Device and method for recycling organic substances and phosphorus in sewage

Abstract

The invention discloses a device and method for recycling organic substances and phosphorus in sewage, and belongs to the technical field of wastewater treatment.The method comprises the following steps that 1, sewage to be treated is pumped into a carbon and phosphorus capturing pool, sludge is inoculated into the sewage to be treated, and preliminary enrichment of the organic substances and the phosphorus is achieved; (2) pumping the enriched sludge into a pre-oxidation pond, adding ferrate, and stirring; (3) pumping outlet water into an anaerobic fermentation tank, adding ethanol into a system for anaerobic fermentation, and converting generated short-chain fatty acid into medium-chain fatty acid; and (4) pumping the mixed solution subjected to anaerobic fermentation into a separation and recovery tank, carrying out stirring reaction, standing and precipitating, and realizing phosphorus recovery in the form of blue iron ore. And (5) refluxing sludge settled in the anaerobic fermentation tank to the carbon and phosphorus capturing tank through a sludge refluxing system, wherein the system continuously and stably operates for more than or equal to 5 cycles. According to the method, conversion of different valence states of iron and corresponding compounds of the iron are used as driving factors, a combination 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 is adopted, and microorganisms are regulated and controlled by biochemical and physicochemical means to efficiently capture organic matters, and iron compounds synergistically adsorb the organic matters and phosphorus; and finally, organic matters and phosphorus in the sewage are recovered in the form of medium-chain fatty acid and blue iron ore with high added values.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of wastewater treatment, and particularly relates to a device and method for recycling organic matter and phosphorus in sewage. BACKGROUND

[0002] Traditional wastewater treatment technology takes the removal of pollutants as the core goal, and has limitations such as high energy consumption, significant carbon emissions and potential resource waste. The potential resource value in wastewater is ignored. It is estimated that if the organic components represented by chemical oxygen demand (COD) in wastewater can be recycled, about 30% of the energy consumption of wastewater treatment can be saved, the wastewater treatment industry can be transformed from energy-intensive to energy self-sufficient, and 35%-50% of the carbon footprint can be reduced. However, the current technical system has a resource bottleneck, and the organic carbon recovery efficiency is generally less than 30%. Therefore, it is urgent to innovate the existing technical system to achieve efficient resource recovery.

[0003] In recent years, although anaerobic treatment technology has been used to recover methane energy, it still has problems such as long conversion period, low added value of products, and low carbon recovery rate. Methane as the main product has limited market value, and part of the organic carbon will still be lost through metabolic pathways. Therefore, the resource direction is changing from low-value energy to high-value chemicals, and the step-up value-added route from short-chain fatty acids (SCFAs) to medium-chain fatty acids (MCFAs) is attracting attention. SCFAs can be efficiently obtained through anaerobic fermentation, while MCFAs (such as caproic 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 difficulties: first, the concentration of organic matter in wastewater is generally low, making it difficult to directly and efficiently ferment; second, the biological barrier composed of cell structure and extracellular polymeric substance (EPS) hinders the release and conversion of organic matter, limiting the conversion efficiency.

[0004] In summary, the existing technology generally has problems such as low organic carbon recovery rate, single resource recovery path, insufficient high-value degree, high energy consumption, and strong dependence on chemicals, and has not achieved efficient and coordinated recovery of multiple resources such as carbon and phosphorus. In particular, there is a lack of an integrated and sustainable technology system that can efficiently enrich low-concentration organic matter, simultaneously break it down and convert it into high-value chemicals, while stably recovering phosphorus resources.

[0005] Therefore, it is urgent to develop a new process that can reduce energy consumption, break through the resource bottleneck, and promote a fundamental change from "pollution control" to "resource factory" in wastewater treatment. SUMMARY

[0006] In view of the above technical problems, the present application provides a device and method for recycling organic matter and phosphorus in sewage.

[0007] To achieve the above object, the present application provides the following technical solutions:

[0008] A device for recovering organic matter and phosphorus in sewage, comprising a carbon-phosphorus capturing pool, a pre-oxidation pool, an anaerobic fermentation pool, a separation and recovery pool, and a sludge reflux system.

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

[0010] The inlet end of the sludge reflux system is connected with the sludge outlet end of the anaerobic fermentation pool, and the outlet end is connected with the inlet end of the carbon-phosphorus capturing pool.

[0011] Optionally, the sludge in the anaerobic fermentation pool is refluxed into the carbon-phosphorus capturing pool through the sludge reflux system by a timing pump.

