CN109019852B - Method for reducing adverse effect of nano zinc oxide on anaerobic biological treatment of sewage - Google Patents
Method for reducing adverse effect of nano zinc oxide on anaerobic biological treatment of sewage Download PDFInfo
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Abstract
A method for reducing the adverse effect of nano zinc oxide on anaerobic biological treatment of sewage includes such steps as acclimatizing and culturing the inoculating mud, preparing dispersing liquid, and anaerobic digestion. The nano ferroferric oxide can partially hinder the effective contact of nano zinc oxide and microorganisms, the resistance capability of extracellular polymer to the nano zinc oxide is enhanced, and the uniionic effect between iron ions and zinc ions weakens the dissolution of the zinc ions and the biotoxicity thereof, so that the adverse effect of the nano zinc oxide on the anaerobic biological treatment of sewage is reduced; further controlling the action condition of the nano ferroferric oxide to construct an interspecies direct electron transfer path between the acid-producing bacteria and the methanogenic bacteria to optimize the methanation process, thereby achieving the purpose of reducing the adverse effect of the nano zinc oxide on the anaerobic biological treatment of the sewage.
Description
Technical Field
The invention belongs to the technical field of biological treatment of sewage (wastewater), and particularly relates to a method for preparing nano ferroferric oxide (Fe)3O4NPs) in a sewage anaerobic biological treatment system stressed by nano zinc oxide (ZnO NPs), and greatly reduces the toxicity of the ZnO NPs to the sewage anaerobic biological treatment.
Background
The nano material pollutant is a new pollution source to gradually attract the attention of environmental workers in the global scope, and particularly, the wide application of ZnO NPs causes the ZnO NPs to leak into the water environment in the processes of production, transportation, use and disposal or due to pollution accidents and to be retained in the residual sludge of sewage plants. The anaerobic digestion technology for treating sewage/sludge is a sustainable biological treatment mode, can synchronously realize pollution control and energy recovery, but ZnO NPs can have certain influence on the anaerobic digestion process. Previous studies by the inventors show that ZnO NPs inhibit the methanation process by affecting enzyme activity, microbial activity and poisoning of Extracellular Polymeric Substances (EPS) to anaerobic acid-producing bacteria and methanogenic bacteria, resulting in a decrease in methane yield.
Currently, there are very limited studies on the reduction of toxicity of ZnO NPs to bio-fermentation methane production. The only reports were from the Joge Gonzalez-Evitrella team at university, Arizona, USA. The report states the utilization of sulfide and Zn2+The combined formation of precipitates is the simplest and straightforward method to cut the toxicity of ZnO NPs to methane bacteria. However, in anaerobic fermentation systems, excessive sulfate substrate can lead to excessive proliferation of sulfate-reducing bacteria, thereby competing with methanogens for substrate production and producing H2S is also toxic to methanogens. In recent years, researchers have tried ZnThe iron doped in the O NPs reduces the dissolution rate of the ZnO NPs, reduces the dissolved zinc ions, and partially reduces the biological toxicity. However, the doping of the nanomaterial may change the characteristics of the nanomaterial itself, affecting the range and effect of its use. The research shows that the method for reducing the biotoxicity of the ZnO NPs from the pollution source has certain limitation, so a new method for reducing the toxicity of the ZnO NPs must be found in another way.
Disclosure of Invention
The invention mainly aims to provide a method for greatly reducing the adverse effect of ZnO NPs on anaerobic biological treatment of sewage (waste water) by utilizing an idea of waste treatment by waste without changing the characteristics of nano materials.
