CN115448438A - Two-section type upflow fixed bed for treating chromium-containing electroplating wastewater - Google Patents
Two-section type upflow fixed bed for treating chromium-containing electroplating wastewater Download PDFInfo
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- 239000011651 chromium Substances 0.000 title claims abstract description 55
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/70—Treatment of water, waste water, or sewage by reduction
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/28—Treatment of water, waste water, or sewage by sorption
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/20—Heavy metals or heavy metal compounds
- C02F2101/22—Chromium or chromium compounds, e.g. chromates
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- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Water Treatment By Sorption (AREA)
Abstract
The invention discloses a two-section type upflow fixed bed for treating chromium-containing electroplating wastewater, which comprises a fixed bed I, a transfer regulating tank and a fixed bed II which are sequentially connected, wherein: the fixed bed I, the transfer regulating tank and the fixed bed II all adopt an up-flow water passing mode; nylon nets are filled in the upper part and the lower part of the adsorption column of the fixed bed I and the fixed bed II; the fixed bed I selects composite modified fungus bran biochar adsorbent particles as an adsorbent; the fixed bed II selects cetyl trimethyl ammonium bromide modified biochar pellets as an adsorbent; and a peristaltic pump is arranged between the transfer regulating tank and the fixed bed II. The two-section upflow fixed bed has the advantages of high adsorption efficiency, strong stability, integration of Cr (VI) reduction and attenuation, pH buffering, cr (III) fixation and the like.
Description
Technical Field
The invention belongs to the technical field of environmental protection, and relates to a two-section upflow fixed bed for treating chromium-containing electroplating wastewater.
Background
With the rapid development of economy and industry in China, the electroplating industry is widely applied to heavy industry, light industry and electronic industry as one of the cornerstones of modern manufacturing industry. If the electroplating wastewater is directly discharged without treatment or is discharged illegally without strict treatment procedures according to standards, the safety of drinking water of residents can be directly threatened, and underground water, surface water and industrial water are polluted. The quantity of enterprises is large but the development conditions are different, the discharge requirement of the electroplating wastewater is high, the discharge supervision difficulty of the waste liquid is high, the components of the waste liquid are complex, and the treatment difficulty is high. Taking a chromium plating workshop as an example, the chromic anhydride which can be effectively deposited on the surface of a plated part only accounts for 15-25% of the total amount, and 40-50% of chromic anhydride enters the wastewater in the cleaning process to form chromium-containing wastewater which is difficult to treat. The main pollutants in the chromium-containing wastewater are hexavalent chromium, trivalent chromium, metal ions such as copper and iron, sulfuric acid and the like, the concentration of the hexavalent chromium in the general wastewater produced in a chromium plating workshop is below 200 mg/L, and the pH value is between 4 and 6. Chromium also exists in the comprehensive wastewater of the electroplating workshop, the total chromium concentration is generally within the range of 50 to 300 mg/L, and the pH value is between 1 and 10. Cr (VI) is far more toxic than Cr (III), has sensitization, teratogenicity and carcinogenicity, and is classified as a human occupational carcinogen by the international cancer research institution.