[0012] A method for recovering organic matter and phosphorus in sewage, using the above-mentioned recovery device to perform the following steps:

[0013] (1) Pumping the sewage to be treated into the carbon-phosphorus capturing pool, and inoculating sludge after anaerobic digestion at the rear end to achieve preliminary solid-phase enrichment of organic matter and phosphorus in the sludge.

[0014] (2) Pumping the enriched sludge into the pre-oxidation pool, adjusting the pH value, and adding ferric salt for stirring.

[0015] (3) Pumping the above-mentioned pre-oxidized sludge mixture into the anaerobic fermentation pool, adding ethanol to the system for anaerobic fermentation, and converting the generated short-chain fatty acids into medium-chain fatty acids.

[0016] (4) Pumping the mixed liquid after anaerobic fermentation into the separation and recovery pool, stirring, standing, and precipitating to achieve recovery of phosphorus in the form of blue vitriol.

[0017] (5) Refluxing the sludge precipitated in the anaerobic fermentation pool to the carbon-phosphorus capturing pool through the sludge reflux system, and continuously and stably operating the system for ≥5 cycles.

[0018] Optionally, the conditions in the carbon-phosphorus capturing pool 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 pool is 10-12, and the stirring time is 3-5 minutes.

[0021] Optionally, the addition amount of ferric salt is 20-40 mg / g VSS (volatile solid 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 acid 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 80wt% of the total sludge amount.

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

[0027] (1) The present application realizes the efficient simultaneous recovery of carbon and phosphorus in wastewater in a single system through iron-mediated adsorption-release-inhibition whole process regulation.

[0028] (2) The use of return sludge realizes the internal circulation of iron elements, significantly reducing the additional dosage of high ferrate and other reagents, and reducing the operating cost.

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

[0030] In summary, the present application realizes the efficient conversion of organic matter in wastewater and the stable recovery of phosphorus through the five-step linkage process of "adsorption enrichment-oxidation depolymerization-anaerobic upgrading-crystallization recovery-sludge return". The whole process fully utilizes various mechanisms such as microbial EPS (microbial extracellular polymeric substance), high ferrate oxidation, iron ion catalysis and blue vitriol precipitation, and has the advantages of high efficiency, resource utilization and environmental friendliness, and is suitable for the advanced treatment and resource recovery of phosphorus-containing organic wastewater such as municipal wastewater and industrial wastewater. The recovery process and effect of organic matter and phosphorus in wastewater and sludge are as follows:

[0031] Organic matter (COD) in wastewater → carbon and phosphorus capture tank (microbial EPS + iron hydroxide adsorption, interception rate 50-80%) → pre-oxidation tank (release of organic matter, release rate up to 90%) → anaerobic fermentation tank (conversion to MCFAs, conversion rate up to 70%);

[0032] Phosphorus in wastewater → carbon and phosphorus capture tank (iron and its hydroxide adsorption, interception rate up to 91%) → anaerobic fermentation tank (release of iron ions, release rate up to 85%) → separation and recovery tank (blue vitriol crystallization, recovery rate up to 93%);

[0033] Sludge→carbon phosphorus capture tank (adsorption)→pre-oxidation tank (active retention)→anaerobic fermentation tank (acid production)→backflow to carbon phosphorus capture tank (recycling, recycling times≥5 times). BRIEF DESCRIPTION OF DRAWINGS

[0034] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application, illustrate preferred embodiments of the application and assist in explaining the application. In the drawings:

[0035] Figure 1 A process flow diagram for recovering organic matter and phosphorus in wastewater according to Embodiment 2 of the present application. DETAILED DESCRIPTION

[0036] The various illustrative embodiments of the present application will now be described in detail in various examples, which should be considered j ust as exemplary embodiments of the present application and not limiting the same. Those of ordinary skill in the art, and others, however, will recognize that the application can comprise a variety of other embodiments with only a few of the presently disclosed embodiments being shown and described.

[0037] It should be understood that the terms used herein are for the purpose of describing particular embodiments and are not intended to limit the present application. Additionally, for numerical ranges that are expressed in a range format, it is intended that any numerical value implicitly recited or suggested, including any value that would be

[0038] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe in further detail the methods and / or materials associated with the documents. In the case of conflict between the present specification and any document incorporated by reference, the present specification will control.

[0039] Many modifications and variations of this application can be made in the light of the above teachings without departing from the spirit and scope thereof, and it is to be understood that all such modifications and variations warrant the patentable subject matter under the patent laws. Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples given are exemplary only.

[0040] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended and do not exclude additional elements or steps.

[0041] The present application takes the transformation of different valence states of iron and corresponding compounds as driving factors, adopts a combination of carbon and phosphorus capture tanks, a pre-oxidation tank, an anaerobic fermentation tank, a separation and recovery tank and a sludge return system, and controls microorganisms to efficiently capture organic matter through biochemical and physical means, iron compounds cooperatively adsorb organic matter and phosphorus, and finally realizes the recovery of organic matter and phosphorus in wastewater in the form of high-value-added medium and long chain fatty acids and blue iron ore.

