CN112342250B - Method for preparing granular sludge for producing methane by degrading propionic acid - Google Patents

Abstract

The invention relates to a method for preparing granular sludge for degrading propionic acid to produce methane, which takes propionic acid degraded sludge and anaerobic digested sludge as inocula and takes composite carbon sources consisting of glucose and propionate in different proportions as feeding substrates to perform acclimation culture on the mixed inocula sludge in an anaerobic sludge bed reactor. Formation of granular sludge is promoted by increasing the Organic Load (OLR) by both increasing the feed substrate concentration and by shortening the Hydraulic Retention Time (HRT).

Description

Method for preparing granular sludge for degrading propionic acid to produce methane

Technical Field

The invention belongs to the field of microbial fermentation and the field of sewage or sludge treatment, and particularly relates to a preparation method of granular sludge for producing methane by degrading propionic acid.

Background

With the increasing environmental pollution and energy crisis, the development and utilization of new energy resources are increasing in all countries of the world. Wherein biomass biogas gasification becomes a research hotspot of researchers at home and abroad. Anaerobic digestion methanogenesis is a very complex process, and therefore, complete anaerobic digestion methanogenesis requires the synergistic action of multiple microorganisms to accomplish. In order to maximize the production of methane, the anaerobic digestion reactors are operated under a high load condition, and the reactors operated under a high load condition often unbalance acid production and methanogenic bacteria, so that volatile acid is accumulated, the pH value is often reduced, the activity of the methanogenic bacteria is further inhibited, and the performance of the reactors is also reduced. Among these accumulated volatile acids, propionic acid is accumulated most seriously.

At present, the problem of propionic acid accumulation at home and abroad is concentrated on bioaugmentation. In 2015, a bioaugmentation microbial inoculum taking Methanospirillum henryi (Methanospirillum hungatei) as a dominant bacterium is obtained by a method of increasing hydrogen in flora in a medium-temperature anaerobic reactor, the propionic acid degradation rate of the bioaugmentation microbial inoculum reaches 70%, and the methane yield is improved by 50%. Venkiteshwaran et al, in 2016, obtained a reaction of mesquite (smithlla) bacteria by increasing the propionic acid concentration in the reactor continuously; propionic acid oxidizing bacteria of Syntrophobacter (Syntrophobacter) and methanogen (Methanosaeta), methanogens of acetate type. The propionic acid degradation rate reaches 65%, and the methane yield is improved by 28%. In the same year, the Guarong topic group performs biological enhancement on a methane phase reactor by using a biological enhancement microbial inoculum taking Syntrophobacter and methanolabetaceae as dominant bacteria, and the methane yield is finally improved by 15%. Tale, j.s.maki et al bioaugmentation of propionate-degraded enriched cultures from 14 different transient overloaded full-scale anaerobic digestion reactors effectively reduced the recovery time of the rancidity system. Utilization of H by Anne E.Schauer-Gimenez et al₂The use of microorganisms as bioaugmenting agents successfully reduced the recovery time of anaerobic digesters that were exposed to toxicity instantaneously. Whether the research on the bioaugmentation is the addition of a single microbial inoculum or a composite microbial inoculum, the propionic acid degradation rate, the methane yield and the system performance are improved to a certain extent, and the recovery time of the system is shortened.

In addition, much research has been conducted on the degradation of propionic acid. Qian Li et al, the university of Seisan construction science and technology, promotes propionic acid consumption by adding sulfate into a reaction system, and further improves anaerobic digestion performance by using coffee grounds and milk as substrates. Xuchang et al improve the system hydrogen partial pressure through a granular anaerobic biofilm to promote propionic acid degradation. In addition, the fermentation type is controlled by adjusting the pH, controlling the reaction temperature of the two-phase anaerobic digestion and controlling the oxidation-reduction potential to inhibit the production of propionic acid, thereby improving the anaerobic digestion performance.

However, sulfur is added to the systemThe amount of acid salts is difficult to control and the addition of sulphate necessarily results in the production of H in the gas₂The content of S is increased, which is not only not beneficial to the growth of methanogens, but also increases the difficulty of methane separation and purification in the later period. It is known that the gepiros free energy of propionic acid degradation is large and the reaction proceeds only at a low hydrogen partial pressure, but it is difficult to reduce the hydrogen partial pressure in a closed anaerobic environment. The methane phase propionic acid degradation is promoted by controlling the two-phase anaerobic digestion reaction temperature, which necessarily increases the capital cost and operational complexity. Adjusting the pH and redox potential controls the type of fermentation inhibiting the production of propionic acid is clearly only suitable for theoretical studies on a laboratory scale.

Other researches on propionic acid degradation also include citation 1, which discloses a domestication method of an acid-resistant trans-trophic propionic acid methanogen system, wherein biogas fermentation liquor is used as an inoculum, propionic acid is used as a carbon source, and the acid-resistant trans-trophic propionic acid methanogen system is obtained by domesticating the biogas fermentation liquor by a method of circularly and stepwisely reducing the pH in a culture medium, so that the obtained acid-resistant trans-trophic propionic acid methanogen system can stably produce gas for a long time under the acidic condition of pH 6.0-5.5, can be used for a gas production reduction or rancidity fermentation system caused by propionic acid accumulation, promotes propionic acid degradation and the methane production of degradation products thereof, and improves the fermentation performance of biogas.

