Integrated hot hydrolysis and vacuum digestion for fluid treatment using biochemical processes

Abstract

Systems and methods for treating a fluid comprising a particulate portion and a soluble portion include feeding the fluid into a hydrothermal treatment apparatus and subjecting the fluid to heating to a temperature of 121°C or higher to obtain a treated fluid, subsequently feeding the hydrothermally treated fluid into a vacuum integrated reactor, wherein at least the particulate portion undergoes fermentation or digestion, during fermentation or digestion, subjecting the fluid in the vacuum integrated reactor to vacuum pressure, and collecting at least a portion of the soluble portion of the fluid as condensate from the vacuum integrated reactor, thereby thickening the remaining portion of the fluid, and recovering the thickened fluid from the vacuum integrated reactor. The vacuum may also be applied upstream or downstream of a non-vacuum integrated reactor and separate from the non-vacuum integrated reactor.

Description

[0001] This application is a non-provisional application filed on May 19, 2022, under U.S. Provisional Application No. 63 / 343,903, the disclosure of which is incorporated herein by reference in its entirety. Background Technology

[0002] Global climate change and the energy crisis caused by fossil fuel combustion have increased interest in biorenewable energy sources. Consequently, wastewater treatment plants (WWTPs) are shifting towards water resource recovery facilities (WRRFs), aiming to treat wastewater and recover value-added products such as volatile fatty acids and biomethane from on-site sludge. Furthermore, in recent years, due to economic conditions such as rising oil prices and negative environmental impacts, many national governments have focused on increasing the use of various renewable energy sources, including solar, wind, biomass, hydropower, tidal, and waste-derived energy.

[0003] One of the leading sludge management technologies is anaerobic digestion. Anaerobic digestion (AD) is a promising technology that can convert organic waste into volatile fatty acids or methane, or both, in two distinct stages: acidification (stage 1) and methanogenesis (stage 2). In stage 1, organic waste is converted into volatile fatty acids by acid-producing and acetic acid-producing microorganisms. Furthermore, hydrogen and volatile fatty acids are converted into methane via methanogenesis in stage 2. Compared to other waste treatment technologies, AD offers numerous benefits such as solids reduction, reduced greenhouse gas emissions, odor reduction, and increased non-market benefits.

[0004] The long hydraulic retention time (HRT) of the soluble fraction of the fluid, along with low methane and VFA yields, are some of the challenges associated with anaerobic digestion (AD). The hydrolysis step is the rate-limiting step in AD for complex organic fluids or substrates, while methanogenesis is the rate-limiting step for readily biodegradable fluids or substrates. Various pretreatment techniques (including mechanical, chemical, biological, and thermal) have been applied in an attempt to facilitate the hydrolysis step. Hydrothermal treatment (HTP) involves heating biomass to above the autoclave temperature (121°C) for a fixed time prior to AD. The mechanism of HTP is the lysis of cell membranes, followed by the release of intracellular substances, which leads to the dissolution of organic compounds. Researchers investigated the effects of HTP on both AD and fermentation of municipal sludge using a wide temperature range (from 50°C to 275°C). Summary of the Invention

[0005] What is still needed is a method and system to improve the efficiency of anaerobic digestion processes in the treatment of fluids such as sludge (e.g., in wastewater treatment facilities) (e.g., in terms of increasing the yield and retention time of value-added products such as volatile fatty acids and biomethane).

[0006] This objective and other objectives are achieved through the novel systems and methods described in this paper.

[0007] The disclosed system and method address the recalcitrant nature of organic waste (such as spent activated sludge) for conventional anaerobic digestion. The addition of hydrothermal pretreatment (HTP) reduces the likelihood of mixing problems in the vacuum reactor due to sludge thickening. Typically, mixing in digesters requires significant energy due to the high viscosity of the sludge. HTP reduces sludge viscosity and facilitates easier operation and less maintenance. Furthermore, the ability to operate digesters with more concentrated feed (due to reduced viscosity) necessitates smaller AD volumes.

[0008] The combination of HTP and vacuum digestion helps overcome the limitations of each process individually, as vacuum digestion is viscosity-limited and heat treatment is ammonia-limited (ammonia generated during HTP has an inhibitory effect on ammonia digestion). This application overcomes these limitations by combining their respective advantages. Heat treatment will reduce viscosity, thus eliminating the bottleneck of vacuum digestion, while vacuum digestion will reduce ammonia content (through vacuum stripping under boiling), which will eliminate the bottleneck of heat treatment. Further synergies are also anticipated: for example, the use of a near-perfect biomass retention process (vacuum extraction / evaporation) allows for the selection of microbial ecologies specifically for the less biodegradable components in the heat-treated feed. Thus, less biodegradable components present in the feed or generated by HTP can be efficiently converted by specialized organisms. Furthermore, the liquid residue produced by the integrated process is unaffected by the presence of non-biodegradable total nitrogen, as the latter is retained in the cake and further digested by a specialized microbial community.

[0009] The disclosed systems and methods aim to minimize the space requirements for anaerobic digesters while enhancing the generation of resources such as VFAs and transferring this carbon source to other processes in the wastewater treatment facility. Typically, AD tanks have a large footprint (depending on the plant's production capacity). The hydraulic retention time and loading rate of the AD determine the volume of the digester that needs to be designed and constructed. With population growth in urban areas, most plants need to increase their digestion capacity by loading more organic matter into their digesters. However, feeding higher loads into the digesters means operating them at lower HRTs. In many countries, biosolids produced by lower HRTs do not meet biosolids standards, forcing utilities to build new digesters to handle higher loads. The novel combination of hydrothermal treatment and vacuum digestion technology described herein not only allows the digester to operate at lower HRTs by separating (decoupling) the hydraulic retention time of the soluble portion (HRT of the soluble component of the fluid being treated) from the residence time of the solid portion of the fluid being treated (HRT, or SRT of the solid component of the fluid), but also enhances methane and / or hydrogen production. The high ammonia concentration and associated pH following HTP lead to high free ammonia concentrations, thereby inhibiting methanogenesis. This inhibition can be addressed using the disclosed systems and methods.

[0010] Therefore, the subject of this paper includes a method for treating a fluid comprising a particulate fraction and a soluble fraction, the method comprising:

[0011] The fluid is fed into a hydrothermal treatment unit and heated to 121°C or higher to obtain a treated fluid;

[0012] The hydrothermally treated fluid is then fed into the reactor, wherein at least the particulate portion undergoes fermentation or anaerobic digestion, wherein the treated fluid is subjected to vacuum pressure upstream of the fermentation or anaerobic digestion in the process direction, during the fermentation or anaerobic digestion, or downstream of the fermentation or anaerobic digestion in the process direction.

[0013] If a vacuum pressure is applied during fermentation or anaerobic digestion, the reactor is a vacuum integrated reactor, and the method includes collecting at least a portion of the soluble portion of the fluid (including water and gas) as condensate from the vacuum integrated reactor and collecting residual gas, thereby thickening the remaining portion of the fluid.

[0014] If a vacuum pressure is applied upstream or downstream of fermentation or anaerobic digestion, the method includes collecting at least a portion of the soluble portion of the fluid (including water and gas) as a condensate from the treated fluid or from a treated and fermented or digested fluid, and collecting residual gas, thereby thickening the remaining portion of the fluid; and

[0015] Recover the thickened fluid.

[0016] A method for treating wastewater fluids comprising biological solids is also described, the method comprising:

[0017] Wastewater fluid is fed into a hydrothermal treatment unit and heated to 121°C or higher to obtain treated fluid;

[0018] The treated fluid is then fed into the reactor, where the wastewater fluid undergoes fermentation or anaerobic digestion, and the treated fluid is subjected to vacuum pressure upstream of the fermentation or anaerobic digestion in the process direction, during the fermentation or anaerobic digestion, or downstream of the fermentation or anaerobic digestion in the process direction.

