METHOD FOR REALIZING SLUDGE SAFE DISPOSAL AND RESOURCE RECOVERY THROUGH SLUDGE LIQUEFACTION AND STRATIFICATION

Abstract

The present invention relates to a method for sludge safe disposal and resource recovery through sludge liquefaction and stratification. The method is to completely liquefy the organic matters in the sludge into soluble organic matters through a thermal-alkaline synergistic treatment. After the treatment, the sludge is stratified, and an anaerobic digestion is performed on a high-concentration soluble liquid of an upper layer to convert organic carbon, nitrogen and phosphorus into biogas, ammonia nitrogen and phosphate, a crude protein recovery is performed on a sludge protein of a middle layer, and a dewatering and a landfill on a sludge inorganic solid of a lower layer.

Claims

1. A method for realizing sludge safe disposal and resource recovery through sludge liquefaction and stratification, comprising the following steps: step S1. concentrating a waste activated sludge to obtain a concentrated sludge; step S2. performing a thermal-alkaline synergistic liquefaction treatment on the concentrated sludge obtained in the step S1; step S3. adjusting pH value of the sludge after the liquefaction treatment in the step S2 to be neutral, and then performing a natural sedimentation to obtain substances of three layers consisting of an upper layer, a middle layer and a lower layer; step S4. performing an anaerobic digestion on the substances of the upper layer obtained in the step S3, collecting generated biogas, and then adding MgCl.sub.2 into a liquid obtained from the anaerobic digestion treatment to react and obtain a struvite sediment; step S5. performing a separation and a sedimentation on the substances of the middle layer obtained in the step S3 to obtain a crude protein; and step S6. performing a dewatering and a landfill disposal on the substances of the lower layer obtained in the step S3, wherein a total suspended solids content of the concentrated sludge in the step S1 is 20 to 60 g/L, wherein a method of the thermal-alkaline synergistic liquefaction treatment in the step S2 is adding NaOH into the concentrated sludge to react, with a reaction time being 60 to 90 min and a reaction temperature being 140 to 170° C.

2. (canceled)

3. (canceled)

4. The method according to claim 1, wherein a dosage ratio of the NaOH to the concentrated sludge is 50 mmol:1 kg to 200 mmol:1 kg.

5. The method according to claim 1, wherein the anaerobic digestion treatment in the step S4 is adding the substances of the upper layer to an anaerobic digestion reactor for an anaerobic digestion; a reaction temperature of the anaerobic digestion reactor is 30 to 40° C., a hydraulic retention time is 24 to 48 h, and a volume loading is 10 to 15 kg COD/(m.sup.3.Math.d).

6. The method according to claim 1, wherein in the step S4, a molar ratio of the MgCl.sub.2 to a phosphate contained in the liquid phase is 1:1 to 1.1:1.

7. The method according to claim 1, wherein the separation and the sedimentation in the step S5 are performed by adjusting pH value of the substances of the middle layer obtained in the step S3 to 6.5 to 8.

8. The method according to claim 1, wherein the dewatering in the step S6 is reducing a moisture content of the sludge to below 60%.

9. (canceled)

10. A waste activated sludge treatment system, comprising a sludge liquefaction device, a salt producing acid and alkali device, a sedimentation device, an anaerobic digestion reactor, a magnesium adding agitation tank, a struvite sedimentation tank, and a crude protein purification sedimentation tank; the sludge liquefaction device comprises a heating component and an agitation component, used to perform a thermal-alkaline synergistic liquefaction on the waste activated sludge; the salt producing acid and alkali device is used to produce acid and alkali respectively, an alkali producing area of the salt producing acid and alkali device is connected with the sludge liquefaction device, used to add alkali to the sludge liquefaction device, and an acid producing area of the salt producing acid and alkali device is connected with an outlet of the sludge liquefaction device, used to adjust pH value of the sludge after the liquefaction treatment; the sedimentation device is connected with the outlet of the sludge liquefaction device, used to perform a static sedimentation on the sludge after pH neutralization; an upper area of the sedimentation device is connected with the anaerobic digestion reactor, used to perform an anaerobic digestion on substances of an upper layer after the static sedimentation; a middle area of the sedimentation device is connected to the crude protein purification sedimentation tank, used to perform a separation and a sedimentation on the substances of a middle layer after the static sedimentation to obtain a crude protein; a lower area of the sedimentation device is connected to an external transport device, used to perform a dewatering and a landfill disposal on the substances of a lower layer; the anaerobic digestion reactor is further connected to the magnesium adding agitation tank, used to perform a magnesium adding treatment on a liquid obtained after the anaerobic digestion treatment; the magnesium adding agitation tank is connected to the struvite sedimentation tank, used to perform a sedimentation on the liquid after the magnesium adding treatment to obtain a struvite sediment.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 is a flow chart of the waste activated sludge treatment in the present invention.

