A method for sludge discharge control in the rapid start-up process of a phosphorus-enriched biofilm process

Abstract

This invention provides a method for controlling sludge discharge during the rapid start-up of a phosphorus enrichment biofilm process. The method involves periodically measuring the anaerobic phosphorus release and carbon source consumption of the mud-film mixing system within the biofilm reactor before sludge discharge, the ratio of anaerobic phosphorus release from the biofilm to that from the mud-film mixing system, and the biofilm thickness. Based on the premise that the carbon source consumption of the mud-film mixing system is increasing and the ratio of anaerobic phosphorus release to carbon source consumption is decreasing, sludge is discharged from the biofilm reactor when the biofilm thickness is 5–10 μm and the anaerobic phosphorus release from the biofilm accounts for 90–110% of the anaerobic phosphorus release from the mud-film mixing system. This method provides a quantitative standard for selecting sludge discharge control methods during the rapid start-up of a phosphorus enrichment biofilm process, aiming to obtain a biofilm with good phosphorus enrichment capacity in a shorter start-up time.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a method for controlling sludge discharge during the rapid start-up of a phosphorus enrichment biofilm process. Background Technology

[0002] Phosphorus is a scarce and polluting natural resource, existing in nature as phosphate rock. Current phosphate rock reserves are only sufficient for human consumption for 50-100 years. Recovering phosphorus from wastewater can meet 15%-20% of human phosphorus needs. The prerequisite for phosphorus recovery is enriching phosphate to above 50 mg / L. Biofilm methods for phosphate enrichment have good application value due to their low sludge production, high enrichment efficiency, and simple operation. However, the prerequisite for the effective application of biofilm methods is cultivating a biofilm with high phosphorus enrichment capacity, i.e., a phosphorus-enriched biofilm, to achieve rapid start-up of the phosphorus-enriched biofilm process. The cultivation process of a phosphorus-enriched biofilm involves first mixing activated sludge with suspended packing material for adhesion and biofilm formation, then discharging the activated sludge for biofilm enrichment cultivation, ultimately obtaining a biofilm with high phosphate enrichment capacity, thus achieving rapid start-up of the phosphorus-enriched biofilm process.

[0003] Sludge removal can facilitate the transformation from a sludge-film mixing system to a biofilm system. Therefore, a key factor in the rapid startup of a phosphorus enrichment biofilm process is sludge removal. The choice of sludge removal control method affects the start-up time and the phosphorus enrichment capacity of the biofilm upon completion of startup. When sludge is removed too late, activated sludge and biofilm coexist, and the two microorganisms compete for carbon sources, resulting in slow growth of biofilm microorganisms due to insufficient carbon source uptake and limited space, leading to a long start-up time and high costs. When sludge is removed too early, the microbial content on the biofilm is low, the proliferation rate is slow, and it takes a long time for a phosphorus enrichment biofilm to form.

[0004] Currently, the methods for controlling sludge discharge in phosphorus enrichment biofilm processes are often determined by the following criteria: (1) the biofilm on the packing material is darker in color; (2) it is not easily detached from the packing material surface; (3) microscopic examination reveals maturation indicator organisms such as rotifers and vorticella; and (4) the biofilm is viscous, evenly distributed, and thickly grown. These current methods rely primarily on subjective experience and lack a quantitative standard for determining the sludge discharge control method for phosphorus enrichment biofilm processes. Furthermore, the sludge discharge control methods determined by these current methods are only for obtaining phosphorus enrichment biofilms and do not consider the impact of the sludge discharge control method on the start-up time and phosphorus enrichment capacity of the phosphorus enrichment biofilm process.

[0005] In order to achieve rapid start-up of phosphorus enrichment biofilm technology and realize economic and energy-saving goals, it is necessary to find a sludge control method to obtain quantitative standards for phosphorus enrichment biofilm. Summary of the Invention

[0006] The purpose of this invention is to provide a method for controlling sludge discharge during the rapid start-up of a phosphorus enrichment biofilm process. By selecting sludge discharge control through quantitative standards, the aim is to obtain a biofilm with good phosphorus enrichment capacity in a shorter start-up time.

[0007] To achieve the above objectives, the present invention provides a method for controlling sludge discharge during the rapid start-up of a phosphorus enrichment biofilm process. In the phosphorus enrichment biofilm process, the biofilm reactor is operated alternately in aerobic / anaerobic mode, and the anaerobic phosphorus release, carbon source consumption, and ratio of anaerobic phosphorus release to carbon source consumption of the sludge-film mixing system in the biofilm reactor are measured periodically during the anaerobic stage.

[0008] The biofilm packing material at the end of the aerobic stage was collected periodically to simulate the anaerobic stage in the biofilm reactor and to conduct an anaerobic phosphorus release experiment of the biofilm, and to determine the amount and thickness of the anaerobic phosphorus release of the biofilm.

[0009] Provided that the carbon source consumption of the mud-film mixing system is increasing and the ratio of anaerobic phosphorus release to carbon source consumption of the mud-film mixing system is decreasing, when the thickness of the biofilm is 5-10 μm and the anaerobic phosphorus release of the biofilm accounts for 90-110% of the anaerobic phosphorus release of the mud-film mixing system, the biofilm reactor is sludge discharged.

