DSpace at VNU: Catalytic Wet Oxidation of Wastewater from Pulping Industry Using Solid Waste Containing Iron Oxides

Coagulation of a birch pulp filtrate taken from the oxygen bleaching stage, which Catalytic Wet Oxidation of Wastewater from Pulping Industry Using Solid Waste Containing Iron Oxides Pha

Pulp and paper production is a particularly

pollut-ing industry as are major material productions The

man-ufacturing process of the pulping industry produces

great quantities of wastewaters which contain high

con-centrations of inorganic compounds (e.g., Na2CO3,

Na2SO4, Na2S, NaOH, NaCl) and organic compounds

(e.g., lignins, alcohols, polysaccharide fragments,

car-boxylic acids) (Adam et al., 1989; Pintar et al., 2001a;

Chakar and Ragauskas, 2004) A recovery and/or

elimi-nation process of these compounds is necessary to

mini-mize the production cost and/or reduce the pollution

generated

Vietnam is a tropical country with very high

bio-mass production; therefore, the pulp and paper industry

(PPI) has a good potential for growth, which is why the

United States government invested $3.6 billion in a

mas-ter plan to develop the Vietnamese PPI in the period of

2000–2010 The target production capacity of the plan is

more than 1 million ton/year of paper pulp by the year

2010, which could almost fully cover the domestic

mar-ket demand (Ministry of Industry of Vietnam, 1997)

Besides its undoubted benefits, PPI could be the heaviest

pollution producer, particularly concerning the aquatic

environment The sketch of material flows and waste

streams of PPI in Vietnam are summarized in Figure 1.

Due to the high contents in organic and inorganic compounds in black liquor, chemical recovery stages are established, including a vacuum evaporation system, Tomlinson’s incinerator with a steam recovery boiler for organics combustion and heat utilization, a caustization stage to recover NaOH and Na2S for reuse in the cook-ing stage This unit is identified by the dotted rectangles

in the right of Figure 1 Therefore, organic contaminants are combusted; 93–95% inorganic chemicals (caustic, sulfide) are recovered and reused in cooking; only solid CaCO3(from caustization) and a small amount of over-flow water and sulfide are produced Nevertheless, in Vietnam, there are only two plants, Bapaco and Cogido (situated at Phu Tho and Dong Nai provinces, Vietnam), which possess this recovery unit Other plants have not been equipped with this technology or other treatment stations Therefore, black liquor and other wastewaters are discharged without adequate treatment

Several studies have focused on the treatment of wastewaters of PPI in which different methods were

pro-posed Wallberg et al (2003) studied the ultrafiltration

of a Kraft black liquor (56 g/L of lignin, 37 g/L of inor-ganic materials, 16% of total dry substance and pH 13–14), using a KERASEP membrane (Novasep Corp.) with a cut-off of 15 kDa The temperature was found to have a significant influence on the flux of black liquor, which was 90, 110 and 130 L/m2h at 60, 75 and 90°C and 100 kPa, respectively Coagulation of a birch pulp filtrate taken from the oxygen bleaching stage, which

Catalytic Wet Oxidation of Wastewater from Pulping Industry Using Solid Waste Containing Iron Oxides

Pham Minh DOAN1, Ngoc Dung TRAN2, Thi Hau VU1

and The Ha CAO1

1The Center for Environmental Technology and Sustainable Development (CETASD), Hanoi University of Science, Vietnam National University,

334 Nguyen Trai, T3 Building, Hanoi, Vietnam

2Faculty of Chemistry, Hanoi University of Science, Vietnam National University,

19, Le Thanh Tong, Hoan Kiem, Hanoi, Vietnam

Keywords: Wet Air Oxidation, Wastewater Treatment, Heterogeneous Catalysis, Black Liquor, Pulping Industry

The pulping industry generates great quantities of wastewaters (WW ), where a small amount of black liquor

accounts for more than 90% of its entire manufacturing process load in organics Treatment of the black liquor

from pulping manufacture in ThaiNguyen province (Vietnam) by catalytic wet oxidation (CWO) under mild

re-action conditions (150–180°C, 15 bar) using solid wastes containing iron oxide as heterogeneous catalysts is

com-municated herein These solid wastes have been found to be active in the oxidation of pollutants in the black

liquor and show a high application potential in CWO processes for the treatment of this kind of industrial

waste-water.

