CN115448438A - A two-stage upflow fixed bed for treating chromium-containing electroplating wastewater - Google Patents

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

A two-stage upflow fixed bed for treating chromium-containing electroplating wastewater

technical field

The invention belongs to the technical field of environmental protection and relates to a two-stage upflow fixed bed for treating chromium-containing electroplating wastewater.

Background technique

With the rapid development of my country's economy and industry, electroplating industry, as one of the cornerstones of modern manufacturing industry, has been widely used in heavy industry, light industry and electronics industry. If the electroplating wastewater is discharged directly without treatment, or if the treatment procedure is not strictly implemented in accordance with the standards, it will directly threaten the safety of drinking water for residents and cause groundwater, surface water, and industrial water pollution. There are a large number of enterprises, but the development situation is uneven, the demand for electroplating wastewater discharge is high, the supervision of waste liquid discharge is difficult, the composition of waste liquid is complex, and the treatment is difficult. Taking the chromium plating workshop as an example, the chromic anhydride that can be effectively deposited on the surface of the plated parts only accounts for 15-25% of the total, and 40-50% of the chromic anhydride enters the wastewater during the cleaning process, forming chromium-containing wastewater that is difficult to treat. The main pollutants in chromium-containing wastewater are hexavalent chromium, trivalent chromium, copper, iron and other metal ions and sulfuric acid. The concentration of hexavalent chromium in the general wastewater produced by chromium plating workshops is below 200 mg/L, and the pH value is 4 ~6 between. There is also chromium in the comprehensive wastewater of the electroplating workshop, the total chromium concentration is generally in the range of 50-300 mg/L, and the pH value is between 1-10. The toxicity of Cr(VI) is much higher than that of Cr(III), and it has sensitization, teratogenicity and carcinogenicity, and is classified as a class I human occupational carcinogen by the International Agency for Research on Cancer.

Adsorption is one of the traditional methods for treating wastewater, which has the advantages of simple operation, high benefit and low cost. As scientists explore the structure and properties of different pollutants, a wide variety of adsorbents and adsorption devices have been developed. The biosorption method is to use some active organism life functions, or the chemical structure and composition characteristics of inactive organisms to absorb metal ions dissolved in water, and then remove the metal ions in the aqueous solution through solid-liquid two-phase separation. method. The biosorption method has the advantages of low cost, environmental friendliness, and high adsorption efficiency. It is suitable for treating large volumes of low-concentration heavy metal wastewater, and can reduce the concentration of heavy metals in the effluent to the nationally permitted discharge level. Cr(VI) in electroplating wastewater has high mobility and high toxicity. Compared with Cr(III), Cr(III) has low mobility and low toxicity. According to the chemical characteristics of different valence states of Cr, a kind of adsorption capacity can be designed. The adsorbent with reducing capacity can reduce Cr(VI) while adsorbing it, so as to reduce the concentration of Cr(VI), weaken the toxicity and reduce the pollution to the environment. In the actual application process, the use scenario of the adsorbent should be considered at the same time. Compared with the application scenarios such as soil, the wastewater has fluidity, and the adsorbent should meet the needs of completing the adsorption process in a dynamic process. Fixed bed device, also known as packed bed reactor, is a reactor filled with solid catalyst or solid reactant to realize heterogeneous reaction process. The solids are usually granular and piled up into a bed of a certain height (or thickness). The bed is stationary and the fluid passes through the bed to react. The fixed bed device can be divided into upflow type and downflow type according to the direction of liquid flow. Compared with the downflow type, the upflow type can relatively avoid the influence of gravity, the contact between liquid and solid is more sufficient, and the treatment effect and efficiency are higher.

Contents of the invention

Aiming at the existence characteristics of Cr(VI) in electroplating wastewater and the practical application device for wastewater treatment, the present invention provides a nano-FeS-loaded bacterial chaff biochar with both adsorption and reduction and detoxification functions and CTAB modified bacteria with immobilization function A two-stage upflow fixed bed system for treating chromium-containing electroplating wastewater with bran biochar as filler.