[0042] The present application discloses a device for recovering organic matter and phosphorus in wastewater, which is composed 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, extracellular polymeric substances (EPS) of microorganisms and iron and its hydroxide colloids carried by sludge return cooperatively adsorb organic matter and phosphorus in wastewater, the temperature is controlled at 15-35℃, the pH value is controlled at 6.5-8, and the sludge concentration is controlled at 3000-10000mg / L.

[0044] In the pre-oxidation tank, the pH value is adjusted to 10-12, 20-40mg / g VSS of ferrate is added, and the stirring time is 3-5 minutes to break the sludge aggregates without damaging the microbial cell membrane.

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

[0046] In the separation and recovery tank, the pH value is adjusted to 7-8 to realize the crystallization recovery of phosphorus in the form of blue iron ore.

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

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

[0049] In some optional embodiments, the pre-oxidation tank is provided with a pH adjusting system and a dosing system.

[0050] In some optional embodiments, the anaerobic fermentation tank is provided with a stirring zone, a dosing system and a sludge-water separation zone.

[0051] In some optional embodiments, the separation and recovery tank is provided with a mixing and sedimentation zone, and a pH adjusting system.

[0052] The present application also discloses a method for recovering organic matter and phosphorus in wastewater by using the above device, which comprises the following steps:

[0053] During operation, the sewage containing organic matter is mixed with sludge in the carbon and phosphorus capture tank, and the sludge in the sludge return system is mixed in an anaerobic state to adsorb the organic matter in the sewage by EPS, and the Fe 2+ / Fe 3+ The colloidal compound formed can adsorb phosphorus in the sewage and further strengthen the adsorption of organic matter. In this process, iron ions also promote the decomposition of complex organic matter by microorganisms and the synthesis of organic matter such as proteins of microorganisms themselves. Then, solid-liquid separation is carried out in the sedimentation zone, and the solid phase flows into the pre-oxidation tank, and the liquid phase is discharged.

[0054] In some optional embodiments, the Fe 6+ produces ·OH to oxidize the sludge and break the sludge aggregates, so that the particle size of the sludge is less than 0.5 mm, the integrity rate of the microbial cell membrane of the sludge is ≥85%, and the dehydrogenase activity is ≥150 μg TF / (g VSS·h).

[0055] In some optional embodiments, the sludge pretreated in the pre-oxidation tank is subjected to anaerobic fermentation in the anaerobic fermentation tank, so that the organic matter adsorbed by the sludge, the extracellular polymeric substance (EPS) after the breakage of the sludge aggregates, etc. are decomposed, and at the same time, the total iron ion concentration in the sludge is controlled to be greater than 300 mg / L to inhibit the activity of methanogens and promote the oxidation of organic matter to be controlled to short-chain organic acids. The original iron ions in the sludge and the added ethanol are used for regulation and control, so that the small-molecule organic acids are converted into medium-chain fatty acids. The anaerobic process promotes the release of phosphorus in the sludge to the liquid phase. During the fermentation process, the sludge secretes extracellular polymeric substance again to form new aggregates. The sludge-water mixture after fermentation is subjected to sedimentation in the sedimentation zone, the sludge is returned to the carbon and phosphorus capture tank through the sludge return system, and the liquid phase enters the separation and recovery tank.

[0056] In some optional embodiments, the yield of the medium-chain fatty acids (C6-C 12 ) in the anaerobic fermentation tank is ≥0.4 g / g COD, and the proportion of hexanoic acid and octanoic acid is ≥70 wt%.

[0057] In the present application, "room temperature" refers to 20-30℃ unless otherwise specified.

[0058] In the present application, "parts" refer to mass parts unless otherwise specified.

[0059] In the present application, all raw materials are obtained by purchase on the market.

[0060] In the following Example 2 and Comparative Example 1, the sewage to be treated is: simulated sewage: COD=400 mg / L (simulated by glucose and peptone), total phosphorus=8 mg / L. Inoculated sludge: sludge taken from the anaerobic digestion tank of a municipal sewage treatment plant, MLSS about 8000 mg / L.

[0061] The technical solutions of the present application are further described below through examples.

