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Treatment-of-APMP-pulping-effluent-based-

Treatment of APMP pulping ef?uent based on aerobic fermentation with Aspergillus niger and post-coagulation/?occulation

Tingzhi Liu a ,b ,?,Zhibin He b ,Huiren Hu a ,Yonghao Ni b

a Tianjin Key Laboratory of Pulp and Paper,Tianjin University of Science and Technology,Tianjin 300457,China b

Limerick Pulp and Paper Centre,University of New Brunswick,Fredericton,NB,Canada E3B 5A3

a r t i c l e i n f o Article history:

Received 9November 2010

Received in revised form 15January 2011Accepted 17January 2011

Available online 22January 2011Keywords:

APMP ef?uent Aspergillus niger

Biological pretreatment Coagulation Flocculation

a b s t r a c t

A novel two-stage biological/?occulation process was developed for treating the pulping ef?uent from the alkaline peroxide mechanical pulping (APMP)process.In the ?rst biological stage,the aerobic fer-mentation by using Aspergillus niger can decrease the chemical oxygen demand (COD)by about 60%while producing about 7g/l of solid biomass.In the second stage (post-coagulation/?occulation),the residual COD,turbidity and color,can be further decreased by using alum and polyacrylamide (PAM).The overall removal ef?ciencies of COD,color and turbidity from the APMP pulping ef?uent by the above two-stage biological-coagulation/?occulation process were 93%,92%and 99%,respectively,under the conditions studied.

1.Introduction

The pulp and paper industry in Asia has been growing rapidly in the past decade.Ef?cient use of the wood raw materials and non-wood ?ber resources have ever become so important in many Asian countries with the booming pulp and paper industry (Hos-seinpour et al.,2010;Jahan et al.,2006).Conventional alkaline per-oxide mechanical pulping (APMP)and pre-conditioning re?ner chemical alkaline peroxide mechanical pulping (P-RC APMP)pro-cesses are relatively new technologies in the pulp and paper indus-try that enable papermakers to produce high quality mechanical pulp at a yield as high as 90%(Xu and Zhou,2007;Xu et al.,2008;Yuan et al.,2006).In China,many new APMP and P-RC APMP lines have been installed in recent years.

A typical conventional APMP or P-RC APMP pulping process generates about 30m 3/t of ef?uent that needs to be treated before it can be discharged into the receiving water bodies,with its chem-ical oxygen demand (COD)load commonly in the range of 5000–10,000mg/l,30–45%of which would be bio-degradable (Wang and Shi,1997).There are two different processes for treating the APMP ef?uent:(1)in paper mills where there are chemical pulping capacities,such as kraft or soda-anthraquinone pulping processes,it may be combined with chemical pulping ef?uent in an existing chemical recovery system;(2)it can be treated in a biological sys-tem.Currently,the most widely employed biological system for treating APMP ef?uent is the three-stage ?occulation-biological-?occulation process (Cui,2008).The main purpose of the pre-?oc-culation stage is to remove the toxic wood extractives,such as col-loidal resin acids from the ef?uent before going to the subsequent anaerobic stage that are toxic to the anaerobic organisms (Kostamo and Kukkonen,2003),and the second ?occulation,or post-?occu-lation,is to remove the residual suspended solids and colored sub-stances.This three-stage process can effectively treat the APMP ef?uent;however,its capital investment and operating cost are high.

To decrease the capital investment and operating cost,we pro-posed that the three-stage process may be simpli?ed into a two-stage process with the development of new bio-treatment technol-ogy and advanced coagulation/?occulation programs.The ?rst ?oc-culation treatment may be omitted in the new process,provided that (1)the organisms used for the bio-treatment can tolerate the wood extractives in the APMP ef?uent,and (2)the effective-ness of the post-?occulation could be improved.It has been re-ported that aerobic organisms,such as white rot fungi,are less sensitive than anaerobic organisms to wood extractives (Liver and Hall,1996;Lo et al.,1991).Gao used white rot fungi to treat a raw chemi-thermo mechanical pulping (CTMP)ef?uent without pre-?occulation and found that the COD and color were removed by 59.0%and 47.5%,respectively,with a 5-day treatment (Gao et al.,2001).Aspergillus niger is another aerobic organism that

?Corresponding author.Address:Tianjin Key Laboratory of Pulp and Paper,Tianjin University of Science and Technology,No.29,13th Avenue,Tianjin Economic and Technological Development Area,Tianjin 300457,PR China.Tel.:+862260601169;fax:+862260602510.

