A device and method for recovering organic matter and phosphorus from sewage

Abstract

This invention discloses a device and method for recovering organic matter and phosphorus from wastewater, belonging to the field of wastewater treatment technology. The method includes the following steps: (1) pumping the wastewater to be treated into a carbon and phosphorus capture tank and inoculating it with sludge to achieve preliminary enrichment of organic matter and phosphorus; (2) pumping the enriched sludge into a pre-oxidation tank and adding ferrate for stirring; (3) pumping the effluent into an anaerobic fermentation tank and adding ethanol to the system for anaerobic fermentation to convert the generated short-chain fatty acids into medium-chain fatty acids; (4) pumping the mixed liquid after anaerobic fermentation into a separation and recovery tank for stirring reaction, settling, and recovering phosphorus in the form of lapis lazuli; (5) returning the sludge settled in the anaerobic fermentation tank to the carbon and phosphorus capture tank through a sludge return system, and the system operates continuously and stably for ≥5 cycles. This invention uses the different valence state transformations of iron and their corresponding compounds as driving factors, and adopts a combination of carbon and phosphorus capture tanks, pre-oxidation tanks, anaerobic fermentation tanks, separation and recovery tanks and sludge return systems. Through biochemical and physicochemical means, microorganisms are regulated to efficiently capture organic matter, and iron compounds synergistically adsorb organic matter and phosphorus, ultimately realizing the recovery of organic matter and phosphorus from wastewater in the form of high-value-added medium-chain fatty acids and lapis lazuli.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and in particular relates to a device and method for recovering organic matter and phosphorus from wastewater. Background Technology

[0002] Traditional wastewater treatment technologies, focusing on pollutant removal, generally suffer from limitations such as high energy consumption, significant carbon emissions, and potential resource waste, neglecting the potential resource value inherent in wastewater. It is estimated that if the organic components in wastewater, characterized by chemical oxygen demand (COD), could be recovered, approximately 30% of wastewater treatment energy consumption could be saved, driving the wastewater treatment industry from an energy-intensive model to one of energy self-sufficiency, and achieving a 35%-50% reduction in carbon footprint. However, current technologies face resource recovery bottlenecks, with organic carbon recovery efficiency generally below 30%. Therefore, innovating existing technologies to achieve efficient resource recovery is urgently needed.

[0003] In recent years, although anaerobic treatment technology has been used to recover methane energy, it still suffers from problems such as long conversion cycles, low product added value, and low carbon recovery rates. Methane, as the main product, has limited market value, and some organic carbon is still lost through metabolic pathways. Therefore, the focus of resource recovery is shifting from low-value energy to high-value-added chemicals, with the stepwise value-added route from short-chain fatty acids (SCFAs) to medium-chain fatty acids (MCFAs) attracting significant attention. SCFAs can be efficiently obtained through anaerobic fermentation, while MCFAs (such as hexanoic acid and octanoic acid) have higher energy density and industrial application value, and can be used as biofuels, food additives, and chemical raw materials, significantly improving the economic benefits of resource recovery. However, this technical route faces two major challenges: first, the concentration of organic matter in wastewater is generally low, making direct and efficient fermentation difficult; second, the biological barrier formed by cell structure and extracellular polymeric substances (EPS) hinders the release and transformation of organic matter, limiting conversion efficiency.

[0004] In summary, existing technologies generally suffer from problems such as low organic carbon recovery rates, limited resource utilization pathways, insufficient high-value conversion, high energy consumption, and strong dependence on reagents. They have not yet achieved efficient and synergistic recovery of multiple resources, including carbon and phosphorus. In particular, there is a lack of an integrated and sustainable technological system capable of efficiently enriching, simultaneously breaking down, and directionally converting low-concentration organic matter into high-value chemicals, while simultaneously achieving stable recovery of phosphorus resources.

[0005] Therefore, there is an urgent need to develop a new process that can reduce energy consumption, break through the bottleneck of resource utilization, and promote the fundamental transformation of wastewater treatment from "pollution control" to "resource factory". Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a device and method for recovering organic matter and phosphorus from wastewater.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A device for recovering organic matter and phosphorus from wastewater includes a carbon and phosphorus capture tank, a pre-oxidation tank, an anaerobic fermentation tank, a separation and recovery tank, and a sludge return system.

[0009] The carbon and phosphorus capture tank, pre-oxidation tank, anaerobic fermentation tank, and separation and recovery tank are connected sequentially by pipelines.

[0010] The inlet of the sludge return system is connected to the sludge outlet of the anaerobic fermentation tank, and the outlet is connected to the inlet of the carbon and phosphorus capture tank.

[0011] Optionally, the sludge from the anaerobic fermentation tank is returned to the carbon and phosphorus capture tank via a timed pump and a sludge return system.