[0062] Example 1

[0063] A device for recovering organic matter and phosphorus in sewage, comprising a carbon-phosphorus capture tank (provided with a stirring zone and a sedimentation zone), a pre-oxidation tank (provided with a pH adjusting system and a dosing system), an anaerobic fermentation tank (provided with a stirring zone, a dosing system and a sludge-water separation zone), a separation and recovery tank (provided with a mixing and sedimentation zone, a pH adjusting system) and a sludge reflux system;

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

[0065] The inlet end of the sludge reflux system is in communication with the sludge outlet end of the anaerobic fermentation tank, and the outlet end of the sludge reflux system is in communication with the inlet end of the carbon-phosphorus capture tank, and the sludge is refluxed by a timing pump.

[0066] Example 2

[0067] As shown in Figure 1 , the recovery device in Example 1 is used to carry out the following recovery process:

[0068] (1) The sewage to be treated enters the carbon-phosphorus capture tank, and under the conditions of a temperature of 25℃, a pH of 7, an HRT (hydraulic retention time) of 1 hour and a sludge inoculation concentration of 6000 mg / L, the organic matter and phosphates in the sewage are efficiently adsorbed by the synergistic action of the extracellular polymeric substance (EPS) secreted by microorganisms and the iron hydroxide colloid from the sludge reflux system, realizing the preliminary enrichment of organic matter and phosphorus; the effluent COD of the carbon-phosphorus capture tank is reduced to ~80 mg / L, and the phosphorus is reduced to ~0.8 mg / L.

[0069] (2) Subsequently, the mixed liquid carrying the enriched sludge enters the pre-oxidation tank, the pH is adjusted to 11, and the ferric salt is added at a ratio of 30 mg / g VSS, and under the condition of stirring for 4 minutes, the sludge aggregates are broken and the microbial cell membrane is not damaged. Results: the sludge particle size is reduced from the initial ~800 μm to ~200 μm; the microscope detects that the cell integrity rate is >90%; the dehydrogenase activity is 180 μgTF / (gVSS·h), and the supernatant COD is increased by 90% compared with the influent, indicating that the organic matter is released.

[0070] (3) Then, the effluent enters the anaerobic fermentation tank, and the hydraulic retention time is 3 days under the condition of pH 5.5 and temperature 35℃; ethanol is added to the system: the total iron ion concentration of the system is about 350 mg / L, and ethanol is added in pulses every day, 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 sludge ferrate oxidation and the added ethanol are used for fermentation, the produced short-chain fatty acids are converted into medium-chain fatty acids, and the phosphorus release rate in the sludge to the liquid phase reaches 95%.

[0071] (4) After that, the mixed liquid after fermentation enters the separation and recovery tank, and the pH is adjusted to 7.8, and the reaction is carried out under slow stirring (50 rpm) for 2 hours, and then the sludge is precipitated to realize the crystallization recovery of phosphorus in the form of blue vitriol.

[0072] (5) Finally, the sludge (80% of the total sludge) precipitated in the anaerobic fermentation tank is backflowed to the carbon and phosphorus capture tank, and the system is continuously and stably operated for more than 5 cycles.

[0073] Results and detection:

[0074] Carbon recovery: The effluent of the anaerobic fermentation tank is detected, and the concentration of medium-chain fatty acids (mainly hexanoic acid and octanoic acid) is 4500 mgCOD / L, and the yield is calculated to be 0.45 g COD / gCOD (based on the influent COD), and the proportion of hexanoic acid and octanoic acid is 75%.

[0075] Phosphorus recovery: Blue precipitate is observed at the bottom of the separation and recovery tank. X-ray diffraction analysis confirms that it is blue vitriol. The recovery efficiency of phosphorus is calculated to be 91%.

[0076] Sludge backflow: The sludge (80% of the total sludge) precipitated in the separation and recovery tank is backflowed to the carbon and phosphorus capture tank, and the system is continuously and stably operated for more than 5 cycles, and the carbon and phosphorus recovery efficiencies are maintained at more than 70% and 90%, respectively, in each cycle.

[0077] Example 3

[0078] This example uses a recovery device with the same structure as example 1, and is aimed at the treatment of municipal domestic sewage (actual influent water quality: COD=350 mg / L, total phosphorus=7 mg / L) in low temperature environment, and the specific recovery process is as follows:

[0079] (1) Carbon and phosphorus capture tank operation control: Pump the municipal sewage to be treated into the carbon and phosphorus capture tank, control the temperature to be 15°C (simulate the low-temperature condition in winter in the north), pH = 6.5, extend the hydraulic retention time (HRT) to 1.5 hours, inoculate the sludge after anaerobic digestion at the rear end, and adjust the sludge concentration (MLSS) to 10000 mg / L. Through the synergistic effect of microbial extracellular polymeric substance (EPS) and iron hydroxide colloid carried by sludge backflow, the adsorption of organic matter and phosphorus in sewage at low temperature is strengthened. The operation results show that the effluent COD of the carbon and phosphorus capture tank is reduced to 95 mg / L, the total phosphorus is reduced to 0.9 mg / L, the organic matter interception rate is 72.9%, and the phosphorus interception rate is 87.1%, which meets the preliminary enrichment requirement in low-temperature environment.

