A method for recovering elemental sulfur from seawater

Abstract

The present application relates to a method for recovering elemental sulfur from seawater. The method comprises the following steps: S1. mixing seaweed and a substrate, carrying out microbial enrichment in an anaerobic environment to obtain supernatant; adding the supernatant and the substrate into a bioelectrochemical reactor, then applying an external voltage, inoculating microorganisms into the anode and the cathode of the bioelectrochemical reactor respectively, and completing the start-up of the bioelectrochemical reactor; S2. connecting the started bioelectrochemical reactor with a sulfide oxidation reactor and adding a substrate, and running; the sulfide oxidation reactor can convert sulfide into elemental sulfur. The method can realize the recovery of a large amount of elemental sulfur in seawater, and the recovery rate can reach more than 70%. At the same time, the reactor of the method can be operated stably for a long time, thereby realizing the long-term stable recovery of elemental sulfur. In addition, the method requires a short time for recovering sulfur, the raw materials are easy to obtain, and the cost is low, so it is easy to realize industrialization and popularization.

Description

Technical Field

[0001] This invention relates to the field of seawater resource recovery technology, and more specifically, to a method for recovering elemental sulfur from seawater. Background Technology

[0002] Sulfur is an important chemical product and basic industrial raw material, widely used in chemical, light industry, pesticide, rubber, dye, and paper industries. Sulfur is mainly consumed in the form of sulfuric acid, an indispensable component in many industrial processes, such as the production of lithium batteries, phosphate fertilizers, and light electric motors. Sulfuric acid is used to extract metals from ores and to manufacture polymers.

[0003] Given the serious environmental pollution caused by sulfur mining, and in order to reduce the harm caused by acid rain, metal and building corrosion, and ozone layer depletion resulting from sulfur dioxide emissions during fossil fuel use, most of the global sulfur supply currently comes from fossil fuel desulfurization.

[0004] Comprehensive utilization of seawater mainly includes three aspects: seawater desalination, direct use of seawater, and utilization of seawater chemical elements. The total sulfur content in seawater is 88.5 kt / km². 3 Sulfate mainly exists in the form of sulfates. High concentrations of sulfates in seawater can easily cause pipeline corrosion when used directly, and it is also a major factor causing scaling in seawater desalination reverse osmosis. The sulfate problem remains a prominent obstacle to the comprehensive utilization of seawater.

[0005] If we can utilize the reduction of sulfates in seawater to generate elemental sulfur in a directional manner, thus achieving sulfur recovery, we can reduce the environmental risks of sulfates in the comprehensive utilization of seawater and alleviate the sulfur shortage problem, which is of great significance for further improving the efficiency of comprehensive seawater utilization.

[0006] Biological methods offer advantages such as mild conditions, low energy consumption, and no risk of secondary pollution. However, during operation, biological methods convert sulfates into sulfides (S...). 2- Sulfides are toxic to microorganisms, making it difficult to continuously and massively convert sulfates, thus hindering the long-term and large-scale recovery of elemental sulfur from seawater.

[0007] The invention patent, titled "A Bioelectrochemical Method for Removing Sulfate from Seawater," provides a method for removing sulfate from seawater. It uses marine mud and seawater containing 1–2 g / L sodium acetate, with a pH of 6–9 and a conductivity of 22–44 mS / cm as a substrate to enrich and activate the electrodes of an electrochemical reactor with microorganisms, achieving highly efficient sulfate removal from seawater (removal rate ≥95%). This method overcomes the problems of poor efficiency and high energy consumption in traditional seawater sulfate removal technologies. However, it does not propose recovering elemental sulfur from seawater; furthermore, the method requires the addition of sodium acetate to the substrate, which is costly and has poor substitutability, making it difficult to promote this technology in practical applications, and thus uneconomical for recovering elemental sulfur.

[0008] In summary, it is necessary to address the current limitations in obtaining elemental sulfur and the difficulty in practically applying technologies for recovering elemental sulfur from seawater using bioelectrochemical methods. Summary of the Invention

[0009] The primary objective of this invention is to overcome the existing problems of limited methods for obtaining elemental sulfur and the difficulty in practical application of bioelectrochemical methods for recovering elemental sulfur from seawater, and to provide a method for recovering elemental sulfur from seawater.