[0043] FIG. 2 is a picture of sludge stratification after the liquefaction treatment of the waste activated sludge in the present invention.

DESCRIPTION OF THE EMBODIMENTS

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the technical field.

[0045] Unless otherwise specified, the reagents and materials used in the following embodiments are all commercially available.

[0046] Embodiment 1: waste activated sludge rapid treatment and resource recovery

[0047] 1. Experimental Method

[0048] As shown in FIG. 1, it is a flow chart of the method for waste activated sludge rapid treatment and resource recovery in the present invention. The specific steps are as follows.

[0049] (1) The waste activated sludge was concentrated to obtain a concentrated sludge with a total suspended solids content of 30 g/L;

[0050] (2) According to a ratio of 100 mmol:1 kg concentrated sludge, NaOH was added into the concentrated sludge for a thermal-alkaline synergistic liquefaction treatment, which was reacted for 70 min at 170° C.; hydrochloric acid was added to adjust a pH value of the sludge after the liquefaction treatment to be neutral;

[0051] (3) A static natural sedimentation was performed on the mixture obtained in step (2) and substances of three layers i.e. a high-concentration organic liquid of an upper layer, a creamy yellow sludge protein of a middle layer, and a sludge inorganic solid of a lower layer as shown in FIG. 2 were obtained;

[0052] (4) The high-concentration organic liquid of the upper layer in step (3) was added into an anaerobic digestion reactor for an anaerobic digestion treatment, the anaerobic digestion reactor was set with an operating temperature of 35° C. and a retention time of 30 h, with a volume loading of 12 kg COD/(m.sup.3.Math.d), and three phases of solid, liquid and gas phases were obtained.

[0053] (5) Biogas obtained in step (4) was collected, a phosphate content in the liquid phase obtained in step (4) was 22.58 mmol/L, MgCl.sub.2 was added at a concentration of 23 mmol/L, and a struvite was precipitated and obtained after the reaction;

[0054] (6) A pH value of a liquid of the middle layer obtained in step (3) was adjusted to 6.5, and a crude protein was collected and obtained after a separation and a sedimentation;

[0055] (7) The substances of the lower layer obtained in step (3) were dewatered using a plate-and-frame filter press to a moisture content of 60%, and then landfill disposed.

[0056] 2. Experimental Results

[0057] (1) In the liquefaction treatment of this embodiment, 80% of the organic matters in the sludge can be released into the liquid phase within 70 min.

[0058] (2) In this embodiment, by the anaerobic digestion reaction in the liquid phase of the upper layer, 88% of the organic matters can be degraded within 30 h.

[0059] (3) In this embodiment, 80% of the crude protein in the liquid phase of the middle layer can be recovered.

[0060] (4) In this embodiment, a recovery amount of the struvite is 5421 mg/L sludge, and thus 93.1% of phosphorus and 80% of nitrogen in the sludge can be recovered.

[0061] (5) A biogas yield is 6 m.sup.3 biogas/(m.sup.3-reactor.Math.day).

[0062] (6) Compared with the traditional anaerobic digestion sludge treatment technology, a volume of sludge treatment equipment in this embodiment is reduced to 1/20 of that of traditional anaerobic digestion sludge treatment equipment.

COMPARATIVE EXAMPLE 1

Traditional Anaerobic Digestion Sludge Treatment Technology

[0063] 1. Experimental Method

[0064] The specific operation includes the following steps:

[0065] (1) According to a ratio of 100 mmol:1 kg concentrated sludge, NaOH was added into the concentrated sludge for a pretreatment, which was reacted for 70 min at 170° C.;

[0066] (2) The pretreated sludge obtained in step (2) was added into a solid-liquid mixing anaerobic reactor to react, the anaerobic digestion reactor was set with an operating temperature of 35° C. and a retention time of 30 d, with a volume loading of 0.5 kg COD/(m.sup.3.Math.d), and generated biogas was collected.

[0067] 2. Experimental Results

[0068] (1) In this comparative example, by the anaerobic digestion reaction in the liquid phase, 70% of the organic matters can be degraded within 30 days.

[0069] (2) According to the method of this comparative example, a final biogas yield is 0.3 m.sup.3 biogas/(m.sup.3-reactor.Math.day).