The purpose of the present invention is achieved through the following technical solutions:

A two-stage upflow fixed bed for treating chromium-containing electroplating wastewater, including fixed bed I, transfer regulating tank and fixed bed II connected in sequence, wherein:

The fixed bed I, the transfer adjustment tank and the fixed bed II all adopt the upflow water passing mode;

Both the fixed bed I and the fixed bed II are filled with nylon mesh at the upper and lower parts of the adsorption column;

The fixed bed I selects composite modified fungus chaff biochar adsorbent particles as the adsorbent;

The fixed bed II selects cetyltrimethylammonium bromide modified biochar (CTAB-BC) pellets as the adsorbent;

A peristaltic pump is arranged between the transfer adjustment tank and the fixed bed II.

In the present invention, the initial concentration of hexavalent chromium in the feed water of the fixed bed I is 10-30 mg/L.

In the present invention, the water inlet speed of the fixed bed I and the fixed bed II is 2-4 mL/min.

In the present invention, the filling height of the adsorbent in the fixed bed I and the fixed bed II is 5-15 cm.

In the present invention, the preparation method of the composite modified bacterial chaff biochar adsorbent particles is as follows:

Step (1) pretreatment of fungus chaff

Sterilize the fungus linden with high-temperature steam, put it in a constant temperature drying incubator, dry it to a constant weight, crush it, sieve it, and store it in a dry environment;

In this step, the fungus bran is cultivated by using straw, sawdust and other raw materials as substitute materials for edible fungi, and the culture medium residue after harvesting is commonly known as edible fungus cultivation waste, fungus residue or leftover material; Bacterial enzymatic hydrolysis, a compound of crude fiber and other components whose structure has undergone qualitative change;

In this step, the autoclaving temperature is 121°C, the mesh size of the sieve is 40 mesh, and the drying temperature is 80-100°C;

Step (2) Preparation of fungus chaff biochar

Rinse the chaff powder repeatedly with distilled water to remove surface impurities, dry it in a constant temperature drying incubator until it reaches a constant weight, and sieve it. The chaff powder under the screen is placed in a muffle furnace and fired under oxygen-limited conditions. Charcoal, taken out and homogenized, stored in a dry environment for later use;

In this step, the drying temperature is 40-60°C, the mesh size of the sieve is 60 mesh, the firing temperature is 350-400°C, and the firing time is 1-3 h;

Step (3) Alkali modification of bacterial chaff biochar

Choose NaOH as the alkali modifier, add the fungus chaff biochar to the NaOH solution with a solid-to-liquid ratio of 0.1%, place it in a constant temperature shaker for modification, filter, rinse repeatedly with deionized water until the pH is stable, and place it at a constant temperature Dried to constant weight in a dry incubator to obtain NaOH pretreated fungus chaff biochar, which was stored in a dry environment for subsequent use;

In this step, 8–12 g of mushroom chaff biochar was added to every 200 mL of NaOH solution, the temperature of the constant temperature shaker was set at 298 K, the rotation speed was 150–180 r/min, the drying time was 1–3 h, and the drying temperature was 30~40℃;

Step (4) Nano-FeS loading of alkali-modified fungal chaff biochar

FeSO ₄ 7H ₂ O and Na ₂ S 9H ₂ O were selected as Fe and S sources to prepare nano-FeS by chemical synthesis, and loaded on fungus chaff biochar under the stabilization of carboxymethyl cellulose (CMC). The specific steps are as follows: add 0.2-0.25 g of alkali-modified fungus chaff biochar to the mixed solution of 211mL FeSO ₄ 7H ₂ O and CMC, drop in 9mL Na ₂ S 9H ₂ O solution at a constant speed, and stir magnetically under N ₂ atmosphere Mix well for 0.5-1 h, seal and age away from light for 20-30 h, filter, and wash with deionized water 2-4 times to remove impurities such as Na ₂ SO ₄ remaining on the surface of the biochar. The fungus chaff biochar was preserved in a glass plate after vacuum freeze-drying;

