Abstract:
The method is for treating a liquid or a slurry of a liquid and solids, such as sludge, soil or fiber webs, with an ultrasonic energy. Movable endless members ( 214, 230 ) are provided that are permeable to the liquid portion of a slurry ( 204 ). An ultrasonic transducer ( 236 ) is disposed adjacent to the member ( 214 ) and the ultrasonic transducer ( 234 ) is disposed adjacent to the member ( 230 ). The slurry is fed in between the members ( 214, 230 ). The transducers ( 234, 236 ) generate pressure pulses through the members ( 230, 214 ) to form imploding bubbles ( 227 ) in the slurry. The bubbles ( 227 ) have a diameter (d 5 ) that is greater than a distance (d 3 ) between the transducer ( 234 ) and the member ( 230 ) and a distance (d 4 ) between the transducer ( 236 ) and the member ( 214 ) to prevent the bubbles ( 227 ) from being captured between the transducers ( 234, 236 ) and the members ( 230, 214 ). In this way, the imploding bubbles can generate intense pressure, temperature and flow speed pulses in the slurry which can create sonochemical or sonophysical changes of the substances in the slurry without harming the ultrasonic transducer surfaces.

Description:
PRIOR APPLICATION 
     This is a continuation-in-part application of U.S. patent application Ser. No. 10/451,962, still pending filed 27 Jun. 2003 that claims priority from PCT application no. PCT/SE02/02195, filed 28 Nov. 2002, that claims priority from U.S. provisional patent application Ser. No. 60/339,380, filed 11 Dec. 2001. 
    
    
     TECHNICAL FIELD 
     The present invention is a method for treating slurry or a liquid, such as sludge or polluted water in sewage works, with ultrasonic transducers. 
     BACKGROUND AND SUMMARY OF INVENTION 
     Ultrasonic energy has been applied to liquids in the past. Sufficiently intense ultrasonic energy applied to a liquid, such as water, produces cavitation that can induce changes in the physiochemical characteristics of the liquid. The subject of sonochemistry, which deals with phenomena of that sort, has grown very much during recent years. 
     The published material in sonochemistry and related subjects all pertains to batch processes, that is, the liquid solution or dispersion to be treated is placed in a container. The liquid in the container is then stirred or otherwise agitated, and ultrasound is applied thereto. It is then necessary to wait until the desired result, physical or chemical change in the liquid, is achieved, or until no improvement in the yield is observed. Then the ultrasound is turned off and the liquid extracted. In this way liquid does not return to its initial state prior to the treatment with ultrasonic energy. In this respect, the ultrasound treatment is regarded as irreversible or only very slowly reversible. 
     Far from all industrial processes using liquids are appropriately carried out in batches, as described above. In fact, almost all large-scale processes are based upon continuous processing. The reasons for treating liquids in continuous processes are many. For example, the fact that a given process may not be irreversible, or only slowly reversible, and requires that the liquid be immediately treated further before it can revert to its previous state. 
     Shock waves external to collapsing bubbles driven onto violent oscillation by ultrasound are necessary for most if not all physiochemical work in liquid solutions. The under-pressure pulses form the bubbles and the pressure pulses compress the bubbles and consequently reduce the bubble diameter. After sufficient number of cycles, the bubble diameter is increased up to the point where the bubble has reached its critical diameter whereupon the bubble is driven to a violent oscillation and collapses whereby a pressure and temperature pulse is generated. A very strong ultrasound field is forming more bubbles, and drives them into violent oscillation and collapse much quicker. 
     A bubble that is generated within a liquid in motion occupies a volume within said liquid, and will follow the speed of flow within said liquid. The weaker ultrasound field it is exposed to, the more pulses it will have to be exposed to in order to come to a violent implosion. This means that the greater the speed of flow is, the stronger the ultrasound field will have to be in order to bring the bubbles to violent implosion and collapse. Otherwise, the bubbles will leave the ultrasound field before they are brought to implosion. A strong ultrasound field requires the field to be generated by very powerful ultrasound transducers, and that the energy these transducers generate is transmitted into the liquid to be treated. Based upon this requirement, Bo Nilsson and H{dot over (a)}kan Dahlberg started a development of new types of piezoelectric transducer that could be driven at voltages up to 13 kV, and therefore capable of generating very strong ultrasonic fields. 
