A device and process for enhancing anaerobic co-digestion of agricultural solid waste using intermittent voltage

Abstract

A device and process for strengthening the anaerobic co-digestion of agricultural solid waste (cow dung and corn stalks) by intermittent voltage, the process steps of which are: starting the device with full sludge, then feeding the pre-treated cow dung and corn stalks into the anaerobic reactor as feed, then setting the working voltage of the DC power supply between 0.4V and 0.8V, and operating the reactor; after 30 days of continuous electrical acclimation, adjusting the working mode of the voltage to: one day on / one day off, and continue to operate the reactor. The present invention utilizes the enrichment effect of conductive materials and voltage on electroactive microorganisms in the anaerobic system and the enhancement of the conductivity and polarization of anaerobic sludge by electrical stimulation to promote the electron transfer rate between microorganisms, thereby strengthening the anaerobic digestion process of agricultural solid waste. At the same time, the device utilizes an intermittent voltage supply method to greatly reduce energy input. The device can effectively solve the problem of low efficiency of anaerobic digestion of agricultural solid waste, and also reduces the economic cost of electrical treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of agricultural solid waste, and relates to a device and a process for strengthening anaerobic co-digestion of agricultural solid waste by using intermittent voltage. Background Art

[0002] MEC-AD coupling system refers to a system that couples electrochemical technology with traditional anaerobic digestion. In recent years, MEC-AD coupling system has been widely used in the field of anaerobic digestion because it can not only overcome the traditional anaerobic digestion 1) the accumulation of VFAs during the digestion process, leading to system acidification and thus destroying the stability of the system; 2) it is also affected by substrate characteristics; 3) pH; 4) temperature and 5) organic load, but also can generate CO 2 Further converted into methane. However, for the anaerobic treatment of agricultural solid waste, the use of continuous electrical treatment will undoubtedly increase its economic cost and reduce the feasibility of the scheme. Therefore, the use of intermittent voltage to enhance the anaerobic digestion of agricultural solid waste is undoubtedly an economically feasible and reasonable solution. Summary of the invention

[0003] In order to solve the problem that the anaerobic start-up period in the anaerobic digestion system of agricultural solid waste is long and the digestion efficiency is low, thereby inhibiting the methane production process, the present invention provides a device and process for strengthening the anaerobic co-digestion of agricultural solid waste by using intermittent voltage.

[0004] The present invention proposes the following technical solutions:

[0005] A device for strengthening anaerobic co-digestion of agricultural solid waste (cow dung and corn stalks) by using intermittent voltage, specifically: an anaerobic digestion reactor provided with a water bath constant temperature layer, a cover plate provided on the top of the anaerobic reactor, one end of tube i connected to the exhaust valve on the right side of the cover plate, and the other end connected to a gas collection device. The upper end is connected to a DC power supply through a wire ii, and the middle part passes through the cover plate to connect a carbon rod electrode as a cathode, and a carbon felt electrode is installed on the inner wall of the reactor and connected to the DC power supply through a wire i as an anode. The lower part is fixedly connected to the reactor base. One end of tube ii is connected to a feed tank through a feed pump, and the other end is connected to the upper left end of the anaerobic reactor through a feed valve. One end of tube iii is connected to a water bath pot through a peristaltic pump, and the other end is connected to the lower left end of the water bath insulation layer through a water inlet valve. One end of tube iv is connected to the upper right end of the water bath insulation layer through a water outlet valve, and the other end is connected to the water bath pot. One end of tube v is connected to the lower right end of the water bath insulation layer through a discharge valve, and the other end enters the discharge tank.

[0006] A process for strengthening anaerobic digestion of agricultural solid waste using the above device comprises the following steps:

[0007] The cow dung is crushed by a wall breaking machine and then mixed with the processed corn stalks (5 mm) to form a suspension with a solid content of 15% to 20%. The mixed liquid of the processed cow dung and corn stalks enters the feed tank (3).

[0008] The optimal solid content of the above suspension is 18%.

[0009] The anaerobic microorganisms in the anaerobic system come from the anaerobic sludge discharged from the anaerobic fermentation tank of a sewage treatment plant in Dalian. The VSS of the anaerobic sludge is 20-30 g / L. The reaction uses the whole sludge to start the reactor, open the feed pump (5) and the feed valve (9), and inject the garbage into the reactor through pipe i (1), with a volume of 1 / 30 of the volume of the anaerobic sludge.

