METHOD FOR ENHANCING ANAEROBIC DIGESTION BASED ON SOLID-LIQUID INTERFACE RENEWAL IN SLUDGE

Abstract

A method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge is disclosed. The method includes subjecting sludge to a centrifugation, a thermal baking and a redissolution in softened water in sequence to renew a solid-liquid interface in sludge, and subjecting the sludge to an anaerobic digestion to increase methane production from organic matter in the sludge by anaerobic biotransformation.

Claims

1. A method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge, comprising subjecting sludge to a centrifugation, a thermal baking, and a redissolution in softened water in sequence to renew a solid-liquid interface in the sludge, and subjecting the sludge to an anaerobic digestion to increase methane production from organic matter in the sludge by anaerobic biotransformation.

2. The method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge as claimed in claim 1, wherein the centrifugation is a low-speed centrifugation.

3. The method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge as claimed in claim 2, wherein the centrifugation comprises centrifuging sludge at a relative centrifugal force of 2,000 to 8,000 g for 5 to 20 minutes, subjecting the sludge to a solid-liquid separation, and collecting residual sludge.

4. The method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge as claimed in claim 1, wherein the thermal baking is a treatment with dry hot air at a constant temperature.

5. The method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge as claimed in claim 4, wherein the dry hot air is provided by an electricthermal blower or a combustion heating blower; and the thermal baking is performed at a temperature of 80° C. to 105° C. for 30 minutes to 120 minutes.

6. The method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge as claimed in claim 1, wherein the redissolution in softened water comprises redissolving sludge in softened water and fully mixing, and the softened water is any one selected from the group consisting of deionized water, distilled water, ultrapure water, and water after removal of calcium, magnesium, aluminum and iron ions.

7. The method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge as claimed in claim 1, wherein the redissolution in softened water is performed by a stirring at a rotation rate of 200 r/min to 400 r/min for 0.5 to 2 hours.

8. The method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge as claimed in claim 1, wherein the anaerobic digestion comprises transferring overall sludge into an anaerobic reactor, regulating a pH of the sludge to 6.0 to 8.0 with an acid liquor or alkali liquor, and subjecting the sludge to an anaerobic digestion at a medium temperature of 30 to 40° C. or a high temperature of 50 to 60° C. for 5 to 15 days with an inoculation ratio of 1:2 to 2:1 (in terms of volatile solid, namely VS).

9. The method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge as claimed in claim 8, wherein the acid liquor is a 6.0 mol/L hydrochloric acid solution, and the alkali liquor is a 6.0 mol/L sodium hydroxide solution, and the sludge is sewage sludge with a total solids (TS) content of 0.5 to 2.5%.

10. The method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge as claimed in claim 1, comprising the specific steps of (1) subjecting sewage sludge to a centrifugation and a solid-liquid separation, and collecting residual sludge; (2) subjecting the residual sludge in step (1) to a treatment with dry hot air at a constant temperature for a period of time; (3) redissolving the sludge after the treatment with dry hot air at a constant temperature in step (2) in softened water, and fully mixing; and (4) transferring overall sludge in step (3) into an anaerobic reactor, regulating a pH of the sludge to 6.0 to 8.0 with an acid liquor or alkali liquor, and subjecting the sludge to an anaerobic digestion at a medium temperature of 30 to 40° C. or a high temperature of 50 to 60° C. for 5 to 15 days with an inoculation ratio of 1:2 to 2:1 (in terms of VS).

11. The method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge as claimed in claim 2, comprising the specific steps of (1) subjecting sewage sludge to a centrifugation and a solid-liquid separation, and collecting residual sludge; (2) subjecting the residual sludge in step (1) to a treatment with dry hot air at a constant temperature for a period of time; (3) redissolving the sludge after the treatment with dry hot air at a constant temperature in step (2) in softened water, and fully mixing; and (4) transferring overall sludge in step (3) into an anaerobic reactor, regulating a pH of the sludge to 6.0 to 8.0 with an acid liquor or alkali liquor, and subjecting the sludge to an anaerobic digestion at a medium temperature of 30 to 40° C. or a high temperature of 50 to 60° C. for 5 to 15 days with an inoculation ratio of 1:2 to 2:1 (in terms of VS).