The adsorption is one of the traditional methods for treating wastewater, and has the advantages of simple operation, high benefit, low cost and the like. As scientists explore the structure and nature of different pollutants, a wide variety of adsorbents and adsorption devices have been developed. The bioadsorption method is a method for removing metal ions in an aqueous solution by utilizing the vital functions of certain active organisms or the chemical structures and component characteristics of inactive organisms to adsorb metal ions dissolved in water and then carrying out solid-liquid two-phase separation. The biological adsorption method has the advantages of low cost, environmental friendliness, high adsorption efficiency and the like, is suitable for treating heavy metal wastewater with large volume and low concentration, and can reduce the concentration of heavy metal in the effluent to the national permitted discharge level. Cr (VI) in the electroplating wastewater has high mobility and high toxicity, and compared with the Cr (III), cr (VI) has low mobility and low toxicity, and aiming at the chemical characteristics of different valence states of Cr, an adsorbent with both adsorption capacity and reduction capacity can be designed, and the adsorbent can be reduced while adsorbing Cr (VI), so that the Cr (VI) concentration is reduced, the toxicity is weakened, and the pollution to the environment is reduced. In the practical application process, the use scene of the adsorbent is considered at the same time, compared with application scenes such as soil and the like, the wastewater has fluidity, and the adsorbent meets the requirement of completing the adsorption process in a dynamic process. Fixed bed units, also known as packed bed reactors, are a type of reactor packed with solid catalyst or solid reactants to achieve a heterogeneous reaction process. The solids are usually in granular form and are packed in a bed of a certain height (or thickness). The bed is stationary and the fluid is passed through the bed for reaction. The fixed bed device can be divided into an up-flow type and a down-flow type according to the flowing direction of liquid, compared with the down-flow type, the up-flow type can relatively avoid the influence of gravity, the liquid is more fully contacted with the solid, and the treatment effect and the treatment efficiency are higher.
Disclosure of Invention
Aiming at the existing characteristics of Cr (VI) in electroplating wastewater and a practical application device for wastewater treatment, the invention provides a two-section upflow fixed bed system which takes nano FeS-loaded mushroom bran biochar with adsorption, reduction and attenuation functions and CTAB (cetyl trimethyl ammonium bromide) modified mushroom bran biochar with a fixing function as fillers for treating chromium-containing electroplating wastewater.
The purpose of the invention is realized by the following technical scheme:
the utility model provides a two segmentation upflow fixed beds of processing chromium-containing electroplating effluent, includes fixed bed I, transfer equalizing basin and fixed bed II that connect gradually, wherein:
the fixed bed I, the transfer regulating tank and the fixed bed II all adopt an up-flow water passing mode;
nylon nets are filled in the upper part and the lower part of the adsorption column of the fixed bed I and the fixed bed II;
the fixed bed I selects composite modified fungus bran biochar adsorbent particles as an adsorbent;
the fixed bed II selects cetyl trimethyl ammonium bromide modified biochar (CTAB-BC) balls as an adsorbent;
and a peristaltic pump is arranged between the transfer regulating tank and the fixed bed II.
In the invention, the initial concentration of hexavalent chromium in the inlet water of the fixed bed I is 10 to 30 mg/L.
In the invention, the water inlet speed of the fixed bed I and the fixed bed II is 2 to 4 mL/min.
In the invention, the filling height of the adsorbent in the fixed bed I and the fixed bed II is 5-15 cm.
In the invention, the preparation method of the composite modified fungus bran biochar adsorbent particle comprises the following steps:
step (1) pretreatment of mushroom bran
Sterilizing Tilia Miqueliana Maxim with high temperature steam, oven drying in constant temperature drying incubator to constant weight, pulverizing, sieving, and storing in dry environment;
in the step, the fungus chaff is obtained by carrying out edible fungus substitute cultivation by utilizing straw, wood chips and other raw materials, and the obtained culture medium residue is commonly called edible fungus cultivation waste, fungus residue or excess material; is a compound of components such as edible fungus mycelium residues and crude fibers with structure changed by enzymolysis of the edible fungus;