Citation 2 discloses a method for enrichment culture of propionic acid oxidizing bacteria and their symbiotic flora under anaerobic condition, which comprises acidifying, adding nitrate and controlling COD/NO in matrix under the condition of inhibiting methanogenesis metabolism^3-And (4) continuously culturing by using the-N value, enriching the bacteria which take the genus of the genus Aleurynonegenus Aleurynia, and the genus of the hydrogen-lntertiarythromobaragonism as the genus of the genus Aleurynis of the genus Alying genus of the genus Alying genus of the.

Citation 3 discloses a domestication method of self-coagulation propionic acid methanogen, which comprises the steps of taking biogas fermentation liquor secreting extracellular polymers, separating to obtain extracellular polymers, inoculating the extracellular polymers into a selective culture medium for producing methane by propionic acid, and putting the extracellular polymers into an anaerobic bottle shaking table to culture for 3-4 weeks at 37 ℃ until spherical microorganism coagulants appear in the culture medium; and adding the bacterial colony into a fresh culture medium, and culturing the self-coagulated methane-producing propionic acid bacterial colony obtained by domestication for 7-10 days, so that the degradation of propionic acid and the production of methane by a degradation product of propionic acid can be promoted, and the fermentation performance of methane is improved.

However, in semi-continuous and continuous reactors, the main challenge facing bioaugmentation is to ensure that the introduced microorganisms are able to grow and not wash out of the reactor, adversely affecting the survival and prolonging the activity of the microorganisms. Meanwhile, the anaerobic digestion system is very complicated, and the treatment effect of the strengthening system is unpredictable due to the fluctuation of organic load, the change of process conditions, the interaction between strengthening bacteria and indigenous microorganisms and the like, so that failure results also occur. There are many unknowns as to whether the activity of the bioaugmentation agent can be reacted in a complicated reaction system.

In summary, a great deal of current research has shown that 35% of the methane production of the system is converted from propionic acid. The problem of accumulation of propionic acid is therefore solved by focusing mainly on the degradation of propionic acid rather than inhibiting the production of propionic acid. In view of the convenience and rapidity of improving the longevity of microbial activity and facilitating continuous production, there is still room for further improvement in a method for promoting the production of methane by degrading propionic acid in an anaerobic digestion method.

Cited documents:

cited document 1: CN 106434518A

Cited document 2: CN 107099471A

Cited document 3: CN 106701671A

Disclosure of Invention

Problems to be solved by the invention

In view of the above prior art, the present invention provides a method for preparing granular sludge for producing methane by degrading propionic acid, which is advantageous for survival and prolonged activity of microorganisms. The propionic acid degrading microorganisms obtained by the invention can be presented in the form of granular sludge, not only has good settleability, but also has high microorganism aggregation degree, is not easy to wash out from a reactor, and simultaneously has the advantages of high biomass, good tolerance and the like of the traditional granular sludge.

Means for solving the problems

After the intensive research of the inventor, the technical problems can be solved by implementing the following technical scheme:

[1] the invention firstly provides a method for preparing granular sludge for degrading propionic acid to produce methane, which is characterized by comprising the following steps:

a step of mixing, in which the inoculum sludge and a feed matrix comprising a complex carbon source comprising glucose and propionate are added to a reactor to form a mixed system;

a step of acclimating the inoculum sludge by the composite carbon source to obtain the granular sludge for degrading propionic acid to produce methane,

in the acclimatization step, the total Organic Load (OLR) of the mixed system is controlled to be gradually increased by increasing the concentration of the feeding substrate and shortening the hydraulic retention time, and the initial glucose_CODPropionate salts_CODThe ratio is maintained above 3.5: 1.

The glucose is_CODRepresents the COD value provided by glucose, the propionate_CODRepresents the COD value provided by propionate.

[2] The method according to [1], wherein the propionate is selected from one or more of alkali metal salts of propionic acid.

[3] The method according to [1] or [2], wherein in the step of acclimatization, the adjustment range of the total Organic Load (OLR) value of the mixed system is 0.5-10; the adjustment range of the total COD value of the mixed system is 300-2500 mg/L; the adjustment range of the hydraulic retention time is 3-15 hours.

[4] The method according to [1] to [3], wherein the step of acclimatization comprises at least three stages of:

the first stage, controlling the glucose in the mixed system_CODPropionate salts_CODIs 3.5:1 to 4.5:1, in totalThe organic load is 0.5-4.5, and the hydraulic retention time is 10-15 hours;

a second stage of controlling the glucose in the mixed system_CODPropionate salts_COD1.8: 1-2.5: 1, total organic load 3.5-5, and hydraulic retention time 10-15 hours;

a third stage of controlling the glucose in the mixed system_CODPropionate salts_COD1.8: 1-2.5: 1, total organic load 5-10, and hydraulic retention time 3-10 hours.

[5] The method according to [4], wherein in the first stage, the concentration of the feed substrate is gradually increased so that the total COD value in the system is adjusted within the range of 300 to 2000 mg/L.

[6]According to [4]]The method, the mixed system glucose in each stage_CODPropionate salts_CODKeeping constant; glucose in the second and third stages_CODPropionate salts_CODThe values are the same.

