wastewater

Wat. Res.  Vol. 35, No. 8, pp. 2087–2091, 2001 #  2001 Elsevier Elsevier Science Ltd. All rights reserved

Printed Printed in Great Britain Britain 0043-1354/01/ 0043-1354/01/$ $ - see front matter

PII: S0043-1354(00)00462-0

TECHNICAL NOTE

APPLICATION OF FERROUS HYDROGEN PEROXIDE FOR TREATMENT OF DSD-ACID MANUFACTURING PROCESS WASTEWATER WANPENG ZHU*, ZHIHUA YANG and LI WANG Department of Environmental Science & Engineering, Tsinghua University, Beijing, 100084, People’s Republic of China (First received 20 March 2000; accepted in revised form 7 September 2000) Abstract}A pretreatment method for the biological treatment of wastewater from 4,40 -diaminostilbene2,20 -disulfonic acid (DSD-acid) manufacturing processes, a refractory dye intermediate wastewater, based on combined ferrous hydrogen peroxide oxidation and coagulation–flocculation, was developed. When the the wast wastew ewat ater er was was trea treate ted d with with ferr ferrou ouss hydr hydrog ogen en pero peroxi xide de oxid oxidat atio ion n ([Fe ([Fe2+]=2.7mmol/L, [H2O2]=0 ]=0.21mol/L .21mol/L)) after after a floccul flocculati ation on using using an organ organic ic floccul flocculant ant TS-1 at a dosage dosage of 3 g/L, g/L, the overall COD and color removals were 64 and 62%, respectively. BOD5/COD value of the effluent was 0.3. Ferrous Ferrous hydrogen peroxide peroxide oxidation oxidation treatment treatment can reduce the solubility solubility of organic organic molecules molecules with sulfonic group and increase the efficiency of coagulation treatment. The COD and color removals were both more than 90% when FeCl 3 was used as the coagulation (dosages of two-step coagulation were 0.031 and 0.012 mol/L respectively) after a ferrous hydrogen peroxide oxidation oxidation pretreatment at a H2O2  dosage of 0.06 mol/L. mol/L. # 2001 Elsevier Elsevier Science Science Ltd. All rights rights reserved

Key words}ferrous ferrous hydrogen hydrogen peroxide, peroxide, Fenton’s Fenton’s reagent, reagent, ferrous ferrous ion, hydrogen hydrogen peroxide, peroxide, DSD-acid, DSD-acid, hydroxyl free radical, dye intermediate, COD, BOD5, ferric chloride, dye manufacturing wastewater

INTRODUCTION

DSD-acid DSD-acid (4,40 -diaminostilbene-2,20 -disulfonic -disulfonic acid) is an import important ant dye interm intermedia ediate. te. Its product production ion processes are complicated and the utilization ratio of  raw raw mate materi rial alss is low. low. The The wast wastew ewat ater er from from the the manufacturing processes is rich in various substituted deriva derivativ tives es of aromat aromatic ic compou compounds nds.. They They are extremely toxic to organisms. The biological processes canno cannott effect effective ively ly degra degrade de thes thesee subs substa tance ncess and decol decolor oriz izee the the DSDDSD-aci acid d wast wastewa ewate terr (An (An Huren Huren et al ., ., 1994). As aromatic ring with –SO 3 H is easily dissol dissolved ved in water, water, the treatm treatment ent efficiency efficiency of the general chemical and physical methods is unsatisfactory. Therefore, DSD-acid wastewater is one of the most refractory wastewaters known so far (Yu Gang ., 1994; Zhou Xueshuang, 1992). et al ., The method of ferrous hydrogen peroxide oxidation tion is also also know known n as Fent Fenton on’s ’s reag reagent ent metho method. d. Hydrogen peroxide reacts with ferrous ion in water and generates the hydroxyl free radical (HO :), which is one one of the the most most acti active ve oxid oxidan ants ts,, (and (and)) whose whose oxidation ability is only next to F 2  among the known oxidants (Johannes, 1985). Fenton’s reagent method is very very efficient efficient to degrade degrade the refrac refractor tory y organi organicc substances in phenol (Eisenhauer, 1964; Smis, 1981),