[0010] The optimal VSS value of anaerobic sludge is 25 g / L.

[0011] The internal temperature of the anaerobic reactor (24) is controlled at 35-37°C.

[0012] The above optimal temperature is 37°C.

[0013] The pH value in the anaerobic reactor (24) is controlled between 7.0 and 8.0.

[0014] The above optimum pH is 7.8.

[0015] Control the hydraulic retention time of the anaerobic reactor between 20 and 30 days.

[0016] The above-mentioned optimal hydraulic retention time is 30 days.

[0017] The working voltage used in the experiment was between 0.4 V and 0.8 V, and the resulting current was between 0.4 mA and 0.7 mA. During the experiment, the power supply was intermittently supplied by manually controlling the power switch (1 day on / 1 day off - i.e., on and off every other day).

[0018] The above optimal working voltage is 0.6V and the optimal current is 0.5 mA.

[0019] The exhaust valve (15) is opened, and the biogas generated by the anaerobic reactor (24) is collected through the gas collection device (17).

[0020] The discharge valve (21) is opened, and the fermentation product discharged from the anaerobic reactor (24) is discharged into the discharge tank (23) through the pipe IV (22).

[0021] The beneficial effects of the present invention are:

[0022] The method adopted by the present invention, firstly, electrical stimulation can enrich more electroactive microorganisms (electrically producing microorganisms and electrotrophic microorganisms) in the anaerobic digestion system, and the acid-base balance in the anaerobic system can be maintained by the action of electricity, so that the pH in the anaerobic system can be suitable for the growth of methanogens, and many biochemical reactions in the system can be promoted, and the activity of anaerobic microorganisms can be enhanced, thereby improving the methane production potential in the system. Secondly, the electrochemical properties of the sludge in the anaerobic system can be changed by electrical stimulation, and the sludge polarization can be induced to enhance the conductivity and capacitance of the sludge, thereby promoting the extracellular electron transfer process of the microorganisms in the anaerobic system, and achieving the purpose of strengthening anaerobic digestion. In addition, the present invention utilizes the input of intermittently controlled voltage, which saves energy input while maintaining the effect of electrical treatment to strengthen the anaerobic digestion process, reduces economic costs and improves energy efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of a device and process for enhancing anaerobic co-digestion of agricultural solid waste (cow dung and corn stalks) by using intermittent voltage according to the present invention;

[0024] Wherein: 1. tube ii, 2. feed tank, 3. tube iii, 4. water bath, 5. feed pump, 6. insulation layer, 7. peristaltic pump, 8. water inlet valve, 9. water inlet valve, 10. cover plate, 11. carbon rod, 12. wire i, 13. DC power supply, 14. wire ii, 15. exhaust valve, 16. tube i, 17. gas collection device, 18. carbon felt electrode, 19. water outlet valve, 20. tube iv, 21. discharge valve, 22. tube v, 23. discharge tank, 24. anaerobic digestion reactor, 25. reactor base. DETAILED DESCRIPTION

[0025] The application mechanism of a device and process for enhancing anaerobic co-digestion of agricultural solid waste (cow dung and corn straw) by using intermittent voltage is:

[0026] 1. Electrical stimulation can enrich electroactive microorganisms, and electroactive microorganisms can use their conductivity pili and release cytochrome C to establish direct interspecies electron transfer between microorganisms. Direct interspecies electron transfer between microorganisms is a new type of interspecies electron exchange mechanism between microorganisms. It does not require the help of hydrogen (formic acid), etc. Electrons can be directly transferred from one cell to another to convert CO 2 Reduction to CH 4 Under this microbial metabolic pathway, fatty acids or ethanol can directly produce methane and carbon dioxide through microbial syntrophic metabolism.

[0027] 2. Electrical stimulation can induce sludge polarization. As an aggregate of anaerobic microorganisms, sludge has abundant functional groups, such as -OH, -C=O, -NH, etc. It polarizes with the stimulation of electrode potential to improve its electron transfer performance, accelerate the rate of mutual trophic metabolism between microorganisms, and improve the rate and efficiency of electron transfer.