[0010] The above-mentioned objective of this invention is achieved through the following technical solution:

[0011] A method for recovering elemental sulfur from seawater includes the following steps:

[0012] S1. Mix marine mud and substrate, enrich microorganisms under anaerobic conditions to obtain supernatant; add the supernatant and substrate to the bioelectrochemical reactor, and then apply an external voltage to inoculate microorganisms at the anode and cathode of the bioelectrochemical reactor respectively, thus completing the start-up of the bioelectrochemical reactor;

[0013] S2. Connect the started bioelectrochemical reactor to the sulfide oxidation reactor and add the substrate, then run the reactor; the sulfide oxidation reactor can convert sulfides into elemental sulfur;

[0014] The substrate described in steps S1 and S2 is seawater containing 2-4 g / L of fermentable organic matter;

[0015] The dominant species of microorganisms inoculated at the genus level in step S1 include Trichococcus and Thioclava, with relative abundances of 18-30% and 7-20%, respectively; the dominant species of microorganisms inoculated at the cathode in step S1 include Desulfobulbus and Desulfovibrio, with relative abundances of 25-45% and 2-15%, respectively.

[0016] The method of the present invention is to first convert sulfates in seawater into sulfides through a bioelectrochemical reactor, and then convert the sulfides into elemental sulfur through a sulfide oxidation reactor, thereby achieving a large-scale recovery of elemental sulfur.

[0017] Since the high salinity of seawater can inhibit or reduce the metabolic activities of microorganisms, the key problem to be solved is how to achieve the continuous and stable operation of the bioelectrochemical reactor and continuously, efficiently and inefficiently convert sulfate into sulfides.

[0018] Through extensive research, the inventors of this invention discovered that by first enriching microorganisms from marine mud under anaerobic conditions, and then inoculating these microorganisms onto the anode and cathode of a bioelectrochemical reactor to form dominant species with specific relative abundances, the bioelectrochemical reactor can be stably operated, and sulfate can be continuously and efficiently converted into sulfides, thereby achieving large-scale recovery of elemental sulfur. Specifically, the method of this invention uses *Trichococcus*, an acid-producing fermenting bacterium capable of utilizing fermentable organic matter, and *Thioclava*, a sulfur-oxidizing bacterium capable of growing on the electrode surface, to inoculate the anode of the bioelectrochemical reactor. These bacteria possess electrochemical activity, and *Trichococcus* and *Thioclava* complete the degradation of organic matter, the generation of current, and the oxidation of sulfides at the anode. The sulfate-reducing bacteria *Desulfobulbus* and *Desulfovibrio* on the biocathode are both involved in sulfate reduction. Sulfur metabolism mainly occurs at the cathode. *Desulfobulbus* and *Desulfovibrio* can both perform extracellular electron transfer, completing sulfate reduction and electron transfer at the cathode. In the presence of fermentable organic matter, these dominant microbial species synergistically maintain excellent metabolic activity and viability in seawater, thereby ensuring the stable operation of the bioelectrochemical reactor and the continuous conversion of sulfate into sulfides. Furthermore, the fermentable organic matter added to the substrate in this invention is widely available, low-cost, and readily obtainable, making the method easily scalable for industrial application.

[0019] The step of enriching microorganisms from marine mud under anaerobic conditions before inoculation is also crucial. Without this enrichment step, it is difficult to start up the bioelectrochemical reactor. In addition, the concentration of fermentable organic matter in the substrate during operation also needs to be controlled within a certain range. If the concentration is not appropriate, such as being too low, the bioelectrochemical reactor will be unable to efficiently convert sulfate into sulfides, thus making it difficult to achieve a large-scale recovery of elemental sulfur.

[0020] The method of this invention can achieve a large-scale recovery of elemental sulfur from seawater, with a recovery rate of over 70%. Furthermore, the reactor used in this method can operate stably for extended periods, thus enabling long-term, stable recovery of elemental sulfur. In addition, this method requires a short sulfur recovery time, and the raw materials (fermented organic matter) are readily available and inexpensive, making it easily applicable for industrial-scale application.

[0021] Preferably, the enrichment process in step S1 is as follows: the marine mud and the substrate are mixed at a ratio of 1g:5-15mL, and cultured under anaerobic conditions at 25-35℃, with the substrate being replaced 4-10 times during the culture process. Typically, the substrate is replaced every 5-7 days.

[0022] More preferably, microbial enrichment is considered complete when the sulfate removal rate of the substrate in a single update reaches 70% or more.

[0023] Preferably, the substrate described in steps S1 and S2 has a pH of 6-9, a sulfate content of 2000-2500 mg / L, and an electrical conductivity of 30-50 mS / cm.

