Patent Publication Number: US-8969067-B2

Title: Process for growing biomass by modulating supply of gas to reaction zone

Description:
FIELD OF THE INVENTION 
     The present invention relates to a process for growing biomass. 
     BACKGROUND 
     The cultivation of phototrophic organisms has been widely practised for purposes of producing a fuel source. Exhaust gases from industrial processes have also been used to promote the growth of phototrophic organisms by supplying carbon dioxide for consumption by phototrophic organisms during photosynthesis. By providing exhaust gases for such purpose, environmental impact is reduced and, in parallel a potentially useful fuel source is produced. Challenges remain, however, to render this approach more economically attractive for incorporation within existing facilities. 
     SUMMARY OF THE INVENTION 
     In one aspect, there is provided a process of growing a phototrophic biomass in a reaction zone. The reaction zone includes an operative reaction mixture. The operative reaction mixture includes the phototrophic biomass disposed in an aqueous medium. Gaseous exhaust material is produced with a gaseous exhaust material producing process, wherein the gaseous exhaust material includes carbon dioxide. Reaction zone feed material is supplied to the reaction zone such that any carbon dioxide of the reaction zone feed material is received by the phototrophic biomass so as to provide a carbon dioxide-enriched phototrophic biomass in the aqueous medium. The carbon dioxide-enriched phototrophic biomass disposed in the aqueous medium is exposed to photosynthetically active light radiation so as to effect photosynthesis. A discharge of the gaseous exhaust material from the gaseous exhaust material producing process is modulated based on sensing of at least one reaction zone parameter. The modulating of the discharge of the gaseous exhaust material includes modulating of a supply of the discharged gaseous exhaust material to the reaction zone feed material, wherein the discharged gaseous exhaust material which is supplied to the reaction zone feed material defines a gaseous exhaust material reaction zone supply, wherein the gaseous exhaust material reaction zone supply includes carbon dioxide. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The process of the preferred embodiments of the invention will now be described with the following accompanying drawing: 
       The FIGURE is a process flow diagram of an embodiment of the process. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the FIGURE, there is provided a process of growing a phototrophic biomass in a reaction zone  10 , wherein the reaction zone  10  includes an operative reaction mixture. The operative reaction mixture includes the phototropic biomass disposed in an aqueous medium. 
     “Phototrophic organism” is an organism capable of phototrophic growth in the aqueous medium upon receiving light energy, such as plant cells and micro-organisms. The phototrophic organism is unicellular or multicellular. In some embodiments, for example, the phototrophic organism is an organism which has been modified artificially or by gene manipulation. In some embodiments, for example, the phototrophic organism is algae. In some embodiments, for example, the algae is microalgae. 
     “Phototrophic biomass” is at least one phototrophic organism. In some embodiments, for example, the phototrophic biomass includes more than one species of phototrophic organisms. 
     “Reaction zone  10 ” defines a space within which the growing of the phototrophic biomass is effected. In some embodiments, for example, the reaction zone  10  is provided in a photobioreactor  12 . 
     “Photobioreactor  12 ” is any structure, arrangement, land formation or area that provides a suitable environment for the growth of phototrophic biomass. Examples of specific structures which can be used as a photobioreactor  12  by allowing for containment and growth of phototrophic biomass using light energy include, without limitation, tanks, ponds, troughs, ditches, pools, pipes, tubes, canals, and channels. Such photobioreactors may be either open, closed, partially closed, covered, or partially covered. In some embodiments, for example, the photobioreactor  12  is a pond, and the pond is open, in which case the pond is susceptible to uncontrolled receiving of materials and light energy from the immediate environments. In other embodiments, for example, the photobioreactor  12  is a covered pond or a partially covered pond, in which case the receiving of materials from the immediate environment is at least partially interfered with. The photobioreactor  12  includes the reaction zone  10 . The photobioreactor  12  is configured to receive a supply of phototrophic reagents (and, in some embodiments other nutrients), and is also configured to effect the recovery or harvesting of biomass which is grown within the reaction zone  10 . In this respect, the photobioreactor  12  includes one or more inlets for receiving the supply of phototrophic reagents and other nutrients, and also includes one or more outlets for effecting the recovery or harvesting of biomass which is grown within the reaction zone  10 . In some embodiments, for example, one or more of the inlets are configured to be temporarily sealed for periodic or intermittent time intervals. In some embodiments, for example, one or more of the outlets are configured to be temporarily sealed or substantially sealed for periodic or intermittent time intervals. The photobioreactor  12  is configured to contain an operative reaction mixture including an aqueous medium and phototrophic biomass, wherein the aqueous medium is disposed in mass transfer relationship with the phototrophic biomass so as to effect mass transfer of phototrophic reagents from the aqueous medium to the phototrophic biomass. The phototrophic reagents are water and carbon dioxide. The photobioreactor  12  is also configured so as to establish photosynthetically active light radiation (for example, a light of a wavelength between about 400-700 nm, which can be emitted by the sun or another light source) within the photobioreactor  12  for exposing the phototrophic biomass. The exposing of the phototrophic biomass, which includes phototrophic reagents transferred from the aqueous medium, to the photosynthetically active light radiation effects photosynthesis by the phototrophic biomass. In some embodiments, for example, the established light radiation is provided by an artificial light source  14  disposed within the photobioreactor  12 . For example, suitable artificial lights sources include submersible fiber optics or light guides, light-emitting diodes (“LEDs”), LED strips and fluorescent lights. Any LED strips known in the art can be adapted for use in the photobioreactor  12 . In the case of the submersible LEDs, in some embodiments, for example, energy sources include alternative energy sources, such as wind, photovoltaic cells, fuel cells, etc. to supply electricity to the LEDs. In the case of fiber optics, solar collectors with selective wavelength filters may be used to bring natural light to the photobioreactor  12 . Fluorescent lights, external or internal to the photobioreactor  12 , can be used as a back-up system. In some embodiments, for example, the established light is derived from a natural light source  16  which has been transmitted from externally of the photobioreactor  12  and through a transmission component. In some embodiments, for example, the transmission component is a portion of a containment structure of the photobioreactor  12  which is at least partially transparent to the photosynthetically active light radiation, and which is configured to provide for transmission of such light to the reaction zone  10  for receiving by the phototrophic biomass. In some embodiments, for example, both natural and artificial lights sources are provided for effecting establishment of the photosynthetically active light radiation within the photobioreactor  12 . 
     “Aqueous medium” is an environment which includes water and sufficient nutrients to facilitate viability and growth of the phototrophic biomass. The nutrients includes dissolved carbon dioxide. In some embodiments, for example, additional nutrients may be included such as one of, or both of, NO X  and SO X . Suitable aqueous media are discussed in detail in: Rogers, L. J. and Gallon J. R. “Biochemistry of the Algae and Cyanobacteria,” Clarendon Press Oxford, 1988; Burlew, John S. “Algal Culture: From Laboratory to Pilot Plant.” Carnegie Institution of Washington Publication 600. Washington, D.C., 1961 (hereinafter “Burlew 1961”); and Round, F. E. The Biology of the Algae. St Martin&#39;s Press, New York, 1965; each of which is incorporated herein by reference). A suitable nutrient composition, known as “Bold&#39;s Basal Medium”, is described in Bold, H. C. 1949,  The morphology of Chlamydomonas chlamydogama sp. nov. Bull. Torrey Bot. Club.  76: 101-8 (see also Bischoff, H. W. and Bold, H. C. 1963.  Phycological Studies IV. Some soil algae from Enchanted Rock and related algal species , Univ. Texas Publ. 6318: 1-95, and Stein, J. (ED.)  Handbook of Phycological Methods, Culture methods and growth measurements , Cambridge University Press, pp. 7-24). 
     The process includes producing a gaseous exhaust material  18  with a gaseous exhaust material producing process  20 . The gaseous exhaust material includes carbon dioxide. The gaseous exhaust material producing process  20  includes any process which effects production of the gaseous exhaust material. In some embodiments, for example, the gaseous exhaust material producing process  20  is a combustion process being effected in a combustion facility. In some of these embodiments, for example, the combustion process effects combustion of a fossil fuel, such as coal, oil, or natural gas. For example, the combustion facility is any one of a fossil fuel-fired power plant, an industrial incineration facility, an industrial furnace, an industrial heater, or an internal combustion engine. In some embodiments, for example, the combustion facility is a cement kiln. 
     Reaction zone feed material  22  is supplied to the reaction zone  10  such that any carbon dioxide of the reaction zone feed material  22  is received by the phototrophic biomass so as to provide a carbon dioxide-enriched phototrophic biomass in the aqueous medium. During at least some periods of operation of the process, at least a fraction of the reaction zone feed material  22  is supplied by the gaseous exhaust material  18  which is discharged from the gaseous exhaust material producing process  20 . The gaseous exhaust material  18  which is supplied to the reaction zone feed material  22  defines a gaseous exhaust material reaction zone supply  24 , and the gaseous exhaust material reaction zone supply  24  includes carbon dioxide. In some embodiments, for example, the gaseous exhaust material  18  includes a carbon dioxide concentration of at least 2 volume % based on the total volume of the gaseous exhaust material  18 . In this respect, in some embodiments, for example, the gaseous exhaust material reaction zone supply  24  includes a carbon dioxide concentration of at least 2 volume % based on the total volume of the gaseous exhaust material reaction zone supply  24 . In some embodiments, for example, the gaseous exhaust material reaction zone supply  24  also includes one of, or both of, NO X  and SO X . 
     In some of these embodiments, for example, the gaseous exhaust material reaction zone supply  24  is at least a fraction of the gaseous exhaust material  18  being produced by the gaseous exhaust material producing process  20 . In some cases, the gaseous exhaust material reaction zone supply  24  is the gaseous exhaust material  18  being produced by the gaseous exhaust material producing process  20 . 
