Patent Application: US-78489004-A

Abstract:
biological nutrient removal in municipal wastewater treatment to remove carbonaceous substrates , nutrients and phosphorus , has recently become increasingly popular worldwide due to increasingly stringent regulations . biological fluidized bed technology , which could be potentially used for bnr processes , can provide some advantages such as high efficiency and compact structure . this present invention incorporates the fixed - film biological fluidized bed technology with the biological nutrient removal in a liquid - solid circulating fluidized bed , which has achieved the simultaneous elimination of organic carbon , nitrogen and phosphorus , in a very efficient manner and with very compact space requirements . the bnr - lscfb has two fluidized beds , running as anoxic / anaerobic and aerobic processes to accomplish simultaneous nitrification and denitrification and to remove carbonaceous substrates , nutrients and phosphorus , with continuous liquid and solids recirculation through the anoxic / anaerobic bed and the aerobic bed . the new bnr - lscfb system is not only an excellent alternative for conventional activated sludge type bnr technologies but is also capable of processing much higher loadings and suitable for industrial applications .

Description:
referring to fig3 the present invention provides a liquid - solid circulating fluidized bed biological nutrient removal system shown generally at 100 comprised of a pair of fluidized beds , including a first fluidized bed 10 which is a downer column ( aerobic bed ) and a second fluidized bed 12 which is a riser column ( anoxic and anaerobic bed ), which are named according to the movement direction of the particles , a liquid - solid separator 46 on the top of the riser and a similar clarifier 76 on the top of the downer column 10 . both the separator 46 and the clarifier 76 also play a critical role for pressure balance between the riser column 12 and the downer column 10 . beds 10 and 12 are interconnected at their adjacent ends by connecting pipes that allow the circulation of solids between the two columns . the first fluidized bed 10 is a conventional counter - current flow liquid - solid or more precisely gas - liquid - solid bed wherein solid particles 18 ( for example , but not limited to , lava rock particles , zeolite , resin , silica sol - gel or other biomass carriers ) enter from the top connecting pipe 19 near the top of the bed 10 as indicated by the line 17 and flow downward and a first fluidizing fluid such as the recycled effluent 20 enters the bed 10 as indicated schematically at 22 at the lower end 24 of the bed 10 and flows upward in a counter current relationship with respect to the particles 18 . additional gas such as air may be injected into the bottom of the bed 10 as shown at 82 , through a gas distributor 80 . such gas will form bubbles in the bed 10 and flow upwards co - currently with the first fluidizing liquid . because of the gas injection , the first fluidized bed in this case is actually a gas - liquid - solid fluidized bed . without the gas injection , the first fluidized bed will be a liquid - solid fluidized bed . the clarifier 76 located at the top of the first fluidized bed 10 allows particles and sloughed sludge entrained by the upflowing fluid ( s ) to settle back into the first fluidized bed 10 in order to minimize the loss of particles through the effluent . the second fluidized bed 12 on the other hand is a riser fluidized bed wherein the solid particles 18 transferred from bed 10 via the bottom connection pipe 42 enter the bed 12 adjacent to the lower end 26 of the bed 12 and flow upward in co - current relation with a second fluidizing fluid 28 ( such as a mixture of the raw waste water feed 72 and the recycle 74 from the liquid - solid separator 46 located at the top of the riser 12 ) which enters the bed 12 under pressure in the illustrated arrangement through nozzle 30 and inlet 32 both adjacent to the lower end 26 of the bed 12 and flows upward through the bed 12 carrying the particles 18 in its flow . the second fluidized bed 12 as described is a liquid - solid riser fluidized bed operated in the liquid - solid circulating fluidization regime . optionally , gas feed ( not shown in fig3 ) may also be injected into the lower end 26 of the bed 12 , to form a gas - liquid - solid fluidized bed operated in the liquid - solid circulating fluidization regime . the second fluidized bed 12 includes a distributor at the bottom end thereof which divides the incoming stream of the fluid 28 which is the mixture of feed 72 and recycle 74 into two sub - streams : a primary stream 60 and an auxiliary 62 streams . the primary stream 60 is introduced through nozzle 30 which projects into the second fluidized bed column 12 . this design increased the pressure drop across the bottom solids return pipe 42 and makes the system more stable . the auxiliary stream 62 is introduced into the bottom 26 of the second fluidized bed 12 through a perforated plate inlet 32 . the function of the auxiliary stream 62 is to stir up the particles 18 at the bottom of the second fluidized bed 12 to be entrained up the second fluidized bed by the combination of the primary and auxiliary liquid streams 60 and 62 . the two streams 60 and 62 may