CN104372030A - Method for coproducing hydrogen gas and methane by sludge-kitchen waste mixed fermentation - Google Patents

Abstract

The invention discloses a method for mixed fermentation of sludge and kitchen waste to co-produce hydrogen and methane, including aeration pretreatment of hydrogen-producing inoculated sludge and anaerobic domestication and cultivation of methane-producing inoculated sludge; sludge and crushed food waste Mixing in an optimized ratio; the effective volume ratio of the hydrogen production reactor and the methanation reactor is 1:5.5; the hydrogen production and methanation reactors are fed in batches, and the methane production reactor is discharged according to the ratio of the volume ratio of the feed to 1 : 1 back to the hydrogen production reactor; the hydrogen production reactor temperature is 55°C, the pH value is 5.0-5.5, and the hydraulic retention time is 0.8-3.3d; the methanogenic reactor temperature is 37°C, the pH value is 7.0-7.5, and the hydraulic retention time 4.5-18d; add K ₂ HPO ₄ to increase the alkalinity and buffer capacity of the reactor. The main purpose of the present invention is to develop a simple and effective two-phase anaerobic fermentation process, to realize an efficient and stable process of hydrogen and methane production on the basis of less chemical dosage, and to simultaneously achieve the treatment of two organic solids, sludge and kitchen waste purpose of waste.

Description

A method for co-producing hydrogen and methane through mixed fermentation of sludge and kitchen waste

technical field

The invention relates to a method for processing kitchen waste and sludge and producing hydrogen and methane in the field of environmental protection. In particular, it relates to a method for continuously and stably producing hydrogen from solid waste to produce methane.

Background technique

In the face of the increasingly depleted fossil fuel resources and the air pollution caused by their combustion, it is particularly important to develop efficient and pollution-free clean energy. Hydrogen is the gas with the highest calorific value per unit mass. Its combustion product is only water and no greenhouse gases are produced. Therefore, hydrogen is the most ideal energy source. At present, the preparation methods of hydrogen are mainly chemical method, electrolysis method, water-gas shift method and steam reforming method, the principle of which is to prepare hydrogen from water or hydrocarbons in a combined state. These hydrogen production methods have the disadvantages of high energy consumption, high equipment requirements and low yield, and some hydrogen production raw materials themselves are directly usable fuels, so the development of low energy consumption production methods and the use of renewable raw materials are the most important. Prospects for the development direction of hydrogen production. In a relatively mild environment, the biological hydrogen production method uses the metabolism of microorganisms to consume organic matter to produce hydrogen and other metabolites, which can greatly reduce the energy consumption of hydrogen production. Compared with other biological hydrogen production methods, anaerobic dark fermentation hydrogen production has the advantages of high hydrogen yield, no need for external light source, and effective treatment of refractory organic matter. It is the most promising biological hydrogen production method.

Sludge is a by-product of the sewage treatment process. With the construction of new sewage treatment plants and the continuous acceleration of the upgrading and transformation of existing sewage treatment plants, the discharge of sludge is increasing year by year. Sludge has a high water content and carries a large number of pathogenic microorganisms and heavy metals. Its treatment and disposal is one of the problems in sewage treatment plants. As an anaerobic fermentation substrate, sludge has a low carbon-to-nitrogen ratio and low content of easily degradable organic matter, so the yields of hydrogen and methane are low. How to improve the efficiency of gas production is still a difficult point in the research of sludge anaerobic fermentation.