     In some embodiments, for example, the reaction zone feed material  22  is cooled prior to supply to the reaction zone  10  so that the temperature of the reaction zone feed material  22  aligns with a suitable temperature at which the phototrophic biomass can grow In some embodiments, for example, the gaseous exhaust material reaction zone supply  24  being supplied to the reaction zone material  22  is disposed at a temperature of between 110 degrees Celsius and 150 degrees Celsius. In some embodiments, for example, the temperature of the gaseous exhaust material reaction zone supply  24  is about 132 degrees Celsius. In some embodiments, the temperature at which the gaseous exhaust material reaction zone supply  24  is disposed is much higher than this, and, in some embodiments, such as the gaseous exhaust material reaction zone supply  24  from a steel mill, the temperature is over 500 degrees Celsius. In some embodiments, for example, the reaction zone feed material  22 , which has been supplied with the gaseous exhaust material reaction zone supply  24 , is cooled to between 20 degrees Celsius and 50 degrees Celsius (for example, about 30 degrees Celsius). Supplying the reaction zone feed material  22  at higher temperatures could hinder growth, or even kill, the phototrophic biomass in the reaction zone  10 . In some of these embodiments, in cooling the reaction zone feed material  22 , at least a fraction of any water vapour in the reaction zone feed material  22  is condensed in a heat exchanger  26  (such as a condenser) and separated from the reaction zone feed material  22  as an aqueous material  70 . In some embodiments, the resulting aqueous material  70  is diverted to a return pond  28  (described below) where it provides supplemental aqueous material for supply to the reaction zone  10 . In some embodiments, the condensing effects heat transfer from the reaction zone feed material  22  to a heat transfer medium  30 , thereby raising the temperature of the heat transfer medium  30  to produce a heated heat transfer medium  30 , and the heat transfer medium  30  is then supplied (for example, flowed) to a dryer  32  (discussed below), and heat transfer is effected from the heated heat transfer medium  30  to an intermediate concentrated biomass product  34  to effect drying of the intermediate concentrated biomass product  34  and thereby effect production of the final biomass product  36 . In some embodiments, for example, after being discharged from the dryer  32 , the heat transfer medium  30  is recirculated to the heat exchanger  26 . Examples of a suitable heat transfer medium  30  include thermal oil and glycol solution. 
     With respect to the reaction zone feed material  22 , the reaction zone feed material  22  is a fluid. In some embodiments, for example, the reaction zone feed material  22  is a gaseous material. In some embodiments, for example, the reaction zone feed material  22  includes gaseous material disposed in liquid material. In some embodiments, for example, the liquid material is an aqueous material. In some of these embodiments, for example, at least a fraction of the gaseous material is dissolved in the liquid material. In some of these embodiments, for example, at least a fraction of the gaseous material is disposed as a gas dispersion in the liquid material. In some of these embodiments, for example, and during at least some periods of operation of the process, the gaseous material of the reaction zone feed material  22  includes carbon dioxide supplied by the gaseous exhaust material reaction zone supply  24 . In some of these embodiments, for example, the reaction zone feed material  22  is supplied to the reaction zone  10  as a flow. 
     In some embodiments, for example, the reaction zone feed material  22  is supplied to the reaction zone  10  as one or more reaction zone feed material flows. For example, each of the one or more reaction zone feed material flows is flowed through a respective reaction zone feed material fluid passage. In some embodiments, for example, a flow of reaction zone feed material  22  is a flow of the gaseous exhaust material reaction zone feed material supply  24 . 
     The supply of the reaction zone feed material  22  to the reaction zone  10  effects agitation of at least a fraction of the phototrophic biomass disposed in the reaction zone  10 . In this respect, in some embodiments, for example, the reaction zone feed material  22  is introduced to a lower portion of the reaction zone  10 . In some embodiments, for example, the reaction zone feed material  22  is introduced from below the reaction zone  10  so as to effect mixing of the contents of the reaction zone  10 . In some of these embodiments, for example, the effected mixing (or agitation) is such that any difference in phototrophic biomass concentration between two points in the reaction zone  10  is less than 20%. In some embodiments, for example, any difference in phototrophic biomass concentration between two points in the reaction zone  10  is less than 10%. In some of these embodiments, for example, the effected mixing is such that a homogeneous suspension is provided in the reaction zone  10 . In those embodiments with a photobioreactor  12 , for some of these embodiments, for example, the supply of the reaction zone feed material  22  is co-operatively configured with the photobioreactor  12  so as to effect the desired agitation of the at least a fraction of the phototrophic biomass disposed in the reaction zone  10 . 
     With further respect to those embodiments where the supply of the reaction zone feed material  22  to the reaction zone  10  effects agitation of at least a fraction of the phototrophic biomass disposed in the reaction zone  10 , in some of these embodiments, for example, the reaction zone feed material  22  flows through a gas injection mechanism, such as a sparger  40 , before being introduced to the reaction zone  10 . In some of these embodiments, for example, the sparger  40  provides reaction zone feed material  22  to the reaction zone  10  in fine bubbles in order to maximize the interface contact area between the phototrophic biomass and the carbon dioxide (and, in some embodiments, for example, one of, or both of, SO X  and NO X ) of the reaction zone feed material  22 . This assists the phototrophic biomass in efficiently absorbing the carbon dioxide (and, in some embodiments, or other gaseous components) required for photosynthesis, thereby promoting the optimization of the growth rate of the phototrophic biomass. As well, in some embodiments, for example, the sparger  40  provides reaction zone feed material  22  in larger bubbles that agitate the phototrophic biomass in the reaction zone  10  to promote mixing of the components of the reaction zone  10 . An example of a suitable sparger  40  is a FLEXAIR™ threaded disc diffuser T-Series Tube Diffuser Model 91×1003 supplied by Environmental Dynamics Inc of Columbia, Mo. In some embodiments, for example, this sparger  40  is disposed in a photobioreactor  12  having a reaction zone  10  volume of 6000 liters and with an algae concentration of between 0.8 grams per liter and 1.5 grams per liter, and the reaction zone feed material  22  is a gaseous fluid flow supplied at a flowrate of between 10 cubic feet per minute and 20 cubic feet per minute, and at a pressure of about 68 inches of water. 
     With respect to the sparger  40 , in some embodiments, for example, the sparger  40  is designed to consider the fluid head of the reaction zone  10 , so that the supplying of the reaction zone feed material  22  to the reaction zone  10  is effected in such a way as to promote the optimization of carbon dioxide absorption by the phototrophic biomass. In this respect, bubble sizes are regulated so that they are fine enough to promote optimal carbon dioxide absorption by the phototrophic biomass from the reaction zone feed material. Concomitantly, the bubble sizes are large enough so that at least a fraction of the bubbles rise through the entire height of the reaction zone  10 , while mitigating against the reaction zone feed material  22  “bubbling through” the reaction zone  10  and being released without being absorbed by the phototrophic biomass. To promote the realization of an optimal bubble size, in some embodiments, the pressure of the reaction zone feed material  22  is controlled using a pressure regulator upstream of the sparger  40 . 
     With respect to those embodiments where the reaction zone  10  is disposed in a photobioreactor  12 , in some of these embodiments, for example, the sparger  40  is disposed externally of the photobioreactor  12 . In other embodiments, for example, the sparger  40  is disposed within the photobioreactor  12 . In some of these embodiments, for example, the sparger  40  extends from a lower portion of the photobioreactor  12  (and within the photobioreactor  12 ). 
     In some embodiments, for example, the reaction zone feed material  22  is supplied at a pressure which effects flow of the reaction zone feed material  22  through at least a seventy (70) inch vertical extent of the aqueous medium. In some of these embodiments, for example, the supplying of the reaction zone feed material  22  is effected while the gaseous exhaust material  18  is being produced by the gaseous exhaust material producing process  20 . In some embodiments, for example, the supplying of the reaction zone feed material  22  to the reaction zone  10  is effected while the gaseous exhaust material reaction zone supply  24  is being supplied to the reaction zone feed material  22 . In some of these embodiments, the exposing of the carbon dioxide-enriched phototrophic biomass disposed in the aqueous medium to photosynthetically active light radiation is effected while the supplying of the reaction zone feed material  22  is being effected. In some of these embodiments, for example, the reaction zone feed material  22  is a gaseous flow. In some of these embodiments, for example, the pressure of the flow of the reaction zone feed material  22  is increased before being supplied to the reaction zone  10 . In some embodiments, for example, the pressure increase is at least partially effected by a prime mover  38 . For those embodiments where the pressure increase is at least partially effected by the prime mover  38 , examples of a suitable prime mover  38  include a blower, a compressor, a pump (for embodiments where the reaction zone feed material  22  includes liquid material), and an air pump. In other embodiments, for example, the pressure increase is effected by a jet pump or eductor. With respect to such embodiments, where the pressure increase is effected by a jet pump or eductor, in some of these embodiments, for example, the gaseous exhaust material reaction zone supply  24  is supplied to the jet pump or eductor and pressure energy is transferred to the gaseous exhaust material reaction zone from another flowing fluid using the venturi effect to effect the pressure increase in the reaction zone feed material  24 . In some of these embodiments, for example, the another flowing fluid includes liquid material and, in this respect, the resulting flow of reaction zone feed material  24  includes a combination of liquid and gaseous material. The pressure increase is designed to overcome the fluid head within the reaction zone  10 . 
     In some embodiments, for example, the photobioreactor  12 , or plurality of photobioreactors  12 , are configured so as to optimize carbon dioxide absorption by the phototrophic biomass and reduce energy requirements. In this respect, the photobioreactor (s) is, or are, configured to provide increased residence time of the carbon dioxide within the reaction zone  10 . As well, movement of the carbon dioxide over horizontal distances is minimized, so as to reduce energy consumption. To this end, the photobioreactor  12  is, or are, relatively taller, and provide a reduced footprint, so as to increase carbon dioxide residence time while conserving energy. 