in the step, the autoclaving temperature is 121 ℃, the sieving mesh number is 40 meshes, and the drying temperature is 80 to 100 ℃;
step (2) preparation of mushroom bran biochar
Repeatedly washing the fungus bran powder with distilled water to remove surface impurities, placing in a constant-temperature drying incubator, drying to constant weight, sieving, placing the fungus bran powder under a screen in a muffle furnace, burning under limited oxygen condition to obtain charcoal, taking out, homogenizing, and storing in a dry environment for later use;
in the step, the drying temperature is 40 to 60 ℃, the sieving mesh number is 60 meshes, the firing temperature is 350 to 400 ℃, and the firing time is 1 to 3 hours;
step (3) alkali modification of mushroom bran biochar
Selecting NaOH as an alkali modifier, adding the mushroom bran biochar into a NaOH solution with a solid-to-liquid ratio of 0.1%, placing the mushroom bran biochar in a constant-temperature shaking table for vibration modification, filtering, repeatedly washing with deionized water until the pH value is stable, placing the mushroom bran biochar in a constant-temperature drying incubator for drying to constant weight to obtain mushroom bran biochar pretreated by the NaOH, and storing the mushroom bran biochar in a dry environment for later use;
in the step, 8-12 g of mushroom fungus chaff biochar is added into every 200 mL of NaOH solution, the temperature of a constant temperature shaking table is set to be 298K, the rotating speed is 150-180 r/min, the time is 1-3 h, and the drying temperature is 30-40 ℃;
step (4) nano FeS load of alkali modified mushroom bran biochar
Selecting FeSO 4 ·7H 2 O and Na 2 S·9H 2 The method is characterized in that O is used as a Fe source and an S source, a chemical synthesis method is adopted to prepare nano FeS, and the nano FeS is loaded on mushroom bran biochar under the stabilizing action of carboxymethyl cellulose (CMC), and the method comprises the following specific steps: to 211mLFeSO 4 ·7H 2 Adding 0.2 to 0.25 g of alkali modified fungus chaff biochar into a mixed solution of O and CMC, and dripping 9mLNa at a constant speed 2 S·9H 2 O solution in N 2 Stirring for 0.5 to 1 hour under magnetic force in the atmosphere to fully mix, sealing and aging for 20 to 30 hours in the dark, filtering, washing with deionized water for 2 to 4 times to remove Na remaining on the surface of the biochar 2 SO 4 And the obtained nano FeS load modified mushroom bran biochar is subjected to vacuum freeze drying and then is stored in a glass plate;
in this step, feSO 4 ·7H 2 The O solution is composed of 0.6 to 0.8g of FeSO 4 ·7H 2 O is in N 2 Dissolved in 200 mL of deionized water under the atmosphere;
in the step, the CMC solution is prepared by dissolving 0.2 to 0.25 g of CMC in 11mL of deionized water;
in this step, each 211mL of the mixed solution contains 0.6 to 0.8g of FeSO 4 ·7H 2 O and 0.2 to 0.25 g CMC;
in this step, na 2 S·9H 2 The O solution is composed of 0.6 to 0.65 g of Na 2 S·9H 2 O is dissolved in 9ml of deionized water;
preparation of composite modified fungus chaff biochar adsorbent particles in step (5)
Uniformly mixing the nano FeS-loaded and modified mushroom bran biochar with a sodium alginate solution according to the w/v =1 2 Preparing granular adsorbent in the solution, filtering, repeatedly washing with deionized water, preparing immediately before use, and temporarily storing in oxygen-removing deionized water;
in the step, the concentration of the sodium alginate solution is 1.8 percent (w/v);
in this step, caCl 2 The concentration of the solution was 4% (w/v);
in this step, the surface area of the adsorbent was 11.737 m 2 Per g, pore volume of 0.051 cm 3 In terms of/g, the mean pore diameter was 17.513 nm.
Compared with the prior art, the invention has the following advantages:
1. the two-section upflow fixed bed has the advantages of high adsorption efficiency, strong stability, integration of Cr (VI) reduction and attenuation, pH buffering, cr (III) fixation and the like.
2. The composite modified fungus chaff biochar adsorbent used by the invention is prepared by taking waste fungus chaff obtained after edible fungi are harvested as a material, so that agricultural waste is recycled, and the composite modified fungus chaff biochar adsorbent has the advantages of rich raw material sources, low cost and simple production process.
3. The composite modified mushroom bran biochar adsorbent mainly utilizes the large specific surface area, rich pore structures and active functional groups of biochar to carry out nano FeS load modification on the biochar, so that toxic hexavalent chromium ions existing in the form of anions in wastewater can be adsorbed and reduced by means of enhancing redox and the like, and the effect of fully reducing toxicity is achieved, and therefore the using effect of the adsorbent is strong.