Journal of Chemical Engineering of Japan, Vol 44, No 2, pp 123–129, 2011

Received on August 26, 2010; accepted on October 8, 2010

Correspondence concerning this article should be addressed to

D Pham Minh (E-mail address: doanhoa2000@yahoo.fr).

Research Paper

contains less than 400 mg/L of wood extractives and

lig-nans, was carried out by Leiviska and Ramo (2008),

with or without the use of a cationic polyelectrolyte The

best result was obtained with a copolymer of acrylamide

and methacrylate of medium molecular weight and

medium charge density at 72°C and pH 5–6 with

extrac-tives removal up to 92% However, the pollutants

sepa-rated with these techniques must be treated, and thermal

treatments are usually applied Font et al (2003) studied

the incineration and pyrolysis of lignin separated by

the precipitation of a black liquor using sulfuric acid (weight percentage: 63.9% C, 25.8% O, 6.2%

H, 0.8% N, 1.7% S) High emissions of CO were found between 25000–90000 mg/kg for incineration and 30–3000 mg/kg for pyrolysis The main by-products formed in the combustion were methane, ethylene, acetylene, benzene, toluene, indene, naphthalene, ace-naphthylene, phenantrene, fluorantene and pyrene Therefore, these by-products limit the efficiency of ther-mal processes Recently, an advanced oxidation process

Fig 1 Sketch of material flows and waste streams of PPI in Vietnam:

WW 1 Wastewaters from raw material washing: This kind of WW contains mainly solid dregs, mud, bamboo or wood husks and chips, etc They can be easily removed by settling techniques with or without coagulation Treated wastewater can

be reused or discharged

WW 2 Black liquor: Black liquor (BL) is the effluent of the cooking of raw materials from the Kraft process to free the

cel-lulose fibres (Smook, 1992) Although this wastewater contributes to only a small amount of total wastewater volume, it contains about 90% organic load of the entire PPI wastewaters or more than half of the energy content of raw materials fed into the digester A high quantity of inorganic compounds was also present as mentioned above

A condensate could be formed from two stages of cooking and BL evaporation The main composition of cooking conden-sate is methanol, volatile organic compounds, and a significant quantity of sulfur compounds, main odor source in PPI

WW 3 Bleaching wastewaters (BWW ): The bleaching technology used in Vietnam dates from the 1970’s BWW is formed

after a chemical process to improve the brightness and whiteness of pulp, using different bleaching reagents (Cl 2 , ClO 2 , NaClO, H2O2, O3, etc.) This effluent is the principal source of organochlorines, which are persistent to conventional biolog-ical treatment

WW 4 Paper making wastewaters: This wastewater comes from a paper making stage; therefore, it contains mostly sus-pended solids and is easily treated.

was thoroughly investigated for the treatment of

differ-ent wastewaters Photocatalysis of an alkaline bleaching

effluent (initial TOC 980 mg/L, pH 10.3 and COD

2255 mg/L) was performed in a batch reactor using TiO2

and ZnO as photocatalysts (Cristina Yeber et al., 2000).

The decolorization was completed and the

mineraliza-tion was at about 50% after 120 min of treatment in the

presence of the catalysts Ko et al (2009) studied the

ozonation of diluted black liquor (initial COD 165 g/L

and COD of diluted effluent between 50 and 600 mg/L)

COD conversion reached 75% for diluted effluent of

150 mg/L of initial COD, but it was only 20% when the

initial COD was 600 mg/L, after 30 min of treatment

More recently, wet air oxidation (WAO), which is

based on the oxidation in liquid phase of pollutants

under high temperature and high pressure, has been

demonstrated to be an effective technology for the

treat-ment of different kinds of wastewater (National

Academy Press, 1993; Luck, 1999) This process was

demonstrated to be efficient for effluent containing a

high concentration of organic compounds, up to 100 g/L

of COD (Mishra et al., 1995) The main disadvantage of

WAO process is the severe conditions required to

achieve sufficient oxygen activation, typically being in

the range of 180–315°C and 20–150 bar (Luck, 1999)

Under such extreme conditions, the selection of reactor

materials and safety requirements become critical The

use of catalyst, heterogeneous or homogeneous (so

CWAO), was usually the best choice for oxygen

activa-tion in much milder condiactiva-tions In other works, CWAO

was generally more efficient than WAO under the same

reaction conditions (Pintar et al., 2001b; Pham Minh et

al., 2005; Barbati et al., 2008; Chaliha et al., 2008).

