System and method for synthesizing biodegradable plastic raw material by recycling sludge

Abstract

The invention discloses a system and a method for synthesizing a biodegradable plastic raw material through sludge resource utilization, and relates to the field of sludge resource utilization. The system comprises a sludge anaerobic acid production unit, a filtering unit, a feeding unit, a phosphorus recovery unit, a nutrient element supplementing unit, a strain domestication and propagation tank, a PHA accumulation synthesis tank, an aeration unit and an online monitoring and automatic control unit. The method comprises the following steps: adding residual sludge and digested sludge into a sludge anaerobic acidogenic unit, conveying discharged acidogenic sludge to a filtering unit, filtering to obtain acidogenic filtrate, and discharging the acidogenic filtrate into a feeding unit; adding the activated sludge into a strain domestication and propagation tank, and regulating and controlling the adding time and the adding amount of the acid-producing filtrate; after flora in the strain domestication and propagation tank is stable, sludge in the strain domestication and propagation tank is discharged into a PHA accumulation synthesis tank, and when the PHA synthesis rate reaches the highest, bacterial liquid is discharged, and a PHA crude product is collected. Therefore, the PHA synthesis rate and the PHA synthetic bacterium biomass can be improved at the same time, and the contradiction between PHA synthetic bacterium biomass amplification and synthesis rate improvement is solved.

Description

Technical Field

[0001] The present 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 Art

[0002] Polyhydroxyalkanoates (PHA) are a type of biodegradable plastic with good performance and wide application. At present, the industrial production of PHA is mainly based on pure bacterial culture or genetically engineered bacteria, which requires strict aseptic conditions and the use of specific carbon sources, so the operating costs are relatively high. In order to reduce the increased costs of PHA production raw materials and sterilization processes, researchers use various waste organic matter such as sludge and its hydrolyzate instead of refined raw materials as carbon sources to reduce the cost of production raw materials, and develop mixed bacterial communities instead of pure strains to reduce sterilization costs, thereby reducing the cost of PHA production.

[0003] The synthesis of PHA by mixed bacterial communities has great development prospects in the field of sludge resource utilization, but the reason why it has not been applied in industry is that its PHA synthesis yield still does not meet the requirements of industrial production. On the one hand, the synthesis rate of PHA synthesized by mixed bacterial communities using sludge as a matrix is ​​only 20% to 60% of the cell dry weight, while the PHA synthesis rate of pure bacteria using refined raw materials is >75%; on the other hand, compared with the biomass of pure bacterial production process (60 to 200 g / L), the biomass of mixed bacterial communities is mostly only 1.2 to 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 that the system outputs a higher biomass. However, a higher PHA synthesis rate can usually be achieved under conditions with a high carbon-nitrogen ratio or a high carbon-phosphorus ratio (C:N>20; C:P>200), and microbial growth requires C:N:P to be maintained at around 100:5:1 to maintain a high biomass growth. At the same time, 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 bacterial community and affect the stability of the system.

[0004] Currently, there is a reaction system that can use sludge as a substrate for PHA synthesis after thermal hydrolysis. However, the PHA synthesis bacterial community culture and PHA synthesis in this system are both carried out in one tank, which will make the PHA synthesis system unstable and the biomass difficult to increase.

[0005] There is also a method for increasing the output of PHA synthetic bacteria. This method increases the biomass of the system by adding an expansion reactor between the strain acclimation reactor and the synthesis reactor. However, the added expansion reactor also needs to be supplemented with a specific carbon source and continuously aerated. If organic waste such as sludge is used as a substrate, some operating costs will be increased, and the more processes added to the process, the greater the difficulty of operation and maintenance.