Drawings
FIG. 1 is a flow diagram of a two-stage upflow fixed bed operation;
FIG. 2 is a graph of the effect of hexavalent chromium initial concentration on the breakthrough curve;
FIG. 3 is a graph showing the effect of water entry rate on penetration curve;
FIG. 4 is the effect of fixed bed packing height on the breakthrough curve;
FIG. 5 is a graph showing the change in total chromium concentration in a two-stage upflow fixed bed.
Detailed Description
The technical solution of the present invention is further described below with reference to the accompanying drawings, but not limited thereto, and any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be covered by the protection scope of the present invention.
Example 1: design of two-section type upflow fixed bed
As shown in fig. 5, the two-stage upflow fixed bed consists of a fixed bed I, a transfer regulating reservoir and a fixed bed II, wherein the fixed bed I, the transfer regulating reservoir and the fixed bed II all adopt an upflow water passing mode, and a peristaltic pump is used as a power supply device and plays a role in controlling the water flow velocity. The fixed bed I and the fixed bed II both use a PC tube with the inner diameter of 1.2 cm and the total length of 30 cm as an adsorption column. Nylon nets are filled in the upper part and the lower part of the adsorption column to fix and fill the adsorbent to prevent the adsorbent from drifting along with the water inflow solution. The fixed bed I selects composite modified fungus bran biochar adsorbent particles as a filling adsorbent, and aims to reduce Cr (VI) in high-acidity comprehensive wastewater into Cr (III) and buffer pH (potential of hydrogen) to play a role in full attenuation. The transit regulating reservoir plays a role in stabilizing and regulating the pH value, and the pH value is stabilized within a range of 5.5 to 6. And a hexadecyl trimethyl ammonium bromide modified biochar (CTAB-BC) globule is selected as a filling adsorbent in the fixed bed II, and the CTAB-BC is a good cationic type biological adsorbent for fixing chromium ions, so that the total chromium is fixed, and the effluent of the system reaches the discharge standard.
The operation procedure of the fixed bed is as follows: and after Cr (VI) solution or actual wastewater with different fixed bed parameters flows into the fixed bed I through the peristaltic pump I, sampling at regular time to test Cr (VI) and total chromium concentration, starting the peristaltic pump II to pump liquid into the fixed bed II after Cr (VI) appears in a water outlet sample test, and sampling at regular time to test total chromium content.
Example 2: preparation of composite modified mushroom bran biochar adsorbent particles
(1) Pretreatment of mushroom bran
Sterilizing Lentinus Edodes Fugu Miqueliana Maxim with steam at 121 deg.C, oven drying at 80 deg.C in a constant temperature drying incubator to constant weight, pulverizing, sieving with 40 mesh sieve, and storing in dry environment.
(2) Preparation of mushroom fungus chaff biochar
Repeatedly washing Lentinus Edodes bran powder with distilled water to remove surface impurities, oven drying at 40 deg.C in a constant temperature drying incubator to constant weight, sieving with 60 mesh sieve, baking Lentinus Edodes bran powder under the sieve in a muffle furnace under oxygen-limiting condition at 350 deg.C for 2 hr, taking out biochar, homogenizing, and storing in dry environment, and marking as NBC.
(3) Alkali modification of mushroom fungus chaff biochar
Selecting NaOH as an alkali modifier, adding 10 g of mushroom fungus chaff biochar into 200 mL of NaOH solution with a solid-to-liquid ratio of 0.1%, placing the mixture in a constant-temperature shaking table, shaking and modifying for 2 h under the conditions of 298K and 160 r/min, filtering, repeatedly washing with deionized water until the pH value is stable, placing the mixture in a constant-temperature drying incubator, drying at 35 ℃ to constant weight to obtain the mushroom fungus chaff biochar pretreated by the NaOH, and storing the mushroom fungus chaff biochar in a drying environment for later use.
