AU2012248673B2

AU2012248673B2 - Sludge-concentrating method and apparatus

Info

Publication number: AU2012248673B2
Application number: AU2012248673A
Authority: AU
Inventors: Naoaki Kataoka; Tateki KUROSAWA; Akinori Nishii; Masaaki Nishimoto
Original assignee: Swing Corp
Current assignee: Swing Corp
Priority date: 2011-04-26
Filing date: 2012-04-03
Publication date: 2017-04-13
Anticipated expiration: 2032-04-03
Also published as: KR20140036162A; CN103492325A; JP6395877B2; WO2012147467A1; JP2017100130A; KR101938024B1; CN109336351A; AU2012248673A1; JP6383150B2; JPWO2012147467A1

Abstract

Provided are a process and an apparatus capable of easily concentrating sludge to high concentrations. The sludge-concentrating method includes: a residue separation step that separates the sludge into residue and sludge from which has residue has been removed; a chemical blending/flocculating step that blends chemicals into the sludge from which residue has been removed; and a concentrate separation step that separates solids and liquids in the concentrated sludge produced by the chemical blending/flocculating step into thickened sludge and separated liquid. The sludge-concentrating apparatus includes a residue separation unit that separates the sludge into residue and sludge from which residue has been removed, a chemical blending/flocculating unit that blends chemicals into the residue-removed sludge, and a concentrate separation unit that separates solids and liquids in the concentrated sludge produced by the chemical blending/flocculating unit into concentrated sludge and separated liquid.

Description

- 1 -

DESCRIPTION

SLUDGE-CONCENTRATING METHOD AND APPARATUS TECHNICAL FIELD

[0001] The present invention relates to a sludge concentration method and a sludge concentration system, specifically, a method and a system that are desirable in the pretreatment before an anaerobic digestion treatment.

BACKGROUND ART

[0002] The anaerobic digestion treatment of sludge is a technology that has been applied as an energy saving process for a long time, since the treatment produces less sludge than an aerobic treatment, quickly kills off pathogenic microorganisms and parasite eggs and stabilizes the sludge, consumes little power since it requires no oxygen supply, and produces biogas whose main component is methane gas. On the other hand, the technology' requires large capacity for an anaerobic digestion tank facility, and the cost of chemicals used in treating digested-sludge is high.

[0003] Thus, it is still common in tire present method for disposing sludge to dewater and dispose sludge in a landfill, or to dew'ater and incinerate it, without anaerobically digesting sludge. An example of a conventional anaerobic treatment of sludge is shown as a flowchart in Figure 2. The process flow is described below.

[0004] Sludge 11 is sent to a storage tank 12, then it is sent to a solid-liquid separation device 13 for solid-liquid separation into a concentrated sludge 14 and a separation liquid 15. The concentrated sludge 14 is sent to an anaerobic digestion device 16, and the anaerobically digested sludge is sent to a digested-sludge flocculation device 17 where a separation liquid 18 is separated and a flocculated digested-sludge 19 is prepared. The flocculated digested-sludge 19 is sent to a dewatering device 20 where a separation liquid 21 is separated and a dewatered cake 22 is prepared. The separation liquid 15, separation liquid 18, and separation liquid 21 are sent to a wastewater treatment plant 23 or the like. A flocculant is often added in the digested-sludge flocculation device 17. -2- [0005] Meanwhile, Patent Document 1 presents a treatment method for night soil, garbage and sludge which treats sludge such as sludge of an organic wastewater treatment plant and private sewage treatment tanjk sludge, night soil and garbage containing animal and plants wastes with reduced energy consumption, and which sanitarily converts insanitary screen residue from night soil and the private sewage treatment tank sludge to compost and solid fuel, the treatment comprising (a) a pretreatment step for performing solid-liquid separation of night soil mixed with sludge, (b) an anaerobic digestion step for anaerobically digesting solid matter separated in the pretreatment step directly without de-watering it, (c) an anaerobic digestion step for anaerobically digesting garbage containing animal and plants wastes and solid matter, (d) a dewatering step for dewatering and separating effluent from the anaerobic digestion step into solid matter and separation water, and (e) a biological treatment step for biologically oxidizing and denitrifying the separation water from the pretreatment step and the separation water from the dewatering step.