In my country, food waste has a large amount of discharge, high moisture content, inconvenient transportation, and is likely to cause rotten odor and other adverse environmental impacts. Therefore, effective treatment of food waste is urgently needed. Separate fermentation of food waste can easily lead to rapid acidification, which seriously affects the gas production rate. In order to maintain the pH stability of the food waste fermentation hydrogen production reactor, a large amount of chemical agents need to be added. Some studies have pointed out that in the two-phase anaerobic fermentation process, returning the effluent from the methane reactor to the hydrogen reactor is a method to maintain the pH stability of the hydrogen reactor. In the two-phase fermentation process with food waste as the substrate, the pH of the hydrogen production reactor can be maintained at 5.3 by using effluent reflux without additional alkalinity (T. Kobayashi, et al. Effect of sludge recirculation on characteristics of hydrogen production in a two-stage hydrogen–methane fermentation process treating food wastes [J]. International Journal of Hydrogen Energy, 2012, 37(7), 5602-5611.). However, in this literature, the reflux ratio must reach 2.9 or add about 20g-NaOH/d to maintain the pH of the hydrogen production reactor, and a higher reflux rate not only increases the operating cost but also reduces the effective volume of the hydrogen production reactor. There are still few studies on further maintaining the pH of the hydrogen production reaction system from food waste and reducing operating costs and reagent consumption.

Batch experiments proved that the mixed fermentation of sludge and food waste can promote the fermentative hydrogen and methane production (X.Liu, et al.Hydrogen and methane production by co-digestion of waste activated sludge and food waste in the two-stage fermentation process: Substrate conversion and energy yield [J]. Bioresource Technology, 2013, 146, 317-323.). At present, the mixed fermentation of sludge and kitchen waste to produce hydrogen and methane is mainly concentrated at medium temperature conditions (35°C or 37°C). However, because the sludge is difficult to degrade and contains a variety of microorganisms, the two-phase reactor needs to operate at a low load under medium temperature conditions (Z.Siddiqui, et al.Energy optimization from co-digested waste using two-phase process to generate hydrogen and methane [J]. International Journal of HydrogenEnergy, 2011, 36 (8), 4792-4799.), and it is easy to breed hydrogen-consuming methane bacteria in hydrogen-producing reactors, and it is necessary to take regular measures to inhibit the process of producing methane (Zhu H, et al .Eliminating methanogenic activity in hydrogen reactor to improve biogas production in a two-stage anaerobic digestion process co-digesting municipalfood waste and sewage sludge[J].Bioresource technology,2011,102(14):7086.709). There are few studies on the use of high-temperature fermentation of sludge and kitchen waste to produce hydrogen, and high-temperature conditions are more conducive to the hydrolysis and acidification of organic matter and can inhibit the process of hydrogen consumption.

Contents of the invention

The main purpose of the present invention is to develop a simple and effective two-phase anaerobic fermentation process, on the basis of less chemical dosage, to realize a highly efficient and stable hydrogen and methane production process, and to simultaneously achieve the treatment of sludge and kitchen waste. purpose of solid waste.

In order to solve the above technical problems, the present invention takes the following technical solutions:

The invention provides a method for co-producing hydrogen and methane through mixed fermentation of sludge and kitchen waste, comprising the following steps:

Step 1, performing aeration pretreatment on the hydrogen-producing inoculated sludge, and performing anaerobic domestication on the methane-producing inoculated sludge;

Step 2, mixing the sludge and the broken food waste according to the optimized mixing ratio, that is, the food waste accounts for 54% of the total volatile solid mass;

Step 3. Build a hydrogen-producing and methanogenic fermentation device including a hydrogen-producing reactor and a methanogenic reactor. The effective volume ratio of the hydrogen-producing reactor and the methanogenic reactor is 1:5.5. Mud, adding fermentation substrate, after a month of acclimatization period, start to run hydrogen production reactor and methane production reactor;

The process conditions for the operation of the hydrogen production reactor and the methane production reactor are as follows:

Feed and reflux mode of the reactor: the hydrogen production reactor and the methane production reactor are fed by intermittent dosing, that is, the mixed matrix is sent into the hydrogen production reactor by the feed pump, and the solid-liquid in the hydrogen production reactor The phase product directly enters the methanogenic reactor, and the sludge from the methanogenic reactor is refluxed to the hydrogen-producing reactor according to the volume ratio of 1:1 to the feed;

Reactor operation mode and continuous hydrogen production and methane production: Among them, the temperature of the hydrogen production reactor is 55°C, the pH value is 5.0-5.5, and the hydraulic retention time is 0.8-3.3d; the temperature of the methane production reactor is 37°C, pH The value is 7.0-7.5, and the hydraulic retention time is 4.5-18d; in order to maintain the pH value of the hydrogen production reactor, a certain amount of K2HPO4 can be added to increase the alkalinity and buffer capacity of the reactor.