     In some embodiments, for example, a nutrient supply  42  is supplied to the reaction zone  10 . In some embodiments, for example, the nutrient supply  42  is effected by a pump, such as a dosing pump. In other embodiments, for example, the nutrient supply  42  is supplied manually to the reaction zone  10 . Nutrients within the reaction zone  10  are processed or consumed by the phototrophic biomass, and it is desirable, in some circumstances, to replenish the processed or consumed nutrients. A suitable nutrient composition is “Bold&#39;s Basal Medium”, and this is described in Bold, H. C. 1949,  The morphology of Chlamydomonas chlamydogama sp. nov. Bull. Torrey Bot. Club.  76: 101-8 (see also Bischoff, H. W. and Bold, H. C. 1963.  Phycological Studies IV. Some soil algae from Enchanted Rock and related algal species , Univ. Texas Publ. 6318: 1-95, and Stein, J. (ED.)  Handbook of Phycological Methods, Culture methods and growth measurements , Cambridge University Press, pp. 7-24). 
     In some of these embodiments, the rate of supply of the nutrient supply  42  to the reaction zone  10  is controlled to align with a desired rate of growth of the phototrophic biomass in the reaction zone  10 . In some embodiments, for example, regulation of nutrient addition is monitored by measuring any combination of pH, NO 3  concentration, and conductivity in the reaction zone  10 . 
     In some embodiments, for example, a supplemental aqueous material supply  44  is supplied to the reaction zone  10 . This is, in part, to effect make-up of those contents of the reaction zone  10  which are discharged from the reaction zone  10  as a photobioreactor discharged biomass product  59 . In some embodiments, for example, the supplemental aqueous material supply  44  is supplied by a pump. In some of these embodiments, for example, the supplemental aqueous material supply  44  is continuously supplied to the reaction zone  10  to effect harvesting of the biomass by overflow of the discharged biomass product  59 . 
     In this respect, in some of these embodiments, for example, the process further includes discharging the biomass product  59  from the photobioreactor  12 , wherein the product includes at least a fraction of the contents of the reaction zone  10  of the photobioreactor  12 . Supply of the supplemental aqueous material supply  44  is effected to the reaction zone  10  so as to replenish the contents of the photobioreactor  12 . The supplemental aqueous material supply  44  includes at least one of: (a) aqueous material which has been condensed from the reaction zone feed material  22  while the reaction zone feed material  22  is cooled before being supplied to the reaction zone  10 , and (b) aqueous material which has been separated from the discharged biomass product  59 . 
     In some of these embodiments, for example, the discharging of the biomass product  59  is effected by an overflow of the at least a fraction of the contents of the reaction zone  10  of the photobioreactor  12 . When the upper level of the contents of the reaction zone  10  within the photobioreactor  12  becomes disposed below a predetermined minimum level, the supplying of, or an increase to the molar rate of supply, of the supplemental aqueous material supply  44  (which has been recovered from the process) is effected to the reaction zone  10 . In some embodiments, for example, the recovered aqueous material is water. 
     In some embodiments, for example, at least a fraction of the supplemental aqueous material supply  44  is supplied from a return pond  28 , which is further described below. At least a fraction of aqueous material which is discharged from the process is recovered and supplied to the return pond  28  to provide supplemental aqueous material in the return pond  28 . 
     In some embodiments, for example, the nutrient supply  42  and the supplemental aqueous material supply  44  are supplied to the reaction zone  10  as a portion of the reaction zone feed material  22 . In this respect, in some of these embodiments, the nutrient supply  42  and the supplemental aqueous material supply  44  are supplied to the reaction zone feed material  22  in the sparger  40  before being supplied to the reaction zone  10 . In those embodiments where the reaction zone  10  is disposed in the photobioreactor  12 , in some of these embodiments, for example, the sparger  40  is disposed externally of the photobioreactor  12 . In some embodiments, it is desirable to mix the gaseous exhaust material reaction zone supply  24  with the nutrient supply  42  and the supplemental aqueous material supply  44  within the sparger  40 , as this effects better mixing of these components versus separate supplies of the reaction zone feed material  22 , the nutrient supply  42 , and the supplemental aqueous material supply  44 . On the other hand, the rate of supply of the reaction zone feed material  22  to the reaction zone  10  is limited by virtue of saturation limits of gaseous material of the reaction zone feed material  22  in the combined mixture. Because of this trade-off, such embodiments are more suitable when response time required for providing a modulated supply of carbon dioxide to the reaction zone  10  is not relatively immediate, and this depends on the biological requirements of the phototrophic organisms being used. 
     In some of the embodiments, for example, at least a fraction of the nutrient supply  42  is mixed with the supplemental aqueous material in the return pond  28  to provide a nutrient-enriched supplemental aqueous material supply  44 , and the nutrient-enriched supplemental aqueous material supply  44  is supplied directly to the reaction zone  10  or is mixed with the reaction zone feed material  22  in the sparger  40 . In some embodiments, for example, the direct or indirect supply of the nutrient-enriched supplemental aqueous material supply is effected by a pump. 
     The carbon dioxide-enriched phototrophic biomass disposed in the aqueous medium is exposed to photosynthetically active light radiation so as to effect photosynthesis. In some embodiments, for example, the light radiation is characterized by a wavelength of between 400-700 nm. In some embodiments, for example, the light radiation is in the form of natural sunlight. In some embodiments, for example, the light radiation is provided by an artificial light source  14 . In some embodiments, for example, light radiation provided is both of natural sunlight and artificial light. 
     In some embodiments, for example, the intensity of the provided light is controlled so as to align with the desired growth rate of the phototrophic biomass in the reaction zone  10 . In some embodiments, regulation of the intensity of the provided light is based on measurements of the growth rate of the phototrophic biomass in the reaction zone  10 . In some embodiments, regulation of the intensity of the provided light is based on the molar rate of supply of carbon dioxide to the reaction zone feed material  22 . 
     In some embodiments, for example, the light is provided at pre-determined wavelengths, depending on the conditions of the reaction zone  10 . Having said that, generally, the light is provided in a blue light source to red light source ratio of 1:4. This ratio varies depending on the phototrophic organism being used. As well, this ratio may vary when attempting to simulate daily cycles. For example, to simulate dawn or dusk, more red light is provided, and to simulate mid-day condition, more blue light is provided. Further, this ratio may be varied to simulate artificial recovery cycles by providing more blue light. 
     It has been found that blue light stimulates algae cells to rebuild internal structures that may become damaged after a period of significant growth, while red light promotes algae growth. Also, it has been found that omitting green light from the spectrum allows algae to continue growing in the reaction zone  10  even beyond what has previously been identified as its “saturation point” in water, so long as sufficient carbon dioxide and, in some embodiments, other nutrients, are supplied. 
     With respect to artificial light sources, for example, suitable artificial light source  14  include submersible fiber optics, light-emitting diodes, LED strips and fluorescent lights. Any LED strips known in the art can be adapted for use in the process. In the case of the submersible LEDs, the design includes the use of solar powered batteries to supply the electricity. In the case of the submersible LEDs, in some embodiments, for example, energy sources include alternative energy sources, such as wind, photovoltaic cells, fuel cells, etc. to supply electricity to the LEDs. In the case of fiber optics, solar collectors with selective wavelength filters may be used to bring natural light to the photobioreactor  12 . In the case of fiber optics, solar collectors with UV filters may be used to bring natural light to the reactor. Fluorescent lights can be used as a back-up system. 
     With respect to those embodiments where the reaction zone  10  is disposed in a photobioreactor  12  which includes a tank, in some of these embodiments, for example, the light energy is provided from a combination of sources, as follows. Natural light source  16  in the form of solar light is captured though solar collectors and filtered with custom mirrors that effect the provision of light of desired wavelengths to the reaction zone  10 . The filtered light from the solar collectors is then transmitted to light tubes in the photobioreactor  12 , where it becomes dispersed within the reaction zone  10 . In addition to solar light, the light tubes in the photobioreactor  12  contains high power LED arrays that can provide light at specific wavelengths to either complement solar light, as necessary, or to provide all of the necessary light to the reaction zone  10  during periods of darkness (for example, at night). In some embodiments, for example, a transparent heat transfer medium (such as a glycol solution) is circulated through light guides within the photobioreactor  12  so as to regulate the temperature in the light tubes and, in some circumstances, provide for the controlled dissipation of heat from the light tubes and into the reaction zone  10 . In some embodiments, for example, the LED power requirements can be predicted and, therefore, controlled, based on trends observed with respect to the gaseous exhaust material  18 , as these observed trends assist in predicting future growth rate of the phototrophic biomass. 
     In some embodiments, for example, the growth rate of the phototrophic biomass is dictated by the available gaseous exhaust material reaction zone supply  24 . In turn, this defines the nutrient, water, and light intensity requirements to maximize phototrophic biomass growth rate. In some embodiments, for example, a controller, e.g. a computer-implemented system, is provided to be used to monitor and control the operation of the various components of the process disclosed herein, including lights, valves, sensors, blowers, fans, dampers, pumps, etc. 
     A discharge of the gaseous exhaust material  18  from the gaseous exhaust material producing process  20  is modulated based on sensing of at least one reaction zone parameter. In some embodiments, for example, the sensing of at least one of the at least one reaction zone parameter is effected in the reaction zone  10 . The modulating of the discharge of the gaseous exhaust material  18  includes modulating of a supply of the discharged gaseous exhaust material  18  to the reaction zone feed material  22 . As described above, the supply of the discharged gaseous exhaust material  18  to the reaction zone feed material  22  defines the gaseous exhaust material reaction zone supply  24 . The gaseous exhaust material reaction zone supply  24  includes carbon dioxide. In some embodiments, for example, the discharged gaseous exhaust material  18  is provided in the form of a gaseous flow. In some embodiments, for example, the gaseous exhaust material reaction zone supply  24  is provided in the form of a gaseous flow. 