[0019] If a vacuum pressure is applied during fermentation or anaerobic digestion, the reactor is a vacuum integrated reactor, and the method includes collecting gases (including but not limited to ammonia) as condensate from the vacuum integrated reactor.

[0020] If a vacuum pressure is applied upstream or downstream of fermentation or anaerobic digestion, the method includes collecting gases (including, but not limited to, ammonia) as condensate from the treated fluid or the treated and fermented or digested fluid; and

[0021] Heat is extracted from the condensate and used to heat the wastewater fluid in the hydrothermal treatment unit.

[0022] A system for processing a fluid comprising a particulate portion and a soluble portion is further described, the system comprising:

[0023] A hydrothermal treatment apparatus configured to treat a fluid fed into it by heating.

[0024] A reactor located downstream of a hydrothermal treatment unit in the process direction, the reactor being configured to receive treated fluid from the hydrothermal treatment unit and subject the treated fluid to fermentation or anaerobic digestion, wherein the reactor is selected from: a vacuum integrated reactor with a vacuum pump for applying a vacuum to the vacuum integrated reactor; and a reactor without a vacuum pump.

[0025] If the reactor is a reactor without a vacuum pump, the system further includes a second reactor or pipeline (upstream or downstream of the reactor in the process direction), which includes a vacuum pump for applying a vacuum to the second reactor or pipeline.

[0026] This process utilizes vacuum to remove condensate; and

[0027] A controller configured to control the application of vacuum and the removal of condensate. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a system that includes both a hydrothermal treatment unit and a vacuum integrated reactor, within a system that includes a downstream anaerobic digester.

[0029] Figure 2 It is a schematic diagram of a system including a hydrothermal treatment unit, a reactor, and a downstream vacuum integrated treatment unit.

[0030] Figure 3 This is a schematic diagram of a system that includes both a hydrothermal treatment unit and a vacuum integrated reactor within an upstream anaerobic digester.

[0031] Figure 4-7 A specific exemplary system employing both hydrothermal treatment (HTP) (in this case utilizing heating obtained by means including heat recovery from the condensate extracted from the self-digestion process) and vacuum digestion is shown.

[0032] Figure 8 The different soluble components, such as VFA, soluble carbohydrates, and soluble protein concentrations, are shown in the hydrothermal treated and original untreated samples.

[0033] Figure 9 The percentage reduction in TSS and VSS due to hydrothermal treatment is shown.

[0034] Figure 10 The particle size distribution (PSD) of the raw and hydrothermally treated (HTP) samples is shown.

[0035] Figure 11 The changes in chemical oxygen demand (COD) dissolution over time are shown in conventional and vacuum fermentation reactors with sludge feed treated with HTP.

[0036] Figure 12 The changes in COD dissolution of sludge over time are shown in two reactors (vacuum and conventional).

[0037] Figure 13The average COD dissolution is shown for four systems (conventional fermentation, HTP-treated sludge using conventional fermentation, vacuum fermentation, and HTP-treated sludge using vacuum fermentation).

[0038] Figure 14 The VFA yield over time is shown for samples treated in conventional and vacuum integrated reactors for fermentation product, condensate, and total fermentation product + condensate.

[0039] Figure 15 and 16 The specific denitrification rate (SDR) and biomass yield are shown for all carbon sources.

[0040] Figure 17 and 18 The cumulative methane production of the four systems over time is shown.

[0041] Figure 19 and 20 The methane production rates of HTP-treated and untreated feeds are shown. Detailed Implementation

[0042] This document describes a system and method comprising both a hydrothermal treatment apparatus and a vacuum-integrated biological and non-biological reactor (e.g., a fermenter). In one aspect, this disclosure provides a system and method for treating a fluid comprising a particulate portion and a soluble portion. The system and method may include biochemical transformation of the solids in the particulate portion of the fluid using microorganisms (e.g., for fermentation), while subjecting the fluid to vacuum pressure and evaporating at least a portion of the soluble portion of the fluid, thereby thickening the remaining portion of the fluid, which may remain in the vacuum-integrated reactor for further processing. The system and method are intended to support systems and methods for processing fluids using fermentation and / or anaerobic digestion (AD).

[0043] Anaerobic digestion (AD) is a multi-step biochemical process in which organic waste materials are decomposed by facultative and anaerobic microorganisms in an anaerobic environment. The basic steps of anaerobic digestion are hydrolysis, acid production, acetic acid production, and methanogenesis.

[0044] In the first step of hydrolysis, hydrolytic bacteria degrade complex organic polymers, such as proteins, carbohydrates, and lipids, into soluble monomers. In waste activated sludge (WAS), most organic compounds are surrounded by a polymer network formed by extracellular polymeric substances (EPS). EPS is a highly hydrated structure that plays a crucial role in the bioflocculation, sedimentation, and dewatering of sludge. EPS in WAS is primarily attributed to proteins and carbohydrates, which require cleavage to make the intracellular contents available to the microorganisms.

[0045] The second step is acid production, such as fermentation, in which the hydrolysis products are further degraded to form volatile fatty acids (VFAs) (such as acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, etc.), ammonia, hydrogen sulfide, carbon dioxide, and other byproducts. In this disclosure, a vacuum-integrated reactor is used for this step, which also leads to the dissolution of organic matter.

[0046] The next step in acetic acid production involves acetic acid-producing bacteria, which convert organic acids into acetic acid, hydrogen, and carbon dioxide.

[0047] The final stage of anaerobic digestion is methanogenesis, in which biogenic methane is produced by two groups of methanogenic organisms: acetoclastic methanogens, which degrade acetate into methane and carbon dioxide; and hydrogenophilic methanogens, which use hydrogen as an electron donor and carbon dioxide as an acceptor to produce methane. Furthermore, methanogenesis can be controlled to favor the formation of biogenic hydrogen and / or bioethanol instead of biogenic methane.

[0048] Therefore, anaerobic digestion treats and stabilizes the sludge, and value-added products in the form of methane or hydrogen and volatile fatty acids (VFAs) are recovered through fermentation. VFAs recovered from fermented sludge can be used in a variety of applications, such as a carbon source for on-site bionutrient removal, biodegradable plastics production, and hydrogen production.

[0049] The systems and methods described herein focus on the application and integration of vacuum pumps (for extracting water and gas from sludge streams) with existing biological processes (such as fermentation or digestion) for solids treatment. Vacuum-integrated bioprocess applications include pumps connected to the top space of a bioprocess vessel, or vacuum being applied in a separate vessel or stream hydraulically connected to a main bioprocess reactor. In one embodiment, a thermally pretreated feed fluid is fed in-situ to a vacuum-integrated reactor, such as a fermenter or digester, with an associated vacuum pump for applying vacuum to the reactor. In another embodiment, a thermally pretreated fluid is fed in-situ to a reactor (without vacuum) and separately to a vacuum-integrated sidestream treatment unit located upstream or downstream of the reactor. In these embodiments, the reactor may be, for example, a fermenter and / or an anaerobic digester. Fermenters and anaerobic digesters are both well-known reactors in the art, and therefore, operational differences are not discussed further herein.

[0050] Therefore, in the systems and methods described herein, hydrothermal treatment (HTP) is utilized as a step preceding vacuum-integrated digestion or fermentation in a vacuum-integrated reactor, in the order of the method. HTP lyses wastewater sludge, increases soluble chemical oxygen demand (SCOD), decomposes the cell walls of bacteria contained in the sludge (thereby releasing intracellular substances), and reduces sludge viscosity.

[0051] The reactor (downstream of the HTP unit in the process direction) is used to separate high-quality condensates containing volatile substances such as VFA and ammonia, and to concentrate inert and particulate solids into smaller volumes. The reactor can be a fermentation reactor (fermenter) or a digester reactor (digester), and as discussed below, may include devices for applying a vacuum (such as a vacuum pump), or these devices may be omitted (vacuum-integrated reactor). By integrating the HTP with the reactor, the production of valuable materials such as VFA can be enhanced, thereby increasing their recovery rate in the condensate. Furthermore, the tendency for mixing problems is reduced.