[0080] (2) Pre-oxidation tank treatment: Pump the enriched sludge mixture into the pre-oxidation tank, adjust the pH to 10 (lower than the pH value in Example 2, to explore the oxidation effect under low alkalinity condition), and add ferric salt at a proportion of 20 mg / g volatile solid concentration (VSS). Stir for 3 minutes (minimum stirring time parameter). After detection, the sludge particle size is reduced from the initial ~ 750 μm to ~ 300 μm, the microbial cell membrane integrity rate is 85% (meeting the activity retention requirement), the dehydrogenase activity is 150 μgTF / (gVSS·h), and the supernatant COD is increased by 85% compared with the influent, realizing the effective release of organic matter.

[0081] (3) Anaerobic fermentation tank reaction: Pump the pre-oxidized sludge-water mixture into the anaerobic fermentation tank, control the pH = 5 (acidic lower limit condition), temperature 30°C (lower limit of mesophilic temperature range), and hydraulic retention time 3 days. The system detects that the total iron ion concentration is 320 mg / L, and ethanol is added at a molar ratio of 2:1 (minimum molar ratio) of ethanol to short-chain fatty acid to inhibit the activity of methanogens and promote the conversion of short-chain fatty acids to medium-chain fatty acids. After fermentation, the concentration of medium-chain fatty acids (C6-C 12 ) in the anaerobic fermentation tank is 3800 mg COD / L, with a yield of 0.42 g / g COD, of which hexanoic acid and octanoic acid account for 70%, meeting the high-value conversion requirement; at the same time, the sludge phosphorus release rate to liquid phase is 82%.

[0082] (4) Phosphorus recovery in separation and recovery tank: Pump the mixed liquid after anaerobic fermentation into the separation and recovery tank, adjust the pH to 7 (neutral lower limit), and slowly stir at a speed of 40 rpm for 2.5 hours, and then stand for precipitation. Blue precipitate is collected at the bottom of the separation and recovery tank, which is confirmed by X-ray diffraction analysis to be blue vitriol, and the phosphorus recovery efficiency is calculated to be 90%.

[0083] (5) Sludge backflow and stable operation of the system: The sludge (80% of the total sludge) precipitated in the anaerobic fermentation tank was backflowed to the carbon and phosphorus capture tank through the sludge backflow system by a timer pump, and the system was continuously and stably operated for 5 cycles.

[0084] The monitoring results showed that the carbon and phosphorus recovery efficiencies were stably above 70% and 89% respectively within 5 cycles, and no significant efficiency decay was observed, verifying the stability of the system under low temperature and low dosage of reagents.

[0085] Example 4

[0086] In this example, the recovery device of Example 1 was used to treat high-concentration industrial organic wastewater (actual influent water quality: COD = 800 mg / L, total phosphorus = 12 mg / L, containing a small amount of industrial additives), and the specific steps were as follows:

[0087] (1) Carbon and phosphorus capture tank enrichment: The industrial wastewater to be treated was pumped into the carbon and phosphorus capture tank, and the temperature was controlled at 35°C (high-temperature condition), the pH was controlled at 8 (alkaline upper limit), the HRT was 1.2 hours, and the sludge concentration was inoculated to 3000 mg / L (minimum sludge concentration parameter). The high-temperature environment was used to improve the metabolic activity of microorganisms, and the iron hydroxide colloid adsorption was used to realize the rapid enrichment of organic matter and phosphorus. The operation results showed that the effluent COD was reduced to 160 mg / L, the total phosphorus was reduced to 1.08 mg / L, the organic matter interception rate was 80%, and the phosphorus interception rate was 91%, which effectively met the enrichment demand of high-concentration organic wastewater.

[0088] (2) Pre-oxidation tank for strengthening the breakage of aggregates: The enriched sludge mixture was introduced into the pre-oxidation tank, the pH was adjusted to 12 (alkaline upper limit), and the ferric salt was added at a dosage of 40 mg / g VSS (maximum ferric salt dosage), and the stirring time was 5 minutes (maximum stirring time). After treatment, the sludge particle size was reduced to ~ 150 μm, the microbial cell membrane integrity rate was 88%, the dehydrogenase activity was 180 μg TF / (g VSS·h), and the supernatant COD was increased by 90% compared with the influent, effectively breaking the biological barrier formed by the sludge aggregates and extracellular polymeric substances (EPS) in the industrial wastewater.