[0070] Embodiment 2: waste activated sludge rapid treatment and resource recovery

[0071] 1. Experimental Method

[0072] (1) The waste activated sludge was concentrated to obtain a concentrated sludge with a TSS content of 60 g/L;

[0073] (2) According to a ratio of 50 mmol:1 kg concentrated sludge, NaOH was added into the concentrated sludge for a liquefaction treatment, which was reacted for 70 min at 170° C.; hydrochloric acid was added to adjust pH value of the sludge after the liquefaction treatment to be neutral;

[0074] (3) A static natural sedimentation was performed on the mixture in step (2) and substances of three layers consisting of an upper layer, a middle layer and a lower layer were obtained;

[0075] (4) The substances of the upper layer obtained in step (3) were added to a up-flow anaerobic sludge bed reactor for an anaerobic digestion treatment, the anaerobic digestion reactor was set with an operating temperature of 30° C. and a retention time of 48 h, with a volume loading of 12 kg COD/(m.sup.3.Math.d), and three phases of solid, liquid and gas phases were obtained;

[0076] (5) Biogas obtained in step (4) was collected, a phosphate content in the liquid phase obtained in step (4) was 22.58 mmol/L, MgCl.sub.2 was added at a concentration of 23 mmol/L, and a struvite was precipitated and obtained after the reaction;

[0077] (6) A pH value of a liquid of the middle layer obtained in step (3) was adjusted to 7, and a crude protein was collected and obtained after a separation and a sedimentation;

[0078] (7) The substances of the lower layer obtained in step (3) were dewatered using a plate-and-frame filter press to a moisture content of 60%, and then landfill disposed.

[0079] 2. Experimental Results

[0080] (1) In the liquefaction treatment of this embodiment, 70% of the organic matters in the sludge can be released into the liquid phase within 70 min.

[0081] (2) In this embodiment, by the anaerobic digestion reaction in the liquid phase, 88% of the organic matters can be degraded within 30 h.

[0082] (3) In this embodiment, a recovery amount of the struvite is 6777 mg/L sludge, and thus 68.6% of phosphorus and 55% of nitrogen in the sludge can be recovered.

[0083] (4) In this embodiment, a final biogas yield is 6 m.sup.3 biogas/(m.sup.3-reactor.Math.day).

[0084] For the concentrated sludge with a TSS content of 60 g/L, if treated with the traditional anaerobic digestion method, it is difficult to ensure a uniformity of the reaction system, and it is difficult for the reactor to operate continuously and stably.

Embodiment 3: Waste Activated Sludge Rapid Treatment and Resource Recovery

[0085] 1. Experimental Method

[0086] (1) The waste activated sludge was concentrated to obtain a concentrated sludge with a total suspended solids content of 30 g/L;

[0087] (2) According to a ratio of 100 mmol:1 kg concentrated sludge, NaOH was added into the concentrated sludge for a liquefaction treatment, which was reacted for 70 min at 140° C.; hydrochloric acid was added to adjust pH value of the sludge after the liquefaction treatment to be neutral;

[0088] (3) A static natural sedimentation was performed on the mixture in step (2) and substances of three layers consisting of an upper layer, a middle layer and a lower layer were obtained;

[0089] (4) The liquid phase of the upper layer in step (3) was added to an up-flow anaerobic sludge bed reactor for an anaerobic digestion treatment, the anaerobic digestion reactor was set with an operating temperature of 40° C. and a retention time of 24 h, with a volume loading of 10.5 kg COD/(m.sup.3.Math.d), and three phases of solid, liquid and gas phases were obtained.

[0090] (5) Biogas obtained in step (4) was collected, a phosphate content in the liquid phase obtained in step (4) was 19.75 mmol/L, MgCl.sub.2 was added at a concentration of 19.75 mmol/L, and a struvite was precipitated and obtained after the reaction;

[0091] (6) A pH value of a liquid of the middle layer obtained in step (3) was adjusted to 8, and a crude protein was collected and obtained after a separation and a sedimentation;

[0092] (7) The substances of the lower layer obtained in step (3) were dewatered using a plate-and-frame filter press to a moisture content of 60%, and then landfill disposed.

[0093] 2. Experimental Results

[0094] (1) In the liquefaction treatment of this embodiment, 83% of the organic matters in the sludge can be released into the liquid phase within 70 min.

[0095] (2) In this embodiment, by the anaerobic digestion reaction in the liquid phase, 85% of the organic matters can be degraded within 30 h.

[0096] (3) According to the method of this embodiment, a recovery amount of the struvite is 3680 mg/L sludge, and thus 81.3% of phosphorus and 70% of nitrogen in the sludge can be recovered.

[0097] (4) According to the method of this embodiment, a final biogas yield is 5 m.sup.3 biogas/(m.sup.3-reactor.Math.day).

