Method for improving anaerobic digestion efficiency of pyrohydrolysis sludge and reducing generation of H2S

Abstract

The invention relates to a method for improving anaerobic digestion efficiency of pyrohydrolysis sludge and reducing generation of H2S, which specifically comprises the following steps: obtaining anaerobic digestion sludge and pyrohydrolysis sludge of a sewage treatment plant, taking the anaerobic digestion sludge as inoculation sludge, and fully mixing the inoculation sludge and the pyrohydrolysis sludge to obtain a sludge mixture; adding the sludge mixture into an anaerobic sequencing batch reactor, and fully and uniformly stirring; the method comprises the following steps: adding iron-rich coal into a reactor, emptying the reactor through nitrogen, sealing, connecting a gas collecting device, operating the reactor for 30 days in a thermostatic water bath at 39-42 DEG C at the rotating speed of 110-130 rpm, and dropping the H2S content in the system to 0 ppm after the operation is stopped. According to the method, the anaerobic digestion gas production efficiency of the sludge can be remarkably improved, the activity of methanogenic archaea is fully excited, meanwhile, the removal effect of organic pollutants in the sludge can be greatly enhanced, the content of hydrogen sulfide in the biogas is efficiently reduced, and the quality of the biogas is effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of sludge treatment technology, specifically relating to a method for improving the anaerobic digestion efficiency of hot hydrolysis sludge and reducing H2S generation. Background Technology

[0002] The rapid improvement of urban sewage treatment capacity and the continuous expansion of sewage treatment plant scale in my country have led to a sustained increase in sludge production. If sludge is not properly treated, it will cause a series of secondary pollution events, such as the spread of pathogens, migration of heavy metals, and release of malodorous gases, posing a significant threat to the ecological environment and human health. At the same time, sludge contains abundant organic resources with significant potential for energy conversion, but traditional treatment technologies have obvious limitations: incineration, while achieving volume reduction, has high investment and operating costs and easily produces toxic gases such as dioxins; composting has stringent requirements for raw material quality and poor product stability; anaerobic digestion technology, which can simultaneously achieve sludge stabilization and methane resource recovery, is considered a core development direction. Traditional anaerobic digestion processes are constrained by the hydrolysis stage, resulting in long hydraulic retention times, low utilization rates of organic pollutants, and low gas production efficiency. Hot hydrolysis pretreatment technology significantly improves pollutant utilization and methane production rates by destroying sludge flocs and cell structures under high temperature and pressure. The combined process of "hot hydrolysis + anaerobic digestion" has been used globally for many years and has demonstrated significant resource recovery advantages. However, in actual anaerobic digestion of sludge using hot hydrolysis, problems still exist, such as rapid conversion of dissolved organic matter and delayed hydrolysis of solid organic matter leading to severely uneven digestion rates between the solid and liquid phases, decreased effective reactor load, ineffective volume occupation, and limited system operating efficiency. Furthermore, the widely used traditional continuous-flow anaerobic digesters have low operating efficiency; the hydraulic retention time in traditional digesters is equal to the solids retention time, resulting in long operating cycles and limited treatment efficiency. Therefore, an anaerobic sequencing batch reactor (SBR) process is considered for anaerobic digestion of sludge. Simultaneously, an iron-coated carrier is added to the reactor to improve system settling properties and enhance microbial activity, thereby promoting the removal of methanogens and pollutants.

[0003] Some recent studies, such as the effects of temperature and organic load on methanogenesis characteristics during the start-up phase of anaerobic digestion of high-temperature, high-solids sludge and the study of multiple electron transport mechanisms by which iron-rich biochar promotes methanogenesis from excess sludge, have not combined the thermal hydrolysis of sludge with improving system settling properties, increasing microbial abundance and activity. Furthermore, the preparation of iron-rich biochar has not been scaled up, and post-reaction recovery is not well-developed. H2S removal has not been further investigated. Therefore, there is an urgent need to develop efficient, stable, and low-cost enhancement methods to promote the hydrolysis of macromolecular organic matter, improve interspecies electron transport and microbial metabolic activity, in order to achieve efficient reactor operation, significantly increase biogas production, and maximize energy recovery.

[0004] In summary, this invention shortens the operating cycle and improves gas production efficiency by batch-producing iron-rich coal and adding it to an anaerobic sequencing batch reactor to treat hydrothermal sludge. Simultaneously, it enhances the system's settling properties to increase microbial abundance, and the iron-rich coal charring promotes interspecies electron transfer, thereby increasing microbial activity, gas production, and the removal of organic pollutants, while reducing the H2S content in methane. Summary of the Invention

[0005] The purpose of this invention is to provide a method and reaction system for improving the efficiency of anaerobic digestion of hot-hydrolyzed sludge and reducing H2S production. This involves adding iron-rich coal to an anaerobic sequencing batch reactor (SBR) to improve both bioavailability and H2S production. It also enhances the interspecies electron transfer efficiency of the methanogenic microbial community, thereby increasing the utilization rate of organic substrates and promoting methane generation. This effectively improves the overall conversion efficiency of pretreated hot-hydrolyzed sludge during anaerobic digestion.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A method for improving the efficiency of anaerobic digestion of sludge by hot water hydrolysis and reducing H2S production, the method comprising the following: Anaerobic digestion sludge and hot hydrolysis sludge from a wastewater treatment plant are obtained. Anaerobic digestion sludge is used as inoculum sludge. The inoculum sludge and hot hydrolysis sludge are thoroughly mixed to obtain a sludge mixture. The sludge mixture is added to an anaerobic sequencing batch reactor and thoroughly mixed. The iron-rich coal was then added to the reactor, and nitrogen was used to purge the reactor. After sealing, a gas collection device was connected, and the reactor was run in a constant temperature water bath at 39-42℃ at a speed of 110-130 rpm for 30 days. After the operation ended, the H2S content in the system dropped back to 0 ppm.