[0089] (3) High-value conversion in the anaerobic fermentation tank: The sludge-water mixture was introduced into the anaerobic fermentation tank, the pH was controlled at 6 (acidic upper limit), the temperature was controlled at 35°C, and the HRT was 3 days. The total iron ion concentration of the system was detected to be 400 mg / L, and the ethanol was added at a molar ratio of 4:1 (maximum molar ratio) of ethanol to short-chain fatty acid to strengthen the stepwise conversion of short-chain fatty acid to medium-chain fatty acid. After fermentation, the concentration of medium-chain fatty acid was 9200 mg COD / L, the yield was 0.45 g / g COD, and the proportion of caproic acid and caprylic acid was 78%, which was significantly higher than that of the traditional anaerobic process; the phosphorus release rate to the liquid phase was 85%.

[0090] (4) Separation and recovery of phosphorus purification: the mixed solution enters the separation and recovery tank, the pH is adjusted to 8 (alkaline upper limit), 50 rpm stirring reaction for 2 hours, and standing precipitation. The collected blue vitriol precipitate has a purity of 95% and a phosphorus recovery efficiency of 93%, meeting the industrial grade phosphorus resource recovery standard.

[0091] (5) Sludge backflow and long-term operation: 80% of the anaerobic fermentation tank sludge is backflowed to the carbon and phosphorus capture tank, and the system is continuously operated for 6 cycles. The monitoring data shows that the carbon recovery efficiency is stable at more than 72% and the phosphorus recovery efficiency is maintained at more than 92% within 6 cycles, and there is no problem of residual reagent or sludge bulging, which verifies the long-term stability of the system under the conditions of high temperature and high reagent dosage, and is suitable for continuous resource recovery treatment of industrial wastewater.

[0092] Comparative Example 1

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

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

[0095] Comparative Example 2: Comparative test of system without sludge backflow

[0096] The difference between this comparative example and the recovery device of Example 1 is only that the sludge backflow system is removed, and the anaerobic fermentation tank sludge is not backflowed to the carbon and phosphorus capture tank. The rest of the recovery parameters remain the same as Example 2, and the simulated wastewater (COD=400 mg / L, total phosphorus=8 mg / L) is treated, and the specific steps are as follows:

[0097] (1) Carbon and phosphorus capture tank operation: the treated simulated wastewater is pumped into the carbon and phosphorus capture tank, the temperature is controlled at 25°C, the pH is 7, the HRT is 1 hour, the sludge concentration is adjusted to 6000 mg / L for the first time (consistent with the initial concentration of Example 2), and there is no sludge backflow supplement. After running for 1 cycle, the MLSS in the carbon and phosphorus capture tank decreased to 3500 mg / L due to the loss of sludge with the effluent; after running for 3 cycles, the MLSS further decreased to 1800 mg / L, which is lower than the range of 3000-10000 mg / L.

[0098] (2) Pre-oxidation tank treatment: The enriched sludge mixture is pumped into the pre-oxidation tank, the pH is adjusted to 11, and 30 mg / g VSS of ferric salt is added, and stirred for 4 minutes. In one cycle, the sludge particle size is reduced from the initial ~ 800 μm to ~ 220 μm, and the cell integrity rate is 88%; in three cycles, due to the low sludge concentration, the sludge aggregates are not fully broken, the particle size is only reduced to ~ 450 μm, and the cell integrity rate is reduced to 75%, and the COD of the supernatant is reduced by 30% compared with Example 2.

[0099] (3) Anaerobic fermentation tank reaction: The pre-oxidized sludge-water mixture is pumped into the anaerobic fermentation tank, the pH is controlled at 5.5, the temperature is 35°C, the HRT is 3 days, and ethanol is added according to a molar ratio of ethanol to short-chain fatty acid of 3:1. In one cycle, the concentration of medium-chain fatty acids is 3200 mg COD / L, the yield is 0.32 g / g COD, and the proportion of hexanoic acid and octanoic acid is 65%; in three cycles, due to the decrease in enrichment efficiency of the carbon-phosphorus capture tank, the organic matter entering the fermentation tank is insufficient, the concentration of medium-chain fatty acids is reduced to 1800 mg COD / L, the yield is only 0.18 g / g COD, the proportion of hexanoic acid and octanoic acid is reduced to 50%, and the total iron ion concentration is reduced from 350 mg / L in Example 2 to 180 mg / L, which cannot effectively inhibit methanogens, and the methane production is increased by 40% compared with Example 2.

