System for synthesizing sludge resource into biodegradable plastic raw material and method therefor

Abstract

Provided are a system for using sludge as a resource to synthesize a biodegradable plastic raw material and a method therefor. The present invention relates to the field of sludge resource utilization. The system comprises a sludge anaerobic acid production unit, a filtration unit, a feeding unit, a phosphorus recovery unit, a nutrient element supplementation unit, a strain acclimatization and expansion culture tank, a PHA accumulation synthesis tank, an aeration unit, and an online monitoring and automatic control unit. Residual sludge and digested sludge are added to the sludge anaerobic acid production unit. The discharged acid-producing sludge is sent to the filtration unit and filtered, and the resulting acid-producing filtrate is discharged into the feeding unit. The activated sludge is added to the strain acclimatization and expansion culture tank, and the timing and quantity of addition of the acid-producing filtrate are regulated. After the bacterial population in the strain acclimatization and expansion culture tank is stable, the sludge in the strain acclimatization and expansion culture tank is discharged into the PHA accumulation synthesis tank. When the PHA synthesis rate reaches the highest point, the bacterial suspension is discharged, and a PHA crude product is collected. The present invention can simultaneously improve the PHA synthesis rate and the biomass of PHA-synthesizing bacteria, thereby solving the contradiction between expanding the biomass of PHA-synthesizing bacteria and improving the synthesis rate.

Description

A system and method for synthesizing biodegradable plastic raw materials from sludge resources. Technical Field

[0001] This invention belongs to the field of sludge resource utilization, and more specifically, relates to a system and method for synthesizing biodegradable plastic raw materials from sludge resources. Background Technology

[0002] Polyhydroxyalkanoates (PHA) are high-performance, versatile biodegradable plastics. Currently, industrial production of PHA primarily relies on pure bacterial cultures or genetically engineered bacteria, requiring strict aseptic conditions and specific carbon sources, resulting in high operating costs. To reduce the increased costs associated with raw materials and sterilization processes in PHA production, researchers are utilizing various waste organic materials, such as sludge and its hydrolysis products, as carbon sources instead of refined raw materials to lower raw material costs, and developing mixed microbial communities to replace pure bacterial strains to reduce sterilization costs, thereby reducing PHA production costs.

[0003] The synthesis of PHA by mixed microbial communities shows great promise in the field of sludge resource utilization, but it has not been applied industrially because the PHA synthesis yield still does not meet the requirements of industrial production. On the one hand, the synthesis rate of PHA using mixed microbial communities with sludge as a substrate is only 20% to 60% of the cell dry weight, while the synthesis rate of PHA using pure microorganisms with refined raw materials is >75%. On the other hand, compared with the biomass of pure microbial production processes (60–200 g / L), the biomass of mixed microbial communities is mostly only 1.2–8 g / L. The yield of PHA synthesis depends on the PHA synthesis rate and the biomass of the synthesizing bacteria. Therefore, while improving the PHA synthesis rate, it is necessary to ensure a high output biomass of the system. However, a high PHA synthesis rate is usually achieved under conditions of high carbon-nitrogen ratio or carbon-phosphorus ratio (C:N>20; C:P>200), and microbial growth requires a C:N:P ratio of around 100:5:1 to maintain a high biomass growth. Meanwhile, the composition of organic waste such as sludge is complex and unstable. Using it as a substrate will lead to instability of the PHA-synthesizing microbial community, thus affecting the stability of the system.

[0004] There is a reaction system that uses sludge to synthesize PHA after thermal hydrolysis. However, the cultivation of PHA-synthesizing bacteria and the synthesis of PHA are both carried out in the same tank, which makes the PHA synthesis system unstable and makes it difficult to increase biomass.

[0005] Another method to increase the output of PHA-synthesizing bacteria is to increase the biomass of the system by adding an expansion reactor between the strain domestication reactor and the synthesis reactor. However, the added expansion reactor also requires the addition of a specific carbon source and continuous aeration. If organic waste such as sludge is used as the substrate, it will increase some operating costs. Moreover, the more processes added to the process, the greater the difficulty of operation and maintenance.

[0006] Another method exists for enriching and expanding the PHA mixed microbial community by adding loading materials to the expanded culture reactor to increase the biomass of the PHA mixed microbial community in the system. However, the growth of microbial biofilm will increase the difficulty and cost of subsequent PHA extraction.

