AU2011339363B2 - Anaerobic treatment method and device - Google Patents

Abstract

The purpose of the present invention is to provide an anaerobic processing method and a device, whereby: an anaerobic digestion device can be made more compact; the generation of phosphorous, siloxane, and other precipitates is reduced; sludge generated at wastewater processing facilities, etc., is stably and efficiently anaerobically digested; biogas (especially methane gas) can be efficiently recovered; digested sludge can be efficiently dewatered; and cost is reduced. Provided is an anaerobic processing method that includes: a preprocessing step that solid/liquid separates a coagulated sludge, which is prepared by adding a coagulant to sludge, into a sludge concentrate with a sludge concentration of 4-12% and a separated liquid; an anaerobic digestion step that anaerobically digests the sludge concentrate and also recovers biogas; a step for preparing a digested sludge coagulant by mixing a coagulant and at least one of either the separated liquid and water, with the anaerobically digested sludge prepared in the anaerobic digestion step; and a step for dewatering a digested sludge concentrate obtained by solid/liquid separating the digested sludge coagulant. Also provided is a device for implementing said processing method.

Description

DESCRIPTION

ANAEROBIC TREATMENT PROCESS AND APPARATUS TECHNICAL FIELD

[0001] The present invention relates to a process and an apparatus for the anaerobic treatment of sludge.

BACKGROUND ART

[0001 A] A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission or a suggestion that that document or matter was known, or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

[0001B] Throughout the description and claims of the specification, the word “comprise” and variations of the word, such as “comprising” and “comprises”, is not intended to exclude other additives, components, integers or steps.

[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 holds many problems in view of the large capacity required for an anaerobic digestion tank facility, the high cost of chemicals used in treating digested-sludge, and the difficulty in reducing the water content of dewatered sludge due to its low dewaterability.

[0003] Thus, it is still common in the present method for disposing sludge to dewater and dispose sludge in a landfill, or dewater and incinerate it, without anaerobically digesting sludge. An example of a conventional anaerobic treatment of sludge is shown as a flowchart in Figure 6. The process flow is described below.

[0004] Sludge 1 is sent to a storage system 2, then it is sent to a solid-liquid separation device 6 for solid-liquid separation into a concentrated sludge 7 and a separation effluent 8, of which the concentrated sludge 7 is sent to an anaerobic digestion device 9 where biogas 10 and an anaerobically-digested-sludge 11 are produced. Biogas 10 is sent to a biogas tank 101, then it is sent to a gas-using facility 102 (e.g. gas turbine, biogas boiler, gas lamp, or a drier heat source) or to a surplus gas combustion system 103. The anaerobically-digested-sludge 11 is sent to a digested-sludge flocculation device 12 where a separation effluent 14 is separated and a flocculated digested-sludge 15 is prepared, of which the flocculated digested-sludge 15 is sent to a dewatering device 16 where a separation effluent 17 is separated and a dewatered cake 18 is prepared. The separation effluent 8, separation effluent 14, and separation effluent 17 are sent to a wastewater treatment plant 104 or the like; A floesulant is often added in the digested-sludge flocculation device 12.

[0005] Meanwhile, Patent Document 1 presents a treatment method for night soil, garbage and sludge which treats sludge of an organic wastewater treatment plant, sludge such as private sewage treatment tank sludge, night soil and garbage containing animal and plants wastes with reduced energy consumptions and which sanitarily converts night soil and insanitary screen residue in the private sewage treatment tank sludge to compost and: solid fuel, the treatment consisting of (a) a pfetfoatmeni. 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 pre-treatment step directly without dewatering it. (c) an anaerobic digestion step for anaerobical ly digesting garbage containing animal and plants wastes and solid matter, (d) a dewatering step for dewatering and separating outflowing liquid of the anaerobic digestion step into solid matter and pp^taflbmw^ and (e) a biological treatment step for biologically oxidizing and denitrifying the separation water of the pretreatment step and tie separation water from thedewateringtstep, [0006] Patent Document 2 presents a sludge treatment method and a system therefore which can maximize the total efficiency # processes % concentrating aid dewatering two kinds of wastewater sludge generated in tie 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 mixfure sludge to perform primary flocculation treatment; the mixture sludge after the primary flocculation treatment is concentrated to a sludge concentration ot 6-8%; a floeeniaoi is added to the mixture sludge after the concentration treatment |o perform secondary flocculation treatment; and the mixture sludge after the secondary flocculation treaunent is subjected to dewatering treatment.

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

CITATION LIST PATENT DOCUMENTS

[0008] Patent Document 1: Japanese unexamined patent publication No. 10-216785 Patent Document 2: Japanese unexamined patent publication No. 2007-264758 Patent Document 3: Japanese unexamined patent publication No. 2003-211293 [0009] The greatest problem in an anaerobic digestion treatment of sludge produced by wastewater treatment plant and the like was that it required an anaerobic digestion tank of a large capacity due to the HRT (Hydraulic retention time) of normal anaerobic digestion treatments being 20 to 30 days. For example, a sludge treatment of sludge having a TS (Total Solids) concentration of 3 wt% at a treatment rate of 100 m3/day normally requires a large anaerobic digestion tank of 2000 to 3000 m3 to be built. Further, problems in treating digested-sludge were a high chemical cost for sludge flocculation and dewatering treatment and a low dewaterability of sludge that made it difficult to reduce the water content of sludge. Such problems result from protein being decomposed in the anaerobic digestion of sludge, thus producing ammonia nitrogen and increasing M alkalinity (acid consumption of up to pH 4.8) to at least about 3,000 mg CaC03/L, which pulls the pH condition away from the weak acidity region which is considered to be the optimum pH condition for sludge flocculation. Another problem was that the decomposition of coarse suspended solids (fiber) in the sludge by sludge digestion reduced the coarse suspended solids content, which contributes greatly to water removal in the sludge dewatering process, and lead to an increase in the water content of dewatered cakes. A further problem was that precipitates of phosphorous, calcium and the like were produced in anaerobic digestion tanks, pipes and the <filename> like. In addition, silicon in the wastewater is normally in the form of siloxan derived from silicon compounds including silicon oils in shampoos, conditioners, cosmetics and the like. A siloxan is an organic compound having a silicon-oxygen bond, whose main chain is Si-O- and whose side chain is hydrocarbon. Examples of siloxans include a linear or cyclic siloxan composed of 2 to 6 silicon atoms and having a methyl group as a hydrocarbon group. Since siloxan has low water solubility, it is distributed into biogas when sewage sludge is anaerobically digested. Accordingly, many cases are known of siloxan precipitating as scales on the generation facility, such as a gas engine, and peripheral equipments when power is generated using biogas, and reducing power generation efficiency and degrading facility maintenance, and a preventative measure is a key issue.

[0010] It would therefore be desirable to provide a low cost anaerobic treatment process and an apparatus that downsize the anaerobic digestion device, as well as reduce the production of precipitates including phosphorous, calcium and siloxan (silicon compounds having a siloxan bond), performs a stable and efficient anaerobic digestion of sludge produced in the wastewater treatment plant, as well as efficiently recover biogas (especially methane gas), and efficiently dewater the digested-sludge.