[0100] (4) Phosphorus recovery in the separation and recovery tank: The mixed liquid after anaerobic fermentation is pumped into the separation and recovery tank, the pH is adjusted to 7.8, and the stirring reaction is carried out at 50 rpm for 2 hours, and then it is allowed to settle. In one cycle, the phosphorus recovery efficiency is 82%; in three cycles, due to the decrease in phosphorus retention rate of the carbon-phosphorus capture tank (from 91% in Example 2 to 65%) and the decrease in phosphorus release rate of the anaerobic fermentation tank to 60%, the phosphorus recovery efficiency is only 58%, which is far lower than the index of 90% or more in the present application.

[0101] (5) System stability: The system is continuously operated for 5 cycles, and the carbon recovery efficiency in cycles 1-5 is 32%, 25%, 18%, 12%, and 8%, respectively, and the phosphorus recovery efficiency is 82%, 70%, 58%, 45%, and 38%, respectively, all showing a significant decreasing trend, and the 5th cycle cannot meet the basic recovery requirements.

[0102] Conclusion: This comparative example proves that the sludge reflux system is the key to maintaining the sludge concentration in the carbon-phosphorus capture tank, ensuring the internal circulation of iron elements, and realizing the continuous and stable operation of the system. The absence of sludge reflux not only greatly reduces the carbon-phosphorus recovery efficiency, but also leads to the inability of the system to meet the stable operation requirements for ≥5 cycles, highlighting the necessity of the sludge reflux technology.

[0103] Comparative Example 3: Comparative test without adding ferrate in the pre-oxidation tank

[0104] The recovery device of Example 1 was used in this comparative example, no ferrate was added in the pre-oxidation tank, only the pH was adjusted to 11 and stirred for 4 minutes, the remaining steps and parameters were completely consistent with Example 2, and the simulated wastewater (COD = 400 mg / L, total phosphorus = 8 mg / L) was treated, and the results were as follows:

[0105] (1) Carbon and phosphorus capture tank: the operating effect was similar to Example 2, the effluent COD was reduced to ~ 85 mg / L, the total phosphorus was reduced to ~ 0.85 mg / L, the organic matter interception rate was 83.7%, the phosphorus interception rate was 89.4%, and it was not affected by the pre-oxidation tank without ferrate.

[0106] (2) Pre-oxidation tank: only by adjusting the pH and stirring, the sludge aggregate breaking effect was very poor, the sludge particle size was only reduced from the initial ~ 800 μm to ~ 650 μm, which did not meet the requirement of "sludge particle size less than 0.5 mm" (reduced to ~ 200 μm in Example 2). The microbial extracellular polymeric substance (EPS) was not effectively broken, and the supernatant COD was only increased by 25% compared with the influent, which was much lower than the increase of more than 80% in Example 2, and the organic matter release amount was seriously insufficient.

[0107] (3) Anaerobic fermentation tank: due to insufficient release of organic matter into the fermentation tank, and no ferrate to provide Fe 6 + converted to Fe 3 + supplement iron ions, the total iron ion concentration of the system was only 120 mg / L, lower than 350 mg / L in Example 2. After anaerobic fermentation, the concentration of medium-chain fatty acids was only 1500 mg COD / L, the yield was 0.15 g / g COD, which did not meet the standard of "medium-chain fatty acid yield ≥ 0.4 g / g COD" in the present application, and the proportion of caproic acid and caprylic acid was only 40%, the proportion of short-chain fatty acids (acetic acid and propionic acid) was 60%, and the methane production was increased by 60% compared with Example 2.

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

[0109] (5) System operation: continuous operation for 5 cycles, carbon recovery efficiency stabilized at 15%~18%, phosphorus recovery efficiency stabilized at 45%~50%, both far lower than the efficiency of 70%, 90% or more in Example 2, and the sludge gradually swelled due to EPS accumulation, and sludge floating phenomenon occurred in the carbon and phosphorus capture tank in the 5th cycle.

[0110] Conclusion: This comparative example verifies the core role of ferrate in the pre-oxidation tank — breaking down EPS and crushing sludge aggregates through oxidation, providing sufficient organic matter for subsequent anaerobic fermentation, and supplementing iron ions to inhibit methanogens. After the absence of ferrate, the release of organic matter, the conversion of medium-chain fatty acids, and the recovery of phosphorus cannot meet the indicators, proving that the addition of ferrate is an indispensable step in the method.

[0111] Comparative Example 4: Comparative test of pH deviation from the range of the inventive examples in the anaerobic fermentation tank

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

[0113] (1) Carbon and phosphorus capture tank and pre-oxidation tank: the operating effect is basically the same as Example 2, the effluent COD of 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%, and the supernatant COD is increased by 82%, which is not affected by the change of pH in the anaerobic fermentation tank.

