Combining submerged membrane technology with anaerobic and ...

Chapter 1incorporating anaerobic and/or anoxic compartments in order to enable simultaneousbiological nutrients removal.Despite the advantages mentioned before, MBR technology increases operatingcosts with respect to activated sludge reactors, due to a higher consumption of electricityand the need to replace the membrane modules, so their use is justified only under thefollowing circumstances:1) Use in areas with high environmental sensitivity, where the legislation force todischarge treated wastewater with a low content of chemical or biological contaminants.2) Use in areas of water scarcity, where is necessary to reuse treated water.3) Wastewater treatment plants (WWTPs) with space limitations, preventing the useof other purification technologies. Under this heading would be included the expansion oftreatment capacity of conventional WWTPs in operation, on which a field expansion is notpossible or desirable.4) Treatment of complex industrial wastewaters in which the use of another treatmenttechnology is not effective or reliable and biological treatment of industrial wastewater inareas with strong seasonal component.1.3.1. BackgroundMBR technology emerged in 1969 when the company Dorr-Oliver replaced thesecondary clarifier in a CAS system by a tangential flow UF membrane. In this study,performed by Smith et al. (1969), the reactor mixed liquor was pumped to the membrane inorder to separate the treated water from the sludge, resulting in a treated effluent orpermeate and a concentrated sludge stream that was returned to the reactor. This type ofsystem is called the sidestream membrane MBR (figure 1.5A). The main problems in theseinitial steps were related with the heavy fouling and the rupture of the filters. All MBRsimplanted between 1969 and the end of the eighties were based on the sidestreamconfiguration and nowadays are mainly applied for the treatment of landfill leachates orwastewater generated by industries, ships and anaerobic digesters.In this configuration, tangential flow tubular modules placed in vertical are commonlyused (flat sheet modules can also be used) to which the sludge is pumped from the bottomat higher speeds, inducing turbulent flow in order to prevent radial gradients. The highpressures justify the high energy consumption, estimated at between 3 and 5 kWh·m -3 ofpurified water, which limits the use of sidestream MBR for the purification of large volumes34