In this step, the FeSO ₄ 7H ₂ O solution is prepared by dissolving 0.6~0.8gg FeSO ₄ 7H ₂ O in 200 mL deionized water under N ₂ atmosphere;

In this step, the CMC solution is prepared by dissolving 0.2-0.25 g of CMC in 11 mL of deionized water;

In this step, each 211mL mixed solution contains 0.6~0.8g FeSO ₄ ·7H ₂ O and 0.2~0.25g CMC;

In this step, the Na ₂ S·9H ₂ O solution is prepared by dissolving 0.6~0.65 g Na ₂ S·9H ₂ O in 9 ml deionized water;

Step (5) Preparation of composite modified bacterial chaff biochar adsorbent particles

Mix the fungus chaff biochar modified by nano-FeS loading and sodium alginate solution at a ratio of w/v=1:10~20, and pump the mixture into the _CaCl2 solution through a peristaltic pump to make a granular adsorbent. Filtrate, rinse repeatedly with deionized water, make it now, and store it in oxygen deionized water for a short time;

In this step, the concentration of the sodium alginate solution is 1.8% (w/v);

In this step, the concentration of the CaCl solution is ₄ % (w/v);

In this step, the surface area of the adsorbent is 11.737 m ² /g, the pore volume is 0.051 cm ³ /g, and the average pore diameter is 17.513 nm.

Compared with the prior art, the present invention has the following advantages:

1. The two-stage upflow fixed bed of the present invention has the advantages of high adsorption efficiency, strong stability, integrated realization of Cr(VI) reduction and detoxification, pH buffering and Cr(III) fixation, and the like.

2. The composite modified fungus chaff biochar adsorbent used in the present invention is prepared from the waste fungus chaff after harvesting edible fungi, and utilizes agricultural waste as a resource. It has rich raw material sources, low cost, and a production process The advantage of simplicity.

3. The composite modified fungus chaff biochar adsorbent used in the present invention mainly utilizes the larger specific surface area, rich pore structure and active functional groups of biochar, and after it is modified with nano-FeS load, it can be enhanced by Adsorption and reduction of toxic hexavalent chromium ions in the form of anions in wastewater through oxidation-reduction and other ways can achieve the effect of sufficient detoxification, so the use of adsorbents is more effective.

Description of drawings

Fig. 1 is a two-stage upflow fixed bed operation flow chart;

Figure 2 is the effect of the initial concentration of hexavalent chromium on the breakthrough curve;

Figure 3 shows the effect of water inlet velocity on the penetration curve;

Figure 4 shows the effect of fixed bed packing height on the breakthrough curve;

Fig. 5 is a graph showing the change of total chromium concentration in the two-stage upflow fixed bed.

detailed description

The technical solution of the present invention will be further described below in conjunction with the accompanying drawings, but it is not limited thereto. 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 should be covered by the present invention. within the scope of protection.

Embodiment 1: Design of two-stage upflow fixed bed

As shown in Figure 5, the two-stage upflow fixed bed consists of a fixed bed I, a transfer regulating tank and a fixed bed II. The fixed bed I, the transfer regulating tank and the fixed bed II all adopt the upflow water flow mode, and the peristaltic pump is used as the power Supply device, and play a role in controlling the water flow speed. Both fixed bed I and fixed bed II used PC tubes with an inner diameter of 1.2 cm and a total length of 30 cm as adsorption columns. The upper and lower parts of the adsorption column are filled with nylon mesh to fix the filled adsorbent and prevent it from drifting with the aqueous solution. The fixed bed I chooses composite modified fungus chaff biochar adsorbent particles as the filling adsorbent, the purpose is to reduce the Cr(VI) in the relatively acidic comprehensive wastewater to Cr(III) and buffer the pH, so as to fully detoxify. The transfer adjustment pool plays the role of stabilizing and adjusting the pH, and the pH is stabilized in the range of 5.5~6. For fixed bed II, cetyltrimethylammonium bromide modified biochar (CTAB-BC) pellets are selected as the packed adsorbent. CTAB-BC is a good cationic biosorbent for fixing chromium ions. The purpose is to Fix the total chromium, so that the effluent of the system can meet the discharge standard.