[0006] Patent Document 2 presents a sludge treatment method and a system therefor which can m aximize the total efficiency of processes for concentrating and dewatering two kinds of sewage sludge generated in the wastewater treatment, namely primary settled sludge and excess sludge, by concentrating the sludge in a single system and concentrating it to a sludge concentration optimal for a subsequent dewatering process and maintaining the state, the treatment method including the following steps: the primary settled sludge and the excess sludge respectively generated from a primary settling tank and a final settling tank in a wastewater treatment system are mixed and stored; a flocculant is added to the mixture sludge to perform primary flocculation treatment; the mixture sludge after the primary flocculation treatment is concentrated to a sludge concentration of 6-8%; a flocculant is added to the mixture sludge after the concentration treatment to perform secondary flocculation treatment; and the mixture sludge after the secondary flocculation treatment is subjected to dewatering treatment.

[0007] Additionally, Patent Document 3 presents a slit-type concentration machine that increases the pressurization effect as well as the carrying capacity of the solid-liquid -3- 2012248673 29 Sep 2016 separator.

CITATION LIST PATENT DOCUMENTS

[0008] Patent Document 1: Japanese unexamined patent publication No. H10-216785 Patent Document 2: Japanese unexamined patent publication No. 2009-90240 Patent Document 3: Japanese unexamined patent publication No. 2003-211293

SUMMARY OF INVENTION

[0009] In a conventional sludge concentration step, screen residues having a particle size of 3 to 4 mm or higher are removed separately in a preceding stage, but screen residues having a smaller particle size are supplied as they are to the concentration step, and they are concentrated together with sludge.

[0010] Concentration methods include gravity concentration, which lets the sludge settle by gravity; belt concentration, which uses a belt-shaped screen that allows the water in the sludge to pass through without allowing solids to pass through; and machine concentration methods, such as centrifugal concentration, which uses liquid-solid separation by centrifugal force. Gravity concentration normally concentrates sludge without chemical feed. However, its concentration rate is only about 2 to 3 folds, and increasing its concentration rate requires securing a sufficient detention period, so concentration tanks having extremely large capacities are provided. Or else, the method requires the addition of chemicals, which makes the method unrealistic for obtaining a highly concentrated sludge. Further, conventional machine concentration methods require large amounts of chemicals to increase the solid recovery rate, and the belt concentration requires a large amount of high-pressure washing water to wash the belt. Additionally, the centrifugal concentration requires large power to rotate the container filled with sludge at a high speed.

[0011] In addition, there was a demand for improving the concentration technology of the sludge that is to be anaerobically digested, to contribute to further shortening the HRT of the conventional anaerobic treatment and down-scaling the digestion tank.

[0012] Also, an issue with the conventional technology, which is the reduction in the dewatering property of sludge after anaerobic treatment, called for an effective means against -4- 2012248673 29 Sep 2016 such problem.

[0013] An issue to be mitigated by the present invention is to provide a method for easily concentrating sludge to a high concentration and a system therefor.

[0014] The present invention is described below. 1) A sludge concentration method comprising a screen residue separation step for separating sludge into a screen residue and a residue-removed sludge; a chemical-mixing/flocculation step for mixing a chemical into the residue-removed sludge; and a concentration/separation step for performing a solid-liquid separation of a flocculated sludge generated in the chemical-mixing/flocculation step into a concentrated sludge and a separation liquid. 2) A sludge concentration system comprising a screen residue separation part for separating sludge into a screen residue and a residue-removed sludge; a chemical-mixing/flocculation part for mixing a chemical into the residue-removed sludge; a concentration/separation part for performing a solid-liquid separation of a flocculated sludge generated in the chemical-mixing/flocculation part into a concentrated sludge and a separation liquid.