In order to achieve the above purpose, the invention adopts the following technical scheme: a method for reducing adverse effects of nano zinc oxide on anaerobic biological treatment of sewage comprises the following steps:
(1) firstly, carrying out acclimatization culture on granular sludge taken from a citric acid plant in an upflow anaerobic reactor in a laboratory to obtain inoculation sludge; (2) fermenting the Fe with particle size of 50-150 nm with nutrient solution3O4Respectively preparing NPs and ZnO NPs with particle size of 10-100 nm into stock solutions of 1g/L, respectively adding sodium dodecyl sulfate dispersant, and finally performing ultrasonic treatment for 0.5 h by using a KQ-250DE type numerical control ultrasonic instrument at 25 ℃ (power of 250W and frequency of 40 KHz) to obtain nano dispersion liquid with good dispersibility; (3) in a reactor, firstly, 1g/L ZnO NPs dispersion liquid is diluted by fermentation nutrient solution, then inoculation mud is added, and then the fermentation nutrient solution is used for adding Fe3O4And diluting the NPs dispersion liquid, and adding the diluted NPs dispersion liquid into a reactor for anaerobic digestion. Controlling the concentration of ZnO NPs to be 30-200 mg/g-TS (g-TS represents each g of dry matter inoculation mud), Fe3O4The concentration of NPs is 50-100 mg/g-TS, the concentration of TS of inoculation sludge (granular sludge) is 1000-2000 mg/L, the temperature is 35-50 ℃, and the anaerobic fermentation time is 5-10 days.
The specific characteristics of the scheme are that the main process of domesticating the inoculation mud in the step (1) is as follows: the initial COD of the influent water is 2000 mg/L, the organic load is 2 kg-COD/m3D, run for 20 days; then the water inflow is improvedOrganic load to 4 kg-COD/m3D, increasing the COD of the inlet water to 3000 mg/L, and domesticating for 20 days; then the organic load of the inlet water is increased to 8 kg-COD/m3D, increasing the COD of the inlet water to 4000 mg/L, and domesticating for 20 days; then the organic load of the inlet water is increased to 10 kg-COD/m3D, feeding water with COD of 5000 mg/L, and domesticating for 20 days.
The domesticated nutrient solution consists of a carbon source, a nitrogen source, a phosphorus source and water, wherein the carbon source comprises glucose, alcohol, sodium acetate, sodium propionate and sodium butyrate, the COD concentration of each carbon source is equal, and the nitrogen source is NH4Cl and KH as phosphorus source2PO4And K2HPO4(ii) a Domestication nutrient solution C: n: p = 100: 5: 1, initial pH of 6.8-7.6.
The particle size range of the ZnO NPs particles is 10-100 nm.
Said Fe3O4The particle size of the NPs particles is 50-150 nm.
The fermentation nutrient solution consists of a carbon source, a nitrogen source, a phosphorus source and water, wherein the carbon source comprises glucose and sodium acetate, and the COD ratio is 1: 1; the nitrogen source is NH4Cl and KH as phosphorus source2PO4And K2HPO4(ii) a And (3) nutrient solution C: n: p = 100: 5: 1; the COD of the nutrient solution is 3000-5000 mg/L, and the initial pH is 6.8-7.6.
The concentration of ZnO NPs is 100 mg/g-TS, Fe3O4NPs concentration is 50mg/g-TS, fermentation nutrient solution is fermented for 7 days under the conditions that COD is 3000 mg/L, TS concentration of inoculation mud is 1500 mg/L, initial pH is 7.2 +/-0.1 and temperature is 37 ℃.
A method for reducing adverse effects of nano zinc oxide on anaerobic biological treatment of sewage comprises the following steps:
(1) the method comprises the following steps of firstly, acclimatizing and culturing granular sludge taken from a citric acid plant in an upflow anaerobic reactor in a laboratory to obtain inoculation sludge. The main process of domesticating the inoculation mud comprises the following steps: the initial COD of the influent water is 2000 mg/L, the organic load is 2 kg-COD/m3D, run for 20 days; then gradually increasing the organic load of the inlet water to 4 kg-COD/m3D, increasing the COD of the inlet water to 3000 mg/L, and domesticating for 20 days; until the organic load of the inlet water is 8 kg-COD/m3D, increasing the COD of the inlet water to 4000 mg/L, and domesticating for 20 days; carrying againHigh water inflow organic load of 10 kg-COD/m3D, domesticating the influent water with COD of 5000 mg/L for 20 days; the domesticated nutrient solution consists of a carbon source (glucose, alcohol, sodium acetate, sodium propionate and sodium butyrate, the COD concentration of various carbon sources is equal), and a nitrogen source (NH)4Cl), a phosphorus source (KH)2PO4And K2HPO4) And water, nutrient solution C: n: p = 100: 5: 1, initial pH of 6.8-7.6.
