Process for treating maleic anhydride wastewater by acid method

Abstract

The invention relates to the technical field of wastewater treatment, in particular to a process for treating maleic anhydride wastewater by an acid process, which comprises the following steps: step 1, adjusting charge, adding sulfuric acid into a high-density sedimentation tank, and supplementing ion concentration; step 2, coagulation and flocculation: adding ferric trichloride into the inlet water of the high-density sedimentation tank, stirring to complete the coagulation process, adding PAM, stirring, standing and settling to complete the flocculation process, and discharging the water from the high-density sedimentation tank; and step 3, ozone oxidation: continuously introducing ozone into the effluent of the high-density sedimentation tank in the ozone contact tank, and further oxidizing the residual COD (Chemical Oxygen Demand). According to the process for treating the maleic anhydride wastewater by the acid method, a large amount of COD in the wastewater is removed before ozone treatment, ozone consumption is reduced, effective ozone addition is ensured, normal operation of a depth line function is realized, the problem of high COD in the maleic anhydride wastewater can be solved at low cost, reclaimed water reuse is realized, and qualified discharge is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, in particular to a process for treating maleic anhydride wastewater by an acid method. Background Art

[0002] n-Butane is partially oxidized by air under the action of vanadium-phosphorus-oxygen catalyst to form maleic anhydride. In the reaction process, there are problems with the control of various conditions, including carbon four separation, n-butane oxidation, solvent absorption and analysis, product refining and other processes. Due to the operation of the maleic anhydride unit, the wastewater will contain organic components such as maleic acid, phthalic anhydride, and dibutyl phthalate. These substances are difficult to degrade through biochemical degradation, resulting in increased COD in the effluent, and the reuse of reclaimed water and the compliance of the system with emission standards are also great challenges. According to current market research, the treatment of maleic anhydride wastewater is a common problem, and the treatment cost is high.

[0003] Lipids and phthalic anhydride substances in maleic anhydride wastewater penetrate in the biochemical stage and interfere with coagulation and flocculation in the deep treatment stage.

[0004] The treatment process of maleic anhydride wastewater is maleic anhydride wastewater-Fenton-anaerobic-aerobic-deep, which improves biodegradability through Fenton, removes high-concentration COD through anaerobic, biologically oxidizes again through aerobic, and deeply oxidizes through ozone. Some aromatic hydrocarbon pollutants in maleic anhydride wastewater penetrate Fenton, anaerobic, biochemical, and deep, and exist in the form of difficult-to-degrade COD, so that the COD of anaerobic effluent rises to 3000mg / l, and the COD of biochemical effluent rises to 500mg / l. As the first structure of deep treatment, high density has the function of removing part of COD in deep treatment. The dispersant component of maleic anhydride wastewater makes high density coagulation and flocculation difficult, which is specifically manifested in that the T-Fe of high density effluent rises to 35mg / l, and the removal capacity of high density for influent COD fails. The treatment pressure is given to the ozone generator. Under the condition of large water volume operation and treatment, the deep ozone addition far exceeds the design capacity, and the operating cost is high. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the idea of ​​the present invention is to fully understand the characteristics of maleic anhydride wastewater, start from the wastewater treatment mechanism, and realize the recovery of coagulation and flocculation function through charge regulation, realize large-scale removal of COD at the front end of the ozone contact tank, reduce ozone consumption, realize the normal operation of the depth line function, and ensure low-cost treatment of maleic anhydride wastewater.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a process for treating maleic anhydride wastewater by acid method, comprising the following steps: Step 1: Adjust the charge and add sulfuric acid to the high-density sedimentation tank to replenish the ion concentration; Step 2: Coagulation and flocculation: add ferric chloride to the influent of the high-density sedimentation tank and stir to complete the coagulation process, add PAM and stir, let it stand and settle to complete the flocculation process, and discharge the water from the high-density sedimentation tank; Step three: ozone oxidation: ozone is continuously introduced into the effluent from the high-density sedimentation tank in the ozone contact tank to further oxidize the remaining COD.

[0007] Furthermore, in step 1, the pH in the high-density pool is adjusted from 7-8 to 4.5-5.5 by adding sulfuric acid.