[0007] In the sludge resource-based PHA synthesis system, in order to balance the relationship between the expansion of PHA-synthesizing bacteria biomass and the improvement of synthesis rate while improving the stability of the PHA synthesis system, it is necessary to develop a system and operation method for sludge resource-based PHA synthesis. This method can expand the PHA-synthesizing bacteria biomass on the basis of obtaining a high PHA synthesis rate and system stability, thereby increasing PHA production at a low cost. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by providing a system and method for synthesizing biodegradable plastic raw materials from sludge resources. This system and method can simultaneously improve the PHA synthesis rate and the biomass of PHA-synthesizing bacteria, thus resolving the contradiction between the expansion of PHA-synthesizing bacteria biomass and the improvement of the synthesis rate.

[0009] To achieve the above objectives, the present invention provides a system for synthesizing biodegradable plastic raw materials from sludge resources, comprising:

[0010] The sludge anaerobic acid production unit is connected to a wastewater treatment plant at its front end and to a filtration unit at its rear end.

[0011] The feeding unit is connected to the filtration unit at its front end and to the front end of the microbial culture and propagation tank at its rear end. A phosphorus recovery unit and a nutrient element supplementation unit are provided between the filtration unit and the microbial culture and propagation tank.

[0012] The front end of the PHA accumulation synthesis tank is connected to the rear end of the strain domestication and expansion tank;

[0013] An aeration unit is connected to the strain domestication and propagation tank and the PHA accumulation and synthesis tank;

[0014] An online monitoring and automatic control unit is connected to the feeding unit, the phosphorus recovery unit, the nutrient element supplementation unit, and the aeration unit.

[0015] Optionally, the strain domestication and propagation tank includes multiple tanks arranged in parallel, a first stirrer is provided in the tank, the tank is connected to the aeration unit, and the online monitoring and automatic control unit is connected to the tank.

[0016] Optionally, a second stirrer is provided inside the PHA accumulation synthesis tank, and the front end of the PHA accumulation synthesis tank is also connected to the phosphorus removal filtrate pipe of the phosphorus recovery unit.

[0017] Optionally, the front end of the phosphorus recovery unit is connected to the filtration unit, and the rear end of the phosphorus recovery unit is connected to the nutrient element supplementation unit and the PHA accumulation synthesis tank.

[0018] Optionally, the online monitoring and automatic control unit includes an online monitoring section and an automatic control section. The online monitoring section includes a dissolved oxygen meter, a pH meter, a thermometer, and a sludge concentration meter. The automatic control section is used to regulate the aeration rate, feed rate, and sludge discharge rate.

[0019] This invention also provides a method for synthesizing biodegradable plastic raw materials from sludge resources. Utilizing the aforementioned system for synthesizing biodegradable plastic raw materials from sludge resources, the method includes:

[0020] The excess sludge and digested sludge from the wastewater treatment plant are added to the sludge anaerobic acidification unit. After the pH value is <6.3, the acidified sludge is discharged and sent to the filtration unit. The acidified filtrate obtained by filtration is discharged into the feeding unit.

[0021] The activated sludge from the wastewater treatment plant is added to the microbial acclimatization and propagation tank, and the time and amount of acid-producing filtrate added to the feeding unit are controlled by the online monitoring and automatic control unit.

[0022] After the microbial community in the strain domestication and expansion tank has stabilized, the sludge in the strain domestication and expansion tank is discharged into the PHA accumulation and synthesis tank. When the PHA synthesis rate reaches its maximum, the bacterial solution is discharged and crude PHA is collected.

[0023] Optionally, the ratio of excess sludge to digested sludge entering the sludge anaerobic acidification unit is 1:1, the sludge retention time is 2 to 5 days, and the temperature is controlled at 30 to 50°C.

[0024] Optionally, the concentration of activated sludge entering the strain domestication and expansion tank is 3000-4000 mg / L, the feed load per cycle is 3000-5000 mg COD / L, the time of each cycle is 4-6 T, the time of the abundant period is controlled at T, and the time of the starvation period is controlled at 3-5 T.

[0025] Optionally, each cycle can be operated in two modes: a first mode and a second mode. In the first mode, no phosphorus supplementation is required, while in the second mode, phosphate salts are added based on the carbon-to-phosphorus ratio in the acid-producing filtrate.

[0026] Optionally, the condition for stable microbial community is that the sludge growth rate is stable at the end of the abundance period and PHA accounts for >25% of the dry weight of the microbial community.