     In some embodiments, for example, the modulating of the discharge of the gaseous exhaust material  18  further includes modulating of a supply of the discharged gaseous exhaust material  18  to another unit operation. The supply of the discharged gaseous exhaust material  18  to another unit operation defines a bypass gaseous exhaust material  60 . The bypass gaseous exhaust material  60  includes carbon dioxide. The another unit operation converts the bypass gaseous exhaust material  60  such that its environmental impact is reduced. In these circumstances, the reaction zone  10  may be unable to adequately remove carbon dioxide from the gaseous exhaust material, and this is effected by the another unit operation. In some embodiments, for example, this is done to effect environmental compliance. 
     The reaction zone parameter which is sensed is any kind of characteristic which provides an indication of the degree to which conditions in the reaction zone  10  are supportive of growth of the phototrophic biomass. In this respect, the sensing of the reaction zone parameter is material to determining whether to modulate an input to the reaction zone  10  in order to promote or optimize growth of the phototrophic biomass. The reaction zone parameter may be an “indication” of a characteristic, in which case the indication can be either a direct or indirect sensing of this characteristic. In some embodiments, for example, the reaction zone parameter is a carbon dioxide supply indication. A carbon dioxide supply indication is an indication of the rate of supply of carbon dioxide to the reaction zone  10 . In some embodiments, for example, the carbon dioxide supply indication is a pH within the reaction zone. In some embodiments, for example, the reaction zone parameter is a phototrophic biomass concentration indication. In some embodiments for example, the modulating of a supply of the discharge of the gaseous exhaust material  18  is based on sensing of two or more characteristic indications within the reaction zone  10 . 
     In some embodiments, for example, when at least a fraction of the reaction zone feed material is supplied by a gaseous exhaust material reaction zone supply  24 , and when a carbon dioxide supply indication is sensed in the reaction zone  10  which is above a predetermined high carbon dioxide supply value, the modulating of the discharge of the gaseous exhaust material  18  includes: (a) reducing the molar rate of supply, or eliminating the supply, of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 , and (b) effecting the supply, or an increase to the molar rate of supply, of the bypass gaseous exhaust material  60  to the another unit operation. 
     In some embodiments, for example, when a carbon dioxide supply indication is sensed in the reaction zone  10  which is below a predetermined low carbon dioxide supply value, the modulating of the discharge of the gaseous exhaust material  18  includes: (a) effecting the supply, or an increase to the molar rate of supply, of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 , and (b) effecting elimination of the supply, or a decrease to the molar rate of supply, of the bypass gaseous exhaust material  60  to the another unit operation. 
     In some embodiments, for example, when at least a fraction of the reaction zone feed material  22  is supplied by a gaseous exhaust material reaction zone supply  24 , and when a phototrophic biomass concentration indication is sensed in the reaction zone  10  which is above a predetermined high phototrophic biomass concentration value, the modulating of the discharge of the gaseous exhaust material  18  includes: (a) reducing the molar rate of supply of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 , and (b) increasing the molar rate of supply of the bypass gaseous exhaust material  60  of the gaseous exhaust material  18  to the another unit operation. 
     In some embodiments, for example, when at least a fraction of the reaction zone feed material  22  is supplied by a gaseous exhaust material reaction zone supply  24 , and when a phototrophic biomass concentration indication is sensed in the reaction zone  10  which is below a predetermined low phototrophic biomass concentration value, the modulating of the discharge of the gaseous exhaust material  18  includes: (a) increasing the molar rate of supply of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 , and (b) decreasing the molar rate of supply of the bypass gaseous exhaust material  60  of the gaseous exhaust material  18  to the another unit operation. 
     In some embodiments, for example, the modulating of the discharge of the gaseous exhaust material  18  is effected while the gaseous exhaust material  18  is being produced by the gaseous exhaust material producing process  20 . 
     In some embodiments, for example, the modulating of the discharge of the gaseous exhaust material  18  is effected while the gaseous exhaust material reaction zone supply  24  is being supplied to the reaction zone feed material  22 . 
     In some embodiments, for example, the modulating of the discharge of the gaseous exhaust material  18  is effected while the reaction zone feed material  24  is being supplied to the reaction zone  10 . 
     In some embodiments, for example, the exposing of the carbon dioxide-enriched phototrophic biomass disposed in the aqueous medium to photosynthetically active light radiation is effected while the modulating of the discharge of the produced gaseous exhaust material  18  is being effected. 
     As discussed above, in some embodiments, for example, the reaction zone feed material  22  is disposed in fluid communication with the reaction zone  10  through a fluid passage and is supplied as a flow to the reaction zone  10 . A flow control element  50  is disposed within the fluid passage and is configured to selectively control the rate of flow of the reaction zone feed material  22  by selectively interfering with the flow of the reaction zone feed material  22  and thereby effecting pressure losses to the flow of the reaction zone feed material  22 . In this respect, the reducing of the molar rate of supply, or the eliminating of the supply, of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22  is effected by the flow control element  50 . In some embodiments, for example, the controller actuates the flow control element  50  to effect at least one of the reducing of the molar rate of supply, the increasing of the molar rate of supply, the eliminating of the supply, or the initiating of the supply, of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 . 
     In some embodiments, for example, the flow control element  50  includes a valve. In some embodiments, for example, the flow control element  50  is a three-way valve which also regulates the supply of a supplemental gas-comprising material  48 , which is further described below. 
     In some embodiments, for example, when the reaction zone feed material  22  is supplied to the reaction zone  10  as a flow of the reaction zone feed material  22  which is flowed through the fluid passage, the flowing of the reaction zone feed material  22  is at least partially effected by a prime mover  38 . For such embodiments, examples of a suitable prime mover  38  include a blower, a compressor, a pump (for pressurizing liquids including the gaseous exhaust material reaction zone supply  24 ), and an air pump. In some embodiments, for example, the prime mover  38  is a variable speed blower and the prime mover  38  also functions as the flow control element  50  which is configured to selectively control the flow rate of the reaction zone feed material  22  and define such flow rate. 
     In some embodiments, for example, the another unit operation is a smokestack  62  which is fluidly coupled to an outlet of the gaseous exhaust material producing process which effects the discharge of the bypass gaseous exhaust material  60 . The bypass gaseous exhaust material  60  being discharged from the outlet is disposed at a pressure which is sufficiently high so as to effect flow through the smokestack  62 . In some of these embodiments, for example, the flow of the bypass gaseous exhaust material  60  through the smokestack  62  is directed to a space remote from the outlet which discharges the bypass gaseous exhaust material  60  from the gaseous exhaust material producing process  20 . Also in some of these embodiments, for example, the bypass gaseous exhaust material  60  is discharged from the outlet when the pressure of the bypass gaseous exhaust material  60  exceeds a predetermined maximum pressure. In such embodiments, for example, the exceeding of the predetermined maximum pressure by the bypass gaseous exhaust material  60  effects an opening of a closure element  64 . For example, the closure element  64  is a valve, or a damper, or a stack cap. 
     In some embodiments, for example, the smokestack  62 , which is fluidly coupled to an outlet of the gaseous exhaust material producing process  20 , is provided to direct flow of a bypass gaseous exhaust material  60  to a space remote from the outlet which discharges the bypass gaseous exhaust material  60  from the gaseous exhaust material producing process  20 , in response to any indication of excessive carbon dioxide, anywhere in the process, so as to mitigate against a gaseous discharge of an unacceptable carbon dioxide concentration to the environment. 
     In some embodiments, for example, the smokestack  62  is an existing smokestack  62  which has been modified to accommodate lower throughput of gaseous flow as provided by the bypass gaseous exhaust material  60 . In this respect, in some embodiments, for example, an inner liner is inserted within the smokestack  62  to accommodate the lower throughput. 
     In some embodiments, for example, the another unit operation is a separator which effects removal of carbon dioxide from the bypass gaseous exhaust material  60 . In some embodiments, for example, the separator is a gas absorber. 
     In some embodiments, for example, when at least a fraction of the reaction zone feed material  22  is supplied by a gaseous exhaust material reaction zone supply  24 , and when a carbon dioxide supply indication is sensed in the reaction zone  10  which is above a predetermined high carbon dioxide supply value, the modulating of the discharge of the gaseous exhaust material  18  includes reducing the molar rate of supply, or eliminating the supply, of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 . Additionally, the process further comprises effecting the supply, or increasing the molar rate of supply, of a supplemental gas-comprising material  48  to the reaction zone feed material  22 . The carbon dioxide concentration, if any, of the supplemental gas-comprising material  48  is lower than the carbon dioxide concentration of the gaseous exhaust material reaction zone supply  24 . In some embodiments, for example, the modulating of the discharge of the gaseous exhaust material  18  is effected while the gaseous exhaust material  18  is being produced by the gaseous exhaust material producing process  20 . In some embodiments, for example, the modulating of the discharge of the gaseous exhaust material  18  is effected while the gaseous exhaust material reaction zone supply  24  is being supplied to the reaction zone feed material  22 . In some embodiments, for example, the modulating of the discharge of the gaseous exhaust material  18  is effected while the reaction zone feed material  22  is being supplied to the reaction zone  10 . In some of these embodiments, for example, the exposing of the carbon dioxide-enriched phototrophic biomass disposed in the aqueous medium to photosynthetically active light radiation is effected while the modulating is being effected. In some embodiments, for example, the molar supply rate reduction, or the elimination of the supply, of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22  effected by the modulating of the discharge of the gaseous exhaust material  18 , co-operates with the supply of the supplemental gas-comprising material  48  to the reaction zone feed material  22  to effect a reduction in the molar rate, or the elimination, of carbon dioxide supply to the reaction zone feed material  22 . In some embodiments, for example, the modulating of the discharge of the gaseous exhaust material  18  further effects the supply, or an increase to the molar rate of supply, from the discharged gaseous exhaust material, of a bypass gaseous exhaust material  60  to another unit operation which converts the bypass gaseous exhaust material  60  such that its environmental impact is reduced. In some embodiments, for example, the reaction zone feed material  22  is disposed in fluid communication with the reaction zone  10  through a fluid passage, and the reaction zone feed material is supplied to the reaction zone  10  as a flow which is flowed through the fluid passage. In this respect, in some embodiments, the reaction zone feed material being supplied to the reaction zone  10  is a reaction zone feed material flow, and the reducing (of the molar rate of supply of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 ) effects a reduction in the fraction of the reaction zone feed material flow which is a gaseous exhaust material reaction zone supply flow. 