[0008] Furthermore, in step 2, the concentration of ferric chloride added is 300-600 mg / l.

[0009] Furthermore, in step 2, the stirring frequency of the coagulation process is 50 Hz and the stirring time is 1 min.

[0010] Furthermore, in step 2, the PAM addition concentration is 1-6 mg / l.

[0011] Furthermore, in step 2, PAM is added and stirred, and small alum flowers are captured by a sedimentation net to form large alum flowers, which are then allowed to settle.

[0012] Furthermore, in step 2, the stirring frequency of the flocculation process is 40 Hz, and the stirring time is 8 min.

[0013] Furthermore, after the coagulation and flocculation treatment in step 2, the COD of the high-density effluent from the high-density sedimentation tank was reduced from 500 mg / l to 150 mg / l.

[0014] Furthermore, through step three, ozone oxidation treatment is performed to reduce the COD content in the water to below 50 mg / l.

[0015] Specifically, the process for treating maleic anhydride wastewater by acid method comprises the following steps: Step 1: Adjust the charge, add sulfuric acid into the high-density sedimentation tank, adjust the pH in the high-density tank from 7-8 to 5, and replenish the ion concentration; Step 2: Coagulation and flocculation. Coagulation and flocculation are completed in the high-density tank. Ferric chloride is added to the influent of the high-density sedimentation tank. The concentration of ferric chloride is 300 mg / l. Stirring is performed synchronously. The stirring frequency is 50 Hz and the stirring time is 1 min. The coagulation process is completed. PAM is then added. The concentration of PAM is 2 mg / l. Stirring is performed synchronously. The stirring frequency is 40 Hz and the stirring time is 8 min. Small alum flowers are captured by a sediment net to form large alum flowers. The flowers are allowed to settle and the flocculation process is completed. The effluent of the high-density sedimentation tank can reduce COD from 500 mg / l to 150 mg / l, and the removal rate is more than 70%. Step 3: Ozone oxidation: ozone is continuously introduced into the effluent from the high-density sedimentation tank in the ozone contact tank to further oxidize the remaining COD and reduce the COD content in the water to below 50 mg / l.

[0016] Based on the above technical solution, the sulfuric acid dosing system introduces H + 、SO4 2- , H + The methyl groups on the benzene ring are replaced, changing the hydrophilic property to hydrophobic property. The concentration of the added compound is fed back according to the reaction pH. The more hydrophilic benzene compounds there are in the water, the more H required. + The larger the number, the lower the pH value that needs to be adjusted. The addition of sulfuric acid is completed during the deep treatment process. After the maleic anhydride wastewater is treated by Fenton, anaerobic and aerobic treatment, there will be 500 mg / l of difficult-to-degrade COD. This part of COD is mainly hydrophilic benzene with functional groups such as carboxyl, hydroxyl, amino and aldehyde groups. + The addition of etc. changes the functional groups and converts them into hydrophobic substances such as benzene. Charge adjustment changes the benzene ring groups, and hydrophilic substances are converted into hydrophobic substances, which are then removed by physical separation. The use of sulfuric acid to adjust the charge is consistent with the effects of iron-carbon-copper micro-electrolysis, electrochemistry, demulsifiers, etc. The advantage is that maleic anhydride wastewater can be treated at low cost without any treatment unit and without increasing any equipment investment.

[0017] The idea of ​​the present invention is to fully understand the drainage characteristics of maleic anhydride wastewater, adopt a back-end treatment method to adjust the charge change group according to the addition of sulfuric acid, reduce the pH to 4.5-5.5, add ferric chloride to a concentration of 300-600 mg / l, and PAM to a concentration of 1-6 mg / l, and allow the high-density sedimentation tank to function. The high-density effluent COD can be reduced from 500 mg / l to 150 mg / l, and the removal rate can reach more than 70%. A certain amount of ozone is then added to remove a small amount of COD, thereby saving treatment costs.

