PMC:4160552 / 3195-5981 JSONTXT

{"project":"2_test","denotations":[{"id":"25215189-21262521-59012422","span":{"begin":2089,"end":2091},"obj":"21262521"}],"text":"Methods\n\nPhysical properties of the system\nFigure 1 shows an overview of the hybrid membrane bioreactor. HMBR is a combination of rotating biological contactor (plus Kaldnes media) and an external membrane. Effluent from bioreactor enters the membrane by a centrifugal pump and the sludge remained behind the membrane, which contains microorganisms, is returned to the bioreactor. Samples were collected from influent/effluent of RBC and effluent of the membrane. Physical properties of RBC and the membrane are shown in Tables 1 and 2, respectively.\nFigure 1 Overview of the hybrid membrane.\nTable 1 Physical properties of the rotating biological contactor\nLength 40 cm Width 27 cm\nHeight 20 cm Total surface 2m2\nTotal volume 21.6 lit Effective volume 18 lit\nCylinder diameter 20 cm Cylinder length 10 cm\nStage 2 Rotational speed 10 rpm\nTable 2 Physical properties of the membrane\nMembrane type Ultra filtration\nMembrane material Polymer\nInternal diameter 1.24 cm\nEffective length 33 cm\nSurface area 0.0128 m2\n\nBioreactor feeding\nIn this study, the sludge of second settling tank of the activated sludge process in Tehran refinery was used. At the first, RBC was prepared and 90% volume of its cylinders was filled with Kaldnes media. Then, some of the sludge plus some water was poured into the bioreactor so that the mixed liquor suspended solids (MLSS) in bioreactor became 1500 mg/l.\nIn order to grow and reproduce microorganisms and biofilm formation, the system was set up in batch process with COD = 1000 mg/l so it fed with carbon (molasses), nitrogen (urea) and phosphorus (ammonium phosphate) for 8 weeks. During the process, a combination of crude oil and gasoline with a ratio of 2/1 (petroleum pollutant in this state would have a wide range of hydrocarbons from C14 to C42) was added to the system for more adaption of microorganisms to the petroleum pollutant. Also, 5-15 μl/l of surfactant twin-80 was added to system so that bonds are formed between water and oil molecules. To speed up the microorganisms growth, some minerals were added to the sludge as well [10].\n\nExperimental process\nOnce the biofilm with a thickness of about 4 mm was formed, the system was started up as continuous process at a HRT of 24 and 18 hours. The external membrane was connected to RBC. Subsequently, wastewater influent and effluent of RBC and effluent of HMBR were examined daily. These tests included the measurement of COD, MLSS, MLVSS, TPH, TSS, pH, temperature, and dissolved oxygen. All tests were performed according to the standard methods [11]. As time passes, membrane fouling causes such a permeate flux decline that the membrane needs to be refreshed. For this reason, bioreactor was switched off and the membrane was washed with water, NaOH 2%, and HNO3 1% [12]."}