COMPARATIVE EXAMPLE 2

Traditional Anaerobic Digestion Sludge Treatment Technology

[0098] 1. Experimental Method

[0099] (1) According to a ratio of 100 mmol:1 kg concentrated sludge, NaOH was added into the concentrated sludge for a pretreatment, which was reacted for 70 min at 140° C.;

[0100] (2) The pretreated sludge obtained in step (2) was added into a solid-liquid mixing anaerobic reactor to react, the anaerobic digestion reactor was set with an operating temperature of 40° C. and a retention time of 30 d, with a volume loading of 0.4 kg COD/(m.sup.3.Math.d), and generated biogas was collected.

[0101] 2. Experimental Results

[0102] (1) According to the method of this comparative example, by performing the anaerobic digestion reaction in the liquid phase, 70% of the organic matters can be degraded within 30 days. (2) According to the method of this comparative example, a final biogas yield is 0.2 m.sup.3 biogas/(m.sup.3-reactor.Math.day).

Embodiment 4: Waste Activated Sludge Rapid Treatment and Resource Recovery

[0103] 1. Experimental Method

[0104] (1) The waste activated sludge was concentrated to obtain a concentrated sludge with a total suspended solids content of 30 g/L;

[0105] (2) According to a ratio of 200 mmol:1 kg concentrated sludge, NaOH was added into the concentrated sludge for a liquefaction treatment, which was reacted for 70 min at 170° C.; hydrochloric acid was added to adjust pH value of the sludge after the liquefaction treatment to be neutral;

[0106] (3) A static natural sedimentation was performed on the mixture in step (2) and substances of three layers consisting of an upper layer, a middle layer and a lower layer were obtained;

[0107] (4) The liquid phase of the upper layer in step (3) was added to an up-flow anaerobic sludge bed reactor for an anaerobic digestion treatment, the anaerobic digestion reactor was set with an operating temperature of 35° C. and a retention time of 30 h, with a volume loading of 12.3 kg COD/(m.sup.3.Math.d), and three phases of solid, liquid and gas phases were obtained.

[0108] (5) Biogas obtained in step (4) was collected, a phosphate content in the liquid phase obtained in step (4) was 23.1 mmol/L, MgCl.sub.2 was added at a concentration of 25.5 mmol/L, and a struvite was precipitated and obtained after the reaction;

[0109] (6) A pH value of a liquid of the middle layer obtained in step (3) was adjusted to 8, and a crude protein was collected and obtained after a separation and a sedimentation;

[0110] (7) The substances of the lower layer obtained in step (3) were dewatered using a plate-and-frame filter press to a moisture content of 60%, and then landfill disposed.

[0111] 2. Experimental Results

[0112] (1) In the liquefaction treatment of this embodiment, 97% of the organic matters in the sludge can be released into the liquid phase within 70 min.

[0113] (2) In this embodiment, by the anaerobic digestion reaction in the liquid phase, 86% of the organic matters can be degraded within 30 h.

[0114] (3) In this embodiment, a recovery amount of the struvite is 5557 mg/L sludge, and thus 95% of phosphorus and 70% of nitrogen in the sludge can be recovered.

[0115] (4) A biogas yield is 6.1 m.sup.3 biogas/(m.sup.3-reactor.Math.day).

COMPARATIVE EXAMPLE 3

Traditional Anaerobic Digestion Sludge Treatment Technology

[0116] 1. Experimental Method

[0117] (1) According to a ratio of 200 mmol:1 kg concentrated sludge, NaOH was added into the concentrated sludge for a pretreatment, which was reacted for 70 min at 170° C.;

[0118] (2) The pretreated sludge obtained in step (2) was added into a solid-liquid mixing anaerobic reactor to react, the anaerobic digestion reactor was set with an operating temperature of 35° C. and a retention time of 30 d, with a volume loading of 0.52 kg COD/(m.sup.3.Math.d), and generated biogas was collected.

[0119] 2. Experimental Results

[0120] (1) According to the method of this comparative example, by performing the anaerobic digestion reaction in the liquid phase, 70% of the organic matters can be degraded within 30 days.

[0121] (2) A biogas yield is 0.31 m.sup.3 biogas/(m.sup.3-reactor.Math.day).

[0122] Obviously, the above-mentioned embodiments of the present invention are merely examples to clearly illustrate the present invention, and are not intended to limit the implementations of the present invention. For those of ordinary skill in the art, other changes or modifications in different forms can be made on the basis of the above description. It is not necessary and impossible to list all the implementations here. Any modification, equivalent replacement and improvement made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.