[0018] The beneficial effects of the present invention are as follows: the process of treating maleic anhydride wastewater with the acid method of the present invention removes a large amount of COD in the wastewater before ozone, reduces ozone consumption, ensures effective ozone addition, realizes the normal function of the depth line, can solve the high COD problem in maleic anhydride wastewater at a low cost, realizes the reuse of reclaimed water, and ensures that the discharge is qualified. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the effect diagram of maleic anhydride wastewater interference coagulation and flocculation, T-Fe35mg / l; Figure 2 This is the coagulation and flocculation recovery effect diagram after the acid method was used to treat maleic anhydride wastewater. The COD removal rate is more than 70%, and T-Fe is 0.97mg / l; Figure 3From left to right, the coagulation and flocculation effect diagrams of Gaomi after the treatment in step 2 are shown in order when the pH value is 5 and the concentration of ferric chloride added is 30, 50, 80, 120, 200, and 300 ppm respectively; Figure 4 From left to right, they are the coagulation and flocculation effect diagrams corresponding to the treatment in step 2 when the ferric chloride addition concentration is 300 ppm and the pH is 9, 8, 7, 6, 5, and 4.5 respectively. DETAILED DESCRIPTION

[0020] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0021] Chemical Oxygen Demand (COD) is a chemical method to measure the amount of reducing substances in a water sample that need to be oxidized. It is the oxygen equivalent of substances (generally organic matter) that can be oxidized by strong oxidants in wastewater, wastewater treatment plant effluent and polluted water. In the study of river pollution and industrial wastewater properties and the operation and management of wastewater treatment plants, it is an important and quickly measured organic pollution parameter, often represented by the symbol COD. The present invention has a comprehensive understanding of the characteristics of maleic anhydride wastewater, starts from the wastewater treatment mechanism, and realizes the recovery of coagulation and flocculation functions through charge regulation, realizes a large amount of COD removal at the front end of the ozone contact tank, reduces ozone consumption, realizes the normal function of the depth line, ensures qualified external discharge, and reuses the reclaimed water.

[0022] A process for treating maleic anhydride wastewater by an acid method of the present invention comprises the following steps: Step 1: Adjust the charge and add sulfuric acid to the high-density sedimentation tank to adjust the pH in the high-density tank from 7-8 to 4.5-5.5, and replenish the ion concentration (the sulfuric acid addition system introduces H + 、SO4 2- , H + The methyl groups on the benzene ring are replaced, changing the hydrophilic property to hydrophobic property. The concentration of the added compound is fed back according to the reaction pH. The more hydrophilic benzene compounds there are in the water, the more H required. + The larger the number, the lower the pH value that needs to be adjusted. The addition of sulfuric acid is completed during the deep treatment process. After the maleic anhydride wastewater is treated by Fenton, anaerobic and aerobic treatment, there will be 500 mg / l of difficult-to-degrade COD. This part of COD is mainly hydrophilic benzene with functional groups such as carboxyl, hydroxyl, amino and aldehyde groups.+ The addition of etc. changes the functional groups and converts them into hydrophobic substances such as benzene. Charge adjustment changes the benzene ring groups, and the hydrophilic substances are converted into hydrophobic substances, which are then removed by physical separation. The use of sulfuric acid to adjust the charge is consistent with the effects of iron-carbon-copper micro-electrolysis, electrochemistry, demulsifiers, etc. The advantage is that maleic anhydride wastewater can be treated at low cost without any treatment unit and without increasing any equipment investment; Step 2: Coagulation and flocculation. Coagulation and flocculation are completed in the high-density tank. Ferric chloride is added to the influent of the high-density sedimentation tank. The concentration of ferric chloride is 300-600 mg / l. Stirring is performed synchronously. The stirring frequency is 50 Hz and the stirring time is 1 min. The coagulation process is completed. Then PAM is added. The concentration of PAM is 1-6 mg / l. Stirring is performed synchronously. The stirring frequency is 40 Hz and the stirring time is 8 min. Small alum flowers are captured by the sediment net to form large alum flowers. The alum flowers are allowed to settle to complete the flocculation process. The effluent of the high-density sedimentation tank can reduce COD from 500 mg / l to 150 mg / l, and the removal rate can reach more than 70%. Step 3: Ozone oxidation: ozone is continuously introduced into the effluent from the high-density sedimentation tank in the ozone contact tank to further oxidize the remaining COD and reduce the COD content in the water to below 50 mg / l.