[0027] This invention provides a system and method for synthesizing biodegradable plastic raw materials from sludge resources, the advantages of which are:

[0028] 1. The system for synthesizing biodegradable plastic raw materials from sludge resources can increase the biomass of PHA synthesizing bacteria in the strain domestication and expansion tank, and carry out the ultimate cumulative synthesis of PHA in the PHA accumulation synthesis tank, which can solve the contradiction between increasing the biomass of PHA synthesizing bacteria and improving the synthesis rate.

[0029] 2. This system addresses the problem of unstable acid-producing liquid and its impact on microbial community caused by unstable sludge sources. This invention uses online monitoring data of pH and dissolved oxygen to control the timing and amount of acid-producing liquid addition, which can improve the stability of strain domestication and expansion and PHA accumulation and synthesis.

[0030] 3. This system recovers phosphorus from a portion of the acid-producing filtrate. On the one hand, it replenishes the recovered phosphorus resources during microbial colony expansion, thereby increasing the biomass of the system. On the other hand, it uses the phosphorus-removed filtrate to enhance the PHA synthesis rate during PHA accumulation and synthesis.

[0031] 4. The system operates on a dynamic control mode based on PHA content detection and online monitoring of sludge concentration, effectively increasing the biomass of the microbial community while ensuring a high PHA synthesis rate during strain domestication and expansion.

[0032] 5. In the method of synthesizing biodegradable plastic raw materials from sludge resources, the strain domestication and expansion tank are dynamically regulated to keep the dissolved oxygen level during the starvation period <1mg / L, thereby reducing the energy consumption required for aeration. The stability of the SVI control system is regulated by monitoring and adding stabilizers.

[0033] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0034] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0035] Figure 1 shows a schematic diagram of a system for synthesizing biodegradable plastic raw materials from sludge according to an embodiment of the present invention.

[0036] Figure 2 shows a flowchart of a method for synthesizing biodegradable plastic raw materials from sludge according to an embodiment of the present invention.

[0037] Explanation of reference numerals in the attached diagram: 1. Anaerobic acid production unit for sludge; 2. Tank; 3. Feeding unit; 4. Phosphorus recovery unit; 5. Nutrient supplementation unit; 6. PHA accumulation and synthesis tank; 7. Aeration unit; 8. Phosphorus removal filtrate pipe; 9. Online monitoring and automatic control unit. Detailed Implementation

[0038] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0039] This invention provides a system for synthesizing biodegradable plastic raw materials from sludge resources, comprising:

[0040] The sludge anaerobic acid production unit is connected to the sewage treatment plant at the front end and to the filtration unit at the rear end.

[0041] The feeding unit is connected to the filtration unit at the front end and to the front end of the microbial culture and expansion tank at the rear end. A phosphorus recovery unit and a nutrient element supplementation unit are set between the filtration unit and the microbial culture and expansion tank.

[0042] The PHA accumulation synthesis tank is connected at the front end to the rear end of the strain domestication and expansion tank.

[0043] The aeration unit is connected to the microbial culture and propagation tank and the PHA accumulation and synthesis tank.

[0044] The online monitoring and automatic control unit is connected to the feeding unit, phosphorus recovery unit, nutrient element supplementation unit, and aeration unit.

[0045] Specifically, the system comprises multiple units, monitored and automatically controlled via online monitoring and an automatic control unit. The sludge anaerobic acid production unit, filtration unit, feeding unit, microbial incubation and propagation tank, and PHA accumulation and synthesis tank are connected sequentially. The sludge anaerobic acid production unit produces acid from sludge and other waste organic matter through anaerobic processes. The filtration unit then filters the acidified sludge solution. The feeding unit controls the feed rate to the microbial incubation and propagation tank based on data monitoring and feedback from the online monitoring and automatic control unit. The microbial incubation and propagation tank cultivates and propagates the PHA-synthesizing microbial community. The PHA accumulation and synthesis tank ultimately discharges microbial communities enriched with a large amount of PHA. Additionally, [further details are needed]. The phosphorus recovery unit recovers phosphorus from the filtrate through flocculation and sedimentation, and uses phosphorus as a nutrient for the amplification and cultivation of the microbial community. Feedback from online monitoring and automatic control units controls the amount of filtrate to be treated for phosphorus recovery and the feed rate to the PHA accumulation synthesis tank. The nutrient replenishment unit, located before the microbial culture and expansion tank, stores phosphorus, carbon, and other nutrients. Monitoring data controls the replenishment of nutrients into the microbial culture and expansion tank. The online monitoring and automatic control unit includes a feedback system connected to each unit and various online instruments within the tank. It controls the aeration rate, nutrient levels, and feed rate by receiving signals from these online instruments.