[0010] As a further improvement of the present invention, the phosphorus enrichment biofilm process includes the following steps: adding activated sludge into the biofilm reactor, alternating between aerobic and anaerobic operation of the biofilm reactor, and cultivating polyphosphate-accumulating bacteria on the suspended packing material in the biofilm reactor, wherein a carbon source is added during the anaerobic stage and the anaerobic effluent is recycled as phosphorus recovery liquid; after sludge removal from the biofilm reactor, the aerobic / anaerobic alternating operation of the biofilm reactor continues until the phosphorus uptake and release of the biofilm no longer increase, thereby obtaining a phosphorus enrichment biofilm and achieving successful start-up of the phosphorus enrichment biofilm process.

[0011] As a further improvement of the present invention, the biofilm reactor is a sequencing batch reactor, an anaerobic-aerobic biofilter, or a trickling filter; wherein, the carbon source is added to the biofilm reactor in the form of no carbon source added for aerobic processes and carbon source added for anaerobic processes.

[0012] As a further improvement of the present invention, before sludge discharge, the dissolved oxygen content in the aerobic stage is controlled at 4-5 mg / L; after sludge discharge, the dissolved oxygen content in the aerobic stage is controlled at 6-8 mg / L, and the pH is controlled at 7-7.5.

[0013] As a further improvement of the present invention, an anaerobic phosphorus release experiment of the biofilm reactor is conducted by simulating the anaerobic stage in the biofilm reactor, including the following steps: placing biofilm packing material at the end of the aerobic stage in a container, adding anaerobic water containing a carbon source, and conducting an anaerobic phosphorus release experiment of the biofilm reactor, wherein the filling ratio of the biofilm packing material relative to the container is the same as the filling ratio of the suspended packing material relative to the biofilm reactor.

[0014] As a further improvement of the present invention, the filling ratio of the suspended packing material to the biofilm reactor is 35-45%.

[0015] As a further improvement of the present invention, the biofilm reactor is operated alternately with one aerobic stage and one anaerobic stage as a cycle. Every day, the mud-film mixing system of one anaerobic stage is sampled to measure the anaerobic phosphorus release, carbon source consumption, and the ratio of anaerobic phosphorus release to carbon source consumption. Every day, biofilm packing material at the end of the aerobic stage, which belongs to the same cycle as the anaerobic stage, is collected to conduct a simulated biofilm anaerobic phosphorus release experiment, and the anaerobic phosphorus release and thickness of the biofilm are measured.

[0016] As a further improvement of the present invention, in each cycle, the hydraulic retention time of the aerobic stage is 2 to 10 hours, and the hydraulic retention time of the anaerobic stage is 1 to 6 hours.

[0017] As a further improvement of the present invention, the thickness of the biofilm at the end of the aerobic phase was measured using a microscope.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] This invention periodically measures the anaerobic phosphorus release, carbon source consumption, and the ratio of anaerobic phosphorus release to carbon source consumption in the mud-film mixing system before sludge discharge. It assumes that the carbon source consumption of the mud-film mixing system is on an upward trend and the ratio of anaerobic phosphorus release to carbon source consumption is on a downward trend. It also combines the following two indicators: (1) the extent to which the phosphorus enrichment capacity of activated sludge is transferred to the biofilm. The percentage of anaerobic phosphorus release in the mud-film mixing system is determined by batch experiments on the biofilm when mud-film competition occurs; (2) the thickness of the biofilm before sludge discharge. A quantitative standard for sludge discharge control method during the rapid start-up of the phosphorus enrichment biofilm process is established.

[0020] This invention provides a quantitatively standardized sludge control method for the rapid start-up of phosphorus enrichment biofilm processes, solving the problems of inconsistent sludge control methods, large fluctuations due to individual subjective factors, and long start-up times in existing phosphorus enrichment biofilm processes. On the one hand, it ensures that the cultivated biofilm has a stable and efficient phosphorus enrichment capacity; on the other hand, it shortens the time, saves manpower and economic costs, and has energy-saving and emission-reduction effects. Attached Figure Description

[0021] Figure 1 This is a flowchart of an apparatus for a phosphorus enrichment biofilm process provided in an embodiment of the present invention. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. However, it should be noted that these embodiments are not intended to limit the present invention. Equivalent changes or substitutions in function, method, or structure made by those skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0023] Combination Figure 1 As shown, the present invention provides a phosphorus enrichment biofilm process. The apparatus involved in the operation of the process includes: a biofilm reactor 1 equipped with suspended packing material 11, an aeration device 12, a stirrer 13 and a data acquisition device 14 connected to the biofilm reactor 1, a wastewater storage device 2, a phosphorus recovery device 3 and a carbon source addition device 4 connected to the biofilm reactor 1.

[0024] The process flow is as follows:

[0025] Activated sludge is added to biofilm reactor 1, and biofilm reactor 1 is operated in alternating aerobic / anaerobic mode. Phosphorus enrichment biofilm is cultured on the suspended packing material 11 in biofilm reactor 1.

