Hydrothermal Processing (HTP) of Algae Grown in HTP Waste Streams

Abstract

A process for the conversion of organic waste to biofuel is provided comprising cultivating organisms in the aqueous product of the HTP conversion process.

Description

BACKGROUND

This invention relates to a process for the chemical conversion of organic waste to liquid fuel. In particular, the invention relates to a high temperature, high pressure conversions of organic biowastes and organisms cultivated in a wastewater stream into a biocrude oil product. The biocrude oil product may be used as a fuel directly or subsequently refined into motor grade fuels, asphalt, plastics, and other products commonly made from crude petroleum.

Economic development demands energy, yet energy consumption has historically led to increased environmental pollution. Despite historical competition between “environment” and “energy”, the future demands both environmental protection and energy sustainability. As a result replacement of a major portion of fossil fuels by renewable energy technologies such as biomass-based fuels has been studied.

First generation biofuels include corn ethanol and soy biodiesel. However, these fuels have the disadvantage that they divert food production to fuel production. Second generation biofuels were developed including cellulostic ethanol to reduce the food versus fuel concerns, but still suffered from sustainability issues such as high water input and degradation of soil nutrients. Third generation biofuels were developed including algae which also addressed the food versus fuel concerns and soil nutrient depletion. Algae can grow in water bodies and other land surfaces that are not suitable for crop production.

The notion of producing biofuels from algae is not new and there have been numerous efforts aimed primarily at producing biodiesel, but also sometimes ethanol or even hydrogen utilizing the prodigious photosynthetic capabilities of algae to capture carbon dioxide and solar energy from the environment and sequester it into biomass (Sheehan, J., T. Dunahay, J. Benemann and P. Roessler. 1998. “A Look Back at the U.S. Department of Energy's Aquatic Species Program: Biodiesel from Algae.” NREUTP-580-24 190, National Renewable Energy Laboratory, 1617 Co-le Boulevard. Golden, Colo.”). One advantage of algae for biofuels are their unparalleled growth rates and the high lipid content of certain species, which have been shown to be sufficiently high that 200,000 hectares (0.1% of arable US land) could potentially produce one quad (10¹⁵ BTU) of fuel (Sheehan et al., 1998). In addition, algae can grow in water bodies and other land surfaces that are not suitable for crop production. Given that the total US oil consumption is less than 50 quads per year, algae based biofuels could completely replace liquid petroleum fuels without significantly compromising the availability of land for food production, a critical limitation of other current bioenergy paradigms. Phototrophic organisms such as cyanobacteria and algae can also produce a wide variety of higher-value co-products including food, nutritional supplements, aquacultural feedstock, and pharmaceuticals that could help support the economic viability of algae biofuels (Shimizu, Y. 1996. “Microalgal metabolites: a new perspective.” Annual Review of Microbiology 50:431-465.; Ghirardi, M. L, L. Zhang, J. W. Lee, T. Flynn, M. Seibert, E. Greenbaum, and A. Melis. 2000. “Microalgae: a green source of renewable hydrogen.” Trends Biotechnol. 18: 506-511).

Despite the potential of algae biofuels, it remains largely untapped because of a few key bottlenecks that have yet to be resolved in a way that is cost effective for scaled-up processing. Specifically, the removal of water content of algal biomass, and the ability to grow a relatively pure culture of high-oil algae at industrial scales have been significant hurdle for developing practical systems for algal biofuels. A cost-effective process must be energy efficient and yield more energy than it consumes. As algae is wet since it grows in water, any process involving drying the algae will typically use a large amount of energy due to the large amount of water and the relatively large heat capacity of water. Algae processing techniques that work with wet algal pastes (water content of 80% or higher) are desirable. Cantrell (Cantrell et al. Bioresource Techonology, 2008, 99, 7941-7953.) discloses a wet gasification approach for processing algal biomass. Wet gasification utilizes relatively high temperatures and pressures for and the energy input requirements may exceed the energy yielded.

Much research and development for algae bio fuels has focused on obtaining relatively high oil contents via algal species selection and control of environmental conditions. This approach has led to some key limitations related to the competition between fast algae and fat algae. Algae that are naturally high in lipids (i.e. fat) often have a tendency to grow slower, and the environmental conditions used to induce higher oil content, such as nitrogen starvation, also typically lead to lower growth rates. These factors are antagonistic to large-scale algae biofuel production. Additionally, the need for selective production of high lipid algae also gives rise to the problem of contamination. Monocultures are difficult to maintain at large scales especially if there are faster growing organisms that grow on the same resources.

What is needed is an algae biofuel process which is efficient and practical for large scale processing, and alleviates the bottlenecks of prior algae processes.

BRIEF SUMMARY

One embodiment of the invention is directed to a process for conversion of organic biowaste to biocrude oil. The process comprises providing a concentrated biosolid fraction and a bypass liquid fraction obtained from organic biowaste. The concentrated biosolid fraction is subjected to a hydrothermal process under conditions sufficient to obtain a biocrude oil product, an aqueous residual product, and a gaseous residual product. In some aspects a solid residual product may also be formed. An organism is cultivated in a culturing media to obtain a cultivated mixture, and a concentrated cultivated organism fraction is recovered from the cultivated mixture. The concentrated cultivated organism fraction and optionally the concentrated biosolid fraction are introduced to the hydrothermal process.