SUMMARY OF THE INVENTION

[0011] The following anaerobic treatment process and anaerobic treatment apparatus is provided according to the present invention. 1) An anaerobic treatment process comprising: a pretreatment step for subjecting a flocculated sludge to a solid-liquid separation into concentrated sludge at a sludge concentration of 4 to 12 wt% and a separation effluent, wherein the flocculated sludge was prepared by adding a flocculant to a sludge; an anaerobic digestion step for anaerobically digesting the concentrated sludge and recovering biogas; a step for preparing a flocculated digested-sludge having M-alkalinity in the range from 2500 mg/1 to 4000 mg/1 by mixing a flocculant and at least one of the separation effluent and a biologically treated water with an anaerobically-digested-sludge prepared in the anaerobic digestion step, wherein the anaerobically-digested-sludge has M-alkalinity in the range from 4490 mg/1 to 8900 mg/1 and a coarse suspended solids content of 5 % to 18 % against SS; and a step of dewatering a concentrated digested-sludge that was obtained by performing solid-liquid separation on the flocculated digested-sludge. 2) An anaerobic treatment apparatus comprising: a flocculation tank for preparing a flocculated sludge by adding a flocculant to sludge; a pretreatment sludge concentration device for subjecting the flocculated sludge from the flocculation tank to a solid-liquid separation into a concentrated sludge having a sludge concentration of 4 to 12 wt% and a separation effluent; an anaerobic digestion device for anaerobically digesting the concentrated sludge from the pretreatment sludge concentration device and recovering biogas; a digested-sludge flocculation device for preparing a flocculated digested-sludge having M-alkalinity in the range from 2500 mg/1 to 4000 mg/1 by mixing a flocculant and at least one of the separation effluent and a biologically treated water with an anaerobically-digested-sludge prepared by the anaerobic digestion device, wherein the anaerobically-digested-sludge has M-alkalinity in the range from 4490 mg/1 to 8900 mg/1 and a coarse suspended solids content of 5 % to 18 % against SS; a dewatering device for dewatering a concentrated digested-sludge that was obtained by subjection the flocculated digested-sludge to a solid-liquid separation; and a piping for delivering the separation effluent from the pretreatment sludge concentration device to the digested-sludge flocculation device.

[0012] In the treatment method of the present invention, the concentrated sludge prepared by solid-liquid separation in the pretreatment step contains sludge at 4 to 12 wt%, which is at least 1.5 to 2 times thicker than conventional methods. Since anaerobic digestion treatment was performed on the concentrated sludge, the anaerobically-digested-sludge in the present invention has a higher M alkalinity and ammonia concentration than the anaerobically-digested-sludge of conventional methods. Accordingly, to obtain a dewaterable floe by adding a flocculant to an anaerobically-digested-sludge per se would require a large amount of flocculant. In the present invention, a dewaterable flocculated digested-sludge is obtained by mixing at least one of the separation effluent or water obtained in the pretreatment step into the anaerobically-digested-sludge to dilute it, and smoothly produces flocculated digested-sludge by the sludge flocculation reaction of the anaerobically-digested-sludge and the added flocculant to reduce the amount of flocculant to be injected. Further, in the pretreatment step of the present invention, the flocculated sludge prepared % adding a ilocculant is separated into concentrated sludge and separation effluent, which allows the separation effluent to contain useful resources that are water-soluble or hydrophilic, suehus phosphorous, and allows efficient recovery of ire useful resources. Additionally, since the petreatment step, which allows the recovery of useful resources, is performed before the anaerobic digestion step, die amount of materials in the concentrated sludge to be sent to the anaerobic digestion step, such as phosphorous and siloxan, is reduced, and the reduction together with the high sladp concentration allows less precipitates, such as phosphorous and siloxan, to be produced in the anaerobic digestion tank. 10013] In the present invention, indicates “massifs” unless otherwise noted. The anaerobic treatment apparatus of the present invention can Include means, such as pipes, pumps and valves, to send sludge from one specific device mentioned above to another, as necessary.

AD VAN TAGEOU S EFFECTS OF INVENTION

[0014] The ppsentsihventii)n not only decomposes organic matters by anaerobic digestion of sludge in wastewater treatment plant and the; Ikes but also allows efficient recovery of biogas (especially methane gas), and thus, significantly improves the energy recovery efficiency. Especially concerning the technical problems of the conventional treatment mefhod, which are the need for a large capacity anaerobic digestion tank facility, a high Chemical cost for digested-sludge treatment, and the difficulty in lowering the water-content of dewatered sludge due to the low dewaterabilitv of sludge, the present invention can concentrate sludge to a high concentration using a concentration device whose running cost is low, largely reduce the anaerobic digestion capacity, and further improve dewatering operation on an anaefobieally-digested-sludge of a low dewaterabHiiy, and thus, provide a low cost anaerobic digestion system that can efficiently dewater digested-sludge. Further, the present invention can reduce the amount of phosphorous^ calcium, siloxan and the like to be introduced into the anaerobic digestion tank to about half the conventional amount, which leads to the reduction of precipitates including those of phosphorous, calcium, and siloxan being formed in the anaerobic digestion tank, arid thus, contributes to cutting maintenance and management costs of fhg anaerobic digestion tank, pipes and the like, as well as enables an efisient recovery i>f useful resources, sue! as phosphorous;

BMP DESGRIPTIGN OF DRAWINGS fOO! 51 Figure 1 is an illustrative di a grain showing the arrangement of the treatment apparatus according to am embodiment of the present invention.

Figure 2 is an ilustrative diagram showing the arrangement of the treatment apparatus according to an embodiment of the present invention,

Figure 3 is; pi illustrative diagram showing: die arrangement of the treatment apparatus according to an embodiment of the present invention.

Figure 4 is Pi illustrative diagram showing the arrangement of the treatment apparatus according to an embodiment of the present invention.

Figure 5 is an illustrative diagram shppirig the arrangement of the treatment apparatus according to an emtedineat of the present invention,

Figure 6 is an illustrative diagram showing the arrangement of a conventional treatment apparatus.

DESCRIPTION OF EMBODIMENTS

[0016] 'Use present invention is described in more detail below by referring to the drawings as necessary. PO ! 7] The anaerobic treatment process of the present invention includes a pretreatment step for subjecting a flocculated sludge to a solid-liquid separation into concentrated sludge having a sludge concentration of 4 to 12 wt% and a separation effluent, wherein the flocculated sludge was prepared by adding a floeculant to a sludge; an anaerobic digestion step for anaerobically digesting the concentrated sludge and recovering: biogas; a step for preparing a flocculated digested-sludge by mixing a floeculant and at least one of the separation liquid and water with an anaerobically-digested-sludge prepared in the anaerobic digestion step; and a step of dewatering a concentrated digested-sludge that was obtained by performing solid-liquid separation on the flocculated digested-sludge.

[0018} la the present invention, “sludge'"' means sludge that is discharged in the step of treating organiG substances, such as sewage,: night soil and garbage.

[0019] lie sludge to be treated in the present invention is preferably at least one of primary settled sludp that is produced in the primary settling tank of the wastewater treatment plant anil excess sludge that is produced in t he final settling tank, and more preferably a mixed sludge of both. Such sludge is preferably store! in the storage tank and subjeetedto gravity doheenuatiom [0020] To the sludge discharged front the storage tank, a flocculant is added to prepare flocculated sludge. The amount of flocculant to be added is preferably 0.2 to 1.0 wt% to the SS (Suspended Solids; suspended particles) in sludge, and more preferably 0.3 to 0.6 wt%, [0021] A commonly used Jloeeulant can te nsed as the flocculant, wi thout any particular limitation. Examples include inorganic floeCulants, such as iron (11) polysulphate, PAC, or aluminum sulphates; and polymeric organic floeculants (hereinafter referred to as polymeric floecuiants), which can each be used singly or in combination, but it is preferable to at least include a polymeric flocculant in use. Polymeric floeculants may include eafionic, piipnic, amphoteric floeculants and the lie, and specifically, amiditi© iocculants* acrylamide floeculants, acrylic acid floeculants.

[0022] The anaerobic treatment process pf the present invention is described below fry steps.