(4) Nano FeS load (nFES-BC) of alkali modified mushroom bran biochar
Selecting FeSO 4 ·7H 2 O and Na 2 S·9H 2 The O is used as a Fe source and an S source, a chemical synthesis method is adopted to prepare the nano FeS, and the nano FeS is loaded on the mushroom bran biochar under the stabilizing action of carboxymethyl cellulose (CMC). To 200 mLFeSO 4 ·7H 2 Adding 0.22 g of biochar into the mixed solution of O and CMC, and dripping Na into the mixed solution at a constant speed 2 S·9H 2 O, in N 2 Stirring with magnetic force for half an hour under atmosphere to mix thoroughly, sealing and aging in dark for 24 h, filtering, washing with deionized water for 3 times to remove residual Na on the surface of biochar 2 SO 4 And the like. The obtained nano FeS loaded alkali modified mushroom biochar (nFeS-BC) is subjected to vacuum freeze drying and then stored in a glass plate.
(5) nFeS-BC adsorbent particle preparation
Uniformly mixing the mushroom fungus chaff biochar modified by the nano FeS loaded alkali and sodium alginate with the concentration of 1.8% (w/v) according to the mass ratio of 1 2 Preparing granular adsorbent in the solution, filtering, repeatedly washing with deionized water, preparing immediately before use, and temporarily storing in oxygen-removing deionized water. When in use, the excessive moisture on the surface of the small ball is absorbed and evenly filled into the fixed bed I.
Example 3: application of composite modified mushroom bran biochar adsorbent in dynamic adsorption of hexavalent chromium
In this embodiment, a fixed bed continuous flow process is adopted, the modified mushroom bran biochar (nFeS-BC) immobilized adsorbent prepared in example 2 is filled in an adsorption column to prepare a fixed bed I, and the CTAB-BC immobilized adsorbent is filled in the adsorption column to prepare a fixed bed II. By the ratio C of the effluent metal ion concentration to the influent metal ion concentration e /C i The ordinate and the abscissa represent the time t. Get C e /C i 5% of the total amount of the components is the penetration point, and the time at this point is the penetration time t b . It is generally considered that when C e /C i At 95%, the adsorption column no longer has the adsorption capacity, so this time is called the exhaustion point, and this time is called the exhaustion time t exh . In this way, the penetration curves of the adsorbent for removing hexavalent chromium from the wastewater under different initial concentrations of hexavalent chromium (10, 20, 30 mg/L) (see FIG. 2), different water inlet speeds (2, 3, 4 mL/min) (see FIG. 3) and different filling heights (5, 10, 15 cm) (see FIG. 4) were determined. As can be seen, higher initial concentrations, higher flow rates and shorter packing layer heights will result in faster bed breakthrough and shorter breakthrough times for the adsorption column. As can be seen from FIGS. 2 to 4, the initial concentration of hexavalent chromium is preferably 20 mg/L, the water inlet rate is preferably 2 mL/min, and the filling height is preferably 10 cm.
Example 4: regeneration of adsorbents
In this example, a 0.1M HCl solution was used as a regenerant, the spent immobilized nfet s-BC adsorbent in fixed bed I was washed with the regenerant in an up-flow and down-flow cycle, the flow direction was changed to cycle three times, the flow rate of the regenerant was 10 mL/min, the bed was then washed with deionized water until the pH of the effluent was about 5.5, air was pumped in to remove excess deionized water from the column, and then the next cycle of adsorption test was performed.