In some aspects, the culturing media may comprise the aqueous residual product and optionally further comprise the bypass liquid fraction in at least 50% by volume, for example. The process may further comprise separating a concentrated biosolid fraction and a bypass liquid fraction from organic biowaste. Preferably the bypass liquid fraction is at least 50 percent of the organic biowaste on a total volume basis, more preferably 80%. The concentrated biosolid fraction may comprise at least 5 percent total solids by weight, preferably at least 10 percent. The concentrated cultivated organism fraction comprises at least 5 percent by weight total solids, preferably at least 10 percent. The ratio of concentrated cultivated organism fraction to concentrated biosolid fraction introduced to the hydrothermal process may be greater than about 5 percent on a total solids basis, preferably greater than about 25 percent.

In some aspects, the process may further comprise introducing the gaseous residual product to the culturing media. The organic biowaste may be animal waste, animal manure, human waste from a municipal sewage stream, or food processing waste. The organism may be algae or bacterial. The hydrothermal process may be carried out at a temperature less than 320° C. and at a pressure above 0.5 MPa.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process schematic of hydrothermal conversion of organic biowaste and algae grown in an HTP aqueous residual waste stream.

FIG. 2 is representative graph of percent refined oil yield and initial lipid content for different feedstocks.

FIG. 3 is representative graphs of mixed algae growth with post-HTP wastewater treatment.

FIG. 4 is representative graphs of mixed algae growth with post-HTP wastewater treatment demonstrated by: (a) biomass increase measured as percent solids; (b) organic pollutants consumption measured as chemical oxygen demand (COD); and (c) nutrient consumption measured as total nitrogen (TN).

FIG. 5 is a representative graph of DNA concentration of antibiotic resistant E. coli before and after HTP treatment.

FIG. 6 is a representative graph product yield versus temperature for HTP conversion of Chlorella pyrenoidosa.

FIG. 7 is a representative graph of growth of UCSD algae (upper line) and COD levels (lower line) with regular addition of post-HTP wastewater.

FIG. 8 is a representative table of HTP conversion tests with algae.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERRED EMBODIMENTS

The process of the present invention uses of waste material inputs to produce a significant quantity of biocrude oil product. The process provides a loop that may recycle nutrients in the hydrothermal process (HTP) aqueous residual product and may recycle the carbon dioxide in the HTP gaseous product as it combines multiple cycles of organism cultivation with subsequent HTP conversion to biocrude oil product. The process improves the cost-effectiveness of other algae-based biofuel production approaches by eliminating several key bottlenecks. First, the process allows multiple use cycles for aqueous residual product which comprises the nutrients for organism growth. Nutrients and carbon dioxide are two of the primary input costs in conventional algae growth processes, which may be reduced or eliminated. Second, HTP conversion of algae biomass does not require high oil content algae, because HTP converts other biomass components to oil. Third, HTP provides cost-effective extraction of oil from wet algae biomass without drying, which is a major energy loss in most contemporary algae to-biofuel paradigms. In short, the present process reduces input costs, increases algae oil production capabilities and reduces the energy inputs required for extracting algae biofuel products.

The process of the present invention also provides environmental benefits during the fuel generation process which may include improving water quality, conserving fresh water resources, sequestering carbon dioxide, reducing solid waste quantities, and destroying residual pharmaceuticals and antibiotic resistant genetic materials in human and animal wastes.

Referring to FIG. 1, a representative process for the conversion of organic biowaste to biocrude oil is shown. A feedstock is provided which comprises organic biowaste. Organic biowaste includes, for example, animal waste, human waste, food processing waste, garden or park waste, paper waste and the like or combinations thereof. Animal waste may include animal feces, animal urine, manure, slaughterhouse waste, and the like. Human waste may include human feces, human urine, bodily fluids, and the like. Human waste may be a component of a municipal sewage stream waste. Municipal sewage streamwaste is water-carried waste from a community, or the used water supply of the community. In addition to human waste, municipal sewage streamwaste may comprise food wastes, pharmaceutical waste including antibiotics and other medicines, antibiotic resistant genetic materials, and other waste products of normal living. Food processing waste is waste produced from during the preparation of food for humans or animals from harvested crops or slaughtered and butchered animal products, particularly in the food processing industry.

With continued reference to FIG. 1, a concentrated biosolid fraction and a bypass liquid fraction are provided. The concentrated biosolid fraction and bypass liquid fraction are obtained from organic biowaste and may be separated from the organic biowaste as part of the present process or in a separate process. The organic biowaste may separated into a concentrated biosolid fraction and a bypass liquid fraction from the organic biowaste feedstock by any suitable separation process method known to one skilled in the art, including for example, gravity settling, centrifugation, membrane filtration, etc. The concentrated biosolid fraction may comprise at least 5% total solids by weight, preferably at least 10%.

The concentrated biosolid fraction is subjected to a hydrothermal process (HTP) under conditions sufficient to obtain a biocrude oil product, an aqueous residual product, a gaseous product and optionally a solid residual product. A hydrothermal process (HTP), also known to one skilled in the art as liquefaction, is a process wherein a fluid stream or slurry is subjected to elevated temperature and pressure which causes chemical reactions to occur, resulting in the conversion of volatile solids into organic oils. Typical temperatures for HTP conversion range from about 200-350° C. Maximum pressures of 3 to 20 MPa are maintained in order to keep water in a liquid form at the elevated temperatures. The hydrothermal process of the present invention uses a temperature between about 200 and about 320° C., preferably less than 250° C. The hydrothermal process uses a pressure less than about 11 MPa, preferably less than 7 mPa, more preferably less than about 4 MPa. The residual solid product when obtained from the hydrothermal process may be used as fertilizer.