     A very strong ultrasonic source will cause a cushion of bubbles near the emitting surface. The ultrasound cannot penetrate through this cushion, and consequently no ultrasound can penetrate into the medium to be treated. The traditional way to overcome this problem is to reduce the power in terms of watts per unit area of emitting surface applied to the ultrasonic transducers. As indicated above, the flow speed of the medium to be treated will require a stronger ultrasound field and therefore an increased power applied to the ultrasonic transducers. The higher the power input is, the quicker the cushion is formed, and the thicker the formed cushion will be. A thick cushion will completely stop all ultrasound penetration into a liquid located on the other side of this cushion. All the cavitation bubbles in this cushion will then stay in the cushion and cause severe cavitation damage to the ultrasound transducer assembly area leading to a necessary exchange of that part of the ultrasound system. This means that little or no useful ultrasound effect is achieved within the substrate to be treated, and that the ultrasound equipment may be severely damaged. 
     The above-outlined cushion problems also apply to treating bacteria clusters in sludge slurries and treating drainage water from sludge slurries in sewage works that are subjected to ultrasonic treatment. The problems also apply to other processes with ultrasonic treatment of slurries, such as the forming of paper webs, de-inking of recycled pulp and cleaning of polluted soil. They also apply to other processes where liquids are treated with ultrasound, such as treatment of water polluted with solvents, and cleaning of drinking water and sonochemical processes. 
     One problem with the currently used sludge ultrasonic treatment plants is that the energy consumption is high and the efficiency could be improved. There is a need to solve the problems outline above so that sewage works may use ultrasonic treatment for bacteria in the sludge without encountering the undesirable cushion effect or the low efficiency. The method of treating a sludge slurry of the present invention provides a solution to the problems outlined above. 
     More particularly, the method of the present invention is for treating a slurry, such as sludge, with an ultrasonic energy without creating the undesirable cushion effect. Movable endless members are provided that are permeable to the liquid part of a sludge slurry and a first ultrasonic transducer is disposed adjacent to a first movable member and a second ultrasonic transducer is disposed adjacent to a second movable member. The slurry is fed in between the two movable members. The transducers generate pressure pulses through the members to form imploding cavitation bubbles in the sludge slurry that have an effect on the bacteria clusters. The cavitation bubbles have a resonance diameter (d 5 ) at the ultrasound frequency used that is greater than a distance (d 3 ) between the first transducer and the first member and a distance (d 4 ) between the second transducer and the second member to prevent the bubbles from imploding between the transducers and the members. By making the distance between the members smaller and smaller along the ultrasonic treatment path, a hydraulic pressure build-up between the members causes a dewatering of the slurry through the members giving a higher and higher dry solids content of the sludge slurry that is favorable for the efficiency of the ultrasonic treatment. The edges of the upper and lower members are pressed together to prevent the sludge from leaving the treatment zone in the cross machine direction. When treating liquids there are wedge formed sidewalls between the members and the edges of the members are pressed towards these sidewalls and the contact areas are water lubricated to minimize friction. The treated sludge may then be pumped to an anaerobic fermentation tank. Biogas can be continuously removed from the sludge by the under-pressure in a degassing pump or other degassing unit in a circulation loop connected to the fermentation tank before any gas bubbles are formed in the fermentation tank. The sludge slurry may again be subject to degassing and ultrasonic treatment before the slurry is sent to a press unit for dewatering. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view of the formation of a reactor of a prior art system; 
         FIG. 2  is a graphical illustration of the correlation between iodine yield and acoustic power; 
         FIG. 3  is a perspective view of the transducer system of the present invention disposed below a movable endless member; 
         FIG. 4  is a cross-sectional view along line  4 — 4  in  FIG. 3 ; 
         FIG. 5  is an enlarged view of cavitation bubbles dispersed in slurry disposed above the movable endless medium. 
