Removal of solids to facilitate recycling of water in a waste treatment facility

Abstract

A waste treatment system including a dilution vessel in fluid communication with sources of organic waste and diluent, said dilution vessel equipped with a mixer and a pump to transfer diluted organic waste to a series of at least three reactors wherein a last reactor in said series is an aerobic reactor; a settling tank receiving a first liquid supernatant from said last reactor in said series; and a conduit transferring a second liquid supernatant from said settling tank to said dilution vessel. A related method is also disclosed.

Description

[0001] TITLE: REMOVAL OF SOLIDS TO FACILITATE RECYCLING OF WATER IN A WASTE TREATMENT FACILITY

[0002] RELATED APPLICATIONS:

[0003] This PCT application claims priority from Israeli patent application IL 317144 filed on November 21, 2024 by the same Applicant and having the same title as the present application. IL 317144 is fully incorporated herein by reference for all that it contains.

[0004] FIELD OF THE INVENTION

[0005] The invention is in the field of waste processing.

[0006] BACKGROUND OF THE INVENTION

[0007] Systems that process agricultural waste to produce biogas have previously been described. See, for example, US 12,006,237; US 11,459,254; US 11,767,248; and US 10,508,050, each of which is fully incorporated herein by reference.

[0008] SUMMARY OF THE INVENTION

[0009] One aspect of some embodiments of the invention relates to recycling processed wastewater as a diluent for a feedstock of a waste treatment system. In some embodiments the processed wastewater is subject to additional particle removal in a settling tank prior to the recycling.

[0010] Another aspect of some embodiments of the invention relates to maintaining a concentration of total solids (TS) in a diluted feedstock input of a waste treatment system in the range of 2.5% to 4%.

[0011] It will be appreciated that the various aspects described above relate to solution of technical problems related to water conservation in a waste treatment plant.

[0012] Alternatively or additionally, it will be appreciated that the various aspects described above relate to solution of technical problems related to increasing methane production in a waste treatment plant.

[0013] In some exemplary embodiments of the invention there is provided a waste treatment system including: a) a dilution vessel in fluid communication with sources of livestock waste and diluent, the dilution vessel equipped with a mixer and a pump to transfer diluted livestock waste to a series of at least three reactors wherein a last reactor in the series is an aerobic reactor; b) a settling tank receiving a first liquid supernatant from the last reactor in the series; and c) a conduit transferring a second liquid supernatant from the settling tank to the dilution vessel. In some embodiments the series of at least three reactors includes at least two anaerobic reactors in recycling communication with one another. Alternatively or additionally, in some embodiments each of the at least two anaerobic reactors is an anaerobic sequencing batch reactor (ASBR). Alternatively or additionally, in some embodiments the last reactor in the series is an aerobic sequencing batch reactor (SBR) in recycling communication with at least one anaerobic reactor in the series. Alternatively or additionally, in some embodiments the settling tank has a conical bottom. Alternatively or additionally, in some embodiments the system includes a second settling tank receiving settled material from the settling tank. Alternatively or additionally, in some embodiments the diluted waste transferred from the dilution vessel to the series of reactors includes 2.5% to 4% total solids (TS). Alternatively or additionally, in some embodiments the system includes a conduit transferring sludge from the settling tank to the aerobic reactor. Alternatively or additionally, in some embodiments the system includes a centrifuge receiving sludge from the settling tank.