[0114] (2) Anaerobic fermentation tank: when pH=7.0, the methanogen activity is not effectively inhibited (pH=5~6 is the methanogen inhibition interval), and the methane production is increased by 120% compared with Example 2. Although the total iron ion concentration reaches 340mg / L, the inhibitory effect of iron ions on methanogens is weakened in a neutral environment, and a large amount of carbon flow goes to methane rather than medium-chain fatty acids. After fermentation, the concentration of medium-chain fatty acids is only 800mg COD / L, the yield is 0.08g / g COD, the proportion of hexanoic acid and octanoic acid is only 25%, and the proportion of acetic acid in short-chain fatty acids is as high as 70%, which completely fails to achieve the core goal of "conversion of short-chain fatty acids to medium-chain fatty acids".

[0115] (3) Separation and recovery tank: the release rate of phosphorus from sludge to liquid phase is reduced from 85% in Example 2 to 55% due to the increase of pH in the anaerobic fermentation tank. After adjusting the pH of the separation and recovery tank to 7.8, the phosphorus recovery efficiency is only 52%, the blue vitriol crystal particles are small and easy to be lost with the supernatant, and the recovery difficulty is significantly increased.

[0116] (4) System stability: continuous operation for 5 cycles, due to the generation of a large amount of methane, the pressure in the fermentation tank is increased, frequent exhaust is required, and the yield of medium-chain fatty acids is always lower than 0.1 g / g COD, and the phosphorus recovery efficiency is stable at 50%-53%, which cannot meet the requirements of high-value recovery.

[0117] Conclusion: this example proves that the pH control of the anaerobic fermentation tank in the range of 5-6 is the key parameter to realize the efficient conversion of medium-chain fatty acids. If the range is deviated, the methanogenic bacteria inhibition fails, the carbon flow direction changes, and the high-value recovery target cannot be achieved, further verifying the rationality and necessity of the pH parameter in the anaerobic fermentation tank.

[0118] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A device for recovering organic matter and phosphorus from wastewater, characterized in that, The carbon and phosphorus capturing tank, the pre-oxidation tank, the anaerobic fermentation tank, the separation and recovery tank and the sludge reflux system are sequentially connected through pipelines. The sludge outlet end of the anaerobic fermentation tank is communicated with the inlet end of the sludge reflux system, and the outlet end of the sludge reflux system is communicated with the inlet end of the carbon and phosphorus capturing tank. The sludge in the anaerobic fermentation tank is refluxed into the carbon and phosphorus capturing tank through the sludge reflux system by a timing pump.

2. The device for recovering organic substances and phosphorus from sewage according to claim 1, characterized in that, The recovery device of any one of claims 1-2 is used to perform the following steps:

3. A method for recovering organic matter and phosphorus from wastewater, characterized in that, (1) pumping the sewage to be treated into the carbon and phosphorus capturing tank, and inoculating the sewage with sludge after end anaerobic digestion to realize preliminary solid-phase enrichment of organic matter and phosphorus in the sludge; (2) pumping the enriched sludge into the pre-oxidation tank, adjusting the pH value and adding ferric salt for stirring; (3) pumping the above pre-oxidized sludge mixture into the anaerobic fermentation tank, adding ethanol to the system for anaerobic fermentation, and converting the generated short-chain fatty acids into medium-chain fatty acids; (4) pumping the mixed liquid after anaerobic fermentation into the separation and recovery tank, stirring, standing and precipitating to realize recovery of phosphorus in the form of blue vitriol; (5) refluxing the sludge precipitated in the anaerobic fermentation tank to the carbon and phosphorus capturing tank through the sludge reflux system, and continuously and stably operating for ≥5 cycles. The temperature in the carbon and phosphorus capturing tank is 15-35℃, and the pH value is 6.5-8.

4. The method according to claim 3, wherein the method is characterized by, The concentration of the sludge in step (1) is 3000-10000 mg / L.

5. The method according to claim 3, wherein the method is characterized by, The pH value in the pre-oxidation tank is 10-12, and the stirring time is 3-5 minutes.

6. The method according to claim 3, wherein the method is characterized by, The addition amount of the ferric salt is 20-40 mg / g of volatile solid concentration.

7. The method according to claim 3, wherein the method is characterized by, The pH value in the anaerobic fermentation tank is 5-6, and the temperature is 30-35℃.

8. The method according to claim 3, wherein the method is characterized by, The molar ratio of ethanol to short-chain fatty acids in the anaerobic fermentation tank is 2-4:

1.

9. The method according to claim 3, wherein the method is characterized by, The pH value in the separation and recovery tank is 7-8.

10. The method according to claim 3, wherein the method is characterized by, ​

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