h (at 14 g/L MLSS) were reported and even higher than 150 mg/L/h at MLSS above 20 g/L. The membrane permeability decreased as the MLSS increased; however, improvement in permeability values was observed between 10 to 14 g/L MLSS. Sludge filterability values in the range of ""poor filterability"" were observed; however, a reduction in the filtration resistance (or a filterability improvement) around the 10 g/L MLSS was noticed. The results obtained at the operational conditions of this research suggest that the existent limitations for achieving a lower footprint on MBRs can be overcome; MBRs may be designed at highly concentrated MLSS values. Operating MBR systems at such high MLSS values will allow the development of innovative MBR systems such as compact and movable MBRs to be used in an emergency sanitation context. In addition, existing treatment facilities may be upgraded by simply increasing the MLSS operational condition allowing the new system to treat a higher flow (or higher load) utilizing the same aerobic tank volume