(2) Adding a sodium dodecyl sulfate dispersing agent into 1g/L ZnO NPs stock solution, and then carrying out ultrasonic treatment (25 ℃, 0.5 h) on the stock solution by using a KQ-250DE type numerical control ultrasonic instrument (power 250W and frequency 40 KHz) to obtain ZnO NPs dispersion solution; the particle size range of the ZnO NPs particles is 10-100 nm.
(3) Fe at 1g/L3O4Adding sodium dodecyl sulfate dispersant into NPs stock solution, and performing ultrasonic treatment (25 deg.C, 0.5 h) on the stock solution with KQ-250DE type numerical control ultrasonic instrument (power 250W, frequency 40 KHz) to obtain Fe3O4NPs dispersions; said Fe3O4The particle size of the NPs particles is 50-150 nm.
(4) The experimental reactor uses a serum bottle with the volume of 500 mL, ZnO NPs dispersion liquid obtained in the step (2) is firstly diluted into the experimental reactor by fermentation nutrient solution, then inoculation mud is added, and finally Fe obtained in the step (3) is obtained by fermentation nutrient solution3O4Diluting the NPs dispersion liquid to a reactor to obtain 400 mL of mixed phase, quickly sealing the reactor by using a rubber plug after removing oxygen in the reactor by using nitrogen, placing the reactor in a constant-temperature (30-50 ℃) shaking table (120 rpm) for shaking culture, and periodically measuring the volume and components of gas, the pH value of a liquid phase, COD (chemical oxygen demand) and volatile short-chain fatty acids (VFAs); the nutrient solution consists of a carbon source (glucose and sodium acetate, the COD ratio is 1: 1) and a nitrogen source (NH)4Cl), a phosphorus source (KH)2PO4And K2HPO4) And water, nutrient solution C: n: p = 100: 5: 1, initial pH is 6.8-7.6; the concentration of ZnO NPs is controlled to be 30-200 mg/g-TS, Fe3O4The concentration of NPs is 50-100 mg/g-TS, the concentration of inoculation mud TS is 1000-2000 mg/L, and the anaerobic fermentation time is 5-10 days.
The method for reducing the adverse effect of ZnO NPs on methane fermentation provided by the invention has the recommended optimal parameters as follows: selecting 50mg/g-TS Fe with better dispersibility (sodium dodecyl sulfate dispersant and ultrasonic-assisted dispersion)3O4NPs are added into a sewage anaerobic biological treatment fermentation methane production system stressed by 100 mg/g-TS ZnO NPs, and waste liquid (fermentation nutrient solution) is fermented for 7 days under the conditions that COD is 3000 mg/L, TS concentration of inoculated sludge is 1500 mg/L, initial pH is 7.2 +/-0.1 and temperature is 37 +/-2 ℃, so that the adverse effect of the ZnO NPs on methane yield can be converted into 6.0% of promotion rate from 46.5% of inhibition rate, and the reduction rate of the methane yield inhibition rate reaches 100%.
The invention has the following beneficial effects: fe used in the method3O4The NPs are easy to adsorb on the surface of the ZnO NPs due to the inherent properties of the nanoparticles, the form or dissolution behavior of the ZnO NPs is changed, the effective contact of the ZnO NPs and microorganisms is partially hindered, and the resistance of extracellular polymers to the ZnO NPs is enhanced; in addition to this, Fe3O4Fe dissolved out from NPs3+/Fe2+Zn dissolved out with ZnO NPs2+The isoionic effect between Zn and Zn can also reduce Zn2+Elution of (2) and reduction of Zn2+The biological toxicity of the ZnO NPs and the toxic effect of the ZnO NPs on the anaerobic biological treatment of the sewage; the invention firstly proposes to use the non-toxic and strong-conductivity Fe3O4NPs, which control the action conditions thereof to construct a direct electron transfer path between acid-producing bacteria and methanogenic bacteria, regulate and control the composition and abundance of microorganisms with the function of producing methane by fermentation, realize the optimization of acidification and methanation processes stressed by ZnO NPs, and reduce the adverse effect of the ZnO NPs on the anaerobic biological treatment of sewage; the method has the advantages of obvious effect, simple and convenient operation and no change of process conditions and the characteristics of the nano material in the aspect of reducing the adverse effect of ZnO NPs on methane fermentation. Adding 50-100 mg/g-TS Fe3O4The NPs can reduce the adverse effect of 30-200 mg/g-TS ZnO NPs on the yield of methane from the maximum inhibition rate of 76.8% to about 42.2%, and the reduction rate of the adverse effect on the methane production by sewage (waste water) fermentation can reach more than 45%.