[0014] In some exemplary embodiments of the invention there is provided a method including: diluting a stream of organic waste with supernatant from a settling tank installed downstream of a waste treatment system including a series of at least three reactors. In some embodiments the at least three reactors include at least two anaerobic reactors. Alternatively or additionally, in some embodiments the at least three reactors include at least one aerobic reactor. Alternatively or additionally, in some embodiments the at least two anaerobic reactors are sequencing batch reactors (ASBR). Alternatively or additionally, in some embodiments the at least one aerobic reactor is an aerobic sequencing batch reactor (SBR). Alternatively or additionally, in some embodiments the method includes sequentially transferring supernatant downstream through the series of reactors and sequentially transferring sludge upstream through the series of reactors. Alternatively or additionally, in some embodiments the method includes instituting a settling time in the settling tank of at least 1 hour, at least 2 hours, at least 3 hours, at least 4 hours, at least 8 hours, at least 12 hours, at least 16 hours, at least 24 hours and intermediate or greater times. Alternatively or additionally, in some embodiments the method includes instituting a settling time in the settling tank of not more than 24 hours, not more than 16 hours, not more than 12 hours, not more than 8 hours, not more than 6 hours, not more than 4 hours, not more than 3 hours, not more than 2 hours or intermediate or shorter times.

[0015] In some exemplary embodiments of the invention, the settling time in the settling tank is between 1 hour and 6 hours. In some exemplary embodiments of the invention, the settling time in the settling tank is between 1 hour and 4 hours. In some exemplary embodiments of the invention, the settling time in the settling tank is between 1 hour and 3 hours. In some exemplary embodiments of the invention, the settling time in the settling tank is between 1 hour and 2 hours. In some exemplary embodiments of the invention, the settling time in the settling tank is between 2 hours and 6 hours. In some exemplary embodiments of the invention, the settling time in the settling tank is between 2 hours and 4 hours. In some exemplary embodiments of the invention, the settling time in the settling tank is between 2 hours and 3 hours. In some exemplary embodiments of the invention, the settling time in the settling tank is between 3 hours and 4 hours.

[0016] For purposes of this specification and the accompanying claims, the term "settling time" denotes a period of time during which liquid contents of the settling tank (and solids suspended therein) are not agitated by stirring and / or aeration and / or addition of liquids and / or removal of liquids. If relevant, any electro-mechanical stirring equipment is turned off during the settling time. As soon as any agitation occurs in the settling tank, the settling time ends. During the settling time at least part of the solid particles suspended in the liquid contents of the settling tank sink towards the bottom of the tank due to gravity. The result is a layer of liquid with lower solids concentration in the top of the tank (supernatant) and a layer with higher solids concentration in the bottom of the tank (sludge). Specific examples of sludge are return activated sludge (RAS), which is recycled into one of the reactors of the system and continues treatment within the system and waste activated sludge (WAS), which is removed from the system.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although suitable methods and materials are described below, methods and materials similar or equivalent to those described herein can be used in the practice of the present invention. In case of conflict, the patent specification, including definitions, will control. All materials, methods, and examples are illustrative only and are not intended to be limiting. As used herein, the terms "comprising" and "including" or grammatical variants thereof are to be taken as specifying inclusion of the stated features, integers, actions or components without precluding the addition of one or more additional features, integers, actions, components or groups thereof. This term is broader than, and includes, the terms "consisting of" and "consisting essentially of" as defined by the Manual of Patent Examination Procedure of the United States Patent and Trademark Office. Thus, any recitation that an embodiment "includes" or "comprises" a feature is a specific statement that sub embodiments "consist essentially of" and / or "consist of" the recited feature.

[0018] The phrase "consisting essentially of" or grammatical variants thereof when used herein are to be taken as specifying the stated features, integers, steps or components but do not preclude the addition of one or more additional features, integers, steps, components or groups thereof but only if the additional features, integers, steps, components or groups thereof do not materially alter the basic and novel characteristics of the claimed composition, device or method.

[0019] The phrase "adapted to" as used in this specification and the accompanying claims imposes additional structural limitations on a previously recited component.

[0020] The term "method" refers to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of architecture and / or computer science.

[0021] Percentages (%) are W / V (weight per volume) unless otherwise indicated.

[0022] For purposes of this specification and the accompanying claims, the term "recycling communication" indicates that liquid and / or waste and / or sludge and / or gas is transferred from one component of the system to another so that a reactor is in recycling communication with another reactor if it transfers waste to another reactor and / or receives waste from another reactor.