[0023] <Prelreatment Step>

The pretreatment step is a sludge concentration step for subjecting a flocculated sludge to a solid-liquid separation into concentrated sludge having a sludge concentration of 4 to 12 wt% and a separation liquid, in which the flocculated sludge was prepared by adding a flocculant to a sludge. In the conventional method, the sludge was concentrated by adding a polymeric flocculant, so it was only possible to concentrate the sludge to a concentration of about 3 to 4 wt%, and about 4 to 5 wt% at maximum. The present: invention allows a high sludge concentration of 4 to 12 wt%. Meanwhile, the separation liquid includes: phosphorous, calcium and siloxan.

[0()24] <Anaerobic Bigestion Step>

Next, the above concentrated sludge is sent to the anaerobic digestion step, where it is anaerobically digested and the resulting biogas is simultaneously recovered, Digestion of concentrated sludge is performed at 30 to 60°C, and preferably at a rnesophilic digestion range of 30 to 40°C or a thermophilic digestion range of 50 to 60°C, A preferable pH during the anaerobic digestion is pH 6 to 8.5* and more preferably pH 6.5 to 8.0.

[0025] In a mixed digestion of the following organic waste liquid and waste mattery which includes much fatgand oil, a higher temperature provides higher dispersibility of neutral fat : and higher fatty acid, so it is preferable to select a digestion method at a thermophilic temperature of 5© to 60°C. Meanwhile, ammonia which resuhsiistm anaerobic digestion of sludge is easily dissociated at a high pH and a high temperature fanp, so it should he noted that a high temperature digestion tends to inhibit ammonia. The methane profepfop reaction is inhibited when die NHT-N concentration in the digestive:]nice is at least 3,500 mg/L in a rnesophilic dipstion, and at least 2,000 mg/L in athermophilic dlgesion. These operation conditions are determined by takingTnto· account tPiliidge and the sludge characteristics of the concentrated sludge, the fluctuation of water amount during anaerobic digestion, and the target treated water quality.

[0026] The anaerobic digestion step should more preferably include a primary digestion step in which the concentrated sludge is subjected to solubilization and acid fermentation treatment at a treatment temperature of 30 to 60 'C and HRT of 1 to 3 days; and a methane fermentation step for preparing if e muerobioally-digested-siudge by subjecting the digested-sludge treated in the primary digestion step to a methane fermentationfoeatment.

[00271 The primary digestion step functions to accelerate the anaerobic treatment of the subsequent methane fermentation step, and contributes to reducing HRT in the methane fermentation step, efficiently and stably recovering biogas, maintainingsa high and stable, coarse suspended solids content ratio, and reducing the fermentation viscosity. In addition, the SS concentration can be adjusted in the primary digestion step.

[0028] The methane fermentation step is preferably performed at a treatment temperature of 30 to 60°C and HRT of 12 to 20 days, to preferably prepare the anaerobically-digested-

Sludge to have a coarse suspended solids content of 3 to 20% against SS. A “coarse suspended solids’' in the above “coarse: suspended solids content” refers to fibrous substances, such as cellulose, particulate substances, and the like. The HR] is more preferably 12 to 15 days, and the coarse suspended solids content is more preferably 5 to 18%; By adjusting the coarse suspended solids content to the above range, the dewaterabiiiiy of the concentrated digested-sludge is improved, and the water content of the dewatered cake can be reduced.

[0029] Further, in die anaerobic digestion step of the present invention, an organic waste liquid or waste matter introduced from outside, that is, outside tire wastewater treatment plant Implemented in theipresent invention can be treated with the sludge. The organic waste liquid and waste matter from outside include at least organic compounds discharged from Mllities, such as m factory or a sewage treatment plant; it may also include sludge and Mbs. The organic waste liquid and waste matter from outside may be iupysduced into any of the pretreatment step, the primary digestion step and the methane fermentation step. When the organic waste liquid and waste mater from outside are anaercMcally digested with sludge, the organic waste liquid or waste mailer are preferably adjusted to a slurry f'S concentration of 1 to 11% (more preferably 3 to 1 ()%.), and added at a mixture condition that provides a Slurry TS (total solids) ratio of 120% or lower (more preferably 5 to 100%) against a TS of the concentrated sludge. A slurry TS concentration is the TS concentration in a slurry, and the slurry TS ratio is the TS ratio of introduced substances contained in the slurry. The slurry TS concentration is determined by taking into account the type, concentration, state, introduction frequency of the organic waste liquid and waste matter; Also, the organic waste:liquid and waste matter introduced front outside should preferably be inteoduced into the anaerobic digestion step after being decomposed physicaiypchemically or biologically, as necessary, to stabilize the digestion reaction. Preferable examples of treatment methods include wet fragmentation, dry fragmentation, heat treatment, high-temperature bjgh~pressure treatment, acid or alkali treatment, biological solubilization or acid fermentation.

[0030] <Fioeeulaled Digested-sludge Preparation Step>

Next, a flocculated digested-sludge is prepared by mixing a floccuiant, and at least one of the separation e 01 uent of the pretreaurgent step and water, with an anaerobicaliy-digested-sludge prepared by the anaerobic digestion step.

[0Θ§|] the; like is preferable as a floccuiant to be added to the anaerobically-digested-siudge. Also, combining an inorganic auxiliary floccuiant, sudh as iron (II) polysulphate or PAC, and a polymeric floccuiant can be effective for iMpovihg the clarity of the separation liquid. Polymeric flocculants to be used are not limited to costly amidine flocculants, but also include relatively low-priced cationic-polymer flocculants like; acrylic ester flocculants and methacrylic ester flocculants, and amphoteric flocculants whose cation level is higher than the anion level. An acrylic ester floccuiant should preferably have a molecular weight of 300 fo 6,000,000 to produce a flocculated digested-sludge with high sedimentation. ! 00321 The amount of floccuiant to be added fluctuates according to the characteristic of the anaerohicaily-digested-sliudge, and art amount that makes the floe size of the flocculation product a few millimeters is preferable to increase the sedimentation property of the flocculated digested-sludge. Spedfically, the floccuiant is added in a range of 1.0 to 2.5%, preferably in the range of 1.5 to 2.0% against SS in the anaerobieally-digested-sfudjp to obtain a flocculation product having a floe size of 5 to 20 mm, preferably 10 to 20 mm.

[0033] The separation eflluent or water (also referred to as “dilution water”) used in the flocculated digested-sludge preparation step Amotions To dilute anaerobically-dige#ed-#iidge. By diluting the concentrated sludge by the separationseffluent or water, the electric conductivity of sludge Ik adjusted to 1200 mShn or lower, peferabiy 750 mS/m or lower, the M alkalinity of sludge is adjusted to 4000 mg/1 or lower, preferably 2500 ffig/1 dr lower, and the temperature of sludge is adjusted to at least 35°C, preferably 50 to 75°C. The temperature of diluted sludge can be adj usted by adding the separation effluent or water in the above temperature range, or heating the sludge after addition. Water that can be used as dilution water includes not. only the separation effluent that is obtained in the pretreatment step, normal drinking water and the like, but also, any processing water in the trealmcnt plant that satisfies water quality conditions, such as a relatively low concentration of dissolved materials (electric conductivity of 500 mS/m or lower, M alkalinity of 1500 mg/L or lower, SS 1500 mg/L or lower, CODCr 15000 mg/L or lower). Further, biological treatment water may be used including activated sludge processing water, or waste fluid from a biological odor control system.

[0034] A concentrated digested-sludge and a separation effluent are prepared by performing a solid-liquid separation on the resulting flocculated digested-sludge. A preferable concentration rate of the concentrated digested-sludge is about 2.5 to 8 times. The concentration rate mentioned herein is a quotient obtained by dividing the volume of flocculated digested-sludge by the volume of concentrated digested-sludge.