[7] The method according to any one of [1] to [6], wherein the inoculum sludge includes propionic acid-degraded sludge and anaerobically digested sludge; the propionic acid degradation sludge is sludge obtained by domesticating propionic acid or salt thereof as a unique carbon source.

[8] The method according to [7], characterized in that the inoculation ratio of the propionic acid-degraded sludge to the anaerobically digested sludge in the inoculum sludge is 1:4 to 1:2 in terms of volume.

[9] The method according to any one of [1] to [8], wherein the feed substrate is wastewater containing metal ions, non-metal ions, and a hydrate of a metal salt, and the pH of the feed substrate is 7.8 to 8.2.

[10] Further, the present invention provides a granular sludge produced by the method according to any one of [1] to [9], the granular sludge having an average particle size of 0.5 to 2.0 cm.

[11] In addition, the invention also provides a treating agent for producing methane by anaerobic digestion, which comprises the granular sludge in the item [10].

ADVANTAGEOUS EFFECTS OF INVENTION

Through the implementation of the technical scheme, the invention can obtain the following technical effects:

according to the invention, sodium propionate and glucose are used as substrates, and the concentration and proportion of a feeding matrix and hydraulic retention time are changed by improving organic load, so that the granular sludge capable of efficiently degrading propionic acid to generate methane for a long time is obtained. Therefore, the method can better adapt to the fluctuation of organic load and the change of process conditions. Meanwhile, the method for preparing the granular sludge is simple, the propionic acid can be efficiently degraded to produce methane, and the problem of propionic acid accumulation in the anaerobic digestion process can be solved due to high microbial activity.

The biogas produced in addition is composed of CH₄And CO₂Mainly, the desulfurization treatment is avoided. And the process conditions are easy to control and the operation is simple. The granular sludge for efficiently degrading propionic acid to produce methane is applied to actual anaerobic digestion to produce methane, so that the anaerobic digestion performance is effectively improved, the production period is greatly saved, and the operation cost is reduced.

Drawings

FIG. 1: SVI₃₀Varying with each stage in the production process;

FIG. 2 is a schematic diagram: SMA varies with each stage in the production process;

FIG. 3: and comparing the degradation rate of the granular sludge propionic acid with that of the sludge.

Detailed Description

The present invention will be described in detail below. The technical features described below are explained based on typical embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples.

It should be noted that:

in the present specification, the numerical range represented by "numerical value a to numerical value B" means a range including the end point numerical value A, B.

In this specification, "substantially free" means that some operation is not actually adopted in performing some method or step so that an operation object does not actually have some characteristic.

In the present specification, the "particle diameter" refers to an "average particle diameter", and can be measured by a commercial particle sizer.

In the present specification, "%" denotes mass% unless otherwise specified.

In this specification, cod (chemical Oxygen demand) is a chemical Oxygen demand, and is a chemical method for measuring the amount of reducing substances to be oxidized in a water sample. Wastewater, wastewater treatment plant effluent, and contaminated water, the oxygen equivalent of a substance (typically an organic substance) that can be oxidized by a strong oxidizing agent. In the research of river pollution and the property of industrial wastewater and the operation management of wastewater treatment plants, it is an important and relatively fast measurable organic pollution parameter, often expressed as COD.

In the present specification, the "feed substrate concentration" can be characterized by the total COD value of the system.

In this specification, the term "SCOD" is used to indicate the amount of dissolved chemical oxygen demand, and can be obtained by tests routine in the art.

In the present specification, olr (organic Loading rate) is an organic load, which means the amount of organic pollutants received by a unit volume of a sewage treatment reactor (or a unit volume of a medium filter) in unit time, and the unit is kilogram/(meter)³Day). In the sewage treatment field, load sign sewage treatment facility can accept the ability of sewage, and in the sewage treatment field, load sign sewage treatment facility can accept the ability of sewage.

In the present specification, hrt (hydraulic Retention time) is hydraulic Retention time, which means the average Retention time of the sewage to be treated in the reactor, i.e. the average reaction time of the sewage and the microorganisms in the bioreactor; the hydraulic retention time can be adjusted by the inflow rate.

In the present specification, "TS" is used to indicate the total solid content, and means the total weight of the solid material remaining after the test sample is evaporated to a constant weight at a certain temperature, wherein the remaining solid material includes the sum of organic and inorganic substances.

In this specification, the volatile solids content is denoted by "VS" and refers to the total weight of organic matter in the test sample in suspension, colloidal matter, and dissolved matter.

In the present specification, the meaning of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

In this specification, "optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

In the present specification, reference to "some particular/preferred embodiments," "other particular/preferred embodiments," "embodiments," and the like, means that a particular element (e.g., feature, structure, property, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.

< first aspect >

In the prior art, the anaerobic granular sludge technology is widely applied, and the sludge granulation is a complicated process, and the forming mechanism of the sludge granulation is not completely clear at present. The acquisition of granular sludge is well established and the process is influenced by a number of factors. Research shows that although granular sludge can be formed at low temperature, medium temperature and high temperature, the treatment efficiency of the waste water of the bottom is low at the low temperature, and NH is generated at the high temperature₃The toxicity of the mixed compound can be increased so as to inhibit the activity of methanogens, so that the method for forming granular sludge under the condition of medium temperature is a hot point of research.