[0015] The greatest characteristic of the present invention is that it removes screen residues having a small particle size and long fiber-like contaminants having a small particle size, such as hair, which were not removed in the conventional method. Since the contaminants and the like are removed sufficiently as compared to conventional methods, the residue-removed sludge obtained with the screen residues are free from mechanical troubles, such as the entanglement of the contaminants and the like to the rotation section during the concentration step, and a highly concentrated sludge can be obtained with low power, and thus, the dewaterability can be improved by mixing the separated screen residue with the anaerobically digested sludge of the subsequent stage.

ADVANTAGEOUS EFFECTS OF INVENTION

[0016] The present invention allows sludge to be concentrated in a reduced space by a low-power device, and the separated screen residue can be used in other steps as a dewatering assistant, or it can be stored and used in a desired sludge treatment at a desired time.

[0016a] A further aspect of the invention is a sludge concentration method comprising: a screen residue separation step for separating sludge into a screen residue and a residue--5 - 2012248673 29 Sep 2016 removed sludge; a chemical-mixing/flocculation step for mixing a chemical into the residue-removed sludge; a concentration/separation step for performing a solid-liquid separation of a flocculated sludge generated in the chemical-mixing/flocculation step into a concentrated sludge and a separation liquid; and a mixing step for mixing a total amount or a part of the screen residue and the separation liquid, each individually or as a mixture, with an anaerobically digested sludge obtained by an anaerobic digestion of the concentrated sludge. [0016b] A further aspect of the invention is a sludge concentration device comprising: a screen residue separation part for separating sludge into a screen residue and a residue-removed sludge; a chemical-mixing/flocculation part for mixing a chemical into the residue-removed sludge; a concentration/separation part for performing a solid-liquid separation of a flocculated sludge generated in the chemical-mixing/flocculation part into a concentrated sludge and a separation liquid; and a mechanism for mixing the total amount or a part of the screen residue and the separation liquid, individually or as a mixture, with an anaerobically digested sludge obtained by an anaerobic digestion of the concentrated sludge.

BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is an illustrative diagram showing an example of a concentration device to perform an embodiment of the method of the present invention.

Figure 2 is an illustrative diagram showing an arrangement of a conventional treatment device.

Figure 3 is an illustrative diagram showing an embodiment comprising an anaerobic digestion tank at the subsequent stage of the sludge separation part and that returns the digested sludge mixed with a concentrated sludge to the anaerobic digestion tank. DESCRIPTION OF EMBODIMENTS

[0018] In the present invention, “sludge” means sludge that is discharged in the treatment step of organic substances, such as sewage, night soil and garbage. Such sludge includes primary settled sludge and excess sludge.

[0019] The “screen residue” in the present invention is the residue separated from the above sludge, and it includes coarse suspended solids which are separated by a sieve having a nominal size of 74 pm, which complies with the sewage test method, and it is preferably 2012248673 29 Sep 2016 - 5a - coarse suspended solids having a particle size of 0.5 mm or higher or a particle size of 2.0 mm or higher, or being separated by a perforated plate having a pore size of 0.5 mm or higher or a pore size of 2.0 mm or higher, or a screen using a metal gauze of 60 to 100 mesh.

[0020] The particle size is a value classified by the sieve, and the pore size is the diameter of a hole.

[0021] Firstly, the screen residue separation step for separating sludge into a screen residue and a residue-removed sludge is explained below.

[0022] The steps of separating and recovering the screen residue contained in the sludge during the screen residue separation step, as well as the device used in the step, are described below.

[0023] The sludge from which the screen residue is separated is in a form of a slurry, and -6-normally, it has a SS of 5 g/L (liter) or higher.

[0024] The screen residue can be separated, in general, according to the particle size of the screen residue, or by using a sieve means having a pore size that is smaller than the particle size of the particle to be separated to filter the sludge, as desired. For example, as a general matter, a screen with large openings is used when a primary' settled sludge having a high screen residue content constitutes a large proportion, and a screen with small openings is used when the excess sludge having a small screen residue content constitutes a large proportion, although this is not always the case.