[0023] Example 1 A process for treating maleic anhydride wastewater by acid method comprises the following steps: Step 1: Adjust the charge, add sulfuric acid into the high-density sedimentation tank, adjust the pH in the high-density tank from 7-8 to 5, and replenish the ion concentration; Step 2: Coagulation and flocculation. Coagulation and flocculation are completed in the high-density tank. Ferric chloride is added to the influent of the high-density sedimentation tank. The concentration of ferric chloride is 300 mg / l (300 ppm). Stirring is performed synchronously with a stirring frequency of 50 Hz and a stirring time of 1 min to complete the coagulation process. Then PAM is added. The concentration of PAM is 2 mg / l (2 ppm). Stirring is performed synchronously with a stirring frequency of 40 Hz and a stirring time of 8 min. Small alum flowers are captured by the sediment net to form large alum flowers. The flowers are allowed to settle to complete the flocculation process. The effluent from the high-density sedimentation tank is clear. COD can be reduced from 500 mg / l to 150 mg / l, and the removal rate can reach more than 70%. Step 3: Ozone oxidation: ozone is continuously introduced into the effluent from the high-density sedimentation tank in the ozone contact tank to further oxidize the remaining COD and reduce the COD content in the water to below 50 mg / l.

[0024] Comparative Examples 1-5 Step 1: Adjust the charge, add sulfuric acid into the high-density sedimentation tank, adjust the pH in the high-density tank from 7-8 to 5, and replenish the ion concentration; Step 2: coagulation and flocculation. Coagulation and flocculation are completed in the high-density tank. Ferric chloride is added to the influent of the high-density sedimentation tank. The concentrations of ferric chloride added in the five groups of experiments are 30 mg / l, 50 mg / l, 80 mg / l, 120 mg / l, and 200 mg / l, respectively. Synchronous stirring is performed with a stirring frequency of 50 Hz and a stirring time of 1 min to complete the coagulation process. PAM is then added with a PAM concentration of 2 mg / l (2 ppm). Synchronous stirring is performed with a stirring frequency of 40 Hz and a stirring time of 8 min. Small alum flowers are captured by a sediment net to form large alum flowers. The alum flowers are allowed to settle and the flocculation process is completed.

[0025] The effluent of Comparative Examples 1-5 was turbid, and the coagulation and flocculation effects were poor.

[0026] The above comparative examples 1-5 and Example 1 process are pH 5, PAM addition concentration is 2ppm, and different ferric chloride addition concentrations (30ppm, 50ppm, 80ppm, 120ppm, 200ppm, 300ppm) are used to treat high density effects. Figure 3 As shown, when the pH value is 4.8-5.2, the lowest concentration of ferric chloride added is 300 mg / l. When the concentration of ferric chloride is lower than 300 mg / l, coagulation and flocculation have no effect and the conversion between benzene series cannot be completed.

[0027] Example 2 A process for treating maleic anhydride wastewater by acid method comprises the following steps: Step 1: Adjust the charge, add sulfuric acid into the high-density sedimentation tank, adjust the pH in the high-density tank from 7-8 to 4.5, and replenish the ion concentration; Step 2: Coagulation and flocculation. Coagulation and flocculation are completed in the high-density tank. Ferric chloride is added to the influent of the high-density sedimentation tank. The concentration of ferric chloride is 300 mg / l. Stirring is performed synchronously. The stirring frequency is 50 Hz and the stirring time is 1 min. The coagulation process is completed. Then PAM is added. The concentration of PAM is 1-6 mg / l. Stirring is performed synchronously. The stirring frequency is 40 Hz and the stirring time is 8 min. Small alum flowers are captured by the sediment net to form large alum flowers. The flowers are allowed to settle and the flocculation process is completed. The effluent of the high-density sedimentation tank is clear. COD can be reduced from 500 mg / l to 150 mg / l, and the removal rate can reach more than 70%. Step 3: Ozone oxidation: ozone is continuously introduced into the effluent from the high-density sedimentation tank in the ozone contact tank to further oxidize the remaining COD and reduce the COD content in the water to below 50 mg / l.