[0024] More preferably, the substrate in steps S1 and S2 has a pH of 7 to 8.5, a sulfate content of 2000 to 2500 mg / L, and an electrical conductivity of 35 to 45 mS / cm.

[0025] Preferably, the fermentable organic matter is at least one of glucose or polysaccharide; the polysaccharide is at least one of maltodextrin or starch.

[0026] Preferably, in step S1, the volume ratio of the supernatant to the matrix added to the bioelectrochemical reactor is 1:(0.8-1.2).

[0027] Preferably, the magnitude of the external voltage in step S1 is 0.6 to 1.5V.

[0028] More preferably, the magnitude of the external voltage in step S1 is 0.8 to 1.2V.

[0029] Preferably, step S1 uses a DC power supply to apply an external voltage.

[0030] Preferably, the dominant species of microorganisms at the genus level in the anode inoculation in step S1 include Trichococcus and Thioclava, with relative abundances of 19-22% and 8-10%, respectively.

[0031] Preferably, the dominant species of microorganisms inoculated at the cathode in step S1 include Desulfobulbus and Desulfovibrio at the genus level, with relative abundances of 25-30% and 3-6%, respectively.

[0032] Preferably, in step S1, when the sulfate removal rate in the substrate of a single cycle in the bioelectrochemical reactor reaches more than 90% and the current density is not less than 3.5 A / m 3 A startup is considered successful if the system runs stably for at least three cycles. Each substrate update constitutes one cycle, which typically lasts 5 to 7 days.

[0033] Preferably, the bioelectrochemical reactor described in step S1 has a single-chamber structure.

[0034] Preferably, both the anode and cathode in step S1 are carbon material electrodes.

[0035] Preferably, both the anode and cathode in step S1 are carbon brushes.

[0036] Preferably, the minimum distance between the anode and cathode in step S1 is 1 to 3 cm.

[0037] Preferably, the ratio of the geometric volume of the anode to the volume of the bioelectrochemical reactor in step S1 is 0.5:(3.5~10).

[0038] Preferably, the ratio of the geometric volume of the cathode to the volume of the bioelectrochemical reactor in step S1 is 0.5:(3.5-10).

[0039] Preferably, the specific process of step S2 is as follows: constructing a sulfide oxidation reactor, which includes an anode chamber and a cathode chamber (i.e., the sulfide oxidation reactor is a dual-chamber electrochemical reactor); connecting the started bioelectrochemical reactor to the anode chamber of the sulfide oxidation reactor and adding a substrate, and running it; the catholyte in the cathode chamber is a potassium ferricyanide solution, a phosphate buffer solution, or a sodium hydroxide solution.

[0040] Elemental sulfur is mainly generated on the anode surface of the anode chamber in the sulfide oxidation reactor, therefore elemental sulfur is mainly collected on the anode surface of the anode chamber in the sulfide oxidation reactor.

[0041] More preferably, the anode chamber and cathode chamber of the sulfide oxidation reactor are separated by an ion exchange membrane.

[0042] More preferably, the anode and cathode of the sulfide oxidation reactor are both made of carbon materials.

[0043] More preferably, the anode of the sulfide oxidation reactor is a carbon plate and the cathode is a carbon fiber brush.

[0044] More preferably, the external load of the sulfide oxidation reactor is 25 to 100 ohms.

[0045] Typically, when the catholyte in the cathode chamber of a sulfide oxidation reactor is a phosphate buffer solution or a sodium hydroxide solution, the catholyte needs to be aerated to provide oxygen.

[0046] More preferably, the concentration of the potassium ferricyanide solution is 50-100 mM; the concentration of the phosphate buffer solution is 25-100 mM; and the concentration of the sodium hydroxide solution is 0.1-0.3 M.

[0047] More preferably, the ratio of the volume of the anode chamber of the sulfide oxidation reactor to the volume of the bioelectrochemical reactor is (0.1-0.5):1.

[0048] More preferably, the volume ratio of the substrate contained in the anode chamber of the sulfide oxidation reactor to the substrate contained in the bioelectrochemical reactor is (0.1-0.5):1.

[0049] More preferably, the ratio of the volume of the anode chamber to the volume of the cathode chamber in the sulfide oxidation reactor is 1:(1-2).

[0050] More preferably, the volume ratio of the substrate contained in the anode chamber to the catholyte contained in the cathode chamber of the sulfide oxidation reactor is 1:(1-2).