[0006] There is also a method for enriching and expanding the PHA mixed bacterial community, which increases the biomass of the PHA mixed bacterial community in the system by adding loading materials to the expanded culture reactor, but the growth of microbial film 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 the biomass of PHA synthesizing bacteria and the improvement of the synthesis rate while improving the stability of the PHA synthesis system, it is necessary to develop a system and operation method for the sludge resource-based PHA synthesis, expand the biomass of PHA synthesizing bacteria on the basis of obtaining a high PHA synthesis rate and system stability, and thus increase PHA production at a low cost. Summary of the invention

[0008] The purpose of the present invention is to address the deficiencies in the prior art and provide a system and method for synthesizing biodegradable plastic raw materials from sludge resources. The system and method can simultaneously improve the PHA synthesis rate and the biomass of PHA synthesizing bacteria, and resolve the contradiction between the expansion of PHA synthesizing bacteria biomass and the improvement of the synthesis rate.

[0009] In order to achieve the above object, the present invention provides a system for synthesizing biodegradable plastic raw materials from sludge resources, comprising:

[0010] A sludge anaerobic acid production unit, the front end of which is used to be connected to a sewage treatment plant, and the rear end of which is connected to a filtration unit;

[0011] A feeding unit, the front end of which is connected to the filtering unit, the rear end of which is connected to the front end of the strain domestication and expansion tank, and a phosphorus recovery unit and a nutrient element supplementation unit are provided between the filtering unit and the strain domestication and expansion tank;

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

[0013] an aeration unit connected to the bacterial strain domestication and expansion tank and the PHA accumulation and synthesis tank;

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

[0015] Optionally, the strain domestication and expansion tank includes a plurality of tank bodies arranged in parallel, a first agitator is arranged in the tank body, the tank body is connected to the aeration unit, and the online monitoring and automatic control unit is connected to the tank body.

[0016] Optionally, a second agitator is provided in 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 filtering unit, and the rear end of the phosphorus recovery unit is connected to the nutrient element supplementing unit and the PHA accumulation synthesis tank.

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

[0019] The present invention also provides a method for synthesizing biodegradable plastic raw materials by recycling sludge resources, using the above-mentioned system for synthesizing biodegradable plastic raw materials by recycling sludge resources, the method comprising:

[0020] The excess sludge and digested sludge of the sewage treatment plant are added to the sludge anaerobic acid production unit, and after the pH value is less than 6.3, the acid-producing sludge is discharged to the filtration unit, and the acid-producing filtrate obtained by filtration is discharged into the feeding unit;

[0021] Adding the activated sludge from the sewage treatment plant into the strain domestication and expansion tank, and controlling the addition time and amount of the acid-producing filtrate in the feeding unit by the online monitoring and automatic control unit;

[0022] After the bacterial flora in the bacterial strain acclimation and expansion tank is stabilized, the sludge in the bacterial strain acclimation and expansion tank is discharged into the PHA accumulation synthesis tank. When the PHA synthesis rate reaches the highest, the bacterial liquid is discharged to collect the crude PHA product.

[0023] Optionally, the ratio of excess sludge to digested sludge entering the sludge anaerobic acid production 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 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 4-6T, the time of the abundant period is controlled to T, and the time of the hungry period is controlled to 3-5T.

[0025] Optionally, the operation mode of each cycle includes a first mode and a second mode, wherein the first mode does not require phosphorus supplementation, and the second mode supplements phosphorus salts based on the carbon-phosphorus ratio in the acidogenic filtrate.

[0026] Optionally, the condition for the stability of the bacterial community is that the sludge growth rate is stable at the end of the prosperous period and PHA accounts for more than 25% of the dry weight of the bacterial cells.

