Process for treating threonine wastewater by activated sludge method

Abstract

This invention discloses a process for treating threonine wastewater using activated sludge, belonging to the field of wastewater treatment technology. The process includes the following steps: (1) pretreating the threonine wastewater to obtain pretreated wastewater; (2) adjusting the pH of the pretreated wastewater to obtain pH-adjusted wastewater; (3) adding modified activated sludge for multi-stage sedimentation to obtain multi-stage sedimented wastewater; and (4) flocculating the multi-stage sedimented wastewater to obtain effluent. This invention optimizes the process based on the characteristics of threonine wastewater, achieving deep purification of high-concentration organic pollutants and ammonia nitrogen in the wastewater, solving the problems of low COD and ammonia nitrogen removal rates and difficulty in meeting standards in traditional processes.

Description

Technical Field

[0001] This invention relates to a process for treating threonine wastewater using activated sludge, belonging to the field of wastewater treatment technology. Background Technology

[0002] Threonine wastewater is generated from the large-scale production of threonine using microbial fermentation. This type of wastewater has a complex composition, containing threonine, microbial protein, residual fermentation substrate, nucleic acid, polysaccharides, and inorganic salts. It exhibits typical characteristics of high chemical oxygen demand, high ammonia nitrogen, and high sulfate. Direct discharge of this wastewater would cause serious pollution to the aquatic ecosystem and waste resources, and has become a key bottleneck restricting the green and sustainable development of the threonine industry.

[0003] Currently, the treatment methods for threonine wastewater are mainly divided into three categories: physical methods, chemical methods, and biological methods. Among them, biological methods have become the mainstream technology for threonine wastewater treatment due to their outstanding advantages such as low treatment cost, environmental friendliness, and no secondary pollution. The activated sludge process, as the most widely used and mature technology in the field of biological treatment, is widely used to remove organic pollutants from wastewater due to its high reliability and good adaptability to various water qualities.

[0004] However, directly applying the traditional activated sludge process to treat threonine wastewater presents numerous intractable technical challenges due to the wastewater's high concentration, high salinity, and high ammonia nitrogen levels, resulting in poor treatment efficiency and unstable process operation. Firstly, the high concentrations of ammonia nitrogen and sulfate in threonine wastewater inhibit microbial activity and disrupt the community structure, leading to low COD and ammonia nitrogen removal rates, making it difficult to meet standards. Secondly, the loose floc structure and poor settling properties of traditional activated sludge make it prone to sludge bulking and loss under high-load wastewater impacts, increasing sludge disposal costs. Furthermore, the complex composition of dissolved organic matter in threonine wastewater means that some recalcitrant substances are difficult for the microorganisms in traditional activated sludge to rapidly degrade, resulting in excessively long hydraulic retention times and high operating costs.

[0005] Therefore, optimizing the process design of the activated sludge process, improving the inhibition resistance, settling performance and degradation efficiency of activated sludge, and solving the technical problems of microbial inhibition, sludge loss and low treatment efficiency in the traditional activated sludge process for treating threonine wastewater, so as to achieve efficient, stable and low-cost treatment of threonine wastewater, has become a key technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a process for treating threonine wastewater using activated sludge, which can effectively remove pollutants from the wastewater.

[0007] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: A process for treating threonine wastewater using activated sludge includes the following steps: (1) Pre-treat the threonine wastewater to obtain pre-treated wastewater; (2) Adjust the pH of the pretreated wastewater to obtain the pH-adjusted wastewater; (3) Add modified activated sludge for multi-stage sedimentation to obtain wastewater after multi-stage sedimentation; (4) After the wastewater has undergone multi-stage sedimentation, it is flocculated to obtain the effluent.

[0008] Furthermore, in step (1), the pretreatment involves aerating and stripping the threonine wastewater before diluting it with effluent return water. The aeration and stripping method is as follows: the pH of the threonine wastewater is adjusted to above 10, and then aeration is carried out at a temperature of 25-30℃ and an aeration intensity of 3-5 m. 3 / (m 2 The wastewater is aerated and stripped for 2-4 hours under the conditions of (·h); the effluent return water is the effluent obtained after threonine wastewater has been treated by the process of this invention, and the volume ratio of effluent return water to the stripped wastewater is (1-2):1. By adjusting the pH, the ammonium ions in the wastewater are converted into free ammonia, which is then stripped out by aeration, reducing the concentration of ammonia nitrogen. The stripped free ammonia can be recovered and utilized through methods such as acid absorption. By diluting the stripped wastewater with effluent return water, the impact concentration of ammonia nitrogen in the wastewater is reduced, the toxicity load of subsequent biological treatment is reduced, and suitable conditions are created for the growth of microorganisms in the modified activated sludge.

[0009] Furthermore, in step (2), the pH of the pretreated wastewater is adjusted to 7.0-8.0 using a compound alkali agent; the compound alkali agent is composed of liquid alkali and quicklime in a mass ratio of 1:(1.0-1.8); the concentration of the liquid alkali is 20-30 wt.%. The strong alkalinity of the liquid alkali can achieve rapid pH adjustment; the alkalinity is mild and slow-release, avoiding the sudden drop in pH and impact on microbial activity caused by using liquid alkali alone, while the Ca released after the quicklime dissolves is also controlled. 2+ It can form complex flocs with carboxymethyl chitosan in the subsequent flocculation process, thereby enhancing sludge settling and flocculation effects.

[0010] Furthermore, in step (3), the method for preparing the modified activated sludge is as follows: (I) Inoculate the spore suspension into a liquid culture medium and culture it to obtain a solution containing mycelial balls; (II) Add magnetic biochar to the solution containing mycelial balls, mix and shake to obtain a solution containing mycelial balls / biochar complex; (III) Add Chlorella solution to a solution containing mycelial balls / biochar complex, mix and aerate to obtain algae-fungus complex solution; (IV) The algae-bacteria complex solution was added to the activated sludge system and mixed to obtain modified activated sludge.

[0011] Furthermore, in step (I), the concentration of spores in the spore suspension is 6.0-6.5 × 10⁻⁶. 6 CFU / mL; the spores are Aspergillus niger spores. The mycelial balls formed by Aspergillus niger provide an attachment carrier for microorganisms, and their dense structure enhances the stability of sludge flocs. At the same time, they can degrade organic pollutants such as threonine and microbial proteins in wastewater.