also be combined into a single stream and fed through a single distributor at the bottom end 26 of the second fluidized bed 12 . as stated above , the solid particles 18 enter downer column 10 at inlet 17 and travel downward through the bed 10 . after they have traversed the fluidized bed 10 the particles 18 enter into the lower connecting pipe 42 , together with some entrained liquid , and are introduced into the second fluidized bed 12 . the column 10 includes the aerobic zone while the column 12 includes the anoxic zone and the anaerobic zone . in the aerobic zone , wastewater rich in organic matter as well as ammonia is biodegraded in the presence of oxygen from the input air , to carbon dioxide , water , and nitrates by the bacteria mainly immobilized on the solid particles . the continuous flow of air and wastewater ensures the sustainability of the aerobic biomass . in the anoxic zone , where the influent wastewater is mixed with the recycled nitrified activated sludge effluent from the aerobic zone , denitrification prevails . nitrates in the nitrified stream from the aerobic section of column 10 is used as a source of oxygen to meet the oxygen demand of the wastewater . the wastewater feed and the decaying biomass sloughed from the aerobic section biofilm provide the carbon source for denitrification . the anaerobic zone is formed as the influent biodegradable wastewater constituents exert an oxygen demand above the anoxic zone . since this demand is not met due to lack of oxygen / air inflow , anaerobic conditions prevail . in the anaerobic zone , stored phosphorus is released and volatile fatty acids are stored for further degradation in the aerobic zone . during operation , biomass carriers with biofilm on them from the aerobic process are transported into the base of the second fluidized bed 12 through the bottom return pipe 42 to make up the particles 18 entrained up along the second fluidized bed 12 . the bottom solids return pipe 42 operates most of the time as a packed moving bed but can also be at a semi - fluidized or conventionally fluidized state . in the lscfb waste water treatment system of the present invention , the circulation rate of the solid particles 18 may be controlled by a butterfly valve 70 located in the bottom return pipe 42 . the splitting of the feed stream to the riser into two streams 60 and 62 with the second stream mobilizing the particles in the bottom section of the riser forms a further hydraulic valve that can also control the circulation rate of the solid particles 18 . there are other possible types of hydraulic valves such as loop seal etc . either a mechanical valve or a hydraulic valve or both can be used to control the flow rate of the solid particles 18 . normally , a mechanical valve is preferred over a hydraulic valve because the mechanical valve usually provides a higher and more stable pressure drop across the return pipe 42 and therefore makes the system more stable and also makes it easier to maintain a pressure balance between the two columns . the auxiliary liquid stream 62 , if used together with the mechanical valve , provides additional control of the circulation rate of the solid particles 18 . the recycle stream 20 from the effluent 44 as above described enters at the bottom of the bed 10 and travels , together with the injected gas ( mostly likely air ) stream , in a countercurrent relationship to the particles 18 through the downer column 10 and leaves at the top of column 10 as indicated at 44 . the clarifier 76 at the top of the first fluidized bed 10 separates out the entrained particles 18 and sloughed sludge formed during the process , and returns them back to bed 10 , before the gas and fluid exiting the column . the clarifier 76 also periodically discharge the sloughed sludge through a port ( or ports ) 45 . the fluid exiting from column 10 at 44 is the effluent , part of which is released as treated water and part of which recycled back to the bottom of the downer column 10 to sustain the operation of the process . the second fluidizing fluid 28 ( which is a combination of raw waste water feed 72 plus the recycle stream 74 from the liquid - solid separator 46 at the top of the riser column 12 ) and the particles 18 along with some of the nitrified effluent from the aerobic zone from pipe 42 travel in co - current relationship upward through the bed 12 and then enter liquid - solid separator 46 ( such as a settler ) having a fluid outlet 48 through which most of the second fluidizing fluid 28 is removed and an outlet 50 for the particles 18 and some of the fluid from the fluidized bed 12 located at the bottom open to the upper connecting pipe 19 . solid particles from the separator 46 , together with some entrained liquid , flows down via the upper connection pipe 19 to the inlet 17 in the downer column 10 . if additional gas is injected to the bottom 26 of the riser column 12 , the gas will travel co - currently upwards , together with the fluid , to fluidize the solid particles . such gas will be separated out in the top separator 46 . the application of the present invention will be further described below in relation to wastewater treatment , but it may be also used in other applications , for example effluent treatment from a host of industrial processes . the present invention