[0023] For purposes of this specification and the accompanying claims, the term "ASBR" or "anaerobic sequencing batch reactor" indicates an anaerobic sequencing batch reactor.

[0024] For purposes of this specification and the accompanying claims, the term "SBR" or "sequencing batch reactor" indicates an aerobic sequencing batch reactor.

[0025] For purposes of this specification and the accompanying claims the term "settling" refers to sinking of at least portion of solid particles suspended in the liquid towards the bottom of a container in which the liquid resides. The force of gravity causes settling. Settling produces a layer of liquid with lower solids concentration at the top of the container (supernatant) and a layer with higher solids concentration in the bottom of the container (sludge). "Settling time" is defined hereinabove.

[0026] For purposes of this specification and the accompanying claims, the terms "sludge", "RAS" and "WAS" each indicate material drawn from the bottom portion of a compartment (e.g. via a drain or a conduit located near the bottom of the compartment). In some embodiments this material has a total solids (TS) concentration of at least 2.5%. Alternatively or additionally, in some embodiments this material has a total solids (TS) concentration of not more than 5%.

[0027] For purposes of this specification and the accompanying claims, the term "supernatant" indicates material drawn from the top portion of a compartment (e.g. via a conduit attached to a float). In some embodiments the supernatant has a total solids (TS) concentration of at least 0.1%. Alternatively or additionally, in some embodiments the supernatant has a total solids (TS) concentration of 3% or less.

[0028] The ranges of % total solids for supernatant and sludge overlap, since they include all reactors and over time the solid mass in the system can change and lead to a decrease or increase in the solid concentration inside each reactor. However, within a specific compartment at a specific time the supernatant will always have a lower TS content than the sludge. For example (referring to Fig. 1) supernatant 111 of reactor 110 will have less TS than sludge 113 from the same reactor, and supernatant 121 of reactor 120 will have less TS than sludge 123 from the same reactor.

[0029] In some exemplary embodiments of the invention, sludge and / or supernatant are withdrawn after a period of settling in the relevant compartment.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying figures. In the figures, identical and similar structures, elements or parts thereof that appear in more than one figure are generally labeled with the same or similar references in the figures in which they appear. Dimensions of components and features shown in the figures are chosen primarily for convenience and clarity of presentation and are not necessarily to scale. The attached figures are:

[0032] Fig. 1 is a schematic overview of a system according to some exemplary embodiments of the invention; Fig. 2 is a simplified flow diagram of a method according to some exemplary embodiments of the invention; and

[0033] Fig. 3 is a scatter plot of BMY (biomethane yield) in [m3CH4 / kgVS] as a function of total solids concentration [%] in an input waste stream.

[0034] Fig. 4A is a bar graph illustrating the concentration [% of total solids (TS) and Volatile solids (VS)] in different compartments of the system (numbers on the X axis correspond to numbers in Fig.l);

[0035] Fig. 4B is a bar graph illustrating the concentration [mg / L] of total suspended solids (TSS) and volatile suspended solids (VSS) in different compartments of the system (numbers on the X axis correspond to numbers in Fig.l);

[0036] Fig. 5A is a bar graph illustrating the concentration [mg / L] of ammonia (given as nitrogen) (NH4-N) and total nitrogen (TN) in different compartments of the system (numbers on the X axis correspond to numbers in Fig.l);

[0037] Fig. 5B is a bar graph illustrating the concentration [mg / L] of phosphate (given as phosphorus) (PO4) and total phosphorus (TP) in different compartments of the system (numbers on the X axis correspond to numbers in Fig.l).

[0038] DETAILED DESCRIPTION OF EMBODIMENTS

[0039] Embodiments of the invention relate to systems and methods for waste treatment.

[0040] Specifically, some embodiments of the invention can be used to produce biogas from animal waste (e.g. cattle manure). In some embodiments the animal waste is combined with an additional organic feedstock.