The adsorption capacity, breakthrough time, and exhaustion time after each regeneration cycle are shown in table 1. As can be seen from table 1, the adsorption amount of hexavalent chromium by the immobilized nfet s-BC adsorbent gradually decreased with increasing cycle number. After the first cycle, the adsorbent capacity is reduced to 2.02 mg/g, and after the second and third cycles, the reduction of the adsorption capacity is small and still reaches 1.91 mg/g and 1.86 mg/g. After 5 cyclesThe adsorption capacity was 50% before regeneration, at which time the adsorption capacity was 1.24 mg/g, probably due to the oxidation of Fe on the surface of the adsorbent after dynamic adsorption of Cr (VI) by 0.1M HCl solution 3+ Removing the aged layer to expose Fe of the inner layer 2+ Active sites, thereby continuing to maintain the adsorption capacity of the fixed bed. Therefore, the modified fungus bran adsorbent can be recycled. Therefore, the two-section upflow fixed bed can be used as an effective integrated water treatment device for removing hexavalent chromium.
TABLE 1
Example 5: integral analysis of total chromium concentration variation trend of two-stage upflow fixed bed
The trend of the total chromium concentration of the effluent of the two-stage upflow fixed bed is shown in figure 5. In order to be able to analyze the overall performance of the fixed bed in a more intuitive manner, the two-stage fixed bed as a whole will be analyzed in terms of the change in the total chromium concentration. After the potassium dichromate solution and the real electroplating wastewater pass through the fixed bed I, the Cr (VI) concentration at the water outlet can be maintained in an undetectable state until the working time reaches the penetration point of the fixed bed I. However, analysis of the total chromium concentration can find that the total chromium concentration can be detected at the water outlet of the fixed bed I, which indicates that Cr (III) remains in the solution after passing through the fixed bed I, and the Cr (III) is lower in toxicity than Cr (VI) but still belongs to toxic substances, the total chromium discharge of the wastewater discharge port of the workshop or production facility cannot exceed 1.5 mg/L in the national Standard of the people's republic of China electroplating pollutant discharge Standard (GB 21900-2008), and the effluent of the fixed bed I cannot be directly discharged, and enters the fixed bed II after the pH value is buffered in the transfer pool. The total chromium concentration of the effluent of the fixed bed II can be maintained in an undetectable state, reaches the national discharge standard and can be discharged. From the overall view, the two-section upflow fixed bed can integrate the reduction, the fixation and the pH adjustment of Cr (VI), and has the advantages of simple flow, simple and convenient operation, low time cost and the like compared with the method for reducing Cr (VI) mentioned in the technical Specification of the national environmental protection standard electroplating wastewater treatment engineering of the people's republic of China.
Claims (10)
1. The utility model provides a two segmentation upflow fixed beds of processing chromium-containing electroplating effluent, its characterized in that two segmentation upflow fixed beds include fixed bed I, transfer equalizing basin and fixed bed II that connect gradually, wherein:
the fixed bed I, the transfer regulating tank and the fixed bed II all adopt an up-flow water passing mode;
nylon nets are filled in the upper part and the lower part of the adsorption column of the fixed bed I and the fixed bed II;
the fixed bed I selects composite modified fungus bran biochar adsorbent particles as an adsorbent;
the fixed bed II selects cetyl trimethyl ammonium bromide modified biochar pellets as an adsorbent;
and a peristaltic pump is arranged between the transfer regulating tank and the fixed bed II.
2. The two-stage upflow fixed bed for treating chromium-containing electroplating wastewater as claimed in claim 1, wherein the initial concentration of hexavalent chromium in the influent water to said fixed bed I is 10 to 30 mg/L.
3. The two-stage upflow fixed bed for treating chromium-containing electroplating wastewater as claimed in claim 1, wherein the water inlet speed of the fixed bed I and the fixed bed II is 2 to 4 mL/min.
4. The two-stage upflow fixed bed for treating chromium-containing electroplating wastewater as claimed in claim 1, wherein the filling height of the adsorbent in the fixed bed I and the fixed bed II is 5 to 15 cm.