[0012] Furthermore, in step (I), the inoculum size is 2.5-3.0%; the culture conditions are: temperature 25-28℃, rotation speed 150-200 rpm, pH 5.5-7.0, and time 48-72 h; the components of the liquid culture medium are: glucose 10-30 g / L, peptone 5-8 g / L, yeast extract 2-3 g / L, KH2PO4 0.5-1.5 g / L, MgSO4·7H2O 0.5 g / L, and NaCl 0.5 g / L.

[0013] Furthermore, in step (II), the ratio of the magnetic biochar to the solution containing mycelial balls is 1g:(200-300)mL.

[0014] Further, in step (II), the preparation method of the magnetic biochar is as follows: walnut shells are crushed, dried, and carbonized to obtain biochar; FeCl3·6H2O and FeCl2·4H2O are dissolved in distilled water to obtain an iron salt solution; biochar is added to the iron salt solution, and ammonia water is slowly added dropwise under an inert atmosphere. After continuous stirring, the mixture is heated in a water bath, and then the magnetic solid is separated, washed, and dried to obtain magnetic biochar. Magnetic biochar can serve as an attachment carrier for fungal mycelial balls and Chlorella, forming a stable algae-bacteria complex, preventing the loss of microorganisms during subsequent multi-stage sedimentation, improving the structural stability of the modified sludge, and also adsorbing pollutants. Fe3O4 can not only inhibit the excessive growth of filamentous fungi and prevent sludge bulking, but also provide trace iron elements for microorganisms and promote microbial metabolism; at the same time, its magnetic and high-density properties can increase the specific gravity of sludge flocs and promote floc aggregation, significantly increasing the settling speed and facilitating solid-liquid separation during multi-stage sedimentation.

[0015] Furthermore, the drying temperature is 60℃ and the drying time is 12h; the carbonization temperature is 500-600℃ and the carbonization time is 2-3h; the stirring time is 30min; ammonia water is slowly added dropwise until the pH is 10-11; the water bath heating temperature is 90℃ and the water bath heating time is 2.5-3.5h; the drying temperature is 60℃ and the drying time is 12h.

[0016] Furthermore, the molar ratio of FeCl3·6H2O to FeCl2·4H2O is 2:1; the concentration of the iron salt solution is 0.1-0.3 mol / L; and the ratio of biochar to iron salt solution is (1-3) g: (20-50) mL.

[0017] Furthermore, in step (III), the volume ratio of the Chlorella solution to the solution containing mycelial balls / biochar complex is 1:1; the OD of the Chlorella solution... 680 =0.6-1.0; the aeration time is 12-24h, and the dissolved oxygen is 3.0-5.0mg / L. Chlorella forms an algae-bacteria symbiotic system with the mycelial balls / biochar composite. Chlorella produces oxygen through photosynthesis, providing oxygen for aerobic microorganisms to degrade pollutants in wastewater. Simultaneously, it absorbs nutrients such as nitrogen and phosphorus from the wastewater and secretes polysaccharides, alleviating the inhibition of microbial activity in the wastewater environment. The carbon dioxide produced by microbial metabolism provides raw materials for Chlorella photosynthesis, and the adsorption of nitrogen and phosphorus from the wastewater onto the surface of the composite provides sufficient nutrients for Chlorella growth. The three components form a structurally stable composite, solving the problems of suppressed microbial activity and easy sludge loss in traditional activated sludge, while also achieving efficient removal of pollutants from threonine wastewater.

[0018] Furthermore, in step (IV), the amount of algae-bacteria complex added is 15-25% (V / V) of the activated sludge; during the addition process, the aeration rate is maintained at 0.4-0.5 L / min, and the mixture is stirred at a speed of 50-60 r / min to ensure that the algae-bacteria complex is evenly dispersed in the activated sludge system.

[0019] Furthermore, in step (3), the multi-stage sedimentation is a seven-stage sedimentation, which is carried out in a seven-stage gradient sedimentation tank. Each sedimentation tank is equipped with an aeration degradation zone and a static sedimentation zone. The volume ratio of the aeration degradation zone to the static sedimentation zone is 3:2. An overflow weir with a grid and a sludge return port are provided between the tanks. The sludge return is carried out by a return pump.

[0020] Furthermore, the specific operation of the multi-stage settlement is as follows: (a) Modified sludge inoculation and stepwise acclimatization: Modified activated sludge was inoculated into the aeration and degradation zone of the primary tank, while wastewater with adjusted pH was introduced. Aeration and stirring were started to ensure thorough mixing. The first to third stage tanks were started simultaneously to complete the initial acclimatization. During the acclimatization process, 85% of the modified sludge settled in each stage was returned to the current stage via a return pump, 5% was returned to the previous stage, and 10% overflowed with the wastewater to the next stage, thus achieving the gradual diffusion and acclimatization of the modified sludge. After 7 days, a wastewater treatment system was formed in the seven-stage sedimentation tanks. (b) Gradual degradation and sedimentation in a seven-stage pool: After acclimatization and stabilization, the wastewater with adjusted pH flows by gravity from the primary sedimentation tank through the overflow weir with a grid into the secondary to tertiary sedimentation tanks. The stirring intensity, static settling time, and sludge return ratio are adjusted in a gradient from the primary to the tertiary tanks along the water flow direction to obtain wastewater after multi-stage sedimentation.

[0021] Furthermore, in step (a), the wastewater after pH adjustment occupies 70-80% of the effective volume of the primary tank; the stirring intensity is 70-80 r / min; and the concentration of modified activated sludge in the wastewater treatment system is 3-5 g / L.

[0022] Furthermore, in step (b), the multi-stage sedimentation process is controlled by aeration to maintain dissolved oxygen (DO) at 2-3 mg / L and temperature at 30-35℃ throughout; the stirring intensity is: 70-80 r / min for stages I-II, 50-60 r / min for stages III-IV, and no stirring for stages V-VII; the static sedimentation time is: 20 min for stage I, 25 min for stage II, 30 min for stage III, 35 min for stage IV, 40 min for stage V, 45 min for stage VI, and 60 min for stage VII; the sludge return ratio is: 50% for stage I, 45% for stage II, 40% for stage III, 35% for stage IV, 30% for stage V, 25% for stage VI, and 20% for stage VII. Here, sludge return refers to returning the activated sludge settled in the sedimentation tank to the aeration and degradation zone of the same stage tank. Accurately returning the settled activated sludge to the aeration and degradation zone of the same stage tank maintains the stability of sludge concentration in each stage tank, ensuring the efficient and long-term stable operation of the seven-stage gradient sedimentation system.