[0041] The principles and operation of a system and / or method to exemplary embodiments of the invention may be better understood with reference to the drawings and accompanying descriptions.

[0042] Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details set forth in the following description or exemplified by the examples. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. Fig. 1 is a schematic overview of a waste treatment system, indicated generally as 100, according to some exemplary embodiments of the invention.

[0043] Depicted exemplary system 100 includes a dilution vessel 102 in fluid communication with sources of livestock waste (or another organic feedstock) and diluent.

[0044] In the depicted embodiment, feedstock 90 is cattle manure. In the depicted embodiment, supernatant 141 from settling tank 140 serves as a diluent stream.

[0045] Dilution vessel 102 is equipped with a mixer and a pump (not depicted) to transfer diluted feed stream 105 to a series of at least three reactors (e.g. 110, 120, and 130) wherein a last reactor in the series is an aerobic reactor 130.

[0046] In the depicted embodiment, system 100 includes a settling tank 140 receiving a first liquid supernatant 131 from the last reactor 130 in the series and a conduit transferring a second liquid supernatant 141 from settling tank 140 to dilution vessel 102. In some exemplary embodiments of the invention, settling tank 140 is equipped with a mixer and a pump (not depicted) to enable cyclic mixing and settling. In some embodiments supernatant 141 and settled solids 145 are withdrawn separately at the end of a settling period.

[0047] In some exemplary embodiments of the invention, the series of at least three reactors includes at least two anaerobic reactors (e.g. 110 and 120) in recycling communication with one another. In the depicted embodiment, supernatant 111 is periodically pumped from first reactor 110 to second reactor 120. Alternatively or additionally, in the depicted embodiment, sludge 123 is periodically pumped from second reactor 120 to first reactor 110. Alternatively or additionally, in some embodiments sludge 113 from reactor 110 leaves the system via 150. In some exemplary embodiments of the invention, reactors 110 and 120 are each equipped with a stirring mechanism that operates intermittently so that the contents of the reactor are alternately mixed and allowed to settle. According to these embodiments, transfers of material occur at the end of a settling period, before the next mixing cycle begins. Alternatively or additionally, in some embodiments reactors 110 and 120 are anaerobic sequencing batch reactors (ASBRs).

[0048] In depicted exemplary system 100, the last reactor in series 130 is an aerobic sequencing batch reactor (SBR) in recycling communication with at least one anaerobic reactor in the series. In Fig. 1, SBR 130 is in recycling communication with ASBR 120. Sludge 133 is intermittently pumped via a conduit from reactor 130 to reactor 120 and supernatant 121 is intermittently pumped via a conduit from reactor 120 to reactor 130. In some exemplary embodiments of the invention, reactor 130 is equipped with a stirring mechanism that operates intermittently so that the contents of the reactor are alternately mixed and allowed to settle. According to these embodiments, transfers of material occur at the end of a settling period, before the next mixing cycle begins.

[0049] In some exemplary embodiments of the invention, settling tank 140 has a conical bottom. In the depicted embodiment, SBR 130 is in recycling communication with settling tank 140. Sludge 143 is intermittently pumped via a conduit from tank 140 to reactor 130 and supernatant 131 is intermittently pumped via a conduit from reactor 130 to tank 140. In some embodiments intermittent pumping transfers substantially all of sludge 143 and / or supernatant 141 in a single aliquot to empty tank 140. In the depicted embodiment, supernatant 141 is also pumped via a conduit to dilution vessel 102 where it is mixed with, and dilutes, organic feedstock 90. Alternatively or additionally, in some embodiments sludge 135 from aerobic reactor 130 is pumped via a conduit to centrifuge 150.

[0050] In some exemplary embodiments of the invention, system 100 includes a second settling tank receiving settled material 145 from said settling tank 140. In the depicted embodiment, the second settling tank is configured as a centrifuge 150. In other exemplary embodiments of the invention, a screw press is used as the second settling tank. Supernatant from second settling tank 150 exits the system as liquid fertilizer 151. Particles from second settling tank 150 exit the system as solid fertilizer 153.