[0052] In previous systems, low methane and VFA yields were partly attributed to the accumulation of inhibitory compounds such as ammonia and other nutrients during fermentation and digestion. Removing these inhibitory compounds significantly improves the system. Applying a vacuum to the fermenter or digester allows for the separation of HRT (Heat Retention Time) from solids retention time (SRT) via vacuum evaporation, resulting in a compact process that can be deployed in a wider range of facilities, including small municipalities and farms. Additionally, this new approach facilitates the separation and recovery of resources such as ammonia and VFA while enhancing sludge thickening.

[0053] The systems and methods described herein combine hydrothermal treatment (HTP) of organic waste with digestion or fermentation and vacuum. Slowly biodegradable fluids or substrates (e.g., fluids or solids comprising recalcitrant organic matter, such as thickened spent activated sludge (TWAS) and / or food waste) are subjected to hydrothermal treatment (HTP). The slowly biodegradable fluids or substrates used for HTP can be any recalcitrant organic biodegradable compound, including but not limited to TWAS, feces, source-separated organic matter (SSO), yard waste, and cellulose and lignocellulosic materials. The pH of the slowly biodegradable substrate (such as sludge) can be acidic, neutral, or alkaline, in the range of, for example, 4–10. The solids content of the recalcitrant substrate can range, for example, from 1% to 20%, such as from 1% to 16%.

[0054] An HTP unit can be any suitable device having an inlet for the feed fluid or substrate, a device for applying heat to the feed fluid or substrate within the unit (such as an external heat source or a heat exchanger that extracts heat from other materials within the system, such as sludge leaving the HTP unit and / or condensate from a vacuum reactor), and an outlet for the treated fluid or substrate. Thus, an HTP unit can utilize the heat recovered from the condensate gas removed by vacuum in the vacuum reactor to perform hydrothermal treatment of the feed fluid.

[0055] HTP can be carried out in a temperature range of, for example, 130 to 300°C (such as 150 to 220°C) for a duration of, for example, 5 to 300 minutes (such as 5 to 100 minutes and 10 to 30 minutes). HTP can be carried out at normal atmospheric pressure, but also at pressures of, for example, 1.1 to 10 bar (such as 2 to 8 bar or 2 to 6 bar). A preferred set of conditions for low retention times is, for example, 170°C, 6 bar, and 30 minutes. The optimal temperature and retention time for HTP for methane production purposes are 160 to 180°C and 20 to 40 minutes, respectively.

[0056] Compared to the original untreated fluid, HTP can increase the concentration of all soluble compounds in the fluid, including soluble proteins, volatile fatty acids, and carbohydrates. Correspondingly, compared to the original untreated fluid, HTP can reduce the content of total suspended solids (TSS) and volatile suspended solids (VSS). For example, TSS reduction can range from, for example, 10% to about 40%, such as 15% to 35%, or 20% to 35%, while VSS reduction can range from, for example, 10% to about 50%, such as 15% to 40%, or 20% to 40%. Furthermore, HTP can reduce the particle size of the treated fluid compared to the original untreated fluid. For example, with the original sample having d10 and d90 values ​​of 27 μm and 187 μm, respectively, HTP can reduce these values ​​to 15 μm and 125 μm, where the increased retention time in HTP reduces the particle size of the treated sample. These changes in the treated fluid are significant because they enable higher value-added product recovery from the anaerobic digestion process, including higher VFA yields and higher methane and / or hydrogen recovery and production.

[0057] After leaving the HTP unit, the treated fluid (such as treated sludge) can then be mixed with a faster-biodegradable fluid or substrate (i.e., a fluid or substrate that biodegrades at a faster rate than a slowly biodegradable fluid or substrate (such as primary sludge)). Thus, the additional fluid biodegrades more rapidly than the slowly biodegradable fluid because it can biodegrade more quickly, for example, through fermentation. If mixed, the ratio between the two types of fluid or substrate (slowly biodegradable: faster-biodegradable) depends on the characteristics of the materials, but can be in the range of 100:0 to 25:75 (such as 75:25 to 25:75), preferably 50:50.

[0058] The treated material (optionally a mixture with untreated fluid or substrate) leaving the HTP unit is fed into a reactor (digester or fermenter). Preferably, to facilitate fermentation and digestion in the reactor, the treated material is cooled to 75°C or lower before entering the reactor. Cooling can be achieved using ambient conditions or promoted by heat removal from any suitable active cooling method and / or heat exchanger (in which case any extracted heat can be reused to heat other fluids or substrates in the HTP unit).

[0059] As a reactor, conventional fermentation or digestion equipment and designs can be used. In one embodiment, the fermenter or digester includes means for applying a vacuum to the reactor, such that a vacuum is applied during fermentation or digestion and condensates (such as water and ammonia) are removed from the reactor during the fermentation or digestion process. The condensates removed via vacuum are used, for example, for a bionutrient removal (BNR) process, and the remaining fermentation material leaving the vacuum-integrated reactor can be directed to an anaerobic digester, a post-pasteurization unit, and / or a dehydration unit.

[0060] Examples of vacuum integrated reactors for systems and methods described herein, as well as the conditions for operating vacuum integrated reactors, are described in U.S. Patent Application No. 17 / 742,905, which is incorporated herein by reference in its entirety.

[0061] In an alternative embodiment, the reactor is a conventional fermenter or digester without a vacuum. In this case, the system and method further include a processing unit or feed line (collectively referred to herein as a vacuum integrated processing unit) located upstream, downstream, or both of the fermenter or digester in the process direction. In this embodiment, the fermented / digested material leaving the reactor undergoes a vacuum to remove condensate as described above.

[0062] Fermentation in the reactor can be carried out under thermophilic, thermophilic, or superthermophilic conditions, with temperatures ranging from, for example, 20 to 100°C, preferably 20 to 70°C. The pH can be adjusted using acids or bases to obtain acidic, neutral, or alkaline conditions, for example, in the range of 3-10. Vacuuming, due to the additional stripping of CO2 gas from the reactor, reduces the amount of alkali that needs to be added.

[0063] The vacuum used in this paper can be operated such that the treatment chamber is, for example, 1 to 999 mbar, 10 to 750 mbar, 25 to 500 mbar, 25 to 400 mbar, or 25 to 300 mbar. This vacuum pressure can be achieved using a vacuum pump. The vacuum can be applied intermittently (including periodically), such that the treatment chamber has a time period in which the fluid is biochemically treated under vacuum pressure and a time period in which the fluid is biochemically treated under pressure greater than vacuum pressure. The treatment can be performed such that the duration of treatment of the fluid at pressure greater than vacuum pressure is equal to or longer than (e.g., 1 to 100 times longer, 2 to 50 times longer, or 4 to 25 times longer) the time period in which the fluid is treated under vacuum pressure.

[0064] The vacuum pump can be controlled by an automatic controller that maintains the processing chamber at the desired pressure, closes the vacuum at the desired time (e.g., based on the amount of condensate collected), etc. The temperature can be in the range of, for example, 10 to 90°C, 20 to 80°C, 30 to 70°C, or 40 to 50°C. The vacuum pressure can be controlled such that the treated fluid boils within these desired temperature ranges. The processing chamber can be heated by any suitable means, such as using a heated stream from another part of the system or using an electric heating element. The pH of the fermentation / digestion can be maintained in the range of, for example, 3 to 10, 4 to 9, 5 to 8, or 5.5 to 6.5. pH and / or temperature adjustments can be made during the process to concentrate desired chemicals in the evaporate or fermentation / digestion. The controller can be configured to control not only the rate of condensate removal from the vacuum reactor or processing unit, but also the residence time of the solids (particulate portion) of the fluid being processed to be at least 25% longer than the residence time of the soluble portion within the vacuum reactor or processing unit.