[0012] A method for recovering organic matter and phosphorus from wastewater, comprising the following steps using the aforementioned recovery device:

[0013] (1) Pump the wastewater to be treated into the carbon and phosphorus capture tank and inoculate it with sludge after anaerobic digestion at the end to achieve the initial solid phase enrichment of organic matter and phosphorus in the sludge;

[0014] (2) Pump the enriched sludge into the pre-oxidation tank, adjust the pH value and add ferrate for stirring;

[0015] (3) Pump the pre-oxidized mud-water mixture into the anaerobic fermentation tank, add ethanol to the system for anaerobic fermentation, and convert the short-chain fatty acids produced into medium-chain fatty acids.

[0016] (4) The mixture after anaerobic fermentation is pumped into the separation and recovery tank for stirring and reaction, and then allowed to settle to achieve the recovery of phosphorus in the form of blue iron ore;

[0017] (5) The sludge settled in the anaerobic fermentation tank is returned to the carbon and phosphorus capture tank through the sludge return system, and the system is continuously and stably operated for ≥5 cycles.

[0018] Optionally, the conditions in the carbon and phosphorus capture tank are: temperature of 15~35℃ and pH of 6.5~8.

[0019] Optionally, the concentration of the inoculated sludge in step (1) is 3000~10000 mg / L.

[0020] Optionally, the pH in the pre-oxidation tank is 10-12, and the stirring time is 3-5 minutes.

[0021] Optionally, the amount of ferrate added is 20~40 mg / g VSS (volatile solids concentration).

[0022] Optionally, the pH in the anaerobic fermentation tank is 5-6 and the temperature is 30-35℃.

[0023] Optionally, the molar ratio of ethanol to short-chain fatty acids in the anaerobic fermentation tank is 2-4:1.

[0024] Optionally, the pH in the separation and recovery tank is 7-8.

[0025] Optionally, the sludge in step (5) is 80 wt% of the total sludge volume.

[0026] Compared with the prior art, the present invention has the following advantages and technical effects:

[0027] (1) This invention achieves efficient and simultaneous recovery of carbon and phosphorus in wastewater in a single system for the first time by regulating the entire process of adsorption-release-inhibition mediated by iron.

[0028] (2) The internal circulation of iron is achieved by using recycled sludge, which significantly reduces the additional dosage of ferrate and other reagents and lowers operating costs.

[0029] (3) By precisely controlling the iron ion concentration and pH of the anaerobic fermentation tank, methanogenesis was effectively suppressed, and the carbon flow was directed to the synthesis of high-value medium-chain fatty acids, with a yield significantly higher than that of traditional anaerobic digestion methanogenesis processes.

[0030] In summary, this invention achieves efficient conversion of organic matter and stable recovery of phosphorus from wastewater through a five-step integrated process: adsorption enrichment, oxidation and polymerization, anaerobic upgrading, crystallization recovery, and sludge recirculation. The entire process fully utilizes multiple mechanisms, including microbial EPS (microbial extracellular polymeric substances), ferrate oxidation, iron ion catalysis, and lapis lazuli precipitation, combining high efficiency, resource utilization, and environmental friendliness. It is suitable for the deep treatment and resource recovery of phosphorus-containing organic wastewater, such as urban sewage and industrial wastewater. The recovery process and effects of organic matter, phosphorus, and sludge from wastewater are as follows:

[0031] Organic matter (COD) in wastewater → Carbon and phosphorus capture tank (microbial EPS + iron hydroxide adsorption, retention rate 50~80%) → Pre-oxidation tank (releases organic matter, release rate up to 90%) → Anaerobic fermentation tank (converted into MCFAs, conversion rate up to 70%).

[0032] Phosphorus in wastewater → Carbon and phosphorus capture tank (adsorption of iron and its hydroxides, with a retention rate of up to 91%) → Anaerobic fermentation tank (release of iron ions, with a release rate of up to 85%) → Separation and recovery tank (crystallization of blue iron ore, with a recovery rate of up to 93%).

[0033] Sludge → Carbon and phosphorus capture tank (adsorption) → Pre-oxidation tank (active retention) → Anaerobic fermentation tank (acid production) → Return to carbon and phosphorus capture tank (recycling, recycling times ≥ 5 times). Attached Figure Description

[0034] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0035] Figure 1 This is a process flow diagram of the recovery of organic matter and phosphorus from wastewater disclosed in Embodiment 2 of the present invention. Detailed Implementation

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0037] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0039] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0040] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0041] This invention uses the different valence state transformations of iron and their corresponding compounds as driving factors. It employs a combination of carbon and phosphorus capture tanks, pre-oxidation tanks, anaerobic fermentation tanks, separation and recovery tanks, and sludge return systems. Through biochemical and physicochemical means, it regulates microorganisms to efficiently capture organic matter, and iron compounds synergistically adsorb organic matter and phosphorus, ultimately achieving the recovery of organic matter and phosphorus from wastewater in the form of high-value-added medium and long-chain fatty acids and lapis lazuli.

[0042] This invention discloses a device for recovering organic matter and phosphorus from wastewater. The device consists of a carbon and phosphorus capture tank, a pre-oxidation tank, an anaerobic fermentation tank, a separation and recovery tank, and a sludge return system.