         FIG. 6  is a cross-sectional view of a second embodiment of the transducer system of the present invention; 
         FIG. 7  is a cross-sectional view of a plurality of transducers disposed below a movable endless medium; 
         FIG. 8  is a schematic view of a portion of a sludge plant of the present invention; 
         FIG. 9  is a detailed view of the wires and ultrasonic transducers of the device of the present invention; 
         FIG. 10  is a schematic view of the sludge and drainage water treatment plant of the present invention; 
         FIG. 11  is a schematic view of the liquid treatment unit of the present invention; and 
         FIG. 12  is a schematic view of another embodiment of the present invention for washing of polluted soil. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a side view of a prior art transducer system  10  that has a container  11 , such as a stainless reactor, with a wall  12  for containing a liquid  13 . A transducer  14  is attached to an outside  16  of the wall  12 . When the transducer  14  is activated, a pillow  18  of cavitation bubbles  20  are formed on an inside  22  of the wall  12  due to the fracture zone in the liquid  13  that may be a result of fracture impressions on the inside  22  of the wall  12 . The bubbles may be held to the inside wall due to the surface tension of the liquid  13 . The bubbles  20  are good insulators and prevent the effective transmission of the ultrasonic energy into the liquid  13 . The under-pressure pulses of the ultrasonic energy transmitted by the transducer  14  create the cavitation bubbles. In this way, the pressure inside the bubbles is very low. 
       FIG. 2  is a graphical illustration that shows the iodine yield is affected by increased acoustic power on the system  10 . The more power is applied, the thicker the formation of the bubbles  20 , as shown in  FIG. 1 , and the yield increase is reduced and drops sharply at power ratings over 100 Watts in this case. In this way, the cavitation bubbles severely limit the usefulness of increasing the acoustic power to improve the iodine yield. 
       FIG. 3  is a perspective view of the transducer system  100  of the present invention. The system has a movable endless permeable medium  102 , such as a woven material, paper machine plastic wire or any other bendable medium permeable to liquids, that is rotatable about rollers  104  that guide the medium  102  in an endless path. As explained below, it is important that the medium is permeable to a liquid that may carry ultrasonic energy to the liquid disposed above the medium  102  so as to effectively create the cavitation bubbles in the liquid or slurry to be treated. The ultrasonic energy may be used to reduce flocculation  163 , best shown in  FIG. 5A , of fibers in the liquid to be treated because the bubbles implode or collapse to generate pressure pulses to the fiber flocculation  163  so that the fibers are separated from one another to evenly distribute or disperse the fibers in the liquid. The pressure pulses may be about 500 to 1000 bars so the pulses are more forceful than the forces that keep the fiber flocculation together. In general, the longer the fibers are or the higher the fiber consistency is, the higher the tendency of flocculation. 
     The medium may have a rotational speed up to 2000 meters per minute in a forward direction as shown by an arrow (F). An elongate foil  106 , made of, for example, steel or titanium is disposed below the permeable medium  102  and extends across a width (W) of the medium  102 . A plurality of transducers  108 , such as magnetostrictive, piezoelectric or any other suitable type of transducers, is in operative engagement with the foil  106  such as by being integrated therewith or attached thereto. 
       FIG. 4  is a detailed view of one of the transducers  108  attached to a mid-portion  118  of the hydrodynamic foil  106 . More particularly, the foil  106  has a rear portion  110  and a front portion  112 . The rear portion  110  has a rectangular extension  114  that extends away from a top surface  116  of the foil  106 . The mid-portion  118  of the foil  106  has a threaded outside  120  of a connecting member  122  also extending away from the top surface  116  so that a cavity  124  is formed between the extension  114  and the connecting member  122 . 
     The front portion  112  has an extension  126  that extends away from the top surface  116  and has a back wall  128  that is perpendicular to a bottom surface  130  of the foil  106  so that a cavity  132  is formed between the back wall  128  and the member  122 . The extension  126  has a front wall  134  that forms an acute angle alpha with the top surface  116 . The cavities  124  and  132  provide resonance to the ultrasound transmitted by the transducers  108  to reinforce the amplitude of the vibrations of the ultrasound. The front wall  134  forms an acute angle alpha with a top surface  116  of the foil  106  to minimize the pressure pulse when the water layer under the member is split by the front wall  134  so a larger part of the water is going down and only a minor part is going between the top side of the foil  116  and the member  102 . When the member  102  is moving over the foil surface  116  a speed dependant under-pressure is created that will force down the member  102  against the foil surface  116 . When the member is leaving the foil  106  there is room to urge the liquid  156  through the member  102 . 
     In other words, the design of the extension  126  is particularly suitable for paper manufacturing that has slurry of water and fibers. The water layer split at the front wall  134  creates an under-pressure pulse so that the water on top of the moving member flows through the member  102  and into a container there below. The design of the extension  126  may also be designed for other applications than paper making that is only used as an illustrative example. 