The operation procedure of the fixed bed is as follows: after the Cr(VI) solution with different parameters of the fixed bed or the actual waste water flows into the fixed bed I through the peristaltic pump I, the Cr(VI) and total chromium concentrations are regularly sampled and tested. After (VI), start the peristaltic pump II to pump liquid into the fixed bed II, and regularly sample and test the total chromium content.

Example 2: Preparation of Composite Modified Bacteria Chaff Biochar Adsorbent Particles

(1) Pretreatment of bacterial chaff

Sterilize the shiitake linden linden at 121°C with high-temperature steam, then place it in a constant temperature drying incubator at 80°C, dry it to constant weight, crush it, pass it through a 40-mesh sieve, and store it in a dry environment.

(2) Preparation of mushroom chaff biochar

Rinse the shiitake chaff powder repeatedly with distilled water to remove surface impurities, place it in a constant temperature drying incubator at 40°C and dry to constant weight, pass through a 60-mesh sieve, put the shiitake mushroom chaff powder under the sieve in a muffle furnace under oxygen limitation Burn at 350°C for 2 h under the same conditions, take out the biochar and homogenize it, store it in a dry environment for later use, and mark it as NBC.

(3) Alkali modification of mushroom chaff biochar

NaOH was selected as the alkali modifier, and 10 g of mushroom chaff biochar was added to 200 mL of NaOH solution with a solid-to-liquid ratio of 0.1 %, and placed in a constant temperature shaker under the conditions of 298 K and 160 r/min. After inactivation for 2 h, filter and wash with deionized water repeatedly until the pH is stable, and then dry in a constant temperature drying incubator at 35 °C to constant weight to obtain NaOH-pretreated shiitake chaff biochar, which is stored in a dry environment for later use.

(4) Nano-FeS loading of alkali-modified shiitake chaff biochar (nFeS-BC)

FeSO ₄ 7H ₂ O and Na ₂ S 9H ₂ O were selected as Fe and S sources to prepare nano-FeS by chemical synthesis and loaded on the biochar of mushroom chaff under the stabilization of carboxymethyl cellulose (CMC) . Add 0.22 g of biochar to the mixed solution of 200 mL FeSO ₄ 7H ₂ O and CMC, add Na ₂ S 9H ₂ O dropwise at a uniform speed, stir magnetically under N ₂ atmosphere for half an hour to fully mix, and seal and age in the dark for 24 h, filtered and washed 3 times with deionized water to remove impurities such as Na ₂ SO ₄ remaining on the surface of the biochar. The obtained nano-FeS-loaded alkali-modified shiitake mushroom biochar (nFeS-BC) was vacuum freeze-dried and stored in a glass plate.

(5) Preparation of nFeS-BC adsorbent particles

Mix the shiitake chaff biochar modified by nano-FeS loading alkali and sodium alginate with a concentration of 1.8% (w/v) according to the mass ratio of 1:15, and pump the mixture with a concentration of 4% through a peristaltic pump (w/v) CaCl ₂ solution, made granular adsorbent, filtered, rinsed repeatedly with deionized water, ready to use, and stored in oxygen-expelled deionized water for a short time. Absorb excess moisture on the surface of the pellets and evenly fill them into the fixed bed I during use.

Example 3: Application of composite modified bacterial chaff biochar adsorbent in dynamic adsorption of hexavalent chromium