[0046] Optionally, the strain domestication and propagation tank includes multiple tanks arranged in parallel, with a first stirrer installed inside each tank. The tank is connected to an aeration unit, and an online monitoring and automatic control unit is connected to the tank.

[0047] Optionally, a second stirrer is installed inside the PHA accumulation synthesis tank, and the front end of the PHA accumulation synthesis tank is also connected to the phosphorus removal filtrate pipe of the phosphorus recovery unit.

[0048] Specifically, the microbial incubation and propagation tanks consist of multiple parallel tanks. Stirring is used to ensure the sludge in the tanks reacts fully and aeration is applied. In the PHA accumulation and synthesis tank, a second stirrer mixes the feed after it is introduced, and filtrate is replenished via a phosphorus recovery unit in conjunction with online monitoring and an automatic control unit. Additionally, the aeration unit is equipped with an air compressor and air storage cylinders, and the aeration rate of each microbial incubation and propagation tank and the PHA accumulation and synthesis tank is controlled by the online monitoring and automatic control unit.

[0049] Optionally, the front end of the phosphorus recovery unit is connected to the filtration unit, and the rear end of the phosphorus recovery unit is connected to the nutrient element supplementation unit and the PHA accumulation synthesis tank.

[0050] Specifically, the phosphorus recovery unit can recover phosphorus from the filtrate through flocculation and sedimentation, and use phosphorus as a nutrient element for the amplification and cultivation of microbial communities. The front end of the phosphorus recovery unit is connected to the filtration unit, and the back end is connected to the nutrient element supplementation unit and the PHA accumulation synthesis tank, respectively. The monitoring data feedback indicates how much filtrate needs to be treated for phosphorus recovery and controls the feed rate of the PHA accumulation synthesis tank.

[0051] Optionally, the online monitoring and automatic control unit includes an online monitoring section and an automatic control section. The online monitoring section includes a dissolved oxygen meter, a pH meter, a thermometer, and a sludge concentration meter. The automatic control section is used to regulate the aeration rate, feed rate, and sludge discharge rate.

[0052] Specifically, the online monitoring and automatic control unit includes two parts: online monitoring and automatic control. The online monitoring part includes online instruments such as dissolved oxygen meters, pH meters, thermometers, and sludge concentration meters, which are used to monitor the pH and temperature of the anaerobic acid production unit of sludge online, and to monitor the dissolved oxygen, pH, temperature, and sludge concentration in the inoculum domestication and expansion tank and the PHA accumulation and synthesis tank online. Based on these real-time data, the aeration rate, feed rate, nutrient elements, and sludge discharge rate are dynamically adjusted. The automatic control part adjusts the aeration rate, feed rate, nutrient elements, and sludge discharge rate in real time based on the online detection data.

[0053] This invention also provides a method for synthesizing biodegradable plastic raw materials from sludge resources. Utilizing the aforementioned system for synthesizing biodegradable plastic raw materials from sludge resources, the method includes:

[0054] The excess sludge and digested sludge from the wastewater treatment plant are added to the sludge anaerobic acidification unit. After the pH value is <6.3, the acidified sludge is discharged and sent to the filtration unit. The acidified filtrate obtained by filtration is discharged into the feeding unit.

[0055] Activated sludge from the wastewater treatment plant is added to the microbial culture and propagation tank, and the time and amount of acid-producing filtrate added to the feeding unit are controlled by online monitoring and automatic control unit.

[0056] After the microbial community in the strain domestication and expansion tank has stabilized, the sludge in the strain domestication and expansion tank is discharged into the PHA accumulation and synthesis tank. When the PHA synthesis rate reaches its maximum, the bacterial solution is discharged and crude PHA is collected.

[0057] Specifically, the method for synthesizing raw materials consists of three steps: anaerobic acid production and filtration of sludge, strain domestication and expansion, and PHA accumulation and synthesis. Combined with the system protected in this invention, it can achieve the effects of increasing the PHA synthesis rate and the biomass of PHA-synthesizing bacteria, thus solving the contradiction between the expansion of PHA-synthesizing bacteria biomass and the improvement of the synthesis rate.

[0058] Optionally, the ratio of excess sludge to digested sludge entering the sludge anaerobic acidification unit is 1:1, the sludge retention time is 2 to 5 days, and the temperature is controlled at 30 to 50°C.