[0027] The present invention provides a system and method for synthesizing biodegradable plastic raw materials from sludge resources, and the beneficial effects thereof are:

[0028] 1. The system for synthesizing biodegradable plastic raw materials from sludge resources can achieve the growth of PHA synthesizing bacteria biomass in the strain domestication and expansion tanks, and perform PHA extreme accumulation synthesis in the PHA accumulation synthesis tank, which can solve the contradiction between the growth of PHA synthesizing bacteria biomass and the improvement of synthesis rate;

[0029] 2. This system aims to solve the problem of unstable sludge source, which leads to unstable acid-producing liquid and unstable bacterial flora. The present invention controls the addition time and amount of acid-producing liquid through the linkage of pH and dissolved oxygen online monitoring data, which can improve the stability of bacterial strain domestication and expansion and PHA accumulation synthesis;

[0030] 3. The system recovers phosphorus from part of the acid-producing filtrate. On the one hand, it supplements the recovered phosphorus resources during bacterial expansion to increase the biomass of the system. On the other hand, it uses the dephosphorized filtrate to improve the PHA synthesis rate during PHA accumulation synthesis.

[0031] 4. The system is based on the dynamic control operation mode of PHA content detection and sludge concentration online monitoring, which effectively improves the biomass of the bacterial community on the basis of ensuring high PHA synthesis rate during bacterial 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 reduce the dissolved oxygen in the starvation period to <1 mg / L, thereby reducing the energy consumption required for aeration, and 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. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0036] Figure 2 A flow chart of a method for synthesizing biodegradable plastic raw materials from sludge resources according to an embodiment of the present invention is shown.

[0037] Description of reference numerals:

[0038] 1. Sludge anaerobic acid production unit; 2. Tank body; 3. Feeding unit; 4. Phosphorus recovery unit; 5. Nutrient element addition unit; 6. PHA accumulation synthesis tank; 7. Aeration unit; 8. Phosphorus removal filtrate pipe; 9. Online monitoring and automatic control unit. DETAILED DESCRIPTION

[0039] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0040] The present invention provides a system for synthesizing biodegradable plastic raw materials from sludge resources, comprising:

[0041] The sludge anaerobic acid production unit has a front end for connecting to a sewage treatment plant, and a rear end for connecting to a filtration unit;

[0042] A feeding unit, the front end of which is connected to the filtering unit, the rear end of which is connected to the front end of the strain domestication and expansion tank, and a phosphorus recovery unit and a nutrient element supplementation unit are provided between the filtering unit and the strain domestication and expansion tank;

[0043] The front end of the PHA accumulation synthesis tank is connected to the rear end of the strain domestication and expansion tank;

[0044] The aeration unit is connected to the bacterial strain domestication and expansion tank and the PHA accumulation synthesis tank;

[0045] The online monitoring and automatic control unit is connected with the feed unit, the phosphorus recovery unit, the nutrient element addition unit and the aeration unit.

[0046] Specifically, the system includes multiple units, and is monitored and automatically controlled by an online monitoring and automatic control unit. The sludge anaerobic acid production unit, the filtration unit, the feeding unit, the strain acclimation and expansion tank, and the PHA accumulation synthesis tank are connected in sequence. The sludge anaerobic acid production unit realizes anaerobic acid production on waste organic matter such as sludge, and then filters the sludge acid production liquid through the filtration unit. The feeding unit controls the feed amount to the strain acclimation and expansion tank based on the data monitoring and feedback of the online monitoring and automatic control unit. The strain acclimation and expansion tank realizes the acclimation and expansion of the PHA synthetic bacterial community, and the PHA accumulation synthesis tank finally discharges the bacterial community enriched with a large amount of PHA. In addition, a The phosphorus recovery unit recovers phosphorus from the filtrate by means of flocculation and sedimentation, and uses phosphorus as a nutrient element for the expansion and cultivation of the bacterial community. The amount of filtrate that needs to be processed for phosphorus recovery is controlled by the monitoring data feedback of the online monitoring and automatic control unit, and the feed amount of the PHA accumulation synthesis tank is controlled; the nutrient element addition unit is arranged before the strain acclimation and expansion tank, and is used for the reserve of nutrient elements such as phosphorus and carbon. The nutrient elements are added to the strain acclimation and expansion tank through monitoring data control; the online monitoring and automatic control unit includes a feedback system connected to each unit and is connected to each online instrument in the tank, and controls the addition of aeration, nutrient elements and feed amount by receiving signals from each online instrument.