[0026] In the aerobic stage, phosphorus-containing wastewater flows from wastewater storage device 2 into biofilm reactor 1. Aeration device 12 provides an aerobic environment. Stirrer 13 is turned on to stir the phosphorus-containing wastewater in biofilm reactor 1 to make the water quality uniform. After the aerobic stage ends, aeration device 12 is turned off and wastewater is discharged. Switching to the anaerobic stage, anaerobic influent from phosphorus recovery device 3 and carbon source from carbon source addition device 4 are simultaneously transported into biofilm reactor 1. Anaerobic effluent is recycled back to phosphorus recovery device 3 as phosphorus recovery liquid.

[0027] By alternating aerobic and anaerobic operation, the aerobic stage involves aeration without adding a carbon source, where polyphosphate-accumulating bacteria on the biofilm absorb phosphate from phosphorus-containing wastewater. In the anaerobic stage, only stirring is performed, and a carbon source is added and mixed with the anaerobic influent before being introduced into biofilm reactor 1. The polyphosphate-accumulating bacteria utilize the carbon source to release the phosphate accumulated within them into the phosphorus recovery solution, which is then recycled to phosphorus recovery device 3. During each cycle, the phosphorus recovery solution from phosphorus recovery device 3 is used as the anaerobic influent, achieving recycling of the phosphorus recovery solution. After sludge removal from biofilm reactor 1, the aerobic / anaerobic alternating operation continues until the phosphorus uptake and release by the biofilm no longer increase, resulting in a phosphorus-enriched biofilm. In this embodiment, the phosphorus-enriched biofilm refers to a biofilm that, through the principle of aerobic phosphorus uptake and anaerobic carbon source consumption for phosphorus release, can enrich low-concentration phosphate in the influent to a high concentration of several hundred milligrams of phosphate per liter.

[0028] The biofilm is enriched and cultivated into a phosphorus-enriched biofilm in biofilm reactor 1, and the phosphate concentration of the phosphorus recovery solution in phosphorus recovery unit 3 also increases. During the stable operation phase of the process, the time taken for the phosphate concentration of the phosphorus recovery solution in phosphorus recovery unit 3 to increase from 0 mg / L to the highest concentration (several hundred milligrams per liter) is defined as one phosphate harvesting cycle (in days).

[0029] In one embodiment, the activated sludge is taken from the secondary sedimentation tank of the A2 / O process in a wastewater treatment plant. The amount of activated sludge used is 3.5–4.5 L, and the concentration of activated sludge is 3000–6000 mg / L. Biofilm reactor 1 is a sequencing batch reactor (BSBR). The volume of biofilm reactor 1 is 10 L (wherein, the suspended packing material has a filling ratio of 35–45%, is made of Kaldnes K1 polyethylene, has a diameter of 15 mm, a height of 5 mm, and an average specific surface area of ​​900 m²). 2 / m 3 The volume of wastewater storage device 2 is 150L, ​​the volume of phosphorus recovery device 3 is 20L, and the volume of carbon source addition device 4 is 4L.

[0030] The influent flow rate of biofilm reactor 1 is 800 mL / min, and the influent time is 5–10 min. The biofilm reactor is operated alternately with one aerobic stage and one anaerobic stage as one cycle. The hydraulic retention time of the aerobic stage is preferably 2–10 hours, and the hydraulic retention time of the anaerobic stage is preferably 1–6 hours. For example, the hydraulic retention time of the aerobic stage is controlled at 4 hours, and the hydraulic retention time of the anaerobic stage is controlled at 2 hours. Before sludge discharge, the dissolved oxygen (DO) in the aerobic stage is controlled at 4–5 mg / L, and after sludge discharge, the dissolved oxygen (DO) in the aerobic stage is controlled at 6–8 mg / L. The pH is controlled at 7.0–7.5.

[0031] Aerobic wastewater components (i.e., phosphorus-containing wastewater components): 10 mg / L KH2PO4, 300 mg / L NaHCO3, 40 mg / L NH4Cl, 8 mg / L CaCl2·2H2O, 30 mg / L MgSO4·7H2O, 2 mg / L EDTA·2Na.

[0032] Anaerobic water composition (i.e., the ratio of carbon source content to anaerobic influent volume): 200 mg / L sodium acetate.

[0033] In other alternative embodiments, the carbon source added during the anaerobic stage can also be acetic acid or propionic acid, and the carbon source concentration can be adjusted accordingly based on the utilization efficiency of polyphosphate-accumulating bacteria.