[0051] More preferably, during operation, the substrate circulates between the anode chamber of the sulfide oxidation reactor and the bioelectrochemical reactor at a flow rate of 0.5–3 mL / min, and the ratio of the hydraulic residence time of the bioelectrochemical reactor to the hydraulic residence time of the anode chamber of the sulfide oxidation reactor is (3–5):1.

[0052] By adjusting the ratio of circulation flow rate to hydraulic residence time within a certain range, the recovery rate of elemental sulfur can be increased.

[0053] Preferably, during the operation described in step S2, an external voltage is applied to the bioelectrochemical reactor, wherein the external voltage is 0.6 to 1.5V, more preferably 0.8 to 1.2V.

[0054] An apparatus for realizing the above-described method for recovering elemental sulfur from seawater includes a connected bioelectrochemical reactor and a sulfide oxidation reactor, the bioelectrochemical reactor including an anode and a cathode, and the sulfide oxidation reactor converting sulfides into elemental sulfur.

[0055] Compared with the prior art, the beneficial effects of the present invention are:

[0056] The method of this invention can achieve a large-scale recovery of elemental sulfur from seawater, with a recovery rate of over 70%. Furthermore, the reactor used in this method can operate stably for extended periods, thus enabling long-term, stable recovery of elemental sulfur. In addition, this method requires a short sulfur recovery time, and the raw materials (fermented organic matter) are readily available and inexpensive, making it easily applicable for industrial-scale application. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the bioelectrochemical reactor used in the method of Example 1.

[0058] Figure 2 This is a schematic diagram of the structure of the dual-chamber electrochemical reactor used in the method of Example 1.

[0059] Figure 3 This is a schematic diagram of the structure of the bioelectrochemical reactor and the dual-chamber electrochemical reactor connected together, which are used in the method of Example 1.

[0060] Figure 4 This is a schematic diagram of the sulfate removal rate and sulfide concentration versus time for the method in Example 1.

[0061] Figure 5 This is a schematic diagram showing the results of the bioelectrochemical reactor used in Example 1 at the phylum level of the anode and cathode microbial community structure after successful startup.

[0062] Figure 6 This is a schematic diagram showing the results of the genus-level analysis of the anode and cathode microbial community structure of the bioelectrochemical reactor used in Example 1 after successful startup.

[0063] Figure 7 This is a schematic diagram of the sulfate removal rate versus time in the bioelectrochemical reactors of Examples 2 and 3.

[0064] Figure 8 This is a schematic diagram showing the sulfate removal rate versus time during long-term operation (240 days) of a bioelectrochemical reactor.

[0065] Figure 9 This is a schematic diagram of the sulfate removal rate versus time for Comparative Example 1.

[0066] Figure 10 This is a schematic diagram of the current density versus time generated by the bioelectrochemical reactors of Example 1 and Comparative Example 2.

[0067] Figure 11 This is a schematic diagram of the sulfate removal rate versus time in the bioelectrochemical reactor of Comparative Example 3. Detailed Implementation

[0068] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0069] Example 1

[0070] This embodiment describes a method for recovering elemental sulfur from seawater, comprising the following steps:

[0071] 1) Construction of a bioelectrochemical reactor and a two-chamber electrochemical reactor

[0072] Constructing bioelectrochemical reactors: such as Figure 1 As shown, the bioelectrochemical reactor includes a chamber, an anode, a cathode, and a DC power supply. The chamber is primarily made of plexiglass, with an inner cylinder diameter of 3 cm and a length of 8 cm, resulting in an effective volume of 56 mL. Both the cathode and anode are carbon brushes with a diameter × length of 3 cm × 3 cm. These brushes are pretreated by heating at 450°C for 30 min in a muffle furnace before use. The ratio of the sum of the geometric volumes of the cathode and anode to the effective volume of the bioelectrochemical reactor is 1:5. The cathode and anode are placed parallel to each other in the middle of the reactor, with a distance of approximately 2 cm between them. The anode, DC power supply, and cathode are connected by titanium wires.