Compared with prior art, the beneficial effect of the present invention is:

The invention utilizes sludge and kitchen waste to produce hydrogen and methane, which not only reduces the environmental pollution caused by the discharge of organic solid waste, but also creates clean energy by utilizing renewable resources. The invention utilizes the synergistic effect of mixed substrates to optimize the process of anaerobic fermentation to produce hydrogen and methane, increase gas production and reduce operating costs. On the one hand, food waste contains a large amount of easily degradable organic matter to promote sludge fermentation to produce hydrogen and methane, and to balance the carbon-nitrogen ratio of the fermentation substrate through mixed fermentation, which is conducive to anaerobic fermentation and gas production; on the other hand, a large amount of pH buffer substances in the sludge are used to make up The shortcoming of insufficient alkalinity of food waste, the over-acidification of the hydrogen production reactor can be alleviated by the way of reflux of the effluent of the methanation reactor, so that the reflux ratio and the external alkalinity of the mixed fermentation are lower than those of the single food waste fermentation. This in turn reduces operating costs. In addition, the present invention uses a two-phase anaerobic fermentation process combining high-temperature hydrogen production and medium-temperature methane production to treat kitchen waste and sludge, which greatly reduces the hydraulic retention time, reduces the total volume of the fermentation tank, and effectively separates the hydrogen production stage from the production stage. methane stage, and obtain stable, high yields of hydrogen and methane.

Description of drawings

Fig. 1 is the device and technological process that realize the method of the present invention adopted.

In the figure: 1-hydrogen-producing reactor, 2-methanogenic reactor, 3-feed tank, 4-feed pump, 5-sludge discharge tank, 6-hydrogen-producing gas flowmeter, 7-methanogenic gas flowmeter , 8-constant temperature water bath, 9-methanogenic controller

Detailed ways

The technical solutions of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments of the present invention are provided for accurate understanding, and by no means limit the present invention.

The hydrogen-producing and methane-producing fermentation device built in the embodiment of the present invention is shown in Figure 1. The device includes a hydrogen-producing reactor 1, a methane-producing reactor 2, a feed tank 3, a feed pump 4, and a sludge discharge tank 5. Hydrogen-producing gas flowmeter 6, methane-producing gas flowmeter 7, constant temperature water bath 8, and methane-producing controller 9. Among them, the effective volume ratio of the hydrogen-producing reactor and the methanogenic reactor is 1:5.5, the hydrogen-producing and methanogenic sludge is inoculated, and the fermentation substrate is added. After a one-month adaptation period, the hydrogen-producing reactor and the producing methane reactor.

The operating process of the device in this embodiment is as follows: the concentration of the fermentation substrate is adjusted to 43.5g-VS/L, the equal volume of the fermentation substrate and the methane-producing sludge are mixed evenly in the feed tank 3, and the mixed substrate is mixed with a feed pump 4 into the hydrogen production reactor 1. At the same time, the sludge from the hydrogen production reactor 1 (i.e. the solid-liquid phase product) flows directly into the methanogenic reactor 2, and the sludge from the methanogenic reactor flows back to the hydrogen production reactor at a ratio of 1:1 to the feed volume. reactor. In order to maintain the effective volume of the methanogenic reactor constant, before feeding, discharge twice the volume of sludge from the methanogenic reactor 2 to the sludge discharge tank 5, return one volume of sludge to the feed tank 3 and drain one double the volume of sludge. Both the hydrogen production reactor 1 and the methanation reactor 2 are completely mixed reactors, and the gas flow is respectively passed through the hydrogen production gas flowmeter 6 arranged on the exhaust pipe of the hydrogen production reactor 1 and the gas flow meter 6 arranged in the methanation reactor 2. Methanogenic gas flow meter 7 on the exhaust pipe is used for metering. The temperature of the hydrogen production reactor 1 is controlled to 55°C by the constant temperature water bath 8, and the agitation and temperature control of the methanation reactor 2 are all realized by the methanation controller 9 (the controller comes with the fermenter commercial product), and the methane production The temperature of Reactor 2 was controlled at 37°C.