[0023] Furthermore, in step (4), the COD of the effluent is ≤50mg / L and the ammonia nitrogen is ≤5mg / L; the flocculation is to add the wastewater after multi-stage sedimentation to the flocculation tank, add plant-based composite flocculant at an addition ratio of 1:100 (m / v), stir for 5 minutes, and let stand for 30-40 minutes.

[0024] Furthermore, the plant-based composite flocculant is a compound of carboxymethyl chitosan and quaternized crosslinked lignin flocculant in a mass ratio of 1:2-3.

[0025] Furthermore, the preparation method of the carboxymethyl chitosan is as follows: chitosan is dispersed in anhydrous ethanol, stirred, and then NaOH is added for alkalization; chloroacetic acid is slowly added, stirred at a constant temperature, the pH is adjusted with hydrochloric acid, filtered, and washed with anhydrous ethanol; vacuum dried to constant weight, and ground into powder to obtain carboxymethyl chitosan. Carboxymethyl chitosan can be directly dissolved in weakly alkaline wastewater without acid dissolution, and reacts with Ca in the system. 2+ It forms a three-dimensional network of complex flocs, which, through bridging, capture and encapsulate destabilized micro-flocs, suspended particles, and some dissolved organic matter, forming large and dense flocs that accelerate sedimentation.

[0026] Furthermore, the stirring time is 30 min; the alkalization temperature is 25-30℃ and the alkalization time is 1-2 h; the constant temperature stirring temperature is 50-60℃ and the constant temperature stirring time is 4-6 h; the pH is 7.0-7.5; and the vacuum drying temperature is 60-65℃.

[0027] Furthermore, the ratio of chitosan, anhydrous ethanol, sodium hydroxide and chloroacetic acid is 1g:(20-30)mL:(0.8-1.0)g:(1.5-1.8)g; the concentration of hydrochloric acid is 8-12wt.%.

[0028] Furthermore, the preparation method of the quaternized cross-linked lignin is as follows: sodium lignin sulfonate is added to deionized water, NaOH is added, and 2,3-epoxypropyltrimethylammonium chloride is slowly added dropwise while stirring. After the addition is complete, the mixture is stirred at a constant temperature to obtain a quaternized lignin solution. Epichlorohydrin is then added to carry out a cross-linking reaction. The mixture is cooled to room temperature, neutralized, filtered, washed, and vacuum dried to obtain quaternized cross-linked lignin. Quaternized cross-linked lignin introduces cationic groups. Impurities such as residual bacterial proteins in threonine wastewater carry negative charges, which can be neutralized to eliminate electrostatic repulsion of particles, causing colloidal instability and aggregation.

[0029] Furthermore, the mass ratio of sodium lignosulfonate, 2,3-epoxypropyltrimethylammonium chloride, NaOH and epichlorohydrin is 1:(0.8-1.0):(0.15-0.20):(0.2-0.4); the ratio of sodium lignosulfonate to deionized water is 1g:(20-30)mL.

[0030] Furthermore, the dropping rate is 5 mL / min; the stirring speed is 250-300 r / min and the temperature is 30-40℃; the cross-linking reaction temperature is 50-60℃ and the cross-linking reaction time is 3-4 h; the neutralization to pH is 7.0-7.5; the vacuum drying temperature is 50-55℃, the vacuum degree is -0.08--0.10 MPa, and the time is 10-12 h.

[0031] This invention addresses the characteristics of threonine wastewater—high concentration, high salinity, and high ammonia nitrogen—by optimizing the process to achieve efficient removal of organic pollutants and ammonia nitrogen. First, the threonine wastewater is pretreated by stripping away some ammonia nitrogen, reducing the toxic load on subsequent biological treatment. The effluent is then recycled back to dilute the raw water, stabilizing the influent quality and lowering the initial concentration of ammonia nitrogen, thus reducing the toxic inhibitory effect of high ammonia nitrogen on subsequent microorganisms. Second, a modified activated sludge is prepared. Mycelial balls provide a dense framework, preventing microorganism loss and improving the sludge's structural strength. Magnetic biochar fills the gaps in the framework, enhancing its mechanical strength. Chlorella adheres to the surface of the mycelia and activated carbon, making the composite structure even denser. Meanwhile, magnetic biochar possesses abundant porous structures and surface functional groups, effectively adsorbing and enriching ammonia nitrogen, phosphate, and organic matter in wastewater. It also serves as an excellent conductive framework and electron transfer medium, enhancing electron migration efficiency among bacterial communities, improving nitrification efficiency, accelerating the oxidative decomposition of organic matter, and increasing COD removal rate. Simultaneously, it provides a carbon source for Chlorella photosynthesis, promoting Chlorella growth. Furthermore, Chlorella can directly absorb and utilize ammonia nitrogen and phosphorus, reducing the inhibitory effect of high ammonia nitrogen on microorganisms. Through metabolism, it provides polysaccharides, amino acids, and other substances to the system, enhancing bacterial activity. It also releases oxygen through photosynthesis, providing endogenous oxygen for aerobic bacteria and fungi, reducing external aeration energy consumption. These three factors synergistically form a highly efficient and stable composite system, significantly improving the degradation capacity, antitoxicity, settling performance, and operational stability of activated sludge. Finally, multi-stage settling and flocculation are employed, gradually reducing the stirring intensity along the water flow direction to extend the settling time, promoting sludge granulation, and improving sludge settling performance and the system's solid-liquid separation efficiency. The carboxymethyl chitosan in the plant-based composite flocculant can react with the CaO in quicklime. 2+ It forms complex flocs, which bridge and capture colloids and fine suspended solids. The cationic groups of quaternized cross-linked lignin neutralize negatively charged pollutants, enhancing flocculation. The two are combined to form a composite flocculation system, which further removes residual suspended solids and dissolved organic matter, ensuring that the effluent water quality meets the standards.

[0032] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention optimizes the process for the characteristics of threonine wastewater, and achieves deep purification of high concentrations of organic pollutants and ammonia nitrogen in threonine wastewater to meet emission standards, thus solving the problem of low COD and ammonia nitrogen removal rates and difficulty in meeting standards in traditional processes.