The bypass liquid fraction obtained from the organic biowaste feedstock is at least 50% of the organic biowaste on a total volume basis, preferably at least 80% of the organic biowaste on a total volume basis. The bypass liquid fraction may be combined with the aqueous residual product from the hydrothermal process, which contains most of the nutrients (such as nitrogen and phosphorous) from the organic biowaste feedstock. Organisms, including for example algae, bacteria and combinations thereof are cultivated in a culturing media. The culturing media may be any media suitable for growing the organism. In some aspects, the culturing media may comprise the aqueous residual product or both the bypass liquid fraction and the aqueous residual product. The ratio of the bypass liquid fraction to the aqueous residual may be about 1:1 to about 20:1 by volume, preferably about 5:1 to about 15:1 by volume.

Any suitable organism known to one skilled in the art that will grow in the bypass liquid fraction or combined aqueous residual product and the bypass liquid fraction may be used. As used herein, organism refers to algae and microorganisms, including for example bacteria, fungi, archaea, protists, rotifers, and nematodes. As used herein, the term algae refers to microalgae, macroalgae, eukaryotic algae, prokaryotic cyanobacteria, green algae, blue-green algae, brown algae, red algae, and diatoms. In some aspects, low lipid algae may be employed, including species of Chlorella, Spirulina, and mixed species grown in wastewater. Low-lipid algae may comprise less than 20 weight % lipid content in some aspects and less than 10 weight % lipid content in other aspects. In yet other aspects, photosynthetic cyanobacteria including Spirulina may be used. In yet other aspects a combination of organisms may be cultivated including a combination of algae and bacteria.

In some aspects, the gaseous product may be combined with the organism cultivation. The gaseous product is mainly comprised of carbon dioxide, but may also be comprised of various other minor gases such as methane, carbon monoxide, hydrogen, hydrogen sulfide and nitrogen. Since photosynthetic bacteria and algae consume carbon dioxide, carbon dioxide present in the gaseous product will be at least partially consumed when it is introduced to the culturing media used for growing organisms.

Previous algae-to biofuel research focused on growing algae with high lipid content and then extracting the oil from it. However, high oil content algae usually have lower yields, which is a critical limitation for economic viability. In contrast, the present invention is not limited to high lipid content algae or high oil content algae, because HTP converts other biomass components to biocrude oil products. With HTP, fast-growing, high-yield but low-lipid algae may be used for biofuel production. Fast-growing algae and photosynthetic bacteria have key advantages over other biofuel paradigms because they can grow at rates at or above other land based plants, can be grown on non-arable land, and have simple cell walls that may be generally easier to convert to useful oils than other crops. Organism growth need not be limited to a single species of organism since HTP can convert mixtures of organisms to biocrude oil product. Thus, mixed algal-bacteria cultures may be employed including those collected from sewage plants.

Growth of the organisms results in reduced aqueous nutrient concentrations and formation of a cultivated mixture. The cultivated mixture may be separated into a liquid fraction comprising clean water and a concentrated cultivated organism fraction comprising the organism growth. The concentrated cultivated organism fraction is then fed back into the HTP reactor as a sole feedstock or mixed with other concentrated biosolids, to produce more biocrude oil product. When the concentrated cultivated organism fraction is combined with the concentrated biosolid fraction, the ratio of concentrated cultivated organism fraction to concentrated biosolid fraction may be greater than about 5:95 on a total solids basis, preferably greater than about 10:90, more preferably greater than about 25:75.

In some aspects, a synergistic effect may be obtained for various combinations of organisms and feedstocks. Referring to FIG. 2, the refined oil yield for mixtures of swine manure with Chlorella and swine manure with Spirulina was higher than the average of two individual components indicating a synergy when mixing these feedstocks. The refined oil yield is only the toluene soluble fraction of the crude oil. Depending on the crude oil quality, refined oil represents anywhere from 40 to 80% of the crude oil. However, the refined oil content usually provides a more consistent measurement of the HTP trials. The biocrude oil product may be characterized by a heating value of at least 25,000 kJ/kg, preferably, 28,000 kJ/kg, more preferably 32,000 kJ/kg.

The following are additional examples of additional embodiments contemplated.

In one embodiment, the process comprises separating a concentrated biosolid fraction and a bypass liquid fraction from organic biowaste and subjecting the concentrated biosolid fraction to a hydrothermal process under conditions sufficient to obtain a biocrude oil product and an aqueous residual product. An organism is cultivated in a culturing media comprising the aqueous residual product, and a concentrated cultivated organism fraction is recovered from the cultivated mixture. The concentrated cultivated organism fraction in introduced into the hydrothermal process with the concentrated biosolid fraction, wherein a ratio of concentrated cultivated organism fraction to concentrated biosolid fraction is greater than about 5:95 on a total solids basis. In some aspects the process further comprises combining the aqueous residual product and the bypass liquid fraction, wherein the culturing media in which the organism is cultivated comprises the combined aqueous residual product and the bypass liquid fraction. In other aspects, the bypass liquid fraction is at least 50 percent of the organic biowaste on a total volume basis; in others the bypass liquid fraction is at least 80 percent of the organic biowaste. In yet other aspects, the concentrated biosolid fraction comprises total solids between about 1 percent and about 50 percent of the total solids of the organic biowaste feedstock. The organism may be algae or bacteria or low lipid algae. The hydrothermal process may be carried out at a temperature less than 250° C. and at a pressure less than 10 MPa. The biocrude oil product may be characterized by a heating value of at least 25,000 kJ/kg.