[0051] In some exemplary embodiments of the invention, diluted livestock waste 105 transferred from dilution vessel 102 to the series of reactors (to first reactor 110 in Fig. 1) includes 2.5% to 4% total solids (TS).

[0052] In some exemplary embodiments of the invention, system 100 includes a conduit transferring sludge 143 from said settling tank 140 to aerobic reactor 130.

[0053] In some exemplary embodiments of the invention, system 100 includes a centrifuge 150 receiving sludge 145 from settling tank 140.

[0054] Exemplary method

[0055] Fig. 2 is a simplified flow diagram of a method of treating a waste stream, indicated generally as 200, according to some exemplary embodiments of the invention.

[0056] Depicted exemplary method 200 includes diluting 210 a stream of organic waste with supernatant from a settling tank installed downstream of a waste treatment system including a series of at least three reactors. In some embodiments the organic waste includes livestock waste, such as cattle manure. In some embodiments the at least three reactors include at least two anaerobic reactors. Alternatively or additionally, in some embodiments the at least three reactors include at least one aerobic reactor. In some exemplary embodiments of the invention, the at least two anaerobic reactors are anaerobic sequencing batch reactors (ASBR). Alternatively or additionally, in some embodiments the at least one aerobic reactor is an aerobic sequencing batch reactor (SBR).

[0057] In some exemplary embodiments of the invention, method 200 includes sequentially transferring 220 supernatant downstream through said series of reactors and sequentially transferring sludge upstream through said series of reactors.

[0058] In some exemplary embodiments of the invention, method 200 includes instituting 230 a settling time of at least 2 hours, at least 4 hours, at least 6 hours, at least 8 hours, at least 10, at least 12 hours, at least 14 hours, at least 16 hours, at least 18 hours, at least 24 hours or intermediate or greater times in said settling tank.

[0059] Alternatively or additionally, in some embodiments method 200 includes instituting 230 a settling time of not more than 4 hours, not more than 6 hours, not more than 8 hours, not more than 10 hours, not more than 12 hours, not more than 14 hours, not more than 16 hours, not more than 18 hours, not more than 20 hours, not more than 22 hours, not more than 24 hours, or intermediate or shorter times in said settling tank.

[0060] In some exemplary embodiments of the invention, method 200 includes instituting 230 a settling time of at least 1 hour and not more than 6 hours in said settling tank.

[0061] Institution of a settling time

[0062] Control of flow(s) of materials though a system 100 (Fig. 1) and / or during practice of method 200 (Fig.2) is well known to those of ordinary skill in the art of waste treatment. Such control relies on one or more pumps and / or valves at relevant places in system 100.

[0063] For purposes of describing settling tank 140 (Fig. 1) it is sufficient to say that during a settling time 230 (Fig. 2) flows of fluid streams 131, 141, 143 and 145 are all stopped. According to various exemplary embodiments of the invention this involves ceasing operation of one or more pumps and / or closing one or more valves.

[0064] At the end of the settling time, an appropriate amount of supernatant 141 is removed by opening a valve and / or activating a pump. During this removal, flow of fluid streams 131, 143 and 145 remains stopped. When a sufficient amount of supernatant 141 has been removed, the flow of supernatant 141 is shut off and flow of 131 and / or 143 and / or 145 resumes until it is time for a next settling phase.

[0065] This procedure ensures that the amount of total solids in 141 is lower than in 143 and / or 145.