[0007] In this invention, the reactor rotation speed is preferably 120 rpm. If the rotation speed is too low, the iron-rich coal cannot rotate effectively; if the rotation speed is too high, the sludge in the system cannot withstand it, which is not conducive to the anaerobic digestion reaction.

[0008] Preferably, the particle size of the iron-rich coal charcoal is 0.2-0.5 mm, and the Fe3O4 in the iron-rich coal charcoal is embedded in the coal charcoal structure and does not fall off. The iron-rich coal charcoal is produced by chemical co-precipitation method, in which the coal charcoal is impregnated in a mixed solution of trivalent and divalent ferric salts.

[0009] Furthermore, the specific process for preparing iron-rich coal charcoal using the chemical co-precipitation method is as follows: Under a nitrogen protective atmosphere, 400g of ferric chloride hexahydrate (FeCl3·6H2O) and 170g of ferrous chloride tetrahydrate (FeCl2·4H2O) are dissolved in 5L of deionized water to prepare Fe... 2+A mixed iron salt solution with a concentration of 0.16 mol / L was prepared. 400 g of coal-based charcoal was placed in the mixed iron salt solution and placed in a constant temperature water bath. The temperature was set at 70°C. A mechanical stirrer was used at a speed of 200 rpm for 30 minutes to ensure that the activated carbon and the mixed iron salt solution were fully mixed. During mechanical stirring, 5 mol / L NaOH solution was slowly added dropwise, and the pH of the solution was monitored and adjusted to 10 in real time. Then, stirring was continued at a constant temperature of 70℃ for 24 hours, and the mixture was allowed to stand overnight to promote complete precipitation. After the reaction, the mixture was filtered through a 35-60 mesh standard sieve to remove suspended nano-iron tetroxide (Fe3O4) particles, and the filtered black precipitate was collected. The precipitate was repeatedly washed with deionized water until the pH of the filtrate reached 7 to remove residual acidic or alkaline substances. The sample was then transferred to a vacuum oven and dried at 70℃, and then transferred to a muffle furnace and calcined at 600℃ for 6 hours to obtain the iron-rich coal charcoal.

[0010] Preferably, the iron content of the iron-rich coal used for char production is 9.4%, and the specific surface area is 900 m². 2 / g; reactor volume greater than 10L, preferably 20~50L.

[0011] Furthermore, the sludge mixture is added to the anaerobic sequencing batch reactor and thoroughly stirred until the initial SCOD content in the tank is 5000~20000 mg / L.

[0012] Furthermore, the dosage of iron-rich coal for char production is 5-20 g / L, meaning that 5-20 g of iron-rich coal for char production needs to be added per liter of sludge.

[0013] Furthermore, before the rich iron coal charcoal is added to the reactor, it is soaked in water to fill the micropores inside the rich iron coal charcoal with water, and then the soaked rich iron coal charcoal is added to the reactor.

[0014] Furthermore, the hot hydrolyzed sludge and the inoculated sludge were mixed at a VS ratio of 1:2.

[0015] Furthermore, during the continuous experiment, a sludge discharge port was set at 75-85% of the reactor height. During the sludge discharge process, the iron-rich coal char produced along with the sludge was collected in a container. A screen was set on the upper part of the container to achieve solid-liquid separation. The screen size was smaller than the particle size of the iron-rich coal char and allowed the sludge to pass through. The sludge was brushed into the container by a brushing method. The iron-rich coal char retained on the screen was added back into the reactor along with the sludge through the feed port, thereby maintaining the relative stability of the concentration of iron-rich coal char in the system.

[0016] Furthermore, during the continuous experiment, the working cycle of iron-rich coal char production is 20 days. After the working cycle is exceeded, the iron-rich coal char production in the reactor needs to be re-prepared with iron. The specific iron-preparation process is as follows: the iron-rich coal char production in the reactor is discharged from the sludge discharge port and after being intercepted and recovered by the screen, it is placed in a mixed iron salt solution as a coal char production carrier and re-prepared by chemical co-precipitation.

[0017] This invention also protects a reaction system for improving the efficiency of anaerobic digestion of hot hydrolyzed sludge and reducing H2S production. The reaction system includes a reactor body, a gas collection device, and a sludge discharge and iron-rich coal charcoal recovery device. An inlet is located at the top of the reactor body for adding a mixture of hot hydrolyzed sludge and digested sludge into the reactor. An outlet is located at the bottom of the reactor for sludge discharge and reactor cleaning after the experiment. The reactor is equipped with a mechanical stirrer and a timed stirring control device to ensure thorough mixing and uniform distribution of materials in the reaction system. A water bath heating jacket is installed outside the reactor body to maintain the constant reaction temperature required for the anaerobic digestion process. A gas-producing space is reserved at the top and connected to a gas collection device to continuously collect biogas produced during anaerobic digestion. A sludge discharge port is set at 75-85% of the reactor height. The sludge discharge port is connected to a sludge discharge and iron-rich coal charcoal recovery device through a pipe. The sludge discharge and iron-rich coal charcoal recovery device includes a container. A screen is set on the upper part of the container to achieve solid-liquid separation. The screen size is smaller than the particle size of iron-rich coal charcoal and allows sludge to pass through. During the sludge discharge process, the iron-rich coal charcoal discharged with the sludge is collected in the container. The sludge is brushed into the container by a brushing method. The iron-rich coal charcoal retained on the screen is added back into the reactor with the sludge through the feed inlet, thereby maintaining the relative stability of the concentration of iron-rich coal charcoal in the system.

