Abstract:
A system and method for algal harvesting and destabilization are provided. The system includes a multifunctional reactive electrochemical membrane (REM). The application of an electrical current generates reactive species at the REM surface and oxidizes algae and soluble organic compounds. This novel type of membrane filtration avoids the use of harmful chemical additives. In addition, it provides the benefits of avoiding polymer aging, membrane fouling, and high costs caused by high transmembrane pressures and frequent membrane cleaning. Traditional membrane separation that significantly suffers from membrane fouling due to either the formation of a cake layer of algal cells, or more commonly due to organic matter adsorption onto the membrane surface is significantly avoided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims the benefit of the filing date of U.S. Provisional Patent Application No. 62/337,940, filed May 18, 2016, the disclosure of which is hereby incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to water treatment and biomass separation. In particular, the present disclosure relates to an electrochemical membrane filtration for water purification and biomass separation. 
       BACKGROUND 
       [0003]    Rapid and high efficient biomass harvesting is not only critical for biomass engineering and biofuel production but also important for water or wastewater treatment industries to produce clean water. High efficient algal biomass removal from water will lower the operational cost and increase the economic viability of produced products (biomass, biofuel or bioenergy, and clean water). Some of the current dewatering technologies, such as flocculation and centrifugation, require a large amount of energy or chemical addition. 
         [0004]    Membrane filtration is a common dewatering technology. During membrane filtration, a membrane serves as a barrier, allowing passage of water while retaining algae or other substances to be collected. Membrane filtration does not utilize any harmful chemical additives. However, traditional membrane filtration faces major challenges such as polymer aging, membrane fouling, and high costs (e.g., caused by high transmembrane pressures and frequent membrane cleaning). In particular, traditional membrane separation significantly suffers from membrane fouling due to either the formation of a cake layer of algal cells, or more commonly due to organic matter adsorption onto the membrane surface. Thus, there is a need to develop innovative membrane filtration processes that can efficiently separate algae with strong antifouling characteristics. 
       SUMMARY 
       [0005]    The present invention solves the problems of current state of the art and provides many more benefits. In accordance with embodiments of the present disclosure, an innovative and multifunctional reactive electrochemical membrane (REM) is provided. The REM acts as a model filtration membrane that exhibits excellent antifouling characteristics and strong surface reactivity. The application of a direct current (DC), alternating current (AC) or a combination of both, generate reactive species at the REM surface oxidizes algae and soluble organic compounds. Algal cell (as a model microorganism) integrity was changed with exposure to the REM, including deformation, photosynthetic activity decline and released intracellular organics, which indicate the effective surface oxidation against biomass. There are additional benefits of REM such as reduced membrane fouling, reduction of organic (toxic) compounds in permeate and energy consumption for backwash and flux recovery, and water purification. 
         [0006]    Any combination and/or permutation of the embodiments are envisioned. Other objects and features will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    To assist those skilled in the art in making and using the disclosed reactive electrochemical membrane and associated systems and methods, reference is made to the accompanying figures, wherein: 
           [0008]      FIG. 1  is a schematic diagram of a multifunctional reactive electrochemical membrane (REM) filtration system with separated feed tank and REM filtration unit in accordance with the present disclosure; and 
           [0009]      FIG. 2  is a schematic diagram of a compact and integrated REM filtration system with less footprint and material utilization in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    A multifunctional reactive electrochemical membrane (REM) filtration systems and methods are disclosed. Depending on the embodiment, the system includes subsystems and components to measure and control process variables, such as permeate flux and pressure, as required for effective performance. The apparatus could employ sensors or other condition detection and control subsystems or components that might be required to process at a particular rate or at a particular scale. 
         [0011]      FIG. 1  is a schematic diagram of multifunctional REM filtration system  100  with a separated feed tank  114  and a REM filtration unit or tank  134 . The filtration system  100  includes a REM  130  and a mesh  132  that surrounds the REM. Depending on the implementation the mesh  132  may be stainless steel or other conductive material. The mesh  132  serves as a counter or auxiliary electrode. It will be understood that other counter or auxiliary electrodes could be used. Depending on the embodiment, the mesh may be cylinder-shaped and made of stainless steel. The mesh could have other shapes and could be made of any other suitable material. Depending on the implementation the mesh may partially or completely surround the REM membrane. 
         [0012]    An alternate current (AC) or direct current (DC) power source, such as an AC or DC generator  160 , is wired to the REM and the stainless steel mess. The power source may also be a combination of both AC and DC power. Depending on the embodiment, the REM may be a 10-cm long Ebonex® one-channel tubular electrode made of sub-stoichiometric titanium oxide (Ti 4 O 7 ) with the outer and inner diameters of 10 mm and 6 mm (Vector Corrosion Technologies, Inc.). While the use of Ti 4 O 7  is exemplary, the REM could be made of any other titanium suboxide or any other suitable material. In addition, the sizes of the electrode could vary depending on the application. 
         [0013]    In  FIG. 1 , two water pipes  124 ,  125  are connected to the top of the REM  130 . One of the water pipes  124  is used for permeate withdraw and the other water pipe  125  is used for backwash water flushing into the REM as indicated by the arrows on the pipe lines. While two water pipes are shown, the number of water pipes could vary. In the shown embodiment, REM  130  is a tube. The bottom of the REM  130  is sealed to allow water to pass through a membrane surface only of the REM  130 . A flat sheet ceramic membrane could also be used in practical applications instead of the shown tube configuration. 