[0033] (2) The present invention prepares improved activated sludge by constructing a mycelial ball-magnetic biochar-Chlorella composite system, which can significantly improve sludge settling performance and system stability, reduce sludge loss, and adopt multi-stage settling, resulting in high degradation efficiency, short hydraulic retention time, and significantly better treatment efficiency than traditional processes.

[0034] (3) The process of the present invention can reduce aeration energy consumption, make the overall operation more economical, reduce treatment costs, and has strong process adaptability. It can be modified on existing facilities, and is stable, easy to operate, and suitable for long-term industrial promotion. Detailed Implementation

[0035] Example 1 A process for treating threonine wastewater using activated sludge includes the following steps: (1) Preparation of modified activated sludge: (1-1) The concentration is 6.5×10 6 A CFU / mL Aspergillus niger spore suspension was inoculated into liquid culture medium at an inoculum size of 2.5% and cultured at 28℃, 150 rpm, and pH 6.0 for 72 h to obtain a solution containing mycelial balls. The liquid culture medium consisted of: glucose 10-30 g / L, peptone 5-8 g / L, yeast extract 2-3 g / L, KH2PO4 0.5-1.5 g / L, MgSO4·7H2O 0.5 g / L, and NaCl 0.5 g / L. (1-2) After crushing the walnut shells, dry them at 60℃ for 12h and carbonize them at 550℃ for 2.5h to obtain biochar; dissolve FeCl3·6H2O and FeCl2·4H2O in distilled water at a molar ratio of 2:1 to obtain an iron salt solution with a concentration of 0.2mol / L; add biochar to the iron salt solution at a ratio of 1g:20mL, and slowly add ammonia water dropwise to pH 10-11 under an inert atmosphere. After stirring continuously for 30min, heat in a water bath at 90℃ for 3.0h, then separate the magnetic solid, wash it and dry it at 60℃ for 12h to obtain magnetic biochar; (1-3) Add magnetic biochar to the solution containing mycelial balls at a ratio of 1g:250mL. After adding, place the solution in a shaker at 140r / min and mix and shake for 45min to obtain a solution containing mycelial balls / biochar complex. (1-4) Add Chlorella solution to a solution containing mycelial balls / biochar complex at a volume ratio of 1:1. The OD of the Chlorella solution... 680 =0.8, and after mixing and aerating at dissolved oxygen of 4.0 mg / L for 18 h, an algae-bacteria complex solution was obtained; (1-5) Add the algae-bacteria complex solution to the activated sludge system at an addition rate of 20% (V / V) and mix. Maintain an aeration rate of 0.45 L / min and stir at a speed of 55 r / min to ensure that the algae-bacteria complex is evenly dispersed in the activated sludge system to obtain modified activated sludge. (2) Preparation of plant-based composite flocculant: (2-1) Chitosan was dispersed in anhydrous ethanol and stirred for 30 min. NaOH was then added and alkalized at 30 °C for 2 h. Chloroacetic acid was slowly added and stirred at 55 °C for 5 h. The pH was adjusted to 7.0 with 10 wt.% hydrochloric acid. The mixture was filtered and washed with anhydrous ethanol. It was then vacuum dried at 60 °C to constant weight and ground into powder to obtain carboxymethyl chitosan. The ratio of chitosan, anhydrous ethanol, sodium hydroxide and chloroacetic acid was 1 g: 25 mL: 0.9 g: 1.7 g. (2-2) Sodium lignosulfonate was added to deionized water at a ratio of 1g:20mL, and NaOH was added. 2,3-epoxypropyltrimethylammonium chloride was slowly added dropwise while stirring at 300r / min and 40℃. After the addition was completed, the mixture was stirred at a constant temperature to obtain a quaternized lignin solution. Epichlorohydrin was then added. The mass ratio of sodium lignosulfonate, 2,3-epoxypropyltrimethylammonium chloride, NaOH and epichlorohydrin was 1:0.9:0.15:0.3. The cross-linking reaction was carried out at 55℃ for 3h. The mixture was cooled to room temperature and neutralized to pH 7.0. After filtration and washing, the mixture was vacuum dried at 50℃ and -0.08MPa for 12h to obtain quaternized cross-linked lignin. (2-3) Carboxymethyl chitosan and quaternized crosslinked lignin are compounded at a mass ratio of 1:2 to obtain a plant-based composite flocculant; (3) Adjust the pH of the threonine wastewater to above 10, and then aerate it at a temperature of 25℃ and an aeration intensity of 5 m. 3 / (m 2 Under the condition of ·h), it is aerated and stripped for 4h; then effluent return water is added, and the volume ratio of effluent return water to stripped wastewater is 1:1 to obtain pretreated wastewater. (4) The pH of the pretreated wastewater was adjusted to 7.5 by mixing 30wt.% liquid alkali and quicklime at a mass ratio of 1:1.5 to obtain the pH-adjusted wastewater; (5) Add modified activated sludge for multi-stage sedimentation to obtain wastewater after multi-stage sedimentation; (5-1) Modified sludge inoculation and gradual acclimatization: Modified activated sludge was inoculated into the aeration and degradation zone of the primary sedimentation tank. Simultaneously, pretreated threonine wastewater was introduced to 80% of the effective volume of the primary tank. Aeration and stirring were initiated at a stirring intensity of 70 r / min to ensure thorough mixing of the sludge and wastewater. The primary, secondary, and tertiary tanks were simultaneously activated to complete the initial acclimation. During the acclimation process, 85% of the settled modified sludge in each sedimentation tank was returned to the current stage via a return pump, 5% was returned to the previous stage, and 10% overflowed with the wastewater to the next stage, achieving gradual diffusion and acclimation of the modified sludge. After 7 days, a wastewater treatment system was formed in all seven sedimentation tanks. The concentration of modified activated sludge in the wastewater treatment system was 4 g / L. (5-2) Gradual degradation and sedimentation in a seven-stage pool: After acclimatization and stabilization, the pH-adjusted wastewater flows by gravity from the primary settling tank through an overflow weir with a screen into the secondary to VII settling tanks. The stirring intensity, static settling time, and sludge return ratio are adjusted gradient from the primary to the VII tanks along the flow direction. The stirring intensity is: 70-80 r / min for primary and secondary stages, 50-60 r / min for tertiary and quaternary stages, and no stirring for tertiary and VII stages. The static settling time is: 20 min for primary stage, 25 min for secondary stage, 30 min for tertiary stage, 35 min for quaternary stage, 40 min for tertiary stage, 45 min for tertiary stage, and 60 min for tertiary stage. The sludge return ratio is: 50% for primary stage, 45% for secondary stage, 40% for tertiary stage, 35% for tertiary stage, 30% for tertiary stage, 25% for tertiary stage, and 20% for tertiary stage. Dissolved oxygen (DO) is controlled to 2-3 mg / L through aeration throughout the process, and the temperature is controlled to 30-35℃, resulting in multi-stage settled wastewater. (6) Add the wastewater after multi-stage sedimentation to the flocculation tank, add plant-based composite flocculant at a ratio of 1:100 (m / v), stir for 5 min, let stand for 30 min, and after flocculation, obtain effluent with COD≤50mg / L and ammonia nitrogen≤5mg / L.