     In some embodiments, for example, when at least a fraction of the reaction zone feed material is supplied by a gaseous exhaust material reaction zone supply  24 , and when a carbon dioxide supply indication is sensed in the reaction zone  10  which is above a predetermined high carbon dioxide supply value, the modulating of the discharge of the gaseous exhaust material  18  includes reducing the molar rate of supply, or eliminating the supply, of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 . Additionally, the process further includes effecting the supply, or increasing the molar rate of supply, of a supplemental gas-comprising material  48  to the reaction zone feed material  22  for at least partially compensating for the reduction in molar supply rate of material, or the elimination of any material supply, to the reaction zone feed material  22  effected by the modulating of the discharge of the gaseous exhaust material  18 . The molar supply rate reduction, or the elimination of the supply, of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22  effected by the modulating of the discharge of the gaseous exhaust material  18  co-operates with the supply of the supplemental gas-comprising material  48  to the reaction zone feed material  22  to effect a reduction in the molar rate, or the elimination, of carbon dioxide supply to the reaction zone feed material  22 . In some embodiments, for example, the modulating is effected while the gaseous exhaust material  18  is being produced by the gaseous exhaust material producing process  20 . In some embodiments, for example, the modulating of the discharge of the gaseous exhaust material  18  is effected while the gaseous exhaust material reaction zone supply  24  is being supplied to the reaction zone feed material  22 . In some embodiments, for example, the modulating of the discharge of the gaseous exhaust material  18  is effected while the reaction zone feed material  22  is being supplied to the reaction zone  10 . In some of these embodiments, for example, the exposing of the carbon dioxide-enriched phototrophic biomass disposed in the aqueous medium to photosynthetically active light radiation is effected while the modulating is being effected. In some embodiments, for example, the concentration of carbon dioxide, if any, in the supplemental gas-comprising material  48 , is less than the concentration of carbon dioxide in the gaseous exhaust material reaction zone supply  24 . In some embodiments, for example, the reaction zone feed material  22  being supplied to the reaction zone  10  is flowed to the reaction zone  10  to effect the supply of the reaction zone feed material  22  to the reaction zone  10 , and the compensation, for the reduction in molar supply rate of material, or the elimination of any material supply, to the reaction zone feed material  22  effected by the modulating of the discharge of the gaseous exhaust material  18 , as effected by the supply of the supplemental gas-comprising material  48 , effects substantially no change to the molar rate of flow of reaction zone feed material  22  to the reaction zone  10 . In some embodiments, for example, the modulating of the discharge of the gaseous exhaust material  18  further effects the supply, or an increase to the molar rate of supply, from the discharged gaseous exhaust material, of a bypass gaseous exhaust material  60  to another unit operation which converts the bypass gaseous exhaust material  60  such that its environmental impact is reduced. In some embodiments, for example, the reaction zone feed material  22  is disposed in fluid communication with the reaction zone  10  through a fluid passage and the reaction zone feed material  22  is supplied to the reaction zone  10  as a flow which is flowed through the fluid passage. In this respect, the reaction zone feed material  22  being supplied to the reaction zone  10  is a reaction zone feed material flow, and the reducing (of the molar rate of supply of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 ) effects a reduction in the fraction of the flow of the reaction zone feed material  22  which is a flow of a gaseous exhaust material reaction zone supply  24 . 
     The combination of: (a) the molar supply rate reduction, or the elimination of the supply, of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 , and (b) the supplying, or the increasing of the supplying, of a supplemental gas-comprising material  48  to the reaction zone feed material  22 , mitigates against the reduced agitation of the reaction zone  10  attributable to the reduction in the molar rate of supply, or elimination of the supply, of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 . 
     In some embodiments, for example, the molar rate of carbon dioxide being supplied, if any, in the supplemental gas-comprising material  48 , is sufficiently low such that the supply of the supplemental gas-comprising material  48 , in co-operation with the molar supply rate reduction, or the elimination of supply, of the gaseous exhaust material reaction zone supply  24 , effects a reduction in the molar rate of carbon dioxide being supplied to the reaction zone feed material  22 . 
     In some embodiments, for example, the reaction zone feed material  22  is flowed to the reaction zone  10  and effects agitation of material in the reaction zone such that any difference in phototrophic biomass concentration between two points in the reaction zone  10  is less than 20%. In some embodiments, for example, the effected agitation is such that any difference in phototrophic biomass concentration between two points in the reaction zone  10  is less than 10%. 
     In some embodiments, for example, the flow control element  50  is a three-way valve which also regulates the supply of the supplemental gas-comprising material  48 , and is actuated by the controller in response to carbon dioxide concentration indications which are sensed within the reaction zone  10 . 
     In some embodiments, for example, the supplemental gas-comprising material  48  is a gaseous material. In some of these embodiments, for example, the supplemental gas-comprising material  48  includes a dispersion of gaseous material in a liquid material. In some of these embodiments, for example, the supplemental gas-comprising material  48  includes air. In some of these embodiments, for example, the supplemental gas-comprising material  48  is provided as a flow. 
     In some embodiments, for example, the supply, or increasing the molar rate of supply, of a supplemental gas-comprising material  48  to the reaction zone feed material  22  is effected while the gaseous exhaust material  18  is being produced by the gaseous exhaust material producing process  20 . In some embodiments, for example, the supply, or increasing the molar rate of supply, of a supplemental gas-comprising material  48  to the reaction zone feed material  22  is effected while the gaseous exhaust material reaction zone supply  24  is being supplied to the reaction zone feed material  22 . In some embodiments, for example, the supply, or increasing the molar rate of supply, of a supplemental gas-comprising material  48  to the reaction zone feed material  22  is effected while the reaction zone feed material  22  is being supplied to the reaction zone  10 . In some of these embodiments, for example, the exposing of the carbon dioxide-enriched phototrophic biomass disposed in the aqueous medium to photosynthetically active light radiation is effected while the supply, or increasing the molar rate of supply, of a supplemental gas-comprising material  48  to the reaction zone feed material  22  is effected. 
     In some embodiments, for example, when the reaction zone parameter is a carbon dioxide supply indication, the carbon dioxide supply indication is a pH. In this respect, for example, the sensing of a reaction zone parameter includes sensing a pH in the reaction zone  10 . In such embodiments, for example, the pH is sensed in the reaction zone  10  with a pH sensor  46 . In some embodiments, for example, upon sensing a pH in the reaction zone  10  which is below a predetermined low pH value (i.e. the predetermined high carbon dioxide supply indication value), the pH sensor  46  transmits a low pH signal to the controller, and the controller responds by effecting decreasing of the molar supply rate of, or effecting elimination of supply of, carbon dioxide supply to the reaction zone feed material  22 . In some embodiments, for example, this is effected by effecting decreasing of the molar supply rate of, or effecting elimination of supply of, the gaseous exhaust material reaction zone supply  24  being to the reaction zone feed material  22 , such as by using flow control element  50 , as described above. The predetermined low pH value depends on the phototrophic organisms of the biomass. In some embodiments, for example, the predetermined low pH value can be as low as 4.0. In some embodiments, for example, upon sensing a pH in the reaction zone  10  which is above a predetermined high pH value (i.e. the predetermined low carbon dioxide supply indication value), the pH sensor  46  transmits a high pH signal to the controller, and the controller responds by effecting increasing of the molar supply rate of, or effecting initiation of supply of, carbon dioxide to the reaction zone feed material. In some embodiments, for example, this is effected by effecting increasing of the molar supply rate of, or effecting initiation of supply of, the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 , such as by using flow control element  50 , as described above. The predetermined high pH value depends on the phototrophic organisms of the biomass. 
     Operating with a pH in the reaction zone  10  which is above the predetermined high pH (indicating an insufficient molar rate of supply of carbon dioxide to the reaction zone feed material  22 ), or which is below the predetermined low pH (indicating an excessive molar rate of supply of carbon dioxide to the reaction zone feed material  22 ), effects less than optimal growth of the phototrophic biomass, and, in the extreme, could effect death of the phototrophic biomass. 
     In some embodiments, for example, when the characteristic indication is a phototrophic biomass concentration indication, the phototrophic biomass concentration indication is sensed by a cell counter. For example, a suitable cell counter is an AS-16F Single Channel Absorption Probe supplied by optek-Danulat, Inc. of Germantown, Wis., U.S.A. Other suitable devices for sensing a phototrophic biomass concentration indication include other light scattering sensors, such as a spectrophotometer. As well, the phototrophic biomass concentration indication can be sensed manually, and then input manually into the controller for effecting the desired response. 