[0059] Specifically, in the anaerobic acid production and filtration steps of sludge, the wastewater treatment plant's excess sludge and digested sludge are added to the sludge anaerobic acid production unit in a 1:1 ratio. The sludge retention time is controlled at 2 to 5 days, and the temperature is 30 to 50°C. After the pH value is <6.3, the acid-producing sludge can be discharged intermittently or continuously, while excess sludge is added at the same time. In the filtration unit, the acid-producing sludge is filtered to obtain acid-producing filtrate through centrifugation, pressure filtration, or membrane filtration.

[0060] Optionally, the concentration of activated sludge entering the microbial acclimatization and expansion tank is 3000-4000 mg / L, the feed load per cycle is 3000-5000 mg COD / L, the time of each cycle is 4-6 T, the time of the abundant period is controlled at T, and the time of the starvation period is controlled at 3-5 T.

[0061] Specifically, in the process of strain domestication and propagation, activated sludge from the wastewater treatment plant is added to the strain domestication and propagation tank as the inoculum, and the concentration of activated sludge is adjusted to 3000-4000 mg / L. The feed load per cycle is 3000-5000 mg COD / L. Feeding can be done in one or multiple additions. Based on online detection data of pH and dissolved oxygen, the addition time and amount of acid-producing filtrate in the feeding unit are controlled. One cycle time is 4-6T, with the abundant period controlled at T and the starvation period controlled at 3-5T.

[0062] The method for controlling the addition time and amount of acid-producing filtrate from the feeding unit based on online detection data of pH and dissolved oxygen is as follows: The pH and VFAs content of the sludge acid-producing filtrate are monitored, and the correlation between the two is calculated. The VFAs content is then calculated based on online pH measurement. If the VFAs content changes by more than 10% of a preset value, the feed is reduced or a carbon source such as sodium acetate is added to maintain the COD of readily available carbon sources in the filtrate within a fluctuation range of less than 10%. The linear relationship curve between the two is obtained by calculating the time required for a "jump" increase in dissolved oxygen at different aeration rates after feeding and the relationship between the time and the added COD. The aeration rate and the addition time of the acid-producing filtrate are dynamically adjusted as needed. The "abundant period" refers to the period from the start of feeding to a "jump" increase in dissolved oxygen, for example, a sudden increase from 1 mg / L to 4 mg / L or higher. This period is recorded as the abundant period. The period excluding the abundant period is recorded as the starvation period. Dissolved oxygen levels during the starvation period are dynamically controlled to be <1 mg / L.

[0063] In the steps of strain domestication and amplification culture, it is also necessary to control the system so that 50 < SVI < 200. When SVI > 200, stabilizers such as activated sludge, sodium hypochlorite, and nutrient salts are added to regulate the SVI of the system to control the stability of the bacterial community and the stability of the system.

[0064] Optionally, the operation mode of each cycle includes a first mode and a second mode. The first mode does not require phosphorus supplementation, and the second mode adds phosphorus salts based on the carbon-phosphorus ratio in the acid-producing filtrate.

[0065] Specifically, the operation mode in each cycle is divided into a first mode (hereinafter referred to as mode I) and a second mode (hereinafter referred to as mode II). The first mode does not require phosphorus supplementation, and the second mode adds phosphorus salts based on the carbon-phosphorus ratio in the sludge acid-producing filtrate; it is necessary to dynamically regulate the operation mode based on the PHA content detection and the online monitoring of the sludge concentration value.

[0066] The basis for dynamically regulating the operation mode based on the PHA content detection and the online monitoring of the sludge concentration value is as follows: when the sludge growth rate at the end of the prosperous period in the strain domestication and amplification culture tank > 150%, the first mode is mainly adopted for operation, i.e., I I II I I II... I I II or I I I II I I I II... I I I II; when the sludge growth rate at the end of the prosperous period < 120%, the second mode is mainly adopted for operation, i.e., I II I II... I II; when the sludge growth rate at the end of the prosperous period < 120% and the PHA accounts for < 25% of the dry weight of the bacteria, the first mode is still mainly adopted for operation.

[0067] Optionally, the condition for the stability of the bacterial community is that the sludge growth rate at the end of the prosperous period is stable and the PHA accounts for > 25% of the dry weight of the bacteria.