[0035] A flocculant and an optional diluted water is added again to the concentrated digested-sludge obtained by solid-liquid separation to prepare a reconcentrated, flocculated sludge. The flocculant and diluted water used herein can be the flocculant and diluted water used in the flocculated digested-sludge preparation step. If the reconcentrated, flocculated sludge has sufficient dewaterability (the TS concentration of concentrated, flocculated sludge is in the range of 4 to 15 wt%, preferably 6 to 10 wt%), it is sent to the dewatering step as the final flocculated digested-sludge. However, if the reconcentrated, flocculated sludge does not have sufficient dewaterability, or if the original design requires (if the TS concentration of concentrated, flocculated sludge is lower than 4 wt%), then, the reintroduction of the above flocculant and the subsequent solid-liquid separation, or the solid-liquid separation alone can be repeated. The flocculant to be used in the flocculant reintroduction can be the same as or different from that used in the flocculated digested-sludge preparation step.

[0036] The final flocculated digested-sludge should preferably be a floe of a strength that allows it to barely maintain its particulate floe shape after it is subjected to a shearing force in the latter dewatering step. The flocculant to obtain such flocculated digested-sludge should preferably be a polymeric flocculant, without being limited thereby. The polymeric flocculant may be those used in the above flocculated sludge preparation step, and it may be the same as or differ from the flocculant of the pretreatment step.

[0037] <Dewatering Step> <filename>

Next, foe flocculated digested-sludge is dewatered and subjected td sdlid-water separa tion into a dewatered cake and a separation effluent. The preferable concentration rate of the dewatered cake is about 4 ίο 10 times in the present invention. The concentration rate herein means the quotient obtained by dividing the volume of flocculated digested-sludge by te volume of dewatered eake. The separation effluent separated in the dewatered cake preparation step is preferable as diluted water to be used in the step of preparing a Speculated digested-sludge, since its SS concentration, M alkalinity and electric conductivity arc low. The dewatered cake has low salt content and low water content, so it can be recycled, and is preferable for fabrication, such as composting, carbonizing and forming fuel. {0038 j <Recovery of Phosphorous and Siioxan>

The separation liquid obtained by the pretreatment step contains materials, such as phosphorous, calcium and siloxan. in the present, invention., the separation liquid containing these materials may be wholly or partially sent to a step for recovering or rimming the materials, such as phosphorous, ealeram and siloxan. Phosphorous can be recovered by methods, such as the contact-dephosphorization method using hydroxy apatite and the MAP method using ammonium magnesium phosphate, [0039] In the MAP method, the seed crystal of MAP is fl lied into a tank beforehand, such as: an uptlow tank, and chemicals to supplement the lacking MAP material, such as MgC'b and MgfOlTh, are added as desired to the separation liquid, and fodher, the pfl of the separation effluent is adjusted to 7.8 to 8.5 as desired, and the: separation effluent is passed through the reaction tank as an uptlow to enlarge the MAP particle size, then the MAP with the enlarged particle size is taken out of the reaction tank p necessary for separation and recovery. The fine MAP generated in the reaction tank is recovered from the top of lie tank and returned to the reaction tank; [00401 Siloxan recovery can be performed by adsorbing the separation liquid as gas or misty or in the original state, using adsorbents, such as activated charcoal, silica get, zeolite, and polymer (e.g, styrene-divinylbenzene copolymer). Also, nitrogen gas is heated as necessary and passed through the adsorbent that had adsorbed siloxan to eliminate and recover siloxan.

Siioxan can be treated with a similar adsorbent for the biogaa #sefohed below, and siioxan can be eliminated and recovered by a similar method.

[0041 ] Since the present invention includes a step of solid-liquid separation into a separation effluent and concentrated ; sludge as mentioned above, it can reduce the amount of phosphorous, siioxan and the like to be introduced into the anaerobic digestion device from conventional methods, which leads to: the reduction of precipitates including those of phosphorous, and siioxan being formed in the anaerobic digestion device, and thus, eontrihates to; cutting the maintenance and managemen t costs of the anaerobic digestion device, pipes and the like.

[0042] <Anaerobic Treatment Apparatus'-

The anaerobic treatment apparatus of the present invention includes ^ flocculation tank for preparing a flocculated sludge by adding a flocculant to qludgef a pretreatffiCst sludge concentration device for subjecting a flocculated sludge to a solid-liquid separation into a concentrated sludge having a sludge conoentration of 4 to 12 wt% and a separation effluent; an anaerobic digestion device for anaifobieally digesting the concentrated sludge and recovering biogas; a digested-sludge flocculation device for preparing a flocculated digested-sludge by mixing a flocculant and at least one of the separation effluent and water with an anaerobieally-dtpsfed-sludgs prepared by foe anaerobic digestion device; and a device for dewatering a concentrated dipStCd-sludge that was obtained by subjection the flocculated digested-sludge to a solid-liquid separation, [0043] The flocculation tank can be a commonly used flocculation tank.

[0044] The pretreatment sludge concentration device can be; a solid-liquid separation tank that performs solid-liquid separation of flocculated sludge into a concentrated sludge and a separation effluent. The solid-liquid separation tank includes a simple tank using gravity concentration, a centrifugal separator using centrifugal concentration, a separator using floatation concentration, a separator using a screen, and a slit-type concentrator, without being limited thereby, A preferable type among these is the slit-type concentrator, and a machine structure of IP 2003-211293 A; (Patent Document 3), in which the slit plate stops the material to be treated, the material to be treated is sent to a discharge side on the slit plate by having masgidisks whose marginil faces are projected on a slit plate having many slits formed thereon eccentrically rotate, around a crank-shah, in the direction for discharging the materia! 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 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 eoneentrator is used, a high concentration of 4 to 12 wt% can he stably and surely achieved at a low running cost.

[0045] The anaerobic digestion device includes at least an anaerobic digestion tank. j| complete mixture digestion tank Is used preferably as an anaerobic digestion tank wMmut being limited thereby. An anaerobic digestion tank requires agitation to prevent scum development as well as to provide a homogenous liquid in the tank and an even temperature distribution. A mechanical agitation process is most efficient in the present invention, but an additional pump agitation process or gas agitation process according to the facility environment or the treatment condition is also effective, f urther, the digestion tank can be made of either reinforced concrete or «loci as long as it satisfies the above requirements and has a watertight and airtight structure, and an existing anaerobic digestion tank can be used by being modified or updated according to the treatment condition. The anaerobic digestion device preferably comprises a solubiI i/ation/acid fermentation treatment tank for the solubilization and acid fermentation treatment of concentrated sludge arid a methane fermentation tank for the: methane fermentation treatment of digested-sludge §reafed in the tank. The anaerobic digestion device preferably eomprises an external biomass storage device that stores organic waste liquid or waste matter introduced from outside; a systefhsSnd a piping for introducing biomass: discharged from the external biomass storage device to at least one device selected from a group: of the sludge: storage device, a device for solubilization and aell fermentation treatment, and a methane fermentation device.

[0046] The digested-sludge flocculation device comprises with a digested-sludge flocculation lank, a means to introduce diluted sludge, a flocculant MdMon means» an agitation means* a heating means, arid a means for drawing out flocculated sludge, §§ necessary:. Further, the device can additionally comprises an in-pipe mixing device for dilution.

[0047 ] The anaerobic treatment system of the present invention preferably- cdmpises a device for preparing a concentrated digested-sludge from a flocculated digested-sludge.

[0048] The device for preparing::a concentrated digested-sludge preferably comprises a sludge flocculation treatment device tor preparing a flocculated sludge with the flocculant; a flocculate! sludge separation/concentration device for preparing a concentrated, flocculated sludge by performing solid-liquid separation on the flocculated sludge;: and a device for preparing a reconcentrated., flocculated sludge from the concentrated, flocculated sludge by-adding a flocculant.