In addition, the pH value of the system is another important influence factor in anaerobic digestion, and the optimal pH value of methanogens is 6.8-7.2. In addition, the growth of microorganisms requires a certain amount of nutrients and trace elements.

In addition to these environmental factors, sludge granulation is closely linked to process parameters. It is believed that increased organic loading increases the hydrophobicity of the microbial cells and facilitates their separation from the aqueous phase, primarily because increased organic loading stimulates the production of cellular polysaccharides, which act as a sludge backbone and increase the organic loading facilitates the conversion of flocculent sludge to granular sludge. Meanwhile, the higher organic load can cause the appearance of filamentous bacteria and is beneficial to the aggregation and adhesion of microorganisms. The organic load can be increased in two ways, one is to increase the concentration of the feed substrate to provide sufficient nutrient substances for the growth of microorganisms; secondly, the hydraulic retention time is shortened, the water shearing force of a reaction system is increased, and the formation of granular sludge is promoted.

A great deal of research currently indicates that traditional granular sludge can be successfully cultured in many substrates. Comprises synthetic wastewater, actual domestic sewage and industrial wastewater which are prepared from glucose, cane sugar, starch and peptone. In addition to this, there are many reports of obtaining granular sludge from inorganic carbon sources. Although the type of substrate is not the most critical factor in determining the formation of granular sludge, the process, microstructure, and composition of microbial species of granular sludge formed under different substrate conditions are greatly different, and uncertainty exists in terms of biological activity.

Nevertheless, the actual effect of sludge granulation is still difficult to predict due to differences in the process control methods, as well as the matrix itself.

Based on the prior art, the granular sludge for synchronously degrading propionic acid and producing methane is obtained by using the glucose and propionate composite carbon source and controlling the process parameters. The obtained granular substance has improved degradation efficiency of propionic acid and improved durability.

Furthermore, in a first aspect of the present invention, there is provided a method for producing granular sludge for degrading propionic acid to produce methane, the method at least comprising: a mixing step and an acclimation step.

In the step of mixing, the inoculum sludge and the feed substrate comprising the complex carbon source are added to the reactor to form a mixed system. The complex carbon source comprises glucose and propionate. In the acclimation step, acclimating the inoculum sludge by the composite carbon source to obtain the granular sludge for degrading propionic acid to produce methane.

In the acclimation step, the total Organic Load (OLR) of the mixed system is controlled to be gradually increased, and the Hydraulic Retention Time (HRT) is controlled to be gradually decreased. At the same time, the initial glucose is controlled_CODPropionate salts_CODThe ratio of glucose is more than 3.5:1, the ratio of glucose is more than 1_CODRepresents the COD value provided by glucose, the propionate_CODRepresents the COD value provided by propionate.

Reaction device

In the present invention, the preparation of the granular sludge is performed by using an anaerobic bioreactor.

In the present invention, the anaerobic bioreactor includes, but is not limited to: an Upflow Anaerobic Sludge Blanket (UASB) reactor, an Expanded Granular Sludge Blanket (EGSB) reactor, an anaerobic sequencing batch Activated Sludge (ASBR) reactor, an Internal Circulation (IC) anaerobic reactor, an anaerobic attached membrane expanded bed (AAFEB) reactor, a Continuous Stirred Tank Reactor (CSTR), etc.; preferably an upflow anaerobic sludge blanket reactor.

Inoculum sludge

In some embodiments of the invention, for inoculum sludge, propionic acid-degraded sludge is included as well as anaerobically digested sludge.

The present invention relates to propionic acid-degraded sludge, which is obtained by acclimating propionic acid or a salt thereof as a sole carbon source. The propionate is not particularly limited, and may be an alkali metal salt or an alkaline earth metal salt of propionic acid. In some preferred embodiments of the present invention, the propionate may be selected from one or more of potassium propionate, sodium propionate, or calcium propionate. In some specific embodiments, the total solid content (TS) of the propionic acid-degraded sludge may be less than 30g/L, and optionally 15 to 25 g/L; the total volatile solid content (VS) can be less than 20g/L, optionally 10-20 g/L. The total dissolved chemical oxygen demand (SCOD) value can be more than 330mg/L, optionally 350-500 mg/L, and more preferably 380-450 mg/L. Conversion of free ammonia to NH₃The content of (b) is 40-60 mg/L. In addition, the pH value of the propionic acid degradation sludge can be 6.8-7.7, and preferably 7.2-7.5.

In the present invention, the propionic acid-degrading sludge may contain the following flora: the genera of the genera Methanobacterium (Syntrophobacter, eg: Syntrophobacter wolfinii, Syntrophobacter sulfatiduens, Syntrophobacter fumaroxinans, Syntrophobacter pfennniigii), Missella (Smithlla), Methanospermia (Pelotomaculum, eg: Pelotomaculum schinkii, Pelotomaculum propionicum), Methanospira (Methanospirillum, eg: Methanospirillum hungatei), Methanosarcina (Methanovullus, eg: Methanovullus Palmoleus, Methanovululus bourneis), Methanosarcina (Methanosarcina, etc.) are capable of degrading methane and/or producing common methanoic acid-producing sludge.