[0068] Specifically, in the PHA cumulative synthesis step, after the bacterial community in the strain domestication and amplification culture tank is stable, it is discharged into the PHA cumulative synthesis tank according to the sludge concentration growth, and the activated sludge concentration is adjusted to 3000 - 4000 mg / L. The feeding load per cycle is 3000 - 5000 mg COD / L. After multiple feedings, the bacterial liquid is discharged when the PHA synthesis rate reaches the highest to collect the crude PHA. In this step, it is also necessary to control the feeding time and feeding amount of the phosphorus-removing filtrate based on the online detection data of pH and dissolved oxygen, and at the same time regulate the dissolved oxygen in the synthesis stage to 0.5 mg / L - 2 mg / L.

[0069] Example

[0070] As shown in Figures 1 to 2, the present invention provides a system for synthesizing biodegradable plastic raw materials from sludge resource, including:

[0071] A sludge anaerobic acid-producing unit 1, the front end of which is used to connect with a sewage treatment plant, and the back end of the sludge anaerobic acid-producing unit 1 is connected with a filtering unit;

[0072] Feeding unit 3 is connected to the filtration unit at the front end and to the front end of the microbial culture and expansion tank at the rear end. A phosphorus recovery unit 4 and a nutrient element supplementation unit 5 are provided between the filtration unit and the microbial culture and expansion tank.

[0073] PHA accumulation synthesis tank 6, the front end of which is connected to the rear end of the strain domestication and expansion tank;

[0074] Aeration unit 7 is connected to the microbial domestication and propagation tank and the PHA accumulation and synthesis tank 6;

[0075] The online monitoring and automatic control unit 9 is connected to the feeding unit 3, phosphorus recovery unit 4, nutrient element supplementation unit 5 and aeration unit 7.

[0076] In this embodiment, the strain domestication and propagation tank includes three tanks 2 arranged in parallel, namely tank A, tank B and tank C. Each tank 2 is equipped with a first stirrer. The tank 2 is connected to the aeration unit 7. The online monitoring and automatic control unit 9 monitors the inside of the tank 2.

[0077] In this embodiment, a second stirrer is provided inside the PHA accumulation synthesis tank 6, and the front end of the PHA accumulation synthesis tank 6 is also connected to the phosphorus removal filtrate pipe 8 of the phosphorus recovery unit 4.

[0078] In this embodiment, the front end of the phosphorus recovery unit 4 is connected to the filtration unit, and the rear end of the phosphorus recovery unit 4 is connected to the nutrient element supplementation unit 5 and the PHA accumulation synthesis tank 6.

[0079] In this embodiment, the online monitoring and automatic control unit 9 includes an online monitoring section and an automatic control section. The online monitoring section includes a dissolved oxygen meter, a pH meter, a thermometer, and a sludge concentration meter. The automatic control section is used to regulate the aeration rate, feed rate, and sludge discharge rate.

[0080] This invention also provides a method for synthesizing biodegradable plastic raw materials from sludge resources. Utilizing the aforementioned system for synthesizing biodegradable plastic raw materials from sludge resources, the method includes:

[0081] The excess sludge and digested sludge from the wastewater treatment plant are added to the sludge anaerobic acid production unit 1. After the pH value is <6.3, the acid-producing sludge is discharged and sent to the filtration unit. The acid-producing filtrate obtained by filtration is discharged into the feeding unit 3.

[0082] The activated sludge from the wastewater treatment plant is added to the microbial culture and propagation tank, and the time and amount of acid-producing filtrate added to the feeding unit 3 are controlled by online monitoring and automatic control unit 9.

[0083] After the microbial community in the strain domestication and expansion tank has stabilized, the sludge in the strain domestication and expansion tank is discharged into the PHA accumulation and synthesis tank 6. When the PHA synthesis rate reaches its maximum, the bacterial solution is discharged and the crude PHA product is collected.

[0084] In this embodiment, the ratio of residual sludge to digested sludge entering the sludge anaerobic acidification unit 1 is 1:1, the sludge retention time is 2 to 5 days, and the temperature is controlled at 30 to 50°C.

[0085] In this embodiment, the concentration of activated sludge entering the microbial acclimatization and expansion tank is 3000-4000 mg / L, the feed load per cycle is 3000-5000 mg COD / L, the time of each cycle is 4-6 T, the time of the abundant period is controlled at T, and the time of the starvation period is controlled at 3-5 T.

[0086] In this embodiment, the operating modes of each cycle include a first mode and a second mode. The first mode does not require phosphorus supplementation, while the second mode supplements phosphorus salts based on the carbon-phosphorus ratio in the acid-producing filtrate.

