Reasearch On The Dynamic Membrane And Its Application In The Recirculated Membrane Bioreactor

The experiments on the 2 μ m ceramic membrane are carried out to confirm the running condition of dynamic membrane and then treat nitrogenous wastewater in a heavy concentration in such a RMBR. This paper studies the appropriate material of dynamic membrane, the optimistic formation conditions of dynamic membrane, the cleaning-up process of polluted dynamic inorganic membrane, the running condition in treating secondary effluent and sludge and the running efficiency of RMBR as well. The permeating flux COD_Cr SS, turbidity value, NH₄⁺-N, NO₃^--N, NO₂^--N, MLSS, MLVSS and OUR (Oxygen Uptake Rate) are measured during experiments.Kaolin was first chosen as the membraning material, because experiments showed that the kaolin dynamic membrane had higher permeating flux than diatomite, wollastonite and heavy calcium carbonate, and kaolin dynamic membrane was more easily renewed after cleaning. With kaolin Particle size increasing the permeating flux went up correspondingly; considering the rejection of little-size molecule, 6000 mesh kaolin was better. The dynamic membrane was formed by circulating0.3g/L of kaolin in 10 minutes under the transmembrane pressure of 0.2MPa and at a crossflow velocity of 0.5m/s.The polluted ceramic membrane was cleaned by high speed flushing - back flushing-flushing with alkali (0.2mol/L NaOH) 1 h-flushing with acid (0.lmol/L HC1) 1 h. As a result the membrane flux would be restored up to 90%. It was proved that the dynamic membrane had a better restoration than the bare tube after the same cleaning process.Secondary effluent and sludge were treated under the transmembrane pressure of 0.2MPa and at a crossflow velocity of lm/s. Considering the permeating flux and the pollutant rejection the kaolin dynamic membrane are much better than bare tubes.We used the kaolin dynamic membrane to treat a kind of heavy-concentration nitrogenous wastewater in a RMBR that was steadily run in 2 mouths. As a result, the average COD_Cr and NH/-N concentration of system effluent were less than 20mg/L and 5mg/L, respectively. The removal rate of COD_Cr was 98.85%. In this RMBR, the NO₂^--N concentration was lower than NO₃^--N. The amount of sludge increased slowly and finally the sludge concentration maintained 6500mg/L. In addition, the OUR fluctuated frequently but generally rose with the sludge concentration increasing. In brief, the permeating flux in RMBR was higher than in normal MBR system and the performance of ceramic membrane would be renewed well after flushing. However, the systemneeds periodic high-speed flushing and back flushing when the permeating flux decreased to lower than 10 L/(m² · h).