[0034] It should be noted that the phosphorus enrichment capacity of biofilms depends on polyphosphate-accumulating bacteria (PABs). Polyphosphate-accumulating bacteria are a type of microorganism that competes with PPAs for carbon sources and does not absorb or release phosphorus. By measuring carbon source consumption and the carbon source utilization efficiency of PPAs, the abundance of PPAs and their metabolic activity in phosphate enrichment can be indirectly reflected. Anaerobic phosphorus release / carbon source consumption (Prel / COD) is an indicator for evaluating the carbon source utilization efficiency of PPAs; a higher Prel / COD value indicates higher carbon source utilization efficiency, stronger phosphorus enrichment capacity, and higher abundance of PPAs. In the sludge-film hybrid system, the carbon source consumption (i.e., COD consumption) is increasing, while the anaerobic phosphorus release / carbon source consumption (Prel / COD) is decreasing. This indicates that the carbon source consumption of activated sludge and biofilm is increasing. However, due to the competitive inhibition that occurs as they coexist and grow to a certain extent, it is actually detrimental to their respective phosphorus enrichment capabilities. Continuing this process would waste resources and hinder the rapid start-up of the biofilm, necessitating sludge removal. However, sludge should not be discharged as soon as competition for sludge-film coexistence occurs. The thickness of the biofilm is an indicator used to measure the growth of microorganisms on the biofilm. It is necessary to wait until a certain proportion of the phosphorus enrichment capacity of the activated sludge is transferred to the biofilm and the microorganisms on the biofilm develop to a certain extent before the rapid growth of the biofilm and the improvement of phosphorus enrichment capacity can be guaranteed after sludge discharge.

[0035] Based on the above principles, a method for controlling sludge discharge during the rapid start-up of the phosphorus enrichment biofilm process is provided in the above-mentioned phosphorus enrichment biofilm process:

[0036] The biofilm reactor was operated in alternating aerobic / anaerobic mode. The anaerobic phosphorus release, carbon source consumption, and the ratio of anaerobic phosphorus release to carbon source consumption in the mud-film mixing system of the biofilm reactor were measured periodically during the anaerobic phase.

[0037] Periodically collect biofilm packing material (i.e., suspended packing material with phosphorus-enriched biofilm adhering to it) at the end of the aerobic stage to conduct anaerobic phosphorus release experiments of biofilm in anaerobic stage of biofilm reactor, and determine the amount and thickness of anaerobic phosphorus release of biofilm.

[0038] Assuming that the carbon source consumption of the mud-film mixing system is increasing and the ratio of anaerobic phosphorus release to carbon source consumption is decreasing, when the biofilm thickness is 5-10 μm and the anaerobic phosphorus release of the biofilm accounts for 90-110% of the anaerobic phosphorus release of the mud-film mixing system, sludge is discharged from biofilm reactor 1.

[0039] In one embodiment, an anaerobic phosphorus release experiment of biofilm is conducted in the anaerobic stage of biofilm reactor 1, including the following steps: placing biofilm packing material at the end of the aerobic stage in a container, adding anaerobic water containing a carbon source, and conducting an anaerobic phosphorus release experiment of biofilm, wherein the filling ratio of biofilm packing material to container is the same as the filling ratio of suspended packing material to biofilm reactor.

[0040] For example, a biofilm packing material at the end of the aerobic stage with a filling ratio of 35-45% was placed in a 2L beaker, and anaerobic water was added to a volume of 1L to simulate the anaerobic process in biofilm reactor 1 for an anaerobic phosphorus release experiment.

[0041] The above-mentioned method for controlling sludge discharge during the rapid start-up of the phosphorus enrichment biofilm process is applicable to the process of alternating aerobic / anaerobic cultivation of phosphorus enrichment biofilm to enrich phosphate. Therefore, in other alternative embodiments, the biofilm reactor 1 can also be an anaerobic-aerobic biofilter or a trickling filter, etc.

[0042] Example 1

[0043] 1. Process operating equipment:

[0044] 10.5 L of activated sludge (6000 mg / L concentration) was taken from the secondary sedimentation tank of the A2 / O process in a wastewater treatment plant and divided into three equal portions (3.5 L each). These portions were placed in phosphorus enrichment biofilm sequencing batch reactors (BSBRs), designated A1, A2, and A3, respectively. The three biofilm reactors had identical setups and operating conditions, differing only in their sludge discharge control methods.

[0045] The flowchart for each group of process operation units is as follows: Figure 1 As shown, each consists of a 10L biofilm reactor 1 (wherein the suspended packing material has a filling ratio of 35%, is made of Kaldnes K1 polyethylene, has a diameter of 15mm, a height of 5mm, and an average specific surface area of ​​900m²). 2 / m 3 It consists of a 150L wastewater storage device 2, a 20L phosphorus recovery device 3, and a 4L carbon source addition device 4.

[0046] 2. Process Operation:

[0047] During the aerobic stage, valve 51 is opened, and phosphorus-containing wastewater flows from wastewater storage device 2 into biofilm reactor 1 under gravity. Aeration device 12 provides an aerobic environment, and simultaneously, stirrer 13 (a magnetic stirrer is used in this embodiment) is turned on to ensure uniform water quality. After the actual influent volume reaches 8L, valve 51 is closed. After 4 hours of aerobic operation, aeration device 12 is turned off, and pump 55 is turned on to discharge the wastewater.

[0048] The system switches to the anaerobic stage, and the base liquid / phosphorus recovery liquid from the phosphorus recovery unit 3 and the sodium acetate from the carbon source addition unit 4 are simultaneously pumped into the biofilm reactor 1 as anaerobic feedwater via pumps 52 and 54. After 2 hours of anaerobic operation, the anaerobic effluent is pumped back to the phosphorus recovery unit 3 by pump 53 as the anaerobic feedwater for the next cycle.