[0036] Example 2 A process for treating threonine wastewater using activated sludge includes the following steps: (1) Preparation of modified activated sludge: (1-1) The concentration is 6.0 × 10 6 A CFU / mL Aspergillus niger spore suspension was inoculated into liquid culture medium at an inoculum size of 3.0% and cultured at 25℃, 150 rpm, and pH 6.0 for 72 h to obtain a solution containing mycelial balls. The liquid culture medium consisted of: glucose 10-30 g / L, peptone 5-8 g / L, yeast extract 2-3 g / L, KH2PO4 0.5-1.5 g / L, MgSO4·7H2O 0.5 g / L, and NaCl 0.5 g / L. (1-2) After crushing the walnut shells, dry them at 60℃ for 12h and carbonize them at 500℃ for 3h to obtain biochar; dissolve FeCl3·6H2O and FeCl2·4H2O in distilled water at a molar ratio of 2:1 to obtain an iron salt solution with a concentration of 0.3mol / L; add biochar to the iron salt solution at a ratio of 1g:40mL, and slowly add ammonia water dropwise to pH 10-11 under an inert atmosphere. After stirring continuously for 30min, heat in a water bath at 90℃ for 3.5h, then separate the magnetic solid, wash it and dry it at 60℃ for 12h to obtain magnetic biochar. (1-3) Add magnetic biochar to the solution containing mycelial balls at a ratio of 1g: 300mL. After adding, place the solution in a shaker at 120r / min and mix and shake for 60min to obtain a solution containing mycelial balls / biochar complex. (1-4) Add Chlorella solution to a solution containing mycelial balls / biochar complex at a volume ratio of 1:1. The OD of the Chlorella solution... 680 =0.6, and after mixing and aerating at dissolved oxygen of 3.0 mg / L for 24 h, an algae-bacterial complex solution was obtained; (1-5) Add the algae-bacteria complex solution to the activated sludge system at an addition rate of 25% (V / V) and mix. Maintain an aeration rate of 0.5 L / min and stir at a speed of 60 r / min to ensure that the algae-bacteria complex is evenly dispersed in the activated sludge system to obtain modified activated sludge. (2) Preparation of plant-based composite flocculant: (2-1) Chitosan was dispersed in anhydrous ethanol and stirred for 30 min. NaOH was then added and alkalized at 30 °C for 2 h. Chloroacetic acid was slowly added and stirred at 55 °C for 5 h. The pH was adjusted to 7.0 with 10 wt.% hydrochloric acid. The mixture was filtered and washed with anhydrous ethanol. It was then vacuum dried at 60 °C to constant weight and ground into powder to obtain carboxymethyl chitosan. The ratio of chitosan, anhydrous ethanol, sodium hydroxide and chloroacetic acid was 1 g: 30 mL: 1.0 g: 1.8 g. (2-2) Sodium lignin sulfonate was added to deionized water at a ratio of 1g:20mL. NaOH was added, and 2,3-epoxypropyltrimethylammonium chloride was slowly added dropwise while stirring at 300r / min and 40℃. After the addition was complete, the mixture was stirred at a constant temperature to obtain a quaternized lignin solution. Epichlorohydrin was then added. The mass ratio of sodium lignin sulfonate, 2,3-epoxypropyltrimethylammonium chloride, NaOH and epichlorohydrin was 1:0.9:0.20:0.4. The cross-linking reaction was carried out at 55℃ for 3h. The mixture was cooled to room temperature and neutralized to pH 7.5. After filtration and washing, the mixture was vacuum dried at 50℃ and -0.10MPa for 12h to obtain quaternized cross-linked lignin. (2-3) Carboxymethyl chitosan and quaternized crosslinked lignin were compounded at a mass ratio of 1:3 to obtain a plant-based composite flocculant; (3) Adjust the pH of the threonine wastewater to above 10, and then aerate it at a temperature of 30℃ and an aeration intensity of 5 m. 3 / (m 2 Under the condition of ·h), it is aerated and stripped for 2h; then effluent return water is added, and the volume ratio of effluent return water to stripped wastewater is 2:1 to obtain pretreated wastewater; (4) The pH of the pretreated wastewater was adjusted to 8.0 by mixing 30wt.% liquid alkali and quicklime at a mass ratio of 1:1.8 to obtain the pH-adjusted wastewater; (5) Add modified activated sludge for multi-stage sedimentation to obtain the wastewater after multi-stage sedimentation: (5-1) Modified sludge inoculation and gradual acclimatization: Modified activated sludge was inoculated into the aeration and degradation zone of the primary tank, while pretreated threonine wastewater was introduced to 80% of the effective volume of the primary tank. Aeration and stirring were started at a stirring intensity of 80 r / min to ensure thorough mixing of the sludge and wastewater. The primary to tertiary tanks were started simultaneously to complete the initial acclimation. During the acclimation process, 85% of the modified sludge settled in each settling tank was returned to the current stage via a return pump, 5% of the settled modified sludge was returned to the previous stage, and 10% of the settled modified sludge overflowed with the wastewater to the next stage, achieving step-by-step diffusion and acclimation of the modified sludge. After 7 days, a wastewater treatment system was formed in all seven settling tanks. The concentration of modified activated sludge in the wastewater treatment system was 3 g / L. (5-2) Gradual degradation and sedimentation in a seven-stage pool: After acclimatization and stabilization, the pH-adjusted wastewater flows by gravity from the primary settling tank through an overflow weir with a grid into the secondary to VII settling tanks. The stirring intensity, static settling time, and sludge return ratio are adjusted gradient from the primary to the VII tanks along the flow direction. The stirring intensity is: 70-80 r / min for primary and secondary stages, 50-60 r / min for tertiary and quaternary stages, and no stirring for tertiary and VII stages. The static settling time is: 20 min for primary stage, 25 min for secondary stage, 30 min for tertiary stage, 35 min for quaternary stage, 40 min for tertiary stage, 45 min for tertiary stage, and 60 min for tertiary stage. The sludge return ratio is: 50% for primary stage, 45% for secondary stage, 40% for tertiary stage, 35% for tertiary stage, 30% for tertiary stage, 25% for tertiary stage, and 20% for tertiary stage. Dissolved oxygen (DO) is controlled at 2-3 mg / L and temperature is controlled at 30-35℃ throughout the process, resulting in multi-stage settled wastewater. (6) Add the wastewater after multi-stage sedimentation to the flocculation tank, add plant-based composite flocculant at a ratio of 1:100 (m / v), stir for 5 min, let stand for 40 min, and after flocculation, obtain effluent with COD≤50mg / L and ammonia nitrogen≤5mg / L.