chlorophenol (Sedlak and Andren, 1991), municipal wastewater wastewater (Bishop (Bishop   et al ., ., 1968 1968)) and printing printing and dyeing wastewater wastewater (Smis, 1983). Its great potential as a kind kind of advan advanced ced oxid oxidat ation ion metho method d has has draw drawn n more and more attention. In our lab, Fenton reagent is successfully used in DSD-aci DSD-acid d wastew wastewater ater treatm treatment ent.. This This method method not only only has the the advan advanta tages ges of both both oxid oxidat atio ion n and and coagula coagulatio tion n process processes, es, but also also increase increasess the disdissolved oxygen in water (Chin and Hicks, 1970). The enhancem enhancement ent of biodeg biodegrad radabi abilit lity y and coagula coagulatio tion n efficiency of DSD-acid wastewater is discussed in this paper.

MATERIALS AND METHODS

Material 

The DSD-acid wastewater used in this experiment was obtained obtained from the mother mother liquor, liquor, which was collected collected in acid precipitation and filtration processes. Its main organic constituents are 4,40 -dinitrostilbene-2,20 -disulfonic acid and 4,40 -diaminostilbene-2,20 -disulfonic acid:

*Author to whom all correspondence should be addressed. E-mail: [email protected] [email protected] 2087

2088

Wanpeng Zhu  et al.

The main characteristics of wastewater from a typical dye mill are summarized in Table 1.

The result suggests that the COD is removed rapidly with the increase in the concentration of Fe 2+ and the optimal Fe2+ dosage is 2.0–4.0 mmol/L.

Methods

The experiments were performed in 250mL beakers according to the following steps: (1) take 100 mL wastewater sample in a 250mL beaker on a stirrer; (2) add definite volume of FeSO4  solution and turn on the stirrer; (3) drip 30% H2O2   solution into the wastewater sample. After reactions had completed, color, COD and BOD5  values of  the sample were measured. The COD concentration was measured with the COD measurement apparatus (Model C-86-3, Chengde, China). The BOD5  concentration was determined with the standard dilution method. The pH value was measured with the Digital Acidimeter (Model pHS-3B, Leichi, China). The color of wastewater was measured with standard dilution multiple method. The ultraviolet absorption spectra were measured with ultraviolet spectrophotometer (Shimadzu Model UV 250, Japan).

RESULTS AND DISCUSSION

Effect of H 2O2  dosage on COD removal  At pH 2.5 (the raw wastewater’s pH value) and the concentration of Fe2+ equal to 2.7 mmol/L, the effects of different amounts of H2O2   on COD removal are shown in Fig. 3. When H 2O2   dosages are 0.26mol/L, the COD and color removals of  wastewater are 25 and 15%, respectively. It illustrates that the substances in the DSD-acid manufacturing process wastewater are difficult to be oxidized. The measurements of absorbance reveals the peak of DSD-acid wastewater at wavelength 361 nm declined gradually, but the absorption at the visible light wavelength at the range of 400–700nm rose at first and then descended steadily with the increase of  oxidant dosage. It corresponds to the observation

Fenton’s reagent method is a homogeneous catalytic oxidation process. If hydrogen peroxide is added to an aqueous system containing organic substances and excess ferrous ions, a complex redox reaction occurs. The main reactions are Fe2þ þH2 O2  !  Fe 3þ þOH þ  HO

ð1Þ

Fe3þ þH2 O2  !  Fe 2þ þHþ þHO2

ð2Þ

The hydroxyl free radical generated would attack the organic substances, such as the unsaturated dye molecules. The chromophore or chromogen of the dye molecules can be destroyed and the wastewater can be decolorized. Effect of pH on COD removal 

Fig. 1. Effect of pH on COD removal (conditions: the H2O2   dosage is 1.24 mol/L, the concentration of Fe2+ is 3.6 mmol/L).

When the H2O2   dosage is 1.24 mol/L (as pure H2O2), the concentration of Fe 2+ is 3.6 mmol/L (as Fe2+), the effect of different wastewater sample’s pH on COD removal is shown in Fig. 1. The results indicate that the COD removal is highest under acid condition (pH=2–4) and it declines remarkably with the increase of pH value. Therefore the raw DSDacid wastewater (its pH value is 2.5) can be directly treated. Effective amount of ferrous sulfate When the H2O2   dosage is 1.24 mol/L (as pure H2O2), the effect of different concentrations of Fe 2+ on COD removal is shown in Fig. 2.