[0066] Exemplary operation parameters

[0067] In some exemplary embodiments of the invention, settling tank 140 with a conical bottom for solids collection is placed downstream of aerobic reactor 130. After a one hour settling phase in 130 at the end of the mixing / settling cycle, supernatant 131 is transferred to settling tank 140. In some exemplary embodiments of the invention, the mixing / settling cycle is about 24 hours. In some embodiments, settling tank 140 has a settling time of at least 1 hour before the supernatant from tank 140 is transferred to vessel 102. In some embodiments the settling time is longer than 1 hour. In some embodiments with a settling time longer than 1 hour, the settling time is interrupted (e.g. after 2 hours) by a mixing phase (e.g. 1 hour) to break up floating sludge that rises to the liquid surface due to Nitrogen gas bubbles produced by continued denitrification. In these embodiments settling time in tank 140 continues for at least 1 hour after the mixing before transfer of the supernatant to vessel 102.

[0068] The contents of settling tank 140 are then separated into supernatant 141, which is decanted from the liquid surface with a floating decanter (low solids concentration) and the sludges 143 (RAS) and 145 (WAS), which are extracted from the bottom of 140 (high solids concentration). In some embodiments the bottom of 140 is conical. The sludge 145 can further be separated by using a separation device such as a centrifuge (150) to utilize liquid fertilizer 151 and solid fertilizer 153. Sludges 143 (RAS) and 145 (WAS) fall within the range of 2.8% TS to 4.7% TS in many embodiments of the invention. The ratio between the effluent, RAS and WAS is determined according to project requirements. Higher RAS and lower WAS increase the solid retention inside the system, with increased amounts of solids being recycled to the anaerobic digesters (110, 120) and increased degradation. Lower RAS and higher WAS increase the removal of solids from the system, balancing the accumulation of non-degradable solids. Table 1: Streams originating from settling tank 140 (reference numerals refer to Fig. 1)

[0069] Exemplary advantages

[0070] Reducing the solids content of supernatant 131 by addition of settling tank 140 contributes to an ability to recirculate liquid 141 for the dilution of feedstock 90. Recirculation of liquid 141 is especially advantageous in large-scale plants where no input stream with sufficiently low solids concentration is available (most cases) to dilute inflow 105 to the plant to the required solids concentration (2-4% total solids (TS)). Reducing the solids concentration in the recirculated liquid 141 for example from 1.6% to 1.3% (ca. 20%) reduces the required amount for dilution by ca. 12%. Correspondingly, this reduces the reactor size at the same hydraulic retention time and heat demands of the plant, contributing significantly to efficiency of operation.

[0071] Alternatively or additionally, settling tank 140 gives more flexibility for manipulating the solids concentration in aerobic reactor 130 and the whole system 100, due to the recirculation communication between the reactors. Increasing or reducing the amount of 143 contributes to a change in the amount of total solids in aerobic reactor 130. When 143 is decreased, 145 is increased correspondingly.

[0072] It is expected that during the life of this patent many reactor types will be developed and the scope of the invention is intended to include all such new technologies a priori.

[0073] As used herein the term "about" refers to ± 10 %. Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

[0074] Specifically, a variety of numerical indicators have been utilized. It should be understood that these numerical indicators could vary even further based upon a variety of engineering principles, materials, intended use and designs incorporated into the various embodiments of the invention. Additionally, components and / or actions ascribed to exemplary embodiments of the invention and depicted as a single unit may be divided into subunits. Conversely, components and / or actions ascribed to exemplary embodiments of the invention and depicted as sub-units / individual actions may be combined into a single unit / action with the described / depicted function.

[0075] Alternatively, or additionally, features used to describe a method can be used to characterize an apparatus and features used to describe an apparatus can be used to characterize a method.

[0076] It should be further understood that the individual features described hereinabove can be combined in all possible combinations and sub-combinations to produce additional embodiments of the invention. The examples given above are exemplary in nature and are not intended to limit the scope of the invention which is defined solely by the following claims.

[0077] Each recitation of an embodiment of the invention that includes a specific feature, part, component, module or process is an explicit statement that additional embodiments of the invention not including the recited feature, part, component, module or process exist.

[0078] Alternatively or additionally, various exemplary embodiments of the invention exclude any specific feature, part, component, module, process or element which is not specifically disclosed herein.