[0028] Comparative Examples 6-7 Step 1: Add alkali solution into the high-density sedimentation tank. In the two groups of experiments, the pH in the high-density tank was adjusted from 7-8 to 9 and 8 respectively; Step 2: Coagulation and flocculation. Coagulation and flocculation are completed in the high-density tank. Ferric chloride is added to the influent of the high-density sedimentation tank. The concentration of ferric chloride is 300 mg / l (300 ppm). Stirring is performed simultaneously with a frequency of 50 Hz and a stirring time of 1 min to complete the coagulation process. PAM is then added at a concentration of 2 mg / l (2 ppm). Stirring is performed simultaneously with a frequency of 40 Hz and a stirring time of 8 min. Small alum flowers are captured by a sediment net to form large alum flowers. The flowers are allowed to settle to complete the flocculation process.

[0029] The effluent of Comparative Example 6-7 was turbid, and the coagulation and flocculation effect was poor.

[0030] Comparative Examples 8-9 Step 1: Adjust the charge and add sulfuric acid to the high-density sedimentation tank. In the two experiments, the pH in the high-density tank was adjusted from 7-8 to 7 and 6 respectively; Step 2: Coagulation and flocculation. Coagulation and flocculation are completed in the high-density tank. Ferric chloride is added to the influent of the high-density sedimentation tank. The concentration of ferric chloride is 300 mg / l (300 ppm). Stirring is performed simultaneously with a frequency of 50 Hz and a stirring time of 1 min to complete the coagulation process. PAM is then added at a concentration of 2 mg / l (2 ppm). Stirring is performed simultaneously with a frequency of 40 Hz and a stirring time of 8 min. Small alum flowers are captured by a sediment net to form large alum flowers. The flowers are allowed to settle to complete the flocculation process.

[0031] The effluent of Comparative Examples 8-9 was turbid, and the coagulation and flocculation effects were poor.

[0032] The above comparative examples 6-9 and examples 1-2 are in different ion concentrations (pH 9, 8, 7, 6, 5, 4.5), the concentration of ferric chloride added is 300ppm, the concentration of PAM added is 2ppm, and the high density treatment effect is as follows Figure 4 As shown, when the pH is above 6, adding 300 mg / l of ferric chloride has no coagulation and flocculation effect.

[0033] Without acid modification, simple coagulation and flocculation can also achieve the purpose of high-density clarification, but the concentration of ferric chloride added is 2000mg / l, and the water operation cost and sludge discharge cost are high. The evaluation of the high-density treatment effect is based on the effluent SS and T-Fe. After the high-density is treated with acid, the hydrophilic substances are converted into hydrophobic substances. The hydrophobic substances formed by the addition of ferric chloride and acid are coagulated into small alum flowers, and PAM flocculates to form large alum flowers. The pollutants are separated from the water phase and enter the solid phase, and the difficult-to-degrade COD is removed by sludge discharge. The ozone oxidation efficiency is higher after the high-density effluent is clear. The treatment of unstable by-products of maleic anhydride wastewater is achieved; the low-cost treatment of maleic anhydride wastewater is completed.

[0034] According to the water quality of the incoming water, the present invention adopts a low-cost demulsifier, realizes coagulation and flocculation through charge regulation, removes more than 70% of COD at the front end of ozone, and the depth line functions normally, and treats maleic anhydride wastewater at a low cost. The maleic anhydride wastewater treatment process of the present invention has good economic benefits and achieves the purpose of low-cost wastewater treatment. The specific comparison is as follows: Cost per ton of water: 1. Use patented technology Sulfuric acid: 25t / d*362 yuan / t=9050 (yuan) Ferric chloride: 25t / d*590 yuan / t=14750 (yuan) PAM: 0.05*22000 yuan / t=1100 (yuan) Summary: (9050+14750+1100) yuan / (400m3 / h*24h)=2.6 (yuan) Using patented technology, according to the calculation of single-line treatment of 400m3 / h wastewater, 30 tons of sulfuric acid are added, the pH is controlled at 4.5-5.5, the daily demulsification cost is 24,900 yuan, and 2.6 yuan per ton of water.