12. The method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge as claimed in claim 3, comprising the specific steps of (1) subjecting sewage sludge to a centrifugation and a solid-liquid separation, and collecting residual sludge; (2) subjecting the residual sludge in step (1) to a treatment with dry hot air at a constant temperature for a period of time; (3) redissolving the sludge after the treatment with dry hot air at a constant temperature in step (2) in softened water, and fully mixing; and (4) transferring overall sludge in step (3) into an anaerobic reactor, regulating a pH of the sludge to 6.0 to 8.0 with an acid liquor or alkali liquor, and subjecting the sludge to an anaerobic digestion at a medium temperature of 30 to 40° C. or a high temperature of 50 to 60° C. for 5 to 15 days with an inoculation ratio of 1:2 to 2:1 (in terms of VS).

13. The method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge as claimed in claim 5, comprising the specific steps of (1) subjecting sewage sludge to a centrifugation and a solid-liquid separation, and collecting residual sludge; (2) subjecting the residual sludge in step (1) to a treatment with dry hot air at a constant temperature for a period of time; (3) redissolving the sludge after the treatment with dry hot air at a constant temperature in step (2) in softened water, and fully mixing; and (4) transferring overall sludge in step (3) into an anaerobic reactor, regulating a pH of the sludge to 6.0 to 8.0 with an acid liquor or alkali liquor, and subjecting the sludge to an anaerobic digestion at a medium temperature of 30 to 40° C. or a high temperature of 50 to 60° C. for 5 to 15 days with an inoculation ratio of 1:2 to 2:1 (in terms of VS).

14. The method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge as claimed in claim 6, comprising the specific steps of (1) subjecting sewage sludge to a centrifugation and a solid-liquid separation, and collecting residual sludge; (2) subjecting the residual sludge in step (1) to a treatment with dry hot air at a constant temperature for a period of time; (3) redissolving the sludge after the treatment with dry hot air at a constant temperature in step (2) in softened water, and fully mixing; and (4) transferring overall sludge in step (3) into an anaerobic reactor, regulating a pH of the sludge to 6.0 to 8.0 with an acid liquor or alkali liquor, and subjecting the sludge to an anaerobic digestion at a medium temperature of 30 to 40° C. or a high temperature of 50 to 60° C. for 5 to 15 days with an inoculation ratio of 1:2 to 2:1 (in terms of VS).

15. The method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge as claimed in claim 7, comprising the specific steps of (1) subjecting sewage sludge to a centrifugation and a solid-liquid separation, and collecting residual sludge; (2) subjecting the residual sludge in step (1) to a treatment with dry hot air at a constant temperature for a period of time; (3) redissolving the sludge after the treatment with dry hot air at a constant temperature in step (2) in softened water, and fully mixing; and (4) transferring overall sludge in step (3) into an anaerobic reactor, regulating a pH of the sludge to 6.0 to 8.0 with an acid liquor or alkali liquor, and subjecting the sludge to an anaerobic digestion at a medium temperature of 30 to 40° C. or a high temperature of 50 to 60° C. for 5 to 15 days with an inoculation ratio of 1:2 to 2:1 (in terms of VS).

16. The method for enhancing anaerobic digestion based on solid-liquid interface renewal in sludge as claimed in claim 9, comprising the specific steps of (1) subjecting sewage sludge to a centrifugation and a solid-liquid separation, and collecting residual sludge; (2) subjecting the residual sludge in step (1) to a treatment with dry hot air at a constant temperature for a period of time; (3) redissolving the sludge after the treatment with dry hot air at a constant temperature in step (2) in softened water, and fully mixing; and (4) transferring overall sludge in step (3) into an anaerobic reactor, regulating a pH of the sludge to 6.0 to 8.0 with an acid liquor or alkali liquor, and subjecting the sludge to an anaerobic digestion at a medium temperature of 30 to 40° C. or a high temperature of 50 to 60° C. for 5 to 15 days with an inoculation ratio of 1:2 to 2:1 (in terms of VS).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIGURE shows a flowchart of a method according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The present disclosure will be described in detail in conjunction with the accompanying drawings and specific examples. The following is detailed description of the present disclosure in conjunction with examples, and the examples are not intended to limit the present disclosure. Any similar methods to the present disclosure and similar alterations thereof shall be encompassed in the scope of the present disclosure.