[0065] Two streams exit the vacuum integrated reactor or vacuum integrated processing unit: (1) a condensate stream consisting of the soluble portion removed from the reactor via vacuum, and (2) a fermentation / digestion stream consisting primarily of the solid portion of the fluid. The fermentation / digestion stream has a higher solids content than the HTP-treated fluid entering the vacuum reactor.

[0066] The reactor can operate with a hydraulic retention time (HRT) of, for example, 0–3 days (such as 0.1–3 days or 1–3 days) for the soluble fraction of the fluid being treated and a hydraulic retention time (SRT) of, for example, 0.5–10 days or longer (such as 1–5 days or 2–3 days). For example, while the typical retention time of the soluble fraction (water and volatile compounds) in a vacuum evaporator can be about 1–10 hours, the retention times of the solid fraction and microbial cells must be much longer (e.g., >10 hours) to enable biochemical reactions (e.g., particle hydrolysis, biomass synthesis, etc.). This can be achieved by using an evaporation process in a vacuum integrated reactor or vacuum integrated processing unit as a means of separating the solid fraction retention time from the soluble fraction retention time, and further separating the solid fraction retention time, the liquid non-volatile matter retention time, and the liquid volatile matter retention time. To achieve optimal performance, one or more variables, such as temperature, pH, pressure, mass transfer, microbial community, nutrients, and particulate fraction retention time, can be considered and controlled simultaneously.

[0067] Therefore, the vacuum integrated reactor or vacuum integrated processing unit described in this paper, located upstream or downstream of a conventional reactor, can achieve selective removal of one or more soluble fractions from the processing chamber via vacuum evaporation. This enables effective separation of the retention times of one or more soluble fractions from the retention times of one or more solid fractions. Thus, using vacuum as the primary mechanism for mass removal and volume release within the processing chamber, one or more solid fractions can be held in the processing chamber for a theoretically infinite time period (due to their relatively insoluble and non-volatile physicochemical properties). Consequently, one or more solid fractions will not be collected in the condensate, thus keeping the condensate exceptionally pure and free of nutrients.

[0068] Furthermore, in order to evaporate volatile components and water, thereby achieving HRT and SRT separation, a vacuum reactor or processing unit can utilize the energy (heat and pressure) already provided to the mixture during the HTP stage. Essentially, water evaporation and volatile stripping are achieved through pressure and temperature variations between the HTP and the evaporation vessel in which a vacuum is applied, and the efficiency of evaporation and stripping can be further enhanced by adjusting the pH and conductivity of the mixture.

[0069] HTP integrated with vacuum reactors or integrated reactors and vacuum treatment units can be used in wastewater treatment plants with biological nutrient removal units.

[0070] Figure 1A system comprising a downstream anaerobic digester 300 and both a hydrothermal treatment unit 100 and a vacuum integrated reactor 200 is illustrated. In this configuration, downstream anaerobic digestion can occur as in a conventional treatment system. Given that the fluids treated in the hydrothermal treatment unit and the vacuum integrated reactor have already undergone the removal of most volatile components (including water) and digestion-inhibiting compounds (such as ammonia), digestion can be optimized, including optimizations in retention time and the recovery of value-added solids products. Specifically, downstream anaerobic digestion can yield additional gases from the biomass, thereby further enhancing the recovery and generation of methane and / or hydrogen.

[0071] Figure 2 A system comprising a hydrothermal treatment unit, a reactor 250 (without vacuum), and a downstream vacuum integrated treatment unit 280 is shown. The vacuum integrated treatment unit can be an anaerobic digester, particularly when the reactor is a fermenter. Therefore, Figure 3 The treatment unit 280 and the anaerobic digester shown can be a single unit. Furthermore, as discussed above, the vacuum integrated treatment unit can be located upstream of the reactor.

[0072] Figure 3 This illustrates a system comprising both a hydrothermal treatment unit 100 and a vacuum integrated reactor 200, including an upstream anaerobic digester 300. (Example) Figure 3 As shown, the fermentation material from the vacuum integrated reactor (in this case, a fermenter) can undergo any further dehydration (i.e., centrifugation) as needed or desired, and any liquid recovered during dehydration can be returned to the anaerobic digester or the vacuum integrated reactor. Furthermore, a portion of the fermentation material from the vacuum integrated reactor can be recycled back to the anaerobic digester.

[0073] Figure 4-7 Specific exemplary systems employing both hydrothermal treatment (in this case utilizing heating obtained through means including heat recovery from the condensate extracted from the self-digestion process) and vacuum digestion (shown using IntensiCarb™ vacuum) are illustrated. In these systems, the biomethanation reactor supplements methane production with biohydrogen stripped from the digestate via IntensiCarb™ vacuum and from other biosources, thereby enhancing the conversion of recovered carbon dioxide from the unit to methane. Figure 5 In this process, a pre-pasteurization unit and vacuum are applied before the digester as a pretreatment for pre-hydrolysis and pasteurization purposes to aid in the recovery of Class A biological solids from the digester. Figure 6 In this process, a second IntensiCarb™ vacuum can be deployed downstream of the digester to achieve dehydration. Figure 7 In the process, after digestion, a post-pasteurization tank is used to obtain Class A biological solids.

[0074] The system and method described can be used to recover one or more value-added products from the system. Many value-added products (precious metals, nutrients, cellulose, coagulants, pharmaceutical compounds, personal care products, etc.) that may be present in wastewater and biosolids are non-volatile and tend to accumulate in the treatment system, thereby facilitating extraction and further purification into high-purity chemicals. In a conventional anaerobic digestion process, the efficiency of the process and the quality of the biosolids produced are primarily attributable to biological activity. In the process of this invention, new biosolids of high quality are produced due to a combination of biological, thermal, and mechanical processes involving many factors. Furthermore, separating a portion of the water and extracting volatile compounds (through vacuum) will produce new solids that are not only rich in nutrients and / or have a high solids content but also possess a novel composition.

[0075] Vacuum-based digestion or fermentation can be operated without periodically removing solids from the system, allowing the technology to be operated for optimal periods and under optimal thermodynamic conditions. Such optimal times and operating conditions can be selected to maximize the accumulation of certain compounds, such as cellulose, with the aim of recovering the accumulated material. The same concept can be applied to other valuable products such as nutrients, microbial products, and precious metals.

[0076] Volatile fatty acids (VFAs) and ammonia products can be selectively obtained using rapid heating and rapid pH adjustment combined with temperature and vacuum—VFAs and ammonia are valuable products of anaerobic digestion. In conventional digesters or fermenters (which have a continuous feed into the digester / fermenter and digestate / fermentation product out of the digester / fermenter), VFA and ammonia concentrations in the reactor do not accumulate to high levels. In the system and method of the present invention, due to the lack of digestate / fermentation product and the discontinuous condensate, the concentrations in the reactor reach much higher levels than in conventional digesters / fermenters. When VFA and ammonia reach high levels, rapid heating and / or pH adjustment under vacuum can promote the recovery of high-purity condensate rich in VFAs and / or ammonia.

[0077] Fertilizers can be recovered by dosing chemicals in a vacuum-based and temperature-assisted digestion process. As a result of the potentially extremely long SRT (stable residual temperature) in this process, the biosolids are expected to be fully stabilized, i.e., Class A biosolids. Once the biosolids are fully stabilized, chemicals (such as potassium) can be precisely dosed to achieve the NPK (nitrogen:phosphorus:potassium) ratio required for commercial-grade fertilizers. Compared to conventional digesters, even with the same stabilization efficiency as vacuum-based digesters, the chemical dosing system must operate continuously.