[0018] Furthermore, multiple sampling ports are set along the height of the reactor to meet the sampling and analysis needs at different operating stages.

[0019] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention significantly improves the removal rate of soluble organic matter such as SCOD, volatile fatty acids, soluble polysaccharides, and proteins in an anaerobic sequencing batch reactor (SBR) system by adding an appropriate amount of iron-rich coal for char production. This is significantly better than traditional anaerobic digestion technology and provides a more efficient energy recovery pathway for sludge resource utilization. The cumulative methane production in the control group was only 409.87 mL / gVS, while the 10 g / L iron-rich coal char production group of this invention reached 481.83 mL / gVS, an increase of 17.6% compared to the control group. Compared with the ordinary activated carbon addition group (which commonly increases by 5%-12% in the literature), the increase is even greater. The maximum methane production rate occurred on day 3 (day 4 in the control group), with a rate increase of 28.3%, which is far better than the conventional zero-valent iron addition process (which usually only shortens the time by 1-2 days and increases the rate by 10%-20%). This indicates that the conductivity and high specific surface area of ​​iron-rich coal char production synergistically promote direct interspecies electron transfer and accelerate the degradation of long-chain fatty acids by thermal hydrolysis, which is significantly better than traditional anaerobic digestion and ordinary carrier addition processes. Regarding the efficiency of organic matter removal, this invention enables more thorough degradation of soluble organic matter. On day 26 of the experiment, with an initial SCOD of 13260 mg / L, the residual SCOD in the conventional blank group was 4880 mg / L, while the residual SCOD in the 10 g / L group of this invention decreased to approximately 2600-3700 mg / L (a reduction of approximately 29.1%); soluble polysaccharides and proteins were reduced by 19.7% and 32.6%, respectively. Compared to conventional activated carbon adsorption processes (which mainly rely on physical adsorption with limited improvement in biodegradation, typically increasing SCOD removal rate by only 10%-20%), this invention achieves significantly higher efficiency.

[0020] (2) This invention improves the settling properties of an anaerobic sequencing batch reactor (SBR) system by adding iron-rich coal to enhance microbial abundance and increase microbial activity through enhanced direct interspecies electron transfer, thereby promoting methane production. In this invention, the TS and VS contents measured at 90% of the reactor were inversely proportional to the amount of iron-rich coal added. The 10 g / L addition group, which showed the best gas production effect, had TS and VS of 5.0 g / g and 2.6 g / g, respectively, significantly lower than the 5.4 g / g and 2.9 g / g of the group without activated carbon. This indicates that more activated sludge was retained inside the reactor, increasing the microbial content and promoting gas production.

[0021] (3) Adding iron-rich coal charcoal can significantly reduce the generation of H2S gas in the system. The polyvalent iron components contained in iron-rich coal charcoal can react with H2S or dissolved sulfides to form stable ferrous sulfide, ferric sulfide and other insoluble substances, thereby significantly reducing the concentration of free H2S in the liquid and gas phases. At the same time, its porous structure and oxygen-containing functional groups on the surface can also adsorb H2S, further weakening its effective presence in the system. The H2S content in traditional anaerobic digestion is 200-500 ppm. The H2S content in the group with added iron-rich coal charcoal is significantly lower than that in the blank group, and it is negatively correlated with the amount added: when the amount added reaches 15 g / L, the H2S content has dropped to 0 ppm on the 5th day of the experiment. This invention not only discovers and solves the problem of H2S generation during anaerobic digestion, but also finds through continuous experiments that the action cycle of iron-rich coal charcoal is 20 days. After the action cycle, the iron-rich coal charcoal in the reactor needs to be used as a carrier to re-prepare iron by chemical precipitation. Soaking the iron-rich coal in water beforehand fills the micropores with moisture, reducing the adsorption of organic matter and preventing the adsorption of large amounts of organic matter into the reactor, which would lead to reduced gas production and weakened H2S removal.

[0022] (4) By adding iron-rich coal prepared by chemical precipitation to the anaerobic sequencing batch reactor system, the methane yield can be significantly increased and H2S production can be basically eliminated, thus replacing the traditional continuous addition of iron salts for desulfurization and achieving a significant improvement in economic benefits. Taking Beijing Drainage Group as an example, its hot hydrolysis + anaerobic digestion process produces about 80 million cubic meters of biogas annually, mainly used for power generation, boiler steam, and blower drive. After introducing this technology, the additional energy output brought about by the increased methane content in the biogas, based on the current power generation grid connection price and efficiency, can increase annual revenue by hundreds of thousands to millions of yuan. At the same time, the traditional process requires continuous addition of iron salt reagents and maintenance of desulfurization equipment, with annual operating costs often reaching hundreds of thousands to millions of yuan, and is prone to pipeline corrosion and additional maintenance costs. This method, through the precipitation and adsorption of iron-rich coal, almost eliminates H2S production, directly saving the expenses of reagent purchase, equipment depreciation, and corrosion repair, reducing overall operating risks and maintenance burdens, with lower initial addition costs, shorter investment recovery period, and outstanding economic advantages.