Example 1:

Anaerobically digested sludge, aerated for 1-3 hours, added glucose or kitchen wastewater for anaerobic culture for 1 day, repeated aeration culture for 1 week, and then used glucose as substrate for fermentation and domestication for 1 week, and finally inoculated sludge as hydrogen production Add it to the hydrogen production reactor 1; inoculate the anaerobic digested sludge into the methane production reactor 2, and regularly add a small amount of kitchen waste for anaerobic cultivation.

The fermentation substrate is a mixture of sludge and crushed food waste, and the sludge and crushed food waste are mixed according to the ratio of food waste to the total volatile solid mass percentage of 54%;

The hydrogen-producing methane-producing fermentation device was constructed as above, wherein the operating temperature of the hydrogen-producing reactor 1 is 55°C, the hydraulic retention time is 3.3 days, the pH value of the hydrogen-producing reactor 1 is controlled at 5.0-5.5 through reflux, and no alkalinity is added , the fermentation substrate is hydrolyzed and acidified in the hydrogen production reactor 1, the gas produced is measured by the hydrogen production gas flow meter 6, and the liquid-solid phase metabolites enter the methanogenic reactor 2 for further digestion. The temperature of the methanogenic reactor 2 is The temperature is 37°C, the hydraulic retention time is 18d, and the pH is between 7.0-7.5.

The method for producing hydrogen and methane by mixed fermentation in Example 1 can run continuously and stably for 30 days without adding alkalinity. Under this operating condition, the yields of hydrogen and methane per unit mass of organic solids are removed are 62.3mL/g-VS and 437.4mL/g-VS, the average concentrations of hydrogen and methane were 60.0% and 81.3%. The energy yield per gram of solid is 4.8kJ/g-VS, while under the same fermentation substrate, the energy yield of single-phase methanogenesis is only 4.5kJ/g-VS.

Example 2:

Embodiment 2 changes some of the process conditions on the basis of Example 1 and continues to operate. The difference from Example 1 is that the hydraulic retention time of the hydrogen-producing reactor 1 is 1.6d, and the hydraulic retention time of the methane-producing reactor 2 for 9d. Under the conditions of Example 2, the hydrogen-producing and methane-producing fermentation device continued to operate stably for 36 days. Due to the increase in organic load, the alkalinity of the return sludge was not enough to maintain the pH of the hydrogen _- producing reactor, so an additional alkalinity of 103 mg-CaCO was required. /d (Convert the added K ₂ HPO ₄ into alkalinity units, that is, calculate according to the H ⁺ concentration required to convert HPO ₄ ^2- into H ₂ PO ₄ ^- , because the main form of phosphate is at pH 5.0-7.0 is HPO ₄ ^2- /H ₂ PO ₄ ^- ). Under these conditions, the yields of hydrogen and methane per unit mass of organic solids were 95.8mL/g-VS and 541.5mL/g-VS, respectively, and the average concentrations of hydrogen and methane were 60.9% and 76.6%. The energy yield per gram of solid is 5.4kJ/g-VS, while under the same fermentation substrate, the energy yield of single-phase methanation is only 3.3kJ/g-VS.