Another embodiment of the present invention is directed to a process for the conversion of animal waste to biocrude oil. The process comprises preparing a feedstock from animal waste. A concentrated biosolid fraction and a bypass liquid fraction is separated from the feedstock and the concentrated biosolid fraction is subjected to a hydrothermal process under conditions sufficient to obtain a biocrude oil product, an aqueous residual product, and a gaseous product. The aqueous residual product and the bypass liquid fraction are combined and algae is cultivated in a culturing media comprising the aqueous residual product and the bypass liquid fraction to obtain a cultivated mixture. A concentrated cultivated algae fraction is recovered from the cultivated mixture, and the concentrated cultivated algae fraction is introduced into the hydrothermal process with the concentrated biosolid fraction. The algae may be low lipid algae or selected from the group consisting of Chlorella and Spirulina. The feedstock may be animal manure. The ratio of algae growth to concentrated biosolid fraction introduced to the hydrothermal process may be between 25:75 and 75:25 on a total solids basis.

Another embodiment of the present invention is directed to a process for conversion of human waste from a municipal sewage stream to biocrude oil. The process comprises preparing a feedstock from a municipal sewage stream. A concentrated biosolid fraction and a bypass liquid fraction are separated from the feedstock, and the concentrated biosolid fraction subjected to a hydrothermal process under conditions sufficient to obtain a biocrude oil product, an aqueous residual product, and a gaseous product. The aqueous residual product and the bypass liquid fraction are combined, and an organism is cultivated in a culturing media comprising the combined aqueous residual product and the bypass liquid fraction to obtain a cultivated mixture. A concentrated cultivated organism fraction is recovered from the cultivated mixture, and the concentrated cultivated organism fraction is introduced to the hydrothermal process with the concentrated biosolid fraction, wherein the ratio of concentrated cultivated organism fraction to concentrated biosolid fraction is between 10:90 and 90:10 on a total solids basis. The organism may be algae or algae comprising less than about 20 weight percent lipid. The concentrated cultivated organism fraction comprises algae and bacteria.

In yet another embodiment, a process for conversion of organic biowaste to biocrude oil is provided. The process comprises providing an organic biowaste feedstock comprising organic biowaste and separating a concentrated biosolid fraction and a bypass liquid fraction from the organic biowaste, wherein the bypass liquid fraction is at least 50 percent of the organic biowaste on a total volume basis. The concentrated biosolid fraction is subjected to a hydrothermal process under conditions sufficient to obtain a biocrude oil product, an aqueous residual product, and a gaseous product. The aqueous residual product and the bypass liquid fraction are combined. A microorganism is cultivated in a cultivating media comprising the combined aqueous residual product and the bypass liquid fraction to obtain a cultivated mixture, and the gaseous product is introduced into the cultivated mixture. A concentrated cultivated microorganism fraction is recovered from the cultivated mixture, and introduced to the hydrothermal process with the concentrated biosolid fraction, wherein a ratio of concentrated cultivated microorganism fraction to concentrated biosolid fraction is between 10:90 and 90:10 on a total solids basis.

Experimental

In general, the HTP process was run according the procedure of He and Ocfemia (He, B. J., Y. Zhang, Y. Yin, T. L. Funk and G. L. Riskowski. Transactions of Amer. Soc. Agr. Engr. 43(6): 1827-1833; He, B. J., Y. Zhang, Y. Yin, T. L. Funk and G. L. Riskowski. Transactions of Amer. Soc. Agr. Engr. 44(6): 1873-1880; He, B. J., Y. Zhang, Y. Yin, T. L. Funk and G. L. Riskowski. Transactions of Amer. Soc. Agr. Engr. 44(6): 1865-1872; He, B. J., Y. Zhang, Y. Yin, T. L. Funk and G. L. Riskowski. Transactions of Amer. Soc. Agr. Engr. 44(3): 697-701; Ocfemia, K., Y. Zhang and T. L. Funk. Transactions of the ASABE: 49(2): 533-541; Ocfemia, K., Y. Zhang, and T. L. Funk. Transactions of the ASABE. 49(6): 1897-1904; these references hereby incorporated by reference in their entirety) without catalyst, at about a temperature of 240-280° C., a pressure of 3-9 MPa, and a retention time of 10-30 minutes.

HTP Refined Oil Yield and Initial Lipid Content

Referring to FIG. 2 the initial lipid content and refined oil yields after hydrothermal processing (HTP) for a variety of feedstocks including several tests with algae is shown. Two specific species of algal feedstocks, chlorella pyrenoidosa (eukaryotic green algae) and spirulina platensis (prokaryotic cyanobacteria, commonly called “blue-green algae”), were purchased in a dry powdered form (Health and Herbs Co.). The mixed algae species were collected from the Urbana-Champaign Sanitary District-North Wastewater Treatment Plant. For these HTP tests, the dry solids content of the feedstock was measured by drying in an oven at 105° C. Before HTP testing, the solids content of the feedstock was adjusted to 20% either by adding tap water or by oven drying, which generally resulted in a slurry consistency. Wet feedstock slurry (800 g) was loaded into an HTP reactor with a total volume of 2 L. After the reactor was carefully sealed, the reactor headspace was purged 3 times with nitrogen to remove the residual air, and then more nitrogen was added to increase the desired initial pressure, typically about 0.65 MPa. The reactor was subsequently heated by an electrical heating element to achieve the desired experimental temperature, generally in the range of 200 to 320° C. The heat-up period may last up to 60 minutes, and then the reaction temperature was maintained for the desired retention time of the reaction, which was varied between 0 and 120 minutes. Reactor pressure was allowed to increase over the course of the heated reaction, but once the desired temperature was reached, pressured remain fairly stable at values generally between 3 to 11 MPa.