Detailed Description
Example 1 (comparative): a method for reducing adverse effects of nano zinc oxide on anaerobic biological treatment of sewage is carried out by the following steps: firstly, granular sludge taken from a reactor for treating citric acid wastewater is acclimated in an upflow anaerobic sludge blanket (UASB, effective volume 4L) in a laboratory, and an acclimated nutrient solution comprises carbon sources (glucose, alcohol, sodium acetate, sodium propionate and sodium butyrate, COD concentration of various carbon sources is equal), a nitrogen source (NH, sodium propionate and sodium butyrate), a sludge treatment system and a sludge treatment system4Cl), a phosphorus source (KH)2PO4And K2HPO4) And water, nutrient solution C: n: p = 100: 5: 1, initial pH of 6.8-7.6. The other major trace elements N, P, Ca, Mg and Fe are respectively from NH4Cl、KH2PO4、CaCl2、MgCl2·6H2O、FeCl3The concentration is 1000, 500, 200, 50 mg/L. The domestication process comprises the following steps: the initial COD of the domesticated nutrient solution is 2000 mg/L, the organic load is 2 kg-COD/m3D, run for 20 days; then gradually increasing the organic load of the inlet water to 4 kg-COD/m3D, increasing the COD of the inlet water to 3000 mg/L, and domesticating for 20 days; until the organic load of the inlet water is 8 kg-COD/m3D, increasing the COD of the inlet water to 4000 mg/L, and domesticating for 20 days; until the organic load of the inlet water is 10 kg-COD/m3D, domesticating the influent water with COD of 5000 mg/L for 20 days.
Inoculating anaerobic granular sludge domesticated by a UASB reactor into a reactor (a serum bottle) as inoculation sludge, wherein the TS concentration is 1500 mg/L, and then adding a fermentation nutrient solution to obtain a 400 mL mixed phase. The fermentation nutrient solution consists of a carbon source (glucose and sodium acetate, the COD ratio is 1: 1) and a nitrogen source (NH)4Cl), a phosphorus source (KH)2PO4And K2HPO4) And water, fermentation nutrient solution C: n: p = 100: 5: 1, initial pH 7.0. + -. 0.2, COD 3000 mg/L. After removing oxygen from the reactor with nitrogen, the reactor was rapidly sealed with a rubber stopper, placed in a constant temperature shaker at 120 rpm and 37. + -. 2 ℃ for shaking culture, and the volume and composition of the gas (when the gas yield was less than 5 mL, the fermentation reaction was considered to be complete), the pH of the liquid phase, COD and organic volatile acid, and the content of Extracellular Polymers of Sludge (EPS) were measured at regular intervals.
After the end of the fermentation (7 days), the cumulative methane, carbon dioxide and hydrogen production rates were measured to be 318, 127 and 64 mL, respectively. The pH of the liquid phase of the inoculation mud is 7.6 plus or minus 0.2; the COD degradation rate is more than 95 percent. The EPS content of the inoculation mud is 520 mg-COD/L.