         [0014]    As shown in  FIG. 1 , biomass feed  113  (e.g., algal suspension) first enters a baffle settling tank  110  to pre-settle and concentrate biomass  112  with the overflow of feed  113  flowing in the feed tank  114 . The concentrated biomass  112  accumulated at the bottom of the baffle settling tank  110  is collected as algae sludge with Sludge Pump  108  (# 1 ). The biomass suspension  115  in the Feed Tank  114  will be pumped into the REM filtration tank  134  by Water Pump  109  (# 2 ), which is also used to pump backwash water to the REM  130  to remove fouling and recover flux. The Flow Meter  111  (# 1 ) is used to monitor the flow rate. Permeate water will be sucked up and pumped by Water Pump  123  (# 3 ) into a Receiving Tank  140  with a water level monitored sensor  142 . The concentrated biomass  112  will settle and accumulate at the bottom of the REM tank  134 . The accumulated biomass at the bottom will be decanted via gravity or Sludge Pump  108  (# 1 ) for further processing. 
         [0015]    To mitigate surface fouling and extend the effective filtration period, DC or AC power supply  160  could be used to generate surface radicals. For example, in one embodiment, AC could be applied intermittently (e.g., 10 minutes every 60 minutes) at 10 V with a radio frequency of 100 to 500 MHz to polarize REM or stainless steel surfaces and induce oxidant or radical production and electrostatic repulsion against potential foulants such as negatively charged biomass or biomolecules such as extracellular organic matters (EOMs). For example, under DC polarization from 50 A·m −2  to 250 A·m −2  or approximately 10 to 22 V of cell voltage, 0.0045 mM to 0.022 mM chlorine can be generated on the cathode surface within 2 hours in the presence of Cl − . Meanwhile, 8 μM to 55 μM H 2 O 2  can also be generated on the anode surface under the same condition. In one embodiment, AC or DC is applied continuously. In another embodiment, AC and DC are both applied. The application (duration and frequency) of DC/AC charging is at user&#39;s discretion and a good criterion would be mitigating fouling as indicated by the extended period of effective filtration time. However, it is anticipated that the energy consumption might be increased consequently with frequent AC/DC charging. 
         [0016]    Surface fouling or pore clogging on the ceramic membrane will be indicated by the changes of permeate flux measured by Flow Meter  109  (# 2 ) or the water level sensor. If the permeate flux declines and drops down to near zero, backwash is performed together with DC or AC polarization. Different backwash sequences could be used to maximize foulant removal and permeate recovery. For example, clean water could be withdrawn from the Receiving Tank  140  by Water Pump  109  (# 2 ) into the REM  130  to physically cleanse the membrane pores of the REM from inside out. Furthermore, the DC or AC power supply could be turned on (e.g., at 10 V or current density of 20 mA/cm 2  or higher) for 5 minutes or longer to promote surface radicals generation and oxidation of surface foulants. 
         [0017]    Depending on the implementation, the controls of pumps and valves of the system  100  are interconnected and function such that the following may occur; 
         [0018]    (1) During a filtration stage, as shown in  FIG. 1 , valves ( 1 ), ( 4 ) and ( 5 ) remain open while valves ( 2 ) and ( 3 ) shut off. Water pumps  109  (# 2 ) and pump  123  (# 3 ) are on. 
         [0019]    (2) During backwash, valves ( 2 ) and ( 3 ) open simultaneously while valves ( 1 ), ( 4 ) and ( 5 ) shut off. Water pump  109  (# 2 ) is on while Water pump  123  (# 3 ) is off. 
         [0020]    (3) Water pump  123  (# 3 ) is controlled with the signal from Flow Meter  119  (# 2 ) or water level sensor  142  in the receiving tank  140 . 
         [0021]    (4) The accumulated biomass concentration at the bottom of the baffle settling tank  110  and tank  134  may be monitored by online turbidity or UV-Vis absorption sensors to control valves ( 6 ) and ( 7 ). When the biomass concentration is greater than 2 g/L (e.g., UV-vis reading reaches 1 or higher), the two valves ( 6 ) and ( 7 ) will be open with the Sludge Pump  108  (# 1 ) turned on to dispose concentrated biomass from the bottom of the settling tank  110  and the REM tank  134 . 
         [0022]    The system  100  could include a controller  150  in communication with a sensor, such as a water level sensor  142  or an absorption sensor (not shown). The controller  150  may receive at least one process parameter, process the at least one process parameter, and adjust operation of the system based upon processing of the at least one process parameter. 
         [0023]      FIG. 2  is a schematic diagram of a REM filtration system  200  in accordance with another embodiment. Similar numbers in the Figures represent similar components and functions of the same. Integrated filtration process with less footprint and material utilization may be built as shown in  FIG. 2  such that a water pump  123  will be used as both suction of permeate during filtration mode and backwash water during backwash mode. The pipes for permeate and backwash water flows could essentially share in one pipeline  129  in one embodiment. The switch of the filtration and the backwash could be realized by changing rotation direction of the water pump  123  and a three-way valve  210  that switches between permeate discharge and backwash water withdraw. 
         [0024]    While exemplary embodiments have been described herein, it is expressly noted that these embodiments should not be construed as limiting, but rather that additions and modifications to what is expressly described herein also are included within the scope of the invention. Moreover, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations are not made express herein, without departing from the spirit and scope of the invention.