After the desired retention time, the reactor contents were rapidly cooled by water flowing through a cooling coil located inside the reactor. Once the reactor contents reached room temperature, the gas phase was carefully released through a control valve, and optionally captured in a gas sampling bag for later chemical analysis. Subsequently, the reactor was opened, and the remaining reaction mixture was removed for further analysis. The reaction mixture generally includes an oil phase, an aqueous phase and a solid phase which are processed as follows. The oil phase of the reaction mixture self separates due to lower density and is recovered by decanting. The oil phase typically retains some water, so the moisture content of the oil phase is determined by using a distillation apparatus in accordance with ASTM Standard D95-99 (ASTM D95-99. (2004) Standard test method for water in petroleum products and bituminous materials by distillation. In: Annual Book of ASTM Standards. West Conshohocken, Pa.: Am. Soc. for Testing Materials). The quantity of raw oil produced is then calculated by subtracting the mass of water removed by distillation from the mass of the oil phase. The raw oil product still contains some sediment, which was measured by using Soxhlet extraction, according to ASTM Standards D473-02 (ASTM D473-02. (2004) Standard test method for sediment in crude oils and fuel oils by the extraction. In: Annual Book of ASTM Standards. West Conshohocken, Pa.: Am. Soc. for Testing Materials) and D4072-98 (ASTM D4072-98. (2004) Standard test method for toluene-insoluble (TI) content of tar and pitch. In: Annual Book of ASTM Standards. West Conshohocken, Pa.: Am. Soc. for Testing Materials). The refined oil product can then be calculated by subtracting the mass of sediment from the raw oil mass. This processing scheme allows calculation of the refined oil yield, which was defined as:

$\mathrm{refined}\mathrm{oil}\mathrm{yield}\left(\%\right)=\frac{\mathrm{mass}\mathrm{of}\mathrm{refined}\mathrm{oil}\mathrm{product}}{\mathrm{mass}\mathrm{of}\mathrm{feedstock}\left(\mathrm{dry}\mathrm{solids}\right)}\times 100\%$

The initial lipid content of the feedstock material was analyzed by Midwest Laboratories, Inc. (Omaha, Nebr.) according to the standard methods of AOAC 945.16 (Association of Official Analytical Chemists) for crude fat determination. Despite low initial lipid content in the algae (Chlorella at 2% lipid) and cyanobacteria (Spirulina below 0.5% lipid), HTP conversion of these algae samples yielded 30-40% refined oil.

A synergistic effect was observed for the HTP refined oil yield of mixtures of equal volumes of swine manure and Chlorella or Spirulina. The refined oil yield with swine manure and Chlorella or swine manure with Spirulina was higher than the average of two individual components indicating a synergy when mixing these feedstocks.

FIG. 2 presents the results from HTP conversion of three types of algal feedstocks that represent a significant range of genetic, physiological, and environmental characteristics. Additional algal samples subjected to HTP conversion and the results are shown in FIG. 8. These additional tests followed the same materials and methods identified above. FIG. 8 shows that 12 different types of algal feedstocks were used in the HTP tests including various pure microalgae species, pure macroalgae species and mixed species samples taken from various cultures and naturally occurring samples. For these various algal feedstocks, raw oil yield varied from 12.9% to 92.5%, and refined oil yields varied from 6.2% to 47.4%. The raw oil yield may in some cases contain a fair amount of ash, which makes it a less reliable measure of HTP conversion efficiency. The refined oil yield, which is defined based on toluene solubility of the HTP conversion products is generally a more consistent and reliable measure of conversion efficiency.

FIG. 6 shows tests using Chlorella algae feedstock to investigate the effects of various HTP operational parameters. For example, HTP tests were conducted at a range of temperatures from 200 to 300° C., while all other variables were held constant. Referring to FIG. 6, the most pronounced increase in refined oil yield (24.2% to 28.9%) occurs between 220° C. and 240° C. In addition, solid residue drops rapidly before 240° C., but only changes slightly for temperatures above 240° C. These factors indicate that efficient HTP conversions of algae to biofuel may occur at temperatures around 240° C., which is significantly lower than those required for other common feedstocks like swine manure used in many past studies.

Retention time was another HTP operational parameter studied using the Chlorella algae feedstock. As the reaction time was systematically varied from 0 to 30 minutes (after the reaction temperature of 240° C. was achieved), refined oil production increased slightly from 26.0% to 28.9%. Further increases of retention time up to 120 minutes, increased oil yields up to 33.4%. While increasing retention time from 0 to 120 minutes does have a positive effect on oil yields, the returns are rather small. In contrast, the sizing of the HTP reactor scales linearly with the increases in the retention time, and thus represents significant effects on the capital cost of the HTP reactor. Successful algal conversions were achieved when the target reaction temperature was held even for short retention times of 10 minutes or less, which corresponds to relatively small HTP reactor sizing and reduced capital cost.

Growth of Mixed Algae Samples

A sample of naturally occurring mixed algae species was obtained from the primary clarifier outlet weirs at the Urbana-Champaign Sanitary District (UCSD), which was subsequently cultured in a common algae growth medium, BG11, which contained the following components (mg/L): NaNO₃ (1500), K₂HPO₄ (40), MgSO₄.7H₂O (75), CaCl₂.2H₂O (36), Citric acid (6), Ferric ammonium citrate (6), EDTA (1), NaCO₃ (20) and distilled water. Culturing was carried out in 250 mL Pyrex flask on magnetic stir plate with moderate mixing at 25° C. and with a light intensity of 180-200 foot candles provided by 55 W full spectrum compact fluorescent light. When the inoculation culture reached an exponential growth phase, it was used to seed the experimental batch reactors used to generate the data in FIG. 3.