[0073] Constructing a two-chamber electrochemical reactor (i.e., a sulfide oxidation reactor): such as Figure 2 As shown, the dual-chamber electrochemical reactor includes an anode chamber, a cathode chamber, an ion exchange membrane (PEM, Nafion 117, DuPont, USA) separating the anode and cathode chambers, an anode located in the anode chamber, a cathode located in the cathode chamber, and an external resistor. The main material of both the anode and cathode chambers is plexiglass. The anode chamber has a volume of 15 mL, and the cathode chamber has a volume of 28 mL. The anode consists of three 30×20×1 mm carbon plates, which are wound together with titanium wire to facilitate conductivity. The effective area of ​​the anode is 15 cm². 2 (Before use, the carbon plate should be sanded with sandpaper, then cleaned sequentially with 1M HCl solution, 1M NaOH solution, and pure water); the cathode is a 3×3cm carbon brush (the carbon brush is heat-treated in a muffle furnace at 450℃ for 30 minutes before use). The cathode chamber is filled with a 50mM potassium ferricyanide solution. The external resistor is 50 ohms.

[0074] 2) Start the bioelectrochemical reactor

[0075] The marine mud (from a certain sea area) was transported to the laboratory with ice packs and stored in a -18℃ freezer. 10g of marine mud was mixed into 100mL of substrate (seawater containing 2g / L glucose, 2200mg / L sulfate, pH 8.2, and conductivity 40mS / cm), placed on a shaker, and cultured under anaerobic conditions at 30℃. The substrate was replaced every 7 days, and after each substrate replacement, nitrogen was ventilated for 15 minutes to maintain the anaerobic environment. After 5 cycles of culture, the sulfate removal rate in the substrate reached 70% in a single cycle, completing the enrichment of microorganisms and obtaining the supernatant. Take 25 mL of the supernatant and add it to the bioelectrochemical reactor. Simultaneously, add and fill the bioelectrochemical reactor with substrate. Cultivate the reactor under conditions of 0.8 V external voltage and 30 °C. Replace the substrate every 5 days. Inoculate the anode and cathode of the bioelectrochemical reactor with microorganisms. After 7 cycles of operation, the sulfate removal rate of the bioelectrochemical reactor reached over 90%, and the current density reached 3.5 A / m³. 3 The bioelectrochemical reactor was considered to have started up successfully. The substrate used in this step was seawater containing 2 g / L glucose, 2200 mg / L sulfate, with a pH of 8.2 and a conductivity of 40 mS / cm.

[0076] 3) Run

[0077] After successful startup of the bioelectrochemical reactor, maintain the applied external voltage (0.8V) and continue operating the reactor. Then, connect the bioelectrochemical reactor to the anode chamber of the dual-chamber electrochemical reactor, filling both chambers with substrate and circulating the substrate between them using a peristaltic pump. Figure 3 As shown in the figure, the circulation flow rate is 1 mL / min, and the ratio of the hydraulic residence time in the anode chamber of the dual-chamber electrochemical reactor to that in the bioelectrochemical reactor is 1:4. Simultaneous operation of the bioelectrochemical reactor and the dual-chamber electrochemical reactor achieves the removal of sulfate and the recovery of elemental sulfur from seawater. Elemental sulfur is mainly collected from the anode surface of the dual-chamber electrochemical reactor, with a small amount collected from the effluent. During operation, when the current density output by the bioelectrochemical reactor is less than 3.5 A / m³, [further details on this point are needed]. 3 The substrate is replaced periodically to maintain stable operation. The substrate used in this step is seawater containing 3 g / L glucose, 2200 mg / L sulfate, with a pH of 8.2 and a conductivity of 40 mS / cm.

[0078] Using the method of this embodiment, after operation, the schematic diagram of the sulfate removal rate and sulfide concentration in seawater versus time is shown below. Figure 4 As shown. From Figure 4 It can be seen that the sulfate removal rate reaches 91% (the sulfate concentration decreased from 2200±220 mg / L to 197 mg / L within 60 hours); after the cycle, the sulfide concentration in seawater is ≤10 mg / L, indicating that the method of this embodiment effectively converts sulfate into sulfide, and further converts sulfide into elemental sulfur. Furthermore, by collecting elemental sulfur and calculating, it can be seen that the method of this embodiment achieves a 71% recovery rate of elemental sulfur within 60 hours.

[0079] The recovery rate (η, %) of elemental sulfur is calculated using the following formula:

[0080]

[0081] In the formula: The mass of elemental sulfur in the effluent (mg·S); The mass (mg·S) of elemental sulfur deposited on the anode surface of a dual-chamber electrochemical reactor; It is the total mass (mg·S) of sulfur in the influent (matrix).