[0043] In the carbon and phosphorus capture tank, microbial extracellular polymeric substances (EPS) and iron and its hydroxide colloids carried by sludge recirculation synergistically adsorb organic matter and phosphorus in wastewater, while controlling the temperature at 15~35℃, pH at 6.5~8, and sludge concentration at 3000~10000 mg / L.

[0044] Adjust the pH in the pre-oxidation tank to 10-12, add 20-40 mg / g VSS ferrate, and stir for 3-5 minutes to break up sludge aggregates without damaging the microbial cell membranes.

[0045] The pH is controlled at 5-6 and the temperature at 30-35℃ in the anaerobic fermentation tank. The iron ions after the ferrate of sludge is oxidized and ethanol (ethanol: short-chain fatty acids = 2:1-4:1) is added for fermentation, and the short-chain fatty acids produced are converted into medium-chain fatty acids.

[0046] The pH in the separation and recovery tank is adjusted to 7-8 to achieve phosphorus recovery via lapis lazuli crystallization.

[0047] The sludge return system returns the sludge from the sedimentation zone of the anaerobic fermentation tank to the carbon and phosphorus capture tank.

[0048] In some alternative embodiments, the carbon and phosphorus capture tank is provided with a stirring zone and a sedimentation zone, which are used for mixing and separating sludge and wastewater, respectively.

[0049] In some alternative embodiments, the pre-oxidation tank is equipped with a pH adjustment system and a dosing system.

[0050] In some alternative embodiments, the anaerobic fermentation tank is equipped with a stirring zone, a dosing system, and a mud-water separation zone.

[0051] In some alternative embodiments, the separation and recovery tank includes a mixing and sedimentation zone, as well as a pH adjustment system.

[0052] This invention also discloses a method for recovering organic matter and phosphorus from wastewater using the above-mentioned device, comprising the following steps:

[0053] During operation, wastewater containing organic matter is mixed with sludge from the sludge return system in the carbon and phosphorus capture tank. Under anaerobic conditions, EPS (expanded phosphorus permeable) adsorbs the organic matter in the wastewater, while Fe in the sludge is also adsorbed. 2+ / Fe 3+ The resulting colloidal compounds adsorb phosphorus from the wastewater and further enhance the adsorption of organic matter. During this process, iron ions also promote the decomposition of complex organic matter by microorganisms, synthesizing their own proteins and other organic matter. Solid-liquid separation then occurs in the sedimentation zone; the solid phase flows into the pre-oxidation tank, while the liquid phase is discharged.

[0054] In some alternative embodiments, Fe in the ferrate is utilized after pre-oxidation. 6+ The production of ·OH oxidizes the extracellular polymers in the sludge, breaking down the aggregates and resulting in sludge particle size of less than 0.5 mm. The integrity of the microbial cell membrane in the sludge is ≥85%, and the dehydrogenase activity is ≥150 μgTF / (gVSS・h).

[0055] In some optional embodiments, the sludge pretreated in the pre-oxidation tank undergoes anaerobic fermentation in an anaerobic fermentation tank. This decomposes the adsorbed organic matter and extracellular polymeric substances (EPS) from the broken-up sludge aggregates. Simultaneously, the total iron ion concentration in the sludge is controlled to be greater than 300 mg / L to inhibit methanogenic bacteria activity, promoting the oxidation of organic matter to short-chain organic acids. The existing iron ions in the sludge and the addition of ethanol regulate the conversion of small-molecule organic acids into medium-chain fatty acids. The anaerobic process promotes the release of phosphorus from the sludge into the liquid phase. During fermentation, the sludge secretes extracellular polymeric substances again, forming new aggregates. The fermented sludge-water mixture enters a sedimentation zone for sedimentation. The sludge is returned to the carbon and phosphorus capture tank via a sludge return system, while the liquid phase enters a separation and recovery tank.

[0056] In some alternative embodiments, medium-chain fatty acids (C6-C6) in the anaerobic digester 12 The yield of ) is ≥0.4g / g COD, of which hexanoic acid and octanoic acid account for ≥70wt%.

[0057] Unless otherwise specified, "room temperature" in this invention refers to 20-30℃.

[0058] Unless otherwise specified, the term "parts" in this invention refers to parts by weight.

[0059] All raw materials used in this invention were purchased from the market.

[0060] The wastewater to be treated in Example 2 and Comparative Example 1 below was as follows: Simulated wastewater: COD = 400 mg / L (simulated with glucose and peptone), total phosphorus = 8 mg / L. Inoculated sludge: sludge taken from the anaerobic digester of a municipal wastewater treatment plant, with an MLSS of approximately 8000 mg / L.

[0061] The technical solution of the present invention will be further illustrated by the following embodiments.