Example 2 (comparative): a method for reducing adverse effects of nano zinc oxide on anaerobic biological treatment of sewage is carried out according to the following steps: first, the acclimatized inoculated sludge was added to a reactor (serum bottle) in the acclimatization manner of example 1 at a TS concentration of 1500 mg/L, and then the fermentation nutrient solution and the ZnO NPs dispersion were added to the serum bottle, and the effective volume of the mixed phase was 400 mL. The fermentation nutrient solution consists of a carbon source (glucose and sodium acetate, the COD ratio is 1: 1) and a nitrogen source (NH)4Cl), a phosphorus source (KH)2PO4And K2HPO4) And water, fermentation nutrient solution C: n: p = 100: 5: 1, the initial pH is 7.0 +/-0.2, and the COD is 3000 mg/L; the grain diameter of the ZnO NPs is controlled to be 50-100nm, and the exposure concentration of the ZnO NPs is 30 mg/g-TS. After removing oxygen in the reactor by nitrogen, the reactor was rapidly sealed by a rubber stopper, placed in a constant temperature shaking table at 120 rpm and 37 + -2 ℃ for shaking culture, and the volume and composition of the gas (when the gas yield was less than 5 mL, the fermentation reaction was considered to be complete), the pH of the liquid phase, COD and organic volatile acid, and the EPS content of the inoculated sludge were measured at regular times.
After 7 days of fermentation, the cumulative methane, carbon dioxide and hydrogen production rates were determined to be 298, 123 and 63 mL, respectively. Compared with example 1, the inhibition rate of 30 mg/g-TS ZnO NPs on the yield of methane is only 6.3%, the pH of the liquid phase is 7.7 +/-0.2, and the COD degradation rate is below 94%. The EPS content of the inoculated mud is reduced to 518 mg-COD/L.
Example 3: a method for reducing adverse effects of nano zinc oxide on anaerobic biological treatment of sewage is carried out by the following steps: first, the acclimatized inoculated sludge was added to a reactor (serum bottle) in the acclimatization manner of example 1 at a TS concentration of 1500 mg/L, then the fermentation nutrient solution and the ZnO NPs dispersion were added to the serum bottle, and finally Fe was added3O4NPs dispersion, the effective volume of the resulting mixed phase is 400 mL. The fermentation tankThe nutrient solution comprises carbon source (glucose and sodium acetate, COD ratio of 1: 1) and nitrogen source (NH)4Cl), a phosphorus source (KH)2PO4And K2HPO4) And water, fermentation nutrient solution C: n: p = 100: 5: 1, the initial pH is 7.0 +/-0.2, and the COD is 3000 mg/L; controlling the grain diameter of ZnO NPs to be 50-100nm, and controlling the exposure concentration of the ZnO NPs to be 30 mg/g-TS; control of Fe3O4The particle size of NPs is 50-100nm, Fe3O4The exposure concentration of NPs was 50 mg/g-TS. After removing oxygen in the reactor by nitrogen, the reactor was rapidly sealed by a rubber stopper, placed in a constant temperature shaking table at 120 rpm and 37 + -2 ℃ for shaking culture, and the volume and composition of the gas (when the gas yield was less than 5 mL, the fermentation reaction was considered to be complete), the pH of the liquid phase, COD and organic volatile acid, and the EPS content of the inoculated sludge were measured at regular times.
After 7 days of fermentation, the cumulative methane, carbon dioxide and hydrogen production rates were determined to be 355, 118 and 15 mL, respectively. In comparison with example 2, 50mg/g-TS Fe3O4The adverse effect of the ZnO NPs on the methane yield is converted from the inhibition rate of 6.3 percent to the promotion rate of 11.6 percent under the action of the NPs, and the reduction rate of the inhibition rate on the methane yield reaches 100 percent; wherein the calculation expression of the reduction rate is as follows: reduction rate =
The pH value of the liquid phase is increased to 7.8 +/-0.2, and the COD degradation rate is increased to more than 96%. The EPS content of the inoculation mud is increased to 510 mg-COD/L.
Example 4 (comparative): the present embodiment is different from embodiment 2 in that: the particle size of ZnO NPs was controlled to 50-100nm, and the exposed concentration of ZnO NPs was controlled to 100 mg/g-TS, under the same conditions as in example 2.
After 7 days of fermentation, the cumulative methane, carbon dioxide and hydrogen production rates were determined to be 170, 109 and 60 mL, respectively. As can be seen from comparison with example 1, the inhibition rate of 100 mg/g-TS ZnO NPs on the yield of methane is 46.5%, the pH of the liquid phase is slightly reduced to 7.3 +/-0.2, and the degradation rate of COD is reduced to below 60%. The EPS content of the inoculated mud is reduced to 212 mg-COD/L.