[0025] The sieve means includes the above perforated plate or screen using a metal gauze.

[0026] The arrangement of the screen residue separation part for separation into the screen residue and the residue-removed sludge is not particularly limited, but it should preferably comprise a device for raking the separated screen residue, a vibration mechanism to prevent the above sieve means from being clogged, or the like.

[0027] Next, the above chemical-mixing/flocculation step is described.

[0028] In the present application, a “chemical” means a chemical agent containing at least a flocculant, and it can also contain chemical agents other than the flocculant, such as a pH adjuster. Further, the chemical is not limited to liquid. The chemical can be used in the form of a flocculant alone, a mixture of the flocculant and other chemical agents, or a combination of the flocculant with other chemical agents added at different timings.

[0029] In the chemical-mixing/'flocculation step, a flocculated sludge is prepared by introducing and mixing at least a flocculant to the residue-removed sludge. The chemical-mixing/flocculation part to mix the flocculant with the residue-removed sludge is normally a flocculation mixing tank comprising a flocculant-introducing means, but it can be a simple tube or a tubular body comprising a flocculant-introducing means as long as the flocculated sludge can be prepared. The chemical mixing/floeculation part can comprise a flocculant storage tank to store a quantitatively dissolved flocculant, and the flocculant solution can be introduced from the storage tank to the flocculation mixing tank containing the residue-removed sludge. The method is preferable since the flocculant can be introduced efficiently without any loss.

[0030] The amount of flocculant to be added in the chemical-mixing/flocculation step is preferably 0.2 to 1.0 mass% to the SS (Suspended Solids) in sludge, and more preferably 0.3 to 0.6 mass%.

[0031 ] A flocculant can be used without any particular limitation. Examples include inorganic flocculants, such as iron (II) polysulphate, PAC or Poly Aluminum Chloride, and aluminum sulphates; and polymeric organic flocculants (hereinafter referred to as polymeric flocculants), which can each be used singly or in combination, but it is preferable to at least include a polymeric flocculant in use. Polymeric flocculants may include cationic, anionic, amphoteric flocculants and the like, and may include, amidine flocculants, acrylamide flocculants, acrylic acid flocculants.

[0032] Next, the concentration/separation step for performing solid-liquid separation of the flocculated sludge prepared in the chemical-mixing/flocculation step into concentrated sludge and separation liquid is described.

[0033] A concentrated sludge of a high concentration can be prepared by performing solid-liquid separation of the flocculated sludge in the concentration/separation step as shown above.

[0034] The concentration/separation part that performs solid-liquid separation of the flocculated sludge into a concentrated sludge and a separation liquid is not limited but may include a simple tank using gravity concentration, a centrifugal separator using centrifugal concentration, a separator using floatation concentration, and a separator using a screen. A preferable type among these is the slit-type concentrator, and a machine structure of JP 2003-211293 A (Patent Document 3), in which the slit plate receives the material to be treated, the material to be treated is sent to a discharge side on the slit plate by having many disks whose marginal faces are projected on a slit plate having many slits formed thereon eccentrically rotate, around a crank-shaft, in the direction for discharging the material to be treated. In the process, the liquid material drops from the gap with the disk in the slit to be filtered, and the solid material in the material to be treated is separated and captured. The machine -8-structure is further provided with a belt conveyer that is proximate the upper surface of the slit plate and rotates in the discharge direction of the matter to be treated, and deliquors the captured matter on the slit plate by pressing. When the slit-type concentrator is used, a high concentration of 4 to 12 mass% can be stably and surely achieved at a low running cost.

[0035] The concentrated sludge that has been separated in the concentration/separation step can be supplied to the desired treatment step to be subjected to a given treatment.