[0023] (5) The main purpose of anaerobic digestion is to remove pollutants and produce gas. The method of this invention is suitable for continuous large-scale production. Iron-rich coal can be effectively recycled and utilized, and H2S can be removed during the reaction process. It also significantly promotes the production of methane and increases the activity and abundance of microorganisms, making it more economical. It fully considers engineering applications and provides the possibility for large-scale production.

[0024] (6) The sludge discharge and iron-rich coal charcoal recovery device in the system of the present invention solves the problem of activated carbon loss with sludge discharge during the continuous experiment of the traditional anaerobic sequential batch process.

[0025] (7) This method is easy to operate, has high processing efficiency, stable system operation, and controllable processing cost. It can effectively improve the efficiency of sludge resource utilization, reduce environmental pollution, is easy to apply in engineering, and is suitable for efficient sludge treatment. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of one embodiment of the reaction system used in this invention. Detailed Implementation

[0027] The present invention will be further explained below with reference to the embodiments and accompanying drawings, but this is not intended to limit the scope of protection of this application.

[0028] This invention discloses a method for improving the efficiency of anaerobic digestion of hot hydrolyzed sludge and reducing H2S production. Anaerobic digested sludge and hot hydrolyzed sludge are added to a reactor at a 2:1 VS ratio. Iron-rich coal is added at a dosage of 5-20 g / L, and the initial pH is adjusted to 7. After aeration and nitrogen purging of the reactor for 15 minutes, the reactor is sealed, and anaerobic digestion is carried out using a constant-temperature water bath. In the initial stage, organic pollutant indicators and methane production are monitored daily; in the later stage, monitoring is reduced to once every 2-3 days as a cycle.

[0029] The initial inoculated sludge of this invention had a total sludge content (TS) of 6.86 g / g and a total sludge volume (VS) of 3.14 g / g. After high-temperature and high-pressure hydrolysis, the organic matter content of the sludge was as follows: TS: 10.10 g / g, VS: 5.93 g / g, SCOD: 13260 mg / L, polysaccharide: 1368 mg / L, and protein: 3825 mg / L. On the first day, the H2S content in all reactors was 0 ppm.

[0030] The charcoal produced by this invention using iron-rich coal has a particle size of 0.2-0.5 mm, preferably 0.3 mm, and a specific surface area of ​​900 m². 2 / g, with an iron content of 9.4%, the optimal dosage is 10~15g / L, and it is prepared by chemical co-precipitation.

[0031] The reaction system used in this invention is as follows: Figure 1 As shown, it includes a feed inlet, sampling ports at different heights, an exhaust port, a mixing device, a water bath insulation jacket, a biogas collection bag, and a sludge removal and iron-rich coal charcoal recovery device (including a screen and a plastic container).

[0032] The reaction system consists of a reactor body, a gas collection device (gas collection bag), and a sludge discharge and iron-rich coal charcoal recovery device. An inlet is located at the top of the reactor body for adding a mixture of hydrolyzed sludge and digested sludge into the reactor. Multiple sampling ports are located along the height of the reactor to meet the sampling and analysis needs at different operational stages. An vent is located at the bottom of the reactor for sludge discharge and reactor cleaning after the experiment; in this embodiment, the vent has an inner diameter of 50 mm. The reactor is equipped with a mechanical stirrer and a timed stirring control device to ensure thorough mixing and uniform distribution of materials in the reaction system. A water bath heating jacket (forming a water bath insulation layer) is installed outside the reactor body to maintain the constant reaction temperature required for the anaerobic digestion process. A gas production space is reserved at the top of the reactor and connected to a gas collection bag to continuously collect the biogas produced during anaerobic digestion. A sludge discharge port (i.e., a DN32 outlet) is set at approximately 80% of the reactor height. During the sludge discharge process, the iron-rich coal char produced along with the sludge is collected in a plastic container. A screen is installed on the upper part of the plastic container to achieve solid-liquid separation. The screen size is smaller than the particle size of the iron-rich coal char and allows the sludge to pass through. The sludge is brushed into the plastic container by a brushing method. The iron-rich coal char retained on the screen is added back into the reactor along with the sludge through the feed port, thereby maintaining a relatively stable concentration of iron-rich coal char in the system.

[0033] Example 1 The method for improving the efficiency of anaerobic digestion of hot water hydrolysis sludge and reducing H2S production in this embodiment is as follows: (1) Take sludge from the primary sedimentation tank and the secondary sedimentation tank of a sewage treatment plant in Beijing and mix them together; (2) The mixed activated sludge is subjected to high-temperature and high-pressure hot water hydrolysis; (3) The sludge from high-temperature and high-pressure hydrolyzed sludge is cooled and then sieved; (4) Anaerobic digestion sludge from the water intake plant was used as inoculation sludge; (5) After thoroughly mixing the hydrolyzed sludge with the inoculated sludge, a sludge mixture is obtained and fed into an anaerobic sequencing batch reactor. (6) The effective volume of the anaerobic sequencing batch reactor is 25L. It has water bath, stirring and anaerobic reaction conditions, and can produce iron-rich coal charcoal by chemical coprecipitation in batches, so that it can be applied in engineering.

[0034] (7) The prepared iron-rich coal charcoal is added to the anaerobic sequencing batch reactor obtained after step (5) to provide a suitable environment for microorganisms to carry out anaerobic digestion for 30 days.

