A method for reducing and recycling excess sludge based on potassium ferrate

Abstract

The present application relates to solid waste treatment technical field, specifically a kind of method for residual sludge reduction and resource based on potassium ferrate.The residual sludge taken from sewage plant is subjected to natural sedimentation, and potassium ferrate is added for pretreatment, to obtain pretreated sludge;Pretreated sludge is subjected to solid-liquid separation, and supernatant is introduced into microbial fuel cell for reaction;Residual solid enters anaerobic fermentation tank.At the same time, the anode and cathode of microbial fuel cell are connected to two electrode plates in anaerobic fermentation tank for power supply;Residual liquid after microbial fuel cell treatment is continuously added to anaerobic fermentation tank, and subjected to anaerobic fermentation, to obtain methane biogas and blue vitriol and other resources finally.The present application proposes a continuous flow treatment system combining bioelectrochemical system and anaerobic fermentation, which has broad application prospect in solid waste treatment technical field.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment technology, specifically a method for reducing and recycling excess sludge based on potassium ferrate. Background Technology

[0002] With the increase in urban population, the construction of new wastewater treatment plants, and technological innovation, the activated sludge process has been widely adopted in many wastewater treatment plants due to its numerous advantages, including handling large influent loads, achieving good nitrogen removal efficiency, wide applicability, and low energy consumption. However, a byproduct of the activated sludge process is a large amount of excess sludge, the treatment of which incurs high costs. Excess sludge mainly consists of bacteria and their extracellular polymers, containing large amounts of proteins, polysaccharides, and lipids, which account for more than 70% of the dry weight of the excess sludge. Therefore, excess sludge has great potential for biomass energy production. However, excess sludge contains many complex organic materials and pathogens, which can easily cause secondary pollution without proper treatment methods. Therefore, finding feasible methods to treat excess sludge is crucial. To achieve resource recovery and utilization, the organic matter in excess sludge can be used for biomass energy production. However, when treating excess sludge, we also need to research and develop safe, efficient, and environmentally friendly technologies to prevent secondary pollution. Such efforts can minimize the cost of treating residual sludge, reduce the occupation of land resources, and achieve effective resource utilization.

[0003] To overcome the shortcomings of existing technologies, this invention provides a method for reducing and recycling excess sludge based on potassium ferrate. Summary of the Invention

[0004] The purpose of this invention is to provide a method for reducing and recycling excess sludge based on potassium ferrate, in order to solve the problems in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] A method for reducing and recycling excess sludge based on potassium ferrate includes the following steps:

[0007] Step 1: After the sludge taken from the sewage treatment plant is allowed to settle naturally, the supernatant is removed. Potassium ferrate is added to the remaining sludge for pretreatment to obtain pretreated sludge.

[0008] Step 2: The pretreated sludge is subjected to solid-liquid separation. The solid is added to the anaerobic digester, and the liquid is added to the microbial fuel cell for reaction, resulting in a liquid enriched with the endogenous redox mediator of the sludge. The output voltage of the microbial fuel cell powers the anaerobic digester.

[0009] Step 3: The liquid containing the endogenous redox mediator of the sludge is added to the anaerobic fermenter to carry out the fermentation reaction and obtain the product.

[0010] Ideally, in step one, the mass ratio of residual sludge to potassium ferrate is 1:0.03-0.15.

[0011] Ideally, the preprocessing time in step one should be 1-2 hours.

[0012] In a more optimized manner, in step two, when preparing the liquid for enriching the endogenous redox mediator of sludge, the hydraulic retention time is 3-5 days.

[0013] Ideally, in step two, the temperature for preparing the liquid enriched with endogenous redox mediators in sludge is 35-40℃.

[0014] In a more optimized approach, in step three, the dissolved oxygen level in the anaerobic fermenter is set to 0.04-0.08 mg / L.

[0015] Ideally, in step three, the water bath temperature during the fermentation reaction is 36-38℃.

[0016] Ideally, in step three, the fermentation reaction should be carried out at a speed of 80-90 rpm.

[0017] Ideally, in step three, the fermentation time is 20-30 days.

[0018] Ideally, in step three, the products obtained through fermentation are methane gas and resources such as lapis lazuli.

[0019] The beneficial effects of this invention are:

[0020] This invention involves allowing residual sludge from a wastewater treatment plant to settle naturally, then pretreating it with potassium ferrate to obtain pretreated sludge. The pretreated sludge is then subjected to solid-liquid separation; the liquid is added to a microbial fuel cell for reaction, while the solid is added to an anaerobic digester. The anode and cathode of the microbial fuel cell are connected to the electrode plates of the anaerobic digester for power supply. The liquid treated by the microbial fuel cell is further added to the anaerobic digester for fermentation, yielding methane gas and resources such as lapis lazuli. Figure 1 This is a flowchart of the above steps.

