A method for advanced dewatering of sludge thermal hydrolysate

Abstract

The application discloses a kind of sludge hot hydrolysate's deep dewatering method, first take sludge hot hydrolysate, determine its moisture content, then according to 1-4% of sludge dry weight Iron salt type conditioning agent is added, after stirring, heating treatment is carried out;Then the sludge after heating treatment is transported to filter pressing dewatering equipment and is deeply dewatered, and forms mud cake.The application aims at the dewatering problem of the hot hydrolysate of residual sludge in sewage plant after hot hydrolysis conditioning, by adding iron salt type conditioning agent to the hot hydrolysate for reconditioning, and keeping at 60 DEG C and above for reaction, and then transported to filter pressing dewatering equipment for deep dewatering, which can significantly improve the dewatering performance of sludge, compared with the direct dewatering method of ordinary sludge hot hydrolysate, the application can significantly improve the efficiency and effect of sludge deep dewatering, can be stably operated and reduce the comprehensive treatment cost of sludge.

Description

TECHNICAL FIELD

[0001] The present application relates to a sludge dewatering method, in particular to a sludge thermal hydrolysis liquid dewatering method. BACKGROUND

[0002] Sludge is a mixture containing microorganisms, inorganic matter, organic matter and other components. Organic matter is an important component of sludge, mainly from refractory substances in raw sewage and degradation products of microorganisms, algae and humus. With the development of economy and the improvement of infrastructure, the COD of the influent of sewage treatment plants is increasing, and the excess sludge is gradually changing into high-organic-content sludge. If high-organic-content sludge is not properly treated, it will not only pollute the surrounding environment, but also eventually cause greenhouse effect and exacerbate climate change. Sludge dewatering technology is one of the main technologies for sludge reduction. After conventional chemical conditioning and mechanical dewatering, the water content of sludge can be reduced from 98% to about 80%. Further dewatering is very difficult, mainly due to the high compressibility and colloidal stability of sludge. The extracellular polymeric substance (EPS) in sludge has strong water locking ability. EPS wraps water and microorganisms to form sludge flocs. The surface of sludge flocs is negatively charged and has a double-layer structure. The flocs are stable because they cannot agglomerate due to the repulsion of surface charges. In addition, when sludge flocs are compressed by mechanical external force, a large amount of water in the sludge flocs is still "locked" in the flocs due to the high hydrophilicity and compressibility of the EPS network structure.

[0003] The current commonly used sludge dewatering methods include: (1) FeCl3 + lime conditioning of sludge for deep dewatering, but this method can only reduce the water content of sludge to about 60%, and 80% of the sludge needs to be diluted to 95% before conditioning. The dewatering filtrate also needs to be further disposed of; (2) sludge is subjected to thermal hydrolysis and then subjected to anaerobic digestion or deep dewatering, but the dewatering properties of sludge thermal hydrolysis liquid are unstable and are greatly affected by temperature, season and sludge properties.

[0004] Patent CN202010903121.2 discloses a sludge thermal hydrolysis process. This process belongs to a sludge pretreatment process. Although the extracellular polymeric substance can be destroyed to some extent and cell water can be released after sludge pyrolysis, the dewatering ability of sludge pyrolysis liquid is affected by sludge properties and seasonal temperature changes, and cannot be stably operated. Patents CN117342776 B and CN114804570 B are both aimed at sewage plant sludge. The dewatering process of sludge without thermal hydrolysis can only reduce the water content of sludge to about 50% to 60%, and it is very difficult to further dewater. SUMMARY

[0005] The application aims to provide a sludge thermal hydrolysis liquid deep dewatering method which can greatly improve sludge dewatering efficiency and dewatering effect.

[0006] The sludge thermal hydrolysis liquid deep dewatering method comprises the following steps:

[0007] (1) Take sludge thermal hydrolysis liquid and measure its water content;

[0008] (2) Add iron salt conditioner to the sludge thermal hydrolysis liquid according to 1-4% of the dry weight of the sludge, and then carry out heat preservation stirring and standing reaction;

[0009] (3) Transport the sludge after heat treatment to a pressure filtration dewatering equipment to carry out deep dewatering and form a sludge cake.