[0035] The primary sludge and residual activated sludge in step (1) were taken from a wastewater treatment plant in Beijing. After centrifugation and dewatering, the moisture content was about 85%. The sludge was then stored in a refrigerator at 4°C for later use.

[0036] In step (2), the hot water hydrolysis temperature is 160℃, and the hot water hydrolysis pressure is set to 0.62MPa. The pressure gauge reading is constantly observed during the material reaction to ensure that the pressure is normal. After hot water hydrolysis, the VS / TS ratios of the primary sludge and the residual sludge decreased to varying degrees (64.56%→64.35% and 58.33%→57.97%). VS degradation is due to the destruction of cell walls, the continuous hydrolysis of large organic molecules in the sludge into small organic molecules, and the hydrolysis of some organic matter at high temperature to generate carbon dioxide, which enters the gas phase.

[0037] In step (3), the hot water hydrolysis sludge is first cooled and then sieved. A 10mm sieve is used for sieving. The sludge is then divided into 10-liter buckets and stored in a 4°C refrigerator for later use.

[0038] The inoculated sludge in step (4) is digested sludge from a wastewater treatment plant in Beijing, with an organic loading ratio (VS) of approximately 3 g / g. In step (5), the hot hydrolyzed sludge and the inoculated sludge are mixed at a VS ratio of 1:2.

[0039] In step (6), a chemical coprecipitation method is used to prepare the Fe solution. Under a nitrogen protective atmosphere, 400g of ferric chloride hexahydrate (FeCl3·6H2O) and 170g of ferrous chloride tetrahydrate (FeCl2·4H2O) are dissolved in 5L of deionized water to prepare the Fe solution. 2+ A 0.16 mol / L mixed iron salt solution was prepared. 400 g of coal-based charcoal was placed in this solution and placed in a constant-temperature water bath at 70°C. The mixture was stirred for 30 minutes using a mechanical stirrer (approximately 200 rpm) to ensure thorough mixing of the activated carbon and the iron salt solution. During the stirring process, a 5 mol / L NaOH solution was slowly added dropwise, with the pH monitored and adjusted to approximately 10. The mixture was then stirred continuously at 70°C for 24 hours and allowed to stand overnight to promote complete precipitation. After the reaction, the mixture was filtered through a 35-60 mesh standard sieve to remove suspended nano-ferric oxide (Fe3O4) particles, and the black precipitate was collected. The precipitate was repeatedly washed with deionized water until the pH of the filtrate reached 7 to remove residual acidic or alkaline substances. The sample was then transferred to a vacuum oven and dried at 70°C, followed by calcination at 600°C for 6 hours in a muffle furnace to obtain the final iron-rich coal-based charcoal material. The particle size of charcoal made from iron-rich coal is 0.3 mm, and the specific surface area is 900 m². 2 / g, with an iron content of 9.4%, and the optimal dosage is 10g / L.

[0040] The reactor maintains an anaerobic environment by filling it with nitrogen gas. It is a 25L cylindrical glass anaerobic reactor (actual usable volume, i.e., the total volume of sludge added), with a height-to-diameter ratio of H / D = 4:1. A timed stirring device is installed, with sampling ports at 90% (sludge discharge), 80%, 60%, 40%, 20%, and 0%. Two-stage internal circulation stirring is performed at timed intervals, using two peristaltic pumps. A water bath jacket and an electric water bath are used to maintain the experimental reaction temperature at the set value. An electric stirrer ensures thorough mixing of materials in an anaerobic batch reactor operation mode. The experimental reaction was started at 40℃ and operated at 120 rpm for 30 days.

[0041] Example 2 Step 1: The sludge taken from the anaerobic digester of a sewage treatment plant in Beijing was filtered through a sieve with a 10 mm aperture to remove impurities. Finally, the treated digested sludge was stored at 4°C for subsequent experiments.

[0042] Step 2: Take sludge from a wastewater treatment plant in Beijing for hot hydrolysis. The raw materials used are primary sedimentation sludge and residual activated sludge from the secondary sedimentation tank of the wastewater treatment plant. After centrifugation and dewatering, the moisture content is about 85%. The hot hydrolysis temperature is 160℃ and the hot hydrolysis pressure is set at 0.62MPa. The sludge after hot hydrolysis has a TS of about 9g / g, a VS of about 5g / g, a SCOD of about 12000mg / L, soluble polysaccharides and proteins of about 1500mg / L and 3500mg / L, respectively, and a volatile fatty acid content of about 80mg / L. The hot hydrolyzed sludge is sieved through a 10mm sieve and stored at 4℃ for subsequent experiments.

[0043] Step 3: An anaerobic sequencing batch reactor (SBR) with a working volume of 25L was used. 20L of digested sludge (inoculation sludge) and 5L of hot hydrolyzed sludge were added at a VS ratio of 2:1. The mixture was thoroughly stirred with a magnetic stirrer until the components were homogeneous. The initial SCOD content in the reactor was measured to be 13260 mg / L, soluble polysaccharide 1368 mg / L, soluble protein 3825 mg / L, and volatile fatty acid 80 mg / L. After mixing, 5g / L of iron-rich coal was added for carbonization. 99.99% nitrogen gas was introduced into the reactor for 10 minutes, followed by sealing and connection of a gas collection bag. The reactor was operated at a constant temperature of 40℃ and a rotation speed of 120 rpm for 30 days. Constant operating conditions were maintained to minimize the impact of external factors on the experiment. Daily samples were taken to analyze pollutant changes, and gas composition was measured using a Biogas 5000 gas composition analyzer to analyze methane production.