[0021] The invention is characterized in that, in step two, the liquid after solid-liquid separation is added to the microbial fuel cell for reaction. This generates electricity to power the fermentation reaction in the anaerobic digester, enabling electron transfer from recalcitrant organic matter. It also produces a liquid enriched with endogenous redox mediators in the sludge, which is further added to the anaerobic digester to enhance electron transfer between microorganisms, thus facilitating methane bioconversion. In step four, the liquid treated by the microbial fuel cell is added to the anaerobic digester for fermentation. During fermentation, methane gas is produced, and simultaneously, iron-reducing bacteria in the sludge convert Fe... 3+ Reduced to Fe 2+ It reacts with phosphates to form lapis lazuli.

[0022] In addition, the anaerobic fermentation sludge pretreated with potassium ferrate was air-dried, ground, and then subjected to X-ray diffraction analysis to obtain... Figure 2 XRD patterns of the anaerobic fermentation sludge, compared with standard spectra of lapis lazuli, revealed multiple crystal faces of the potassium ferrate-pretreated anaerobic fermentation sludge that matched those of lapis lazuli, indicating the formation of lapis lazuli in the pretreated anaerobic fermentation sludge. Scanning electron microscopy analysis of the potassium ferrate-pretreated anaerobic fermentation sludge solids yielded... Figure 3 The SEM image of the anaerobic fermentation sludge shows smooth, blocky precipitates. Combined with the XRD pattern, the precipitates are identified as lapis lazuli, indicating that lapis lazuli is produced in the solids of the anaerobic fermentation sludge. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0024] Figure 1 This is a flowchart of the process for reducing and recycling excess sludge based on potassium ferrate, as described in this invention.

[0025] Figure 2 This is the XRD pattern of the anaerobic fermentation sludge after potassium ferrate pretreatment in Example 1;

[0026] Figure 3 This is an SEM image of the anaerobic fermentation sludge from Example 1 after pretreatment with potassium ferrate. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Raw material source:

[0029] The sludge was the return sludge from the secondary sedimentation tank of a general wastewater treatment plant. After natural sedimentation and removal of the supernatant, the remaining sludge was 17.78±0.56 g / L.

[0030] Example 1: Step 1: After the 500ml sludge taken from the sewage treatment plant is allowed to settle naturally, the supernatant is removed. 1.88g of potassium ferrate is added to the remaining sludge for pretreatment for 2 hours to obtain pretreated sludge.

[0031] Step 2: The pretreated sludge is subjected to solid-liquid separation. The solid is added to the anaerobic digester, and the liquid is added to the microbial fuel cell for reaction. The hydraulic retention time is 5 days and the temperature is 40°C. The resulting liquid enriched with the endogenous redox mediator of the sludge (i.e., the residual liquid after treatment) enters the anaerobic digester. The output voltage of the microbial fuel cell powers the anaerobic digester.

[0032] Step 3: The liquid treated by the microbial fuel cell is added to the anaerobic fermenter for fermentation. The water bath temperature is 38℃, the rotation speed is 90rpm, the dissolved oxygen is 0.08mg / L, and the fermentation time is 30 days.

[0033] Example 2: Step 1: After the 500ml sludge taken from the sewage treatment plant is allowed to settle naturally, the supernatant is removed. 0.94g of potassium ferrate is added to the remaining sludge for pretreatment for 1.7h to obtain pretreated sludge.

[0034] Step 2: The pretreated sludge is subjected to solid-liquid separation. The solid is added to the anaerobic digester, and the liquid is added to the microbial fuel cell for reaction. The hydraulic retention time is 4.5 days and the temperature is 38°C. The resulting liquid enriched with the endogenous redox mediator of the sludge (i.e., the residual liquid after treatment) enters the anaerobic digester. The output voltage of the microbial fuel cell powers the anaerobic digester.

[0035] Step 3: The liquid treated by the microbial fuel cell is added to the anaerobic fermenter for fermentation. The water bath temperature is 37.5℃, the rotation speed is 87 rpm, the dissolved oxygen is 0.07 mg / L, and the fermentation time is 27 days.

[0036] Example 3: Step 1: After the 500ml sludge taken from the sewage treatment plant is allowed to settle naturally, the supernatant is removed. 2.82g of potassium ferrate is added to the remaining sludge for pretreatment for 1.5h to obtain pretreated sludge.