[0078] Gases and volatile compounds can also be fractionated and selectively extracted from biosolids treatment processes. Gases and volatiles produced in digesters or fermenters have different vapor pressures and can be more or less removed by deploying a continuous vacuum gradient due to the cyclical nature of vacuum evaporator operation, resulting in partial selective removal and condensation of volatiles. The application of vacuum can enhance the stripping of dissolved anaerobic digestion gases from the reactor, including carbon dioxide, hydrogen, ammonia, hydrogen sulfide, etc. The stripping / removal of these different gases directly and indirectly affects many aspects related to the digester, including: (1) the removal of carbon dioxide (an acidic gas) causes an increase in sludge pH. Thus, the digester pH can be controlled to a state where the production of volatile fatty acids is maximized; otherwise, the pH tends to be over-acidified to a state where the production of alcohols and ketones (solvent generation) is favorable; (2) the removal of hydrogen (a key component in methane production) causes a shift to fermentative microorganisms (acid-forming agents), which leads to the accumulation of VFA levels and a slowdown in methane production; (3) hydrogen is also required by sulfate-reducing bacteria, and therefore the removal of hydrogen reduces the rate of hydrogen sulfide generation. The removal of hydrogen sulfide (a metal binder) releases essential micronutrients (iron, cobalt, nickel) for the extracellular production of hydrolytic enzymes, and thus accelerates the fermentation process; (4) the removal of ammonia (a microbial inhibitor) prevents its accumulation in the reactor, thereby allowing for long solids retention times without inhibited methane production; and (5) the removal of volatile fatty acids (an important supplemental carbon source) prevents their further conversion to methane in the reactor, thereby allowing for their recovery to support plant processes such as biochemical phosphorus removal and denitrification. Therefore, by controlling pH, temperature, and vacuum, some of these gases can be made more or less volatile, allowing for more or less selective removal from the reactor. Thus, the aforementioned advantages can be selectively controlled.

[0079] In addition to the aforementioned advantages derived from using a vacuum integrated reactor or vacuum integrated processing unit, the further inclusion of HTP prior to the vacuum integrated reactor or vacuum integrated processing unit is novel, and the combined use of HTP with the vacuum integrated reactor or vacuum integrated processing unit reduces viscosity and mixing problems caused by thickening in the vacuum reactor. HTP enhances the reactor's intensification potential. It has been found that fermentation and AD reactors integrated with HTP contain large amounts of ammonia, which inhibits acetic acid and methanogenesis activities, resulting in lower VFA and methane production (given the large amount of ammonia released during HTP). However, by integrating HTP with a vacuum integrated reactor or vacuum integrated processing unit, ammonia is continuously recovered. The recovered ammonia not only improves digester / fermenter performance but also captures ammonia that can be used for other purposes.

[0080] Microbial community diversity can also be reduced by HTP, thereby eliminating methanogens in a vacuum reactor when used as a fermenter. In conventional fermenters, methanogens can inhibit acetic acid production, while in a vacuum fermenter integrated with HTP, methanogens cannot survive at high temperatures (e.g., above 70°C). Therefore, integrating HTP into a system with a vacuum integrated reactor also improves organic matter dissolution, VFA production, and ammonia production. Hydrolysis is the rate-limiting step in conventional digesters, but HTP overcomes this challenge by dissolving organic compounds by up to, for example, 40% at 170°C. The vacuum reactor or vacuum integrated processing unit further dissolves the material and ultimately produces and recovers greater quantities of VFA and ammonia.

[0081] The topics in this article will be further illustrated by the following examples.

[0082] Example 1

[0083] The substrate used in this embodiment was thickened spent activated sludge (TWAS) obtained from the Ashbridge's Bay wastewater treatment plant in Toronto, Canada. Hydrothermal treatment of the substrate was conducted under six different conditions—a constant temperature of 170°C—and six retention times of 10, 20, 30, 40, 50, and 60 minutes were tested. A 2 L Parr 4848 hydrothermal reactor (Parr Instrument Company, IL, US) was used for HTP. The volume of TWAS treated per cycle was 1 L.

[0084] Compared to the original untreated samples, all treated samples had higher levels of soluble compounds. Figure 8 The concentrations of different soluble components, such as VFA, soluble carbohydrates, and soluble proteins, are shown for the treated and untreated samples. Comparison of the soluble content in the original sample with that in the hydrothermally treated sample confirms that HTP increases the concentration of all soluble compounds.

[0085] Figure 9 The percentage reduction in TSS and VSS due to hydrothermal treatment is shown. As shown in the figure, increasing the retention time up to 30 minutes resulted in an increase in solids reduction, which then stabilized. The TSS reduction of the hydrothermally pretreated samples ranged from 20% to approximately 35%. On the other hand, the VSS reduction ranged from 23% to approximately 40%. A 23% VSS reduction was achieved at a retention time of 10 minutes; this percentage increased to 32% at a retention time of 20 minutes, and reached a maximum of 40% at a retention time of 30 minutes. After a retention time of 30 minutes, the VSS reduction did not change significantly.

[0086] Figure 10 The particle size distribution (PSD) of the original and hydrothermally treated samples is shown. As shown in the figure, all treated samples exhibited lower particle sizes compared to the original samples. The d10 and d90 of the original samples were 27 μm and 187 μm, respectively. For the pretreated samples, these values ​​decreased to 15 μm and 125 μm. Increasing retention time was associated with a reduction in particle size in the pretreated samples (p < 0.05). The smallest particle size was observed for the samples pretreated for 60 minutes. At a retention time of 60 minutes, d10, d50, and d90 were 15.2 ± 2.4 μm, 47.8 ± 11.8 μm, and 145.5 ± 1.7 μm, respectively, representing particle size reductions of 45%, 42%, and 22% compared to the original samples.

[0087] Example 2

[0088] The substrates used in this embodiment were thickened spent activated sludge (TWAS) and primary sludge (PS) obtained from the Ashbridge Wastewater Treatment Plant in Toronto, Ontario. The substrates underwent secondary treatment and thickening. The inoculum used was also obtained from the anaerobic digestion (AD) tanks at the Ashbridge plant, which operated the sludge at a mesophilic temperature range (34–38 °C) and an HRT of 18 days. The properties of the raw TWAS and inoculum are shown in Table 1. Recycled activated sludge (RAS) was collected from the Greenway Wastewater Treatment Plant (London, Ontario) and used as the source of biomass for denitrification testing. Detailed characterization of the RAS is also summarized in Table 1.

[0089] Table 1

[0090]

[0091] Both raw and treated sludge were fed into the fermentation process to evaluate the effectiveness of HTP in conventional and vacuum modes. Therefore, four systems were evaluated: S1 = conventional fermentation (without HTP or vacuum) (with raw TWAS and PS as feed); S2 = vacuum integrated reactor fermentation (with raw TWAS and PS as feed); S3 = HTP and conventional fermentation (with HTP-treated TWAS and raw PS as feed); and S4 = HTP + vacuum integrated reactor fermentation (with HTP-treated TWAS and raw PS as feed). HTP in TWAS was conducted at 170°C, a holding time of 30 minutes, and a pressure of 6 bar.

[0092] The S4 enables enhanced biochemical fermentation and simultaneous thickening of municipal biosolids via vacuum-driven evaporation at temperatures ranging from 20 to 60°C. This process combines thickening, hydrolysis, acidification, gas stripping, and dehydration through near-ideal solid-liquid separation, thereby enhancing both biochemical and physicochemical treatment processes. The intense bubbling during vacuum boiling enhances the mass transfer rate between gaseous, liquid, and solid components. In contrast, mass removal via vacuum evaporation allows for the complete retention of the non-volatile soluble portions of the fermented biosolids (including nutrients such as ammonia and phosphates). An auxiliary unit for heat recovery is integrated with the vacuum evaporation chamber to recycle the latent heat of evaporation back into the process. The complete system consists of the following components: (1) a heat exchanger for preheating the feedstock using the recovered latent heat of evaporation; (2) a main reactor vessel operating under vacuum (which can perform both the fermentation and thickening processes of the biosolids); (3) a vacuum pump for extracting the steam generated during evaporation; and (4) a second heat exchanger for recovering the available heat from the fermented sludge.