[0049] The aerobic cycle was repeated for 4 hours, followed by an anaerobic cycle for 2 hours. During the aerobic phase, no carbon source was added during aeration, and polyphosphate-accumulating bacteria on the phosphorus-rich biofilm absorbed phosphate from the phosphorus-containing wastewater. During the anaerobic phase, sodium acetate was added and stirred, and the mixture was introduced into biofilm reactor 1 along with the phosphate recovery solution. The polyphosphate-accumulating bacteria on the biofilm used the carbon source to release the phosphate accumulated in their bodies into the phosphate recovery solution. The polyphosphate-accumulating bacteria were enriched and cultured in biofilm reactor 1, and the phosphate concentration in the phosphate recovery solution in phosphorus recovery device 3 gradually increased until it stopped increasing.

[0050] 3. Process influent composition and operating parameters of the biofilm reactor:

[0051] The influent flow rate of biofilm reactor 1 is 800 mL / min, and the influent time is 5–10 min. The dissolved oxygen (DO) in the aerobic stage before sludge discharge is controlled at 4–5 mg / L, and the dissolved oxygen (DO) in the aerobic stage after sludge discharge is controlled at 6–8 mg / L, and the pH is controlled at 7.0–7.5.

[0052] The process involves using a low dissolved oxygen concentration of 4–5 mg / L before sludge discharge to promote biofilm growth in activated sludge. This avoids the shear force generated by excessive aeration, which is detrimental to biofilm formation. After sludge discharge, a high dissolved oxygen concentration of 6–8 mg / L is used to enhance oxygen mass transfer and promote the metabolic activity of polyphosphate-accumulating bacteria. By varying the dissolved oxygen concentration before and after sludge discharge, the goal is to shorten start-up time and increase phosphorus enrichment capacity upon completion of start-up.

[0053] Aerobic wastewater components (i.e., phosphorus-containing wastewater components): 10 mg / L KH2PO4, 300 mg / L NaHCO3, 40 mg / L NH4Cl, 8 mg / L CaCl2·2H2O, 30 mg / L MgSO4·7H2O, 2 mg / L EDTA·2Na.

[0054] Anaerobic water composition (i.e., the ratio of carbon source content to anaerobic influent volume): 200 mg / L sodium acetate.

[0055] 4. Sludge discharge control methods were measured in groups:

[0056] Each day, one anaerobic stage was taken, and the anaerobic phosphorus release, carbon source consumption (characterized by COD in this embodiment), and anaerobic phosphorus release / carbon source consumption ratio (characterized by Prel / COD in this embodiment) of the anaerobic stage mud-film mixing system were monitored. Simultaneously, biofilm packing material from the end of the aerobic stage, belonging to the same cycle as the anaerobic stage, was placed in a 2L beaker at a filling ratio of 35% (approximately 90 beakers). Anaerobic water was added to a volume of 1L to simulate the anaerobic process in biofilm reactor 1, and an anaerobic phosphorus release experiment was conducted. The anaerobic phosphorus release, carbon source consumption, and anaerobic phosphorus release / carbon source consumption ratio of the biofilm were calculated. Then, the thickness of the biofilm at the end of the aerobic stage was measured separately using a microscope.

[0057] Assuming that the carbon source consumption (COD) of the mud-film mixing system is increasing and the anaerobic phosphorus release / carbon source consumption (Prel / COD) of the mud-film mixing system is decreasing, sludge is discharged from biofilm reactors A1, A2, and A3 under the following three conditions: (1) When the biofilm thickness is less than 5 μm and the anaerobic phosphorus release of the biofilm accounts for 70-89% of the anaerobic phosphorus release of the mud-film mixing system, sludge is discharged from biofilm reactor A1; (2) When the biofilm thickness is 5-10 μm and the anaerobic phosphorus release of the biofilm accounts for 90-110% of the anaerobic phosphorus release of the mud-film mixing system, sludge is discharged from biofilm reactor A2; (3) When the biofilm thickness is greater than 10 μm and the anaerobic phosphorus release of the biofilm is greater than 110% of the anaerobic phosphorus release of the mud-film mixing system, sludge is discharged from biofilm reactor A3. The results of the determination of carbon source consumption (i.e. COD consumption of the mud-film mixing system), anaerobic phosphorus release / carbon source consumption (i.e., Prel / COD of the mud-film mixing system), biofilm thickness, and percentage of anaerobic phosphorus release from the biofilm to the total anaerobic phosphorus release from the mud-film mixing system during the above-mentioned sludge discharge are shown in Table 1.

[0058] After sludge discharge from biofilm reactors A1, A2, and A3, they continued to operate in alternating aerobic and anaerobic conditions. The concentration of phosphorus recovery solution in the corresponding systems of biofilm reactors A1, A2, and A3 was measured daily. If the concentration of phosphorus recovery solution did not increase significantly for three consecutive days, the concentration of phosphorus recovery solution on the first day was recorded as the concentration of the phosphorus-rich solution at the time of startup completion. The period from biofilm formation to that day was recorded as the startup time. The results are shown in Table 1.