will now be illustrated using the following non - limiting example . a flow diagram illustrating the fixed - film bnr process used in the lscfb 100 ( fig3 ) of the present invention is illustrated in fig2 . in connection with fig3 , the aerobic process takes place in the downer bed 10 and the anoxic process takes place in the lower part of the riser bed 12 and the anaerobic process takes place in the upper part of the riser bed 12 . an alternative is to have the anoxic process in the upper part of the riser and the anaerobic in the lower part of the riser . in this case , however , most of the nitrified effluent from the aerobic zone needs to be fed half way in the riser to the bottom of the anoxic zone . raw wastewater 72 ( primary influent or primary effluent ) is first mixed with the anoxic / anaerobic effluent recycle stream 74 from the liquid - solid separator 46 at the top of the riser and then fed into the bottom of the riser bed 12 where the activated sludge loaded on the recirculating solid particles along with some previously nitrified wastewater from the aerobic process in the downer bed 10 which is also mixed with the raw wastewater 72 and the anoxic / anaerobic effluent recycle stream 74 . the fluid containing the raw wastewater , effluent recycle stream 74 , the previously nitrified wastewater and the solid particles loaded with microbes , flow co - currently up the riser 12 while contacting each other . the riser column 12 operates in the liquid - solid circulating fluidization regime and provides excellent interfacial mass transfer between the liquid and the activated sludge , thus significantly enhancing the process intensity . in the lower section of the riser 12 , anoxic conditions that are conducive to denitrification prevail . the carbon source for denitrification in the bottom half of the riser can either be a portion of the wastewater feed or the decaying biomass sloughed from the downer bed biofilm , or both . then , wastewater flows further upwards into the anaerobic zone maintained in the upper half of the riser , where stored phosphorus is released and volatile fatty acids are stored for further degradation in the aerobic zone . the elimination of nitrates upstream of the anaerobic zone will greatly enhance phosphorus release and subsequent uptake in the aerobic downer bed 10 . it is important to note that since liquid - solid separation and subsequent solid recycle to the downer bed 10 occurs immediately after the anaerobic phase , enhanced phosphorus uptake in the aerobic downer bed will also likely take place . in the liquid - solid separator 46 at the top of the riser 12 , the solid particles loaded with microbes are separated out from the liquid stream and , along with some effluent liquid also from the liquid - solid separator 46 , are introduced into the top of the downer bed 10 through the upper connecting pipe 19 . treated wastewater that comes with the recirculated solids from the riser 12 is joined at the top inlet 17 of the downer bed 10 by recycled effluent from downer column 10 flowing up through the downer bed 10 . part 20 of the combined stream equivalent to approximately 5 - 15 times of the wastewater feedrate is recycled into the downer bed 10 and the remaining part 44 exits the system as treated effluent . the recycled liquid 20 is also used to fluidize the downer bed 10 so that it is essential to introduce it into the downer bed 10 from the bottom , near the injection port for air ( or oxygen containing gas ). by provision of air in the downer bed 10 and control of air flowrate , and by control of the recycled liquid flowrate , the aerobic zone can be well maintained in the downer bed 10 under the conventional gas - liquid - solid three - phase fluidization regime . the solids attached with biomass flow by gravity to the bottom of the downer bed 10 , and then into the riser bottom through the bottom inclined connection pipe 42 . some of the sloughed sludge formed during the process is periodically discharged from the aerobic zone through outlet 45 in clarifier 76 . the system can be designed such that the fluid flow from the downer bed to the bottom of the riser 12 is of an appropriate recycle flowrate ( e . g ., 4 folds the influent flow rate ), to simulate recirculation of nitrified mixed liquor from the aeration tank to the anoxic tank in a conventional activated sludge type bnr system . another alternative is to feed the wastewater halfway in the riser to the anaerobic zone , as shown by the dotted line in both fig2 and 3 ( 78 ). in such a case , a portion of the effluent from the riser needs to be recycled to the bottom of the riser , to fluidize the bottom anoxic portion of the riser . this fixed - film biological nutrient removal ( bnr ) lscfb process combines the advantages of the suspended growth bnr process with those of the fixed - film in a single unit . in addition to the advantages of the fixed - film processes with respect to sludge settle - ability and accordingly to the reduced size of the clarifiers for liquid - solid separation , the lscfb re - circulates attachment media with high settling velocities , such that only a small liquid - solid separation tank is needed instead of a separate clarifier . furthermore , due to fluidization , the bnr - lscfb can handle both soluble and particulate - laden wastewater , thus possibly eliminating the need for primary clarifiers . more specifically , the bnr - lscfb system disclosed herein offers the following advantages over the widely employed conventional activated sludge and the more recently developed suspended growth bnr systems . 