[0087] In this embodiment, the conditions for stable microbial community are that the sludge growth rate is stable at the end of the abundance period and PHA accounts for >25% of the dry weight of the microbial community.

[0088] In summary, during operation, the system first adds hydrolyzed sludge and digested sludge from the wastewater treatment plant to the anaerobic acidification unit at a 1:1 ratio. The sludge retention time is controlled at 3 days, and the temperature is maintained at 35℃. Once the pH value is <6.3, the acidified sludge is discharged while hydrolyzed sludge is added. The acidified sludge is then filtered through a membrane in the filtration unit to obtain acidified filtrate. The acidified filtrate contains approximately 14,000 mg COD / L of VFAs, and the VFAs / SCOD ratio can reach 61%. By adding 80 mg / L of calcium chloride, some phosphorus in the filtrate is removed, and the orthophosphate removal rate can reach 94%.

[0089] Acid-producing liquid water quality information

[0090] Then, activated sludge from the wastewater treatment plant was added as a starter culture to the inoculum acclimatization and propagation tank, and the activated sludge concentration was adjusted to 3000 mg / L. The method for controlling the addition time and amount of acid-producing filtrate from the feed unit based on online pH and dissolved oxygen monitoring data is as follows: By measuring pH and VFA content, it was found that: when pH is in the range of 6–6.3, a VFA content of 9000–1000 mg COD / L meets the feed requirements; if 6.4 > pH > 6.3, a VFA content of 8500–9000 mg COD / L requires the addition of 500 mg COD / L of sodium acetate; if 6.5 > pH > 6.4, a VFA content of 7500–8500 mg COD / L requires the addition of 100 mg COD / L of sodium acetate; if pH > 6.5, the feed load of the acid-producing unit needs to be adjusted. In this embodiment, the pH of the filtrate is between 6 and 6.3 based on online pH detection, so no additional carbon source needs to be added to the acid-producing filtrate.

[0091] Using acid-producing filtrate as substrate, the feed load per cycle was 4000 mg COD / L, and the feed was added in 5 times. One cycle lasted 1 day. The gluten period was controlled to be 6 hours and the starvation period to be 18 hours. The dissolved oxygen during the gluten period was dynamically adjusted to be 0.5 mg / L and the dissolved oxygen during the starvation period to be <1 mg / L.

[0092] When the system SVI is 230, add 1% by volume of 10000 mg / L activated sludge from the wastewater treatment plant once, while simultaneously supplementing sodium hypochlorite daily at a controlled chlorination rate of 10 mg / L. Stop adding sodium hypochlorite when the system SVI < 200. The operation mode for each cycle is divided into Mode I (hereinafter referred to as Mode I) and Mode II (hereinafter referred to as Mode II). Mode I does not require phosphorus supplementation. Mode II supplements phosphate salts to make the carbon-phosphorus ratio in the acidic filtrate of the sludge 100:1 (COD:TP 100:1), and adjusts the sludge concentration growth rate to over 150%. The operation mode is I I II I I II... I I II. When the sludge concentration increases to over 5 g / L, the PHA synthesis rate can reach 30% of the cell dry weight, and the PHA content can reach 1.5 g / L.

[0093] Finally, after the bacterial strain has been domesticated and the bacterial community in the expansion tank has stabilized, one-third of the mixed bacterial community in tank A is discharged into the PHA accumulation and synthesis tank, with an activated sludge concentration of 5000 mg / L. The acid-producing filtrate after phosphorus removal is used as the substrate (VFAs: orthophosphate 3300). The feed load per cycle is 5000 mg COD / L, and the feed is added 5 times until the PHA synthesis rate reaches its maximum. The bacterial solution is then discharged to collect crude PHA, which takes about 8 hours. The mixed bacterial communities in tanks B and C are also discharged into the PHA accumulation and synthesis tank, and the above operation is repeated. The mixed bacterial community concentration in the PHA accumulation and synthesis tank can reach 5500 mg / L, the PHA synthesis rate can reach 65% of the cell dry weight, and the PHA content can reach 3.6 g / L. Three batches can be collected every day.