[0035] 2. Use pure ozone treatment Ozone quantity per hour: 4gO3 / gCOD (500-150) g / m3*400m3 / h=560kgO3 Ozone unit price 560kw*h*1h*0.446 / 90kgO3 / h=2.7 yuan / kgO3 Summary: 560kg / h*2.7 (yuan / kg) / 400m3 / h=3.78 yuan / m3 Using pure ozone oxidation treatment, eliminating the influence of ozone dosage capacity, tail breaking capacity, reaction efficiency, etc., without taking into account investments in equipment and pool expansion, the cost per ton of water is 3.78 yuan.

[0036] It should be noted that the parts not described in detail in the present invention are prior art.

[0037] The above examples are only the best embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and many variations are possible. All variations that can be directly derived or associated with the contents disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A process for treating maleic anhydride wastewater by acid method, characterized in that: The following steps are involved: Step 1: Adjust the charge and add sulfuric acid to the high-density sedimentation tank to replenish the ion concentration; Step 2: Coagulation and flocculation: add ferric chloride to the influent of the high-density sedimentation tank for stirring to complete the coagulation process, add PAM for stirring, let it stand for sedimentation to complete the flocculation process, and discharge the water from the high-density sedimentation tank; Step three: ozone oxidation: ozone is continuously introduced into the effluent from the high-density sedimentation tank in the ozone contact tank to further oxidize the remaining COD.

2. The process for treating maleic anhydride wastewater by acid method according to claim 1, characterized in that: In step 1, the pH in the high-density pool is adjusted from 7-8 to 4.5-5.5 by adding sulfuric acid.

3. The process for treating maleic anhydride wastewater by acid method according to claim 1, characterized in that: In step 2, the concentration of ferric chloride added is 300-600 mg / l.

4. The process for treating maleic anhydride wastewater by acid method according to claim 1, characterized in that: In step 2, the stirring frequency of the coagulation process is 50 Hz and the stirring time is 1 min.

5. The process for treating maleic anhydride wastewater by acid method according to claim 1, characterized in that: In step 2, the PAM addition concentration is 1-6 mg / l.

6. The process for treating maleic anhydride wastewater by acid method according to claim 1, characterized in that: In step 2, PAM is added and stirred, and small alum flowers are captured by a sedimentation net to form large alum flowers, which are then allowed to settle.

7. The process for treating maleic anhydride wastewater by acid method according to claim 1, characterized in that: In step 2, the stirring frequency of the flocculation process is 40 Hz and the stirring time is 8 min.

8. The process for treating maleic anhydride wastewater by acid method according to claim 1, characterized in that: After the coagulation and flocculation treatment in step 2, the COD of the high-density effluent from the high-density sedimentation tank was reduced from 500 mg / l to 150 mg / l.

9. The process for treating maleic anhydride wastewater by acid method according to claim 1, characterized in that: After step three of ozone oxidation treatment, the COD content in the water is reduced to below 50 mg / l.

10. A process for treating maleic anhydride wastewater by acid method according to any one of claims 1 to 9, characterized in that: The following steps are involved: Step 1: Adjust the charge, add sulfuric acid into the high-density sedimentation tank, adjust the pH in the high-density tank from 7-8 to 5, and replenish the ion concentration; Step 2: Coagulation and flocculation. Coagulation and flocculation are completed in the high-density tank. Ferric chloride is added to the influent of the high-density sedimentation tank. The concentration of ferric chloride is 300 mg / l. Stirring is performed synchronously. The stirring frequency is 50 Hz and the stirring time is 1 min. The coagulation process is completed. PAM is then added. The concentration of PAM is 2 mg / l. Stirring is performed synchronously. The stirring frequency is 40 Hz and the stirring time is 8 min. Small alum flowers are captured by a sediment net to form large alum flowers. The flowers are allowed to settle and the flocculation process is completed. The effluent of the high-density sedimentation tank can reduce COD from 500 mg / l to 150 mg / l, and the removal rate is more than 70%. Step 3: Ozone oxidation: ozone is continuously introduced into the effluent from the high-density sedimentation tank in the ozone contact tank to further oxidize the remaining COD and reduce the COD content in the water to below 50 mg / l.

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