[0037] Example 3 A process for treating threonine wastewater using activated sludge includes the following steps: (1) Preparation of modified activated sludge: (1-1) The concentration is 6.2 × 10 6A CFU / mL Aspergillus niger spore suspension was inoculated into liquid culture medium at an inoculum size of 2.8% and cultured at 27℃, 150 rpm, and pH 6.0 for 72 h to obtain a solution containing mycelial balls. The liquid culture medium consisted of: glucose 10-30 g / L, peptone 5-8 g / L, yeast extract 2-3 g / L, KH2PO4 0.5-1.5 g / L, MgSO4·7H2O 0.5 g / L, and NaCl 0.5 g / L. (1-2) After crushing the walnut shells, dry them at 60℃ for 12h and carbonize them at 600℃ for 3h to obtain biochar; dissolve FeCl3·6H2O and FeCl2·4H2O in distilled water at a molar ratio of 2:1 to obtain an iron salt solution with a concentration of 0.1mol / L; add biochar to the iron salt solution at a ratio of 1g:50mL, and slowly add ammonia water dropwise to pH 10-11 under an inert atmosphere. After stirring continuously for 30min, heat in a water bath at 90℃ for 2.5h, then separate the magnetic solid, wash it and dry it at 60℃ for 12h to obtain magnetic biochar. (1-3) Add magnetic biochar to the solution containing mycelial balls at a ratio of 1g:200mL. After adding, place the solution in a shaker at 150r / min and mix and shake for 30min to obtain a solution containing mycelial balls / biochar complex. (1-4) Add Chlorella solution to a solution containing mycelial balls / biochar complex at a volume ratio of 1:1. The OD of the Chlorella solution... 680 =1.0, and mixed and aerated at dissolved oxygen of 5.0 mg / L for 12 h to obtain algae-bacteria complex solution; (1-5) Add the algae-bacteria complex solution to the activated sludge system at an addition rate of 15% (V / V) and mix. Maintain an aeration rate of 0.5 L / min and stir at a speed of 60 r / min to ensure that the algae-bacteria complex is evenly dispersed in the activated sludge system to obtain modified activated sludge. (2) Preparation of plant-based composite flocculant: (2-1) Chitosan was dispersed in anhydrous ethanol and stirred for 30 min. NaOH was then added and alkalized at 30 °C for 1 h. Chloroacetic acid was slowly added and stirred at 50 °C for 6 h. The pH was adjusted to 7.0 with 10 wt.% hydrochloric acid. The mixture was filtered and washed with anhydrous ethanol. It was then vacuum dried at 60 °C to constant weight and ground into powder to obtain carboxymethyl chitosan. The ratio of chitosan, anhydrous ethanol, sodium hydroxide and chloroacetic acid was 1 g: 20 mL: 0.8 g: 1.5 g. (2-2) Sodium lignin sulfonate was added to deionized water at a ratio of 1g:20mL. NaOH was added, and 2,3-epoxypropyltrimethylammonium chloride was slowly added dropwise while stirring at 300r / min and 40℃. After the addition was complete, the mixture was stirred at a constant temperature to obtain a quaternized lignin solution. Epichlorohydrin was then added. The mass ratio of sodium lignin sulfonate, 2,3-epoxypropyltrimethylammonium chloride, NaOH and epichlorohydrin was 1:1:0.2:0.2. The cross-linking reaction was carried out at 55℃ for 3h. The mixture was cooled to room temperature and neutralized to pH 7.0. After filtration and washing, the mixture was vacuum dried at 50℃ and -0.09MPa for 12h to obtain quaternized cross-linked lignin. (2-3) Carboxymethyl chitosan and quaternized crosslinked lignin were compounded at a mass ratio of 1:3 to obtain a plant-based composite flocculant; (3) Adjust the pH of the threonine wastewater to above 10, and then aerate it at a temperature of 25℃ and an aeration intensity of 3m. 3 / (m 2 Under the condition of ·h), it is aerated and stripped for 4h; then effluent return water is added, and the volume ratio of effluent return water to stripped wastewater is 2:1 to obtain pretreated wastewater; (4) The pH of the pretreated wastewater was adjusted to 7.0 by mixing 30wt.% liquid alkali and quicklime at a mass ratio of 1:1.0 to obtain the pH-adjusted wastewater; (5) Add modified activated sludge for multi-stage sedimentation to obtain the wastewater after multi-stage sedimentation: (5-1) Modified sludge inoculation and gradual acclimatization: Modified activated sludge was inoculated into the aeration and degradation zone of the primary sedimentation tank. Simultaneously, pH-adjusted wastewater was introduced to 80% of the effective volume of the primary tank. Aeration and stirring were initiated at a stirring intensity of 80 r / min to ensure thorough mixing of the sludge and wastewater. The primary, secondary, and tertiary tanks were simultaneously activated to complete the initial acclimation. During the acclimation process, 85% of the settled modified sludge in each sedimentation tank was returned to the current stage via a return pump, 5% was returned to the previous stage, and 10% overflowed with the wastewater to the next stage, achieving gradual diffusion and acclimation of the modified sludge. After 7 days, a wastewater treatment system was formed in all seven sedimentation tanks; the sludge concentration in the wastewater treatment system was 5 g / L. (5-2) Gradual degradation and sedimentation in a seven-stage pool: After acclimatization and stabilization, the pH-adjusted wastewater flows by gravity from the primary settling tank through an overflow weir with a grid into the secondary to VII settling tanks. The stirring intensity, static settling time, and sludge return ratio are adjusted gradient from the primary to the VII tanks along the flow direction. The stirring intensity is: 70-80 r / min for primary and secondary stages, 50-60 r / min for tertiary and quaternary stages, and no stirring for tertiary and VII stages. The static settling time is: 20 min for primary stage, 25 min for secondary stage, 30 min for tertiary stage, 35 min for quaternary stage, 40 min for tertiary stage, 45 min for tertiary stage, and 60 min for tertiary stage. The sludge return ratio is: 50% for primary stage, 45% for secondary stage, 40% for tertiary stage, 35% for tertiary stage, 30% for tertiary stage, 25% for tertiary stage, and 20% for tertiary stage. Dissolved oxygen (DO) is controlled at 2-3 mg / L and temperature is controlled at 30-35℃ throughout the process, resulting in multi-stage settled wastewater.