The algae culture (100 mL) described above during the exponential growth phase was inoculated into two 2000 mL flasks, each containing 900 mL of BG11 medium. For one of the two flasks, 5 mL of post-HTP wastewater (pw) was added at the beginning of the experiment and after 2 days. Both of the flasks were then incubated under the same culturing conditions as listed above. The pw was obtained from the reaction products of HTP conversion of swine manure into biocrude oil as described earlier. Chemical characteristics of HTP post water have been analyzed and are summarized below (Appleford, J. M., Analysis and Optimization of Thermochemical Converstion Process to Produce Oil from Biomass, 2004, Masters Thesis at the University of Illinois, Urbana, Ill.; Ocfemia K. C. S. Hydrothermal Process of Swine Manure to Oil Using a Continuous Reactor System, 2005, Doctoral Thesis at the University of Illinois, Urbana, Ill.). For this experiment, a sample of HTP pw was obtained, filtered through Whatman glass microfiber filters (Type 934-AH) to remove any large particles, and several key characteristics (COD, Ammonia, Phosphorus, and pH) were confirmed to be within the stated ranges of Table 1. Growth in the two culturing flasks was analyzed by measuring the optical density at 680 nm (OD 680) using a visible light spectrophotometer (HACH Model 2000). OD 680 targets absorbance in the range where chlorophyll absorbs light and thus was used to delineate the photosynthetic growth of algae.

TABLE 1
Typical chemical characteristics of HTP post-water
Water Quality
Characteristic Concentration (mg/L)
COD            80,000-10,000
BOD5           35000
Ammonia        3400-3600
Nitrate        1
Phosphate      950
Sulphate       400
Nitrogen       6000
Phosphorus     333-434
Sulfur         9561
Potassium      1500
Magnesium      242
pH             5-6
Solids content 4-8%

FIG. 3 shows that the mixed species UCSD wastewater algae grew better in batch culture when a small amount of HTP pw (squares, approximately 0.5% of batch volume) was added on day zero and day two than without post-HTP water (circles). In a similar follow-up experiment, HTP pw was added six times over the course of seven days with small doses the first 4 times (approximately 1% of total volume and larger doses the last two days (approximately 3% of the total volume). As shown in FIG. 7, OD 680 was measured regularly during this test, and showed steady algae growth while HTP pw was being added, but algae growth peaked shortly after HTP pw dosing was stopped. During the period shown in FIG. 7, the total amount of HTP pw added accounted for about 15% of the culture media. This batch culture was allowed to grow for another 40 days without further addition of HTP pw, but bacteria started to proliferate and eventually became predominant.

Another set of batch experiments was conducted to investigate the potential for inhibitory effects of HTP pw on algae growth. Batch cultures with three different types of algae were prepared with various dilutions of HTP pw to determine which ones would grow. Mixed species UCSD algae were one type of algae used, and they were seeded into vials with BG11 media (see recipe earlier) and spiked with the following percentages of HTP pw: 1%, 2%, 3%, 4%, 5%, 30%, 50%, and 100%. Initially, algae growth only occurred in the vials with 3% or less HTP pw. After 1 month of incubation, the vial with 4% HTP pw also grew algae, but the other higher strength mixtures did not support algae growth. Algae that grew in the first set of tests were spiked into another round, and it was found that the UCSD algae culture could grow immediately in HTP pw concentrations of up to 5%. These experiments highlight that dilution of HTP pw will be highly advantageous for supporting algae growth, which subsequently reduces the concentration of excess nutrients and organics in HTP pw. Additionally, these results show some potential for the algal cultures to adapt over time to increasing concentrations of HTP pw. This type of test was also conducted with pure algal cultures of B. braunii that did not grow at any dilution of HTP pw from 1% to 100%. Spirulina cultures fared slightly better, growing with an initial HTP pw concentration of 1%. These later results confirm the need to dilute HTP pw and that individual species have varying degrees of sensitivity to the strength of HTP pw used in the culturing media. In the overall process diagram, FIG. 1, dilution of HTP pw is shown by the combination of HTP pw with the biowaste decant liquid that bypasses the HTP process.

Growth of Mixed Algal Species and Consumption of Key Pollutants

FIG. 4(a) shows an example of a onetime dose of post-HTP wastewater. The biomass increase was monitored as percent solids, which showed a rapid growth of cells in response to the post-HTP wastewater addition at time zero. FIG. 4(b) shows that the algae consumed organic pollutants measured as chemical oxygen demand (COD). FIG. 4(c) shows that the algae consumed nutrients measured as total nitrogen (TN) to demonstrate clean up of the post-HTP wastewater.

The data in FIG. 4 was generated in a batch test using algae to degrade post-HTP wastewater. Specifically, 10 mL filtered of post-HTP wastewater was added into 990 mL BG11 medium and 100 mL of a mixed algae culture grown up from a seed taken at the USCD wastewater treatment plant as described earlier. Algae growth was quantified in terms of dry weight, which was measured by filtration of aliquots on Millipore mixed cellulose ester 0.45 pm filter that were subsequently dried at 105° C. for 24 h. This dry weight data is presented on the left side of FIG. 4. Algae growth was also measured by OD 680, and there was a direct correlation between OD 680 and dry cell weight.