[0037] Step 2: The pretreated sludge is subjected to solid-liquid separation. The solid is added to the anaerobic digester, and the liquid is added to the microbial fuel cell for reaction. The hydraulic retention time is 4 days and the temperature is 37°C. The resulting liquid enriched with the endogenous redox mediator of the sludge (i.e., the residual liquid after treatment) enters the anaerobic digester. The output voltage of the microbial fuel cell powers the anaerobic digester.

[0038] Step 3: The liquid treated by the microbial fuel cell is added to the anaerobic fermenter for fermentation. The water bath temperature is 37℃, the rotation speed is 85rpm, the dissolved oxygen is 0.06mg / L, and the fermentation time is 25 days.

[0039] Example 4: Step 1: After the 500ml sludge taken from the sewage treatment plant is allowed to settle naturally, the supernatant is removed. 3.76g of potassium ferrate is added to the remaining sludge for pretreatment for 1.3h to obtain pretreated sludge.

[0040] Step 2: The pretreated sludge is subjected to solid-liquid separation. The solid is added to the anaerobic digester, and the liquid is added to the microbial fuel cell for reaction. The hydraulic retention time is 3.5 days and the temperature is 36°C. The resulting liquid enriched with the endogenous redox mediator of the sludge (i.e., the residual liquid after treatment) enters the anaerobic digester. The output voltage of the microbial fuel cell powers the anaerobic digester.

[0041] Step 3: The liquid treated by the microbial fuel cell is added to the anaerobic fermenter for fermentation. The water bath temperature is 36.5℃, the rotation speed is 83rpm, the dissolved oxygen is 0.05mg / L, and the fermentation time is 23 days.

[0042] Example 5: Step 1: After the 500ml sludge taken from the sewage treatment plant is allowed to settle naturally, the supernatant is removed. 4.7g of potassium ferrate is added to the remaining sludge for pretreatment for 1 hour to obtain pretreated sludge.

[0043] Step 2: The pretreated sludge is subjected to solid-liquid separation. The solid is added to the anaerobic digester, and the liquid is added to the microbial fuel cell for reaction. The hydraulic retention time is 3 days and the temperature is 35°C. The resulting liquid enriched with the endogenous redox mediator of the sludge (i.e., the residual liquid after treatment) enters the anaerobic digester. The output voltage of the microbial fuel cell powers the anaerobic digester.

[0044] Step 3: The liquid treated by the microbial fuel cell is added to the anaerobic fermenter for fermentation. The water bath temperature is 36℃, the rotation speed is 80rpm, the dissolved oxygen is 0.04mg / L, and the fermentation time is 20 days.

[0045] Comparative Example 1: The pretreatment step, solid-liquid separation step and microbial fuel cell test device were removed, and the rest were the same as in Example 1. The specific steps are as follows: Step 1: 500ml of sludge taken from the sewage treatment plant was allowed to settle naturally and the supernatant was removed without adding any reagents to obtain pretreated sludge.

[0046] Step 2: Transfer the pretreated sludge to an anaerobic fermenter for fermentation reaction, with a water bath temperature of 38℃, a rotation speed of 90 rpm, a dissolved oxygen of 0.08 mg / L, and a fermentation time of 30 days.

[0047] Comparative Example 2: The solid-liquid separation step and the microbial fuel cell test device were removed, and the rest was the same as in Example 1. The specific steps are as follows: Step 1: After the 500ml sludge taken from the sewage treatment plant was allowed to settle naturally, the supernatant was removed. 1.88g of potassium ferrate was added to the remaining sludge for pretreatment for 2h to obtain pretreated sludge.

[0048] Step 2: Transfer the pretreated sludge to an anaerobic fermenter for fermentation reaction, with a water bath temperature of 38℃, a rotation speed of 90 rpm, a dissolved oxygen of 0.08 mg / L, and a fermentation time of 30 days.

[0049] Testing and experimentation:

[0050] Methane determination by gas chromatography (SP-7802): Gas chromatography (SP-7802) was used for determination. For each test, 100 μL of the analyte gas was drawn using a VICI airtight micro-syringe. Chromatographic conditions: TCD detector, SE-30 column, high-purity N2 carrier gas flow rate 30 mL / min, column temperature 70℃, injection port temperature 120℃, detector temperature 120℃, bridge current 80 mA, split ratio 16:1, injection volume 1 μL.