[0049] The flocculated sludge separation/concentration device is a device for the solid-liquid separation of the flocculated sludge to a concentrated flocculated sludge and a separation effluent, The flocculated sludge separation/concentration device may include a simple tank using gravity concentration, a centrifugal separator using centrifugal concentration, a separator using floatation concentration, a separator using a screen, without being limited thereby. A preferable type among these is the solid -liquid separation device equipped with a screen, for example, a solid-liquid separation device equipped with multiple parallel screens arranged at a constant interval and multiple discs, each placed between two adjacenf screens., that rotate to physically remove the flocculated sludge in a gap between the adjacent screens and to separate the sludge into a concentrate·..! flocculated sludge and a separation water. The screen siii width is shorter than the floe size of tie flocculated digested-Sludge by principle, and is preferably Q.l to 2.5 mm.

[0050] The reconcentrated, flocculated sludge preparation device comprises an introduction means for reconcentrated, flocculated sludge, a flocculant addition means, an agitation means, attd a means for drawing out reconcentrated, flocculated sludge, as necessary.

[0051 ] The device to dewater concentrated digested-siudge can normally be' a same device as the flocculated sludge sepamtion/concentration device, in principle, without being limited thereby, but. the stress to flocculated dipsied-sladgf for separating the dewatered cake should normally be higher than the flocculated sludge separation/concentration device, Mid a wel! known means can be used, lire: dewatered cake preparation device preferably comprises a means to add stress to reconeentrated, flocculated sludge and a filtration means that is permeated by the separation effluent Mid that captures the flocculated digested-siudge. Means to add stress to the flocculated digested-siudge may include a press and a centrifuge, A filtration means may Include a screen having an aperture size of 0.1 to 2.5 mm.

[0052] Next, an ekahtple of the present invention is explained further by referring to the drawing, [0053] Figure 1 is a flow diagram showing the first embodiment of the present invention, iMli an illustrative diagram showing the arrangement of an anaerobic treatment system.

[0054] Sludge 1 is sent to a storage tank 2. Then, the sludge 1 is discharged from the storage tank 2 and sent to a flocculation tank 3 via a piping. In the flocculation tank 3, a floeeuiaht 4 is added to the sludge 1 and a flocculated sludge 5 is prepared. The flocculated sludge 5 is sent to the pretreatment sludge concentration tank 6 and subjected to a solid-liquid separation into a concentrated sludge 7 having a sludge concentration of 4 to 12% and a separation effluent 8. The concentrated sludge 7 is sent to the anaerobic digestion tank I, and a biogas 10 and an anaerobically-digested-sludge 11 is produced by an anaerobic digestion of sludge. Biogas 10 is sent to a biogas tank 101, then the biogas K) is sent to a gas using facility 102 ic.g, a gas turbine, a biogas boiler, a gas lamp, and a drier heal source) or a surplus gas combustion facility 103. The anaerobically-digesied-sludge 11 is sent to a digested-siudge flocculation device 12, To the digested-siudge flocculation device 12 is introduced a part of a separation effluent 8 formed in the pretreatment sludge concentration tank 6, in the digested-siudge flocculation device 12, a separation effluent 8 and; a floceuiant 13 are added to the anaerobically-digested-sludge 11, and a flocculated digested-siudge 15 and a separation effluent 14 are formed. The flocculated digested-siudge 15 from: the digested-sludge flocculation device 12 is sent to the dewatering device 16, where the separation liquid 17 is Separated and the dewatered cake 18 is prepared. A part of a separation effluent 8, a separation effluent 14, arid a separation effluent 17 are sent to the wastewater treatment plant 104 and the like for phosphorous recovery and other purposes. Note that a sdoxan removal or recovery device can be provided before the biogas tank.

[0055] Next, figure 2 is a flow diagram showing the second embodiment of the present invention, and an illustrative diagram show-ng the arrangement of an anaerobic treatment system, which performs solubilization add acid fermentation treatment in a primary stage of anaerobic digestion, [0056] in the process flow of Figure 1, the concentrated sludge 7 separated in the pretreatment sludge concentration tank 6 is sent to the solubilization and acid fermentation treatment tank la before:being sent to the anaerobic digestion tank 9.. and a digested-sludge 7a that has been solubilized: and treated by acid fermentation treatment is produced. The digested-sludge 7a is sent to the anaerobic digestion tank % and then treated according to the process flow of Figure 1.

[0057] Next, Figure § is a flow diagram; showing the third epbodiment of the present invention, and an illustrative diagram showing the arrangement of an anaerobic treatment system, which divides the Sludge flocculat ion treatment of the anaerobicaliy-digested-siudgc by a iloccuiant to he performed at two separate timings.

[0058] In the present process flow, the process flow of Figure 1 fe modified in its step of sending theanaerobically-digested-sludge 11 and a pari of the separation effluent 8 to the digested-sludge flocculation device 12, and preparing the flocculated digested-sludge 15 as well as separating the separation liquid 14 through: adding a flocculant 13 as follows,: [0059] The anaerobicallyffligested-sludge 11 and |he part of separation effluent 8 are sent, to the sludge floceulaiion treatment tank 12a, where a Socculant 13a is added to prepare a flocculated sludge 12e. The flocculated sludge 12c is introduced into the flocculated sludge separation/concentration device 14A and is subjected to solid-liquid separation into a separation effluent 14 and a concentrated, flocculated sludge 12d. Then, the concentrated,

SltMaied siuige 12d is sgiit to the reconcentrated, flocculated ϋϋ|β preparation device 12b, where a fioeculant 13b added to prepare a reconcentrated, flocculated sludge, which is recognized as the final flocculated digested-sludge i 5. 10060] Next, F igure 4 is a flow diagram showing the fourth embodiment of the present invention, and an illustrative: diagram showing the arrangement of an anaerobic treatment sptem, which is the process flow of Figure § modified by an additional step of addinga biological treatment water 19 to the sludge flocculation treatment tank 12a to dilute sludge, with other processes being the same as Figure 3.

[0061 ] 1'he biologically treated water may include an activated; sludge ePuenf, biological odor-controlled effluent, iiitrification-dendrification effluent. The type and concentration of the content material of the biologically heated water are determined aeeordingto the purpose of tbe treatment, since they affect the type and addition amount of tlocculant, and consequently its cost.

[0:1)62] Next, Figure § is a flow diagram showing the fifth embodiment of the present invention, and an illustrative diagram showing the arrangement of atfiO&amp;erobic treatment system, which is the process flow of Figure 4 modified by subjecting the organic waste liquid and waste matter introduced from the outside to the anaerobic digestion treatment as well, with other processes being the same as Figure 4.

[0063 j The organic waste liquid and waste matter:20 in the present flow is stored in the biomass storage tank 21 as a slurry. The slurry 22 from the biomass: stomgptank 21 Ms its TI concentration adjusted as required, then it is introduced into gt least one offhe storage tank 2, the solubilization/aeid fermentation treatment device 9a, and the anaerobic digestion device 9 to be treated, 1()()64] The anaerobic treatment system of Figures 1 to 5 can run by automatic control or batch processing, or a combination of both. The tempera! ure control of various types of sludge can be automated as we!!.

EXAMPLES PQ65] The Examples of the present invention are described below. The sewage sludge produced in the A Sewage Treatment Plant was subjected to an anaerobic treatment test of the present invention. Note that the present invention is not limited by the Examples in any way.

[006b ] In the test, a cationic-polymer floceulant (mean molecule amount 3,000,000) was aided to the sludge at 0.4% (against SB) and mixed for flocculation treatment, then, it was subjected to sohd-Iqiii separation into a concentrated sludge and a separation effluent in the mechanical concentrator equipped with a back pressure plate. The characteristics of sludge, concentrated sludge, and separation liquid are shown in Table 1.