[0093] S1 was fed with a 50:50 (by volume) mixture of raw PS and TWAS, while S3 was fed with a 50:50 mixture of hydrothermally treated TWAS and raw PS. The semi-continuous conventional fermentation systems were operated under thermophilic conditions (45°C). Conventional fermenters (SRT=HRT=3 days) were operated using 1 / 3 of the waste sludge (500 mL) (1.5 L fermentation volume). Both S1 and S3 were started by mixing 1 L of thermally pretreated seed (heated at 70°C for 30 minutes to inhibit methanogenesis) with 0.5 L of feed.

[0094] S2 and S4 (SRT=3 days, HRT=1.5 days) were operated daily under vacuum for 10 hours at -900 mbar (or +100 mbar absolute pressure, equivalent to a boiling point of 45°C) to evaporate 1,500 mL of a 3 L fermentation volume. To maintain the same SRT as the conventional control fermenter S1 (3 days), one-third (1 / 3) of the remaining sludge volume after evaporation was discarded daily and replaced with fresh, mixed sludge. Between vacuum applications, S2 and S4 were maintained at 45°C using a water bath, and pressure and temperature were continuously monitored during vacuum operation. All systems S1-S4 were operated until pseudo-steady-state conditions were reached.

[0095] The suitability of condensate (high-grade VFA) as a carbon source for denitrification testing was tested, and fermentation broth was used as feed for anaerobic digestion (AD). To assess the impact of HTP and vacuum on fermentation broth and condensate as carbon sources for bionutrient removal, a series of batch tests were conducted to enhance denitrification. These samples included fermentation broth from both conventional and vacuum systems, fed with both raw and treated samples. Additionally, condensate from the vacuum system and supernatant from the fermentation broth were used as carbon sources. To avoid carbon limitation during testing, the soluble chemical oxygen demand (COD) to nitrate ratio was kept to a minimum of 8:10. Mixed liquor suspended solids (MLSS control) or RAS without an additional carbon source were also tested to examine background denitrification activity (MLSS control). To compare and analyze the SDNR of external carbon sources with commonly used commercial carbon sources, acetate was also fed into one reactor in the batch series.

[0096] Fermentation products and fermentation centers from four systems were used as substrates for the biochemical methane potential (BMP) test. The BMP test was used to determine the methane productivity and biodegradability fraction of the samples.

[0097] Water and gas quality analyses were performed, including total suspended solids (TSS), volatile suspended solids (VSS), total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD), carbohydrates, protein, VFA, biogas production, and biogas composition. The viscosity of the samples was measured using a Fungilab™ Viscolead One viscometer (Fungilab Inc.) with an L3 spindle and a rotation speed of 100 rpm.

[0098] Hydrothermal treatment and vacuum fermentation, as individual and combined factors, significantly affected sludge pyrolysis (p>0.005). Figure 11 The figure shows the change in chemical oxygen demand (COD) dissolution over time in conventional and vacuum fermentation reactors fed with HTP-treated sludge. As observed in the figure, higher dissolution was produced in the vacuum fermentation reactor compared to the conventional fermenter. During the steady-state phase, vacuum fermentation showed a 10-15% improvement in COD dissolution compared to conventional fermentation. Furthermore, the total COD dissolution in vacuum fermentation ranged from 44-47%, while the total COD dissolution in conventional fermentation ranged from 35-40%. Total COD dissolution includes dissolution due to HTP (25-30%) and fermentation.

[0099] On the other hand, the study of two fermentation reactors (conventional and vacuum) with raw sludge feed highlighted the advantages of vacuum fermentation over conventional fermentation. Figure 12The changes in COD dissolution of sludge over time are shown in two reactors (vacuum and conventional). A 25-30% improvement was detected in the vacuum reactor compared to the conventional reactor. The higher pyrolysis rate in vacuum fermentation relative to conventional fermentation is likely due to the lower pressure in the vacuum reactor and therefore the higher stress on the biomass cell walls. Furthermore, liquid extraction from vacuum fermentation is likely another factor, as the solids content in the vacuum reactor increases over time. Sludge accumulation can contribute to retaining a higher sludge volume / solids ratio in the reactor.

[0100] Furthermore, the results showed that the integration of hydrothermal treatment and vacuum fermentation significantly improved overall sludge hydrolysis (p>0.005), while its effect on fermentation was similar to that of the original feed. Figure 13 The average COD dissolution for all four systems is reported for comparison. The figure shows that the two vacuum fermentation systems (with HTP-treated sludge feed or with raw sludge feed) have nearly similar dissolution efficiencies of 29% and 31% (due to fermentation alone). On the other hand, the total COD dissolution of the HTP-treated feed in the vacuum reactor is 32% higher than that of the raw feed reactor due to both HTP and fermentation. This percentage implies that most of the dissolution occurs during HTP, not fermentation.

[0101] In summary, HTP combined with vacuum fermentation can potentially lead to higher hydrolysis rates, improved solids reduction efficiency, and reduced energy required to heat the fermenter, as the HTP-treated TWAS provides additional heat to the fermenter. For example, with an adiabatic system and minimal heat loss, the heated substrate may be sufficient to maintain the fermenter temperature at the desired level or reduce the energy input required to heat the fermenter.

[0102] In the current study, significant differences in VFA yield were observed for the four systems (p>0.005). Furthermore, the integration of vacuum and hydrothermal pretreatment showed superior results compared to those without both vacuum and pretreatment. Figure 14 The figure shows the changes in VFA yields of fermentation product, condensate, and total fermentation product + condensate over time for samples treated in conventional and vacuum integrated reactors. No significant hysteresis phase was observed during either fermentation process, and VFA yields gradually increased throughout the fermentation, reaching a steady-state level. This figure compares the VFA yields of the novel configuration of the integrated HTP-vacuum reactor with those of conventional fermentation using HTP-treated samples as feed, highlighting the impact of the vacuum application on VFA, which increased it by approximately 30% (considering VFA generated from both condensate and fermentation product of the integrated system).

[0103] Biological nutrient removal processes in wastewater treatment plants require on-site biomass-generated carbon sources. VFAs produced during fermentation are a significant source of biomass carbon. In this embodiment, the effluents from four different fermentation systems were tested as potential carbon sources for denitrification. Furthermore, the fermentation effluents from all four reactors were centrifuged to obtain a pure liquid (supernatant) with low solids content, which was used as a carbon source. The specific denitrification rate (SDR) and biomass yield of all these carbon sources are shown in [data missing]. Figure 15 and 16 The results showed that the condensates from reactors S2 and S4 (without HTP treatment and with HTP treatment) exhibited the highest specific denitrification rates, at 7.6 and 7.2 mg NO3-N / g VSS•h, respectively, compared to all other samples and the control (acetate). The high efficiency of the condensates is likely due to the presence of highly biodegradable compounds (high-grade VFA) and low solids concentration. Furthermore, due to the low biomass concentration in the condensates, the only active bacteria were denitrifying bacteria. On the other hand, the fermented samples contained fermenting bacteria, which altered the bacterial diversity during the process and thus reduced the denitrification rate.

[0104] Furthermore, HTP improved the denitrification process regardless of the fermentation reactor configuration. All reactors containing HTP-treated samples exhibited slightly higher SDRs (up to 10%) compared to systems with pristine TWAS feed. Additionally, carbon sources from S2 and S4 showed accelerated denitrification rates compared to conventional reactors. The production of high-grade and higher concentrations of VFAs, due to the simultaneous removal of inhibitory compounds such as ammonia, is likely the most significant factor contributing to the higher efficiency of the S2 and S4 effluents. During vacuum fermentation, ammonia is removed and produced at higher concentrations, which can be further recovered through various methods. Ammonia production itself is another advantage of vacuum fermentation. Finally, the integration of vacuum and HTP is also associated with higher ammonia production, which increases the benefits of this novel process integration (due to the potential for significant nutrient recovery via ammonia stripping and other pathways).