For anaerobically digested sludge, anaerobically digested sludge suitable for use in the present invention may be an anaerobe sludge bed reactor taken from a laboratory or plant operating for a long period of time, and in some preferred embodiments, such a reactor may be an upflow anaerobic sludge bed reactor (UASB). The sludge obtained from these reactors is not particularly limited, and in some specific embodiments, such sludge may have a total solids content (TS) of 25g/L or less, optionally 12-20 g/L; the total volatile solids content (VS) can be less than 20g/L, optionally 8-15 g/L. The total dissolved chemical oxygen demand (SCOD) value can be more than 250mg/L, optionally 280-350 mg/L, optionally 290-330 mg/L. Conversion of free ammonia to NH₃The content of (b) is 35-50 mg/L. In addition, the pH value of the propionic acid degradation sludge can be 6.8-7.2, and is preferably 6.9-7.1.

In the present invention, the flora in the anaerobically digested sludge may comprise the following flora: microorganisms commonly found in anaerobic sludge such as Methanobacterium (Methanobacterium), Methanocystis (Methanovuleus), Methanococcus (Methanococcus), Methanomicrobium (Methanomicrobium), Methanosarcina (Methanosarcina), and Methanothrix (Methanosaeta), Methanotrichia (Methanothrix), Proteobacteria (Proteobacteria), Methanospira (Methanopirillum), Pyrobacillus (Methanothribacterium), Bacteroides (Bacteroides), Anammox (Anammox), and Rhodopseudomonas palustris (Rhodopseudomonas palusta).

The present invention does not specifically require the form of the propionic acid-degraded sludge and anaerobic-digested sludge, and the propionic acid-degraded sludge and anaerobic-digested sludge may be flocculent, slurry, or semisolid. In addition, for the proportion of the two kinds of sludge, in some specific embodiments of the invention, the inoculation ratio of the propionic acid degradation sludge and the anaerobic digestion sludge in the inoculum sludge is 1: 4-1: 2 in volume. The proportioning of the invention refers to the quotient of the respective dosage of the two sludges and the final mixture when the two sludges are mixed.

In a specific embodiment of the invention, the properties of the propionic acid-degrading sludge and anaerobic digestion sludge used in the inoculum sludge are listed below:

TABLE 1 propionic acid-degraded sludge and anaerobically digested sludge Properties in inoculum sludge

The propionic acid-degraded sludge and anaerobic digested sludge of the present invention can be prepared by methods generally used in the art or obtained by other means.

Feed matrix

The feeding substrate of the present invention is not particularly limited as long as it is a feeding substrate containing glucose and propionate as carbon sources. In some specific embodiments, the carbon source (total COD value) in the feed matrix is derived solely from the glucose and propionate. The propionate salt has the same definition as the propionate salt disclosed above.

In addition to the carbon source, the feed matrix may also contain metal ions and metal salt hydrates, which have no significant effect on the growth of microorganisms in the sludge or are beneficial to the growth of microorganisms, providing elements necessary for the growth of microorganisms. The metal ion species may be selected from alkali metal ions, alkaline earth metal ions, and transition metal ionsOne or more of (a). The counter ion for these metal ions may be Cl^-One or more of sulfate, sulfite, phosphate, hypophosphite or nitrate. As the hydrate of the metal acid salt, there may be mentioned a monohydrate to a decahydrate of a compound formed by the above metal and the above acid ion.

For the feeding matrix, acid or alkali can be used for adjusting the pH value to 7.8-8.2 when needed; preferably, the concentration of the surfactant is 7.9 to 8.1. The pH adjuster that can be used may be a weak acid, a weak base, a buffer solution, or the like, and typically sodium bicarbonate or the like.

In some specific embodiments of the present invention, the feed matrix of the present invention may be (industrial) wastewater containing glucose and propionate, and the like, and exemplary feed matrices may have the following composition:

for the synthetic wastewater of 500mgCOD/L, 400mg/L of glucose, 125mg/L of sodium propionate and NH are needed₄Cl 172mg/L，KH₂PO₄ 19.7mg/L，MgSO₄·6H₂O 39mg/L，KCl 40mg/L，CaCl₂·2H₂O 36.8mg/L，FeCl₃·6H₂O 5.0mg/L，CoCl₂·6H₂O 1.2mg/L，NiCl₂·6H₂O 1.2mg/L，Na₂Mo₄·2H₂O 1.0mg/L，CuSO₄·5H₂O 5.0mg/L，MnSO₄·4H₂O 5.0mg/L，ZnSO₄·7H₂O5.0 mg/L with NaHCO₃Adjusting the pH value to 7.8-8.2.

Mixed system

In the mixing step of the present invention, the inoculum sludge and the feed substrate comprising the complex carbon source are added to the reactor to form a mixed system. The specific mixing method is not particularly limited, and the feeding and mixing may be performed using a feed port of an anaerobic bioreactor which is generally used in the art.

The temperature of the mixed system is not particularly limited, and the mixed system of the present invention may be formed at 15 to 40 ℃. Preferably, the mixed system can be formed under the condition of 25-35 ℃. It should be noted that the mixing temperature in the present invention does not significantly affect the properties of the subsequent granular sludge, and therefore, the mixing can be performed at or near room temperature.

