Patent Application: US-201313987795-A

Abstract:
a method to recover and harvest nutrients from a liquid stream by incorporating them into microorganisms grown in a rotating photobioreactor . the method further includes optionally integrating the rotating photobioreactor with a composting or biogenic drying process .

Description:
the rotating photobioreactor ( rpb ) is a fixed film reactor upon which autotrophic organisms are grown as a biofilm . a basic schematic of the reactor is shown in fig1 - a and 1 - b . it consists of a series of solid or semi - solid rotating plates or discs ( 5 ) that support the growth of a biofilm . the photobioreactor can be open or closed , covered ( 10 ) or uncovered . it can be mounted in a vessel such as a reactor tank ( 9 ), stream channel or water body , waste conveyance channel , etc . the reactor can use natural or artificial light ( 6 ). lighting can be above ( 6 ), between ( 11 ), or below the rotating discs . the discs are supported on a shaft ( 8 ) and driven by any other variety of drives ( 7 ) that can impart a rotating movement to the media . the media upon which the autotrophic organisms are grown may consist of a variety of substances such as wood , cloth , porous ceramics , glass fiber , carbon fiber , etc . modifying the topography or roughness of the surface can increase the plate area . the rpb may incorporate a variety of biomass harvesting devices ( 20 ) such as doctor blades that removed excess biomass growth and discharge the mass to the liquid stream for downstream removal . vacuum suction devices may remove excess growth from any portion of the rotating discs and discharge the concentrated solids to a vacuum receiver . operation of the rotating photobioreactor requires an influent stream ( 1 ) containing essential nutrients , light ( 6 ), and a carbon source such as air with carbon dioxide ( 3 ), carbon dioxide , or bicarbonate . while recovering nutrients , the reactors produce an effluent gas ( 4 ) containing oxygen . the reactor may operate at thermophilic , mesophilic , or psychrophilic temperatures depending on the requirements for the growth of organisms retained on the rotating media . growth of the autotrophic organisms removes a portion of the soluble essential nutrients from the influent stream and carbon dioxide from the gas stream to produce particulate biomass that can be harvested ( 25 ), thereby removing the essential nutrients from the liquid stream and producing an effluent ( 2 ) deficient in nutrients . the rotating photobioreactor may also be used to harvest a variety of gaseous chemicals , such as ammonia , directly or indirectly produced by the autotrophic organisms . the rpb is a unique reactor in that the organisms are exposed to a liquid stream for a portion of the time and a gaseous stream for the remainder of the time . the fraction of the time exposed to either the liquid or the gaseous medium is controlled by the disk submergence or liquid level within the reactor . products within the influent , or produced in the liquid medium , are carried to the gaseous portion of the reactor and thereby stripped with a circulating gas stream ( 3 ). fig2 presents an illustration of the stripping and recovery process . an influent stream ( 1 ) such as anaerobic digestate containing dissolved bicarbonate and dissolved ammonium enters an enclosed ( 10 ) rotating photobioreactor ( 9 ) having any of a variety of light sources ( 6 ) at a lower ph . as a liquid flows through the rpb the autotrophic organisms consume the bicarbonate causing the ph to increase from the influent value to values necessary to causes the ammonium to shift to ammonia gas that can be stripped by a gas flowing over the surface of the rotating plates . supplemental bicarbonate ( hco 3 ) or carbon dioxide may be added to the influent streams to control growth . the liquid influent may enter at any of a variety of ports along the lower portion of the reactor . the influent may also contain recirculated effluent to dilute the influent concentration and bicarbonate as required to maintain autotroph growth . the stripping gas ( 3 ), deficient in the product to be stripped , enters the upper portion , or gaseous portion , of the rpb at any of a variety of ports along the rpb necessary to achieve optimum gas flow over each plate surface . the stripping gas may exit ( 4 ) the rpb at any of a variety of outlet ports along the rpb necessary to achieve optimum product stripping and gas conveyance over each plate surface . the stripping gas ( 4 ) containing the stripped product is conveyed to a condenser ( 15 ) cooled by a chiller ( 12 ) operating at a temperature less than the photobioreactor wherein the stripped water vapor and product ( 4 ) are condensed to form a condensate product ( 21 ) to be used for any beneficial purpose . the condenser produces an influent gas ( 3 ) deficient in the product that is then conveyed by a blower through a heater , if necessary , to the rpb to provide further stripping . depending on the application the blower may provide sufficient heat . excess stripping gas can be discharged and make up gas provided by a pressure and vacuum relief valve ( p & amp ; vr ) ( 17 ). the process of stripping any gas from a liquid stream also removes water vapor that , when condensed , reduces the concentration of the product in the liquid stream since both liquid water and product are produced in the condenser . the concentration of the condensate is directly proportional to the product / water ratio of the stripped gas . as a result most stripping processes produce