E-mail address:liutzhi3260@https://www.wendangku.net/doc/2311123973.html, (T.Liu).

can be cultured for the production of many useful enzymes,such as glucoamylase,pectinase and galactosidase.It is known as one of the most important microorganisms used in biotechnology,which has been in use for many decades to produce extracellular(food) enzymes and citric acid(Schuster et al.,2002).The safety related issues have been reviewed and it was concluded that A.niger is a safe production microorganism(Schuster et al.,2002).The use of A.niger has been approved by the Ministry of Agriculture of the People’s Republic of China.We proposed to use a two-step process: a biological treatment by using A.niger,followed by a coagulation/?occulation step to further decrease the COD and color.The biolog-ical stage can also produce a large amount of biomass in solid form that is rich in amino acids and minerals.This solid by-product may be used as raw material to produce fertilizer and/or animal feed. Due to the fact that there would be no pre-?occulation treatment, thus the fungi to be used must be reasonably active even in the presence of wood extractives.Our hypothesis is that A.niger may serve for this purpose well.

The post-coagulation/?occulation is another key unit operation affecting the overall performance of the proposed two-step pro-cess.Aluminum salts are widely used as coagulants in water and wastewater treatment(Ahmad et al.,2007).It has been reported that post-coagulation/?occulation of bio-treated waste water with aluminum or ferric chloride can decrease the COD and color by up to90%and98%,respectively(Buzzini et al.,2007).

In this study,we determine the effectiveness of the proposed two-stage process:?rst by aerobic fermentation with A.niger S13 fungi,followed by a post-coagulation/?occulation stage,in treating the APMP pulping ef?uent.

2.Methods

2.1.APMP pulping ef?uent

The APMP pulping ef?uent sample used in this study was ob-tained from an integrated pulp and paper mill in Shandong prov-ince in China.The mill had a new P-RC APMP line,producing APMP high yield pulp with its brightness of78%ISO and its free-ness of400ml(Canadian Standard Freeness,CSF)from poplar wood chips as the main raw materials.The pulp yield was about 90%,and the pulping process generated about30m3ef?uent per ton of pulp.The pulp was used,together with bleached kraft pulps, to make printing and writing paper products.The waste water sample was a combination of several ef?uent streams from the APMP pulping process,including chip washing,hot water impreg-nation,chemical impregnation,pressing and mechanical re?ning. It was passed through a200-mesh screen to remove any?bers,?nes and debris,and then stored in a refrigerator until use.Its ini-tial properties were:7521mg/l COD,977.2C.U.(Color Unit)color, 510NTU(Nephelometric Turbidity Unit)turbidity,354mg/l sus-pended solid(SS),pH7.43,and147.2mg/l methyl tertiary butyl ether(MTBE)extractives.

A.niger S13culture was prepared in our laboratory.The Alum sample(Alummix-2,30%solid content)was obtained from Nalco Company in Shanghai,China,and the polyacrylamide sample (PAM,C-4440)from SNF(China)Flocculant Co.Ltd.in Taixing City, Jiangsu Province,China.

2.2.Preparation of A.niger S13culture in the lab

A.niger S13was obtained from the microbiology laboratory of Tianjin University of Science and Technology,China.It was cul-tured at30°C,160rpm for48h in a modi?ed Czapek’s medium, which contained1000ml of deionized water,1000ml of the APMP waste water,3g of sodium nitrate,1g of potassium monohydro-gen phosphate,0.5g of magnesium sulfate heptahydrate,0.5g of potassium chloride,30g of sucrose.The prepared bacterium was stored in a refrigerator and used as the inoculum for the aerobic fermentation treatment of the APMP pulping ef?uent.