[0082] Furthermore, high-throughput sequencing technology was used to analyze the microbial communities attached to the cathode and anode of the bioelectrochemical reactor. Specifically, following the method described in this embodiment, after successful startup of the bioelectrochemical reactor, sterile scissors were used to cut and sample the cathode and anode, with each sample having an area of ​​approximately 1 cm². 2After rinsing the sample surface with sterile physiological saline, DNA extraction was performed using electrodes. A DNA extraction kit (12888-50, MOBIO) was used to extract sample DNA, and the extracted DNA samples were detected by 1% agarose gel electrophoresis. The amplification region was V3-V4, and the primers were 338F (5'-ACTCCTACGGGAGGCAGCAG-3') and 806R (5'-GGACTACHVGGGTWTCTAAT-3'). After total DNA extraction, bacterial polymerase chain reaction (PCR) was initiated, with initial denaturation at 98℃ for 30 s, for a total of 30 cycles (each cycle including 15 s at 98℃, 15 s at 58℃, and 15 s at 72℃). A final extension step was performed at 72℃ for 1 min. The amplicon was purified using an AxyPrep DNA gel extraction kit and quantified using Quanti Fluor. The quality-tested library was analyzed using Illumina amplification products. Sequencing and bioinformatics analysis were performed using the HiSeq sequencing platform (BioMarker, Beijing, China) (Huang J, Zeng C, Luo H, Bai J, Liu G, and Zhang R. Enhanced sulfur recovery and sulfate reduction using single-chamber bioelectrochemical system. Science of The Total Environment. 2022, 823, 153789.).

[0083] Figure 5 This presents the phylum-level analysis results of the microbial community structure at the anode and cathode of a bioelectrochemical reactor. Figure 5 At the phylum level, in the anodic community, Firmicutes (relative abundance 26.43%), Proteobacteria (relative abundance 34.87%), and Desulfobacterota (relative abundance 7.13%) had the highest relative abundance. In the cathode community, Desulfobacterota (relative abundance 37.40%), Chloroflexi (relative abundance 10.85%), and Proteobacteria (relative abundance 19.58%) had the highest relative abundance. Desulfobacterota was more abundant in the cathode than in the anode. Firmicutes are mainly associated with organic matter degradation, while Chloroflexi can degrade organic matter, such as hydrolyzing complex organic matter and polysaccharides into monosaccharides, acetic acid, lactose, etc.

[0084] Figure 6This represents the results of algebraic-level analysis of the microbial community structure at the anode and cathode of a bioelectrochemical reactor. For example... Figure 6 As shown, *Trichococcus* (relative abundance 19.10%) and *Thioclava* (relative abundance 8.27%) were dominant in the anode community. In the cathode community, sulfate-reducing bacteria *Desulfobulbus* (relative abundance 28.75%) and *Desulfovibrio* (relative abundance 3.84%) were dominant; the abundance of sulfate-reducing bacteria in the cathode community was significantly higher than that in the bioanolyte.

[0085] The *Trichococcus* genus, enriched on the anode, is an acid-producing fermenting bacterium capable of utilizing glucose-based organic matter. *Thioclava*, a sulfur-oxidizing bacterium that grows on the electrode surface, possesses electrochemical activity. *Trichococcus* and *Thioclava* complete the degradation of organic matter, current generation, and sulfide oxidation at the anode. The sulfate-reducing bacteria *Desulfobulbus* and *Desulfovibrio* on the biocathode are both involved in sulfate reduction. Sulfur metabolism mainly occurs at the biocathode. *Desulfobulbus* and *Desulfovibrio* are electrochemically active bacteria capable of extracellular electron transfer, completing sulfate reduction and electron transfer at the cathode. These dominant bacterial species work synergistically, maintaining excellent metabolic activity and activity even in seawater, thus ensuring the stable operation of the bioelectrochemical reactor and continuously converting sulfate into sulfides.

[0086] Example 2: Investigation of glucose concentration in the matrix

[0087] In this embodiment, the bioelectrochemical reactor is first constructed according to step 1) of Example 1, and then the bioelectrochemical reactor is started according to step 2) of Example 1.

[0088] After starting the bioelectrochemical reactor, maintain a constant external voltage (0.8V) applied to it, fill the reactor with the substrate, and operate the reactor independently (without connecting it to the anode chamber of the dual-chamber electrochemical reactor). During operation, when the output current density of the bioelectrochemical reactor is less than 3.5A / m... 3 The substrate is updated periodically to maintain stable operation.