In this example, the fixed bed continuous flow process is adopted, and the modified fungal chaff biochar (nFeS-BC) immobilized adsorbent prepared in Example 2 is filled into the adsorption column to prepare fixed bed I, and the CTAB-BC immobilized adsorbent Fill to the adsorption column to prepare fixed bed II. The curve obtained by plotting the ratio C _e /C _i of the concentration of metal ions in the effluent liquid to the concentration of influent metal ions on the ordinate and time t as the abscissa. The breakthrough point is taken when C _e /C _i is 5%, and the time at this time becomes the breakthrough time t _b . It is generally believed that when C _e /C _i is 95%, the adsorption column no longer has the adsorption capacity, so this time is called the exhaustion point, and the time at this time is called the exhaustion time t _exh . In this way, different initial concentrations of hexavalent chromium (10, 20, 30 mg/L) (see Figure 2), different water inflow rates (2, 3, 4mL/min) (see Figure 3) and different filling heights (5 , 10, 15 cm) (see Figure 4) under the condition of adsorbent to remove hexavalent chromium in wastewater breakthrough curve. It can be seen from the figure that higher initial concentration, larger flow rate and shorter packing layer height will accelerate the penetration of the adsorption column bed and shorten the breakthrough time. According to Figures 2 to 4, it can be seen that the initial concentration of hexavalent chromium is preferably 20 mg/L, the water inflow rate is preferably 2 mL/min, and the filling height is preferably 10 cm.

Example 4: Regeneration of Adsorbent

In this embodiment, 0.1M HCl solution is used as the regenerant, and the depleted immobilized nFeS-BC adsorbent in the fixed bed I is flushed with the regenerant upflow and downflow cycles, and the flow direction is changed to circulate each cycle three times, and the flow rate of the regenerant is 10 mL/min, then rinse the column bed with deionized water until the pH of the effluent water is about 5.5, pump air to remove excess deionized water in the column, and then perform the next cycle of adsorption test.

The adsorption capacity, breakthrough time and depletion time after each regeneration cycle are shown in Table 1. It can be seen from Table 1 that the adsorption amount of hexavalent chromium by the immobilized nFeS-BC adsorbent gradually decreases with the increase of the number of cycles. After the first cycle, the adsorbent capacity decreased to 2.02 mg/g, while after the second and third cycles, the adsorption capacity decreased slightly, still reaching 1.91 mg/g and 1.86 mg/g. After 5 cycles, the adsorption capacity was 50% of that before regeneration. At this time, the adsorption capacity was 1.24 mg/g, probably because the 0.1 M HCl solution removed the oxidized Fe ³⁺ aging layer on the surface of the adsorbent after dynamic adsorption of Cr(VI) , exposing the Fe ²⁺ active sites in the inner layer, thereby continuing to maintain the adsorption capacity of the fixed bed. It can be seen that the modified bacterial chaff adsorbent can be regenerated and recycled. Therefore, the two-stage upflow fixed bed of the present invention can be used as an effective integrated water treatment device for removing hexavalent chromium.

Table 1

Example 5: Overall analysis of the change trend of total chromium concentration in two-stage upflow fixed bed

The change trend of the total chromium concentration in the effluent of the two-stage upflow fixed bed is shown in Figure 5. In order to analyze the overall performance of the fixed bed from a more intuitive perspective, the following will analyze the overall performance of the two-stage fixed bed from the perspective of changes in the total chromium concentration. After the potassium dichromate solution and real electroplating wastewater pass through the fixed bed I, the concentration of Cr(VI) at the outlet can remain undetectable until the working time reaches the breakthrough point of the fixed bed I. However, analyzing the total chromium concentration, it can be found that the total chromium concentration can be detected at the outlet of fixed bed I, indicating that Cr(III) remains in the solution after passing through fixed bed I. Although Cr(III) is less toxic than Cr(VI), it is still It is a toxic substance. The "National Standard of the People's Republic of China Electroplating Pollutant Discharge Standard" (GB 21900-2008) stipulates that the total chromium discharge at the wastewater discharge outlet of workshops or production facilities shall not exceed 1.5 mg/L, and the effluent of fixed bed I cannot be discharged directly. After buffering the pH in the transfer tank, it should enter the fixed bed II. The total chromium concentration in the effluent of the fixed bed II can be maintained at an undetectable state, which meets the national discharge standard and can be discharged. From an overall point of view, the two-stage upflow fixed bed can integrate the reduction, fixation and pH adjustment of Cr(VI), which is consistent with the reduction mentioned in the "Technical Specifications for Electroplating Wastewater Treatment Engineering of the National Environmental Protection Standard of the People's Republic of China". Compared with the Cr(VI) method, it has the advantages of simple process, easy operation, and low time cost.

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).

Images