Large scale application of membrane bioreactor technology for the treatment and reuse of an anionic surfactant wastewater

The treatment of an anionic surfactant rich wastewater by a powerful Citrobacter braakii strain was investigated at large scale. This bacterium was inoculated into a 4.5 m3 continuous stirred tank reactor (CSTR) without a membrane. At volumetric loading rates ranged between 0.44 and 0.96 g COD l−1 d−1, a weak C. braakii population density was observed in the reactor which results in slow anionic surfactants degradation kinetics. The augmented bacterium was diluted and replaced by protozoa and other forms of bacteria after a prolonged experience run. The CSTR was then coupled to a cross-flow ultrafiltration membrane. This allowed complete biomass recycling and partially retention of the surfactants in the reactor. C. braakii became again dominant in the medium. At volumetric loading rates of 0.6–1.5 g l−1 d−1, the anionic surfactant concentration in the permeate varied from 0 to 40 mg l−1 with a mean value of 18 mg l−1. After 2 months of running, mixed liquor volatile suspended solids (MLVSS) in the reactor increased from 0.71 to 5.92 g l−1 and the permeate-flux slightly decreased from 28.75 to 23.75 l h−1 m−2. The reclaimed water could be reused either for the washing of the material and soil, and to irrigate the parkland of the factory.