[0067] Table 2 shows an anaerobic digestion test condition in the anaerobic digestion divide. The anaerobic treatment test is performed by using % complete mixture digestion test device (total volume: ID L, effective volume 25 I.,, jacket warm wafer circulation type) of heat-resistant vinyl chloride. Further, a jar ferffientor MDL produced by Tokyo Rikakikai Co.. Ltd. (a complete mixture type of total volume 10 L, operates at a depth of 4 L) for a solubilixatlon/aeid fermentation device.. The anaerobic treatment system (digestion tank) was operated at 37°C, and the: sohibihzation/acid fermentation device (solubilization tank) was operated at 45°C. Note that a high temperature anaerobic treatment test was performed at S5°C in Comparative Example 2. The materials were input using a tube pump MM5Q (produced by Tokyo Rikakikai Co., Ltd J, and the input was at a frequency of 4 to 8 times a day under timer-control.

[0068] [Example 1 j

The test Was performed according: to the process flow of Figure 1..

[0069] [Example 2]

The rest was performed according Jo the process flow of Figure 2, The treatments of Figures 3 and 4 were also performed as the dewatering treatment of anaerobicaily-digested-sludge.

[0070] [Comparative Example]

The test was performed according to the process flow ofFigure 6. No.e that the flocculated digested-sludge 15 was prepared by sludge flocculation using a polymeric tloecuiant.

[0071] [Table! I

Table 1 Charae[eristics of Sewage Sludge Samples

* unit: mg/L

[0072] [ Table 2]

Table 2 Anaerobic Treatment Test Conditions

[0073] The following method was used for analysis, - TS (Total solals, fotal residue); weight of residue after evaporation at 105°C (JT:S K 0101] - VTS (Volatile total solids, ignition loss]; fogs op ignition at 6O0°C (JIS K 0102) - SS (Suspended solids, suspended particles); weight of precipity^tai £ ^gifiigal separation at a rotation of 3,000 rpm, for 10 minutes (J1S K 0102) - VSS (Volatile suspended solids, volatile suspendeiparticles); loss on ignition at 600°C of suspended particles (J IS K 0102) -CODcr (Chemical Oxygen Demand); potassium dichromate method (IIS K 0102): - BOD (Biochemical Oxygen Demand); sodium azide modification to the Winkler method (JIS&amp;0102) - Frqtein: (Kjeldahl nitrogen-ammonia - Volatile organic acid (VFA); high performance liquid chromatograph plmer Optics, ERC-87.10, detector RL column ihGdexRSpak KC-81 1, column temperature 60°C, mobile phase 0.1% phosphoric acid) - Pethane gas, carbonic acid gas; gas chromatography ipB Science GC-32% detector TO% T'CD current 120Jh> separation column Active Carbon 30/60, column temperature 95°C, cariler gas He) - Siloxan in the digestion gas: Quantitative analysis is performed using a gas chromatograph mass spectrometer GC/MS to measure siloxan that has been edheeiitrated after it had been captured by passing the digestion gas through the hexane solution at a flow rate of 0.6 I ./minute. The deeamethyleyclopentasiloxane (D5) of cyclic siloxan that is said to be the largest in content in the sewage sludge digestion gas was analyzed by quantitative analysis,: - Soluble fraction; filtrate at GF/B (1 μιΡ) - 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 hydroehloricxolution of 0.1 mol/L (sewage test method) - Coa>se suspended solids; a coarse suspended solids analysis by using a sieve of a nominal dimension of 74 μιη. (sewage test method) [0074] [Table 3 j

Table 3 Anaerobic Treatment Result

__ _ 1J calculated from the difference between the introduced singe andihe digestion solution of each material ··* ·. z.,1

D: digestion ratio \iSi organic fraction of introduced sludge (%) VS:.·: organic fraction of digested sludge (%)

Ai. inorganic fraction of introduced iSfudge · %} A?: inorganic fraction of digested siudoe [0075] As shown in an anaerobic treatment test result of Table 3, it can be understood that the T® decomposition rate, the VTS decomposition rate, and the methane gas generation rate of the anaerobic treatment of Examples 1 and 2 are equivalent to those of conventional art. [Q0f6| Fnxfber, when the; sioxan 135 concentration in the digestion gas is compared,/the consent rate, is low in Examples 1 and 2, which leads to a presumption that the decrease of the SllOxan concentration in the digestion gas occurs when the digested-sludge SS inaction, maintained aba high concentration, adsorbs siloxan compounds.

[()077] Further, when the coarse suspended solids are compared, the eoPteht rate is high in Examples 1 and 1, which shows that the sludge condition is more advantageous ihr sludge dewatering than that of a conventional digested-sludge.

[0078] Further, no residue of volatiioorganic acid was recognized in any of the digestion tanks of the Comparative Examples or the Examples, which shows that the anaerobic treatment reaction proceeded without any problem.

[0079] The sludge dewatering treatment performance was assessed using the anaerobically-digested-sludge; obtained in Comparative Examples 1 and 2, and Examples I and 2. A cationic polymer flocculant (mean molecular weight 3,000,0()0) 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 IcN/'m and a filter cloth, speed of 1.0 m/minute.

[0® 80] To begin with, dewatering treatment was performed for the anaerobically-digested-sludge of Comparative Examples 1 ami 2, which resulted in polymeric fioeculant injection rates and dewatered cake water contents of'fable 4.

[0081] jTable 4]

Table 4 Dewatering Treatment Result of Anaerobic Digested-SJudge (1)

[0082] Next, dewatering treatment was performed for the anaerobiealiy-digesfed-sludge of

Examples 1 and 2, which respited in polymeric flocculant injection rates and dewatered cake

Ml dewatering methods showed higher performances than the conventional method, hot the most efficient treatment method was that in Figure 4, in which the introduction of the flocculant was divided into two separate timings, and the biologically treated water was used in combination. Further, when a polymeric Ooccuiant was injected into the anaerobicaiy-digested-sludge obtained in Example 1 without haying the digested-sludge diluted with separation water, to flocculate and dewater sludge, the polymeric flocculant injection rate was 3.8% (against SS) and the dewatered cake water content was 83%.

[0083] [Table 5]

Table 5 Dewatering Treatment Result of Anaerobic Digested-Sludge (2)

* For all tests, the rate of anaerobically-digested-sludge: separation effiuenf is 1:0.5, separation effluent is diluted and mixed in the Γ1 injection of flocculant. and the M alkalinity at dilution mixture is 2,500 to 3,600 mg/L.