[0105] Furthermore, the consumption of nitrates and COD over time showed better results for both HTP-treated and vacuum-treated samples (compared to the original samples). All HTP-treated samples were associated with higher nitrate removal rates, as the nitrite peak occurred within 45 minutes, compared to acetate and the original samples delayed to 60 and 120 minutes, respectively.

[0106] BMP results indicate that the novel configuration of the HTP and vacuum integrated reactor promotes hydrolysis and VFA production, and significantly enhances methane production yield. Figure 17 and 18The cumulative methane production over time is shown for the four systems. As can be seen in both figures, the hydrothermally treated samples generally exhibited greater enhancement potential than the original samples. The methane production of the HTP-treated and fermented samples increased by 46–59% compared to the original feed. Furthermore, comparing the effect of HTP on each fermentation reactor, the original conventional fermentation sample had a lower methane production (225 mL CH4 / g added TCOD) compared to the HTP-treated sample (255 mL CH4 / g added TCOD). Similarly, in S2 and S4, the treated samples were associated with higher methane production (267 mL CH4 / g added TCOD) compared to the original vacuum fermentation sample (237 mL CH4 / g added TCOD).

[0107] Conventional fermentation contributes to enhanced methane production, but vacuum fermentation exhibits a greater impact on improving methane production. Ignoring the effects of HTP, the original conventionally fermented and original vacuum-fermented samples showed increases in methane yield of 28% and 36%, respectively, compared to the original samples, implying the influence of the integrated system (HTP + vacuum) on AD performance.

[0108] Similarly, the biodegradability of the samples was improved by applying HTP and vacuum. The biodegradability of both systems fed with the original samples (56-59%) was lower than that of the two systems fed with HTP-treated samples (64-67%), which demonstrates the advantage of HTP (regardless of the fermentation reactor configuration).

[0109] In batch BMP testing, besides methane production yield, methane generation rate is also a key process response parameter for evaluating the biodegradability of the substrate. The methane generation rates of the HTP-treated feed and the original feed are shown... Figure 19 and 20 In the BMP test, given that the inoculum and substrate were identical, no significant hysteresis phase was observed for any of the samples. Two main peaks were observed for all samples throughout the test. The first peak, associated with the largest methane production, occurred between days 2 and 4 for the pretreated samples and between days 2 and 3 for the original samples. A second minor peak was detected during week 2 of the test, coinciding with the initiation of slow-biodegradable organic matter degradation. Furthermore, the methane production rate of the HTP-treated samples was demonstrated by the detection of a maximum methane production of 64 mL CH4 / g of added COD.

[0110] Furthermore, BMP data indicate that the application of vacuum enhances methane production by up to 25% compared to conventional reactors without vacuum. The maximum methane production for the HTP-treated sample in the vacuum reactor was 64 mL CH4 / g added COD, while this decreased to 48 mL CH4 / g added COD in the conventional reactor. The effect of vacuum application in improving methane production is likely related to the high solubility during vacuum fermentation, resulting from high heat and microbial activity, ultimately producing a large amount of readily biodegradable compounds for AD. In conclusion, the novel configuration of HTP and a vacuum reactor improves VFA production and demonstrates excellent results in terms of methane production rate and yield.

[0111] According to this embodiment, integrating a vacuum into the fermentation reactor results in the following benefits: (1) Vacuum application enhances mass transfer due to bubbling during reactor operation above the boiling point, and the possibility of simultaneously concentrating solids and evaporating liquids; (2) Fermentation process performance is enhanced by removing inhibitory substances generated during the fermentation process. VFA yield is increased by approximately 40% through vacuum application; (3) Acid accumulation is controlled by continuously extracting VFA from the system. The integration of HTP with vacuum fermentation results in the following additional benefits: (1) accelerated fermentation process and reduced required HRT to 1.5 days; (2) enhanced fermentation productivity, i.e., higher VFA yield (330 mg COD / g VSS) in vacuum fermentation (using HTP) compared to conventional fermentation (using HTP) (210 mg COD / g VSS); (3) enhanced solubility (45% for vacuum (using HTP) and 39% for conventional (using HTP)) and improved solids reduction efficiency; and (4) reduced energy required to heat the fermenter, as pretreated TWAS provides additional heat to the fermenter, i.e., excellent insulation and minimal heat loss; the heated substrate is sufficient to maintain the fermenter temperature at the required temperature or at least reduce the energy input required to heat the fermenter.

[0112] Example 3

[0113] The microbial communities of a novel configuration combining hydrothermal treatment and vacuum fermentation were investigated, thus comparing the application of vacuum fermentation with conventional, HTP-based, and HTP-free treatments. In the investigation, each semi-continuous system operated under similar conditions for approximately 20 days using a feed of TWAS + raw PS at HTP (170°C and 30-minute response time) and HRT (1.5 days).

[0114] Genomic DNA was extracted from biomass using the PowerSoil DNA Isolation Kit (MoBio Laboratories Inc.). DNA samples were sent to the Genome Quebec Research and Testing Laboratory in Montréal, Quebec, for 16S rRNA gene sequencing (Illumina MiSeq). DNA samples were amplified using PCR for amplicon preparation. The V3-V4 region of the 16S rRNA gene was amplified using primers 347F (GGAGGCAGCAGTRRGGAAT) and 803R (CTACCRGGGT ATCTAATCC). A second PCR reaction was performed to integrate sample-specific barcodes. The DNA concentration of all PCR reactions was measured using Picogreen to ensure that all samples at equimolar concentrations were available for sequencing. Amplicon libraries with insert sizes of approximately 450 bases were sequenced using the Paired End 250 Kit (Illumina MiSeq). The 16S rRNA gene sequences were used to generate an Operational Taxonomic Unit (OTU) table and corresponding FASTA files. Analysis was performed at the Canadian Centre for Computational Genomics, McGill University. The analysis was conducted using the GenPipes version 4.0.0 (Bourgey et al., 2019) amplicon sequencing pipeline. This pipeline was based on the DADA2 package in the R environment. First, trimming was performed using Trimmomatic (Bolger et al., 2014), removing 16 bp from the beginning of each read. Then, 5,308,340 paired-end reads were passed through the applied quality filtering parameters [truncLen=c(234,234); max N = 0; max EE=c(2,2); trunc Q =2], with an average of 186,983 reads / sample, and were thus merged (minimum overlap 20 bp) and underwent de novo chimera removal. The resulting amplicon sequence variants (ASVs) were classified using the Silva database version 123.

[0115] The results showed that a rich microbial population was observed in all four systems (no HTP, no vacuum; no HTP, vacuum; HTP, no vacuum; and HTP, vacuum). The most abundant bacterial types were Coprothermobactereota, followed by Synergistetes, Thermotogae, and Firmicutes, which are primarily anaerobic bacteria that grow under thermophilic conditions (55°C–70°C). The presence of these bacteria indicates that anaerobic conditions were well maintained during the experiment. Not all of the aforementioned bacteria were detected in the feed.

[0116] Alpha diversity measurements evaluated the richness of microbial community diversity compared between control and vacuum fermentation reactors. The number of amplicon sequence variants (ASVs) observed in both systems gradually decreased with fermentation time, indicating lower diversity in these systems as the fermenters grew into the dominant microbial community. ASVs decreased in all systems during the steady-state period compared to start-up, indicating good reactor (fermenter) performance. Furthermore, the application of vacuum showed a significant impact on alpha diversity. For all sample points, ASVs used in the vacuum reactor were 15–20% lower than those in the conventional reactor. Considering the steady-state data, the mean ASV values ​​for the vacuum and conventional reactors were 14 and 16, respectively. Typically, 10 phyla types were detected in the fermented samples in both reactors, while the lower number of phyla in the vacuum reactor confirmed the effect of vacuum on changes in microbial structure. The dominant bacteria present in all samples were divided into two main phyla (fecal thermobacters and symtrophic bacteria), followed by Firmicutes, Thermomycota, Actinobacteria, and Euryarchaeota. Furthermore, Euryarchaeota phylum (an archaea responsible for methane production) was completely suppressed as the reactor pH increased during fermentation. During the steady-state phase of fermentation, the mean relative abundance of fecal thermobacters in the vacuum and conventional systems was 75% and 65%, respectively, compared to 15% and 25% for symtrophic bacteria, confirming favorable conditions for each phylum.