[0047] Optionally, the strain domestication and expansion tank includes a plurality of tank bodies arranged in parallel, a first agitator is arranged in the tank body, the tank body is connected to an aeration unit, and an online monitoring and automatic control unit is connected to the tank body.

[0048] Optionally, a second agitator is provided in 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.

[0049] Specifically, multiple parallel tanks are set in the strain domestication and expansion tank, and the sludge in the tank is fully reacted and aerated in the tank by stirring; the second agitator in the PHA accumulation synthesis tank stirs and mixes the feed after it enters, and supplements the filtrate through the phosphorus recovery unit with the cooperation of online monitoring and automatic control unit. In addition, the aeration unit is equipped with an air compressor and a gas storage bottle, etc., and the aeration volume of each strain domestication and expansion tank and the PHA accumulation synthesis tank is regulated with the cooperation of online monitoring and automatic control unit.

[0050] Optionally, the front end of the phosphorus recovery unit is connected to the filtering unit, and the rear end of the phosphorus recovery unit is connected to the nutrient element supplementation unit and the PHA accumulation synthesis tank.

[0051] Specifically, the phosphorus recovery unit can recover phosphorus in the filtrate by flocculation and sedimentation, and use phosphorus as a nutrient element for the expansion and cultivation of the bacterial flora. The front end of the phosphorus recovery unit is connected to the filtration unit, and the rear end is connected to the nutrient element supplement unit and the PHA accumulation synthesis tank respectively. The monitoring data feedback is used to determine how much filtrate needs to be processed for phosphorus recovery, and the feed amount of the PHA accumulation synthesis tank is controlled.

[0052] Optionally, the online monitoring and automatic control unit includes an online monitoring part and an automatic control part. The online monitoring part includes a dissolved oxygen meter, a pH meter, a thermometer, and a sludge concentration meter. The automatic control part is used to adjust the aeration amount, the feed amount, and the sludge discharge amount.

[0053] Specifically, the online monitoring and automatic control unit includes two parts: online monitoring and automatic control. The online instruments in the online monitoring part include a dissolved oxygen meter, a pH meter, a thermometer, and a sludge concentration meter, which are used for online monitoring of the pH value and temperature of the sludge anaerobic acid production unit, and for online monitoring of dissolved oxygen, pH, temperature and sludge concentration in the strain acclimatization and expansion tank and the PHA accumulation synthesis tank, and dynamically adjusting the aeration volume, feed volume, nutrients and sludge discharge volume based on these real-time data; the automatic control part adjusts the aeration volume, feed volume, nutrients and sludge discharge volume in real time based on the online detection data.

[0054] The present invention also provides a method for synthesizing biodegradable plastic raw materials by recycling sludge resources, using the above-mentioned system for synthesizing biodegradable plastic raw materials by recycling sludge resources, the method comprising:

[0055] The excess sludge and digested sludge from the sewage treatment plant are added to the anaerobic sludge acid production unit. When the pH value is less than 6.3, the acid-producing sludge is discharged to the filtration unit, and the acid-producing filtrate obtained by filtration is discharged into the feeding unit;

[0056] The activated sludge from the sewage treatment plant is added to the strain domestication and expansion tank, and the addition time and amount of the acid-producing filtrate in the feeding unit are controlled by online monitoring and automatic control unit;

[0057] After the bacterial flora in the strain acclimation and expansion tank is stabilized, the sludge in the strain acclimation and expansion tank is discharged into the PHA accumulation synthesis tank. When the PHA synthesis rate reaches the highest, the bacterial liquid is discharged to collect the crude PHA product.