Fig. 2. Effect of Fe2+ dosages on COD removal (conditions: the H2O2  dosage is 1.24 mol/L, the pH of wastewater is 2.5).

Table 1. Main characteristics of wastewater from a dye mill COD (mg/L)

BOD 5 (mg/L)

TOC (mg/L)

Cl (g/L)

pH

Color (Multiple)

60,000

0

12,920

250

2.3

1.4  105

Application of ferrous hydrogen peroxide

Fig. 3. Effect of H2O2   dosages on COD or color removal (conditions: the concentration of Fe 2+ is 2.7mmol/L, the pH of wastewater is 2.5).

that the color of wastewater deepened at first and then became lighter gradually.

2089

Fig. 4. Effect of H2O2   dosages on coagulation efficiency (COD removal) (conditions: the pH is 4.0, the concentrations of FeCl3   were 0.031 mol/L in the first stage and 0.012 mol/L in the second stage).

Effect of Fenton’s reagent oxidation treatment on coagulation A solution in COD concentration of 60 g/L was prepared with pure DSD-acid, which is one of the major constituents of DSD-acid wastewater, and its pH was adjusted to 2.5. FeSO4  solution was added to adjust the concentration of Fe2+ in the solution to 3.60 mmol/L. H2O2  solution (30%) was dripped into the solution and the change of SO 24 concentration in the solution was measured after the reaction was completed. The results show that the concentration of SO24 increases rapidly with the increase of H 2O2 dosage. It indicates that during the oxidation process, sulfo-group has already been substituted by HO and oxidized to SO24 in the solution, which markedly decreases the solubility of the organics in water. Therefore, Fenton’s reagent oxidation process can also improve the effect of the coagulation. DSD-acid wastewater was treated with Fenton’s reagent method first and its pH value was adjusted to 4.0. A two-stage coagulation test was then carried out by using FeCl3. In the first stage coagulation, the concentration of FeCl3   was 0.031 mol/L and in the second stage was 0.012 mol/L. The COD value of the wastewater was measured after oxidation, coagulation and clarification. The results were shown in Fig. 4. As shown in Fig. 4, Fenton’s reagent oxidation process can improve the efficiency of coagulation treatment. Combination of Fe2þ –H 2 O2  oxidation and organic coagulation The combination of Fe2+ –H2O2   oxidation and organic coagulation might be a more economic and effective approach. The organic coagulant TS-1 developed by Beijing Environment Protection Science Institute was used in this experiment. TS-1 is a white-powdered cation coagulant, whose main

Fig. 5. Effect of TS-1 dosage on COD and color removal (conditions: the pH of the wastewater is 2.7).

constituent is quaternary ammonium salt. Organic compounds are primarily in anionic form (R-SO 3 ) in DSD-acid wastewater, so adopting cation coagulant is feasible. The results reported in Fig. 5 illustrate that TS-1 is effective in decoloration of DSD-acid wastewater, but due to the wastewater’s high concentration, if  TS-1 is used singly, the dosage may be too large. So the combination of coagulation and oxidation is desirable. Two kinds of processes were adopted in this experiment: (1) The wastewater sample was first coagulated with TS 1 dosage 3 g/L, then FeSO4   solution was added to adjust the concentration of Fe 2+ in the solution to 2.7 mmol/L, and finally different H2O2  dosage was dripped. (2) In reverse order: the wastewater sample was first oxidized with Fe2+ H2O2, and then coagulated with TS 1, in the same condition. The experimental results are presented in Figs 6 and 7. It indicates that:

2090

Wanpeng Zhu  et al.

Comparing Figs 6 and 7 with Fig. 3, it is revealed that in the same H2O2   dosage, the combination of  coagulation and Fe2+ –H2O2  oxidization can apparently improve COD and color removal. The initial value of BOD 5   of the wastewater was zero (Table 1). BOD5  value of the wastewater treated in process (1) was measured. The results showed that the value of BOD5/COD has reached 0.3; the COD and color removal were 64 and 62% respectively, when the H2O2   dosage is 0.21 mmol/L, and the wastewater is biodegradable.