10084] [Example 3J

Next, Examples of anaerobic treatment performed on sewage sludge, food waste (waste sugar solution anddessert wastes) and grass from river beds; is described basil ort Figure 5, [0085] <Treatmerit Condition'^ - Sewage sludge amount (mixed sludge of primary settled sludge and excess sludge) 30 nfi/day (TS concentration 3*1%) - Amount of introduced food waste I Ji t/day (TS concent ration 9.9%) - Amount of introduced grass from river beds 0.15 t/day (water content 70.0%) - biomass storage tank I nr'*2 tanks <Fretreatment soiid-lapid separator (for mixed sludge from the sswage)> - Slit-type concentrator (screen slit width 1.0 mm, equipped with a back pressure plate) - Cationfo-poiymer flocculant (mean molecular weight 3,000,000) injection rafe 0.4% (rate against SS) - amount #f concentrated sludge 12 t/day (TS concentration 7.9%) - amount of separation e®uent 19.5 m7day (SS concentration 395 mg/L) - SS recovery rate 97% - pulverizer for cut grass «'Anaerobic digestion: soluliizaridn/acid fermentation device (vertical mechanical agitatorp* ~ Amount of a mixture of food waste, cut grass from river beds, and concentrated sludge introduced into a solubilization/acid fermentation device 3 irrVday (slurry JS coneentratipn 10%) - TS .ratio of food waste and cut grass from river beds against the TS of concentrated sludge -19% - MRT 2 days - Effective volume 6 m'

- Water temperature 45°C <Anaerobic Digestion: Anaerobic Digestion Device (vertical mechanical agitator)> - Amount of sludge introduced to anaerobic digestion devie©T3.5:m'/|ay * ΗΜΓ 14.8 days - Effective volume 200 nr

- Water temperature 37°C <iiF10igiuiation step of ahaerobically-digested-slpdg#» - Slit-type concentrator (seamen slit width 1.0 mrn) - Amount of sludge separation effluent, to be mixed 10.5 nv’/day (M alkalinity 690 mg

CaCOy'L) - Amouttt ofbiologtcal^oF^^^Jevice waste liquid to be mixed 3.5 mJ/day (M alkalinity 1250 rng/L) - Injection rate of cationic-polymer flocculant (mean molecular weight 3,000,000) 1.7% (ag.ai.ost SS) (Injection rate broken down; injection rate at tie primary stage flocculation tank - 1,3%, injection rate at the reflccculation tank · 0.4%) <Dewatering machine·* - Screw press dewatering machine <Power genera tor> - Micro gas turbine power generator ^Treatment Result-* - Anaerobicaily-digested-sludge characteristics (TS concentration 3,9%, VTS 68%, SS concentration 3,0%, M alkalinity 89(30 mg CaCbb/T, coarse suspended solids content 16.7% (rate against SS)) - Biogas generation amount 570 nr’/'day (ΝΓΓΡ) - Methane gas generation amount 365 nr’/day (NTP) - Methane gas concentration 64% ~ Methane gas generation rate 0.37 m3/introduction |§ ¥T| (NTP); - Siloxan D5 concentration in biogas 2.3 mghn3 - Power production 686 kwh/day - Dewatered cake produced 2.1 May (water content 77%>) - Wastewater 37.6 mvday [0086] As seen above, it is shown that the present invention enables stable production of high quality biogas by the anaerobic treatment of sludge and organic waste using a greatly downsized anaerobic digestion device, and also enable biogas power generation. Compared to the conventional treatment method at an f 1RT of 20 to 30 days required an anaerobic digestion tank of 630 to 045 nr, the anaerobic digestion device of the present invention is 206 rrr, so an anaerobic treatment isspossible with a s>stcm having a; anaerobic tank size that is i /3 to 1/4:: the conventional size, Further, the generated anaerobieally-digested-sludge can be flocculated and dewatered easily at a low cost, and the dewatered cake water content obtained was 77%, which is low compared to the conventional rate of about 82% (Table % and the extern;;! appearance did not differ from conventional products, no unpleasant odor existed, and the cake was sanitary. 10087! [Example 4]

Similarly to Example 3, anaerobic treatment was;performed on sewage sludge, and food waste (pomace of oranges lor Juice) in a sewage treatment plant based on Figure:#. Using a mixed sludge of primary settled concentrated sludge from gravity concentrafron and excess sludge as the sewage sludge, sludge concentration whs performed. The anaerobic digeshon was performed at a mixture ratio of the solids of sewage sludge and the orange pomace at approximately equal amounts.

[00881 ''Treatment Condition'-' - Sewage sludge amount (mixed sludge of primary settled sludge and excess sludge) 35 m3/day (primary: settled sludge: T| concentration 3#8%, excess sludge: TS concentration 0.93%, mixed sludge! TS concentration 1.39%) - Introduced food waste 4.0 t/day (TS concentration 12.5%) -j * Biomass storage tank 3 nr tanks <i3retreatment solid-liquid separator (for mixed sludge from the sewage)> - Slit-type concentrator (screen slit width 1.0 mm, equipped with a back pressure plate) - Amount of injection of cationic polymer floccuiant (mean molecular weight 3,000,000, concentration of solution 2.0 g/L) 0.95 nvVday - Polymer floccuiant injection rate 0.44 % (against SS) - amount of concentrated sludge 6.2 i/day (TS concentration 7.5%) - amount of separation effluent :29,8 nfVday (SS concentration 2ll mg/L) - SS recovery rate 98% <Solubilization/acid fermentation device of food waste>

- 6.0 ϊτγ xl tank, vertical mechanical agitator, heated at 37°C - TS ratio of food waste against the PS of concentrated sludge - 102% < Anaerobic Digestion Device (vertical mechanical agitator)^ - Amount of Sludge introduced to anaerobic digestion device 1&amp;2 mVday - HRT 19.6 lays: - Effective volume 200 m3

- Water temperature 37°C <Roccuiation step of anaerobtcailyfoigcsicd-sludgc> - Slit-type concentrator (screen slit width 1.0 mm) - Amounl of sludge separation effluent to be mixed 2.0 rn'Vday (M alkalinity 320 mg

CaCCA/L) - Injection rate of cat i onic-polymer fiocculant (mean molecular weight 3,000,000) - 1.6% (against SS) - Floccuiant injection step— once ^Dewatering rnachine> - Screw press dewatering machine <Power generator'-5· - Micro gas turbine power generator treatment Result-'- - Anaerofeically-dlgesled'Sludge characteristics (TS concentration 3»8%, VTS 70%, SS concentration 3 Jl% M alkalinity 4490 mg CaCCtyL, coarse suspended solids content 12; 1% (rate against: SS)) - Biogas generation amount 59 ! m3/day (NTP) - Methane gas geuciation amount 349 nr/day (NTP) - Methane gas concentration 59% ~ Methane gas generation rate 0.38 mJ/introduciion kg VI'S (NTP) - Siioxan D5 concentration in hiogas 1.2 mg/nv’ - Power production 656 kwh/day - Dewatered cake produced 1.6 tMay (Water content 78%) - Wastewater 41.5 nr/day [0089] As seen above, the sewage sludge concentrat ion of the present invention enables efficient concentration treatment to a TS concentration of 7.5% against a mixed sludge (TS concentration 1.39%) of primary concentration sludge, on which only gravity concentratin and no mechanical concentration was performed, and excess sludgy and various mechanical concentration facilities conventionally used in large; numbers can be; eliminated. Furthers the generated asaerobically-diigested-sludge can be flocculated ani dewatered easily at a low cost as in Example 3, and the dewatered cake water content obtained was; 78%, which is Sow compared to the conventional rate, j 00901 j Example 5] 1'hc efficient use of was te liquid and dewatered cake produced in Examples 3 and 4 was considered Tire separation effluent produced by the solid-liquid separation of sewage sludge in a pretercaiment step in the present invention and the dewatered separation effluent of the dewatering step were subjected to phosphorous recovery, and the dewatered cake produced through the dewatering step of the concentrated anaerobicaliy-digested -sludge was composted.