Water quality samples were taken after the algal biomass was filtered through a 0.45 μm filter. FIG. 4(b) shows the chemical oxygen demand (COD) as determined by visible light absorbance after dichromate digestion according to standard methods. Total nitrogen and total phosphorous were measured in the filtrate according to standard methods approved the Environmental Protection Agency.

Genetic Material in Organic Biowaste

E. coli (strain S17-1 lambda pir) that contains a plasmid DNA tagged with the green fluorescent protein (GFP) gene was used as DNA donor. E. coli was grown in Luria-Bertani medium containing 5 μg/mL of carbenicillin at 37° C. with vigorous shaking overnight (12-16 hours). This overnight culture was used to extract plasmid DNA generally following a method reported by Maloy (Maloy, S. R., Experimental Techniques in Bacterial Genetics. 1st ed.: Jones & Bartlett Publishers: 1989; p 180) with some minor modifications. Specifically, 1.5 mL of freshly grown liquid culture was placed into a microcentrifuge tube and centrifuged at 12,000×g for 1 min. Subsequently, the supernatant was removed and the bacterial pellet was allowed to air dry before being re-suspended with 100 μL of ice-cold cell resuspension solution. After 5 min of incubation time at room temperature, 200 μL of fresh prepared 0.2 N NaOH, 1% SDS cell lysis solution was added into the test tube and the cell was incubated for 5 min on ice. Next, 150 μL of ice-cold potassium acetate solution (pH 4.8) was added to neutralize the lysate. The cell was incubated for 5 min and then centrifuged at 12,000×g for 5 min. Then, the supernatant was transferred to a new test tube and mixed with 0.5 μL of 100 μg/μL DNase-free RNase A and incubated for 5 min at room temperature. A solution of phenol:chloroform:isoamyl alcohol (25:24:1) was then added to the test tube, and centrifuged for 5 min at 12,000×g. The upper aqueous phase was transferred to a fresh tube and mixed with an equal volume of chloroform: isoamyl alcohol (24:1) and centrifuged at 12,000×g for 2 min. The upper aqueous phase was transferred to a fresh tube and mixed with 2.5 volume of ice-cold 100% ethanol and allowed to precipitated 5 min on dry ice. Finally, the test tube was centrifuged at 12,000×g, the supernatant was removed, and the pellet was rinsed with 70% ethanol. The pellet was dried under vacuum and dissolved in 50 μL of Nuclease-free water or TE buffer and kept at −20° C. before use.

A similar procedure was used for E. coli liquid culture after HTP treatment to extract plasmid DNA. Realizing that the HTP process would likely reduce the amount of extracted DNA, the DNA after HTP treatment was further concentrated by ethanol precipitation (Russell, J., Molecular Cloning: A Laboratory Manual. 3 Lab edition ed.; Cold Spring Harbor Laboratory Press: 2001; Vol. 3, p 999). Specifically, 2.5-3 volumes of an ethanol/acetate solution was added to the DNA sample and incubated at −20° C. overnight. The precipitated DNA was then recovered by centrifugation at 12,000 rpm in a microcentrifuge tube for 15 min. The supernatant was discarded, and the DNA pellet was placed on the bench for 10-20 minutes to allow the ethanol to evaporate, and dissolved in 10:0.1 TE buffer (pH 8). The final concentration of extracted plasmid DNA was determined by measuring the optical density of the DNA sample at 260 nm, using a spectrophotometer and assuming that OD₂₆₀=50 μg/mL of plasmid DNA/mL (FIG. 5). The yield of plasmid DNA extracted from liquid culture before and after running through the HTP were further verified by electrophoresis on an agarose gel, which separates DNA fragments by size. Without wishing to be bound by theory, the elevated heat and pressure of HTP treatment is believed to effectively degrade genetic materials (plasmid DNA) so that there is less potential for transfer of antibiotic resistance from human and animal wastes.

Mass Balance of HTP Conversion of Chlorella Algal Biomass

The elemental mass balance of the initial dry chlorella algae feedstock and HTP reaction products for this algae were determined using a rapid elemental analyzer that combines combustion with thermal conductivity detection (TCD) to measure the weight fraction of several primary elements including carbon, hydrogen, nitrogen and oxygen. In this case the initial feedstock, the refined oil, and solid residue product were analyzed using the rapid elemental analyzer. The gas product was analyzed by a Varian CP-3600 Gas Chromatograph coupled with TCD to determine the amount of several typical gasses (carbon dioxide, hydrogen, nitrogen, oxygen, carbon monoxide, and methane). The GC analysis of gas products used a Haysep D 100/120 column (20-ft, ⅛-in diam), with an injection temperature of 120° C., and a filament temperature of 140° C. The carrier gas was Helium at 30 mL/min. Most of the elemental components of the aqueous product were calculated by subtraction of the quantities measured in the other products from the quantity measured in the initial feedstock. The one exception was phosporus, which was measured in the aqueous phase product by standard methods. The phosphorus quantity in the initial feedstock was determined by ICP-MS (Inductively coupled plasma-mass spectrometry), and it was not measured in the other reaction products.

The refined oil product was analyzed and found to comprise 57.5% of the carbon in the original feedstock, 56.0% of the hydrogen, 23.8% of the nitrogen and 21.1% of the oxygen as shown in Table 3. After HTP conversion, the resulting aqueous wastewater contained 73.1% of the nitrogen from the original feedstock and 85% of the original phosphorus. Because most of the nitrogen and phosphorus nutrients are released during the HTP process to the aqueous product, these nutrients may be recycled back to growing another round of biomass and subsequently converted into more oil. In addition, the aqueous HTP wastewater also contains 27.4% and 40.5% of the original carbon and hydrogen, respectively, which may also potentially be captured and converted to more oil by treatment of the HTP wastewater in a mixed culture bioreactor with algae and/or bacteria.