5. The two-stage upflow fixed bed for treating chromium-containing electroplating wastewater as claimed in claim 1, wherein said composite modified fungus chaff biochar adsorbent particles are prepared by the following steps:
step (1) pretreatment of mushroom bran
Sterilizing Tilia Miqueliana Maxim with high temperature steam, oven drying in constant temperature drying incubator to constant weight, pulverizing, sieving, and storing in dry environment;
step (2) preparation of mushroom bran biochar
Repeatedly washing the fungus bran powder with distilled water to remove surface impurities, placing in a constant-temperature drying incubator, drying to constant weight, sieving, placing the fungus bran powder under a screen in a muffle furnace, burning under oxygen-limited conditions to obtain biochar, taking out, homogenizing, and storing in a dry environment for later use;
step (3) alkali modification of mushroom bran biochar
Selecting NaOH as an alkali modifier, adding 8-12 g of mushroom bran biochar into 200 ml of NaOH solution, placing the mushroom bran biochar in a constant-temperature shaking table for vibration modification, filtering, repeatedly washing with deionized water until the pH value is stable, placing the mushroom bran biochar in a constant-temperature drying incubator for drying to a constant weight to obtain NaOH-pretreated mushroom bran biochar, and storing the mushroom bran biochar in a dry environment for later use;
step (4) nanometer FeS load of alkali modified mushroom bran biochar
To 211mLFeSO 4 ·7H 2 Adding 0.2 to 0.25 g of alkali modified mushroom bran biochar into a mixed solution of O and CMC, and dripping 9mLNa at a constant speed 2 S·9H 2 O solution in N 2 Stirring for 0.5 to 1 hour by magnetic force in the atmosphere to be fully mixed, sealing and aging for 20 to 30 hours in a dark place, filtering, washing for 2 to 4 times by using deionized water to remove impurities remained on the surface of the biochar, and storing the obtained nano FeS load modified fungus chaff biochar in a glass plate after vacuum freeze drying;
preparation of composite modified fungus chaff biochar adsorbent particles in step (5)
Uniformly mixing the nano FeS-loaded and modified mushroom bran biochar with a sodium alginate solution according to the w/v =1 2 And (4) preparing the granular adsorbent in the solution.
6. The two-stage upflow fixed bed for treating chromium-containing electroplating wastewater as claimed in claim 5, wherein in step (1), the autoclaving temperature is 121 ℃, the sieving mesh number is 40 meshes, and the drying temperature is 80-100 ℃.
7. The two-stage upflow fixed bed for treating chromium-containing electroplating wastewater as claimed in claim 5, wherein in step (2), the drying temperature is 40 to 60 ℃, the sieving mesh number is 60 meshes, the firing temperature is 350 to 400 ℃, and the firing time is 1 to 3 hours.
8. The two-stage upflow fixed bed for treating chromium-containing electroplating wastewater as claimed in claim 5, wherein in step (3), the solid-to-liquid ratio of NaOH solution is 0.1%, the temperature of the constant temperature shaking table is 298K, the rotation speed is 150 to 180 r/min, the time is 1 to 3 h, and the drying temperature is 30 to 40 ℃.
9. The two-stage upflow fixed bed for treating chromium-containing electroplating wastewater as claimed in claim 5, wherein in the step (4), feSO is added 4 ·7H 2 The O solution is composed of 0.6 to 0.8g of FeSO 4 ·7H 2 O is in N 2 Dissolved in 200 mL of deionized water under the atmosphere; the CMC solution is prepared by dissolving 0.2 to 0.25 g of CMC in 11mL of deionized water; na (Na) 2 S·9H 2 The O solution is composed of 0.6 to 0.65 g of Na 2 S·9H 2 O is dissolved in 9mL of deionized water, and each 211mL of mixed solution contains 0.6 to 0.8g of FeSO 4 ·7H 2 O and 0.2 to 0.25 g of CMC.
10. The two-stage upflow fixed bed for treating chromium-containing electroplating wastewater as claimed in claim 5, wherein in said step (5), the concentration of the sodium alginate solution is 1.8% (w/v), caCl 2 The concentration of the solution was 4% (w/v).
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