[0059] Table 1. Statistical Table of Relevant Parameters for Sludge Discharge Control Methods

[0060]

[0061] Table 1 shows that, as the sludge discharge time is delayed, the carbon source consumption (i.e., COD consumption) of the mud-film mixing system gradually increases, while the anaerobic phosphorus release / carbon source consumption (i.e., Prel / COD of the mud-film mixing system) gradually decreases. This indicates that the carbon source consumption (i.e., COD consumption) of group A2 is on an increasing trend, while the anaerobic phosphorus release / carbon source consumption (i.e., Prel / COD of the mud-film mixing system) is on a decreasing trend. Considering that the start-up time and phosphorus enrichment capacity of group A2 are both better than those of groups A1 and A3, the sludge discharge control method of group A2 is more appropriate than that of groups A1 or A3.

[0062] Example 2

[0063] 1. Process operating equipment and operating procedures:

[0064] 12L of activated sludge (sludge concentration of 4500mg / L) was taken from the secondary sedimentation tank of the A2 / O process in a wastewater treatment plant and divided into three equal portions (4L of activated sludge per portion). These portions were placed in phosphorus enrichment biofilm sequencing batch reactors (BSBRs), designated B1, B2, and B3, respectively. The three biofilm reactors had identical equipment and operating conditions, differing only in their sludge discharge control methods.

[0065] The apparatus and operation of the three biofilm reactors B1, B2, and B3 are the same as in Example 1, except that the suspended packing material filling ratio in biofilm reactors B1, B2, and B3 is 40%.

[0066] The process feed water components and operating parameters of the biofilm reactor are also consistent with those in Example 1.

[0067] 2. Group testing of sludge discharge control methods:

[0068] The detection indicators and sampling process were the same as in Example 1, except that approximately 95 biofilm packing materials at the end of the aerobic stage were placed in a 2L beaker with a filling ratio of 40%.

[0069] Assuming that the carbon source consumption (COD) of the mud-film mixing system is increasing and the anaerobic phosphorus release / carbon source consumption (Prel / COD) of the mud-film mixing system is decreasing, sludge is discharged from biofilm reactors B1, B2, and B3 under the following three conditions: (1) When the biofilm thickness is less than 5 μm and the biofilm phosphorus release accounts for 70-89% of the mud-film mixing system, biofilm reactor B1 is discharged; (2) When the biofilm thickness is 5-10 μm and the biofilm anaerobic phosphorus release accounts for 90-110% of the anaerobic phosphorus release of the mud-film mixing system, biofilm reactor B2 is discharged; (3) When the biofilm thickness is greater than 10 μm and the biofilm anaerobic phosphorus release is greater than 110% of the anaerobic phosphorus release of the mud-film mixing system, biofilm reactor B3 is discharged. The results of the determination of carbon source consumption (i.e. COD consumption of the mud-film mixing system), anaerobic phosphorus release / carbon source consumption (i.e. Prel / COD of the mud-film mixing system), biofilm thickness, and percentage of anaerobic phosphorus release from the biofilm to the total anaerobic phosphorus release from the mud-film mixing system during the above-mentioned sludge discharge are shown in Table 2.

[0070] After sludge discharge from biofilm reactors B1, B2, and B3, they continued to operate in alternating aerobic and anaerobic conditions. The concentration of phosphorus recovery solution in the corresponding systems of biofilm reactors B1, B2, and B3 was measured daily. If the concentration of phosphorus recovery solution did not increase significantly for three consecutive days, the concentration of phosphorus recovery solution on the first day was recorded as the concentration of the phosphorus-rich solution at the time of startup completion. The period from biofilm formation to that day was recorded as the startup time. The results are shown in Table 2.

[0071] Table 2. Statistical Table of Relevant Parameters for Sludge Discharge Control Methods

[0072]

[0073] Table 2 shows that, as the sludge discharge time is delayed, the carbon source consumption (i.e., COD consumption) of the mud-film mixing system gradually increases, while the anaerobic phosphorus release / carbon source consumption (i.e., Prel / COD) gradually decreases. This indicates that the carbon source consumption (i.e., COD consumption) of group B2 is on an increasing trend, while the anaerobic phosphorus release / carbon source consumption (i.e., Prel / COD) is on a decreasing trend. Considering that the start-up time and phosphorus enrichment capacity of group B2 are both better than those of groups B1 and B3, the sludge discharge control method of group B2 is more appropriate than that of groups B1 or B3.

[0074] Example 3

[0075] 1. Process operating equipment and operating procedures:

[0076] 13.5 L of activated sludge (sludge concentration of 3000 mg / L) was taken from the secondary sedimentation tank of the A2 / O process in a wastewater treatment plant and divided into three equal portions (4.5 L each). These portions were placed in phosphorus enrichment biofilm sequencing batch reactors (BSBRs), designated C1, C2, and C3. The three biofilm reactors had identical equipment and operating conditions, differing only in their sludge discharge control methods.

[0077] The apparatus and operation process of the three biofilm reactors C1, C2, and C3 are the same as in Example 1, except that the suspended packing material filling ratio in biofilm reactors C1, C2, and C3 is 45%.

[0078] The process feed water components and operating parameters of the biofilm reactor are also consistent with those in Example 1.

[0079] 2. Group testing of sludge discharge control methods:

[0080] The detection indicators and sampling process were the same as in Example 1, except that about 100 biofilm packing materials at the end of the aerobic stage were placed in a 2L beaker with a filling ratio of 45%.