[0010] In step (1), the preparation process of the sludge thermal hydrolysis liquid is as follows: heat the sludge to 160-200 DEG C to carry out thermal hydrolysis or carry out alkaline thermal hydrolysis reaction of the sludge and alkali agent at 100-120 DEG C to obtain the sludge thermal hydrolysis liquid; after flash evaporation heat release, the temperature of the hydrolyzed sludge is 80-100 DEG C; the water content of the sludge thermal hydrolysis liquid is 80-85%.

[0011] In step (1), the sludge thermal hydrolysis liquid is transported to the pressure filtration dewatering equipment after pressure relief and temperature reduction, and the temperature is 70-80 DEG C.

[0012] In step (2), the iron salt conditioner is FeCl3 and / or polymeric ferric sulfate.

[0013] In step (2), the mixing ratio of the iron salt conditioner is 1-4% of mass ratio: Fe / dry weight of sludge*100%.

[0014] In step (2), the temperature of the sludge thermal hydrolysis liquid is 80-100 DEG C.

[0015] In step (2), after adding the iron salt conditioner, the reaction temperature of the sludge thermal hydrolysis liquid is 60-80 DEG C.

[0016] In step (2), the temperature of heat preservation is 65-90 DEG C, the stirring time is 20-30 min, the standing reaction temperature is 65-90 DEG C, and the standing reaction time is 10-20 min.

[0017] In step (2), after the iron salt conditioner is dissolved, it is added to the sludge hydrolysis liquid to carry out sufficient mixing and stirring to promote the reaction.

[0018] In step (3), the feed pressure during the filter press dewatering process is ≥0.6MPa and the pressing pressure is ≥1.0MPa, so that the moisture content of the sludge after filter press is reduced to below 45%; preferably, the feed pressure is 0.6~0.8MPa and the pressing pressure is 1.0~2.0MPa.

[0019] In step (3), the sludge feeding and conveying can be carried out using pressure conveying equipment such as pneumatic pipelines, plunger pumps, screw pumps, and diaphragm pumps; the sludge dewatering and pressing can be carried out using diaphragm plate and frame filter presses.

[0020] The filtrate obtained in step (3) is rich in crude protein and has a high COD content. It can be used as a carbon source for sewage treatment plants, greening liquid fertilizer, or concentrated protein liquid for resource utilization. The dewatered cement cake can be used as a raw material for biomass fuel, compost, etc.

[0021] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0022] (1) This invention addresses the problem of dewatering the hydrolysate from wastewater treatment plant sludge after hydrolysis. By adding iron salt conditioners to the hydrolysate for further conditioning and maintaining the reaction at 60°C or above, the solution is then transported to a filter press for deep dewatering. This significantly improves the dewatering performance of the sludge. Compared with ordinary direct dewatering methods using hydrolysate, this invention significantly enhances the efficiency and effectiveness of deep sludge dewatering, ensuring stable operation and reducing overall sludge treatment costs. (2) The deep sludge dewatering method provided by this invention can stably reduce the sludge moisture content to below 45%, meeting the moisture content requirements for self-sustaining incineration of sludge in general thermal power plants. (3) The sludge conditioning and deep dewatering method provided by this invention is less affected by seasonal changes and can operate stably. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the deep dewatering method for sludge hydrolysate according to the present invention. Detailed Implementation

[0024] The present invention will now be described in further detail.

[0025] Example 1

[0026] like Figure 1 As shown, a method for conditioning and deep dewatering of sludge hydrolysate includes the following steps:

[0027] (1) Preparation of sludge alkaline thermal hydrolysis liquid: the residual sludge from a municipal sewage treatment plant was centrifugally dewatered to about 80% moisture content after PAM conditioning, then 30% CaO and 2000% water of the dry weight of the sludge were added to the sludge, the sludge was subjected to alkaline hydrolysis by heating to 120°C for 2h, and the alkaline hydrolysis liquid was flash-cooled to 80°C with a pH of 12.6.