[0062] Example 1

[0063] A device for recovering organic matter and phosphorus from wastewater includes a carbon and phosphorus capture tank (equipped with a stirring zone and a sedimentation zone), a pre-oxidation tank (equipped with a pH adjustment system and a dosing system), an anaerobic fermentation tank (equipped with a stirring zone, a dosing system and a sludge-water separation zone), a separation and recovery tank (equipped with a mixing and sedimentation zone and a pH adjustment system), and a sludge return system.

[0064] The carbon and phosphorus capture tank, pre-oxidation tank, anaerobic fermentation tank, and separation and recovery tank are connected sequentially by pipelines.

[0065] The inlet of the sludge return system is connected to the sludge outlet of the anaerobic fermentation tank, and the outlet of the sludge return system is connected to the inlet of the carbon and phosphorus capture tank. The sludge is returned by a timed pump.

[0066] Example 2

[0067] like Figure 1 As shown, the recycling process is performed using the recycling device in Example 1:

[0068] (1) The wastewater to be treated enters the carbon and phosphorus capture tank. Under the conditions of temperature 25℃, pH 7, HRT (hydraulic retention time) 1 hour and inoculated sludge concentration of 6000 mg / L, the extracellular polymeric substances (EPS) secreted by microorganisms and the iron hydroxide colloids from the sludge return system work together to efficiently adsorb organic matter and phosphate in the wastewater, thus achieving the initial enrichment of organic matter and phosphorus. The COD of the effluent from the carbon and phosphorus capture tank is reduced to ~80 mg / L and the phosphorus is reduced to ~0.8 mg / L.

[0069] (2) Subsequently, the mixed liquor carrying the enriched sludge was introduced into the pre-oxidation tank, the pH was adjusted to 11, and ferrate was added at a ratio of 30 mg / g VSS. Under stirring for 4 minutes, the sludge aggregates were broken up without damaging the microbial cell membranes. Results: The sludge particle size decreased from the initial ~800 μm to ~200 μm; the cell integrity rate was >90% as detected by microscopy; the dehydrogenase activity was 180 μg TF / (g VSS・h); and the COD of the supernatant increased by 90% compared with the influent, indicating the release of organic matter.

[0070] (3) Next, the effluent enters the anaerobic fermentation tank. Under the conditions of pH 5.5 and temperature 35℃, the hydraulic retention time is 3 days. Ethanol is added to the system: the total iron ion concentration of the system is measured to be approximately 350 mg / L. Ethanol is added in pulses daily, and the theoretical molar ratio of ethanol to short-chain fatty acids entering the fermentation tank is controlled to be 3:1. That is, the iron ions after oxidation of ferrate in sludge and the addition of ethanol are used for fermentation to convert the produced short-chain fatty acids into medium-chain fatty acids. The phosphorus release rate from the sludge into the liquid phase reaches 95%.

[0071] (4) After that, the fermented mixture enters the separation and recovery tank, the pH is adjusted to 7.8, and the reaction is carried out for 2 hours under slow stirring (50 rpm). After settling, phosphorus is recovered by crystallization of blue iron ore.

[0072] (5) Finally, the sludge settled in the anaerobic fermentation tank (accounting for 80% of the total sludge) is returned to the carbon and phosphorus capture tank, and the system has been running continuously and stably for more than 5 cycles.

[0073] Results and Detection:

[0074] Carbon recovery: The effluent from the anaerobic fermentation tank was tested and found to contain 4500 mg COD / L of medium-chain fatty acids (mainly hexanoic acid and octanoic acid). The yield was calculated to be 0.45 g COD / g COD (based on influent COD), with hexanoic acid and octanoic acid accounting for 75%.

[0075] Phosphorus recovery: A blue precipitate was observed at the bottom of the separation and recovery tank. X-ray diffraction analysis confirmed it to be vivianite. The calculated phosphorus recovery efficiency was 91%.

[0076] Sludge return: The sludge settled in the separation and recovery tank (accounting for 80% of the total sludge) is returned to the carbon and phosphorus capture tank. The system has been running continuously and stably for more than 5 cycles, and the carbon and phosphorus recovery efficiencies have been maintained at over 70% and 90% respectively in each cycle.

[0077] Example 3

[0078] This embodiment uses a recovery device with the same structure as that in Embodiment 1, targeting the treatment of urban domestic sewage (actual influent water quality: COD=350mg / L, total phosphorus=7mg / L) under low-temperature conditions. The specific recovery process is as follows:

[0079] (1) Operation and control of the carbon and phosphorus capture tank: The municipal sewage to be treated was pumped into the carbon and phosphorus capture tank, and the temperature was controlled at 15℃ (simulating the low temperature conditions in northern winter), pH=6.5, and the hydraulic retention time (HRT) was extended to 1.5 hours. Sludge from the anaerobic digestion process was inoculated, and the sludge concentration (MLSS) was adjusted to 10000 mg / L. Through the synergistic effect of microbial extracellular polymers (EPS) and iron hydroxide colloids carried by sludge recirculation, the adsorption of organic matter and phosphorus in sewage at low temperature was enhanced. The operation results showed that the COD of the effluent from the carbon and phosphorus capture tank was reduced to 95 mg / L, the total phosphorus was reduced to 0.9 mg / L, the organic matter retention rate reached 72.9%, and the phosphorus retention rate reached 87.1%, which met the initial enrichment requirements under low temperature conditions.