WAO and CWAO of wastewaters from the Kraft

bleach plant were carried out by Pintar et al (2001a,

2001b, 2004) WAO was efficient for the oxidation of

ganic compounds present in these wastewaters (total

or-ganic carbon-TOC between 665 and 1331 mg/L) at

190°C and 5.5 MPa in a batch reactor TOC abatement

was up to 87% after 8 h of reaction Adding a TiO2

sup-port or supsup-ported ruthenium (3 wt%) catalyst enhanced

the efficiency of the treatment with TOC removal being

nearly total Acetic acid was found to be the final organic

product after oxidation Titanium dioxide and supported

ruthenium catalysts were shown to be stable over a long

reaction time (more than 150 h) in a fixed-bed reactor

No leaching of metals was observed after the reaction

Other work on the CWAO of effluents from a bleaching

plant was carried out by Zhang and Chuang (1998) using

different catalysts A supported palladium catalyst was

found to be more effective than supported manganese,

iron, or platinum catalysts for the oxidation of

waste-waters with initial TOC of 720–1500 mg/L at 190°C and

1.5 MPa oxygen pressure WAO and CWAO of diluted

black liquor (initial COD after dilution 2700 mg/L,

pH 8) were also realized in a batch reactor in the

ab-sence and in the preab-sence of different homogeneous and

heterogeneous catalysts (CuSO4, 5%CuO/C, 60%CuO– 40%MnO2and 60%CuO–40%CeO2) (Garg et al., 2007).

The best results were obtained with 5%CuO/C and 60%CuO–40%CeO2, yielding 78%COD conversion after 4 h of reaction at 150°C and 0.85 MPa

One important factor in selection of catalysts for wastewater treatment is the cost The present paper shows the results on the use of solid wastes from differ-ent production process in Vietnam in WAO, using pure oxygen as an oxidation agent

1 Experimental

The wastewater used in this study was taken from HoangVanThu alkaline pulping manufacturer (ThaiNguyen province, Vietnam) It was black in color and had an unpleasant odor It was stored in a deep-freezer and was defrosted just before use Some

parame-ters of this effluent are shown in Table 1.

The catalyst precursors were solid wastes taken from four manufacturers in Vietnam: 1—GiaLam water plant (named Cat-1; sludge of ground water processing); 2—LamThao superphosphate plant (named Cat-2; solid waste of SO2production by incineration of pyrite-FeS2); 3—Vietnam Ford Co (named Cat-3; solid waste from the treatment of wastewater of metal processing shop, facility by FeCl3 and lime coagulation); 4—TanBinh Chem Co (named Cat-4; solid waste of alumina pro-duction from bauxite) The choice of these solid wastes was based on their possible richness in iron oxides, which could be used as a heterogeneous catalyst in

CWAO (Quintanilla et al., 2008), and their very low

costs The original catalysts were obtained by simple a preparation procedure: drying, grinding and sieving to yield particles smaller than 0.5 mm, then thermal treat-ing in air at 400°C Modified catalysts could be obtained

by the addition of copper, manganese and magnesium

Table 1 Some parameters of the black liquor used in this

study

Solid in suspension ⫺ SS a [g/L] 1.2

ABS: UV adsorption at 390 nm

a : mass of substances in black liquor remaining on filter paper

in blue band and drying at 103°C

b : mass of solid substances in 1 L of black liquor after drying at 103°C

c : residue after calcination of dried TS at 700°C with respect to the mass of dried solid substances