[0079] Specifically, the invention has been described in the context of processing agricultural waste but might also be used to process other types of waste streams.

[0080] All publications, references, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.

[0081] The terms "include", and "have" and their conjugates as used herein mean "including but not necessarily limited to".

[0082] Additional objects, advantages, and novel features of various embodiments of the invention will become apparent to one ordinarily skilled in the art upon examination of the following examples, which are not intended to be limiting. Additionally, each of the various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below finds experimental support in the following examples.

[0083] EXAMPLES

[0084] Reference is now made to the following examples, which together with the above descriptions, illustrate the invention in a non-limiting fashion.

[0085] EXAMPLE 1:

[0086] Effect of total solids in input stream on biomethane production

[0087] In order to examine the effect of varying the concentration of total solids in the input waste stream (e.g. 105 in Fig. 1) on the biomethane yield, the total solids concentration was varied between 2.5 and 4%.

[0088] Fig. 3 is a scatter plot of biomethane yield [m3CH4 / kgVS] as a function of total solids [%] in an input waste stream.

[0089] Results presented in Fig. 3 indicate a clear reduction in biomethane yield with increasing total solids from a maximum 0.34m3CH4 / kgVS at 2.5% total solids to a minimum of 0.24m3CH4 / kgVS at 4% total solids.

[0090] EXAMPLE 2:

[0091] Effect of settling tank on various operational parameters

[0092] In order to examine the effect of settling tank 140 on system 100 (Fig. 1), a pilot system was implemented in Beerot Yitzchak during 2023 with dilution vessel 102 having a volume of 10 m3; anaerobic reactors 110 and 120 each having a volume of 100 m3; aerobic reactor 130 having a volume of 100 m3; and settling tank 140 having a volume of 20 m3.

[0093] In this system most of supernatant 141 is required for recirculation to dilute feedstock 90 to the required solids concentration. Therefore, the quality of supernatant 141 contributes greatly to the stable operation of system 100. Based on the average data for the pilot plant, all solids measures, organic matter and nutrients are further reduced from the supernatant 131 of aerobic reactor 130 by the additional settling in 140 (See Figs. 4A, 4B, 5A and 5B). Concentrations are reduced by an average of 17% for total solids (TS) and up to 30% for total suspended solids (TSS).

[0094] Fig. 4A is a bar graph illustrating the concentration [%] of total solids (TS) and Volatile solids (VS) in different compartments of the system (numbers on the X axis correspond to numbers in Fig. 1)

[0095] Results presented in Fig. 4A indicate an average reduction of about 20% in TS from supernatant 131 with 1.6% to supernatant 141 of the settling tank with 1.3%. This reduces the required total size of the tanks in the system (110, 120, 130, 140) by about 10%-15% due to a reduction in the required amount of effluent for dilution. The solids are instead accumulated in the sludge (143 and 145) with 3.7%, with an average increase of 230% from the aerobic effluent 131.

[0096] Fig. 4B is a bar graph illustrating the concentration [mg / L] of total suspended solids (TSS) and volatile suspended solids (VSS), in different compartments of the system (numbers on the X axis correspond to numbers in Fig. 1).

[0097] Results presented in Fig. 4B indicate an average reduction of about 30% in TSS from supernatant 131 with 10,000 mg / L to supernatant 141 of the settling tank with 7,000 mg / L. The solids are instead accumulated in the sludge (143 and 145) with 37,000 mg / L, with an average increase of 370% from the aerobic effluent 131.

[0098] Fig. 5A is a bar graph illustrating the concentration [mg / L] of ammonia (given as nitrogen) (NH4-N) and total nitrogen (TN) in different compartments of the system (numbers on the X axis correspond to numbers in Fig. 1).

[0099] Results presented in Fig. 5A indicate an average reduction of about 25% in TN, which reduces nitrogen load in system 100 due to the use of a dilution stream and stabilizes the system.