[0094] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A system for synthesizing biodegradable plastic raw materials from sludge resources, characterized in that, include: The sludge anaerobic acid production unit is connected to a wastewater treatment plant at its front end and to a filtration unit at its rear end. The feeding unit is connected to the filtration unit at its front end and to the front end of the microbial culture and propagation tank at its rear end. A phosphorus recovery unit and a nutrient element supplementation unit are provided between the filtration unit and the microbial culture and propagation tank. The front end of the PHA accumulation synthesis tank is connected to the rear end of the strain domestication and expansion tank; An aeration unit is connected to the strain domestication and propagation tank and the PHA accumulation and synthesis tank; An online monitoring and automatic control unit is connected to the feeding unit, the phosphorus recovery unit, the nutrient element supplementation unit, and the aeration unit.

2. The system for synthesizing biodegradable plastic raw materials from sludge according to claim 1, characterized in that, The strain domestication and propagation tank includes multiple tanks arranged in parallel. A first stirrer is installed inside each tank. The tank is connected to the aeration unit, and the online monitoring and automatic control unit is connected to the tank.

3. The system for synthesizing biodegradable plastic raw materials from sludge according to claim 1, characterized in that, The PHA accumulation and synthesis tank is equipped with a second stirrer, and the front end of the PHA accumulation and synthesis tank is also connected to the phosphorus removal filtrate pipe of the phosphorus recovery unit.

4. The system for synthesizing biodegradable plastic raw materials from sludge according to claim 1, characterized in that, The front end of the phosphorus recovery unit is connected to the filtration unit, and the rear end of the phosphorus recovery unit is connected to the nutrient element supplementation unit and the PHA accumulation and synthesis tank.

5. The system for synthesizing biodegradable plastic raw materials from sludge according to claim 1, characterized in that, The online monitoring and automatic control unit includes an online monitoring section and an automatic control section. The online monitoring section includes a dissolved oxygen meter, a pH meter, a thermometer, and a sludge concentration meter. The automatic control section is used to regulate the aeration rate, feed rate, and sludge discharge rate.

6. A method for synthesizing biodegradable plastic raw materials from sludge resources, utilizing the system for synthesizing biodegradable plastic raw materials from sludge resources according to any one of claims 1-5, characterized in that, The method includes: The excess sludge and digested sludge from the wastewater treatment plant are added to the sludge anaerobic acidification unit. After the pH value is <6.3, the acidified sludge is discharged and sent to the filtration unit. The acidified filtrate obtained by filtration is discharged into the feeding unit. The activated sludge from the wastewater treatment plant is added to the microbial acclimatization and propagation tank, and the time and amount of acid-producing filtrate added to the feeding unit are controlled by the online monitoring and automatic control unit. After the microbial community in the strain domestication and expansion tank has stabilized, the sludge in the strain domestication and expansion tank is discharged into the PHA accumulation and synthesis tank. When the PHA synthesis rate reaches its maximum, the bacterial solution is discharged and crude PHA is collected.

7. The method for synthesizing biodegradable plastic raw materials from sludge according to claim 6, characterized in that, The ratio of excess sludge to digested sludge entering the sludge anaerobic acidification unit is 1:1, the sludge retention time is 2 to 5 days, and the temperature is controlled at 30 to 50°C.

8. The method for synthesizing biodegradable plastic raw materials from sludge according to claim 6, characterized in that, The concentration of activated sludge entering the microbial acclimatization and expansion tank is 3000-4000 mg / L, the feed load per cycle is 3000-5000 mg COD / L, the time of each cycle is 4-6 T, the time of the abundant period is controlled at T, and the time of the starvation period is controlled at 3-5 T.

9. The method for synthesizing biodegradable plastic raw materials from sludge according to claim 8, characterized in that, Each cycle includes a first mode and a second mode. The first mode does not require phosphorus supplementation, while the second mode supplements phosphate salts based on the carbon-phosphorus ratio in the acid-producing filtrate. The basis for the selection of the first mode and the second mode is as follows: if the sludge growth rate at the end of the abundant period in the strain domestication and expansion tank > 150%, the first mode is mainly adopted for operation; if the sludge growth rate at the end of the abundant period < 120%, the second mode is mainly adopted for operation; if the sludge growth rate at the end of the abundant period < 120%, but the PHA accounts for less than 25% of the dry weight of the thallus, the first mode is still mainly adopted for operation.

10. The method for synthesizing biodegradable plastic raw materials from sludge according to claim 6, characterized in that, The condition for the stability of the bacterial community is that the sludge growth rate at the end of the abundant period is stable and the PHA accounts for more than 25% of the dry weight of the thallus; Another condition for the stability of the bacterial community is that 50 < SVI < 200 in the system. If SVI > 200, the stability of the bacterial community and the system stability are controlled by adding a stabilizer to regulate the SVI of the system.

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