Example 3:

This embodiment 3 changes part of process conditions wherein to continue to run on the basis of embodiment 2, and difference with embodiment 2 is: hydrogen production reaction: the hydraulic retention time of 1 is 1.1d, and the hydraulic retention time of methane reactor 2 The time is 6d. Under the conditions of this example, the hydrogen-producing and methane-producing fermentation device continued to operate stably for 30 days. Due to the further increase of the organic load, it was necessary to increase the added alkalinity to 164 mg-CaCO ₃ /d. Under these conditions, the yields of hydrogen and methane per unit mass of organic solids were 159.8mL/g-VS and 554.3mL/g-VS, respectively, and the average concentrations of hydrogen and methane were 60.0% and 80.6%. The energy yield per gram of solid is 6.2kJ/g-VS, while under the same fermentation substrate, the energy yield of single-phase methanation is only 2.8kJ/g-VS, and the dosage of alkalinity is increased to 620mg-CaCO ₃ /d, indicating that the two-phase fermentation process has obvious advantages in high-load conditions.

Example 4:

In this embodiment 4, on the basis of embodiment 3, the whole part of the process conditions is changed to continue to operate. The difference from embodiment 3 is that the hydraulic retention time of hydrogen production reactor 1 is 0.8d, and the hydraulic retention time of methane production reactor 2 is 0.8d. The time is 4.5d. Under this embodiment, the hydrogen-producing and methane-producing fermentation device has been continuously and stably operated for 24 days. Due to the further increase of the organic load, it is necessary to increase the external alkalinity to 437 mg-CaCO ₃ /d, which is still significantly lower than that produced by kitchen waste alone. Alkalinity required for hydrogen. Under these conditions, the yields of hydrogen and methane per unit mass of organic solids were 207.5mL/g-VS and 475.2mL/g-VS, respectively, and the average concentrations of hydrogen and methane were 54.4% and 71.5%. The energy yield per gram of solid is 6.1kJ/g-VS, while under the same fermentation substrate, the energy yield of single-phase methanation is only 2.7kJ/g-VS, and the dosage of alkalinity needs to be increased The pH of the single-phase methanogenic reactor can be kept stable until 1321mg-CaCO ₃ /d.

Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments, and the above-mentioned specific embodiments are only illustrative, rather than restrictive. Under the enlightenment of the present invention, many modifications can be made without departing from the gist of the present invention, and these all belong to the protection of the present invention.

Claims (2)

1. A method for mixed fermentation of sludge and kitchen waste to co-produce hydrogen and methane, comprising the following steps: Step 1, performing aeration pretreatment on the hydrogen-producing inoculated sludge, and performing anaerobic domestication on the methane-producing inoculated sludge; Step 2, mixing the sludge and the broken kitchen waste according to the proportion that the food waste accounts for 54% of the total volatile solid mass percentage; Step 3. Build a hydrogen-producing and methanogenic fermentation device including a hydrogen-producing reactor and a methanogenic reactor. The effective volume ratio of the hydrogen-producing reactor and the methanogenic reactor is 1:5.5. Mud, adding fermentation substrate, after a month of acclimatization period, start to run hydrogen production reactor and methane production reactor; The process conditions for the operation of the hydrogen production reactor and the methane production reactor are as follows: The hydrogen-producing reactor and the methane-producing reactor are fed in batches, and the mixed matrix is fed into the hydrogen-producing reactor by a feed pump. The sludge from the methane reactor is refluxed to the hydrogen production reactor according to the volume ratio of 1:1 to the feed; The temperature of the hydrogen-producing reactor is 55°C, the pH value is 5.0-5.5, and the hydraulic retention time is 0.8-3.3d; the temperature of the methane-producing reactor is 37°C, the pH value is 7.0-7.5, and the hydraulic retention time is 4.5-18d . 2. A method for co-producing hydrogen and methane through mixed fermentation of sludge and kitchen waste according to claim 1, wherein the pH value of the hydrogen production reactor is controlled by adding K ₂ HPO ₄ .