	TABLE 3
	C	H	N	O	P
Refined oil	57.5%	56.0%	23.8%	21.1%	—
Aqueous products	27.4%	40.5%	73.1%	27.1%	85%
Gas products	9.8%	—	—	50.1%	—
Solid product	5.3%	3.5%	3.1%	1.7%	—
Total Recovered	100.0%	100.0%	100.0%	100.0%	85%

From the forgoing description of the structure and operation of a preferred embodiment of the present invention, it will be apparent to those skilled in the art that the present invention is susceptible to numerous modifications and embodiments within the ability of those skilled in the art and without exercise of the inventive facility. Accordingly, the scope of the present invention is defined as set forth of the following claims.

Claims

1. A process for conversion of organic biowaste to biocrude oil comprising:

providing a concentrated biosolid fraction and a bypass liquid fraction obtained from organic biowaste;

subjecting the concentrated biosolid fraction to a hydrothermal process under conditions sufficient to obtain a biocrude oil product, an aqueous residual product, and a gaseous residual product;

cultivating an organism in a culturing media to obtain a cultivated mixture;

recovering a concentrated cultivated organism fraction from the cultivated mixture; and

introducing the concentrated cultivated organism fraction and optionally the concentrated biosolid fraction to the hydrothermal process.

2. The process of claim 1, wherein the culturing media comprises the aqueous residual product.

3. The process of claim 2, wherein the culturing media further comprises the bypass liquid fraction.

4. The process of claim 3, wherein at least 50% of the culturing media by volume is bypass liquid fraction.

5. The process of claim 1, further comprising separating a concentrated biosolid fraction and a bypass liquid fraction from organic biowaste.

6. The process of claim 3, further comprising separating a concentrated biosolid fraction and a bypass liquid fraction from organic biowaste.

7. The process of claim 5, wherein the bypass liquid fraction is at least 50 percent of the organic biowaste on a total volume basis.

8. The process of claim 5, wherein the bypass liquid fraction is at least 80 percent of the organic biowaste on a total volume basis.

9. The process of claim 1, wherein the concentrated biosolid fraction comprises at least 5 percent total solids by weight.

10. The process of claim 1, wherein the concentrated biosolid fraction comprises at least 10 percent total solids by weight.

11. The process of claim 1, wherein the concentrated cultivated organism fraction comprises at least 5 percent by weight total solids.

12. The process of claim 1, wherein the concentrated cultivated organism fraction comprises at least 10 percent by weight total solids.

13. The process of claim 1, wherein the ratio of concentrated cultivated organism fraction to concentrated biosolid fraction introduced to the hydrothermal process is greater than about 5 percent on a total solids basis.

14. The process of claim 6, wherein the ratio of concentrated cultivated organism fraction to concentrated biosolid fraction introduced to the hydrothermal process is greater than about 5 percent on a total solids basis.

15. The process of claim 1, wherein the ratio of concentrated cultivated organism fraction to concentrated biosolid fraction introduced to the hydrothermal process is greater than about 25 percent on a total solids basis.

16. The process of claim 6, wherein the ratio of concentrated cultivated organism fraction to concentrated biosolid fraction introduced to the hydrothermal process is greater than about 25 percent on a total solids basis.

17. The process of claim 1, further comprising introducing the gaseous residual product to the culturing media.

18. The process of claim 6, further comprising introducing the gaseous residual product to the culturing media.

19. (canceled)

20. The process of claim 1, wherein the organic biowaste is animal waste.

21. (canceled)

22. The process of claim 1, wherein the organic biowaste is human waste from a municipal sewage stream.

23. (canceled)

24. The process of claim 1, wherein the organism is algae or bacteria.

25. (canceled)

26. (canceled)

27. The process of claim 1, wherein the organism is Chlorella or Spirulina.

28. The process of claim 1, wherein the algae comprises less than 20 weight percent lipid.

29. The process of claim 1, wherein the hydrothermal process is carried out at a temperature less than 320° C. and at a pressure above 0.5 MPa.

30. The process of claim 1, wherein the biocrude oil product is characterized by a heating value of at least 25,000 kJ/kg.

31. The process of claim 1, wherein the concentrated cultivated organism fraction comprises algae and bacteria.

32. (canceled)

33. A process for conversion of organic biowaste to biocrude oil comprising:

separating a concentrated biosolid fraction and a bypass liquid fraction obtained from organic biowaste; wherein the organic waste is selected from the group consisting of animal waste, human waste and food processing waste;

introducing the concentrated biosolid fraction to a hydrothermal process under conditions sufficient to obtain a biocrude oil product, an aqueous residual product, and a gaseous residual product; wherein the hydrothermal process is carried out at a temperature less than 320° C. and at a pressure above 0.5 MPa;

cultivating an organism comprising algae in a culturing media comprising the aqueous product and the bypass liquid fraction to obtain a cultivated mixture;

recovering a concentrated cultivated organism fraction from the cultivated mixture;

introducing the concentrated cultivated organism fraction to the hydrothermal process;

wherein the ratio of concentrated cultivated organism fraction to concentrated biosolid fraction introduced to the hydrothermal process is greater than about 25 percent on a total solids basis.