Step of acclimatization

In the acclimating step, the inoculum sludge is acclimated by the composite carbon source to obtain the granular sludge for degrading propionic acid to generate methane. In the acclimatization step, the total Organic Load (OLR) of the mixed system is controlled to be gradually/continuously increased, the Hydraulic Retention Time (HRT) is controlled to be gradually/continuously decreased, and the initial glucose is controlled to be_CODPropionate salts_CODIs more than 3.5: 1. In the present invention, the term "gradually" or "continuously" refers in some embodiments to a continuous change over time, or in other embodiments to an intermittent change over time.

According to the invention, in the domestication step, the change of the OLR, the HRT and the total COD value of the system in the whole process is controlled, so that the granular sludge for propionic acid degradation is obtained. Specifically, in the acclimation step, an increase in Organic Load (OLR) in the mixed system is achieved by increasing the concentration of the carbon source substances in the system (i.e., the total COD value in the mixed system) and decreasing the Hydraulic Retention Time (HRT), thereby obtaining the granular sludge. Total COD values for the mixed system under some conditions were allowed to pass by varying glucose_CODPropionate salts_CODThe ratio of (a) to (b) and the total content.

In some embodiments, the control process may be implemented in a staged control manner. More specifically, the following three stages may be included:

the first stage is as follows: setting initial glucose_CODPropionate salts_CODThe ratio of (b) is generally 3.5:1 or more, and in some preferred embodiments, 3.5:1 to 4.5:1, and more preferably 3.8 to 4.2: 1. And, while controlling the above ratio, the total COD value of the mixed system is controlled to be 300-2000 mg/L, preferably 400-2000 mg/L. In some embodiments of the inventionIn the first stage, the HRT value is controlled to be 10-15 hours, preferably 11-13 hours, and the concentration of the carbon source in the system (or the total COD value of the system) is continuously increased to continuously increase the total organic load of the mixed system, preferably, in the first stage, the total organic load can be 0.5-4.5. In other embodiments, the hydraulic retention time and glucose are maintained in the first stage while the total COD of the mixed system is continuously increased_CODPropionate salts_CODThe ratio of (a) is constant, so that the total organic load of the system is more effectively improved, and the primary formation of granular sludge is promoted.

And a second stage: in the second stage of the acclimation step, granular sludge is basically formed. In some specific embodiments, the total COD value of the mixed system can be controlled to be 1800-2500 mg/L, the total organic load is controlled to be 3.5-5, the hydraulic retention time is 10-15 hours, and the glucose is added in the stage_CODPropionate salt_CODThe ratio of (A) to (B) is 1.8: 1-2.5: 1. In other embodiments, the total COD and total organic loading in the mixed system reach the maximum values of the first stage at the end of the first stage, and these parameters are maintained constant while maintaining the same hydraulic retention time as at the end of the first stage and adjusting the glucose concentration at the end of the second stage_CODPropionate salts_CODThe ratio of (c) to (d) increases relative to the end of the first phase.

And a third stage: in the third stage of the acclimation step, the granular sludge obtained in the second stage is matured. In the stage, the total COD value of the mixed system can be controlled to be 1800-2500 mg/L, the total organic load is controlled to be 5-10, the hydraulic retention time is controlled to be 3-10 hours, and the glucose is controlled_CODPropionate salt_CODThe ratio of (A) to (B) is 1.8: 1-2.5: 1. Compared with the second stage, the total organic load of the system in the third stage is further increased, and the hydraulic retention time is further reduced. In some preferred embodiments, the present invention maintains the same total COD value of the system in the third stage as in the second stage, increasing the total organic loading of the system by reducing the hydraulic retention time.

Furthermore, it is preferred that the mixed system glucose in each stage_CODPropionate salts_CODKeeping constant; glucose in the second and third stages_CODPropionate salts_CODThe values are the same.

The granular sludge formation stage of the present invention can be divided into three stages, the first stage is the initial stage of granular sludge formation, the second stage is the middle stage of granular sludge formation, and the third stage is the mature stage of granular sludge. The first stage is further divided into three periods, the second stage is one period, and the third stage is divided into two periods. However, it goes without saying that the three stages of the present invention may be performed intermittently or continuously, and thus, when the technical solution of the present invention is implemented using a continuously controlled method, the second and three stages of the present invention may be regarded as one stage in which it is preferable to maintain glucose_CODPropionate_CODThe total COD value of the system is kept to be the same as the final value of the first stage, and the total organic load of the system is continuously increased by reducing the hydraulic retention time.

The treatment time in the above three stages is not particularly limited, and in a preferred embodiment of the present invention, the treatment time in the first stage is 55 to 70 days, the treatment time in the second stage is 18 to 22 days, and the treatment time in the third stage is 35 to 45 days.

In some specific embodiments of the present invention, the first stage can be further divided into three periods, the initial glucose_CODPropionate salt_CODThe ratio of the total COD in the system in the three periods is 3.8-4.2: 1, the total COD in the system in the three periods is 300-600 mg/L, 800-1500 mg/L and 1600-2000 mg/L in sequence, and the total OLR in the three periods is 0.5-1.2 g of COD/L/d, 1.3-2.5 g of COD/L/d and 2.6-4.5 g of COD/L/d in sequence. And the hydraulic retention time in each period is 10-15 h, preferably, the hydraulic retention time is kept unchanged in the three periods.