1 ) a much smaller area and very compact reactor sizes , due to higher biomass density per unit bioreactor volume and the elimination of both primary and secondary clarifiers ; 2 ) the minimization of operational labour requirements with the elimination of routine tasks such as solids analysis in the aeration tank and the return of activated sludge , cleaning of clarifier weir launders , wasting sludge , control of chemical dosing and maintenance of chemical feed systems ; 3 ) an enhanced process stability as a result of better biosolids retention ; 4 ) the capability to handle simultaneously soluble and particulate wastes due to the suspension of particulates within the fluidized - beds ; 5 ) less vulnerability to shock loadings of toxicants and inhibitory substances as a result of lower toxicant - to - biomass ratios than in suspended - growth ; 6 ) the minimization / elimination of chemical addition for phosphorus removal ; 7 ) a significant reduction in sludge generation and the minimization of chemical sludge compared to the activated sludge system due to lower bacterial yields in the anoxic tank , and the minimization of biological sludge compared to the bnr system due to its operation at a much longer solids residence time and accordingly much higher biomass decay rates ; 8 ) a substantial reduction in oxygen requirements and thus major savings in energy requirements ; 9 ) the potential reduction in organic carbon requirements for nutrient - removal due to enhanced utilization of particulate substrates as a result of better entrapment in the fluidized bed as well as decaying biofilm as a carbon source . in summary , the process offers the potential to achieve a highly treated effluent quality at significant cost savings in capital and operation / maintenance costs compared to existing technologies , with remarkable process stability . in addition , while this fixed - film bnr lscfb process is applicable to any municipal wastewater treatment application , it is particularly advantageous for treatment of wastes from industries that very often have space limitations and special needs . for example , this technology can be used to treat specific concentrated streams of industrial wastewater as well as to provide end - of - pipe treatment to the overall wastewater . the other potential principal application of the technology would be small communities and new developments , which have limited financial resources , given the drastically reduced cost , space , and energy requirements . in studies carried out by the inventors , experiments , soluble cod concentrations in the effluent ranging from 4 to 20 mg / l were obtained at varying cod loading rates ; ammonia nitrogen removal efficiencies averaged in excess of 99 % at a minimum total hydraulic retention time ( hrt ) of 2 . 2 hours over a temperature range of 25 ° c . to 28 ° c . effluent nitrate nitrogen concentration of less than 5 mg / l was achieved by increasing nitrified liquid recycle rate . no nitrite accumulation could be observed either in the anoxic bed or in the aerobic bed . the bnr - lscfb appears to be not only an excellent alternative for conventional activated sludge type bnr technologies but also capable of processing much higher loadings and suitable for industrial applications . it will be appreciated that the apparatus and process of the present invention are not limited to having the aerobic section in the downer column 10 and the anoxic and anaerobic sections in the riser column 12 , and that these may be reversed so that the aerobic section with gas injection may be located in the riser column 12 and the anoxic and anaerobic sections may be in the downer column 10 . it will be understood by those skilled in the art that the relative sizes of the riser bed 12 and downer bed 10 are dictated by the wastewater characteristics and treatment goals , and accordingly should specific requirements necessitate different relative sizing , the technology can readily be adapted to have an aerobic riser and an anoxic / anaerobic downer . as used herein , the terms “ comprises ”, “ comprising ”, “ including ” and “ includes ” are to be construed as being inclusive and open ended , and not exclusive . specifically , when used in this specification including claims , the terms “ comprises ”, “ comprising ”, “ including ” and “ includes ” and variations thereof mean the specified features , steps or components are included . these terms are not to be interpreted to exclude the presence of other features , steps or components . the foregoing description of the preferred embodiments of the invention has been presented to illustrate the principles of the invention and not to limit the invention to the particular embodiments illustrated . it is intended that the scope of the invention be defined by all of the embodiments encompassed within the following claims and their equivalents . 1 kunii , d . and levenspiel , o ., fluidization engineering , butterworth - 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