[0091] <ffreatment Condition· (1) Phosphorous recovery from solid-liquid separation waste Jiqwd of sludge (MAP method) - pH 8.3 add Mg concentration of 30 mg/1 or higher at reaction time * 1 tank reactor (reaction part: diameter 35 cm>height 2.2 m, settling part: diameter 80 pnxheighf 11®, seed crystal of particle size about 0.4 to 1.0 mm is tilled in advance) - Phosphorous volume load 20 k.g-P/mJ*day (2) Composting of dewatered cake - Test equipment for composting 15 nr’ (high speed coih|psting vertical fermentation tankf - water adjustment of dewatered sludge: sludge is; mechanically dried to a water content of 45 to 55% - No addition of sub-material ~ Aeration speed during composting; 0,15 nr/t minutes «Treatment Resuit> [0092] [Table 6]

Table 6 Phosphoro us Recovery

[0093] [Table 7]

Table 7 Product Compost Characteristics _

[0094] As shown above, the waste liquid produced in l^aniplps 3 find 4 of the present invention is subjected to phosphorous recovery and the; dewatered cake can be composted. ami the quality does net substantially differ from conventional products (the compos! characteristies of m id-temperature methane-fermented sludge from raw garbage ate listed as comparative examples|. The decomposition rate of organic: matters in composting is 24% in the sludge of Ekample 3 and 28% in Example 4. Note that tire high level heat generation of dewatered cake is 17 MJ|k|~dry for the sludge of Example 3. and 17,3 M j/kg-dry for the sludge of Example 4, so they are of qualities that al low efficient nsesas sludge fuel alter the dewatered shidjpis mechanically dried (the quality standard of foelatedssuSstahces (grannlafed/driM matter) is set at a calorific potetial of 4000 kalfleg or higher (16.7 Milkg Of Elghef).

REFERENCE SIGNS LISE

[0095] 1...sludge*:2...storage tank, 3...flocculation tank, 4...flocculant*#...flocculated sludge, 6... pretreatment sludge concentration tank, 7,, ^concentrated sludge, 7a... digested-sludge, 8...separation effluent, |i,.anaerobic digestion tank, 9a...solubilization-'acid fermentation treatment tank, 10... biogas, 11... anaerobical ly-digested-sludge, 12... digested-sludge flocculation device, 12a.. sludge flocculation tank, 12b...reconeentrated, flocculated sludge preparation device, 12c...flocculated sludge, 12d.,.concentrated, flocculated sludge, 14Λ--.flocculated sludge separation/concentration device, 15...flocculated digested~sludgea: 11,13a, 13b...flocculant, 14... separation effluent, 15., .flocculated digested-sludge, 16.. .dewatering device, 17...separation effluent. 18.. Jewgteiedsake, 19...biologically treated water, 20...organic waste liquid or waste matter, 21s...biomass storage tank, 101.. .biogas tank. 102.,,gas-using facility, 103...surplus gas combustion facility, 104,:.. waste water treatment plant.

Claims (14)

1. THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

   1. An anaerobic treatment process comprising: a pretreatment step for subjecting a flocculated sludge to a solid-liquid separation into concentrated sludge at a sludge concentration of 4 to 12 wt% and a separation effluent, wherein the flocculated sludge was prepared by adding a flocculant to a sludge; an anaerobic digestion step for anaerobically digesting the concentrated sludge and recovering biogas; a step for preparing a flocculated digested-sludge having M-alkalinity in the range from 2500 mg/1 to 4000 mg/1 by mixing a flocculant and at least one of the separation effluent and a biologically treated water with an anaerobically-digested-sludge prepared in the anaerobic digestion step, wherein the anaerobically-digested-sludge has M-alkalinity in the range from 4490 mg/1 to 8900 mg/1 and a coarse suspended solids content of 5% to 18% against SS; and a step of dewatering a concentrated digested-sludge that was obtained by performing solid-liquid separation on the flocculated digested-sludge.
2. 2. The method according to Claim 1, wherein the sludge is at least one of a primary settled sludge from a primary settling tank and an excess sludge from a final settling tank of a wastewater treatment plant.
3. 3. The method according to Claim 1 or 2, wherein the flocculated sludge is prepared by using 0.2 to 1.0% of flocculant against SS of sludge.
4. 4. The method according to any one of Claims 1 to 3, wherein the anaerobic digestion step comprises: a primary digestion step in which the concentrated sludge is subjected to solubilization and acid fermentation treatment at a treatment temperature of 30 to 60°C and HRT of 1 to 3 days; and a methane fermentation step for preparing the anaerobically-digested-sludge by subjecting the digested-sludge treated in the primary digestion step to a methane fermentation treatment.
5. 5. The method according to Claim 4, wherein the methane fermentation step is characterized by a treatment temperature of 30 to 60°C and HRT of 12 to 20 days to, prepare the anaerobically-digested-sludge to have the coarse suspended solids content of 5 to 18% against SS.
6. 6. The method according to any one of Claims 1 to 5, wherein an organic waste liquid or waste matter introduced from outside is adjusted to a slurry TS concentration of 1 to 15%, sent to the anaerobic digestion step, and subjected to anaerobic digestion at a mixture condition that provides a slurry TS ratio of 120% against a TS of the concentrated sludge.
7. 7. The method according to any one of Claims 1 to 6, wherein the concentrated digested-sludge is prepared by performing a flocculant injection step at least twice, in a step comprising a flocculant injection step and a subsequent solid-liquid separation step.
8. 8. An anaerobic treatment apparatus comprising: a flocculation tank for preparing a flocculated sludge by adding a flocculant to sludge; a pretreatment sludge concentration device for subjecting the flocculated sludge from the flocculation tank to a solid-liquid separation into a concentrated sludge having a sludge concentration of 4 to 12 wt% and a separation effluent; an anaerobic digestion device for anaerobically digesting the concentrated sludge from the pre-treatment sludge concentration device and recovering biogas; a digested-sludge flocculation device for preparing a flocculated digested-sludge having M-alkalinity in the range from 2500 mg/1 to 4000 mg/1 by mixing a flocculant and at least one of the separation effluent and a biologically treated water with an anaerobically-digested-sludge prepared by the anaerobic digestion device, wherein the anaerobically-digested sludge has a M-alkalinity in the range from 4490 mg/1 to 8900 mg/1 and a coarse suspended solids content of 5% to 18% against SS; a dewatering device for dewatering a concentrated digested-sludge that was obtained by subjection the flocculated digested-sludge to a solid-liquid separation; and a piping for delivering the separation effluent from the pre-treatment sludge concentration device to the digested-sludge flocculation device.
9. 9. The apparatus according to Claim 8 further comprising a sludge storage device for storing sludge, in which the sludge is at least one of a primary settled sludge from a primary settling tank and an excess sludge from a final settling tank of a wastewater treatment plant.
10. 10. The apparatus of Claim 9 further comprising a system for supplying a flocculant to sludge discharged from the sludge storage device and a piping for delivering sludge.
11. 11. The apparatus according to Claim 9 or 10, wherein the anaerobic digestion device comprises a device for performing solubilization and acid fermentation treatment on the concentrated sludge and a device for performing methane fermentation treatment on a digested-sludge treated in the device for performing solubilization and acid fermentation treatment.
12. 12. The apparatus according to Claim 11, wherein a treatment temperature of the device for performing solubilisation and acid fermentation treatment and the device for performing methane fermentation treatment is 30 to 60°C.
13. 13. The apparatus according to any one of Claims 8 to 12, wherein the digested-sludge flocculation device further comprises a flocculated sludge separation/concentration device for preparing a concentrated, flocculated sludge by performing solid-liquid separation on the flocculated sludge; and a reconcentrated, flocculated sludge preparation device for preparing a reconcentrated, flocculated sludge from the concentrated, flocculated sludge with a flocculant, and wherein the reconcentrated flocculated sludge is delivered to the dewatering device.
14. 14. The apparatus according to any one of Claims 12 to 13, wherein the anaerobic digestion device comprises a device for performing solubilisation and acid fermentation treatment on the concentrated sludge and a device for performing methane fermentation treatment on a digested-sludge treated in the device for performing solubilization and acid fermentation treatment, and further comprising an external biomass storage device that stores organic waste liquid or waste matter introduced from outside; a system and a piping for introducing biomass discharged from the external biomass storage device to at least one device selected from a group of the sludge storage device, the device for performing solubilization and acid fermentation treatment, and the device for performing methane fermentation treatment.