In the present invention, the formation of granular sludge is initially promoted by raising the reactor Organic Load (OLR) at the early stage of granular sludge formation. Meanwhile, in this stage, the sludge is acclimatized and cultured by a composite carbon source substrate with a low ratio of glucose to propionate. On one hand, considering that the granular sludge formed by taking glucose as a main matrix generally has richer and more diverse flora structures, the granular sludge is beneficial to formation; on the other hand, the distribution of specific microorganisms in the sludge is related to the type and concentration of the reactor feed substrate. Thus, to maintain the metabolic activity of the propionic acid-degrading microorganisms in the inoculum, the propionate stress load is kept low.

In the invention, in the middle stage of forming the granular sludge, on one hand, higher OLR in the early stage is maintained, the formation of the granular sludge is continuously promoted, and simultaneously, the concentration of propionate in the composite matrix is increased, so that the granular sludge capable of efficiently degrading propionic acid is primarily obtained.

In the invention, in the later stage of forming the granular sludge, on the basis of obtaining the granular sludge capable of efficiently degrading propionic acid in the early stage, the comprehensive efficiency of the reactor OLR and the shearing force is regulated and controlled by shortening the hydraulic retention time, so that the stable maturity of the granular sludge is promoted, namely the mechanical strength of the granular sludge is increased.

The invention obtains granular sludge by continuously increasing the concentration of the composite carbon source in the mixing system (or in the feeding substrate) and reducing the hydraulic retention time, and simultaneously changes the glucose_CODPropionate salts_CODThe ratio of (A) to (B) finally obtains the granular sludge with good mechanical strength, improved anaerobic digestion performance and improved activity.

< second aspect >

In a second aspect, the present invention relates to a granular sludge obtained by the method according to the first aspect, wherein the granules of the sludge have a particle size in the range of 0.5 to 2.0cm, preferably 0.8 to 1.5 cm.

< third aspect >

In a third aspect of the present invention, there is provided a treating agent for methanogenesis by anaerobic digestion, comprising the granular sludge according to the second aspect described above.

Without limitation, such treatment agents may include other components that aid in the anaerobic digestion of methanogenesis in addition to the granular sludge described above.

In some specific embodiments, the mixing ratio of the granular sludge of the present invention in the treatment agent may be 50% or more, preferably 70% or more, and more preferably 90% or more, by weight of the initial ratio.

Examples

Example 1

Inoculum and substrate:

propionic acid-degraded sludge is obtained by acclimation with sodium propionate as the only carbon source, and anaerobic digested sludge is obtained from an Upflow Anaerobic Sludge Blanket (UASB) reactor which is operated in a laboratory for a long time.

Inoculum volume: propionic acid-degraded sludge and anaerobically digested sludge in the inoculum sludge were 250mL and 750mL, respectively.

Inoculum attributes:

TABLE 2 propionic acid-degraded sludge and anaerobically digested sludge Properties in inoculum sludge

A feeding matrix:

for the synthetic wastewater of 500mgCOD/L, 400mg/L of glucose, 125mg/L of sodium propionate and NH are needed₄Cl 172mg/L，KH₂PO₄ 19.7mg/L，MgSO₄·6H₂O 39mg/L，KCl 40mg/L，CaCl₂·2H₂O 36.8mg/L，FeCl₃·6H₂O 5.0mg/L，CoCl₂·6H₂O 1.2mg/L，NiCl₂·6H₂O 1.2mg/L，Na₂Mo₄·2H₂O 1.0mg/L，CuSO₄·5H₂O 5.0mg/L，MnSO₄·4H₂O 5.0mg/L，ZnSO₄·7H₂O5.0 mg/L with NaHCO₃The pH was adjusted to 8.0.

Table 3 Upflow Anaerobic Sludge Blanket (UASB) reactor operating parameters:

sludge volume index results

The Sludge Volume Index (Sludge Volume Index, SIV) is a parameter representing the Sludge settling performance. SVI₃₀Namely, the volume occupied by 1g of dry sludge after the mixed sludge is stood for 30 minutes can objectively and well reflect the coagulation degree and sedimentation performance of the sludge. Low SVI₃₀The values indicate a higher degree of sludge coagulation and better settling properties and a higher biomass retention in the reactor. SVI of sludge grown in glucose and sodium propionate solutions in this study₃₀The reduction from 55.6mL/g of inoculated sludge to the last 16.4mL/g of the third stage indicated an increasing degree of granulation of the sludge. SVI of sludge₃₀The decrease with increasing organic loading rate is probably due to the loose sludge being discharged from the reactor by sludge bulking, while the more settling granular sludge remains in the reactor. (see FIG. 1)