[0036] The concentrated sludge supply part that recovers and quantitatively supplies a concentrated sludge to the treatment device should preferably comprise a pump that integrates a quantifying means and a transportation means, and an example may include a single-axis-screw-type pump integrated with a feeder. However, it is also possible to arrange at least the sludge concentration part in the sludge concentration system of the present invention on top of the anaerobic digestion tank to let the concentrated sludge that is discharged from the concentration part fall directly or via a screw conveyor into the digestion tank to be introduced into the digestion tank. Such embodiment requires no introduction pump and the like, so the corresponding power can be reduced.

[0037] Further, when the subsequent treatment step is the digestion step, the digested-sludge-pulling piping can be branched to provide a return piping to the anaerobic digestion tank, in which the concentrated sludge and the digested sludge are mixed along the way before being introduced into the tank so that the concentration and the viscosity of the sludge to be Introduced into the anaerobic digestion tank can be reduced, and the pump power required for introduction of the sludge can also be reduced.

[0038] Further, a part or all of the separation liquid obtained by the solid-liquid separation of the flocculated sludge in the concentration/separation step can be mixed into a given treatment step. The separation liquid to be mixed into the treatment step may be mixed or not mixed with the above screen residue.

[0039] Next, the present specification will provide an example of applying the sludge concentration technology of the present invention as a pretreatment before the anaerobic treatment. -9- [0040] The present embodiment uses the screen residue obtained in the screen residue separation step to improve the dewaterabiiity of the sludge after the anaerobic treatment.

After the screen residue is recovered, the residue-removed sludge is prepared by adding and mixing a chemical, then concentrating the sludge to a high concentration (e.g. 4 to 12 raass%), A part or all of the separation liquid separated in the concentration step and the screen residue separated in the prior stage are mixed with the anaerobically digested sludge after the anaerobic treatment, and supplied to the dewatering treatment step.

[0041] The concentrated sludge separated in the concentration/separation step is introduced in the anaerobic digestion step. Conventionally, sludge was concentrated by gravity concentration or various mechanical concentrations, but the concentra tion of the sludge supplied to the anaerobic digestion step was 3 to 4% in reality, and at most about 5%.

Further, since the screen residue in the sludge was not separated in the concentration step, it was introduced into the anaerobic digestion step and most of it was decomposed in the anaerobic digestion treatment.

[0042] As shown above, the sludge from which the screen residue was recovered (residue-removed sludge) is subjected to the chemical-mixing/flocculation step, and the separated and recovered screen residue is mixed with the anaerobically digested sludge after anaerobic treatment, in its entirety or in part. In case the anaerobically digested sludge is to be further treated with a ilocculant, the addition of a screen residue to the digested sludge can be appropriately selected from before or after the addition of a ilocculant or at the same time as the addition of a ilocculant, or those timings can be combined, according to conditions such as the particle size of the screen residue or the pore size of the means to separate the flocculated sludge generated by the ilocculant. If the addition of the screen residue is after the addition of the ilocculant it is preferable for the screen residue to be added to the flocculated sludge at least during or before the treatment of the generated flocculated sludge in the dewatering step.

[0043] The recovered screen residue may be stored after being subjected to a drying treatment or the like if desired. - 10- [0044] The concentrated sludge separated in the concentration/separation step is supplied to the anaerobic digestion step as show above. When the sludge concentration part can be arranged on top of the anaerobic digestion tank, the discharged, concentrated sl udge is directly introduced to the digestion tank by gravity, but otherwise, it is preferable to include a concentrated sludge supply step in which the concentrated sludge may be recovered and quantitatively supplied to the anaerobic digestion step to perform an anaerobic treatment of a more efficient operation management.

[0045] The concentrated sludge supply part for recovering concentrated sludge and quantitatively supplying the concentrated sludge to the anaerobic digestion device may include the above pump that integrates a quantifying means and a transportation means.

[0046] Further, a part or all of the separation liquid obtained by the solid-liquid separation of the flocculated sludge in the concentration/separation step can be mixed with the anaerobically digested sludge obtained in the anaerobic digestion step. The separation liquid may be mixed or not mixed with the above screen residue.