Example 5: the present embodiment is different from embodiment 4 in that: fe was additionally added to the fermentation system of example 43O4NPs dispersion, control of Fe3O4The particle size of NPs is 50-100nm, Fe3O4The NPs were exposed to a concentration of 50mg/g-TS, otherwise as in example 4.
After 7 days of fermentation, the cumulative methane, carbon dioxide and hydrogen production rates were determined to be 337, 114 and 13 mL, respectively. In comparison with example 4, 50mg/g-TS Fe3O4The adverse effect of the ZnO NPs on the methane yield is converted from the inhibition rate of 46.5 percent to the promotion rate of 6.0 percent by the action of the NPs, and the reduction rate of the inhibition rate on the methane yield reaches 100 percent; the pH value of the liquid phase is increased to 7.8 +/-0.2, and the COD degradation rate is increased to more than 96%. The EPS content of the inoculation mud is increased to 510 mg-COD/L.
Example 6: this embodiment is different from embodiment 5 in that: said Fe3O4The NPs concentration was 100 mg/g-TS, the other was the same as in example 5.
After 7 days of fermentation, the cumulative methane, carbon dioxide and hydrogen production rates were measured to be 302, 104 and 19 mL, respectively. Compared with example 4, the added Fe of 100 mg/L in this example3O4NPs cause the inhibition rate of ZnO NPs on the methane yield to be reduced from 46.5 percent to 5.0 percent, and the reduction rate of the inhibition rate on the methane yield reaches 89.2 percent; the pH value of the liquid phase is increased to 7.9 +/-0.2, and the COD degradation rate is increased to more than 85%. The EPS content of the inoculated mud is increased to 435 mg-COD/L.
Example 7: this embodiment is different from embodiment 6 in that: said Fe3O4The particle size of the NPs is 100-150nm, Fe3O4The NPs concentration was 100 mg/g-TS, and the other conditions were the same as in example 6.
After 7 days of fermentation, the cumulative methane, carbon dioxide and hydrogen production rates were measured to be 302, 104 and 19 mL, respectively. Compared with example 4, the added Fe of 100 mg/L in this example3O4NPs enable the inhibition rate of ZnO NPs on the methane yield to be reduced from 46.5% to 15.2%, and the reduction rate of the inhibition rate on the methane yield reaches 67.1%; the pH value of the liquid phase is increased to 7.9 +/-0.2, and the COD degradation rate is increased to more than 80%. The EPS content of the inoculated mud is increased to 405 mg-COD/L.
Example 8 (comparative): the present embodiment is different from embodiment 2 in that: the exposed concentration of ZnO NPs was 200 mg/g-TS, and the rest was the same as in example 2.
After 7 days of fermentation, the cumulative methane, carbon dioxide and hydrogen yields were 74, 90 and 54 mL, respectively. Compared with example 1, the inhibition rate of 200 mg/g-TS ZnO NPs on the yield of methane is 76.8%, the pH value of the liquid phase is reduced to 7.0 +/-0.2, and the COD degradation rate is reduced to below 30%. The EPS content of the inoculated mud is reduced to 102 mg-COD/L.
Example 9: the present embodiment is different from embodiment 8 in that: fe was additionally added to the fermentation system of example 83O4NPs dispersion, control of Fe3O4The particle size of NPs is 50-100nm, Fe3O4The NPs were exposed to a concentration of 50mg/g-TS, otherwise as in example 8.
After 7 days of fermentation, the cumulative methane, carbon dioxide and hydrogen production rates were determined to be 184, 110 and 32 mL, respectively. In comparison with example 8, this example added 50mg/g-TS Fe3O4NPs cause the inhibition rate of ZnO NPs on the methane yield to be reduced from 76.8 percent to 42.2 percent, and the reduction rate of the inhibition effect is 45.0 percent; the pH value of the liquid phase is increased to 7.3 +/-0.2, and the COD degradation rate is increased to more than 50%. The EPS content of the inoculated mud is increased to 243 mg-COD/L.
Example 10: this embodiment is different from embodiment 9 in that: said Fe3O4The particle size of the NPs is 100-150nm, Fe3O4The NPs were exposed at a concentration of 100 mg/g-TS, the other being the same as in example 9.