2.3.Aerobic fermentation with A.niger S13

The pH of the waste water sample was?rst adjusted to6.0by using1%NaOH solution and1%H2SO4solution,and a100ml of it was transferred into a250ml baf?ed?ask that was then stopped with a cotton plug and sterilized at121°C for30min in a pressur-ized steamer.After the?ask and its content have cooled down to room temperature,3ml(or otherwise as speci?ed)of the A.niger S13culture was added to inoculate the system.The?ask with the cotton plug on was then placed on a water-bath shaker to start the biological treatment.The air permeable cotton plug on the?ask and the mixing of the substrate created by the shaking action pro-vided suf?cient dissolved oxygen for the aerobic fermentation pro-cess which lasted from12to72h.At the end of the fermentation, the treated sample was settled for30min(simulating for industrial practice),and the supernatant was taken for the analyses of COD, turbidity,UV–vis absorbance,and MTBE extractives;in addition, part of the supernatant was used for the subsequent coagulation/?occulation process.The biomass settled at the bottom of the?ask was then?ltered with a0.45l m nylon membrane?lter,and washed two times with50ml deionized water each time.The solid retained on the?lter was then dried in an oven at105°C to con-stant weight.

2.4.Post-coagulation/?occulation

Fifty microliters of the supernatant from the bio-treatment was transferred into a beaker,and its pH adjusted to5.0,or otherwise speci?ed.Alum was then added to the?ask with magnetic stirring at400rpm.After3min,PAM was added and the stirring was con-tinued at250rpm for another5min.The beaker with the mixture was then let stand for120min,and30ml of the supernatant was then taken from the beaker for the determination of turbidity, COD and light absorbance.The dosage of alum and PAM were 1000and2mg/l,respectively,unless speci?ed.

2.5.Analyses

The chemical oxygen demand(COD cr)of the water sample was determined according to the standard procedures(APHA,2005). The turbidity of the water sample was measured on an ASN2000 turbidity meter,and the UV and visible light absorbance was mea-sured on a Miltron Roy Spectronic1001plus UV–vis spectropho-tometer.Before the measurement of the light absorbance,the water samples were?ltered through a0.45l m Millipore mem-brane?lter to remove the particulates.The color removal ef?ciency was calculated according to a method reported earlier(Chen and Luo,2003),based on the reduction of the light absorbance at the wavelength of257,275,325and465nm.The content of methyl tertiary butyl ether(MTBE)extractives was quanti?ed by multiple liquid/liquid extraction with MTBE according to a method de-scribed in the literature(Magnus et al.,2000).The lignin concen-tration was determined based on its UV light absorbance at 280nm wavelength and the absorptivity of20g là1cmà1for lignin (Ni and van Heiningen,1996),the furfural content was very low in the ef?uent sample because the pulping process is performed un-der an alkaline condition,therefore the disturbance originating from furfural is negligible.For the determination of the lignin con-tent in the biomass,the biomass was treated with1N NaOH to re-lease the lignin that was absorbed on the biomass according to the

T.Liu et al./Bioresource Technology102(2011)4712–47174713

procedures reported in the literature(Chen et al.,2003),and then the dissolved lignin was quanti?ed based on the UV method.

The protein and amino acid contents of the biomass were deter-mined according to a method reported in the literature(Chen et al., 2003).The yield of the bio-sludge(biomass)was measured based on the gravimetric method.The biomass settled at the bottom of the?ask was?ltered with a0.45l m nylon membrane?lter,and washed two times with50ml deionized water each time.The solid retained on the?lter was then dried in an oven at105°C to con-stant weight.The yield of the biomass was calculated as grams of dry solid per liter of ef?uent.

For the determination of the total carbohydrates,1ml of the ef?uent sample was mixed with4ml of5%sulfuric acid solution in a glass vial that was then placed in an autoclave for thermal

treatment at120°C for an hour.The monomeric sugars hydrolyzed from the polysaccharides were then analyzed in a high perfor-mance anionic exchange chromatography with pulse amperomet-ric detection(HPAE–PAD)on a Dionex D-300system(Li et al., 2010).To determine the concentrations of monomeric sugars,the sample was?ltered using a0.45l m nylon?lter and analyzed di-rectly without acid hydrolysis.The activity of the enzymes devel-oped in the fermentation process such as cellulase and xylanase, was determined according to a method reported in the literature (Bailey and Nevalainen,1981).