[0031] FIGURE shows a flowchart of a method according to one embodiment of the present disclosure. According to the present disclosure, sludge was subjected to a centrifugation, a thermal baking and a redissolution in softened water, so that the solid-liquid interface in sludge was renewed to reduce the energy barrier for the dissolution of organic matter, increase sites and driving force for effective binding of organic matter in sludge and enzyme molecules, reduce extracellular electron transport resistance during biochemical reaction and improve the electron utilization efficiency during anaerobic digestion, thereby increasing a yield of methane from organic matter per unit of sludge and enhancing the anaerobic digestion efficiency of sludge. All devices and chemicals were those commonly used.

[0032] Sludge used in examples was excess sludge (VS=51.2% to 65.7%, TS=0.8% to 2.3%) from a sewage treatment plant in Suzhou, and seeding sludge (VS=37.5% to 48.7%, TS=2.6% to 5.1%) used in anaerobic digestion was sludge discharged from a semi-batch anaerobic reactor.

Example 1

[0033] 1. 1,000 mL of sewage sludge was centrifuged at a relative centrifugal force (RCF) of 2,000 g for 20 minutes and subjected to a solid-liquid separation, and residual sludge was collected.

[0034] 2. The residual sludge in step 1 was put into a drying oven at 80° C. and subjected to a treatment with dry hot air at the constant temperature for 120 minutes.

[0035] 3. The sludge after the treatment with dry hot air at 80° C. in step 2 was redissolved in 500 mL of softened water by a stirring at 200 r/min for 2 hours.

[0036] 4. Overall sludge in step 3 was transferred into an anaerobic reactor and its pH was regulated to a range of 6.0 to 8.0 with an acid liquor or alkali liquor, and the sludge was subjected to an anaerobic digestion at 37° C. for 15 days with an inoculation ratio of 1:2 (in terms of VS). Biochemical methane potential (BMP) tester of an automatic methane potential test system (AMPTS II) was used to record data automatically, and a methane yield (mL CH.sub.4/g VS) per unit of organic matter was calculated. The result showed that the methane yield (mL CH.sub.4/g VS) per unit of organic matter was increased by 80% after the sludge was treated by this method.

Example 2

[0037] 1. 1,000 mL of sewage sludge was centrifuged at an RCF of 4,000 g for 10 minutes and subjected to a solid-liquid separation, and residual sludge was collected.

[0038] 2. The residual sludge in step 1 was put into a drying oven at 105° C. and subjected to a treatment with dry hot air at the constant temperature for 90 minutes.

[0039] 3. The sludge after the treatment with dry hot air at 105° C. in step 2 was redissolved in 500 mL of softened water by a stirring at 300 r/min for 2 hours.

[0040] 4. Overall sludge in step 3 was transferred into an anaerobic reactor and its pH was regulated to a range of 6.0 to 8.0 with an acid liquor or alkali liquor, and the sludge was subjected to an anaerobic digestion at 37° C. for 15 days with an inoculation ratio of 1:1 (in terms of VS). BMP tester of an AMPTS II was used to record data automatically, and a methane yield (mL CH.sub.4/g VS) per unit of organic matter was calculated.

[0041] The result showed that the methane yield (mL CH.sub.4/g VS) per unit of organic matter was increased by 200% after the sludge was treated by this method.

Example 3

[0042] 1. 1,000 mL of sewage sludge was centrifugated at an RCF of 6,000 g for 10 minutes and subjected to a solid-liquid separation, and residual sludge was collected.

[0043] 2. The residual sludge in step 1 was put into a drying oven at 95° C. and subjected to a treatment with dry hot air at the constant temperature for 90 minutes.

[0044] 3. The sludge after the treatment with dry hot air at the constant temperature in step 2 was redissolved in 500 mL of softened water by a stirring at 400 r/min for 0.5 hour.

[0045] 4. Overall sludge in step 3 was transferred into an anaerobic reactor and its pH was regulated to a range of 6.0 to 8.0 with an acid liquor or alkali liquor, and the sludge was subjected to an anaerobic digestion at 37° C. for 15 days with an inoculation ratio of 1:2 (in terms of VS). BMP tester of an AMPTS II was used to record data automatically, and a methane yield (mL CH.sub.4/g VS) per unit of organic matter was calculated.

[0046] The result showed that the methane yield (mL CH.sub.4/g VS) per unit of organic matter was increased by 100% after the sludge was treated by this method.

Example 4

[0047] 1. 1,000 mL of sewage sludge was centrifuged at an RCF of 4,000 g for 15 minutes and subjected to a solid-liquid separation, and residual sludge was collected.