[0080] (2) Pre-oxidation tank treatment: The enriched sludge mixture was pumped into the pre-oxidation tank, and the pH was adjusted to 10 (lower than the pH value in Example 2, to explore the oxidation effect under low alkalinity conditions). Ferrate was added at a ratio of 20 mg / g volatile solids (VSS), and the mixture was stirred for 3 minutes (the shortest stirring time parameter). Testing showed that the sludge particle size decreased from the initial ~750 μm to ~300 μm, the microbial cell membrane integrity rate reached 85% (meeting the activity retention requirements), the dehydrogenase activity was 150 μg TF / (g VSS・h), and the COD of the supernatant increased by 85% compared to the influent, achieving effective release of organic matter.

[0081] (3) Anaerobic fermentation tank reaction: The pre-oxidized sludge-water mixture was pumped into the anaerobic fermentation tank, and the pH was controlled at 5 (lower limit of acidity), the temperature at 30℃ (lower limit of mesothermal range), and the hydraulic retention time was 3 days. The total iron ion concentration was measured to be 320 mg / L. Ethanol was added at a molar ratio of ethanol to short-chain fatty acids of 2:1 (minimum molar ratio) to inhibit the activity of methanogens and promote the conversion of short-chain fatty acids to medium-chain fatty acids. After fermentation, the medium-chain fatty acids (C6-C6) in the anaerobic fermentation tank were measured. 12 The concentration was 3800 mg COD / L, and the yield reached 0.42 g / g COD, of which hexanoic acid and octanoic acid accounted for 70%, meeting the requirements for high-value conversion; at the same time, the phosphorus release rate from the sludge to the liquid phase reached 82%.

[0082] (4) Phosphorus recovery in the separation and recovery tank: The anaerobic fermentation mixture was pumped into the separation and recovery tank, the pH was adjusted to 7 (lower limit of neutrality), and the mixture was stirred slowly at 40 rpm for 2.5 hours, followed by settling. Blue precipitate was collected at the bottom of the separation and recovery tank, and X-ray diffraction analysis confirmed it to be vivianite. The phosphorus recovery efficiency was calculated to be 90%.

[0083] (5) Sludge return and stable system operation: The sludge settled in the anaerobic fermentation tank (accounting for 80% of the total sludge) is returned to the carbon and phosphorus capture tank through the sludge return system via a timed pump. The system operates continuously and stably for 5 cycles.

[0084] Monitoring results showed that the carbon and phosphorus recovery efficiencies remained stable at over 70% and 89% in the five cycles, respectively, without significant efficiency decline, verifying the stability of the system under low temperature and low reagent dosage conditions.

[0085] Example 4

[0086] This embodiment uses the recovery device from Example 1 to treat high-concentration industrial organic wastewater (actual influent water quality: COD=800mg / L, total phosphorus=12mg / L, containing a small amount of industrial additives). The specific steps are as follows:

[0087] (1) Carbon and phosphorus capture tank enrichment: The industrial wastewater to be treated is pumped into the carbon and phosphorus capture tank, and the temperature is controlled at 35℃ (high temperature condition), pH=8 (upper limit of alkalinity), HRT=1.2 hours, and the concentration of inoculated sludge is adjusted to 3000mg / L (minimum sludge concentration parameter). The high temperature environment enhances the metabolic activity of microorganisms, and combined with the adsorption of iron hydroxide colloids, the rapid enrichment of organic matter and phosphorus is achieved. The operation results show that the effluent COD is reduced to 160mg / L, the total phosphorus is reduced to 1.08mg / L, the organic matter retention rate reaches 80%, and the phosphorus retention rate reaches 91%, which effectively meets the enrichment needs of high-concentration organic wastewater.

[0088] (2) Enhanced Aggregate Breaking in the Pre-oxidation Tank: The enriched sludge mixture enters the pre-oxidation tank, the pH is adjusted to 12 (upper limit of alkalinity), and ferrate is added at 40 mg / g VSS (maximum ferrate dosage), and stirred for 5 minutes (maximum stirring time). After treatment, the sludge particle size is reduced to ~150 μm, the microbial cell membrane integrity rate reaches 88%, the dehydrogenase activity is 180 μg TF / (g VSS・h), and the COD of the supernatant is increased by 90% compared with the influent, effectively breaking down the biological barrier formed by sludge aggregates and extracellular polymers (EPS) in industrial wastewater.