[0089] In this embodiment, the bioelectrochemical reactor was operated using either seawater containing 2 g / L glucose, 2200 mg / L sulfate, pH 8.2, and a conductivity of 40 mS / cm, or seawater containing 3 g / L glucose, 2200 mg / L sulfate, pH 8.2, and a conductivity of 40 mS / cm, to investigate the effect of glucose concentration in the substrate on sulfate removal rate.

[0090] Example 3: Investigation of the magnitude of external voltage

[0091] In this embodiment, the bioelectrochemical reactor is first constructed according to step 1) of Example 1, and then the bioelectrochemical reactor is started according to step 2) of Example 1.

[0092] After starting the bioelectrochemical reactor, continue applying an external voltage to the reactor, filling it with substrate, and operate the reactor independently (without connecting it to the anode chamber of the dual-chamber electrochemical reactor). During operation, when the output current density of the bioelectrochemical reactor is less than 3.5 A / m... 3 The substrate is updated periodically to maintain stable operation.

[0093] In this embodiment, the external voltage applied to the bioelectrochemical reactor during operation was 0.8V, 1.0V, or 1.2V to investigate the effect of the external voltage on the sulfate removal rate.

[0094] The graphs of sulfate removal rate versus time (120 hours) for Examples 2 and 3 are shown in the figure. Figure 7 As shown. From Figure 7 It can be seen that when the glucose concentration of the substrate is 2 g / L or 3 g / L, or when the applied external voltage is 0.8 V, 1 V, or 1.2 V, the sulfate removal rate can reach over 96%, comparable to Example 1. Test data from Examples 2 and 3 show that under the established conditions, the sulfate removal rate is high, indicating a high conversion rate of sulfate to sulfides. This allows for the generation of sufficient sulfides, which are then oxidized at the anode of the dual-chamber electrochemical reactor, thereby achieving a large-scale recovery of elemental sulfur.

[0095] Furthermore, the bioelectrochemical reactor was operated for 240 days under the conditions of a glucose concentration of 2 g / L in the substrate and an applied external voltage of 0.8 V, with other conditions the same as in Example 2. The curve of sulfate removal rate versus operating days is shown in the figure below. Figure 8 As shown. From Figure 8It can be seen that the sulfate removal rate in the effluent remains stable at about 96%, which indicates that the bioelectrochemical reactor can operate stably for a long time and has a high sulfate removal rate during long-term operation, that is, a high conversion rate of sulfate to sulfide. Therefore, it can be combined with a dual-chamber electrochemical reactor to achieve a large amount of long-term recovery of elemental sulfur.

[0096] Comparative Example 1

[0097] In this comparative example, a bioelectrochemical reactor was constructed following step 1) of Example 1. Then, instead of inoculating the anode and cathode of the bioelectrochemical reactor with microorganisms (i.e., step 2) of Example 1 was omitted), an external voltage of 0.8V was directly applied to the bioelectrochemical reactor, filling it with a substrate, and the reactor was operated independently. The substrate used was seawater containing 2 g / L glucose, 2200 mg / L sulfate, with a pH of 8.2 and a conductivity of 40 mS / cm.

[0098] Using the method of this comparative example, the curves of sulfate concentration and removal rate in seawater versus time are as follows: Figure 9 As shown, from Figure 9 It is known that sulfate removal is slow, with a removal rate of only 13.8% within 120 hours. This indicates that when microorganisms are not enriched on the anode and cathode of the bioelectrochemical reactor, the sulfate removal effect is poor, and the amount of sulfides generated is correspondingly small, thus making it impossible to recover a large amount of elemental sulfur.

[0099] Comparative Example 2

[0100] In this comparative example, a bioelectrochemical reactor was constructed following step 1) of Example 1, and then the reactor was started up. The start-up process for the bioelectrochemical reactor in this comparative example was as follows: instead of enriching microorganisms, 10g of marine mud was directly added to the bioelectrochemical reactor, along with the substrate. Cultivation was carried out under conditions of an external voltage of 0.8V and a temperature of 30℃, with the substrate being replaced every 5 days. The substrate used was seawater containing 2g / L glucose, 2200mg / L sulfate, with a pH of 8.2 and a conductivity of 40mS / cm.

[0101] The current density versus time curve generated by the bioelectrochemical reactor is shown in the figure. Figure 10 As shown, from Figure 10 It can be seen that the current density generated in Comparative Example 2 remains at a very low level (≤1.2A / m). 3 The bioelectrochemical reactor could not be started successfully.