     In some embodiments, for example, it is desirable to control concentration of the phototrophic biomass in the reaction zone  10 . For example, higher overall yield of harvested phototrophic biomass is effected when the concentration of the phototrophic biomass in the reaction zone  10  is controlled at a predetermined concentration or within a predetermined concentration range. In some embodiments, for example, upon sensing a phototrophic biomass concentration indication in the reaction zone  10  which is below the predetermined low phototrophic biomass concentration value, the cell counter transmits a low phototrophic biomass concentration signal to the controller, and the controller responds by effecting increasing of the molar supply rate of, or effecting initiation of supply of, carbon dioxide to the reaction zone  10 . In some embodiments, for example, this is effected by effecting increasing of the molar supply rate of, or effecting initiation of supply of, the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 , such as by using flow control element  50 , as described above. The predetermined low phototrophic biomass concentration value depends on the phototrophic organisms of the biomass. In some embodiments, for example, upon sensing a phototrophic biomass concentration indication in the reaction zone  10  which is above the predetermined high phototrophic biomass concentration value, the cell counter transmits a high phototrophic biomass concentration signal to the controller, and the controller responds by effecting decreasing of the molar supply rate of, or effecting elimination of supply of, carbon dioxide to the reaction zone feed material  22 . In some embodiments, for example, this is effected by effecting decreasing of the molar supply rate of, or effecting elimination of supply of, the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 , such as by using flow control element  50 , as described above. The predetermined high phototrophic biomass concentration value depends on the phototrophic organisms of the biomass. 
     In some embodiments, for example, the phototrophic biomass is recovered or harvested. With respect to those embodiments where the reaction zone  10  is disposed in a photobioreactor  12 , in some of these embodiments, the upper portion of phototrophic biomass suspension in the reaction zone  10  overflows the photobioreactor  12  (for example, the phototrophic biomass is discharged through an overflow port of the photobioreactor  12 ) to provide the harvested biomass  58 . In those embodiments where the phototrophic biomass includes algae, the harvesting is effected at a rate which matches the growth rate of the algae, in order to mitigate shocking of the algae in the reaction zone  10 . With respect to some embodiments, for example, the harvesting is controlled through the rate of supply of supplemental aqueous material supply  44 , which influences the displacement from the photobioreactor  12  of the photobioreactor overflow  59  (including the harvested biomass  58 ) from the photobioreactor  12 . In other embodiments, for example, the harvesting is controlled with a valve disposed in a fluid passage which is fluidly communicating with an outlet of the photobioreactor  12 . 
     In some embodiments, for example, the harvesting is effected continuously. In other embodiments, for example, the harvesting is effected periodically. In some embodiments, for example, the harvesting is designed such that the concentration of the biomass in the harvested biomass  58  is relatively low. In those embodiments where the phototrophic biomass includes algae, it is desirable, for some embodiments, to harvest at lower concentrations to mitigate against sudden changes in the growth rate of the algae in the reaction zone  10 . Such sudden changes could effect shocking of the algae, which thereby contributes to lower yield over the longer term. In some embodiments, where the phototrophic biomass is algae and, more specifically, scenedesmus obliquus, the concentration of this algae in the harvested biomass  58  could be between 0.5 and 3 grams per liter. The desired concentration of the harvested algae depends on the strain of algae such that this concentration range changes depending on the strain of algae. In this respect, in some embodiments, maintaining a predetermined water content in the reaction zone is desirable to promote the optimal growth of the phototrophic biomass, and this can also be influenced by controlling the supply of the supplemental aqueous material supply  44 . 
     The harvested biomass  58  includes water. In some embodiments, for example, the harvested biomass  58  is supplied to a separator  52  for effecting removal of at least a fraction of the water from the harvested biomass  58  to effect production of an intermediate concentrated biomass product  34  and a recovered aqueous material  72  (generally, water). In some embodiments, for example, the separator  52  is a high speed centrifugal separator  52 . Other suitable examples of a separator  52  include a decanter, a settling vessel or pond, a flocculation device, or a flotation device. In some embodiments, the recovered aqueous material  72  is supplied to a return pond  28  for re-use by the process. 
     In some embodiments, for example, after harvesting, and before being supplied to the separator  52 , the harvested biomass  58  is supplied to a harvest pond  54 . The harvest pond  54  functions both as a buffer between the photobioreactor  12  and the separator  52 , as well as a mixing vessel in cases where the harvest pond  54  receives different biomass strains from multiple photobioreactors. In the latter case, customization of a blend of biomass strains can be effected with a predetermined set of characteristics tailored to the fuel type or grade that will be produced from the blend. 
     As described above, the return pond  28  provides a source of supplemental aqueous material supply  44  for the reaction zone  10 . Loss of water is experienced in some embodiments as moisture in the final biomass product  36 , as well as through evaporation in the dryer  32 . The supplemental aqueous material in the return pond  28 , which is recovered from the process, can be supplied to the reaction zone  10  as the supplemental aqueous material supply  44 . In some embodiments, for example, the supplemental aqueous material supply  44  is supplied to the reaction zone  10  with a pump. In other embodiments, the supply can be effected by gravity, if the layout of the process equipment of the system, which embodies the process, permits. In some embodiments, for example, the supplemental aqueous material recovered from the process includes at least one of: (a) aqueous material  70  which has been condensed from the reaction zone feed material  22  while the reaction zone feed material  22  is being cooled before being supplied to the reaction zone  10 , and (b) aqueous material  72  which has been separated from the discharged product  59 . In some embodiments, for example, the supplemental aqueous material supply  44  is supplied to the reaction zone  10  to influence overflow of the photobioreactor overflow  59  by increasing the upper level of the contents of the reaction zone  10 . In some embodiments, for example, the supplemental aqueous material supply  44  is supplied to the reaction zone  10  to influence a desired predetermined concentration of phototrophic biomass to the reaction zone by diluting the contents of the reaction zone. 
     Examples of specific structures which can be used as a return pond  28  by allowing for containment of aqueous material recovered from the process, as above-described, include, without limitation, tanks, ponds, troughs, ditches, pools, pipes, tubes, canals, and channels. 
     In some embodiments, for example, the supplying of the supplemental aqueous material supply to the reaction zone  10  is effected while the gaseous exhaust material  18  is being produced by the gaseous exhaust material producing process  20 . In some embodiments, for example, the supplying of the supplemental aqueous material supply to the reaction zone is effected while the gaseous exhaust material reaction zone supply  24  is being supplied to the reaction zone feed material  22 . In some embodiments, for example, the supplying of the supplemental aqueous material supply to the reaction zone  10  is effected while the reaction zone feed material  24  is being supplied to the reaction zone  10 . In some embodiments, for example, the exposing of the carbon dioxide-enriched phototrophic biomass disposed in the aqueous medium to photosynthetically active light radiation is effected while the supplying of the supplemental aqueous material supply to the reaction zone  10  is being effected. 
     As described above, in some embodiments, for example, the discharging of the product  59  is effected by an overflow of the at least a fraction of the contents of the reaction zone  10  of the photobioreactor  12 . When the upper level of the contents of the reaction zone  10  within the photobioreactor  12  becomes disposed below a predetermined minimum level, the supplying of, or an increase to the molar rate of supply, of the supplemental aqueous material supply  44  (which has been recovered from the process) is effected to the reaction zone  10 . In some of these embodiments, for example, a level sensor  76  is provided, and when the level sensor  76  senses a predetermined low level of the upper level of the contents of the reaction zone  10  within the photobioreactor  12 , the level sensor transmits a low level signal to the controller. When the supply of the supplemental aqueous material supply  44  to the reaction zone  10  is effected by a pump, the controller actuates the pump to effect commencement of supply, or an increase to the rate of supply, of the supplemental aqueous material supply  44  to the reaction zone  10 . When the supply of the supplemental aqueous material supply  44  to the reaction zone  10  is effected by gravity, the controller actuates the opening of a control valve to effect commencement of supply, or an increase to the rate of supply, of the supplemental aqueous material supply  44  to the reaction zone  10 . 
     In other embodiments, for example, where the harvesting is controlled with a valve disposed in a fluid passage which is fluidly communicating with an outlet of the photobioreactor  12 , algae concentration in the reaction zone is sensed by a cell counter, such as the cell counters described above. The sensed algae concentration is transmitted to the controller, and the controller responds by actuating a pump  281  to effect supply of the supplemental aqueous material supply  44  to the reaction zone  10 . 
     In some embodiments, for example, a source of additional make-up water  68  is provided to mitigate against circumstances when the supplemental aqueous material supply  44  is insufficient to make-up for water which is lost during operation of the process. In this respect, in some embodiments, for example, the supplemental aqueous material supply  44  is mixed with the reaction zone feed material  22  in the sparger  40 . Conversely, in some embodiments, for example, accommodation for draining of the return pond  28  to drain  66  is provided to mitigate against the circumstances when aqueous material recovered from the process exceeds the make-up requirements. 
     In some embodiments, for example, a reaction zone gaseous effluent  80  is discharged from the reaction zone  10 . At least a fraction of the reaction zone gaseous effluent  80  is recovered and supplied to a reaction zone  110  of a combustion process unit operation  100 . As a result of the photosynthesis being effected in the reaction zone  10 , the reaction zone gaseous effluent  80  is rich in oxygen relative to the gaseous exhaust material reaction zone supply  24 . The gaseous effluent  80  is supplied to the combustion zone  110  of a combustion process unit operation  100  (such as a combustion zone  110  disposed in a reaction vessel), and, therefore, functions as a useful reagent for the combustion process being effected in the combustion process unit operation  100 . The reaction zone gaseous effluent  80  is contacted with combustible material (such as carbon-comprising material) in the combustion zone  100 , and a reactive process is effected whereby the combustible material is combusted. Examples of suitable combustion process unit operations  100  include those in a fossil fuel-fired power plant, an industrial incineration facility, an industrial furnace, an industrial heater, an internal combustion engine, and a cement kiln. 
     In some embodiments, for example, the contacting of the recovered reaction zone gaseous effluent with a combustible material is effected while the gaseous exhaust material is being produced by the gaseous exhaust material producing process. In some embodiments, for example, the contacting of the recovered reaction zone gaseous effluent with a combustible material is effected while the gaseous exhaust material reaction zone supply is being supplied to the reaction zone feed material. In some embodiments, for example, the contacting of the recovered reaction zone gaseous effluent with a combustible material is effected while the reaction zone feed material is being supplied to the reaction zone. In some embodiments, for example, the exposing of the carbon dioxide-enriched phototrophic biomass disposed in the aqueous medium to photosynthetically active light radiation is effected while the contacting of the recovered reaction zone gaseous effluent with a combustible material is being effected. 