Specific methanogenic activity

Specific Methanogenic Activity (SMA), the Methanogenic Activity of anaerobic sludge, refers to the amount of methane that can be produced per weight of sludge (in VSS) per unit time. To assess the effect of each stage on microbial activity, a sample of sludge was withdrawn from the reactor at the end of each stage for SMA testing (at 35 ℃) with 0.25g propionic acid as the sole carbon source. After the end of the first stage, the SMA was 0.163g CH₄COD/g VSSd, in the second stage, SMA is 0.233g CH₄COD/g VSS d, thereby indicating a significant increase in the methanogenic capacity of the sludge, an increase in SMA indicating successful conversion of the seeded sludge to granular sludge, an increase in adhesion and agglomeration of microorganisms with an increase in SMA, and an increase in extracellular polymer secreted by the bacteria resulting in the aggregation of cells into granules. Although in the third stage, the SMA was 0.225g CH₄COD/g VSS d, was not significantly changed compared to the second stage (see FIG. 2). This is mainly due to the fact that in the third stage, e.g. HRT (hydraulic retention time) is reduced, i.e. the contact time of the substrate with the sludge is reduced, but the methanogenic capacity of the sludge can still be maintained at a higher level, while the sludge activity is still increased relatively. In addition, under the condition of almost constant methanogenic activity, the third stageThe sludge has better settling properties than the second stage. Meanwhile, the methanogenic activity of the sludge can also reflect the potential of the sludge for degrading substrates, and is an important parameter of the sludge quality, and the remarkable increase of SMA is a direct embodiment of continuously improving the propionic acid utilization capacity of microorganisms, so that the obtained granular sludge has high propionic acid degradation capacity.

Comparison of degradation rates of flocculent sludge and granular sludge propionic acid

In order to further verify the ability of the granular sludge to degrade propionic acid, a comparative experiment was performed on the propionic acid degradation rate by using the conventional flocculent sludge (rich in propionic acid-degrading bacteria) and the granular sludge as inoculum sludge and using propionic acid as a sole carbon source, and the results are shown in the following figure. After the reaction system is carried out for 4 hours, the propionic acid degradation rate of the reaction system with the granular sludge as the inoculum reaches 57.3 percent, and the propionic acid degradation rate of the reaction system with the flocculent sludge as the inoculum reaches 42.4 percent, so that the granular sludge system has higher reaction rate and better activity. After 8 hours, the propionic acid degradation rate of the reaction system taking the granular sludge as the inoculum reaches 97.6 percent, which is close to 100 percent, and the propionic acid degradation rate of the reaction system taking the flocculent sludge as the inoculum reaches 80.7 percent. The results further demonstrate that the granular sludge is well tolerated, start-up time is fast, and the reaction cycle is shortened, thus making the reaction system more efficient at degrading propionic acid in the same time (see fig. 3).

It should be noted that, although the technical solutions of the present invention are described by specific examples, those skilled in the art can understand that the present disclosure should not be limited thereto.

Having described embodiments of the present disclosure, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen in order to best explain the principles of the embodiments, the practical application, or improvements made to the technology in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Industrial applicability

The production method of granular sludge provided by the invention can be industrially applied.

Claims (10)

1. A method for preparing granular sludge for degrading propionic acid to produce methane is characterized by comprising the following steps:

a step of mixing, in which the inoculum sludge and a feed matrix comprising a complex carbon source comprising glucose and propionate are added to a reactor to form a mixed system;

a step of acclimating the inoculum sludge by the composite carbon source to obtain the granular sludge for degrading propionic acid to generate methane,

in the step of acclimatization, the total organic load of the mixed system is controlled to be gradually increased by increasing the concentration of the feeding substrate and shortening the hydraulic retention time, and the initial glucose_CODPropionate salts_CODThe ratio of the first to the second is kept above 3.5:1,

the glucose is_CODRepresents the COD value provided by glucose, the propionate_CODRepresents the COD value provided by propionate;

in the step of domestication, the adjustment range of the total organic load value of the mixed system is 0.5-10; the adjustment range of the total COD value of the mixed system is 300-2500 mg/L; the adjustment range of the hydraulic retention time is 3-15 hours.

2. The method according to claim 1, wherein the propionate is selected from one or more of the alkali metal salts of propionic acid.

3. The method according to claim 1 or 2, characterized in that said step of acclimatization comprises at least three phases:

the first stage, controlling the glucose in the mixed system_CODPropionate salts_COD3.5: 1-4.5: 1, total organic load of 0.5-4.5, and hydraulic retention time of 10-15 hours;

a second stage of controlling the glucose in the mixed system_CODPropionate salts_COD1.8: 1-2.5: 1, total organic load 3.5-5, and hydraulic retention time 10-15 hours;

a third stage of controlling the glucose in the mixed system_CODPropionate salts_COD1.8: 1-2.5: 1, total organic load 5-10, and hydraulic retention time 3-10 hours.

4. The method according to claim 3, wherein in the first stage, the concentration of the feeding substrate is gradually increased so that the total COD value in the system is adjusted within the range of 300-2000 mg/L.

5. The method of claim 3, wherein the mixed system glucose is present in each stage_CODPropionate salts_CODKeeping constant; glucose in the second and third stages_CODPropionate salts_CODThe values are the same.

6. The method of claim 1 or 2, wherein the inoculum sludge comprises propionic acid-degraded sludge and anaerobically digested sludge; the propionic acid degradation sludge is sludge obtained by domesticating propionic acid or a salt thereof as a unique carbon source.

7. The method according to claim 6, wherein the inoculation ratio of the propionic acid-degraded sludge to the anaerobically digested sludge in the inoculum sludge is 1:4 to 1:2 by volume.

8. The method according to claim 1 or 2, wherein the feed matrix is wastewater containing metal ions, non-metal ions and metal salt hydrates, and the pH value of the feed matrix is 7.8-8.2.

9. A granular sludge produced by the method according to any one of claims 1 to 8, having an average particle size of 0.5 to 2.0 cm.

10. A treating agent for producing methane by anaerobic digestion, comprising the granular sludge according to claim 9.

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