3.Results and discussion

3.1.Fermentation with A.niger S13

As shown in Table1,the fermentation treatment with A.niger S13led to a60.22%removal of COD on average(from7521to 2992mg/l),while the production of solid biomass was7.12g/l. The removal of color and turbidity was43%and77%,respectively. These results are compared to the removals of59%COD and47% color,reported by Gao et al.(2001)by using white rot fungi(Gao et al.,2001).

It is interesting to note that the removal ef?ciency of MTBE extractives in Table1was very high(about97%).The MTBE extrac-tives consist mainly of resin and fatty acids that are generally re-garded as the main toxicity contributors in pulping ef?uents (Brumley et al.,1997).These results further support the notion that APMP pulping ef?uent can be bio-treated directly with A.niger, without the pre-coagulation/?occulation treatment.

It is also worth noting that the A.niger fermentation process had a high yield of solid biomass as a byproduct.The biomass sludge contained8.91%protein,and9.16%amino acid,47.16%of which were essential amino acids.Table2lists the amino acids found in the biomass.The high protein content of the biomass makes it a potential raw material for the production of animal feeds and or-ganic fertilizers(Li et al.,2009;Liu et al.,2009).The application of organic fertilizers is considered important for sustainable devel-opment of the agriculture industry in China.Excess use of chemical fertilizers and over exploitation of the soil have resulted in many problems,such as decreased organic content,soil hardening and environment pollution.For this reason,organic fertilizers are good substitute for the chemical fertilizers,and the biomass byproduct from the A.niger fermentation can be a good candidate.

The biomass byproduct may also be used as the raw material for animal feed.Indeed,the biomass from the A.niger fermentation of APMP pulping ef?uent has8.91%protein,which is higher than that in corn and rice,8.5%and7.8%,respectively(Zhao,2008).Further studies are undergoing in China to evaluate the potential use of the bio-sludge as animal feeds.

In addition to the high contents of protein and amino acids,the biomass from the bio-treatment of the APMP pulping ef?uent also contains lignin,cellulose and hemicelluloses.It has been reported that lignin can have both antimicrobial and nutritional values in beef cattle production(Phillip et al.,2000;Wang et al.,2009). The lignin content in the biomass from the A.niger fermentation of APMP pulping process was in the range of35–50g/kg.The pres-ence of enzymes,such as xylanase,cellulase and pectinase in the biomass from the A.niger fermentation may also have bene?cial ef-fects on the digestive system of animals(Del Alamo et al.,2008).

3.2.Effect of wood extractives on the A.niger S13fermentation

It is well documented that the performance of ef?uent biologi-cal treatment process is affected by the concentration of wood extractives in the system.As shown in Fig.1,for an APMP pulping ef?uent sample containing147.2mg/l wood extractives,it needed about13days for the activated sludge system to reach a steady state with a COD removal of about50%;at the18th day,a distur-bance was made to the system by increasing the concentration of wood extractives to441.6mg/l(equivalent to three times of the

Table1

Biological treatment of the APMP pulping ef?uent with A.niger S13(3%inoculum,pH 6.0,30°C,160rpm,72h).

Original Bio-treated

COD cr(mg/l)75212992

SS(mg/l)35499

Turbidity(NTU)510116

pH7.43 5.96

Color(C.U.)977.2561.2

MTBE(mg/l)147.2 4.7

Biomass(g/l)–7.12Table2

Amino acids found in the bio-mass from the A.niger fermentation of APMP pulping ef?uent.

Amino acid Content,%Amino acid Content,%

Aspartic acid 1.04Isoleucine0.51

Threonine0.47Leucine0.69

Serine0.10Tyrosine0.37

Glutamic acid 1.21Phenylalanine0.50

Glycine0.57Lysine0.57

Alanine0.67Histidine0.57

Cysteine0.24Arginine0.40

Valine0.67Proline0.27

Methionine0.30Total9.16

4714T.Liu et al./Bioresource Technology102(2011)4712–4717

usual concentration),it can be found that the COD removal and the settled sludge volume(SV30)was negatively affected:a60%de-crease in COD removal ef?ciency(from50%to20%)and a43%in-crease in the settled sludge volume(SV30)(from35%to50%).These results suggested a signi?cant sludge bulking caused by the in-

crease in the wood extractive concentration.Therefore it is evident that the wood extractives in the APMP pulping ef?uent have signif-icant negative impact on the activated sludge system.