     The transducer  108  has a top cavity  136  with a threaded inside wall  138  for threadedly receiving the member  122 . The transducer  108  may be attached to the foil  106  in other ways. For example, adhesion or mechanical fasteners may attach the transducer. The present invention is not limited to the threaded connection described above. 
     Below the top cavity  136 , a second housing cavity  140  is defined therein. The cavity  140  has a central segment  141  to hold a bottom cooling spacer  142 , a lower piezoelectric element  144 , a middle cooling spacer  146 , an upper piezoelectric element  148  and a top cooling spacer  150  that bears against a bottom surface  152  of the connecting member  122 . The spacers  142 ,  146 ,  150  are used to lead away the frictional heat that is created by the elements  144 ,  148 . 
     By using three spacers, all the surfaces of the elements  144 ,  148  may be cooled. As the piezoelectric elements  144 ,  148  are activated, the thickness of the elements is changed in a pulsating manner and ultrasonic energy is transmitted to the member  122 . For example, by using a power unit with alternating voltage of a level and frequency selected to suit the application at hand, the elements  144 ,  148  start to vibrate axially. In this way, if the AC frequency is 20 kHz then a sound at the same frequency of 20 kHz is transmitted. It is to be understood that any suitable transducer may be used to generate the ultrasonic energy and the invention is not limited to piezoelectric transducers. 
       FIG. 5  is an enlarged view of a central segment  154  so that the permeable movable member  102  bears or is pressed against the top surface  116  of the member  122  of the foil  106  so there is not sufficient space therebetween to capture cavitation bubbles. In other words, an important feature of the present invention is that a gap  155  defined between the foil  106  and the member  102  is much less than the critical bubble diameter so that no bubbles of critical size can be captured therebetween. The gap  155  between the member  102  and the foil  106  is defined by the tension in the member  102 , the in-going angle between the member  102  and the foil  106 , the pressure pulse induced by the water layer split at the front of the foil  106 , the geometry of the foil  106 , the under-pressure pulse when the member  102  leave the foil  106  and the out-going angle of the member  102 . The bubbles  158  have a diameter d 1  that is much longer than the distance d 2  of the gap  155  between the top surface  116  of the foil  106  and the bottom surface  161  of the permeable member  102 . In this way and by the fact that the member  102  is moving, the cavitation bubbles  158  are forced to be created above the permeable member  102  and by imploding disperse the liquid substance  156  that is subject to the ultrasonic treatment and disposed above the member  102 . The liquid substance  156  has a top surface  160  so that the bubbles  158  are free to move between the top surface  160  of the substance  156  and a top surface  162  of the member  102 . In general, the effect of the ultrasonic energy is reduced by the square of the distance because the liquid absorbs the energy. In this way, there are likely to be more cavitation bubbles formed close to the member  102  compared to the amount of bubbles formed at the surface  160 . An important feature is that because the member  102  is moving and there is not enough room between the foil  106  and the member  102 , no cavitation bubbles are captured therebetween or along the top surface  162  of the movable member  102 . 
     The second embodiment of a transducer system  173  shown in  FIG. 6  is virtually identical to the embodiment shown in  FIG. 4  except that the transducer system  173  has a first channel  164  and a second channel  166  defined therein that are in fluid communication with an inlet  168  defined in a foil member  169 . The channels  164 ,  166  extend perpendicularly to a top surface  170  of a connecting member  172 . The channels  164 ,  166  may extend along the foil  169  and may be used to inject water, containing chemicals, therethrough. For example, in papermaking, the chemicals may be bleaching or softening agents. Other substances such as foaming agents, surfactant or any other substance may be used depending upon the application at hand. The ultrasonic energy may be used to provide a high pressure and temperature that may be required to create a chemical reaction between the chemicals added and the medium. The channels  164 ,  166  may also be used to add regular water, when the slurry above the moving member is too dry, so as to improve the transmission of the ultrasonic energy into the slurry. The chemicals or other liquids mentioned above may also be added via channels in the front part of the transducer assembly bar  106 . If the liquid content of the medium to be treated is very low, the liquid may simply be applied by means of spray nozzles under the web. Also in those cases may the applied liquid be forced into the web by the ultrasonic energy and afterwards be exposed to sufficient ultrasound energy to cause the desired reaction to take place between the chemicals and the medium to be treated. 