[0081] Assuming that the carbon source consumption (COD) of the mud-film mixing system is increasing and the anaerobic phosphorus release / carbon source consumption (Prel / COD) of the mud-film mixing system is decreasing, sludge is discharged from biofilm reactors C1, C2, and C3 under the following three conditions: (1) When the biofilm thickness is less than 5 μm and the biofilm phosphorus release accounts for 70-89% of the mud-film mixing system, biofilm reactor C1 is discharged; (2) When the biofilm thickness is 5-10 μm and the biofilm anaerobic phosphorus release accounts for 90-110% of the anaerobic phosphorus release of the mud-film mixing system, biofilm reactor C2 is discharged; (3) When the biofilm thickness is greater than 10 μm and the biofilm anaerobic phosphorus release is greater than 110% of the anaerobic phosphorus release of the mud-film mixing system, biofilm reactor C3 is discharged. The results of the determination of carbon source consumption (i.e. COD consumption of the mud-film mixing system), anaerobic phosphorus release / carbon source consumption (i.e. Prel / COD of the mud-film mixing system), biofilm thickness, and percentage of anaerobic phosphorus release from the biofilm to the total anaerobic phosphorus release from the mud-film mixing system during the above-mentioned sludge discharge are shown in Table 3.

[0082] After sludge discharge from biofilm reactors C1, C2, and C3, they continued to operate in alternating aerobic and anaerobic conditions. The concentration of phosphorus recovery solution in the corresponding systems of biofilm reactors C1, C2, and C3 was measured daily. If the concentration of phosphorus recovery solution did not increase significantly for three consecutive days, the concentration of phosphorus recovery solution on the first day was recorded as the concentration of the phosphorus-rich solution at the time of startup completion. The period from biofilm formation to that day was recorded as the startup time. The results are shown in Table 3.

[0083] Table 3. Statistical Table of Relevant Parameters for Sludge Discharge Control Methods

[0084]

[0085] Table 2 shows that, as the sludge discharge time is delayed, the carbon source consumption (i.e., COD consumption) of the mud-film mixing system gradually increases, while the anaerobic phosphorus release / carbon source consumption (i.e., Prel / COD of the mud-film mixing system) gradually decreases. This indicates that the carbon source consumption (i.e., COD consumption) of group C2 is on an increasing trend, while the anaerobic phosphorus release / carbon source consumption (i.e., Prel / COD of the mud-film mixing system) is on a decreasing trend. Considering that the start-up time and phosphorus enrichment capacity of group C2 are both better than those of groups C1 and C3, the sludge discharge control method of group C2 is more appropriate than that of groups C1 or C3.

[0086] In Examples 1-3, when conducting group operation experiments on activated sludge inoculated into the biofilm reactor, the amount of sludge added was adjusted according to the concentration of the inoculated activated sludge. For high-concentration activated sludge, the amount added was reduced; for low-concentration activated sludge, the amount added was increased. This ensured that the sludge concentration after addition was within a suitable range, avoiding excessively high sludge concentrations where sludge fails to form a biofilm, resulting in increased carbon consumption and costs, and insufficient sludge concentrations where the probability of biofilm formation is low, delaying the start-up process. The amount of packing material in each batch experiment was adjusted according to the filling ratio of the suspended packing material in the biofilm reactor to maximize the comparability of the batch test results with the performance of the biofilm reactor sludge-film mixing system, improving the scientific validity and accuracy of the results. Combining batch testing with routine biofilm reactor testing, the selection of sludge control methods considered multiple indicators from various perspectives, including COD consumption of the sludge-film mixing system, the Prel / COD value of the sludge-film mixing system, biofilm thickness, and the percentage of anaerobic phosphorus release from the biofilm relative to the total anaerobic phosphorus release from the sludge-film mixing system. This comprehensive evaluation and multi-layered screening improved the accuracy and representativeness of the results.

[0087] The premise for sludge discharge is that the COD consumption of the sludge-film mixing system is increasing and the Prel / COD of the sludge-film mixing system is decreasing. At this stage, the coexistence of activated sludge and biofilm competes for carbon sources and space, which is not conducive to the growth of biofilm and the phosphorus metabolism capacity of polyphosphate-accumulating bacteria in biofilm. Sludge discharge at this time can significantly improve the growth of biofilm and phosphorus metabolism capacity. Further experimental research based on this is conducive to quickly and accurately obtaining the optimal sludge discharge control method.

[0088] Given the premise that there is competition between carbon sources and living space for the biofilm, the biofilm thickness of 5-10 μm and the anaerobic phosphorus release of the biofilm accounting for 90-110% of the anaerobic phosphorus release of the biofilm in the biofilm mixing system are used as important indicators for sludge discharge. On the one hand, this quantifies the growth of microorganisms in the biofilm, and on the other hand, it quantifies the transfer of phosphorus enrichment capacity from activated sludge to the biofilm. Using the quantified indicators as a reference, the stable start-up time and phosphorus enrichment capacity of the phosphorus enrichment biofilm process can be guaranteed under the premise of scientific accuracy.