oxides on the original catalysts using impregnation

tech-nique The original catalyst was impregnated with a

so-lution of CuSO4or MnSO4 After drying, the solid was

re-impregnated with a solution of NaOH to transform

copper and manganese sulfates into hydroxides The

solid was dried again and finally calcinated in air at

400°C for 4 h The modified catalysts containing

magne-sium oxide were prepared with MgO in powder form

Original catalysts were characterized by X-ray

diffrac-tion (XRD) using a Siemens D5005 diffractometer with

Cu Ka1 ⫹ 2radiation at 0.154184 nm

The oxidation of black liquor was performed in a

450-mL batch reactor, equipped with a magnetic stirrer

and an electric heating jacket The internal face of the

reactor was coated with a Teflon layer to avoid the

possi-ble influence from the metal wall For the reaction,

100–150 mL of black liquor, with or without dilution,

and 2–3 g of catalyst were introduced into the reactor

After purging and heating to the working temperature

(150–180°C), the reactor was pressurized and

main-tained at 15 bar with O2 The oxidation was started by

setting of magnetic stirrer speed (1000 rpm) Samples

withdrawn from the reactor were analyzed in terms of

COD, color and pH The analysis of COD was carried

out using a classical dichromate method (APHA, 1995)

The color was measured as absorption value (ABS) at

390 nm using a cuvette with a thickness of 1 cm on a

UV-VIS 1201 (Shimadzu Corp.) The pH was measured

with a pH-meter installed in our laboratory COD and

color reductions were calculated with the following Eqs

(1) and (2)

XCOD[%] ⫽ 100(CODt⫺ COD0) / COD0 (1)

XABS[%] ⫽ 100(ABSt⫺ ABS0) / ABS0 (2)

(COD0, CODt, ABS0, ABSt: COD and UV absorption

values of effluents before and after CWO treatment,

re-spectively)

2 Results and Discussion

2.1 XRD

Three original catalysts including Cat-1, Cat-3,

Cat-4, pretreated at 400°C in air, were found to be

amor-phous materials As an example, Figure 2 shows a XRD

pattern of Cat-1, which originated from ground water

processing

On the other hand, Cat-2 seems to have higher

crys-tallinity (Figure 3) We found the presence of magnetite

in this sample Other peaks are presently not identified

2.2 Catalytic activity of original and modified

cata-lysts at mild temperature

Table 2 shows the results obtained in CWO of the

black liquor in the absence of catalyst and in the

pres-ence of the heterogeneous catalysts after 1 h of reaction

at 150°C and 15 bar oxygen pressure These conditions

are typical for CWO because no activity is known at

am-bient temperature and pressure

Comparative activity of catalysts can be evaluated according to the conversion of COD under the same re-action conditions Obviously, CWO is much better than simple WAO Non-catalytic (WAO) can remove only 13% COD of black liquor, while all CWAO experiments reached between 28 and 38% after 1 h of reaction, which

is as much as 2–3 times more It should be noted that 150°C and 15 bar are very mild conditions for WAO and CWO process

Among four original catalysts, Cat-1 and Cat-3 (re-actions No 2 and 11) were slightly better than Cat-2 and Cat-4 (reactions No 3 and 19), with 34% of COD re-moval To make the catalysts more active, some active components such as CuO, MnO2and MgO were added Copper and manganese oxides are currently used as the active phase of catalysts in the total oxidation of organic

pollutants (Akyurtlu et al., 1998; Hocevar et al., 2000;

Hu et al., 2001; Santos et al., 2001; Yoon et al., 2001; Akolekar et al., 2002) Particularly, in the case of black

liquor, MgO was added to confirm the results of Robert (Tutorski, 1998), in that Mg salt is active in oxygen

Fig 2 XRD pattern of Cat-1

Fig 3 XRD pattern of Cat-2; *: diffraction of magnetite phase Fe 3 O 4

delignification Therefore, the modification of original

catalysts was carried out on Cat-2 and Cat-3 This

modi-fication enhanced the catalytic activity of Cat-2, but

de-creased the catalytic activity of Cat-3 We presently have

no explanation for the last case Further study on the

characterization of these catalysts will be necessary to

explain these results

For the modified catalysts with the addition of one

metal oxide (CuO or MnO2 or MgO), we observed an

order of activity as follows: MgO ⬇ CuO ⬎ MnO2 This

means that MgO was also active in the oxidation of

or-ganic pollutants For modified catalysts with the addition

of two metal oxides, catalysts containing copper and

magnesium oxides showed the highest activity Finally,

the highest COD conversion was obtained at 38% with

6%CuO–6%MgO/Cat-2 after 1 h of reaction (No 8)