       FIG. 7  is an overall side view showing an endless bendable permeable member  174  that is supported by rollers  176   a-e . Below the member  174  is a plurality of transducer systems  178   a-e  for increased output by adding more ultrasonic energy to the system. By using a plurality of transducers, different chemicals may be added to the slurry  179 , as required. The slurry  179  contains fibers or other solids, to be treated with ultrasonic energy, is pumped by a pump  180  in a conduit  181  via a distributor  182  onto the member  174  that moves along an arrow (G). The treated fibers may fall into a container  184 . 
     The transducer system of the present invention is very flexible because there is no formation of cavitation bubble pillows in the path of the ultrasonic energy. By using a plurality of transducers, it is possible to substantially increase the ultrasonic energy without running into the problem of excessive cavitation bubbles to block the ultrasound transmission. The plurality of transducers also makes it possible to add chemicals to the reactor in different places along the moving member, as required. 
       FIG. 8  shows a portion of a sludge treatment plant  200  that has a sludge inlet  202  of a pipe  203  so that a slurry such as a sludge  204  may be pumped through a fiberizer device  206  for dispersing lumps and other aggregates that may have been formed in the sludge  204 . The plant  200  may be a full flow system that permits the continuous feeding in with ultrasonic treatment, continuous circulation with ultrasonic treatment and continuous feeding out with ultrasonic treatment of the sludge slurry  204 , but in that case three separate ultrasound treatment units are needed. The shown plant  200  is meant for part time input with ultrasonic treatment, full time circulation, part time circulation with ultrasonic treatment and part time output to press with ultrasonic treatment 
     Biological drainage and retention aid tube  208  may be in fluid communication with the pipe  203  to permit the addition of biological drainage substances and other treatment substances into the pipe  203 . The sludge  204  flows into a specialized pump  212  that not only functions as a regular pump but also deaerates the sludge before pumping the sludge onto an endless member such as a continuous movable under-wire  214  that may be similar to the endless member  102 , described above. The deaeration is used to improve drainage of the sludge on the wire  214  and to reduce the required length of the ultrasound treatment. The centrifugal pump  212  may have a centrifuge drum connected to the pump wheel and an outlet  210  at the center of the pump inlet to allow low-density substances, such as air and other gases, to be separated from the sludge  204  that exits the pump along the outward periphery of the pump  212 . The use of the fiberizer device  206  and the pump  212  provide for improved dewatering and higher effectiveness of the ultrasound treatment. 
     When the sludge enters the rotatable under-wire  214 , the sludge is further dewatered by gravitation in a pre-drain zone  215  so that the dry substance content of the sludge  204  is increased to about 5-8%. The wire  214  extends and is supported by the rollers  216 ,  224  so that an endless loop is formed. 
     The plant system  200  also has an upper wire  230  that extends between and is supported by the rollers  220 ,  222 . The upper wire  230  exerts some pressure on the sludge disposed on the under wire  214 . The rollers  222  and  224  form a nip  226 . A plurality of vacuum or suction units  231  is disposed above the upper wire  230 . In this way, the sludge is subjected to both an upwardly directed, via vacuum and hydraulic pressure, and downwardly directed, via gravitation and hydraulic pressure, dewatering processes so that the dry substance content of the sludge is increased from about 5-8% at the roller  220  to about 10-15% after the nip  226 . A vacuum or suction unit  231  is disposed under the lower wire  214  to bring the sludge cake to follow the lower wire  214  when the wires separate after the nip  226 . Ultrasonic transducers  234  are disposed above the upper wire  230  and ultrasonic transducers  236  are disposed below the under-wire  214  so that the sludge is continuously subjected to ultrasound treatment, similar to the ultrasound treatment described in detail above, between the rollers  220 ,  222 . As a result of the dewatering process, the average dry substance content of the sludge is about 8-11% during the ultrasonic treatment in the nip  226 . The very high dry substance content reduces the specific energy consumption to about half of conventional systems. 
     After the first ultrasound treatment, most of the bacteria cell walls are punctured and those bacteria are killed. In this way, the inside bacteria protoplasm is dispersed into the sludge/water suspension so that anaerobic bacteria in the fermentation tank can attack and chemically degrade the exposed bacteria, bacteria walls and protoplasm much faster, as described in detail below. 