[0028] (2) The sludge alkaline hydrolysis liquid at 80°C obtained in step (1) was taken, and the moisture content was determined to be 82%;

[0029] (3) Liquid polymeric ferric sulfate was added to the sludge alkaline hydrolysis liquid in step (2) at 3% of the dry weight of the sludge in terms of Fe in the liquid polymeric ferric sulfate, i.e. Fe(m) / dry weight of sludge*100% = 3%, stirring for 20min, and keeping the sludge temperature at 70°C for 10min of continuous reaction;

[0030] (4) The conditioned sludge was transported to a small diaphragm plate-and-frame filter press using a diaphragm pump, the feeding pressure was 0.7MPa, the feeding time was 30min, the pressing pressure was 1.0MPa, the pressing time was 30min, the plate-and-frame filter press was opened, the cake thickness was determined to be 27mm, and the cake moisture content was 42%. The cake was transported for disposal, and the filter press liquor was concentrated by evaporation to form concentrated protein liquid for sale.

[0031] The parameters of this example are shown in Table 1 below.

[0032] Table 1

[0033]

[0034]

[0035] Example 2

[0036] A sludge thermal hydrolysis liquid conditioning and deep dewatering method, comprising the following steps:

[0037] (1) Preparation of sludge alkaline thermal hydrolysis liquid: the residual sludge from a municipal sewage treatment plant was centrifugally dewatered to 80% moisture content after PAM conditioning, then 200% water of the dry weight of the sludge was added to the sludge with 80% moisture content, the sludge was subjected to thermal hydrolysis by heating to 180°C for 1h, and the thermal hydrolysis liquid was flash-cooled to 90°C with a pH of 6.8.

[0038] (2) The sludge alkaline thermal hydrolysis liquid at 90°C was taken, and the moisture content was determined to be 83.3%;

[0039] (3) Liquid polymeric ferric sulfate was added at 4% of the dry weight of the sludge in terms of Fe, stirring for 20min, and keeping the sludge temperature at 80°C for 10min of continuous reaction;

[0040] (4) The conditioned sludge is transported to a small diaphragm plate and frame filter press by a diaphragm pump, the feeding pressure is 0.7 MPa, the feeding time is 30 min, the squeezing pressure is 1.0 MPa, the squeezing time is 30 min, the small plate and frame filter press is opened, the cake thickness is 25 mm, and the moisture content is 43%. The cake is transported out for disposal, and the filter press liquor is concentrated by evaporation to form concentrated protein liquid for sale.

[0041] The parameters of the embodiment are shown in Table 2 as follows:

[0042] Table 2

[0043]

[0044]

[0045] Example 3

[0046] On the basis of Example 1, different from Example 1 is that the iron salt content is adjusted to 1%. The dewatered cake thickness is 25 mm, and the cake moisture content is 45%. The parameters are shown in Table 3 as follows.

[0047] Table 3

[0048]

[0049] Example 4

[0050] On the basis of Example 1, different from Example 1 is that the iron salt content is adjusted to 4%. The dewatered cake thickness is 28 mm, and the cake moisture content is 40%. The parameters are shown in Table 4 as follows.

[0051] Table 4

[0052]

[0053] Comparative Example 1

[0054] On the basis of Example 1, different from Example 1 is that no iron salt conditioner is added. The cake thickness is 18 mm, and the cake moisture content is 61%. The parameters are shown in Table 5 as follows.

[0055] Table 5

[0056]

[0057]

[0058] Comparative Example 2

[0059] On the basis of Example 2, different from Example 2 is that no iron salt conditioner is added. The cake thickness is 17 mm, and the cake moisture content is 63%. The parameters are shown in Table 6 as follows.

[0060]

[0061] Table 6

[0062] Comparative Example 3

[0063] Based on Example 2, different from Example 2, the hydrolysis sludge after alkaline hydrolysis reaction was cooled to 40°C before adding 3% iron salt conditioner. The obtained cake thickness was 21 mm, and the cake moisture content was 55%. The parameters are shown in Table 7 as follows.