[0089] Based on the statistical analysis of COD consumption, Prel / COD ratio, anaerobic phosphorus release from biofilm reactors A1-C1, A2-C2, and A3-C3 during sludge discharge from the above Examples 1-3, the optimal sludge discharge control method is as follows: assuming an increasing trend in COD consumption and a decreasing trend in Prel / COD ratio of the sludge-film mixing system, a biofilm thickness of 5-10 μm, and anaerobic phosphorus release from the biofilm accounting for 90-110% of the anaerobic phosphorus release from the sludge-film mixing system. Under this method, the phosphorus enrichment biofilm process has the shortest start-up time and the highest concentration of enriched phosphorus solution.

[0090] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

[0091] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0092] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for controlling sludge discharge during the rapid start-up of a phosphorus enrichment biofilm process, characterized in that... It lies in, In the phosphorus enrichment biofilm process, the biofilm reactor is operated alternately in aerobic / anaerobic mode, and the anaerobic phosphorus release, carbon source consumption, and ratio of anaerobic phosphorus release to carbon source consumption in the mud-film mixing system of the biofilm reactor are measured periodically during the anaerobic stage. The biofilm packing material at the end of the aerobic stage was collected periodically to simulate the anaerobic stage in the biofilm reactor and to conduct an anaerobic phosphorus release experiment of the biofilm, and to determine the amount and thickness of the anaerobic phosphorus release of the biofilm. Provided that the carbon source consumption of the mud-film mixing system is increasing and the ratio of anaerobic phosphorus release to carbon source consumption of the mud-film mixing system is decreasing, when the thickness of the biofilm is 5~10μm and the anaerobic phosphorus release of the biofilm accounts for 90~110% of the anaerobic phosphorus release of the mud-film mixing system, the biofilm reactor is sludge discharged.

2. The method for controlling sludge discharge during the rapid start-up of a phosphorus enrichment biofilm process according to claim 1, characterized in that, The phosphorus enrichment biofilm process includes the following steps: adding activated sludge into a biofilm reactor, alternating between aerobic and anaerobic operation of the biofilm reactor, cultivating polyphosphate-accumulating bacteria on the suspended packing material within the biofilm reactor, wherein a carbon source is added during the anaerobic stage and the anaerobic effluent is recycled as phosphorus recovery liquid; after sludge removal from the biofilm reactor, the aerobic / anaerobic alternating operation of the biofilm reactor continues until the phosphorus uptake and release of the biofilm no longer increase, thus obtaining a phosphorus enrichment biofilm.

3. The method for controlling sludge discharge during the rapid start-up of a phosphorus enrichment biofilm process according to claim 1 or 2, characterized in that, The biofilm reactor is a sequencing batch reactor or an anaerobic-aerobic biofilter. The carbon source is added to the biofilm reactor in the following manner: no carbon source is added during the aerobic stage, and carbon source is added during the anaerobic stage.

4. The method for controlling sludge discharge during the rapid start-up of a phosphorus enrichment biofilm process according to claim 1 or 2, characterized in that, Before sludge discharge, the dissolved oxygen content in the aerobic stage is controlled at 4-5 mg / L; after sludge discharge, the dissolved oxygen content in the aerobic stage is controlled at 6-8 mg / L, and the pH is controlled at 7-7.

5.

5. The method for controlling sludge discharge during the rapid start-up of a phosphorus enrichment biofilm process according to claim 2, characterized in that, An anaerobic phosphorus release experiment of a biofilm reactor simulating the anaerobic stage includes the following steps: placing biofilm packing material at the end of the aerobic stage in a container, adding anaerobic water containing a carbon source, and conducting an anaerobic phosphorus release experiment of the biofilm, wherein the filling ratio of the biofilm packing material relative to the container is the same as the filling ratio of the suspended packing material relative to the biofilm reactor.

6. The method for controlling sludge discharge during the rapid start-up of a phosphorus enrichment biofilm process according to claim 5, characterized in that, The filling ratio of the suspended packing material to the biofilm reactor is 35-45%.

7. The method for controlling sludge discharge during the rapid start-up of a phosphorus enrichment biofilm process according to claim 1, characterized in that, The biofilm reactor is operated alternately with one aerobic stage and one anaerobic stage as a cycle. Every day, the mud-film mixing system of one anaerobic stage is sampled to measure the anaerobic phosphorus release, carbon source consumption, and the ratio of anaerobic phosphorus release to carbon source consumption. Every day, biofilm packing material at the end of the aerobic stage, which belongs to the same cycle as the anaerobic stage, is collected to conduct an anaerobic phosphorus release experiment simulating the biofilm, and the anaerobic phosphorus release and thickness of the biofilm are measured.

8. The method for controlling sludge discharge during the rapid start-up of a phosphorus enrichment biofilm process according to claim 7, characterized in that, In each cycle, the hydraulic retention time for the aerobic phase is 2 to 10 hours, and the hydraulic retention time for the anaerobic phase is 1 to 6 hours.

9. The method for controlling sludge discharge during rapid start-up of a phosphorus enrichment biofilm process according to claim 1 or 7, characterized in that, The thickness of the biofilm at the end of the aerobic phase was measured using a microscope.

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