[0089] (3) High-value conversion in anaerobic fermentation tank: The mud-water mixture enters the anaerobic fermentation tank, and the pH is controlled at 6 (upper limit of acidity), the temperature at 35℃, and the HRT at 3 days. The total iron concentration of the system is detected to be 400 mg / L. Ethanol is added at a molar ratio of 4:1 (maximum molar ratio) to short-chain fatty acids to enhance the stepwise conversion of short-chain fatty acids to medium-chain fatty acids. After fermentation, the concentration of medium-chain fatty acids reaches 9200 mg COD / L, the yield is 0.45 g / g COD, and the proportion of hexanoic acid and octanoic acid reaches 78%, which is significantly higher than that of traditional anaerobic processes; the phosphorus release rate into the liquid phase reaches 85%.

[0090] (4) Phosphorus purification in the separation and recovery tank: The mixed liquid enters the separation and recovery tank, the pH is adjusted to 8 (the upper limit of alkalinity), the mixture is stirred at 50 rpm for 2 hours, and then allowed to settle. The collected blue iron ore precipitate was tested and found to have a purity of 95% and a phosphorus recovery efficiency of 93%, which meets the industrial-grade phosphorus resource recovery standard.

[0091] (5) Sludge return and long-term operation: 80% of the sludge settled in the anaerobic fermentation tank was returned to the carbon and phosphorus capture tank, and the system operated continuously for 6 cycles. Monitoring data showed that the carbon recovery efficiency remained stable at over 72% and the phosphorus recovery efficiency remained above 92% during the 6 cycles, and no problems of reagent residue or sludge bulking occurred. This verified the long-term stability of the system under high temperature and high reagent dosage conditions, and it is suitable for continuous resource recovery and treatment of industrial wastewater.

[0092] Comparative Example 1

[0093] The only difference from Example 2 is that no ethanol is added to the anaerobic fermentation tank.

[0094] Results: The main anaerobic fermentation products were acetic acid and propionic acid, with almost no hexanoic acid and octanoic acid detected. The yield of MCFAs was <0.05 g / g COD; the phosphorus recovery efficiency was 90%. This comparative example demonstrates that ethanol addition is crucial for chain elongation.

[0095] Comparative Example 2: Comparative Test of Sludge-Free Recirculation System

[0096] The only difference between this comparative example and the recovery device in Example 1 is that the sludge return system is removed, and the sludge settled in the anaerobic fermentation tank is not returned to the carbon and phosphorus capture tank. All other recovery parameters remain the same as in Example 2. The simulated wastewater (COD = 400 mg / L, total phosphorus = 8 mg / L) is treated using the following specific steps:

[0097] (1) Operation of the carbon and phosphorus capture tank: The simulated wastewater to be treated was pumped into the carbon and phosphorus capture tank, and the temperature was controlled at 25°C, pH=7, and HRT=1 hour. The initial sludge concentration was adjusted to 6000 mg / L (consistent with the initial concentration in Example 2), and there was no sludge return replenishment. After one cycle of operation, due to the loss of sludge with the effluent, the MLSS in the carbon and phosphorus capture tank dropped to 3500 mg / L; after three cycles of operation, the MLSS further dropped to 1800 mg / L, which is below the range of 3000~10000 mg / L.

[0098] (2) Pre-oxidation tank treatment: The enriched sludge mixture was pumped into the pre-oxidation tank, the pH was adjusted to 11, and ferrate was added at 30 mg / g VSS, and stirred for 4 minutes. In one cycle, the sludge particle size decreased from the initial ~800 μm to ~220 μm, and the cell integrity rate was 88%; in three cycles, due to the low sludge concentration, the sludge aggregates were not sufficiently broken down, the particle size only decreased to ~450 μm, the cell integrity rate dropped to 75%, and the increase in COD of the supernatant was 30% lower than that in Example 2.

[0099] (3) Anaerobic fermentation tank reaction: The pre-oxidized sludge-water mixture was pumped into the anaerobic fermentation tank, and the pH was controlled at 5.5, the temperature at 35℃, and the HRT at 3 days. Ethanol was added at a molar ratio of ethanol to short-chain fatty acids of 3:1. In one cycle, the concentration of medium-chain fatty acids was 3200 mg COD / L, the yield was 0.32 g / g COD, and the proportion of hexanoic acid and octanoic acid was 65%. In three cycles, due to the decrease in the enrichment efficiency of the carbon and phosphorus capture tank, the organic matter entering the fermentation tank was insufficient, the concentration of medium-chain fatty acids dropped to 1800 mg COD / L, the yield was only 0.18 g / g COD, the proportion of hexanoic acid and octanoic acid dropped to 50%, and the total iron ion concentration dropped from 350 mg / L in Example 2 to 180 mg / L, which could not effectively inhibit methanogenic bacteria. The amount of methane generated was detected to be 40% higher than that in Example 2.

[0100] (4) Phosphorus recovery in the separation and recovery tank: The mixed liquor after anaerobic fermentation is pumped into the separation and recovery tank, the pH is adjusted to 7.8, and the mixture is stirred at 50 rpm for 2 hours, followed by settling. In one cycle, the phosphorus recovery efficiency is 82%; in three cycles, due to the decrease in phosphorus retention rate in the carbon-phosphorus capture tank (from 91% in Example 2 to 65%), and the decrease in phosphorus release rate in the anaerobic fermentation tank to 60%, the phosphorus recovery efficiency is only 58%, which is far lower than the index of over 90% in the present invention.