[0064] Table 7

[0065]

[0066] Comparative Example 4

[0067] Based on Example 1, different from Example 1, the iron salt conditioner was stirred for 20 min, and then the reaction was not continued under heating conditions. The obtained cake thickness was 24 mm, and the cake moisture content was 51%. The parameters are shown in Table 8 as follows.

[0068] Table 8

[0069]

[0070]

[0071] Comparative Example 5

[0072] Based on Example 1, different from Example 1, when the iron salt conditioner was added, no stirring was performed, and the reaction was directly performed at 70°C for 10 min. The obtained cake thickness was 21 mm, and the cake moisture content was 58%. The parameters are shown in Table 9 as follows.

[0073] Table 9

[0074]

[0075]

[0076] Comparative Example 1 and Example 1 were compared. When no iron salt conditioner was added during the secondary conditioning, the obtained cake parameters were thickness 18 mm and moisture content 61%. Comparative Example 2 and Example 2 were compared. When no iron salt conditioner was added during the secondary conditioning, the obtained cake parameters were thickness 17 mm and moisture content 63%. It was shown that under the condition of thermal hydrolysis conditioning, no iron salt was added, and under the same pressure filtration dewatering parameter conditions, the cake thickness was reduced by more than 50%, and the cake moisture content was increased by about 20%.

[0077] Compared with Example 2, the hydrolysis sludge after the alkaline hydrolysis reaction is cooled to 40℃ and then 3% iron salt is added for conditioning, and the thickness of the dewatered cake is 21mm and the moisture content is 55%, compared with Comparative Example 1, the thickness of the cake is reduced by 22% and the moisture content is increased by 13%, which indicates that the secondary conditioning of the cooled hydrolysis sludge by adding iron salt will significantly reduce the dewatering performance.

[0078] As can be seen from Comparative Example 4 and Comparative Example 5, in the secondary conditioning, the stirring reaction is omitted or the reaction is continued, and the dewatering performance of the sludge is significantly reduced.

[0079] As can be seen from the above, the iron salt is added to the thermal hydrolysis sludge for secondary conditioning, and the test results show that after the iron salt is added to the hydrolysis sludge at 60℃ and above for stirring reaction and continued reaction, the dewatering performance of the sludge can be significantly improved, and the efficiency and effect of sludge dewatering treatment are greatly improved.

Claims

1. A method for advanced dewatering of sludge thermal hydrolysate, characterized by, The method comprises the following steps: (1) taking sludge hot hydrolysate, and determining the water content thereof; The preparation process of the sludge hot hydrolysate is as follows: the sludge is heated to 160-200 DEG C for thermal hydrolysis or the sludge is reacted with an alkali agent at 100-120 DEG C for alkali thermal hydrolysis to obtain hydrolyzed sludge, and after flash evaporation heat release, the temperature of the hydrolyzed sludge is 80-100 DEG C; (2) according to 1-4% of the dry weight of the sludge, an iron salt conditioner is added to the sludge hot hydrolysate, and after heat preservation and stirring, the reaction is carried out by standing; when the iron salt conditioner is added, the temperature of the sludge hot hydrolysate is 60-80 DEG C; the temperature of heat preservation is 65-90 DEG C, and the stirring time is 20-30 min; the standing reaction temperature is 65-90 DEG C, and the standing reaction time is 10-20 min; (3) the sludge after heat treatment is transported to a pressure filtration dewatering equipment for deep dewatering to form a mud cake; the feeding pressure in the pressure filtration dewatering process is greater than or equal to 0.6 MPa, the squeezing pressure is greater than or equal to 1.0 MPa, so that the water content of the sludge after pressure filtration is reduced to less than 45%.

2. The method for advanced dewatering of sludge thermal hydrolysate according to claim 1, characterized in that, In step (2), the iron salt conditioner is FeCl3 and / or polymeric ferric sulfate.

3. The process for advanced dewatering of sludge thermal hydrolysate according to claim 1, characterized in that, In step (2), after the iron salt conditioner is dissolved, it is added to the sludge hot hydrolysate for sufficient mixing and stirring to promote the reaction.

4. The method for advanced dewatering of sludge thermal hydrolysate according to claim 1, characterized in that, In step (1), the water content of the sludge hot hydrolysate is 80-85%.

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