Integrated waste reduction system
A waste reduction system that utilizes organic solids suspended in a waste stream to produce carboxylic acids, which can then be employed as an input to a microbial fuel cell or other biological processes to further enhance biogas production, is provided. The organic waste stream influent undergoes a multistage fermentation process in which fermentative microorganism metabolize the organic waste materials and produce one or more carboxylic acids, especially short chain fatty acids. The carboxylic acids serve as a food source for bacteria within an anode compartment of an MFC that generates useable electricity therefrom.
1. A system for treating an organic waste feedstock comprising:
(a) a first fermentation vessel comprising:
a waste stream inlet configured to direct the organic waste feedstock into the first fermentation vessel,
an upflow tube having a lower tube inlet and an upper tube outlet,
a liquid circulation device configured to cause the organic waste feedstock to enter the upflow tube at the lower tube inlet and exit the upflow tube at the upper tube outlet,
a first fermentation vessel outlet; and
one or more species of microorganisms that ferment an organic material contained within the organic waste feedstock and produce one or more carboxylic acids; and
(b) a second fermentation vessel comprising:
a second fermentation vessel inlet configured to receive an organic waste stream from the first fermentation vessel and introduce the organic waste stream into the second fermentation vessel,
a second fermentation vessel outlet; and
one or more species of microorganisms, which can be the same or different from the one or more species of microorganisms present within the first fermentation vessel, that ferment the organic material contained within the organic waste stream to produce one or more carboxylic acids, which can be the same or different from the one or more carboxylic acids produced within the first fermentation vessel.
2. The system of claim 1 , wherein the first fermentation vessel outlet is located within the upper half of the first fermentation vessel.
3. The system of claim 1 , wherein the first fermentation vessel further comprises a vertical plenum that is laterally disposed from the upflow tube and has a lower plenum inlet and an upper plenum outlet that is connected to the first fermentation vessel outlet.
4. The system of claim 1 , wherein the second fermentation vessel comprises a transition zone in which the organic waste enters through a zone inlet located in the upper half of the second fermentation vessel, flows downwardly through a first passage, and then flows upwardly through a second passage before exiting the second fermentation vessel through the second fermentation vessel outlet, and wherein the transition zone comprises a sludge wasting valve located in segment of the transition zone interconnecting the first and second passages.
5. The system of claim 1 , wherein each of the first and second fermentation vessels comprises at least one sludge wasting valve operable to remove sludge that has accumulated within each respective fermentation vessel.
6. The system of claim 1 , wherein the one or more carboxylic acids produced in the first and/or second fermentation vessels comprise one or more short chain fatty acids selected from the group consisting of formic acid, acetic acid, propionic acid, isobutyric acid, butyric acid, isovaleric acid, valeric acid, isocaproic acid, caproic acid, and heptanoic acid.
7. The system of claim 1 , wherein the organic waste feedstock comprises wastewater derived solids, agricultural waste solids, and/or food-waste solids.
8. The system of claim 1 , the system further comprising a recirculation system configured to recirculate at least a portion of the organic waste stream from within the second fermentation vessel into the first fermentation vessel.
9. The system of claim 1 , the system comprising an organic waste stream heater located upstream from the first fermentation vessel and downstream from a point where at least a portion of the recirculated organic waste stream is mixed with at least a portion of the organic waste feedstock.
10. The system of claim 1 , wherein the second fermentation vessel comprises a feed tube extending from the second fermentation vessel inlet located in an upper half of the second fermentation vessel and having an opening communicating the feed tube with an interior of the second fermentation vessel, the opening being located within the lower half of the second fermentation vessel.
11. The system of claim 1 , further comprising:
(c) one or more microbial fuel cells configured to receive a liquid comprising the one or more carboxylic acids produced in the first and second fermentation vessels, the one or more microbial fuel cells comprising:
(i) a cylindrical anode chamber comprising one or more anodes that are immersed within a first quantity of the liquid comprising the one or more carboxylic acids, the anode chamber comprising one or more microorganisms capable of hydrolyzing the one or more carboxylic acids and producing protons;
(ii) an annular cathode chamber located outboard of the anode chamber and comprising one or more cathodes, the one or more cathodes being immersed in a second quantity of the liquid comprising the one or more carboxylic acids, and further comprising a dissolved electron receptor, wherein within the cathode chamber protons produced in the anode chamber are reacted with the dissolved electron receptor to produce water; and
(iii) a gas-permeable membrane separating the anode chamber from the cathode chamber, the gas-permeable membrane permitting protons to pass between the anode chamber and the cathode chamber.