[0117] Given the significant differences in the observed ASV counts, hydrothermal treatment significantly impacted microbial community diversity. Regardless of the fermentation technology, the ASV counts of HTP-treated samples were higher than those of the original samples. Compared to the original samples, HTP-treated samples from vacuum and conventional systems showed an increase of approximately 12% and 20% in ASV values, respectively. This increased diversity in HTP-treated samples is likely due to changes in the chemical composition of the feed and the elimination of bacteria present in the TWAS during HTP. Furthermore, results from α-diversity analysis indicate that the type of fermentation reactor is a key factor in microbial diversity richness when the system is fed with HTP-treated sludge. Conversely, without hydrothermal treatment, the type of technology did not have a significant impact on microbial community diversity. Moreover, relative abundance analysis further demonstrated the effect of HTP on microbial communities and the enrichment of specific bacterial communities. The dominant bacterial types found in HTP-treated samples from both systems and the original sample from the vacuum system were *Femtobacter* and *Symtrophozoa*, while for the original-conventional samples, *Thermobacter* and *Symtrophozoa* were the most abundant phyla. HTP has been shown to nourish and accelerate the growth of thermophilic bacteria.

[0118] In addition to the starter culture and hydrolytic bacteria, small communities of methanogens and nitrifying bacteria were observed at low percentages. The low relative abundance of archaea and bacteria (such as *Gastroarchaea* (methane producers) and *Planctomycetes* (nitrifying bacteria)) indicates excellent fermentation performance and configuration that mitigates the function and growth rate of the inhibitory microbial community.

[0119] In all the systems studied, bacteria were the dominant microbial community. Microbial community analysis showed that the application of vacuum fermentation significantly affected microbial diversity and composition. This effect was confirmed by the lower ASV values ​​under vacuum compared to conventional reactors and the presence of abundant fecal thermobacterial and symbiotic communities in the vacuum system. Furthermore, hydrothermal HTP treatment enriched the thermophilic microbial community and exhibited a higher ASV value than the original samples.

[0120] Although specific embodiments are described herein, the scope of the invention is not limited to these specific embodiments. The scope of the invention is defined by the appended claims and any equivalents thereof. As will be understood by those skilled in the art, aspects of this disclosure can be embodied in apparatus, systems, or methods.

[0121] The diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of apparatus and methods according to various embodiments of this disclosure. In this regard, each block or feature in the drawings may represent a module, segment, or portion of the method or apparatus, and the functions indicated therein may occur in a non-linear order as shown in the drawings. For example, two blocks or features shown consecutively may actually be executed substantially simultaneously, or these blocks or features may sometimes be executed in reverse order, depending on the functions involved.

Claims

1. A method for treating a fluid comprising a particulate portion and a soluble portion, the method comprising: The fluid is fed into a hydrothermal treatment apparatus and heated to a temperature of 121°C to 300°C to obtain a treated fluid; The hydrothermally treated fluid is then fed into the reactor, wherein at least the particulate portion undergoes fermentation or anaerobic digestion, wherein the treated fluid is subjected to vacuum pressure upstream of the fermentation or anaerobic digestion in the process direction, during the fermentation or anaerobic digestion, or downstream of the fermentation or anaerobic digestion in the process direction. If the vacuum pressure is applied during the fermentation or anaerobic digestion, the reactor is a vacuum integrated reactor, and the method includes collecting at least a portion of the soluble portion of the fluid as condensate from the vacuum integrated reactor and collecting residual gas, thereby thickening the remaining portion of the fluid. If the vacuum pressure is applied upstream or downstream of the fermentation or anaerobic digestion in the vacuum integrated processing unit, the method includes collecting at least a portion of the soluble portion of the fluid, which comprises water and gas, as condensate from the treated fluid or from the treated and fermented or anaerobic digested fluid, and collecting residual gas, thereby thickening the remaining portion of the fluid. as well as Recover the thickened fluid.

2. The method according to claim 1, wherein the reactor is a vacuum integrated reactor selected from a vacuum integrated fermenter or a vacuum integrated digester.

3. The method according to claim 1, wherein the heating in the hydrothermal treatment apparatus is carried out at a pressure of 2 to 10 bar and a temperature of 130 to 300°C for 5 to 100 minutes.

4. The method according to claim 1, wherein the fluid is thickened waste activated sludge with a solid content of 1% to 16%.

5. The method of claim 1, wherein, prior to feeding the hydrothermally treated fluid into the reactor, the treated fluid is mixed with an additional fluid comprising a particulate portion and a soluble portion, the additional fluid having a higher degree of biodegradability than the treated fluid.

6. The method according to claim 1 or 2, wherein the vacuum pressure is 10 to 750 millibars.

7. The method of claim 6, wherein the vacuum is applied intermittently during the fermentation or anaerobic digestion.

8. The method according to claim 1, wherein water evaporation and volatile stripping are achieved by pressure and temperature variations between the hydrothermal treatment apparatus and the vacuum integrated reactor or vacuum integrated treatment unit, and the efficiency of evaporation and volatile stripping is further enhanced by adjusting the pH and conductivity of the treated fluid.

9. The method of claim 1, wherein heat is extracted from the condensate and used to heat the fluid in the hydrothermal treatment apparatus.

10. The method of claim 1, wherein the recovered thickened fluid is subjected to further processing, said further processing comprising one or more of anaerobic digestion, dehydration, and post-pasteurization.

11. The method of claim 1, wherein the condensate is subjected to further processing including denitrification or biomethanation.

12. The method of claim 1, wherein the fluid is subjected to a treatment selected from the group consisting of anaerobic digestion and pre-pasteurization before being fed into the hydrothermal treatment apparatus.

13. The method of claim 1, wherein the method further comprises feeding at least a portion of the recovered thickened fluid into a bionutrient removal process.

14. The method of claim 1, wherein the method further comprises cooling the hydrothermally treated fluid to below 75°C before feeding the hydrothermally treated fluid into the reactor.

15. The method of claim 1, wherein the fluid is subjected to heating to a temperature of 121°C to 180°C to obtain a treated fluid.

16. The method of claim 1, wherein the fluid is heated at a pressure of 1.1 to 10 bar to obtain the treated fluid.

17. The method of claim 1, wherein the total suspended solids of the hydrothermally treated fluid are 10% to 40% lower than the total suspended solids of the fluid before hydrothermal treatment, and the volatile suspended solids of the hydrothermally treated fluid are 10% to 50% lower than the volatile suspended solids of the fluid before hydrothermal treatment.

18. A system for treating a fluid comprising a particulate portion and a soluble portion, the system comprising: A hydrothermal treatment apparatus configured to treat a fluid fed into it by heating. A reactor downstream of the hydrothermal treatment apparatus in the process direction, the reactor being configured to receive treated fluid from the hydrothermal treatment apparatus and subject the treated fluid to fermentation or anaerobic digestion, wherein the reactor is selected from: a vacuum integrated reactor with a vacuum pump for applying a vacuum to the vacuum integrated reactor; or a reactor without a vacuum pump. If the reactor is a reactor without a vacuum pump, the system further includes a vacuum integrated processing unit upstream and / or downstream of the reactor in the process direction, the vacuum integrated processing unit including a vacuum pump for applying a vacuum to the vacuum integrated processing unit, and The condensate is removed using the vacuum provided. as well as A controller configured to control the vacuum and the removal of the condensate, and to control the residence time of the particulate portion in the reactor to be at least 25% longer than the residence time of the soluble portion.

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