[0047] The digested sludge of the concentrated sludge treated in the anaerobic digestion step can further be treated with a flocculant, which may be combined with the screen residue as desired, as shown above, but the digested sludge as it is has a high M alkalinity, which makes it difficult to treat with a flocculant, so the digested sludge should preferably be diluted, and a separation liquid can be used in the dilution. In such a ease, the screen residue to be added may be mixed or not mixed with the separation liquid.

[0048] The separation liquid contains phosphorous, calcium, siloxane and the like, so it can be introduced to the step for recovering the materials for their recovery.

[0049] An example of the present invention is further explained by referring to the drawing.

[0050] Figure 1 is a flowchart showing an embodiment of the present invention. The sludge concentration device of the present invention comprises at least a screen residue separation part 1, a chemical mixture/flocculadon part including a flocculating mixture tank 2 and a chemical storage tank 3, and a sludge concentration part 4. Firstly, the sludge is sent to a screen residue separation part 1, and it is separated into a screen residue and a residue--11 -removed sludge. Then, the residue-removed sludge is sent to the flocculation mixing tank 2 via the piping, and it is flocculated and prepared by having a chemical from the chemical storage tank 3 added in the middle of the piping or in the flocculation mixing tank 2. The flocculated sludge is introduced into the sludge concentration part 4, and separated into a highly concentrated sludge and a separation liquid. The concentrated sludge is supplied to the pump via the feeder attached to the concentrated sludge transportation pump 5, and it is quantitatively transported to the subsequent anaerobic digestion step. Further, the screen residue separated in the screen residue separation part and the separation liquid separated in the sludge concentration part are mixed in the screen residue/separation liquid receiving tank 6, and mixed with the digested sludge after anaerobic digestion treatment to be supplied to the dewatering step.

[0051 ] Figure 3 is a flowchart showing an embodiment in which an anaerobic digestion tank 7 is arranged in a subsequent stage of the concentration./separation part 4. T he concentrated sludge separated at the concentration/separation part 4 is anaerobically digested in the anaerobic digestion tank 7 to form an anaerobically digested sludge, and it is drawn out via the digested-sludge-withdrawing piping 10a. The digested-sludge-withdrawing piping 10a branches out to a return piping for digested sludge 10b, via which at least a part of the anaerobically digested sludge is returned to the anaerobic digestion tank 7. The return piping for digested sludge 10b comprises a mixing tank 9 to mix a concentrated sludge and an anaerobically digested sludge and supplies the mixed sludge to the anaerobic digestion tank 7. The embodiment in the drawing uses an introduction pump 8 for supplying a concentrated sludge or a mixture of a concentrated sludge and an anaerobically digested sludge, and a sludge-pulling pump 10 for drawing out anaerobically digested sludge from the anaerobic digestion tank 7, but the pump is unnecessary if sludge can be supplied or drawn out by tare.

EXAMPLES

[0052] The examples of the present invention is described below. The sludge concentration test of the present invention was performed concerning the sewage sludge - 12-produced in the Sewage Treatment Plant A according to the embodiment of Figure 1. The sewage sludge used in the test is a mixed sludge of a primary settled sludge and a excess sludge at about 1:1 subjected to gravity concentration.

[0053] Note that the present invention is not limited in any way by this Example.

[0054] The specification of the sludge concentration device used in the test is shown in Table 1. A cationic polymer fiocculant (average molecular weight 3,000,000) was added to residue-removed sludge at 0.5% (ratio against SS) in the test.

[0055] Table 2 shows characteristics of the sludge before and after the concentration treatment and the separation liquid obtained in the concentration/separation step. The original sludge is introduced sludge.