[0058] Specifically, the method for synthesizing raw materials uses three steps, namely, anaerobic acid production and filtration of sludge, bacterial strain domestication and expansion, and PHA cumulative synthesis, and cooperates with the system protected in the present invention to achieve the effect of increasing the PHA synthesis rate and the biomass of PHA synthesizing bacteria, and solves the contradiction between the expansion of the biomass of PHA synthesizing bacteria and the improvement of the synthesis rate.

[0059] Optionally, the ratio of excess sludge to digested sludge entering the sludge anaerobic acid production unit is 1:1, the sludge retention time is 2 to 5 days, and the temperature is controlled at 30 to 50°C.

[0060] Specifically, in the step of anaerobic acid production and filtration of sludge, the excess sludge from the sewage treatment plant and the digested sludge are added to the anaerobic acid production unit of sludge in a ratio of 1:1, the sludge retention time is controlled at 2 to 5 days, the temperature is 30 to 50°C, and after the pH value is <6.3, the acid-producing sludge can be discharged intermittently or continuously, and the excess sludge is added at the same time. The acid-producing sludge is filtered in the filtration unit to obtain an acid-producing filtrate by centrifugation, filter press or membrane filtration.

[0061] Optionally, the concentration of activated sludge entering the strain 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 4-6T, the time of the abundant period is controlled to T, and the time of the hungry period is controlled to 3-5T.

[0062] Specifically, in the step of bacterial strain domestication and expansion, the activated sludge in the sewage treatment plant is added as bacterial strain into the bacterial strain domestication and expansion tank, and the activated sludge concentration is adjusted to 3000-4000 mg / L; the feed load of each cycle is 3000-5000 mg COD / L, and the feed can be added once or multiple times. Based on the online detection data of pH and dissolved oxygen, the addition time and amount of the acid-producing filtrate of the feed unit are controlled. The cycle time is 4-6T, the abundant period time is controlled to be T, and the starvation period time is 3-5T.

[0063] Among them, the method of controlling the addition time and amount of the acid-producing filtrate of the feeding unit based on the 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 corresponding relationship between the two is calculated, and then the VFAs content is calculated by online pH measurement. If the VFAs content changes by more than 10% of the preset value, the feed is reduced or carbon sources such as sodium acetate are added to maintain the COD of the easily available carbon source in the filtrate within a fluctuation range of less than 10%; by calculating the relationship between the time required for the "jump" increase of dissolved oxygen at different aeration amounts after feeding and the feed COD, a linear relationship curve between the two is obtained, and the aeration amount and the addition time of the acid-producing filtrate are dynamically adjusted as needed. The "abundant period" refers to the period from feeding to the "jump" increase of dissolved oxygen, for example, a sudden increase from 1mg / L to 4mg / L and above. This period is recorded as the abundant period, and the period other than the abundant period is recorded as the starvation period in a cycle. The dissolved oxygen in the starvation period is dynamically regulated to be <1mg / L.

[0064] In the steps of strain domestication and expansion 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 system stability.

[0065] 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 supplements phosphorus salts based on the carbon-phosphorus ratio in the acid-producing filtrate.

[0066] 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 supplements 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.

[0067] 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 expansion culture tank > 150%, the first mode Ⅰ is mainly adopted for operation, ⅠⅠⅡⅠⅠⅡ……ⅠⅠⅡ or ⅠⅠⅠⅡⅠⅠⅠⅡ……ⅠⅠⅠⅡ; when the sludge growth rate at the end of the prosperous period < 120%, the second mode Ⅱ is mainly adopted for operation, ⅠⅡⅠⅡ……ⅠⅡ; 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 bacterial cells, the first mode Ⅰ is still mainly adopted for operation.

[0068] 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 bacterial cells.

[0069] Specifically, in the PHA cumulative synthesis step, after the bacterial community in the strain domestication and expansion culture tank is stable, it is discharged into the PHA cumulative synthesis tank according to the sludge concentration increase, 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, when the PHA synthesis rate reaches the highest, the bacterial liquid is discharged 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.