     The intermediate concentrated biomass product  34  is supplied to a dryer  32  which supplies heat to the intermediate concentrated biomass product  34  to effect evaporation of at least a fraction of the water of the intermediate concentrated biomass product  34 , and thereby effect production of a final biomass product  36 . As discussed above, in some embodiments, the heat supplied to the intermediate concentrated biomass product  34  is provided by a heat transfer medium  30  which has been used to effect the cooling of the reaction zone feed material  22  prior to supply of the reaction zone feed material  22  to the reaction zone  10 . By effecting such cooling, heat is transferred from the reaction zone feed material  22  to the heat transfer medium  30 , thereby raising the temperature of the heat transfer medium  30 . In such embodiments, the intermediate concentrated biomass product  34  is at a relatively warm temperature, and the heat requirement to effect evaporation of water from the intermediate concentrated biomass product  34  is not significant, thereby rendering it feasible to use the heated heat transfer medium  30  as a source of heat to effect the drying of the intermediate concentrated biomass product  34 . As discussed above, after heating the intermediate concentrated biomass product  34 , the heat transfer product, having lost some energy and becoming disposed at a lower temperature, is recirculated to the heat exchanger  26  to effect cooling of the reaction zone feed material  22 . The heating requirements of the dryer  32  is based upon the rate of supply of intermediate concentrated biomass product  34  to the dryer  32 . Cooling requirements (of the heat exchanger  26 ) and heating requirements (of the dryer  32 ) are adjusted by the controller to balance the two operations by monitoring flowrates and temperatures of each of the reaction zone feed material  22  and the rate of harvesting of the harvested biomass  58 . 
     In some embodiments, changes to the phototrophic biomass growth rate related to changes to the rate of supply of the gaseous exhaust material reaction zone supply  24  to the reaction zone material feed  22  are realized after a significant time lag (for example, in some cases, more than three (3) hours, and sometimes even longer) from the time when the change is effected to the rate of supply of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 . In comparison, changes to the thermal value of the heat transfer medium  30 , which are based on the changes in the rate of supply of the gaseous exhaust material reaction zone supply  24  to the reaction zone feed material  22 , are realized more quickly. In this respect, in some embodiments, a thermal buffer is provided for storing any excess heat (in the form of the heat transfer medium  30 ) and introducing a time lag to the response of the heat transfer characteristics of the dryer  32  to the changes in the gaseous exhaust material reaction zone supply  24 . Alternatively, an external source of heat may be required to supplement heating requirements of the dryer  32  during transient periods of supply of the gaseous exhaust material reaction zone supply  24  to the reaction zone material  22 . The use of a thermal buffer or additional heat may be required to accommodate changes to the rate of growth of the phototrophic biomass, or to accommodate start-up or shutdown of the process. For example, if growth of the phototrophic biomass is decreased or stopped, the dryer  32  can continue operating by using the stored heat in the buffer until it is consumed, or, in some embodiments, use a secondary source of heat. 
     In some embodiments, for example, when at least a fraction of the reaction zone feed material  22  is supplied by a gaseous exhaust material reaction zone supply  24 , and when an indication of a change in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24  (i.e. supply to the reaction zone feed material  22 ) is sensed, modulation of at least one input to the reaction zone  10  is effected. The modulating of at least one input includes at least one of: (a) effecting or eliminating supply of, or modulating the intensity of, the photosynthetically active light radiation to which at least a fraction of the carbon dioxide-enriched phototrophic biomass is exposed, and (b) effecting, modulating, or eliminating the molar rate of supply, or commencing supply, of a nutrient supply  42  to the reaction zone  10 . In some embodiments, for example, the modulating of at least one input is effected while the gaseous exhaust material  18  is being produced by the gaseous exhaust material producing process  20 . In some embodiments, for example, the modulating of at least one input is effected while the gaseous exhaust material reaction zone supply  24  is being supplied to the reaction zone feed material  22 . In some embodiments, for example, the modulating of at least one input is effected while the reaction zone feed material  22  is being supplied to the reaction zone  10 . In some of these embodiments, the exposing of the carbon dioxide-enriched phototrophic biomass disposed in the aqueous medium to photosynthetically active light radiation is effected while the modulating of at least one input is being effected. 
     In some embodiments, for example, the effecting or the eliminating of the supply of, or modulating the intensity of, the photosynthetically active light radiation is effected by the controller. To increase or decrease light intensity, the controller changes the power output from the power supply, and this can be effected by controlling either one of voltage or current. As well, in some embodiments, for example, the effecting, modulating, or eliminating the molar rate of supply, or commencing supply, of a nutrient supply  42  is also effected by the controller. To increase or decrease nutrient supply  42 , the controller can control a dosing pump  421  to provide a desired flow rate of the nutrient supply  42 . 
     In some of these embodiments, for example, when at least a fraction of the reaction zone feed material  22  is supplied by a gaseous exhaust material reaction zone supply  24 , and when an indication of an increase in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24  (i.e. supply to the reaction zone feed material  22 ) is sensed, the modulating of at least one input includes effecting at least one of: (a) an increase in the intensity of the photosynthetically active light radiation to which at least a fraction of the carbon dioxide-enriched phototrophic biomass is exposed, and (b) an increase in the molar rate of supply, or commencement of supply, of a nutrient supply  42  to the reaction zone  10 . In some embodiments, for example, the increase in the intensity of the photosynthetically active light radiation is proportional to the increase in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24 . 
     In some embodiments, for example, the gaseous exhaust material reaction zone supply  24  is supplied as a flow to the reaction zone feed material  22 , and the indication of an increase in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24  which is sensed is an increase in molar flowrate of the gaseous exhaust material  18  being produced by the gaseous exhaust material producing process  20 . In this respect, in some embodiments, for example, a flow sensor  78  is provided, and upon sensing an increase in the molar flow rate of the gaseous exhaust material  18  being produced, the flow sensor  78  transmits a signal to the controller, and the controller effects at least one of: (a) an increase in the intensity of the photosynthetically active light radiation to which at least a fraction of the carbon dioxide-enriched phototrophic biomass is exposed, and (b) an increase in the molar rate of supply, or commencement of supply, of a nutrient supply  42  to the reaction zone  10 . 
     In some embodiments, for example, the indication of an increase in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24  which is sensed is an increase in carbon dioxide concentration of the discharged gaseous effluent  18 . In this respect, in some embodiments, for example, a carbon dioxide sensor  781  is provided, and upon sensing an increase in the carbon dioxide concentration of the gaseous exhaust material  18  being produced, the carbon dioxide sensor  781  transmits a signal to the controller, and the controller effects at least one of: (a) an increase in the intensity of the photosynthetically active light radiation to which at least a fraction of the carbon dioxide-enriched phototrophic biomass is exposed, and (b) an increase in the molar rate of supply, or commencement of supply, of a nutrient supply  42  to the reaction zone  10 . 
     In some embodiments, for example, at least one of: (a) an indication of an increase in the molar flow rate of the gaseous exhaust material  18  being produced, and (b) an indication of an increase in the carbon dioxide concentration of the gaseous exhaust material  18  being produced, is a signal of an impending increase in the rate of molar supply of carbon dioxide to the reaction zone feed material  22 . Because an increase in the rate of molar supply of carbon dioxide to the reaction zone feed material  22  is impending, the molar rate of supply of at least one condition for growth (i.e. increased rate of supply of carbon dioxide) of the phototrophic biomass is increased, and the rates of supply of other inputs, relevant to such growth, are correspondingly increased, in anticipation of growth of the phototrophic biomass in the reaction zone  10 . 
     In some embodiments, for example, when at least a fraction of the reaction zone feed material  22  is supplied by a gaseous exhaust material reaction zone supply  24 , and when an indication of a decrease in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24  (i.e. supply to the reaction zone feed material  22 ) is sensed, the modulating of at least one input includes effecting at least one of: (a) a decrease in the intensity of the photosynthetically active light radiation to which at least a fraction of the carbon dioxide-enriched phototrophic biomass is exposed, and (b) a decrease in the molar rate of supply, or elimination of supply, of a nutrient supply  42  to the reaction zone  10 . In some embodiments, for example, the decrease in the intensity of the photosynthetically active light radiation is proportional to the decrease in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24 . 
     In some embodiments, for example, when the gaseous exhaust material reaction zone supply  24  is supplied as a flow to the reaction zone feed material  22 , the indication of a decrease in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24  which is sensed is a decrease in flow of the gaseous exhaust material  18  being produced by the gaseous exhaust material producing process  20 . In this respect, in some embodiments, for example, a flow sensor  78  is provided, and upon sensing a decrease in the flow, the flow sensor  78  transmits a signal to the controller, and the controller effects at least one of: (a) a decrease in the intensity of the photosynthetically active light radiation to which at least a fraction of the carbon dioxide-enriched phototrophic biomass is exposed, and (b) a decrease in the molar rate of supply, or elimination of supply, of a nutrient supply  42  to the reaction zone  10 . 
     In some embodiments, for example, the indication of a decrease in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24  which is sensed is a decrease in carbon dioxide concentration of the discharged gaseous effluent  18 . In this respect, in some embodiments, for example, a carbon dioxide sensor  781  is provided, and upon sensing a decrease in the carbon dioxide concentration of the gaseous exhaust material  18  being produced, the carbon dioxide sensor  781  transmits a signal to the controller, and the controller effects at least one of: (a) a decrease in the intensity of the photosynthetically active light radiation to which at least a fraction of the carbon dioxide-enriched phototrophic biomass is exposed, and (b) a decrease in the molar rate of supply, or commencement of supply, of a nutrient supply  42  to the reaction zone  10 . 