[0056] The following method was used for analysis. - TS (Total solids, total residue after e vaporation); weight of residue after evaporation at 105°C (JISK0102) - VTS (Volatile total solids, loss on ignition); loss on ignition at 600°C (JIS K 0102) - SS (Suspended solids, suspended particles); weight of precipitates from a centrifugal separation at a rotation of 3,000 rpm, for 10 minutes (JIS K 0102) - VSS (Volatile suspended solids, volatile suspended particles); loss on ignition at 600°C of suspended particles (JIS K 0102) - M alkalinity; titration to pH 4.8 of a supernatant liquor from a centrifugal separator rotated at 3,000 rpm for 3 minutes by adding a hydrochloric solution of 0.1 mol/L (sewage test method) - Coarse suspended solids; coarse suspended solids analysis by using a sieve of a nominal dimension of 74 pm (sewage test method) [0057] [Table 1]

Table 1 Specifiction of Sludge Concentration System screen residue separation part screen residue separator based on an osciliicating screen screen: φ 2 mm punching metal, motor power: 0.4 kW (for osciliicating), 0.1 kW (for raking) flocculation mixing tank effective capacity: 30 L agitator: rotation - 150 /min, power 0.1 kW sludge concentration part slit-type concentration machine width of treatment: 200 mm, opening: 1 mm, motor power 60 W concentrated sludge transport pump single-axis-screw-type pump (integrated with a feeder) aperture: φ 50 mm, motor power 0.75 kW><2 (main body, feeder) [0058] [Table 2]

Table 2 Characteristics of sludge and separation liquid before arid after the treatment original sludge residue-removed sludge concentrated sludge separation liquid oH 5.2 5.2 5.3 5.2 M alkalinity (mg/L as CaC03) 480 470 960 480 is (g/L) 18.4 17.4 78.7 - VTS (%) 86 85 84 - ss (g/L) 15.0 14.2 71.8 364 vss (%) 88 86 87 - coarse suspended solids (%, SS ratio) 37 30 31 - [0059] As shown above, it is clear that the sludge can be efficiently concentrated to a high concentration.

[0060] Next, a dewatering test was performed concerning the sludge after an anaerobic treatment of the above concentrated sl udge, and the variance in dewaterability due to whether the screen residue separated in the pretreatment was added or not was assessed.

[0061] The conditions of anaerobic treatment is as shown in Table 3. The characteristics of sludge before and after the anaerobic treatment is shown in Table 4.

[0062] [Table 3]

Table 3 Condition of Anaerobic Treatment

Anaerobic treatment tank (-) I Digestion tank treatment temperature (°C) | 37 HRT (days) i 20 introduced material (-) | concentrated sludge TS concentration of introduced material ---------p (mg/L) I 78,700 VTS concentration of introduced material (%) 84 . 14- [0063] [Table 4]

Table 4 Characteristics of Introduced Sludge, Sludge after Anaerobic Digestion Treatment

Introduced Sludge Digested Sludge pH 5.3 7.5 M alkalinity (mg/L as CaCG3! 960 8900 TS (g/L) 78.7 38.9 VTS (%) 84 68 ss (g/L) 71.8 31.2 vss (%) 87 69 coarse suspended solids (%, SS ratio) 31 14 [0064] A sludge that mixes the total amount of the screen residue and the total amount of concentrated separation liquid separated in the pretreatment before anaerobic digestion with the anaerobically digested sludge at a ratio of 1:1 was subjected to a dewatering test. A dewatering test of a sludge comprising a mixture of an anaerobically digested sludge and a concentrated separation liquid at a ratio of 1:1 was also perfonned as a comparative example. A cationic polymer flocculant (mean molecular weight 3,000,000) was used for sludge dewatering. Further, the belt press dewatering machine was used as the dewatering machine at dewatering conditions of a filter cloth tonicity of 4.9 kN/m and a filter cloth speed of 1.0 m/minute. The resulting polymeric flocculant injection rates and dewatered cake water contents are as shown in Table 5.