[0070] Example

[0071] As Figure 1 to Figure 2 shown, the present invention provides a system for resourcefully synthesizing biodegradable plastic raw materials from sludge, including:

[0072] A sludge anaerobic acid-producing unit 1, the front end of which is used to connect with a sewage treatment plant, and the rear end of the sludge anaerobic acid-producing unit 1 is connected with a filtering unit;

[0073] The front end of the feeding unit 3 is connected to the filtering unit, the rear end of the feeding unit 3 is connected to the front end of the strain domestication and expansion tank, and a phosphorus recovery unit 4 and a nutrient element supplementation unit 5 are arranged between the filtering unit and the strain domestication and expansion tank;

[0074] The front end of the PHA accumulation synthesis tank 6 is connected to the rear end of the strain domestication and expansion tank;

[0075] The aeration unit 7 is connected to the bacterial strain domestication and expansion tank and the PHA accumulation synthesis tank 6;

[0076] The online monitoring and automatic control unit 9 is control-connected with the feeding unit 3 , the phosphorus recovery unit 4 , the nutrient element supplementation unit 5 and the aeration unit 7 .

[0077] In this embodiment, the strain domestication and expansion tank includes three tank bodies 2 arranged in parallel, namely tank A, tank B and tank C. Each tank body 2 is provided with a first agitator. The tank body 2 is connected to the aeration unit 7, and the online monitoring and automatic control unit 9 monitors the inside of the tank body 2.

[0078] In this embodiment, a second agitator is provided in 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 .

[0079] In this embodiment, the front end of the phosphorus recovery unit 4 is connected to the filtering unit, and the rear end of the phosphorus recovery unit 4 is connected to the nutrient element supplementing unit 5 and the PHA accumulation synthesis tank 6 .

[0080] In this embodiment, the online monitoring and automatic control unit 9 includes an online monitoring part and an automatic control part. The online monitoring part includes a dissolved oxygen meter, a pH meter, a thermometer, and a sludge concentration meter. The automatic control part is used to adjust the aeration amount, feed amount, and sludge discharge amount.

[0081] The present invention also provides a method for synthesizing biodegradable plastic raw materials by recycling sludge resources, using the above-mentioned system for synthesizing biodegradable plastic raw materials by recycling sludge resources, the method comprising:

[0082] The excess sludge and digested sludge of the sewage treatment plant are added to the anaerobic sludge acid production unit 1. When the pH value is less than 6.3, the acid-producing sludge is discharged to the filtration unit, and the acid-producing filtrate obtained by filtration is discharged into the feeding unit 3;

[0083] The activated sludge from the sewage treatment plant is added to the strain domestication and expansion tank, and the addition time and amount of the acid-producing filtrate in the feeding unit 3 are controlled by the online monitoring and automatic control unit 9;

[0084] After the bacterial flora in the strain acclimation and expansion tank is stabilized, the sludge in the strain acclimation and expansion tank is discharged into the PHA accumulation synthesis tank 6. When the PHA synthesis rate reaches the highest, the bacterial liquid is discharged to collect the crude PHA product.

[0085] In this embodiment, the ratio of the excess sludge to the digested sludge entering the anaerobic sludge acid production unit 1 is 1:1, the sludge retention time is 2 to 5 days, and the temperature is controlled at 30 to 50°C.

[0086] In this embodiment, the concentration of activated sludge entering the strain 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 4-6T, the time of the abundant period is controlled to T, and the time of the hungry period is controlled to 3-5T.

[0087] In this embodiment, 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 supplements phosphorus salts based on the carbon-phosphorus ratio in the acidogenic filtrate.

[0088] In this embodiment, the condition for the stability of the bacterial community is that the sludge growth rate is stable at the end of the prosperous period and the PHA accounts for more than 25% of the dry weight of the bacterial cells.