[0028] See attached Figure 1 , a device for strengthening anaerobic co-digestion of agricultural solid waste (cow dung and corn stalks) by using intermittent voltage, characterized in that: an anaerobic digestion reactor 24 is provided with a water bath constant temperature layer 6, a cover plate 10 is provided above the anaerobic reactor 24, one end of the tube i-16 is connected to the exhaust valve 15 on the right side of the cover plate 10, and the other end is connected to the gas collection device 17. The upper end is connected to the DC power supply 13 through the wire ii-14 and a carbon rod electrode 11 connected to the cover plate 10 in the middle is used as a cathode, a carbon felt electrode 18 is installed on the inner wall of the anaerobic reactor 24 and connected to the DC power supply 13 through the wire i-12 as an anode, and the lower part is fixedly connected to the reactor base 25. One end of the tube ii-1 is connected to the feed tank 2 through the feed pump 5, and the other end is connected to the upper left end of the anaerobic reactor 24 through the feed valve 9. One end of the tube iii-3 is connected to the water bath 4 through the peristaltic pump 7, and the other end is connected to the lower end of the left side of the water bath insulation layer through the water inlet valve 8. One end of pipe iv-20 is connected to the upper right end of water bath insulation layer 6 through outlet valve 19, and the other end is connected to water bath pot 4. One end of pipe v-22 is connected to the lower right end of water bath insulation layer 6 through discharge valve 21, and the other end enters discharge pool 23.

[0029] Embodiment 1: Cow dung is crushed with a wall-breaking machine, and then mixed with treated corn stalks (5 mm) into a suspension, and then the treated cow dung and corn stalks are mixed into a suspension with an optimal solid content of 15% to 20% as feed, and the optimal solid content of the suspension is 18.0%. An anaerobic digestion reactor 24 with a water bath constant temperature layer 6 is used, and a cover plate 10 is provided above the anaerobic reactor 24. One end of the tube i-16 is connected to the exhaust valve 15 on the right side of the cover plate 10, and the other end is connected to the gas collection device 17. The upper end is connected to the DC power supply 13 through the wire ii-14, and a carbon rod electrode 11 connected to the middle through the cover plate 10 is used as a cathode. A carbon felt electrode 18 is installed on the inner wall of the anaerobic reactor 24, which is connected to the DC power supply 13 through the wire i-12 as an anode, and the lower part is fixedly connected to the reactor base 25. One end of the tube ii-1 is connected to the feed tank 2 through the feed pump 5, and the other end is connected to the upper left end of the anaerobic reactor 24 through the feed valve 9. One end of the tube iii-3 is connected to the water bath 4 via the peristaltic pump 7, and the other end is connected to the lower end of the left side of the water bath insulation layer through the water inlet valve 8. One end of the tube iv-20 is connected to the upper end of the right side of the water bath insulation layer 6 via the outlet valve 19, and the other end is connected to the water bath 4. One end of the tube v-22 is connected to the lower end of the right side of the water bath insulation layer 6 via the discharge valve 21, and the other end enters the discharge tank 23. The full sludge start-up is adopted, the cover plate 10 of the anaerobic reactor 24 is opened, 900 ml of anaerobic sludge (anaerobic sludge VSS is 20-30 g / L, and the optimal value is 25 g / L) is poured into the anaerobic reactor 24, and the cover plate 10 is covered to seal the anaerobic reactor 24. Turn on the switch of the water bath 4 to control the temperature to 37°C, turn on the switch of the power supply 13 and set the working voltage to 0.4 V~0.8 V, the optimal working voltage to 0.6 V, the current formed to be 0.4 mA~0.7 mA, the optimal current to be 0.5 mA, and start running the anaerobic reactor 24. Every day, the feed is put into the anaerobic reactor 24 at a feed to reactor volume ratio of 1 / 30, and the temperature in the anaerobic reactor 24 is maintained at 35~37°C, and the optimal temperature is 37°C. The pH is between 7.0~8.0, the optimal pH is 7.8, and the hydraulic retention time is 20~30 d (the hydraulic retention time is 30d in this example). The anaerobic sludge is continuously electrically domesticated in the first 30 days, and the power switch is manually controlled from 31 to 60 days to achieve the purpose of intermittent power supply (1 day on / 1 day off - that is, switch on every other day). After the experiment, the methane production increased by 19.2% compared with the blank, and the organic matter removal rate increased by 9.5% compared with the blank.