[0038] (6) Add the wastewater after multi-stage sedimentation to the flocculation tank, add plant-based composite flocculant at a ratio of 1:100 (m / v), stir for 5 min, let stand for 30 min, and after flocculation, obtain effluent with COD≤50mg / L and ammonia nitrogen≤5mg / L.

[0039] Experimental Example 1 Take 3 groups of threonine protonate wastewater, 3L per group, and treat them according to the following grouping: Control group 1: No pH adjustment to above 10, aeration stripping, or effluent recirculation was performed on the threonine wastewater. Control group 2: First, adjust the pH of the threonine wastewater to above 10, aerate and strip at 25-30℃ for 3 hours, and do not perform effluent recirculation. Experimental group: First, adjust the pH of the threonine wastewater to above 10, aerate and strip at 25-30℃ for 3 hours, and then recycle the effluent (volume ratio 1:1). The treated threonine wastewater was tested. The results are shown in Table 1.

[0040] Table 1. Substance content of threonine wastewater Table 1 shows that the ammonia nitrogen removal rate in the experimental group reached 69.3%, significantly higher than that in the two control groups. This indicates that aeration and stripping after pH adjustment can convert ammonium ions into free ammonia and strip it out as effluent. The effluent is then recycled back to dilute the raw water, effectively reducing the ammonia nitrogen concentration. This demonstrates that the present invention, through aeration and stripping and effluent recycling, can significantly reduce the ammonia nitrogen content in water, greatly reduce the inhibitory effect of high ammonia nitrogen on microorganisms, and enhance microbial activity.

[0041] Experiment Example 2 Five groups of activated sludge were prepared according to the method in Example 1: Conventional activated sludge group: the activated sludge in steps (1-5) of Example 1; Group without mycelium balls: Modified activated sludge prepared according to the method in Example 1 without the addition of mycelium balls; Non-magnetic biochar group: Modified activated sludge prepared according to the method of Example 1 without the addition of biochar; Chlorella-deficient group: Modified activated sludge prepared according to the method of Example 1 without the addition of Chlorella; Modified activated sludge group: Modified activated sludge prepared according to the method in Example 1; Following the process described in Example 1, the activated sludge was used to treat the pH-adjusted wastewater under the same conditions for 7 days. The COD removal rate, ammonia nitrogen removal rate, and sludge loss were measured. The results are listed in Table 2.

[0042] Table 2. Effects of modified activated sludge on threonine wastewater As shown in Table 2, compared with the modified activated sludge group, the ordinary sludge group was inhibited by high salt and high ammonia nitrogen, resulting in a decrease in COD removal rate and ammonia nitrogen removal rate, and an increase in sludge loss. The COD removal rate and ammonia nitrogen removal rate were all reduced in the mycelium ball-deficient group, the magnetic biochar-deficient group, and the Chlorella-deficient group, and the sludge loss was increased. It is evident that this invention improves ordinary activated sludge by adding mycelial balls, magnetic biochar, and Chlorella. The resulting improved activated sludge significantly increases COD and ammonia nitrogen removal rates while substantially reducing sludge loss. This is because the magnetic biochar in the improved activated sludge adsorbs pollutants, inhibits excessive growth of filamentous fungi, and increases sludge settling speed. The mycelial balls provide a framework, acting as an attachment carrier for microorganisms and enhancing sludge floc stability. Chlorella produces oxygen through photosynthesis, providing oxygen for aerobic microbial metabolism and absorbing nitrogen and phosphorus nutrients from wastewater, thus alleviating microbial activity inhibition. These three elements synergistically construct a stable algae-bacteria-sludge symbiotic system, which not only enhances pollutant degradation capabilities but also optimizes sludge settling performance, achieving efficient treatment of threonine wastewater and reducing sludge loss.

[0043] Experimental Example 3 Following the process described in Example 1, single-stage, four-stage, five-stage, six-stage, seven-stage, and eight-stage sedimentation treatments were employed, with total retention time controlled. The COD and ammonia nitrogen content, as well as the sludge loss rate, of the effluent after sedimentation were measured. The results are listed in Table 3.

[0044] Table 3. Effects of multi-stage sedimentation on threonine wastewater Table 3 shows that the single-stage sedimentation process resulted in the worst removal efficiency, with effluent COD at 86.3 mg / L and ammonia nitrogen at 9.6 mg / L. This is because single-stage mixed sedimentation causes significant disturbance, insufficient gradient degradation stratification, and weak tolerance to high-load shocks. The COD, ammonia nitrogen, and sludge loss rates of the effluent from the four- to seven-stage sedimentation processes gradually decreased. The eight-stage sedimentation process resulted in effluent COD at 52.1 mg / L and ammonia nitrogen at 5.1 mg / L, showing a slight increase. This is because the excessive number of stages slowed hydraulic flow, increased local endogenous respiration, and a slight deterioration in effluent quality. Therefore, compared to other groups, the seven-stage sedimentation process had the lowest effluent COD and ammonia nitrogen content, the shortest residence time, and the least sludge loss. This demonstrates that the gradient reflux and staged sedimentation structure of the seven-stage process in this invention can significantly reduce effluent COD and ammonia nitrogen content, significantly reduce sludge loss, achieve water quality improvement in the shortest time, and has low operating costs, making it suitable for industrial applications.

