Carbon and nitrogen removal from tannery wastewater with a membrane bioreactor

A 3.5 L Membrane Sequencing Batch Reactor (MSBR) was used for the treatment of a wastewater coming from the beamhouse section of a tannery. The wastewater, produced after the oxidation of sulphide compounds, contained average COD and ammonium concentrations of 550 and 90 mg/L respectively. The system was operated for a period of 150 days, with no sludge removal during the whole period of operation. The biomass concentration inside the reactor varied considerably, with maximum values close to 10 g/L at the end of operation. Low biomass yield values were achieved probably due to the low feed/microorganisms (F/M) ratio. An important accumulation of organic matter in the reactor was noticed, although the COD effluent was not affected due to the permeation through the membrane. The nature of this organic matter is finally discussed. Removal efficiencies close to 100% in ammonium and 90% in COD were achieved and the TN removal efficiency ranged from 60 to 90%.