[0051] Methane yield test: Maximum specific methane production rate (U max CH4) represents the maximum methane production per unit mass of substrate per unit time, providing a strong basis for comparing the anaerobic methanogenesis activity of different substrates. The calculation method is shown in the following formula. Using Comparative Example 1 as a control group, the methane yield of Comparative Example 1 was calculated to be 100%. This was used as a reference to obtain the methane yield improvement efficiency of Examples 1-5 and Comparative Example 2. The results are shown in the table below;

[0052]

[0053] In the formula:

[0054] UmaxCH4 — Maximum specific rate of methanogenesis, mL CH4 / (g TS·d);

[0055] K—Slope of the straight segment of the cumulative curve;

[0056] X — Sludge concentration, g TSS / L;

[0057] V—Sludge volume, L;

[0058] Methane yield improvement efficiency / % Example 1 25 Example 2 23 Example 3 21 Example 4 19 Example 5 16 Comparative Example 2 8

[0059] Conclusion: Pretreatment with potassium ferrate in the residual sludge yields pretreated sludge. The pretreated sludge undergoes solid-liquid separation; the solids are added to an anaerobic digester, and the liquid is added to a microbial fuel cell for reaction. In this process, the sludge undergoes ferrate pretreatment, resulting in the hydrolysis and solubilization of some biological solids and the release of a large amount of organic matter (including redox substances) into the liquid phase. The supernatant from the liquid phase, after treatment in the microbial fuel cell, achieves the following:

[0060] (1) Ferrate pretreatment can realize the hydrolysis and solubilization of solid organic matter in sludge, and enhance the anaerobic fermentation methanogenic efficiency of sludge (the methanogenic efficiency of sludge after ferrate pretreatment in Comparative Example 2 is higher than that in Comparative Example 1).

[0061] (2) Microbial fuel cells can enrich the endogenous redox mediators in the supernatant of sludge pretreatment, which can enhance the extracellular electron transfer of microorganisms and improve the methanogenesis efficiency (see Examples 1-5).

[0062] (3) The electrical output of the microbial fuel cell can provide DC voltage to the anaerobic fermenter, forming an electrically assisted anaerobic fermentation system, which further facilitates the anaerobic fermentation process for producing methane (see Examples 1-5).

[0063] In summary, by using the system provided by this invention for sludge treatment, the methane yield can be increased by 16%-25%, while the Fe content in the fermentation system is also reduced. 3+ It can be reduced to Fe 2+ Fe 2+ It reacts with phosphates released during sludge fermentation to form lapis lazuli, which is beneficial for the recovery of phosphorus resources from sludge.

[0064] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process method article or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process method article or apparatus.

[0065] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for excess sludge reduction and resource recovery based on potassium ferrate, characterized in that: The method comprises the following steps: Step one: removing supernatant after natural sedimentation of sludge taken from a sewage plant, adding potassium ferrate to the remaining sludge for pretreatment, and obtaining pretreated sludge; The mass ratio of the remaining sludge to potassium ferrate is 1:0.03-0.15; Step two: performing solid-liquid separation on the pretreated sludge, adding the solid to an anaerobic fermentation tank, adding the liquid to a microbial fuel cell for reaction, and obtaining liquid rich in endogenous redox mediators in sludge; and the output voltage of the microbial fuel cell is used to power the anaerobic fermentation tank; When preparing the liquid rich in endogenous redox mediators in sludge, the hydraulic retention time is 3-5d, and the temperature is 35-40℃; Step three: continuing to add the liquid rich in endogenous redox mediators in sludge to the anaerobic fermentation tank for fermentation reaction, and obtaining a product; the product obtained through the fermentation reaction is methane gas and blue vitriol resources.

2. A process for sludge minimization and resource recovery based on potassium ferrate as claimed in claim 1, wherein: In step one, the pretreatment time is 1-2h.

3. A method for residual sludge minimization and resource recovery based on potassium ferrate as claimed in claim 1, wherein: In step three, the anaerobic fermentation tank is set to have a dissolved oxygen of 0.04-0.08mg / L.

4. The method for excess sludge reduction and resource recovery based on potassium ferrate according to claim 1, characterized in that: In step three, during the fermentation reaction, the water bath temperature is 36-38℃.

5. A method for residual sludge minimization and resource recovery based on potassium ferrate as claimed in claim 1, wherein: In step three, during the fermentation reaction, the rotation speed is 80-90rpm.

6. A method for residual sludge minimization and resource recovery based on potassium ferrate as claimed in claim 1, wherein: In step three, during the fermentation reaction, the fermentation time is 20-30d.

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