In parallel with the COD reduction, color removal

was also observed In all cases, color reduction was

more important than COD reduction This observation

could be explained by the fact that color removal needs

only destructive oxidation, while COD removal requires

complete oxidation In fact, under CWO conditions,

polyphenolic compounds (lignin) were firstly

decom-posed into smaller colorless molecules such as acetic

acid (Pintar et al., 2001a, 2001b, 2004) Heterogeneous

catalysts are known to promote the formation of

O-radi-cal species which effectively decompose colored organic

compounds (Arena et al., 2010) CWO also oxidizes

sul-fur based compounds into sulfates having no particular

odor The pH of treated effluent was also decreased in

comparison with that of crude effluent by the formation

of shorter acidic molecules in oxidation conditions of WAO and CWO Despite a high COD reduction of up to 38%, the pH of treated effluent was, in most cases, found to be about 8.2–8.4 This may be due to the pres-ence of a buffer system, for example, Na2CO3/NaHCO3,

in the black liquor, as illustrated in Figure 4 for the

titra-tion of the black liquor with a solutitra-tion of H2SO4 (9.8 wt%), where we observed a pH buffer domain above

Table 2 Results on the oxidation of black liquor; temperature: 150°C, pressure: 15 bar with oxygen, stirrer speed:

1000 rpm, reaction time: 1 h, catalyst mass: 2 g, volume of black liquor: 100 mL, initial COD: 44.4 g/L, ini-tial ABS at 390 nm: 72.9%; iniini-tial pH: 11.8

pHt

Fig 4 Titration of 50 mL of black liquor with sulfuric acid (9.8 wt%) at ambient temperature

the value of pH 9.5 This observation was important in

confirming that transition metals present in the catalysts

do not dissolve Deactivation of catalysts is known to

occur under lower pH conditions when large amounts of

organic acid intermediates are produced (Besson and

Gallezot, 2003)

2.3 Influence of temperature

The influence of the temperature on COD and color

removal was investigated between 150 and 180°C using

3 g of 6%CuO–6%MnO2/Cat-3 and 150 mL of diluted

black liquor (COD and ABS at 390 nm after dilution

with distilled water: 23.5 g/L and 51%, respectively) In

these experiments, samples were withdrawn periodically,

and thus we used a higher volume of effluent Then, to

assure the quantity of oxygen introduced in gas phase of

reactor would be sufficient for possible total oxidation,

dilution of the effluent with the diluted water was

neces-sary The results are shown in Figure 5.

At each temperature, the COD and color of effluent

continuously reduced over the reaction time The

tem-perature had an evident influence on COD abatement

COD abatement improved with higher temperatures The

best result for COD conversion of 58% was obtained at

180°C after 3 h of reaction From these results, the

acti-vation energy for COD reduction under experimental

conditions was calculated to be a value of 97 kJ/mol On

the other hand, the effect of the temperature on the color

removal was less evident The best result for color re-moval was 74% at 180°C after 3 h of reaction

2.4 Influence of the ratio of catalyst mass to effluent volume

The influence of the ratio of catalyst mass to efflu-ent volume was also investigated Oxidation of 100 mL

of diluted black liquor was carried out in the presence of 1–4 g of 6%CuO–6%MgO/Cat-3 at 150°C and 15 bar oxygen pressure The results after 1 h of reaction are

psented in Table 3 As expected, the COD and color

re-moval increased with an increase in the catalyst mass to effluent volume ratio

2.5 Discussion

Black liquor of the pulping industry is well-known

as an important source of industrial wastewater, charac-terized by high contents of organic and inorganic pollu-tants In this study, we chose the CWO process as a method for the treatment of black liquor containing 44.4 g of COD The objective of this work was to con-firm the efficiency of different solid wastes in the CWO treatment of this effluent The most important result of this work is demonstrating the technical feasibility of using available waste material for the preparation of CWO catalysts

Conclusions

The present study is the first to prove that industrial solid wastes containing iron oxides are active in CWO of black liquor from PPI Furthermore, MgO was also found to be an active component In the case of the solid wastes from the production of SO2(Cat-2), the catalytic activity can be enhanced by the addition of a well-known catalytic component such as CuO, MnO2 or MgO For practical application, further research on the composi-tion and nature of the catalysts should be performed to better understand the catalytic behavior of the original and modified catalysts The stability of these catalysts also must be confirmed The reduction in toxicity and biotoxicity of treated wastewaters could be verified prior