After 7 days of fermentation, the cumulative methane, carbon dioxide and hydrogen production rates were measured to be 256, 104 and 22 mL, respectively. As compared with example 8, the addition of 100 mg/g-TS Fe in this example3O4NPs cause the inhibition rate of ZnO NPs on the methane yield to be reduced from 76.8 percent to 39.5 percent, and the reduction rate of the inhibition effect is 48.6 percent; the pH value of the liquid phase is increased to 7.1 +/-0.2, and the COD degradation rate is increased to more than 30%. The EPS content of the inoculated mud is increased to 203 mg-COD/L.
Example 11: this embodiment is different from embodiment 5 in that: control of Fe3O4The NPs were exposed at a concentration of 25 mg/g-TS, otherwise as in example 5.
After 7 days of fermentation, the cumulative methane, carbon dioxide and hydrogen production rates were measured to be 166, 96 and 63 mL, respectively. As can be seen in comparison with example 4, 25 mg/g-TS Fe3O4The effect of NPs did not produce significant change to ZnO NPs on methane production, the methane inhibition ratio of this example was 47.8%, and Fe was added3O4The inhibition rates of the first 46.5% of NPs are not very different, and are supposed to be mainly two-way. One is low concentration of Fe3O4NPs (25 mg/g-TS) can no longer prevent the effective contact of high-concentration ZnO NPs (100 mg/g-TS) with microorganisms; second, 25 mg/g-TS Fe3O4Fe released by NPs3+/Fe2+Is not enough to meet the needs of the microorganism producing the demand. The pH value of the liquid phase is 7.4 +/-0.2, and the COD degradation rate is below 62%. The EPS content of the inoculated mud is 226 mg-COD/L.
Example 12: this embodiment is different from embodiment 11 in that: the carbon source for the fermentation broth no longer consisted of glucose and sodium acetate, but was provided by only sodium acetate alone, otherwise the conditions were the same as in example 11.
After 7 days of fermentation, the cumulative methane, carbon dioxide and hydrogen production rates were determined to be 162, 100 and 65 mL, respectively. In comparison with example 4, 25 mg/g-TS Fe3O4The effect of NPs does not produce obvious change to the yield of methane by ZnO NPs, and the methane inhibition rate of the embodiment is 49.1 percent, and is specific to Fe3O4The inhibition rate of 46.5% before NPs addition is slightly larger. On the one hand, the low Fe concentration as illustrated in example 113O4The cause of NPs, the most important, can be attributed to changes in the substrate carbon source. When the methanogenic nutrient carbon source consists of glucose and sodium acetate, the methanation process involves two processes of acidification and methanation, the methanation process involves hydrogen type and acetic acid type methane production fermentation ways, and Fe is added3O4The direct electron transfer system between the acid-producing bacteria and the methanogenic bacteria constructed by the NPs and the methanogenic bacteria interruns the methane production system can promote the methane yield; whereas when the methanogenic nutrient carbon source consists only of sodium acetate, the methanogenic process involves only an acetate-type single pathway for methanogenesis， Fe3O4NPs are no longer able to successfully establish direct electron transfer between acid-forming bacteria and methanogenic bacteria, and thus are no longer able to curtail the adverse effects of ZnO NPs on methanogenesis. The pH value of the liquid phase is 7.6 +/-0.2, and the COD degradation rate is below 60 percent. The EPS content of the inoculation mud is 223 mg-COD/L.
Example 13: the present embodiment is different from embodiment 12 in that: control of Fe3O4The NPs were exposed at a concentration of 200 mg/g-TS, otherwise as in example 12.
After 7 days of fermentation, the cumulative methane, carbon dioxide and hydrogen production rates were measured to be 140, 98 and 52 mL, respectively. In comparison with example 4, 200 mg/g-TS Fe3O4The effect of the NPs causes the inhibition rate of the ZnO NPs on the methane production to be increased from 46.5 percent to 56.0 percent. High dose of Fe3O4NPs although able to hinder the effective contact of stressors ZnO NPs with microorganisms, high doses of Fe3O4NPs also prevent the microorganisms from contacting the fermentation nutrient source, thereby reducing the methanogenic efficiency. The pH value of the liquid phase is 7.6 +/-0.2, and the COD degradation rate is below 54 percent. The EPS content of the inoculation mud is 203 mg-COD/L.