[0044] The experimental results showed that the cumulative methane production over 30 days was 432.11 mL / g VS, soluble COD decreased to 3620 mg / L, soluble polysaccharides and proteins decreased to 595.2 mg / L and 1359.8 mg / L respectively, and volatile fatty acid content decreased to 0.66 mg / L. Regarding the dynamic changes in H2S content, the content was 0 ppm on day 1 of the experiment. As the experiment progressed, the content gradually increased, reaching a peak of 210 ppm on day 4. Thereafter, the H2S content continuously decreased, dropping to 5 ppm on day 25, and returning to 0 ppm on day 30.

[0045] Example 3 The steps in this embodiment are the same as in embodiment 2, except that the dosage of iron-rich coal for char production in this embodiment is 10 g / L.

[0046] Step 1: The sludge taken from the anaerobic digester of a sewage treatment plant in Beijing was filtered through a sieve with a 10 mm aperture to remove impurities. Finally, the treated sludge was stored at 4℃ for subsequent experiments.

[0047] Step 2: Take sludge from a wastewater treatment plant in Beijing for hot hydrolysis. The raw materials used are primary sedimentation sludge and residual activated sludge from the secondary sedimentation tank of the wastewater treatment plant. After centrifugation and dewatering, the moisture content is about 85%. The hot hydrolysis temperature is 160℃ and the hot hydrolysis pressure is set at 0.62MPa. The sludge after hot hydrolysis has a TS of about 9g / g, a VS of about 5g / g, a SCOD of about 12000mg / L, soluble polysaccharides and proteins of about 1500mg / L and 3500mg / L, respectively, and a volatile fatty acid content of about 80mg / L. The hot hydrolyzed sludge is sieved through a 10mm sieve and stored at 4℃ for subsequent experiments.

[0048] Step 3: An anaerobic sequencing batch reactor (SBR) with a working volume of 25L was used. 20L of digested sludge and 5L of hot hydrolyzed sludge were added at a VS ratio of 2:1. The mixture was thoroughly stirred with a magnetic stirrer until the components were homogeneous. The initial SCOD content in the reactor was measured to be 13260 mg / L, soluble polysaccharides 1368 mg / L, soluble protein 3825 mg / L, and volatile fatty acids 80 mg / L. After mixing, 10 g / L of iron-rich coal was added for carbonization. 99.99% nitrogen gas was introduced into the reactor for 10 minutes, followed by sealing and connection of a gas collection bag. The reactor was operated at a constant temperature of 40℃ and a rotation speed of 120 rpm for 30 days. Constant operating conditions were maintained to minimize the impact of external factors on the experiment. Daily samples were taken to analyze pollutant changes, and gas composition was measured using a Biogas 5000 gas composition analyzer to analyze methane production.

[0049] The experimental results showed that the cumulative methane production over 30 days was 481.83 mL / g VS, soluble COD decreased to 3320 mg / L, and soluble polysaccharides and proteins decreased to 568.0 and 1091.8 mg / L, respectively. Regarding the dynamic changes in H2S content, the content was 0 ppm on day 1 of the experiment. As the experiment progressed, the content gradually increased, reaching a peak of 233 ppm on day 4. Thereafter, the H2S content continuously decreased, dropping to 3 ppm on day 25, and returning to 0 ppm on day 30.

[0050] Example 4 The steps in this embodiment are the same as in embodiment 2, except that the dosage of iron-rich coal for char production in this embodiment is 15g / L.

[0051] Step 1: The sludge taken from the anaerobic digester of a sewage treatment plant in Beijing was filtered through a sieve with a 10 mm aperture to remove impurities. Finally, the treated sludge was stored at 4℃ for subsequent experiments.

[0052] Step 2: Take sludge from a wastewater treatment plant in Beijing for hot hydrolysis. The raw materials used are primary sedimentation sludge and residual activated sludge from the secondary sedimentation tank of the wastewater treatment plant. After centrifugation and dewatering, the moisture content is about 85%. The hot hydrolysis temperature is 160℃ and the hot hydrolysis pressure is set at 0.62MPa. The sludge after hot hydrolysis has a TS of about 9g / g, a VS of about 5g / g, a SCOD of about 12000mg / L, soluble polysaccharides and proteins of about 1500mg / L and 3500mg / L, respectively, and a volatile fatty acid content of about 80mg / L. The hot hydrolyzed sludge is sieved through a 10mm sieve and stored at 4℃ for subsequent experiments.

[0053] Step 3: An anaerobic sequencing batch reactor (SBR) with a working volume of 25L was used. 20L of digested sludge and 5L of hot hydrolyzed sludge were added at a VS ratio of 2:1. The mixture was thoroughly stirred with a magnetic stirrer until the components were homogeneous. The initial SCOD content in the reactor was measured to be 13260 mg / L, soluble polysaccharide 1368 mg / L, soluble protein 3825 mg / L, and volatile fatty acid 80 mg / L. After mixing, 15 g / L of iron-rich coal was added for carbonization. 99.99% nitrogen gas was introduced into the reactor for 10 minutes, followed by sealing and connection of a gas collection bag. The reactor was operated at a constant temperature of 37℃ and a rotation speed of 120 rpm for 30 days. Constant operating conditions were maintained to minimize the impact of external factors on the experiment. Daily samples were taken to analyze pollutant changes, and gas composition was measured using a Biogas 5000 gas composition analyzer to analyze methane production.