     As best shown in  FIG. 9 , the transducers  234 ,  236  are placed so close to the wires  214 ,  230  so that the distance (d 3 ) between the transducers  234  and the wire  230  is significant less than a diameter (d 5 ) of a cavitation bubble  227  of critical size at used ultrasonic frequency. Similarly, the distance (d 4 ) between the transducers  236  and the under-wire  214  is less than the diameter (d 5 ) so that no cavitation bubbles  227  of critical size at used ultrasonic frequency may be captured between the transducers and the wires  214 ,  230 . The wire  214  may be slightly angled or wedged relative to the upper wire  230  so that a gap  233  at an incoming end is slightly greater than a downstream gap  235 . The pressure on the sludge is thus gradually increased between the rotatable wires  214 ,  230  as the sludge dryness increases. The wires  214 ,  230  may also be parallel, if desired. 
     The sludge that has been treated with the ultrasound then falls from the wire  214  into a mixer  238  that tears substances into pieces with the spiral formed fins on the cylinders  239 ,  241 . The mixer  238  mixes the treated sludge  204  with water  240  that comes from the ultrasound portion of the wire  214 . This water  240  includes all the enzymes and other biologically degradable substances  242  that may be in liquid form drained from the punctured bacteria in the sludge slurry. The sludge is then deaerated in a specialized pump  246 . 
       FIG. 10  shows a bigger portion of the plant  200  compared to FIG.  8 . The drainage water from the pre-drain zone  215  is led into a conduit  252  that may later be fed back into the mixer  238  or into the water treatment section  300  of the plant. A portion of the drainage water that includes the protoplasm from the collapsed bacteria flows through the vacuum or suction devices  231  and pumped direct into the mixer  238 . Another portion of the ultrasound treated drainage water flows into a conduit  254  and is led back into the mixer  238 . The sludge concentration is now reduced to about 5-6% in view of the added treated drainage water and is forwarded to the pump  246 . The pump  246  deaerates the sludge so that air is removed in view of the anaerobic environment and reactions in the fermentation tank  248 . The pump  246  then pumps the treated sludge including the treated drainage water, via a conduit  256 , to the fermentation tank  248 . The conduit  256  may have valves  258 ,  260 . The tank  248  is filled with sludge  250  that has a dry substance content of about 5-6% that is the about the same as the sludge dry substance content in the mixer  238  that, in turn, is about the same as the sludge dry substance content prior to the ultrasonic treatment at the roller  220 . It may also be possible to add retention/drainage chemicals and fibers directly into the mixers  238 . This is done only when the sludge is destined to the dewatering press. No or very little gas should remain at the top of the tank  248  since the pump  246  removes the gas. Preferably, some gas should remain at the top of the tank  248  and the tank may be equipped with two safety valves in case of power outages. The biogas that is produced in the tank  248  has a much higher methane concentration compared to conventional treatment methods. The methane concentration is about 70-75% compared to 58-62% when conventional methods have been used. Also, the amount of biogas produced is higher. The sludge may be circulated in a conduit  262  connected to a third specialized pump  264  that removes biogas from the system. There is methane producing anaerobic bacteria in the sludge slurry  250  in the tank  248 . The methane gas is produced inside the cell membrane of the anaerobic bacteria and if the methane concentration is high in the slurry  250 , it becomes more difficult for the methane gas to escape through the cell membrane and into the slurry. By removing some of the methane gas in the slurry  250 , the osmotic transfer of the methane gas from the inside of the cell membrane out to the slurry is enhanced. If no methane gas is removed from the slurry  250 , the osmotic transfer may slow down drastically when the methane gas concentration is so high in the slurry  250  that it goes into saturation and gas bubbles start to grow. It should be noted that it with this invention is not necessary to wait until biogas bubbles are formed and float to the surface of the slurry  250  so that the biogas can be withdrawn from the top of the tank  248  as in conventional systems. The pump  264  returns the sludge back into the tank  248  but with substantially less biogas concentration. The biogas retrieved by the pump  264  may flow into a conduit  266 . 