[0089] In summary, during the operation of the system, the thermal hydrolysis sludge and digested sludge from the sewage treatment plant are first added to the sludge anaerobic acid production unit in a ratio of 1:1, the sludge retention time is controlled to be 3 days, the temperature is controlled at 35°C, and the acidogenic sludge is discharged after the pH value is <6.3, and the thermal hydrolysis sludge is added at the same time. The acidogenic sludge is filtered through a membrane in the filtration unit to obtain an acidogenic filtrate. The VFAs in the acidogenic liquid are about 14000 mg COD / L, and the VFAs / SCOD can reach 61%. By adding 80 mg / L calcium chloride to remove phosphorus from part of the filtrate, the orthophosphate removal rate can reach 94%.

[0090] Acid-generating liquid water quality information

[0091] sample SCOD(mg / L) VFAs(mg COD / L) Ammonia nitrogen (mg / L) Orthophosphate (mg / L) Acid filtrate 25920 14414 2763 70.5 Filtrate after phosphorus removal 24785 13894 2788 4.2

[0092] Then, the activated sludge from the sewage treatment plant was added as the strain into the strain acclimatization and expansion tank, and the activated sludge concentration was adjusted to 3000 mg / L; the method of controlling the addition time and amount of the acid-producing filtrate of the feeding unit based on the online detection data of pH and dissolved oxygen, the adjustment process is as follows: by measuring the pH and VFAs content, it was found that: when the pH was in the range of 6 to 6.3, the VFAs content was 9000 to 1000 mg COD / L, which met the feeding requirements; if 6.4>pH>6.3, the VFAs content was 8500 to 9000 mg COD / L, and 500 mg COD / L of sodium acetate needed to be supplemented; if 6.5>pH>6.4, the VFAs content was 7500 to 8500 mgCOD / L, and 100 mg COD / L of sodium acetate needed to be supplemented; if pH>6.5, the feed load of the acid-producing unit needed to be adjusted. In this embodiment, based on the online pH detection, if the pH of the filtrate is between 6 and 6.3, no additional carbon source needs to be added to the acid-producing filtrate.

[0093] The acid-producing filtrate was used as the substrate, with a feed load of 4000 mg COD / L per cycle. The feed was added in 5 times, with a cycle time of 1 day. The abundant period was controlled to be 6 hours, and the starvation period was 18 hours. The dissolved oxygen in the abundant period was dynamically controlled to be 0.5 mg / L, and the dissolved oxygen in the starvation period was <1 mg / L.

[0094] When the system SVI is 230, 10000 mg / L of sewage plant activated sludge with a volume ratio of 1% is added once, and sodium hypochlorite is supplemented every day to control the chlorine addition amount to 10 mg / L. When the system SVI is <200, the addition of sodium hypochlorite is stopped; the operation mode of each cycle is divided into the first mode (hereinafter referred to as mode I) and the second mode (hereinafter referred to as mode II). Mode I does not require phosphorus supplementation. Mode II adds phosphate salts to make the carbon-phosphorus ratio in the sludge acidification filtrate 100:1 (COD:TP 100:1), adjusts the sludge concentration growth rate to more than 150%, and adopts ⅠⅠⅡⅠⅡⅡⅡ mode; when the sludge concentration increases to more than 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.

[0095] Finally, after the strains are acclimated and the bacterial flora in the expansion tank is stable, one-third of the mixed bacterial flora in tank A is discharged to the PHA accumulation synthesis tank, and the activated sludge concentration is 5000 mg / L; the acid-producing filtrate after phosphorus removal is used as the substrate (VFAs: orthophosphate 3300), the feed load for each cycle is 5000 mg COD / L, and after 5 feedings, when the PHA synthesis rate reaches the highest, it takes about 8 hours to discharge the bacterial liquid and collect the PHA crude product; the mixed bacterial flora in tanks B and C are also discharged into the PHA accumulation synthesis tank, and the above operations are repeated; the concentration of the mixed bacterial flora in the PHA accumulation synthesis tank can reach 5500 mg / L, the PHA synthesis rate can reach 65% of the cell dry weight, the PHA content can reach 3.6 g / L, and three batches can be collected every day.