dilute solutions that have reduced value . in addition to producing a dilute solution the water vapor removes substantial quantities of heat from the reactor . this is a problem inherent in most stripping reactors . minimizing the gas flow rate , stripping temperature , and condensing at higher temperatures will minimize dilution of the condensate product . further concentration can be achieved through the use of a gas permeable membrane or membranes ( 16 ). the concentration process consists of utilizing a high water vapor permeable membrane such as a silicon gas permeable membrane ssp - m823 , available from specialty silicone products , inc ., ballston spa , n . y ., which has a high permeability rate for water vapor ( 3 , 500 +) and lower permeability rates for ammonia ( 500 ), and stripping gases such as methane ( 80 ), nitrogen ( 25 ), and oxygen ( 50 ). the membrane is placed between the stripped gas stream and a plenum . a differential pressure is applied between the stripping gas stream consisting of the stripping gas , water vapor , and ammonia gas ( retentate ) and the lower pressure plenum gas stream ( 18 )( permeate ) composed of water vapor with lower concentrations of the stripping gas and ammonia . after passing through the membrane the stripping gas is depleted of water vapor while the plenum gas ( 18 ) is enriched . the plenum gas is then combined with the influent stripping gas from the condensate unit , thereby enriching the stripping gas with heat , water vapor , and minor concentrations of the product such as ammonia without significant loss of latent heat as shown in fig3 - a and 3 - b . as shown in fig3 - a and 3 - b , one or more water vapor permeable membranes are installed on the stripping gas stream leaving the reactor , but prior to the chiller / condenser ( 15 ). the water permeable membranes are placed under a vacuum by the recirculating blower ( 11 ) and control valve ( 14 ), or another pressurization device , to cause the return flow of water vapor permeate with its latent heat to the photobioreactor . the above - described product concentration process can be applied to a variety of stripping processes using a variety of substrates . “ substrate ” is broadly defined to include , without limitation , a liquid stream or waste substance containing nitrogen , phosphorus , potassium and other essential nutrients , including light required for autotrophic or heterotrophic organism growth , including organic compounds derived from the pretreatment or hydrolysis of cellulosic or lignocellulosic biomass selected from the group consisting of waste materials corn cobs , crop residues , corn husks , corn stover , grasses , wheat straw , barley straw , hay , rice straw , switchgrass , waste paper , sugar cane bagasse , sorghum , soy , components obtained from milling of grains , trees , branches , roots , leaves , wood chips , sawdust , shrubs and bushes , vegetables , fruits , flowers , animal manure , human waste , sugar , algae , cyanobacteria and mixtures thereof . a highly concentrated aqua ammonia stream has significantly greater value if used in ammonia - soaking pretreatment of lignocellulosic biomass for renewable energy production ( 12 +%) as well as in the production of diesel exhaust fluids ( 20 +%). the membrane system presented here can produce both products . the product recovery process ( fig2 ) and the product concentration process ( fig3 - b ) described above may also be applied to heterotrophic bioreactors such as the rbc to strip and recover “ end products ” such as butanol and other alcohols from fermentation processes without producing foam or utilizing excess energy . the rpb may also be integrated with composting or compost drying without producing odors inherent in those processes . such a low pressure integration is shown in fig4 . the photobioreactor ( 9 ) is coupled with a solids compost or compost drying reactor ( 22 ). the photobioreactor receives a liquid or solid stream containing sufficient nutrients for autotrophic growth and produces a liquid stream deficient in nutrients . the photobioreactor also produces a biomass stream that can be harvested ( 25 ) for production of an organic fertilizer , input to the compost dryer , or converted to energy through any of a variety of thermochemical or biological processes such as anaerobic digestion . the photobioreactor also produces oxygen that can be stripped and transported through a suction or discharge blower ( 11 ) with or without a gas heat exchanger ( 27 ) to the enclosed biogenic compost dryer ( 22 ). wet solids ( 20 ) are also input into the compost dryer with or without photobioreactor harvested biomass . the highly oxygenated organic biomass reacts in the reactor ( 22 ) producing carbon dioxide , heat , and water vapor . the reduced and biogenically dried organic compost is discharged from the reactor ( 22 ). the carbon dioxide enriched circulating gas stream containing heat and water vapor exits the compost reactor . the carbon dioxide gas stream may be cooled ( 26 ) and the condensate ( 24 ) recovered , a portion of which may be used in the photobioreactor . cooling for condensate recovery ( 26 ) and heating ( 27 ) for the compost / dryer may be provided by a heat pump ( 23 ). the co 2 produced in the compost / dryer ( 22 ) is then used in the photobioreactor to produce biomass and oxygen in the photobioreactor in a closed loop system . the process provides a means of compost drying without discharging odorous gases to the environment . casey , t . j . 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