[0054] The experimental results showed that the cumulative methane production over 30 days was 481.83 mL / g VS, soluble COD decreased to 3040 mg / L, and soluble polysaccharides and proteins decreased to 568.0 and 1091.8 mg / L, respectively. Regarding the dynamic changes in H2S content, the content was 0 ppm on day 1 of the experiment. As the experiment progressed, the content gradually increased, reaching a peak of 88 ppm on day 4. Thereafter, the H2S content continuously decreased, dropping to 0 ppm on day 25, and finally returning to 0 ppm on day 30.

[0055] Comparative Example 1 The steps in this comparative example are the same as in Example 2, except that no iron-rich coal is added for char production in this comparative example.

[0056] Step 1: The sludge taken from the anaerobic digester of a sewage treatment plant in Beijing was filtered through a sieve with a 10 mm aperture to remove impurities. Finally, the treated sludge was stored at 4℃ for subsequent experiments.

[0057] Step 2: Take sludge from a wastewater treatment plant in Beijing for hot hydrolysis. The raw materials used are primary sedimentation sludge and residual activated sludge from the secondary sedimentation tank of the wastewater treatment plant. After centrifugation and dewatering, the moisture content is about 85%. The hot hydrolysis temperature is 160℃ and the hot hydrolysis pressure is set at 0.62MPa. The sludge after hot hydrolysis has a TS of about 9g / g, a VS of about 5g / g, a SCOD of about 12000mg / L, soluble polysaccharides and proteins of about 1500mg / L and 3500mg / L, respectively, and a volatile fatty acid content of about 80mg / L. The hot hydrolyzed sludge is sieved through a 10mm sieve and stored at 4℃ for subsequent experiments.

[0058] Step 3: An anaerobic sequencing batch reactor (SBR) with a working volume of 25L was used. 10L of digested sludge and 5L of hot hydrolyzed sludge were added at a VS ratio of 2:1. The mixture was thoroughly stirred with a magnetic stirrer until the components were homogeneous. The initial SCOD content in the reactor was measured to be 13260 mg / L, soluble polysaccharide 1368 mg / L, soluble protein 3825 mg / L, and volatile fatty acid 80 mg / L. No iron-rich coal was added after mixing. The reactor was then purged with 99.99% nitrogen for 10 minutes, sealed, and connected to a gas collection bag. The reactor was operated at a constant temperature of 40℃ and 120 rpm for 30 days. Constant operating conditions were maintained to minimize the impact of external factors on the experiment. Daily samples were taken to analyze pollutant changes, and gas composition was measured using a Biogas 5000 gas composition analyzer to analyze methane production.

[0059] The experimental results showed that the cumulative methane production over 30 days was 409.87 mL / gVS, soluble COD decreased to 4620 mg / L, and soluble polysaccharides and proteins decreased to 707 and 1621 mg / L, respectively. Regarding the dynamic changes in H2S content, the content was 0 ppm on day 1, gradually increasing as the experiment progressed, reaching a peak of 260 ppm on day 4. Subsequently, the H2S content continuously decreased, dropping to 28 ppm on day 25, and finally falling back to 18 ppm on day 30.

[0060] The experimental results showed that the control group without added iron-rich coal had a 17.6% lower methane yield compared to the group with the highest methane production at a dosage of 10 g / L. The methane production was also lower in other groups with added iron-rich coal, indicating that adding iron-rich coal can enhance direct interspecies electron transfer and increase the activity of methanogens, thereby increasing methane production. In the first two days of the anaerobic digestion experiment, the SCOD content first decreased and then increased, indicating that some SCOD was utilized before the hydrolysis and acidification stage, hence the initial pH value decreased and then increased. The initial SCOD content in the tank was 13260 mg / L. On day 30 of the experiment, the SCOD content in the control group decreased to 4620 mg / L, while the SCOD content in the iron-rich coal-added groups decreased to 3040-3620 mg / L. The SCOD content in the group with the highest gas production at a dosage of 10 g / L decreased by 29.1%, and the contents of soluble polysaccharides and soluble proteins decreased by 19.7% and 32.2%, respectively. Furthermore, the H2S content showed a significant negative correlation with the dosage. It can be seen that when the dosage reached 15 g / L, the H2S content decreased significantly, and by the fifth day of the experiment, the H2S content had decreased to 0. Considering the removal of pollutants, the generation of methane, and the inhibition of H2S, the addition of iron-rich coal for coking has a significant effect on improving the anaerobic digestion efficiency of hydrolyzed sludge and reducing H2S generation, and 10 g / L is a relatively suitable dosage.

[0061] Experimental studies have shown that when preparing iron-rich coal for char production, if zero-valent iron, divalent iron, or trivalent iron is selected as the loading medium, either effective adsorption of H2S cannot be achieved, or the loading on the coal for char production cannot be effectively achieved, resulting in severe iron loss and inability to be reused, leading to poor engineering applicability and economic efficiency. This invention, using a mixed divalent and trivalent iron co-precipitation method to prepare iron-rich coal for char production, offers significant advantages in terms of biocompatibility, sedimentation properties, hydrogen sulfide removal, and economic efficiency for reuse.