[0065] [Table 5]

Tabie 5 Resuit of Dewatering Treatment of Anaerobically Digested Sludge

Examples Comparative Examples Injection rate or polymeric flocculant (%, SS ratio) 1.8 2.0 Water content of dewatered sludge (%) 81 83

[0066] From the above results, it can be seen that a dewatered sludge having a low water content can be obtained by a low water content at a small chemical injection rate. REFERENCE SIGNS LIST

[0067] 1.., screen residue separation part, 2... flocculation mixing tank, 3...chemical storage tank, 4...sludge concentration part, 5.,.concentrated sludge transport pump, 6...screen 2012248673 29 Sep 2016 - 15- residue/separation liquid receiving tank, 7.. .anaerobic digestion tank, 8.. .injection pump, 9.. .mixing tank, 10...sludge-withdrawing pump, 10a...digested-sludge-withdrawing piping, 10b.. .return piping for digested sludge, 11... sludge, 12... storage device, 13... solid-liquid separator, 14...concentrated sludge, 16...anaerobic digestion device, 17...flocculated digested-sludge preparation device, 18. . . separation liquid, 19. . . flocculated digested-sludge, 20.. . dewatering device, 21... separation liquid, 23... wastewater treatment plant [0067a] Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof.

[0067b] The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

Claims

The claims defining the invention are as follows:

1. A sludge concentration method comprising: a screen residue separation step for separating sludge into a screen residue and a residue-removed sludge; a chemical-mixing/flocculation step for mixing a chemical into the residue-removed sludge; a concentration/separation step for performing a solid-liquid separation of a flocculated sludge generated in the chemical-mixing/flocculation step into a concentrated sludge and a separation liquid; and a mixing step for mixing a total amount or a part of the screen residue and the separation liquid, each individually or as a mixture, with an anaerobically digested sludge obtained by an anaerobic digestion of the concentrated sludge.
2. The sludge concentration method according to Claim 1, comprising a concentrated-sludge supply step for recovering the concentrated sludge and quantitatively supplying the concentrated sludge to an anaerobic digestion step.
3. The sludge concentration method according to either Claim 1 or 2, comprising a step for mixing an anaerobically digested sludge that was digested in the anaerobic digestion step and returning the anaerobically digested sludge to the anaerobic digestion step.
4. The sludge concentration method according to Claim 1, wherein the mixing step is a step for dewatering sludge or a step before the step for dewatering sludge.
5. The sludge concentration method according to any one of Claims 1 to 4, wherein the screen residue separation step separates a screen residue having a particle size of 0.5 mm or higher or a particle size of 2.0 mm or higher.
6. A sludge concentration device comprising: a screen residue separation part for separating sludge into a screen residue and a residue-removed sludge; a chemical-mixing/flocculation part for mixing a chemical into the residue-removed sludge; a concentration/separation part for performing a solid-liquid separation of a flocculated sludge generated in the chemical-mixing/flocculation part into a concentrated sludge and a separation liquid; and a mechanism for mixing the total amount or a part of the screen residue and the separation liquid, individually or as a mixture, with an anaerobically digested sludge obtained by an anaerobic digestion of the concentrated sludge.
7. A sludge concentration device according to Claim 6, comprising a concentrated sludge supply part that may recover the concentrated sludge and quantitatively supply the concentrated sludge to an anaerobic digestion device.
8. The sludge concentration device according to Claim 7, wherein the concentrated sludge supply part comprises a quantification pump.
9. The sludge concentration device according to Claim 7 or 8, wherein the concentrated sludge supply part is positioned higher than the anaerobic digestion device.
10. The sludge concentration device according to any one of Claims 7 to 9, comprising a piping for discharging anaerobically digested sludge from the anaerobic digestion device; a return piping for digested sludge that is branched from the piping; a mixing part for mixing the anaerobically digested sludge from the return piping for digested sludge with the concentrated sludge, wherein the anaerobically digested sludge mixed with a concentrated sludge at the mixing part is returned to the anaerobic digestion device.
11. The sludge concentration device according to any one of Claims 6 to 10, wherein the mechanism communicates with a step for dewatering sludge or a step before the step for dewatering sludge.
12. The sludge concentration device according to any one of Claims 6 to 11, wherein the screen residue separation part comprises a perforated plate having a pore size of 0.5 mm or higher or a pore size of 2.0 mm or higher, or a screen having a metal gauze of 60 to 100 mesh.