[0101] (5) System stability: After 5 consecutive cycles, the carbon recovery efficiency was 32%, 25%, 18%, 12% and 8% respectively in the first to fifth cycles, and the phosphorus recovery efficiency was 82%, 70%, 58%, 45% and 38% respectively. All showed a significant decline trend, and the fifth cycle could not meet the basic recovery requirements.

[0102] Conclusion: This comparative study demonstrates that a sludge recirculation system is crucial for maintaining sludge concentration in the carbon and phosphorus capture tank, ensuring iron circulation, and achieving continuous and stable system operation. Without sludge recirculation, not only does the carbon and phosphorus recovery efficiency decrease significantly, but the system also fails to meet the requirement of stable operation for ≥5 cycles, highlighting the necessity of sludge recirculation technology.

[0103] Comparative Example 3: A comparative experiment in which no ferrate was added to the pre-oxidation tank.

[0104] This comparative example uses the recovery device from Example 1. No ferrate is added to the pre-oxidation tank; only the pH is adjusted to 11 and stirred for 4 minutes. All other steps and parameters are identical to those in Example 2. The simulated wastewater (COD = 400 mg / L, total phosphorus = 8 mg / L) was treated, and the results are as follows:

[0105] (1) Carbon and phosphorus capture tank: The operation effect is similar to that of Example 2. The COD of the effluent is reduced to ~85mg / L, the total phosphorus is reduced to ~0.85mg / L, the organic matter retention rate is 83.7%, and the phosphorus retention rate is 89.4%. It is not affected by the absence of ferrate in the pre-oxidation tank.

[0106] (2) Pre-oxidation tank: The sludge aggregates were poorly broken down by pH adjustment and stirring alone. The sludge particle size only decreased from the initial ~800μm to ~650μm, failing to meet the requirement of "sludge particle size less than 0.5mm" (reduced to ~200μm in Example 2). Microbial extracellular polymers (EPS) were not effectively broken down, and the COD of the supernatant only increased by 25% compared to the influent, far lower than the increase of more than 80% in Example 2, indicating a serious deficiency in the release of organic matter.

[0107] (3) Anaerobic fermentation tank: Because the organic matter entering the fermentation tank is not fully released, and there is no Fe provided by ferrate. 6 + Converted to Fe 3 + Iron ions were supplemented, and the total iron ion concentration in the system was only 120 mg / L, lower than the 350 mg / L in Example 2. After anaerobic fermentation, the medium-chain fatty acid concentration was only 1500 mg COD / L, with a yield of 0.15 g / g COD, which did not meet the standard of "medium-chain fatty acid yield ≥ 0.4 g / g COD" of this invention. Moreover, the proportion of hexanoic acid and octanoic acid was only 40%, while the proportion of short-chain fatty acids (acetic acid and propionic acid) reached 60%, and the methane production increased by 60% compared with Example 2.

[0108] (4) Separation and recovery tank: Because the phosphorus release rate of the anaerobic fermentation tank decreased from 85% in Example 2 to 45%, the phosphorus recovery efficiency was only 48%. The amount of blue iron ore precipitate collected was very small, and it was mixed with a large number of unbroken sludge particles. The purity was only 65%, which did not meet the requirements for industrial-grade phosphorus resource recovery.

[0109] (5) System operation: After 5 consecutive cycles, the carbon recovery efficiency was stable at 15%~18% and the phosphorus recovery efficiency was stable at 45%~50%, which were far lower than the efficiency of 70% and 90% or more in Example 2. Moreover, the sludge gradually expanded due to the accumulation of EPS, and the sludge floated up in the carbon and phosphorus capture tank in the 5th cycle.

[0110] Conclusion: This comparative study verifies the core role of ferrate in the pre-oxidation tank—by oxidizing and breaking down EPS and sludge aggregates, it provides sufficient organic matter for subsequent anaerobic fermentation and supplements iron ions to inhibit methanogens. Without ferrate, organic matter release, medium-chain fatty acid conversion, and phosphorus recovery all fail to meet targets, proving that ferrate addition is an indispensable step in the method of this invention.

[0111] Comparative Example 4: Comparative test on the pH deviation of the anaerobic fermentation tank from the range of the embodiments of the present invention.

[0112] This comparative example uses the recovery device from Example 1, adjusting the pH of the anaerobic fermentation tank to 7.0 (exceeding the range of Examples 5-6 of this invention). The remaining steps and parameters are completely consistent with Example 2. Simulated wastewater (COD = 400 mg / L, total phosphorus = 8 mg / L) was treated, and the results are as follows:

[0113] (1) Carbon and phosphorus capture tank and pre-oxidation tank: The operation effect is basically the same as that in Example 2. The COD of the effluent from the carbon and phosphorus capture tank is ~82mg / L and the total phosphorus is ~0.78mg / L; the sludge particle size in the pre-oxidation tank is reduced to ~210μm, the cell integrity rate is 91%, the COD of the supernatant is increased by 82%, and it is not affected by the pH change of the anaerobic fermentation tank.