[0096] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes 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: A sludge anaerobic acid production unit, the front end of which is used to be connected to a sewage treatment plant, and the rear end of which is connected to a filtration unit; A feeding unit, the front end of which is connected to the filtering unit, the rear end of which is connected to the front end of the strain domestication and expansion tank, and a phosphorus recovery unit and a nutrient element supplementation unit are provided between the filtering unit and the strain domestication and expansion tank; A PHA accumulation synthesis tank, the front end of which is connected to the rear end of the strain domestication and expansion tank; an aeration unit connected to the bacterial strain domestication and expansion tank and the PHA accumulation and synthesis tank; An online monitoring and automatic control unit is controllably connected to the feed 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 resources according to claim 1 is characterized in that: The strain domestication and expansion tank comprises a plurality of tank bodies arranged in parallel, a first agitator is arranged in the tank body, the tank body is connected to the aeration unit, and the online monitoring and automatic control unit is connected to the tank body.

3. The system for synthesizing biodegradable plastic raw materials from sludge resources according to claim 1 is characterized in that: A second agitator is arranged in 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.

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

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

6. A method for synthesizing biodegradable plastic raw materials from sludge resources, using the system for synthesizing biodegradable plastic raw materials from sludge resources according to any one of claims 1 to 5, characterized in that: The method includes: The excess sludge and digested sludge of the sewage treatment plant are added to the sludge anaerobic acid production unit, and after the pH value is less than 6.3, the acid-producing sludge is discharged to the filtration unit, and the acid-producing filtrate obtained by filtration is discharged into the feeding unit; Adding the activated sludge from the sewage treatment plant into the strain domestication and expansion tank, and controlling the addition time and amount of the acid-producing filtrate in the feeding unit by the online monitoring and automatic control unit; After the bacterial flora in the bacterial strain acclimation and expansion tank is stabilized, the sludge in the bacterial strain acclimation and expansion tank is discharged into the PHA accumulation synthesis tank. When the PHA synthesis rate reaches the highest, the bacterial liquid is discharged to collect the crude PHA product.

7. The method for synthesizing biodegradable plastic raw materials from sewage sludge resources according to claim 6, characterized in that: The ratio of the residual sludge to the digested sludge entering the sludge anaerobic acid production 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 resources according to claim 6, characterized in that: The concentration of activated sludge entering the strain acclimatization and expansion tank is 3000-4000 mg / L, the feed load of each cycle is 3000-5000 mg COD / L, the time of each cycle is 4-6T, the time of the abundant period is controlled to T, and the time of the hungry period is controlled to 3-5T.

9. The method for synthesizing biodegradable plastic raw materials from sludge resources according to claim 8, characterized in that: The operation mode of each cycle includes a first mode and a second mode, wherein the first mode does not require phosphorus supplementation, and the second mode supplements phosphorus salts based on the carbon-phosphorus ratio in the acidogenic filtrate; The basis for selecting the first mode and the second mode is as follows: if the sludge growth rate at the end of the prosperous 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 prosperous period < 120%, the second mode is mainly adopted for operation; if the sludge growth rate at the end of the prosperous period < 120%, but the PHA content in the dry weight of the bacterial cells < 25%, the first mode is still mainly adopted for operation.

10. The method for synthesizing biodegradable plastic raw materials from sludge resources 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 prosperous period is stable and the PHA content in the dry weight of the bacterial cells > 25%; Another condition for the stability of the bacterial community is that 50 < SVI < 200 in the system. When SVI > 200, the stability of the bacterial community and the system is controlled by adding a stabilizer to regulate the SVI of the system.

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