[0062] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A method for improving the efficiency of anaerobic digestion of hot water hydrolysis sludge and reducing H2S generation, characterized in that, The method includes the following: Anaerobic digestion sludge and hot hydrolysis sludge from a wastewater treatment plant are obtained. Anaerobic digestion sludge is used as inoculum sludge. The inoculum sludge and hot hydrolysis sludge are thoroughly mixed to obtain a sludge mixture. The sludge mixture is added to an anaerobic sequencing batch reactor and thoroughly mixed. The iron-rich coal was then added to the reactor, and nitrogen was used to purge the reactor. After sealing, a gas collection device was connected, and the reactor was run in a constant temperature water bath at 39-42℃ at a speed of 110-130 rpm for 30 days. After the operation ended, the H2S content in the system dropped back to 0 ppm.

2. The method according to claim 1, characterized in that, The particle size of charcoal made from iron-rich coal is 0.2-0.5 mm. In charcoal made from iron-rich coal, Fe3O4 is embedded in the coal structure and does not fall off.

3. The method according to claim 1, characterized in that, The iron-rich coal is produced by chemical co-precipitation. Under a nitrogen protective atmosphere, 400g of ferric chloride hexahydrate (FeCl3·6H2O) and 170g of ferrous chloride tetrahydrate (FeCl2·4H2O) are dissolved in 5L of deionized water to prepare Fe... 2+ A mixed iron salt solution with a concentration of 0.16 mol / L was prepared. 400 g of coal-based charcoal was placed in the mixed iron salt solution and placed in a constant temperature water bath. The temperature was set at 70°C. A mechanical stirrer was used at a speed of 200 rpm for 30 minutes to ensure that the activated carbon and the mixed iron salt solution were fully mixed. During mechanical stirring, 5 mol / L NaOH solution was slowly added dropwise, and the pH of the solution was monitored and adjusted to 10 in real time. Then, stirring was continued at a constant temperature of 70℃ for 24 hours, and the mixture was allowed to stand overnight to promote complete precipitation. After the reaction, the mixture was filtered through a 35-60 mesh standard sieve to remove suspended nano-iron tetroxide (Fe3O4) particles, and the filtered black precipitate was collected. The precipitate was repeatedly washed with deionized water until the pH of the filtrate reached 7 to remove residual acidic or alkaline substances. The sample was then transferred to a vacuum oven and dried at 70℃, and then transferred to a muffle furnace and calcined at 600℃ for 6 hours to obtain the iron-rich coal charcoal.

4. The method according to claim 3, characterized in that, It has an iron content of 9.4% and a specific surface area of ​​900 m². 2 / g; reactor volume greater than 10L, preferably 20~50L.

5. The method according to claim 1, characterized in that, The sludge mixture is added to the anaerobic sequencing batch reactor and thoroughly stirred. The initial SCOD content in the tank is 5000~20000 mg / L.

6. The method according to claim 1, characterized in that, The dosage of iron-rich coal for char production is 5-20 g / L, meaning that 5-20 g of iron-rich coal needs to be added per liter of sludge.

7. The method according to claim 1, characterized in that, Before the iron-rich coal is added to the reactor, it is soaked in water to fill the micropores inside the iron-rich coal with water, and then the soaked iron-rich coal is added to the reactor.

8. The method according to claim 1, characterized in that, The hot hydrolyzed sludge and the inoculated sludge were mixed at a VS ratio of 1:

2.

9. The method according to claim 1, characterized in that, During the continuous experiment, a sludge discharge port was set at 75-85% of the reactor height. The iron-rich coal char produced with the sludge was collected in a container. A screen was set on the upper part of the container to achieve solid-liquid separation. The screen size was smaller than the particle size of the iron-rich coal char and allowed the sludge to pass through. The sludge was brushed into the container by a brushing method. The iron-rich coal char retained on the screen was added back into the reactor with the sludge through the feed port, thereby maintaining the relative stability of the concentration of iron-rich coal char in the system. During the continuous experiment, the working cycle of iron-rich coal char production is 20 days. After the working cycle is exceeded, the iron-rich coal char production in the reactor needs to be re-prepared by iron attachment. The specific iron attachment preparation process is as follows: the iron-rich coal char production in the reactor is discharged from the sludge discharge port, and after being intercepted and recovered by the screen, it is placed in a mixed iron salt solution as a coal char carrier and re-prepared by chemical co-precipitation.

10. A reaction system for improving the efficiency of anaerobic digestion of hot water hydrolysis sludge and reducing H2S generation, characterized in that, The reaction system includes a reactor body, a gas collection device, and a sludge discharge and iron-rich coal char recovery device. An inlet is located at the top of the reactor body for adding a mixture of hydrolyzed sludge and digested sludge into the reactor. An outlet is located at the bottom of the reactor for sludge discharge and reactor cleaning after the experiment. The reactor is equipped with a mechanical stirrer and a timed stirring control device to ensure thorough mixing and uniform distribution of materials in the reaction system. A water bath heating jacket is installed outside the reactor body to maintain the constant reaction temperature required for the anaerobic digestion process. A gas production space is reserved at the top of the reactor and connected to a gas collection device. A device is set up to continuously collect biogas produced during anaerobic digestion. A sludge discharge port is set at 75-85% of the reactor height. The sludge discharge port is connected to a sludge discharge and iron-rich coal char recovery device through a pipe. The sludge discharge and iron-rich coal char recovery device includes a container. A screen is set on the upper part of the container to achieve solid-liquid separation. The screen size is smaller than the particle size of iron-rich coal char and allows sludge to pass through. During the sludge discharge process, the iron-rich coal char discharged with the sludge is collected in the container. The sludge is brushed into the container by a brushing method. The iron-rich coal char retained on the screen is added back into the reactor with the sludge through the feed port, thereby maintaining the relative stability of the iron-rich coal char concentration in the system.

Images