The Research Of A Submerged Double-shaft Rotary Anaerobic Membrane Bioreactor

Anaerobic membrane bioreactor (AnMBR) is an effective process to treat high concentration organic wastewater and has become one of research emphases of foreign associations such as WERF (Water Environmental Research Foundation). The application of submerged MBRs is very extensive because of lower energy consumption and low transmembrane pressure(TMP) and small footprint. However, most of AnMBR have been conducted with external configureations at present, owing to membrane contamination control of submerged AnMBR has never been able to solve effectively so as to limit its application. In order to control and resolve membrane fouling problem in submerged AnMBR, we developed a set of submerged double-shaft rotary anaerobic membrane bioreactor (SDRAnMBR). System container is filled with flat-sheet Ultrafiltration membrane. Internal rotary membrane module adopted double shaft rotation in the same direction. Turbulence coming from membrane rotation could undermine concentration polarization on the membrane surface and formation of gel layer ,so as to control the membrane fouling effectively and make it reduce to the minimum. It is necessary to realize the concept of submerged AnMBR into implementation. We used the developed reactor to treat synthetic bear wastewater. Discussed and studied some characteristics of SDRAnMBR in detail such as launch characteristics,operation efficiency , performance and mechanism of membrane fouling within SDRAnMBR, the main research results as follows:(1) A set of SDRAnMBR system was designed and developed. System volume of container and its effect one were 120 L and 100 L , respectively, filled with innovative double-shaft rotary flat-plate Ultrafiltration membrane module, loaded with the largest membrane area of 2.4 m~2, maximum double-shaft rotary speed was 500 rpm, the average maximum theoretical value for the shear velocity is 4.4 m / s. So that it can meet the general requirements for the feed fluid treatment, suitable for treating feed fluid of high suspended substances, moderate and high concentration. Thereinto, the double-shaft rotational membrane module was the key and novel part of the newly reactor.(2) The results of theoretics analysis on characteristics of hydraulics dynamics indicated that the effects of equality, interleaving oscillation and three-state rotating flow were produced within SDRAnMBR. So it enhanced the characteristics of shear , turbulence, oscillation and mass transfer within rotating fluid. It were prevented and reduced that composite whirlpool and permeate backpressure from rotational membrane module. It resolved successfully problems of one-shaft rotational membrane module in submerged AnMBR. In a certain extent,it was realized that increasing velocity of flow on membrane surface , reducing concentration polarization and main body concentration of permeate fluid and resistance inside and outside of membrane. So that it could furthest decrease membrane fouling and increase permeate flux.(3) Characteristics of SDRAnMBR start-up was well. Compared to the start-up of conventional anaerobic bioreactor, its start-up velocity was rapid during 26 days, strong ability of endurance impact loading, high COD removal rate which stabilized at above 92% ,about more 10% higher than conventional anaerobic bioreactor. The reactor run steadily and the acidification phenomenon has not happened. Furthermore, the effluent volatile fatty acid (VFA) and effluent alkalinity changed in the larger range and acidification phenomenon will not happen. Effluent alkalinity were in the range 1200-2600mg/L, effluent VFA were in the range 200-600mg/L,and the rate of alkalinity on VFA were between 3.5 and 6.5. However, the conventional anaerobic bioreactor was vulnerable to acidification with poor stability. Direct use of membrane bioreactor to start up anaerobic reactor was suggested.(4) SDRAnMBR had good treatment effect for synthetic beer wastewater and the system not only run steadily but organic loading enhanced fast , had a strong impact resistance capacity and a high rate of organic substrate removal. During the normal operation, When influent COD were in the range 2900-5200mg/L and volume loading rate were in the range 4.97-12.48 kgCOD/m~3·d, COD removal rate was an average of 95.15%. Because of common action of membrane interception and three-state rotating fluid , the effluent quality and operation stability were strengthened consumedly at high mixed liquor suspended solids (MLSS) and high volume loading rate.( 5 ) SDRAnMBR had good anti-contamination performance. Membrane flux ,TMP , filtration resistance immovability and long-term steady running were its mainly running characteristics, when operated at definite range of MLSS and hydraulic retention time(HRT) and membrane rotational speed .The optimal operation parameters were that HRT was 10h, volume loading rate were in the range 10.52-12.09 kgCOD/m~3·d, MLSS were in the range 18-19.5g/L, membrane rotational speed was 150rpm, membrane flux were in the range 30.75-31.31L/m~2·h and TMP were between 12 and 13 kPa under this test condition. Therefore, SDRAnMBR can furthest decrease membrane fouling under high volume loading rate and MLSS. It was realized long-term steady running when operated at lower membrane rotational speed, shorter HRT, higher volume loading rate, biggish MLSS, lower TMP and larger membrane flux.(6) The well characteristics of hydraulics dynamics(equality, interleaving oscillation and three-state rotating flow effect) and cooperate action with membrane interception , anaerobic granules sludge in SDRAnMBR, could decrease the effects on sludge activity come from the shear stress excess bigness, restrain speediness accumulation of extracellular polymeric substances(EPS) in sludge mixed liquor due to MLSS accretion, as well as restrain speediness accretion of sludge dynamic viscosity too. Thereby membrane fouling was reduced consumedly and resulted in membrane filtration resistance immovability when operated at definite range of MLSS and sludge viscosity. It was realized steady running when operated at biggish MLSS (between 18 to 19.5g/L)> higher EPS (between 50.9 to 63.9 mg/gMLSS),small sludge particle size (between 4.00 to 36.54μm)和larger sludge viscosity(between 6.6 to 7.5 mPa·s). The finging was more identified that membrane module strengthened anti-contamination performance.(7) We also put forward the fouling mechanism in SAnRMBR. Firstly membrane fouling resistance (concentration polarization and cake layer formation) was 89.68%,The external resistance was 76.34% of total resistance.Accordingly,the intrinsic membrane resistance and internal fouling resistance were 10.32% and 13.34% of the total resistance, respectively. Therefore , membrane filtration resistance was arose from the cake layer, its controlling was the predominant during whole operated period. Furthermore ,cake layer was thinner , membrane fouling velocity was very slowly and membrane fouling was very slight with running time during operated 146 days. The membrane filtration resistance was immovability when operated at definite membrane rotational speed . The finging was more identified that SDRAnMBR was effective in minimizing concentration polarization resistance by reducing the accumulation of solute molecules on the membrane surface, and consequently reduced the potential for membrane fouling. Secondly, among membrane fouling 3 stage, which occurs only the stage 1 (an initial short term rise in TMP ) and stage 2 (long-term rise in TMP, either linear or weakly exponential), and that stage 3 (sudden TMP rise, also known as the TMP jump) without occurs in running 145 days by SDRAnMBR. moreover, So sustainable operation the aim was realized by limiting shorter time of stage 1 (40min), prolonging stage 2 consumedly and avoiding stage 3 since it could be difficult to restore.In a word , SDRAnMBR could furthest decrease and control membrane fouling of submerged AnMBR ,and that was realized long-term steady running when operated at lower membrane fouling and higher volume loading rate, with could keep steady flux. So it does not demand to clean chronically, thereby energy consumption was reduced consumedly. The problems of membrane contamination control in submerged AnMBR were resolved successfully, and it became system of high-efficiency and stabilization. The theoretics analysis on double-shaft rotating fluid was identified ,and that it will have well application prospect by SDRAnMBR.