[0100] Fig. 5B is a bar graph illustrating the concentration [mg / L] of phosphate (given as phosphorus) (PO4) and total phosphorus (TP) in different compartments of the system (numbers on the X axis correspond to numbers in Fig. 1).

[0101] Results presented in Fig. 5B indicate an average reduction of about 20% in TP, which reduces phosphorus load in the system 100 due to the use of a dilution stream and stabilizes the system. Phosphorus is instead accumulated in the sludge (143 and 145), with an average increase of 285% from the aerobic effluent 131. The accumulation of Phosphorus in the sludge increases its potential as a base material for fertilizer production.

[0102] This example illustrates that settling tank 140 reduces contamination in the diluted stream, which enables extended stable operation of the system and more economical system operation relative to previously reported systems which do not include settling tank 140 with separate streams of supernatant (141) and sludges (143 and 145) but only include a storage tank from which the mixed liquid is taken when needed (see for example US 12,006,237 ; US 11,459,254; US 11,767,248; and US 10508050).

Claims

CLAIMS:

1. A waste treatment system comprising: a) a dilution vessel in fluid communication with sources of organic waste and diluent, said dilution vessel equipped with a mixer and a pump to transfer diluted organic waste to a series of at least three reactors wherein a last reactor in said series is an aerobic reactor; b) a settling tank receiving a first liquid supernatant from said last reactor in said series; and c) a conduit transferring a second liquid supernatant from said settling tank to said dilution vessel.

2. A waste treatment system according to claim 1, wherein said series of at least three reactors comprises at least two anaerobic reactors in recycling communication with one another.

3. A waste treatment system according to claim 1 or claim 1, wherein each of said at least two anaerobic reactors is an anaerobic sequencing batch reactor (ASBR).

4. A waste treatment system according to any one of claims 1 to 3, wherein said last reactor in said series is an aerobic sequencing batch reactor (SBR) in recycling communication with at least one anaerobic reactor in said series.

5. A waste treatment system according to any one of claims 1 to 4, wherein said settling tank has a conical bottom.

6. A waste treatment system according to any one of claims 1 to 5, comprising a second settling tank receiving settled material from said settling tank.

7. A waste treatment system according to any one of claims 1 to 6, wherein said diluted waste transferred from said dilution vessel to said series of reactors comprises 2.5% to 4% total solids (TS).

8. A waste treatment system according to any one of claims 1 to 7 , comprising a conduit transferring sludge from said settling tank to said aerobic reactor.

9. A waste treatment system according to any one of claims 1 to 8, comprising a centrifuge receiving sludge from said settling tank.

10. A waste treatment system according to any one of claims 1 to 9, wherein said second liquid supernatant has a total solids (TS) concentration not exceeding 2%.

11. A waste treatment system according to any one of claims 1 to 9, characterized by a settling time of at least 1 hour in said settling tank.

12. A method comprising: diluting a stream of organic waste with supernatant from a settling tank installed downstream of a waste treatment system including a series of at least three reactors.

13. A method according to claim 12, wherein said at least three reactors include at least two anaerobic reactors.

14. A method according to claim 12 or claim 13, wherein said at least three reactors include at least one aerobic reactor.

15. A method according to any one of claims 12 to 14, wherein said at least two anaerobic reactors are sequencing batch reactors (ASBR).

16. A method according to any one of claims 14 to 15, wherein said at least one aerobic reactor is an aerobic sequencing batch reactor (SBR).

17. A method according to any one of claims 12 to 16, comprising sequentially transferring supernatant downstream through said series of reactors and sequentially transferring sludge upstream through said series of reactors.

18. A method according to any one of claims 12 to 17, comprising instituting a settling time of at least 1 hour in said settling tank.

19. A method according to any one of claims 12 to 18, comprising instituting a settling time of not more than 24 hours in said settling tank.

20. A method according to claim 19, comprising instituting a settling time of not more than 6 hours in said settling tank.

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