[0048] 2. The residual sludge in step 1 was put into a drying oven at 100° C. to and subjected to a treatment with dry hot air at the constant temperature for 80 minutes.

[0049] 3. The sludge after the treatment with dry hot air at the constant temperature in step 2 was redissolved in 500 mL of softened water by a stirring at 300 r/min for 1 hour.

[0050] 4. Overall sludge in step 3 was transferred into an anaerobic reactor and its pH was regulated to a range of 6.0 to 8.0 with an acid liquor or alkali liquor, and the sludge was subjected to an anaerobic digestion at 37° C. for 15 days with an inoculation ratio of 1:2 (in terms of VS). BMP tester of an AMPTS II was used to record data automatically, and a methane yield (mL CH.sub.4/g VS) per unit of organic matter was calculated.

[0051] The result showed that the methane yield (mL CH.sub.4/g VS) per unit of organic matter was increased by 150% after the sludge was treated by this method.

Example 5

[0052] 1. 1,000 mL of sewage sludge was centrifugated at an RCF of 8,000 g for 15 minutes and subjected to a solid-liquid separation, and residual sludge was collected.

[0053] 2. The residual sludge in step 1 was put into a drying oven at 105° C. and subjected to a treatment with dry hot air at the constant temperature for 60 minutes.

[0054] 3. The sludge after the treatment with dry hot air at the constant temperature in step 2 was redissolved in 500 mL of softened water by a stirring at 300 r/min for 2 hours.

[0055] 4. Overall sludge in step 3 was transferred into an anaerobic reactor and its pH was regulated to a range of 6.0 to 8.0 with an acid liquor or alkali liquor, and the sludge was subjected to an anaerobic digestion at 55° C. for 10 days with an inoculation ratio of 2:1 (in terms of VS). BMP tester of an AMPTS II was used to record data automatically, and a methane yield (mL CH.sub.4/g VS) per unit of organic matter was calculated.

[0056] The result showed that the methane yield (mL CH.sub.4/g VS) per unit of organic matter was increased by 160% after the sludge was treated by this method.

Example 6

[0057] 1. 1,000 mL of sewage sludge was centrifuged at an RCF of 3,000 g for 15 minutes and subjected to a solid-liquid separation, and residual sludge was collected.

[0058] 2. The residual sludge in step 1 was put into a drying oven at 80° C. and subjected to a treatment with dry hot air at the constant temperature for 30 minutes.

[0059] 3. The sludge after the treatment with dry hot air at the constant temperature in step 2 was redissolved in 500 mL of softened water by a stirring at 200 r/min for 0.5 hour.

[0060] 4. Overall sludge in step 3 was transferred into an anaerobic reactor and its pH was regulated to a range of 6.0 to 8.0 with an acid liquor or alkali liquor, and the sludge was subjected to an anaerobic digestion at 55° C. for 5 days with an inoculation ratio of 2:1 (in terms of VS). BMP tester of an AMPTS II was used to record data automatically, and a methane yield (mL CH.sub.4/g VS) per unit of organic matter was calculated.

[0061] The result showed that the methane yield (mL CH.sub.4/g VS) per unit of organic matter was increased by 50% after the sludge was treated by this method.

[0062] The following comparative examples were carried out with reference to Example 6.

Comparative Example 1

[0063] This comparative example was the same as Example 6, except that the sewage sludge was not centrifugated and not subjected to a solid-liquid separation here.

[0064] 1. 1,000 mL of sewage sludge was put into a drying oven at 80° C. and subjected to a treatment with dry hot air at the constant temperature for 30 minutes.

[0065] 2. The sludge after the treatment with dry hot air at the constant temperature in step 1 was redissolved in 500 mL of softened water by a stirring at 200 r/min for 0.5 hour.

[0066] 3. Overall sludge in step 2 was transferred into an anaerobic reactor and its pH was regulated to a range of 6.0 to 8.0 with an acid liquor or alkali liquor, and the sludge was subjected to an anaerobic digestion at 55° C. for 5 days with an inoculation ratio of 2:1 (in terms of VS). BMP tester of an AMPTS II was used to record data automatically, and a methane yield (mL CH.sub.4/g VS) per unit of organic matter was calculated.

[0067] The result showed that the methane yield (mL CH.sub.4/g VS) per unit of organic matter was increased by 10% after the sludge was treated by this method.