Claims (7)
1. A method for reducing adverse effects of nano zinc oxide on anaerobic biological treatment of sewage is characterized by comprising the following steps: (1) firstly, carrying out acclimatization culture on granular sludge taken from a citric acid plant in an upflow anaerobic reactor in a laboratory to obtain inoculation sludge; (2) fermenting the Fe with particle size of 50-150 nm with nutrient solution3O4Respectively preparing 1g/L stock solution from NPs and ZnO NPs with particle size of 10-100 nm, respectively adding sodium dodecyl sulfate dispersant, and finally performing ultrasonic treatment for 0.5 h at 25 ℃ by using a numerical control ultrasonic instrument to obtain a nano dispersion liquid with good dispersibility; (3) in a reactor, firstly, 1g/L ZnO NPs dispersion liquid is diluted by fermentation nutrient solution, then inoculation mud is added, and then the fermentation nutrient solution is used for adding Fe3O4Diluting the NPs dispersion liquid, and adding the diluted NPs dispersion liquid into a reactor for anaerobic digestion; the concentration of ZnO NPs is controlled to be 30-200 mg/g-TS, Fe3O4NPs concentration is 50-100 mg/g-TS, and inoculation mud TS concentration is 1000-2000 mg/L, the temperature is 35-50 ℃, and the anaerobic fermentation time is 5-10 days.
2. The method for reducing the adverse effect of nano zinc oxide on the anaerobic biological treatment of sewage according to claim 1, wherein the main process of domesticating the inoculation sludge in the step (1) is as follows: the initial COD of the influent water is 2000 mg/L, the organic load is 2 kg-COD/m3D, run for 20 days; then the organic load of the inlet water is increased to 4 kg-COD/m3D, increasing the COD of the inlet water to 3000 mg/L, and domesticating for 20 days; then the organic load of the inlet water is increased to 8 kg-COD/m3D, increasing the COD of the inlet water to 4000 mg/L, and domesticating for 20 days; then the organic load of the inlet water is increased to 10 kg-COD/m3D, feeding water with COD of 5000 mg/L, and domesticating for 20 days.
3. The method for reducing adverse effects of nano zinc oxide on anaerobic biological treatment of sewage according to claim 1, wherein the acclimatization nutrient solution required for acclimatization culture of granular sludge in the step (1) is composed of a carbon source, a nitrogen source, a phosphorus source and water, the carbon source comprises glucose, alcohol, sodium acetate, sodium propionate and sodium butyrate, COD concentration of each carbon source is equal, and the nitrogen source is NH4Cl and KH as phosphorus source2PO4And K2HPO4(ii) a Domestication nutrient solution C: n: p = 100: 5: 1, initial pH of 6.8-7.6.
4. The method for reducing the adverse effect of nano zinc oxide on anaerobic biological treatment of wastewater as claimed in claim 1, wherein said ZnO NPs particles have a particle size in the range of 10-100 nm.
5. The method for reducing the adverse effect of nano zinc oxide on anaerobic biological treatment of wastewater as claimed in claim 1, wherein said Fe is3O4The particle size of the NPs particles is 50-150 nm.
6. The method for reducing adverse effects of nano zinc oxide on anaerobic biological treatment of wastewater as claimed in claim 1, wherein said fermentation nutrient solution is composed of carbon source and nitrogen sourceThe carbon source comprises glucose and sodium acetate, and the COD ratio is 1: 1; the nitrogen source is NH4Cl and KH as phosphorus source2PO4And K2HPO4(ii) a And (3) nutrient solution C: n: p = 100: 5: 1; the COD of the nutrient solution is 3000-5000 mg/L, and the initial pH is 6.8-7.6.
7. The method as claimed in claim 1, wherein the concentration of ZnO NPs is 100 mg/g-TS, Fe3O4NPs concentration is 50mg/g-TS, fermentation nutrient solution is fermented for 7 days under the conditions that COD is 3000 mg/L, TS concentration of inoculation mud is 1500 mg/L, initial pH is 7.2 +/-0.1 and temperature is 37 ℃.
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