Fig 5 Influence of the temperature in the oxidation of

di-luted black liquor; pressure: 15 bar with oxygen,

stir-rer speed: 1000 rpm, catalyst mass: 3 g, volume of

black liquor: 150 mL, COD and ABS at 390 nm after

dilution: 23.5 g/L and 51%, respectively

Table 3 Influence of ratio of catalyst mass to effluent

vol-ume in the oxidation of diluted black liquor; temper-ature: 150°C, pressure: 15 bar with oxygen, stirrer speed: 1000 rpm, reaction time: 1 h, catalyst: 6%CuO–6%MgO/Cat-3, volume of diluted black liquor: 100 mL, COD and ABS at 390 nm after dilu-tion: 23.5 g/L and 51%, respectively

mcat/ Veffluent COD t XCOD ABS t XABS

to subsequent final biological treatment Furthermore, it

can be expected that the efficiency of the process will be

improved by optimizing reactor engineering aspects of

the process

Acknowledgments

We would like to express our deep gratitude to Prof Nguyen

Huu Phu, NCST, Vietnam, for the use of Parr Instrument We are also

grateful to Nafosted for financial support and our colleagues at

CETASD for their technical assistance.

Literature Cited

Adams, T., B Cowan, D Clayton, D Easty, D Einspahr, D E Fletcher

and T M Malcolm; Alkaline Pulping (Pulp and Paper

Manufac-ture), 3rd ed., Tappi Press, Atlanta, U.S.A (1989)

Akolekar, D B., S K Bhargava, I Shirgoankar and J Prasad;

“Cat-alytic Wet Oxidation: An Environmental Solution for Organic

Pol-lutant Removal from Paper and Pulp Industrial Waste Liquor,”

Appl Catal., A, 236, 255–262 (2002)

Akyurtlu, J F., A Akyurtlu and S Kovenklioglu; “Catalytic Oxidation

of Phenol in Aqueous Solutions,” Catal Today, 40, 343–352

(1998)

APHA; Standard Methods for the Examination of Water and

Waste-water, Method 5220 D, 19th ed., American Public Health

Associa-tion, Washington, D.C., U.S.A (1995)

Arena, F., C Italiano, A Raneri and C Saja; “Mechanistic and Kinetic

Insights into the Wet Air Oxidation of Phenol with Oxygen

(CWAO) by Homogeneous and Heterogeneous Transition-Metal

Catalysts,” Appl Catal., B, 99, 321–328 (2010)

Barbati, S., V Fontanier and M Ambrosio; “Wet Air Oxidation of

Meat-and-Bone Meal and Raw Animal Byproducts,” Ind Eng.

Chem Res., 47, 2849–2854 (2008)

Besson, M and P Gallezot; “Deactivation of Metal Catalysts in Liquid

Phase Organic Reactions,” Catal Today, 81, 547–559 (2003)

Chakar, F S and A J Ragauskas; “Review of Current and Future

Soft-wood Kraft Lignin Process Chemistry,” Ind Crops Prod., 20,

131–141 (2004)

Chaliha, S., K G Bhattacharyya and P Paul; “Catalytic Destruction of

4-Chlorophenol in Water,” Clean, 36, 488–497 (2008)

Cristina Yeber, M., J Rodriguez, J Freer, N Duran and H D Mansilla;

“Photocatalytic Degradation of Cellulose Bleaching Effluent by

Supported TiO2and ZnO,” Chemosphere, 41, 1193–1197 (2000)

Font, R., M Esperanza and A N Garcia; “Toxic By-Products from the

Combustion of Kraft Lignin,” Chemosphere, 52, 1047–1058

(2003)

Garg, A., I M Mishra and S Chand; “Catalytic Wet Oxidation of the

Pretreated Synthetic Pulp and Paper Mill Effluent under Moderate

Conditions,” Chemosphere, 66, 1799–1805 (2007)

Hocevar, S., U O Krasovec, B Orel, A S Arico and H Kim; “CWO

of Phenol on Two Differently Prepared CuO–CeO2 Catalysts,”