Comparative Example 2

[0068] This comparative example was the same as Example 6 except that the sewage sludge was not subjected to a treatment with dry hot air at a constant temperature here.

[0069] 1. 1,000 mL of sewage sludge was centrifuged at an RCF of 3,000 g for 15 minutes and subjected to a solid-liquid separation, and residual sludge was collected.

[0070] 2. The sludge obtained in step 1 was redissolved in 500 mL of softened water by a stirring at 200 r/min for 0.5 hour.

[0071] 3. Overall sludge in step 2 was transferred into an anaerobic reactor and its pH was regulated to a range of 6.0 to 8.0 with an acid liquor or alkali liquor, and the sludge was subjected to an anaerobic digestion at 55° C. for 5 days with an inoculation ratio of 2:1 (in terms of VS). BMP tester of an AMPTS II was used to record data automatically, and a methane yield (mL CH.sub.4/g VS) per unit of organic matter was calculated.

[0072] The result showed that the methane yield (mL CH.sub.4/g VS) per unit of organic matter was only increased by 5% after the sludge was treated by this method.

Comparative Example 3

[0073] This comparative example was the same as Example 6, except that the sludge was not redissolved in softened water here.

[0074] 1. 1,000 mL of sewage sludge was centrifuged at an RCF of 3,000 g for 15 minutes, and subjected to a solid-liquid separation, and residual sludge was collected.

[0075] 2. The residual sludge in step 1 was put into a drying oven at 80° C., and subjected to a treatment with dry hot air at the constant temperature for 30 minutes.

[0076] 3. Overall sludge in step 2 was transferred into an anaerobic reactor and its pH was regulated to a range of 6.0 to 8.0 with an acid liquor or alkali liquor, and the sludge was subjected to an anaerobic digestion at 55° C. for 5 days with an inoculation ratio of 2:1 (in terms of VS). BMP tester of an AMPTS II was used to record data automatically, and a methane yield (mL CH.sub.4/g VS) per unit of organic matter was calculated.

[0077] The result showed that the methane yield (mL CH.sub.4/g VS) per unit of organic matter was only increased by 15% after the sludge was treated by this method.

Comparative Example 4

[0078] This comparative example was the same as Example 6, except that the sequence of centrifugation and the treatment with dry hot air at the constant temperature was changed here.

[0079] 1. 1,000 mL of sewage sludge was put into a drying oven at 80° C., and subjected to a treatment with dry hot air at the constant temperature for 30 minutes.

[0080] 2. The sludge from step 1 was centrifuged at an RCF of 3,000 g for 15 minutes and subjected to a solid-liquid separation, and residual sludge was collected.

[0081] 3. The residual sludge in step 2 was redissolved in 500 mL of softened water by a stirring at 200 r/min for 0.5 hour.

[0082] 4. Overall sludge in step 3 was transferred into an anaerobic reactor and its pH was regulated to a range of 6.0 to 8.0 with an acid liquor or alkali liquor, and the sludge was subjected to an anaerobic digestion at 55° C. for 5 days with an inoculation ratio of 2:1 (in terms of VS). BMP tester of an AMPTS II was used to record data automatically, and a methane yield (mL CH.sub.4/g VS) per unit of organic matter was calculated.

[0083] The results showed that the methane yield (mL CH.sub.4/g VS) per unit of organic matter was only increased by 20% after the sludge was treated by this method. From Comparative Examples 1 to 4, during the treatment of sludge, if the sludge was not subjected to a centrifugation, a thermal baking and a redissolution in softened water in sequence, it was impossible to achieve a good effect and the methane yield from organic matter was at a low level. If the sequence of the treatment steps was changed (e.g., in Comparative Example 4), the effect was still unsatisfactory. The solid-liquid interface in sludge could be renewed better and the methane production from organic matter in the sludge by anaerobic biotransformation could be increased only when the sludge was subjected to a centrifugation, a thermal baking and a redissolution in softened water in sequence.

[0084] The above description of the embodiments is intended to help a person of ordinary skill in the art to understand and use the disclosure. Obviously, a person skilled in the art could easily make various modifications to these embodiments, and apply a general principle described herein to other embodiments without creative efforts. Therefore, the disclosure is not limited to the above embodiments. All improvements and modifications made by a person skilled in the art according to implication of the disclosure without departing from the spirit of the disclosure should fall within the scope of the disclosure.