[0102] Comparative Example 3

[0103] In this comparative example, the bioelectrochemical reactor was first constructed according to step 1) of Example 1, and then started according to step 2) of Example 1.

[0104] After starting the bioelectrochemical reactor, maintain a constant external voltage (0.8V) applied to it, fill the reactor with the substrate, and operate the reactor independently (without connecting it to the anode chamber of the dual-chamber electrochemical reactor). During operation, when the output current of the bioelectrochemical reactor is less than 3.5A / m... 3 The substrate is replaced periodically to maintain stable operation. The substrate used during operation is seawater containing 1 g / L glucose, 2200 mg / L sulfate, pH 8.2, and conductivity 40 mS / cm.

[0105] The graph of sulfate removal rate versus time in this comparative example is shown in the figure below. Figure 11 As shown. From Figure 11 It can be seen that the sulfate concentration decreased from 2200±220 mg / L to 543±55 mg / L within 120 hours, with a removal rate of 76%. It can be observed that under the conditions of this comparative example, the sulfate removal rate is significantly reduced, which is unfavorable for sulfide formation and thus prevents the large-scale recovery of elemental sulfur.

[0106] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for recovering elemental sulfur from seawater, characterized in that, Includes the following steps: S1. Mix marine mud and substrate, enrich microorganisms under anaerobic conditions to obtain supernatant; add the supernatant and substrate to the bioelectrochemical reactor, and then apply an external voltage to inoculate microorganisms at the anode and cathode of the bioelectrochemical reactor respectively, thus completing the start-up of the bioelectrochemical reactor; S2. Connect the started bioelectrochemical reactor to the sulfide oxidation reactor and add the substrate, then run the reactor; the sulfide oxidation reactor can convert sulfides into elemental sulfur; The substrate described in steps S1 and S2 is seawater containing 2-4 g / L of fermentable organic matter; The dominant species types of microorganisms at the genus level in the anode inoculation described in step S1 include: Trichococcus and Thioclava Their relative abundances were 18-30% and 7-20%, respectively; the dominant species types of the cathode-inoculated microorganisms in step S1 at the genus level included Desulfobulbus and Desulfovibrio Their relative abundances were 25–45% and 2–15%, respectively; The specific process of enrichment in step S1 is as follows: mix the marine mud and the substrate at a ratio of 1g:(5~15)mL, and culture them under anaerobic conditions and at 25~35℃. During the culture process, the substrate is replaced 4~10 times. In step S1, when the sulfate removal rate in the substrate of a single cycle in the bioelectrochemical reactor reaches more than 90% and the current density is not less than 3.5 A / m 3 If the system operates stably for at least 3 cycles, the startup is considered successful; each cycle is 5-7 days, and the substrate is replaced once per cycle. In step S2, the volume ratio of the substrate contained in the anode chamber of the sulfide oxidation reactor to that contained in the bioelectrochemical reactor is (0.1~0.5):1; during the operation in step S2, the substrate circulates between the anode chamber of the sulfide oxidation reactor and the bioelectrochemical reactor, the circulation flow rate is 0.5~3 mL / min, and the hydraulic residence time of the anode chamber of the bioelectrochemical reactor and the sulfide oxidation reactor is (3~5):

1.

2. The method according to claim 1, characterized in that, The substrates described in steps S1 and S2 have a pH of 6-9, a sulfate content of 2000-2500 mg / L, and an electrical conductivity of 30-50 mS / cm.

3. The method according to claim 1, characterized in that, The external voltage mentioned in step S1 is 0.6~1.5V.

4. The method according to claim 1, characterized in that, The dominant species types of microorganisms at the genus level in the anode inoculation described in step S1 include: Trichococcus and Thioclava Their relative abundances were 19–22% and 8–10%, respectively.

5. The method according to claim 1, characterized in that, The dominant species types of microorganisms at the genus level inoculated at the cathode in step S1 include: Desulfobulbus and Desulfovibrio Their relative abundances were 25-30% and 3-6%, respectively.

6. The method according to claim 1, characterized in that, The fermentable organic matter is at least one of glucose or polysaccharide.

7. The method according to claim 1, characterized in that, The specific process of step S2 is as follows: construct a sulfide oxidation reactor, which includes an anode chamber and a cathode chamber; connect the started bioelectrochemical reactor to the anode chamber of the sulfide oxidation reactor and add a matrix, and run it; the catholyte in the cathode chamber is a potassium ferricyanide solution, a phosphate buffer solution, or a sodium hydroxide solution.

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