12. The system of claim 11 , wherein the cylindrical anode chamber comprising a quantity of graphite-containing granules in contact with the one or more anodes, and wherein the annular cathode chamber comprises one or more diffusers operable to introduce the dissolved electron receptor into the cathode chamber.
13. The system of claim 11 , wherein the cylindrical anode chamber comprises a plurality of the anodes arranged in a radially symmetric pattern therein, and wherein the annular cathode chamber comprises a plurality of the cathodes evenly distributed around the cylindrical anode chamber.
14. The system of claim 11 , wherein the cylindrical anode chamber is configured to receive the first quantity of the liquid at a location beneath the one or more anodes and cause the first quantity of the liquid to flow upwardly through the cylindrical anode chamber toward a microbial fuel cell effluent outlet located in the upper half of the microbial fuel cell, and wherein the first quantity of the liquid is introduced into the cylindrical anode chamber through an inlet plenum located beneath the cylindrical anode chamber.
15. A fermentation vessel for fermenting organic material contained within an organic waste feedstock comprising:
a waste stream inlet configured to direct the organic waste feedstock into the fermentation vessel;
an upflow tube having a lower tube inlet and an upper tube outlet, the waste stream inlet introducing the organic waste feedstock directly into the upflow tube at a point in between the lower tube inlet and the upper tube outlet;
a liquid circulation device located within the upflow tube configured to cause the intake of a liquid fermentation media being circulated within the fermentation vessel through the lower tube inlet and expel the liquid fermentation media through the upper tube outlet;
an upflow transition zone disposed laterally from the upflow tube configured to conduct the liquid fermentation media between a lower transition zone inlet toward an upper transition zone outlet; and
a waste stream outlet connected to the upflow transition zone and configured to direct the liquid fermentation media out of the fermentation vessel.
16. The fermentation vessel of claim 15 , wherein the liquid fermentation media comprises one or more species of microorganisms that ferment the organic material contained within the organic waste feedstock and produce one or more carboxylic acids.
17. The fermentation vessel of claim 15 , wherein the upflow transition zone comprises a vertical plenum that is defined at least in part by an inner surface of an outer wall of the fermentation vessel.
18. The fermentation vessel of claim 15 , wherein the liquid circulation device comprises an agitator attached to an elongate shaft, at least a portion of which is positioned inside the upflow tube.
19. The fermentation vessel of claim 15 , wherein the upflow transition zone is configured to provide a fluid linear velocity for the fermentation media of from about 0.1 to about 3 m/h.
20. A fermentation vessel for fermenting organic material contained in a liquid waste stream comprising:
a waste stream inlet located in an upper half of the fermentation vessel and configured to direct the liquid waste stream into the fermentation vessel;
a feed tube extending from the waste stream inlet and having an opening communicating the feed tube with an interior of the fermentation vessel, the opening being located within the lower half of the second fermentation vessel;
an agitating device located within the interior of the fermentation vessel and configured for continuous or intermittent operation to stir a liquid fermentation media contained within the fermentation vessel, the liquid fermentation media comprising the liquid waste stream introduced into the fermentation vessel through the waste stream inlet; and
a vertical duct comprising a first passage extending between the bottom of the fermentation vessel and a vessel outlet located in the upper half of the fermentation vessel configured to direct a portion of the liquid fermentation media upward toward a vessel outlet.
21. The fermentation vessel of claim 20 , wherein the vertical duct comprises a second passage configured to intake a portion of the liquid fermentation media from a location in the upper half of the fermentation vessel and direct it downward toward the bottom of the fermentation vessel and into the first passage.
22. The fermentation vessel of claim 21 , wherein the vertical duct comprises a sludge wasting valve located in a segment that interconnects the first and second passages.
23. The fermentation vessel of claim 20 , wherein the feed tube opening and agitating device are located within a vessel main chamber, the vertical duct being disposed laterally from the main chamber.
24. The fermentation vessel of claim 23 , wherein the main chamber comprises a sludge wasting valve that is operable to remove sludge that has accumulated within the main chamber.