Appl Catal., B, 28, 113–125 (2000)

Hu, X., L Lei, G Chen and P L Yue; “On the Degradability of

Print-ing and DyePrint-ing Wastewater by Wet Air Oxidation,” Water Res.,

35, 2078–2080 (2001)

Ko, C.-H., P.-H Hsieh, M.-W Chang, J.-M Chern, S.-M Chiang and C.-J Tzeng; “Kinetics of Pulp Mill Effluent Treatment by

Ozone-Based Processes,” J Hazard Mater., 168, 875–881 (2009)

Leiviska, T and J Ramo; “Coagulation of Wood Extractives in

Chemi-cal Pulp Bleaching Filtrate by Cationic Polyelectrolytes,” J

Haz-ard Mater., 153, 525–531 (2008)

Luck, F.; “Wet Air Oxidation: Past, Present and Future,” Catal Today,

53, 81–91 (1999)

Ministry of Industry of Vietnam ed.; Master Plan of Vietnamese Pulp and Paper Industry up to 2010 (in Vietnamese), Ministry of Indus-try of Vietnam, Hanoi, Vietnam (1997)

Mishra, V S., V V Mahajani and J B Joshi; “Wet Air Oxidation,” Ind.

Eng Chem Res., 34, 2–48 (1995)

National Academy Press ed.; Alternative Technologies for the Destruc-tion of Chemical Agents and MuniDestruc-tions, pp 185–208, Washing-ton, D.C., U.S.A (1993)

Pham Minh, D., M Besson and P Gallezot; “Degradation of Olive Oil Mill Effluents by Catalytic Wet Air Oxidation 1 Reactivity of

p-Coumaric Acid over Pt and Ru Supported Catalysts,” Appl Catal.,

B, 63, 68–75 (2005)

Pintar, A., M Besson and P Gallezot; “Catalytic Wet Air Oxidation of Kraft Bleaching Plant Effluents in the Presence of Titania and

Zirconia Supported Ruthenium,” Appl Catal., B, 30, 123–139

(2001a) Pintar, A., M Besson and P Gallezot; “Catalytic Wet Air Oxidation of Kraft Bleach Plant Effluents in a Trickle-bed Reactor over a Ru/TiO2Catalyst,” Appl Catal., B, 31, 275–290 (2001b)

Pintar, A., G Bercic, M Besson and P Gallezot; “Catalytic Wet-Air Oxidation of Industrial Effluents: Total Mineralization of Organics

and Lumped Kinetic Modeling,” Appl Catal., B, 47, 143–152

(2004) Quintanilla, A., N Menéndez, J Tornero, J A Casas and J J Rodríguez; “Surface Modification of Carbon-Supported Iron Cat-alyst during the Wet Air Oxidation of Phenol: Influence on

Activ-ity, Selectivity and StabilActiv-ity,” Appl Catal., B, 81, 105–114 (2008)

Santos, A., P Yustos, B Durban and F Garcia-Ochoa; “Catalytic Wet

Oxidation of Phenol: Kinetics of Phenol Uptake,” Environ Sci.

Technol., 35, 2828–2835 (2001)

Smook, G A.; Handbook for Pulp and Paper Technologists, vol 11, 2nd ed, pp 163–183, Angus Wilde Publications, Vancouver, Canada (1992)

Tutorski, V.; Chlorine and Chlorine Compounds in the Paper Industry,

pp 25–39, Ann Arbor Press, Chelsea, U.S.A (1998) Wallberg, O., A S Jarwon and R Wimmerstedt; “Ultrafiltration of

Kraft Black Liquor with a Ceramic Membrane,” Desalination,

156, 145–153 (2003)

Yoon, C H., S H Cho, S H Kim and S R Ha; “Catalytic Wet Air Oxidation of p-Nitrophenol (PNP) Aqueous Solution using

Multi-component Heterogeneous Catalysts,” Water Sci Technol., 43,

229–236 (2001) Zhang, Q and K T Chuang; “Alumina-Supported Noble Metal Cata-lysts for Destructive Oxidation of Organic Pollutants in Effluent

from a Softwood Kraft Pulp Mill,” Ind Eng Chem Res., 37,

3343–3349 (1998)