Fig. 6. Effect of H2O2   dosages on COD removal in two processes (conditions: TS-1 dosage is 3 g/L, [Fe2+] is 2.7 mmol/L).

Fig. 7. Effect of H2O2   dosages on colour removal in two processes (conditions: [Fe 2+] is 2.7 mmol/L, TS-1 dosage is 3g/L).

Process (1) is apparently more efficient than process (2) with a view to COD and color removals. The dye sulfonate anion is bonded with quaternary ammonia cation and forms water-immiscible compound in acidic solution. They can be easily removed in the process of coagulation: 2R3 N þ H 2 SO4  ) ðR3 NHþ Þ2 SO24 þ

mðR3 NH

Þ2 SO24 þR0



 ðSO3 Þn

2 0 ) ð R3 NHþ Þ2m ðSO 3  Þn    R þmSO4

where R3NH+ is quaternary ammonia cation, + R0 (SO )2m 3 )n  is dye sulfonate anion and (R 3  NH  0 (SO3 )n –R is water-immiscible compound. The sulfonate anion in the organic compound is substituted when the wastewater sample is first oxidized with Fe2+ –H2O2. It tends to decrease water solubility of compound in the wastewater and improve coagulation with organic coagulants. However, organic compounds no longer existed as anion, which weakened flocculation ability of TS-1, and so tends to lower total removal rate.

CONCLUSIONS

(1) Hydroxyl free radical generated in the decomposition of H2O2   induced by Fe2+ can rapidly oxidize organic compounds in DSD-acid wastewater, which are difficult to be oxidized by general oxidants. The process of combination of  Fe2+ –H2O2   oxidation and organic coagulation can effectively increase removal rate of COD and color and improve the biodegradability of  the wastewater. (2) Water solubility of organic compounds with sulfonic groups decreases, and coagulation of  inorganic coagulant is strengthened after they are oxidized by Fe2+ –H2O2. When [Fe2+]= 2.7 mmol/L, [H2O2]=0.059 mol/L, and in twostep coagulation the FeCl3   dosage is 0.031 and 0.012 mmol/L respectively, the COD and color removal are above 90 and 95%, respectively. (3) The combination of TS-1 coagulation and Fe2+ –H2O2   oxidization is one of the effective pretreatment approaches of the biological treatment of DSD-acid wastewater. When [TS1]=3g/L and [H2O2]=0.21 mol/L, the COD removal is 64%, the color removal is 62%, and BOD5/COD=0.3.

REFERENCES

Huren A.,   et al . (1994) Biodegradabilities of dyes under the aerobic conditions.   Chin. J. Environ. Sci. 15(6), 16–19. Bishop D. B., Stern G., Fleischman M. and Marshall L. S. (1968) Hydrogen peroxide catalytic oxidation of refractory organic in municipal wastewater. I&EC Process Des. Dev.  7 , 110–117. Chin C. and Hicks M. G. (1970) Hydrogen peroxide studies of oxygen demand.  J.W.P.C.F.  42 , 1327–1342. Eisenhauer H. R. (1964) Oxidation of phenolic wastes. J. W.P.C.F.  36 , 1110–1128. Johannes S. (1985) Decomposion of ozone in water in presence of organic solutes action as promotors and inhibitors of radical reaction.  ES & T  19 , 1206–1213. Sedlak D. L. and Andren A. W. (1991) Oxidation of  chlorobenzene with Fenton’s reagent.   ES & T   25, 777–782. Smis A. F. E. (1981) Phenol oxidation with hydrogen peroxide.  J. Effluent Water Treatment  3 , 109–112.

Application of ferrous hydrogen peroxide Smis A. F. E. (1983) Industrial effluent treatment with hydrogen peroxide.  Chem. Ind.  18 , 555–558. Gang Y.,   et al . (1994) Advances in physical and chemical treatment technologies for decolorization of dye wastewater.  Chin. J. En viron. Sci.  15 (4), 75–79 (in Chinese).

2091

Zhou Xueshuang (1992) Prospect of treatment of wastewater, waste gases and waste residues in dye synthesis industries.   Chin. J. Chem. Ind. Environ. Protect. 12(6), 333–335 (in Chinese).