[0045] Experiment Example 4 Wastewater from the multi-stage sedimentation process in Example 1 was divided into 5 groups, each containing 2L, and experiments were conducted according to the following groupings: Group 1: No flocculant added; Group 2: Add carboxymethyl chitosan from Example 1; Group 3: Add quaternized cross-linked lignin from Example 1; Group 4: Add the composite flocculant from Example 1; Group 5: Add conventional polyaluminum chloride + polyacrylamide (mass ratio 1:2); The dosage ratio was 1:100 (m / v), stirred for 5 minutes, and allowed to stand for 30 minutes. The COD and ammonia nitrogen content in the water were then measured. The results are listed in Table 4.

[0046] Table 4. Effects of composite flocculants on threonine wastewater Table 4 shows that Group 1, without flocculant, had higher COD and ammonia nitrogen contents than the groups with various flocculants. Compared to Group 1, Groups 2-3 showed lower COD and ammonia nitrogen contents, but still higher than Group 4. Group 4 had the lowest COD and ammonia nitrogen contents, demonstrating a synergistic effect between carboxymethyl chitosan and quaternized cross-linked lignin, which improved flocculation and purification efficiency. Group 5 used conventional flocculants, and its flocculation effect was worse than Group 4, proving that the plant-based composite flocculant prepared in this invention has stronger adaptability to threonine wastewater and better flocculation and purification effects compared to traditional inorganic-organic composite flocculants. Furthermore, the plant-based material is more environmentally friendly, reducing secondary pollution and meeting the green environmental protection requirements of wastewater treatment. In summary, the composite flocculant prepared in this invention can effectively flocculate pollutants in wastewater, achieving deep purification of threonine wastewater.

Claims

1. A process for treating threonine wastewater using activated sludge, characterized in that: Includes the following steps: (1) Pre-treat the threonine wastewater to obtain pre-treated wastewater; (2) Adjust the pH of the pretreated wastewater to obtain the pH-adjusted wastewater; (3) Add modified activated sludge for multi-stage sedimentation to obtain wastewater after multi-stage sedimentation; (4) After the wastewater has undergone multi-stage sedimentation, it is flocculated to obtain the effluent.

2. The process for treating threonine wastewater using activated sludge according to claim 1, characterized in that: In step (1), the pretreatment involves aerating and stripping the threonine wastewater before adding effluent return water for dilution.

3. The process for treating threonine wastewater using activated sludge according to claim 2, characterized in that: In step (2), the pH of the pretreated wastewater is adjusted to 7.0-8.0 using a compound alkali agent; the compound alkali agent is composed of liquid alkali and quicklime in a mass ratio of 1:(1.0-1.8).

4. The process for treating threonine wastewater using activated sludge according to claim 3, characterized in that: In step (3), the method for preparing the modified activated sludge is as follows: (I) Inoculate the spore suspension into a liquid culture medium and culture it to obtain a solution containing mycelial balls; (II) Add magnetic biochar to the solution containing mycelial balls, mix and shake to obtain a solution containing mycelial balls / biochar complex; (III) Add Chlorella solution to a solution containing mycelial balls / biochar complex, mix and aerate to obtain algae-fungus complex solution; (IV) The algae-bacteria complex solution was added to the activated sludge system and mixed to obtain modified activated sludge.

5. The process for treating threonine wastewater using activated sludge according to claim 4, characterized in that: In step (II), the ratio of the magnetic biochar to the solution containing mycelial balls is 1g:(200-300)mL.

6. The process for treating threonine wastewater using activated sludge according to claim 5, characterized in that: In step (II), the magnetic biochar is prepared by: crushing walnut shells, drying and carbonizing them to obtain biochar; dissolving FeCl3·6H2O and FeCl2·4H2O in distilled water to obtain an iron salt solution; adding biochar to the iron salt solution, slowly adding ammonia water under an inert atmosphere, continuously stirring and heating in a water bath, then separating the magnetic solid, washing and drying to obtain magnetic biochar.

7. The process for treating threonine wastewater using activated sludge according to claim 6, characterized in that: In step (III), the volume ratio of the Chlorella solution to the solution containing mycelial balls / biochar complex is 1:

1.

8. The process for treating threonine wastewater using activated sludge according to claim 1, characterized in that: In step (3), the multi-stage sedimentation is a seven-stage sedimentation, which is carried out in a seven-stage gradient sedimentation tank. Each sedimentation tank is equipped with an aeration degradation zone and a static sedimentation zone. The volume ratio of the aeration degradation zone to the static sedimentation zone is 3:

2. An overflow weir with a grid and a sludge return port are provided between the tanks. The sludge return is carried out by a return pump.

9. The process for treating threonine wastewater using activated sludge according to claim 8, characterized in that: The specific operation of the multi-stage settlement is as follows: (a) Modified sludge inoculation and stepwise acclimatization: Modified activated sludge was inoculated into the aeration and degradation zone of the primary tank, while wastewater with adjusted pH was introduced. Aeration and stirring were started to ensure thorough mixing. The first to third stage tanks were started simultaneously to complete the initial acclimatization. During the acclimatization process, 85% of the modified sludge settled in each stage was returned to the current stage via a return pump, 5% was returned to the previous stage, and 10% overflowed with the wastewater to the next stage, thus achieving the gradual diffusion and acclimatization of the modified sludge. After 7 days, a wastewater treatment system was formed in the seven-stage sedimentation tanks. (b) Gradual degradation and sedimentation in a seven-stage pool: After acclimatization and stabilization, the wastewater with adjusted pH flows by gravity from the primary sedimentation tank through the overflow weir with a grid into the secondary to tertiary sedimentation tanks. The stirring intensity, static settling time, and sludge return ratio are adjusted in a gradient from the primary to the tertiary tanks along the water flow direction to obtain wastewater after multi-stage sedimentation.

10. The process for treating threonine wastewater using activated sludge according to claim 1, characterized in that: In step (4), the flocculation is to add the wastewater after multi-stage sedimentation to the flocculation tank and add plant-based composite flocculant at an addition ratio of 1:100 (m / v); the plant-based composite flocculant is a compound of carboxymethyl chitosan and quaternized crosslinked lignin flocculant in a mass ratio of 1:2-3.

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