Method and system for preparation of substrate for use in anaerobic digestion of organic waste

Abstract

There is disclosed a method for preparation of substrate for use in anaerobic digestion of organic waste. The method can be executed in a substrate pretreatment system, the method comprising: loading of a substrate into the substrate pretreatment system, mixing the substrate with liquid; heating the substrate and liquid to a pre-determined processing temperature; exposing the mixture to radiation; transferring the processed substrate to a bioreactor, during the heating, the method further comprises: degassing the mixture using vacuum extraction; and circulating the mixture past an ultrasonic hydrodynamic radiator.

Claims

1. A method for preparation of a substrate for use in anaerobic digestion of organic waste, the method being implemented in a substrate pretreatment system, the method comprising: a) simultaneously loading under pressure into an airtight chamber within the substrate pretreatment system i) an organic substrate, wherein the organic substrate comprises a liquid and a solid phase of the organic waste; and ii) a heated organic fluid from a bioreactor, to form a mixture; b) simultaneously heating and degassing the mixture, wherein the mixture is heated to and maintained at a temperature of about 37 C. to sustain growth of microorganisms; c) subjecting the mixture of step b) to treatment of an ultrasonic hydrodynamic device in a closed loop to create vibrations in the mixture that cause: i) periodic pressure; ii) cavitation; or iii) both i) and ii) to break down cell walls within the ultrasonic hydrodynamic device comprising a radiator which is connected to the airtight chamber to form the closed loop, and wherein the mixture is circulating within the closed loop during the treatment; and d) transferring the mixture of step c) to the bioreactor.

2. The method of claim 1, further comprising supplying an oxygen-free gas within the airtight chamber.

3. The method of claim 2, wherein the oxygen-free gas is supplied from the bioreactor.

4. The method of claim 1, wherein the liquid is supplied from the bioreactor.

5. The method of claim 1, wherein the degassing is performed by creating a vacuum in the substrate pretreatment system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present technology will be described with reference to drawings, in which:

(2) FIG. 1 depicts a schematic illustration of a substrate pretreatment installation for organic waste anaerobic processing, the substrate pretreatment installation being implemented in accordance with non-limiting embodiments of the present technology.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(3) With reference to FIG. 1, the substrate pretreatment installation includes an airtight chamber 1. The substrate pretreatment installation can be used as part of a system that includes a bioreactor (not depicted). The airtight chamber 1 is coupled to a source of organic substrate 2 and a source of fluid 3 (these are referred together, from time to time, as sources of organic substrate and fluid 2,3).

(4) The airtight chamber 1 is further coupled to a vacuum pump 4 and a gas source 5. The gas source 5 is configured for supplying gas from the bioreactor (not depicted). The airtight chamber 1 is further coupled to a substrate output 6 for supplying the processed substrate to the bioreactor (not depicted).

(5) The airtight chamber 1 further comprises a heater 7 and an ultrasonic hydrodynamic radiator 8. The ultrasonic hydrodynamic radiator 8 can be implemented as a laminar or a rod type. A radiator chamber (not separately numbered) of the ultrasonic hydrodynamic radiator 8 is connected to the airtight chamber 1 via a pump 9 forming a closed circulation loop therewith.

(6) The installation of FIG. 1 is configured to implement a method of pretreatment of substrates as follows.

(7) The airtight chamber 1 is configured to receive substrate. The substrate is received from a storage hopper (not depicted) via the source 2. The airtight chamber 1 is further configured to receive a heated liquid from the wet organic fertilizer drained from the bioreactor via the source 3. The supply of the substrate and liquid can be done under pressure.

(8) Once the airtight chamber 1 is loaded, the temperature of the mixture is determined, then heater 7 is turned on in order to heat the mixture to a pre-determined operational temperature of a first stage of the bioreactor process. This temperature can be, as an example, 37 C.

(9) The vacuum pump 4 is configured to implement a degassing process simultaneously with the mixture heating. The degassing process can be executed, as an example, for 15-20 minutes. Vacuuming helps to evacuate unwanted vapors and to remove the bulk of the oxygen dissolved in the substrate (as it is poisonous for the microorganisms performing in the digestion). Then vacuum pump 4 is switched off, the line is closed by a valve 10. The pump 9 is then switched on, the ultrasonic hydrodynamic radiator 8 starts and gas supply is commenced via the gas source 5 from the bioreactor.

(10) The mixture is simultaneously heated and circulated in a closed loop past the ultrasonic hydrodynamic radiator 8. Surplus gas is evacuated via a valve 11.

(11) As a result of the recirculation past the ultrasonic hydrodynamic radiator 8 the fluid is made turbulent by the vibrations of the mechanical resonators and the oscillations of these resonators also cause harmonic oscillations in the fluid through the form of periodic pressure impulses.

(12) Periodic impulses simulate natural frequency oscillations by providing feedback and continuous acoustic excitation. As a result the amplitude of the oscillations increases due to resonance with oscillations of the radiator 8 mechanical resonators' oscillations.

(13) This increased vibration causes cavitation bubbles to form, which act to break down the cell walls and provide an intensified breaking down of the mixture. Under the influence of the acoustic and ultrasonic waves excess pressure and tensile stresses appear in the fluid, hence oxidation-reduction processes start at the border of the liquid and solid phases, so a stable emulsion with high dispersion of fine particles is achieved.

(14) Additional supply of oxygen-free gas to the cavitation zone via gas source 5 facilitates the creation of developed cavitation flow, optimizes the process and generates multiple tiny carbon dioxide bubbles. These bubbles are supplied to the bioreactor and serve as food for the methanogens, i.e. they promote increase the methane content of the biogas. Processing lasts for 10-30 minutes and finishes when the mixture is heated to the predetermined temperature. After the treatment the substrate is pumped to the bioreactor through the substrate output 6. Then the pretreatment process is repeated.

(15) The operation of the installation of FIG. 1 can be fully automated.

(16) Thus within the airtight chamber 1, the mixture is simultaneously heated, degassed and thoroughly treated, significantly increasing the efficiency of the process of high quality pretreatment of substrates of many kinds.

(17) An installation equipped with the chamber of 1.5 m3 and a purge pump with capacity of 20-50 m3/hour, provides pretreatment of 50 m3 of substrate per day.

(18) It was established experimentally that in some embodiments of the present technology, the duration of chicken manure digestion by the proposed method in the claimed substrate pretreatment installation decreases from 14 to 9 days, and the amount of received biogas increases 2.2 fold. Moreover, as a result of oxygen removal from the mixed components the reaction starts faster and carbon dioxide contents in the biogas are lowered.

(19) Embodiments of the present technology can be implemented within a pretreatment flow line by means of serial installation of the disclosed equipment.