     The plant  200  may be run in sequences. The first ⅓ of the time the tank  248  may be fed with ultrasonic treated and deaerated sludge according to the system described above. It is possible to subject the sludge to further ultrasound treatment, according to the system described above. For example, valves may be opened to permit the sludge in the tank  248  to flow into a conduit  268  and back on the wire  214  to again be subjected to the ultrasound treatment. This may be done the second ⅓ of the time, the plant  200  is used so that a part of all new bacteria that have been formed in the tank  248  may be punctured. All drain water, including the drain water from the pre-drain zone  215 , may be used in the mixer  238  to bring down the dry substance content to about 6% again before it is deaerated and pumped back into the tank  248 . The third ⅓ of the time may be used for feeding the treated sludge into a press unit  270  via a conduit  272 . The sludge may be ultrasound treated before the sludge is sent to the press unit  270  to make sure as many bacteria cells as possible are punctured since the presses in the press unit can only press out water between the bacteria cells and not fluid that may be disposed inside the cells. In this way, the press efficiency is improved by the ultrasound treatment of the sludge. All the time the plant  200  may at least partly be used for re-circulation in the conduit  262  to remove biogas. 
     When the fermentation is started in the tank  248 , the tank should have a carbon dioxide atmosphere so that the anaerobic bacteria may start working at full capacity on the sludge right away without any competition from aerobic bacteria. For example, the carbon dioxide may be pumped into the tank  248  before any processing has taken place in the tank  248 . In this way, any aerobic bacteria in the tank  248  and in the incoming sludge will die due to lack of oxygen and the anaerobic bacteria in the first incoming, at start up not ultrasound treated, sludge may start reproducing without any competition. The ultrasound treatment may be started when a sufficient amount of sludge with live bacteria has been pumped into the fermentation tank  248  with the sludge. The methane producing anaerobic bacteria are used to degrade as big part of the sludge that is pumped into the tank  248  as possible. 
     It is also possible to serially connect many fermentation tanks so that the gas that is withdrawn by the specialized pump in the circulation conduit from the first tank may be sent forwardly to the circulation of the second tank. The gas that is withdrawn from the second tank may be sent forwardly to the third tank etc. The gas that is withdrawn from the last fermentation tank may be sent away for gas purification. The effectiveness of the methane fermentation is thus further increased so that the methane concentration may reach 80% or higher. 
       FIG. 11  is a schematic view of the liquid treatment plant  300  of the present invention. A liquid  301 , such as water, is conveyed in a conduit  302  that has a pump  305  and passed through a filter  303 . The filter  303  removes particles from the liquid that could not pass through the rotatable wires  312 ,  314 . The liquid may then go up into a tank  304  and is then passed through a degassing pump  306  connected to conduits  308  and  310 . The tank  304  may be used to regulate the pressure in the pump  306 . Gas may be passed through a conduit  307  to that, for example, air or other gas that is dissolved in the liquid is removed from the liquid in the conduit  310 . The conduit  310  extends in between two rotatably wires  312 ,  314  and ozone water may be added at the inlet conduit  311  to kill some of the bacteria and oxidize solvents or other impurities in the liquid. As described in detail above, ultrasound transducers  316  are disposed adjacent to the wire  312  while ultrasound transducers  318  are disposed adjacent to the wire  314 . Ozone water may be added into the conduit  310  and also at the transducers  316 ,  318 . The liquid that is passed between the wires  312 ,  314  is subjected to the ultrasound and the ozone water treatment,  315 ,  317 , respectively, to further reduce the bacteria level in the liquid. There are very good synergy between ultrasonic energy and ozone when dealing with killing rate of bacteria. The treated liquid is then drained at drainage or suction units  320 ,  322  and into drainage cavities  321 ,  323 . The liquid may be subjected to ultraviolet light  325 ,  327  at passages  324 ,  326  to even further reduce the bacteria level. The liquid has to be quite transparent by the time it passes the passages  324 ,  326  to get good synergy for ultraviolet light together with ultrasonic energy and eventually used ozone according to bacteria killing rate. The liquid may then be conveyed in conduits  328 ,  330  into a common conduit  332  for degassing treatment in a degassing pump  334  with a gas outlet  336 . The treated liquid may be pumped away in a conduit  338 . It may be possible to modify the system  300  so that the liquid may be re-circulated several times, as desired. 
       FIG. 12  is a schematic illustration of a second embodiment  400  of the present invention for washing of polluted soil in slurry. Polluted soil slurry  402  is conveyed through a pump  404  between movable wires  406 ,  408 . The soil is subjected to ultrasound transducers  410  and the washed soil is collect at a collection site  412 . The water  414  that is collected from the soil slurry may be sent to the liquid treatment plant described above. The same ultrasound principles apply as described above. 
     While the present invention has been described in accordance with preferred compositions and embodiments, it is to be understood that certain substitutions and alterations may be made thereto without departing from the spirit and scope of the following claims.