     In some embodiments, for example, at least one of: (a) an indication of a decrease in the molar flow rate of the gaseous exhaust material  18  being produced, and (b) an indication of a decrease in the carbon dioxide concentration of the gaseous exhaust material  18  being produced, is a signal of an impending decrease in the rate of molar supply of carbon dioxide to the reaction zone feed material  22 . Because a decrease in the rate of molar supply of carbon dioxide to reaction zone feed material  22  is impending, the rate of supply of other inputs, which would otherwise be relevant to phototrophic biomass growth, are correspondingly reduced to conserve such inputs. In these circumstances, the molar rate of supply of carbon dioxide to the reaction zone feed material  22  is still sufficient so that phototrophic biomass growth continues, albeit at a reduced rate, and efficient growth of the phototrophic biomass continues to be promoted, albeit at a reduced rate. 
     On the other hand, in some embodiments, the indication of a decrease in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply which is sensed is sufficiently significant such that there is a risk of conditions being created in the reaction zone  10  which are adverse to growth of the phototrophic biomass or, in the extreme, which may result in the death of at least a fraction of the phototrophic biomass. However, because it is believed that the decrease in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24  is of a temporary nature, it is desirable to take steps to preserve the phototrophic biomass in the reaction zone  10  until the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24  returns to levels which are capable of sustaining meaningful growth of the phototrophic biomass in the reaction zone  10 . 
     In this respect, in some embodiments, when at least a fraction of the reaction zone feed material  22  is supplied by a gaseous exhaust material reaction zone supply  24 , and when an indication of a decrease in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24  (i.e. supply the reaction zone feed material  22 ) is sensed, either the molar rate of supply of a supplemental carbon dioxide supply  92  to the reaction zone feed material  22  is increased, or supply of the supplemental carbon dioxide supply  92  to the reaction zone feed material  22  is initiated. In some of these embodiments, for example, the increasing of the molar rate of supply, or the initiation of supply, of a supplemental carbon dioxide supply  92  to the reaction zone feed material  22  is effected while the gaseous exhaust material  18  is being produced by the gaseous exhaust material producing process  20 . In some of these embodiments, for example, the increasing of the molar rate of supply, or the initiation of supply, of a supplemental carbon dioxide supply  92  to the reaction zone feed material  22  is effected while the gaseous exhaust material reaction zone supply  24  is being supplied to the reaction zone feed material  22 . In some embodiments, for example, the increasing of the molar rate of supply, or the initiation of supply, of a supplemental carbon dioxide supply  92  to the reaction zone feed material  22  is effected while the reaction zone feed material  22  is being supplied to the reaction zone  10 . In some of these embodiments, the exposing of the carbon dioxide-enriched phototrophic biomass disposed in the aqueous medium to photosynthetically active light radiation is effected while the increasing of the molar rate of supply, or the initiation of supply, of the supplemental carbon dioxide supply  92  to the reaction zone feed material  22  is being effected. 
     In those embodiments where the increasing of the molar rate of supply, or the initiation of supply, of a supplemental carbon dioxide supply  92  to the reaction zone  10  is effected in response to an indication of a decrease in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24 , in some of these embodiments, for example, when the gaseous exhaust material reaction zone supply  24  is supplied as a flow to the reaction zone feed material  22 , the indication of a decrease in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24  which is sensed is a decrease in flow of the gaseous exhaust material  18  being produced by the gaseous exhaust material producing process  20 . In this respect, in some of these embodiments, for example, a flow sensor  78  is provided, and upon sensing the decrease in the flow of the gaseous exhaust material  18  being produced by the gaseous exhaust material producing process  22 , the flow sensor  78  transmits a signal to the controller, and the controller actuates the opening of a flow control element, such as a valve  921 , to effect supply of the supplemental carbon dioxide supply  92  to the reaction zone feed material  22 , or to effect increasing of the molar rate of supply of the supplemental carbon dioxide supply  92  to the reaction zone feed material  22 . 
     In those embodiments where the increasing of the molar rate of supply, or the initiation of supply, of a supplemental carbon dioxide supply  92  to the reaction zone  10  is effected in response to an indication of a decrease in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24 , in some of these embodiments, for example, the indication of a decrease in the molar rate of supply of carbon dioxide in the gaseous exhaust material reaction zone supply  24  which is sensed is a decrease in molar concentration of carbon dioxide within the gaseous exhaust material  18  being produced by the gaseous exhaust material producing process  20 . In this respect, in some embodiments, for example, a carbon dioxide sensor  781  is provided, and upon sensing a decrease in the carbon dioxide concentration of the gaseous exhaust material  18  being produced, the carbon dioxide sensor  781  transmits a signal to the controller, and the controller actuates the opening of a flow control element, such as a valve  921 , to effect supply of the supplemental carbon dioxide supply  92  to the reaction zone feed material  22 , or to effect increasing of the molar rate of supply of the supplemental carbon dioxide supply  92  to the reaction zone feed material  22 . 
     In some circumstances, it is desirable to grow phototrophic biomass using carbon dioxide of the gaseous exhaust material  18  being discharged from the gaseous exhaust material producing process  20 , but the carbon dioxide concentration in the discharged gaseous exhaust material  18  is excessive for effecting optimal growth of the phototrophic biomass. In this respect, the phototrophic biomass responds adversely when exposed to the reaction zone feed material  22  which is supplied by the gaseous exhaust material reaction zone supply  24  of the gaseous exhaust material  18 , by virtue of the carbon dioxide concentration of the reaction zone feed material  22 , which is attributable to the carbon dioxide concentration of the gaseous exhaust reaction zone supply  24 . 
     In this respect, in some embodiments, for example, when at least a fraction of the reaction zone feed material  22  is supplied by a gaseous exhaust material reaction zone supply  24 , the process further includes, supplying the reaction zone feed material  22  with a supplemental gaseous dilution agent  90 , wherein the carbon dioxide concentration of the supplemental gaseous dilution agent  90  is less than the carbon dioxide concentration of the gaseous exhaust material reaction zone supply  24  which is supplied to the reaction zone feed material  22 . In some of these embodiments, for example, the supplying of the supplemental gaseous dilution agent  90  to the reaction zone feed material  22  provides a carbon dioxide concentration in the reaction zone feed material  22  being supplied to the reaction zone  10  which is below a predetermined maximum carbon dioxide concentration value. In some of these embodiments, for example, the supplying of the supplemental gaseous dilution agent  90  to the reaction zone feed material  22  effects dilution of the reaction zone feed material  22  with respect to carbon dioxide concentration (i.e. effects reduction of carbon dioxide concentration in the reaction zone feed material  22 ). 
     In some of these embodiments, for example, the reaction zone feed material  22  includes an upstream reaction zone feed material  22 A and a downstream reaction zone feed material  22 B, wherein the downstream reaction zone feed material  22 B is downstream of the upstream reaction zone feed material  22 A relative to the reaction zone  10 . The supplemental gaseous dilution agent  90  is admixed with the upstream reaction zone feed material  22 A to provide the downstream reaction zone feed material  22 B such that the concentration of carbon dioxide in the downstream reaction zone feed material  22 B is less than the concentration of carbon dioxide in the upstream reaction zone feed material  22 A. In some embodiments, for example, the upstream reaction zone feed material  22 A is a gaseous material. 
     In some embodiments, for example, the supplying of the supplemental gaseous dilution agent  90  to the reaction zone feed material  22  is effected in response to sensing of a carbon dioxide concentration in the gaseous exhaust material  18  being discharged from the carbon dioxide producing process  20  which is greater than a predetermined maximum carbon dioxide concentration value. In some embodiments, when a carbon dioxide concentration of the gaseous exhaust material  18  is sensed which is greater than a predetermined maximum carbon dioxide concentration value, a signal is transmitted to the controller, and the controller actuates opening of a control valve  901  which effects supply of the supplemental gaseous dilution agent  90  to the reaction zone feed material  22 . 
     In some of these embodiments, for example, the supplying of the reaction zone feed material  22  with a supplemental gaseous dilution agent  90  is effected while the gaseous exhaust material  18  is being produced by the gaseous exhaust material producing process  20 . In some of these embodiments, for example, the supplying of the reaction zone feed material  22  with a supplemental gaseous dilution agent  90  is effected while the gaseous exhaust material reaction zone supply  24  is being supplied to the reaction zone feed material  22 . In some embodiments, for example, the supplying of the reaction zone feed material  22  with a supplemental gaseous dilution agent  90  is effected while the reaction zone feed material  22  is being supplied to the reaction zone  10 . In some of these embodiments, the exposing of the carbon dioxide-enriched phototrophic biomass disposed in the aqueous medium to photosynthetically active light radiation is effected while the supplying of the reaction zone feed material  22  with a supplemental gaseous dilution agent  90  is being effected. 
     In some embodiments, the reaction zone feed material  22  is supplied to the reaction zone  10  as a flow. In some embodiments, for example, the supplemental gaseous dilution agent  90  is gaseous material. In some embodiments, for example, the supplemental gaseous dilution agent  90  includes air. In some embodiments, for example, the supplemental gaseous dilution agent  90  is being supplied to the reaction zone feed material  22  as a flow. In some embodiments, for example, the supplemental gaseous dilution agent  90  is a gaseous material and is supplied as a flow for admixing with the upstream reaction zone material supply  22 A. 
     In the above description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to one skilled in the art that these specific details are not required in order to practice the present disclosure. Although certain dimensions and materials are described for implementing the disclosed example embodiments, other suitable dimensions and/or materials may be used within the scope of this disclosure. All such modifications and variations, including all suitable current and future changes in technology, are believed to be within the sphere and scope of the present disclosure. All references mentioned are hereby incorporated by reference in their entirety.