Claims

1. A process for enhancing anaerobic co-digestion of agricultural solid waste using intermittent voltage. It is characterized in that The process is implemented based on an apparatus, and the apparatus is as follows: An anaerobic digestion reactor provided with a water bath thermostatic layer, wherein a cover plate is provided above the anaerobic digestion reactor, one end of a tube i is connected to an exhaust valve on the right side of the cover plate, and the other end is connected to a gas collecting device; the upper end is connected to a DC power supply through a wire ii, and a carbon rod electrode connected through the cover plate in the middle is used as a cathode; a carbon felt electrode is installed on the inner wall of the anaerobic digestion reactor and connected to a DC power supply through a wire i as an anode, and the lower part is fixedly connected to a reactor base; one end of the tube ii is connected to a feed tank through a feed pump, and the other end is connected to the upper left end of the anaerobic digestion reactor through a feed valve; one end of the tube iii is connected to a water bath pot through a peristaltic pump, and the other end is connected to the lower left end of the water bath insulation layer through a water inlet valve; one end of the tube iv is connected to the upper right end of the water bath insulation layer through a water outlet valve, and the other end is connected to the water bath pot; one end of the tube v is connected to the lower right end of the water bath insulation layer through a discharge valve, and the other end enters the discharge tank; The process comprises the following steps: Step 1, pulverizing cow dung with a wall breaking machine, and then mixing it with the treated corn stalks into a suspension with a solid content of 15% to 20%, and the mixed liquid of the treated cow dung and corn stalks enters a feed tank; Step 2, the anaerobic microorganisms of the anaerobic digestion reactor come from the anaerobic sludge discharged from the anaerobic fermentation tank of a sewage treatment plant in Dalian, and the VSS of the anaerobic sludge is 20-30 g / L; the anaerobic digestion reactor is started with full sludge, the feed pump and the feed valve are opened, and the garbage is injected into the anaerobic digestion reactor through pipe i, and the volume is 1 / 30 of the volume of the anaerobic sludge; Step 3, the internal temperature of the anaerobic digestion reactor is controlled at 35-37°C; Step 4, the pH value in the anaerobic digestion reactor is controlled between 7.0 and 8.0; Step 5, controlling the hydraulic retention time of the anaerobic digestion reactor to be between 20 and 30 days; Step 6: The working voltage used in the experiment is between 0.4 V and 0.8 V, and the current formed is between 0.4 mA and 0.7 mA. During the experiment, the power supply is intermittently controlled by manually controlling the power switch, 1 day on / 1 day off - that is, on every other day; Step 7, opening the exhaust valve, and collecting the biogas generated by the anaerobic digestion reactor through a gas collection device; Step 8, open the discharge valve, and discharge the fermentation product discharged from the anaerobic digestion reactor into the discharge tank through pipe iv.

2. A process for enhancing anaerobic co-digestion of agricultural solid waste using intermittent voltage according to claim 1, It is characterized in that In the step 1, the solid content is 18%.

3. The process for enhancing anaerobic co-digestion of agricultural solid waste using intermittent voltage according to claim 1, It is characterized in that In step 2, the VSS of the anaerobic sludge is 25 g / L.

4. The process for enhancing anaerobic co-digestion of agricultural solid waste using intermittent voltage according to claim 1, It is characterized in that In step 3, the internal temperature of the anaerobic digestion reactor is controlled at 37°C.

5. The process for enhancing anaerobic co-digestion of agricultural solid waste by using intermittent voltage according to claim 1, It is characterized in that In step 4, the pH value in the anaerobic digestion reactor is controlled at 7.

8.

6. The process for enhancing anaerobic co-digestion of agricultural solid waste using intermittent voltage according to claim 1, It is characterized in that In step 5, the hydraulic retention time of the anaerobic digestion reactor is controlled to be 30 days.

7. The process for enhancing anaerobic co-digestion of agricultural solid waste using intermittent voltage according to claim 1, It is characterized in that In step 6, the operating voltage is 0.6 V and the current is 0.5 mA.

Images