[0114] (2) Anaerobic fermentation tank: At pH=7.0, the activity of methanogens was not effectively inhibited (pH=5~6 is the inhibition range for methanogens), and the methane production was increased by 120% compared to Example 2. Although the total iron ion concentration of the system reached 340 mg / L, the inhibitory effect of iron ions on methanogens was weakened under neutral conditions, and a large amount of carbon flowed to methane rather than medium-chain fatty acids. After fermentation, the concentration of medium-chain fatty acids was only 800 mg COD / L, the yield was 0.08 g / g COD, the proportion of hexanoic acid and octanoic acid was only 25%, and the proportion of acetic acid in short-chain fatty acids reached 70%, which completely failed to achieve the core goal of "converting short-chain fatty acids to medium-chain fatty acids".

[0115] (3) Separation and recovery tank: The increase in pH of the anaerobic fermentation tank caused the phosphorus release rate from the sludge to the liquid phase to decrease from 85% in Example 2 to 55%. After adjusting the pH of the separation and recovery tank to 7.8, the phosphorus recovery efficiency was only 52%. The blue iron ore crystals are small and easily lost with the supernatant, which significantly increases the difficulty of recovery.

[0116] (4) System stability: After five consecutive cycles of operation, the pressure in the fermentation tank increased due to the large amount of methane generated, requiring frequent venting. Furthermore, the yield of medium-chain fatty acids remained below 0.1 g / g COD, and the phosphorus recovery efficiency remained stable at 50%~53%, which could not meet the requirements for high-value recovery.

[0117] Conclusion: This comparative study demonstrates that maintaining the pH in the anaerobic digester within the range of 5-6 is a key parameter for achieving efficient conversion of medium-chain fatty acids. Deviations from this range lead to the ineffective inhibition of methanogens, altered carbon flow direction, and failure to achieve the goal of high-value recovery, further validating the rationality and necessity of the pH parameter in the anaerobic digester.

[0118] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for recovering organic matter and phosphorus from wastewater, characterized in that, The following steps are performed using a recycling device: (1) Pump the wastewater to be treated into the carbon and phosphorus capture tank and inoculate it with sludge after anaerobic digestion at the end to achieve the initial solid phase enrichment of organic matter and phosphorus in the sludge; (2) Pump the enriched sludge into the pre-oxidation tank, adjust the pH value and add ferrate for stirring; (3) Pump the pre-oxidized mud-water mixture into the anaerobic fermentation tank, add ethanol to the system for anaerobic fermentation, and convert the short-chain fatty acids produced into medium-chain fatty acids. (4) The mixture after anaerobic fermentation is pumped into the separation and recovery tank for stirring and reaction, and then allowed to settle to achieve the recovery of phosphorus in the form of blue iron ore; (5) The sludge settled in the anaerobic fermentation tank is returned to the carbon and phosphorus capture tank through the sludge return system and operated continuously and stably for ≥5 cycles. The recovery device includes a carbon and phosphorus capture tank, a pre-oxidation tank, an anaerobic fermentation tank, a separation and recovery tank, and a sludge return system. The carbon and phosphorus capture tank, pre-oxidation tank, anaerobic fermentation tank, and separation and recovery tank are connected sequentially by pipelines. The inlet of the sludge return system is connected to the sludge outlet of the anaerobic fermentation tank, and the outlet of the sludge return system is connected to the inlet of the carbon and phosphorus capture tank. The sludge from the anaerobic fermentation tank is returned to the carbon and phosphorus capture tank via a timed pump and sludge return system.

2. The method for recovering organic matter and phosphorus from wastewater according to claim 1, characterized in that, The conditions in the carbon and phosphorus capture tank are: temperature 15~35℃, pH 6.5~8.

3. The method for recovering organic matter and phosphorus from wastewater according to claim 1, characterized in that, The concentration of the sludge in step (1) is 3000~10000 mg / L.

4. The method for recovering organic matter and phosphorus from wastewater according to claim 1, characterized in that, The pH in the pre-oxidation tank in step (2) is 10-12, and the stirring time is 3-5 minutes.

5. The method for recovering organic matter and phosphorus from wastewater according to claim 1, characterized in that, The amount of ferrate added is 20~40 mg / g of volatile solids concentration.

6. The method for recovering organic matter and phosphorus from wastewater according to claim 1, characterized in that, The pH in the anaerobic fermentation tank is 5-6 and the temperature is 30-35℃.

7. The method for recovering organic matter and phosphorus from wastewater according to claim 1, characterized in that, The molar ratio of ethanol to short-chain fatty acids in the anaerobic fermentation tank is 2-4:

1.

8. The method for recovering organic matter and phosphorus from wastewater according to claim 1, characterized in that, The pH in the separation and recovery tank is 7-8.

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