To determine the tolerance of the aerobic A.niger S13fermenta-tion to the concentration change of wood extractives in the APMP pulping ef?uent,we compared its COD removal ef?ciency at differ-ent concentrations of wood extractives prepared by the procedures reported in the literature(Sundberg et al.,1996).The results are summarized in Table3.At147.2mg/l wood extractives,the COD removal ef?ciency was about60%,When the concentration of wood extractives was increased to441.6mg/l,the COD removal ef?ciency decreased by33%(from60%to40%),which was com-pared to a60%decrease in the activated sludge system.Therefore, in comparison to the activated sludge system,the A.niger fermen-tation system has higher tolerance to wood extractives in the APMP pulping ef?uent.Table3also shows that the production of solid biomass in the A.niger system also decreased due to the in-crease of wood extractives(from0.65%to0.45%).

3.3.Effect of A.niger fermentation on the carbohydrates,lignin and wood extractives in the APMP pulping ef?uent

To demonstrate the enzymatic hydrolysis of carbohydrates dur-ing the A.niger fermentation,we determined the amounts of sugars in the original and the bio-treated ef?uent samples.The concentra-tions of both glucose and xylose increased signi?cantly(glucose: from29.7to75.1mg/l,xylose:from115.6to192.7mg/l)after the bio-treatment with A.niger S13,indicating that some of the cel-lulose and xylan are hydrolyzed into mono sugars during the fer-mentation process.The high concentration of xylose(192.7mg/l) after the bio-treatment is a good indicator of xylanase that was produced in the process of A.niger S13fermentation.It is interest-ing to note that no mannose was present after the A.niger S13fer-mentation,although some mannose(50mg/l)was found in the original ef?uent sample.This may suggest that no mannase was produced in the system,while the mannose in the original ef?uent was consumed in the fermentation process.The concentrations of arabinose and galactose increased slightly after the bio-treatment (arabinose:from59to70.0mg/l,galactose:from67.5to 70.7mg/l).

Shown in Fig.2are the developments of three key enzymes, namely,xylanase,cellulase and pectinase,found in the A.niger fer-mentation process.Their activities increased as the fermentation progressed,and reached a maximum after about50–60h,and then started to decrease.However,the xylanase had a much higher activity than cellulase and pectinase,indicating that the A.niger fermentation is a xylanase-dominant process.This is in agreement with the results of sugar concentrations that xylose was the dom-inant sugar found.The maximum enzyme activity also coincided with the maximum COD removal obtained(at about the50th hour of fermentation).

The concentration of lignin in the ef?uent sample decreased from516to225mg/l after the fermentation treatment.Some of the lignin in the ef?uent was adsorbed by the biomass and thus separated from the water phase in the fermentation process.This is con?rmed by measuring the lignin content in the biomass,and it was found that the biomass had a lignin content of about4%, which was equivalent to about300mg/l(on the ef?uent).Based on the lignin mass balance,it can be concluded that the A.niger fer-mentation had negligible effect on lignin,and the decrease in the lignin can be accounted for by the amount of lignin adsorbed by the biomass.

The concentration of wood extractives(MTBE extractives)in the ef?uent sample decreased from147to4.7mg/l after the bio-treat-ment,with a removal ef?ciency of about97%(Table1).Negligible amount of MTBE extractives was found in the biomass.Therefore, the wood extractives were all consumed by the organisms in the fermentation process.

3.4.Post-coagulation/?occulation

3.4.1.Effect of alum dosage

Alum is commonly used as coagulation agents in industrial waste water treatment process.When added,polymeric aluminum with cationic charges can be formed,and would then interact with the colloidal materials present in the system by either charge neu-tralization or adsorption,leading to coagulation/?occulation(Ste-phenson and Duff,1996).As shown in Fig.3,the removal of turbidity and COD increased sharply with the increase of the alum dosage from200to600mg/l,and reached a plateau at about 1000mg/l.The maximum removal of turbidity and COD was about 96%and81%,respectively.The above results indicated that the bio-treated APMP pulping ef?uent is easy to be coagulated/?occulated. Unlike the removal of turbidity and COD,color removal increased continuously with the increase in the alum dosage,with no plateau reached under the conditions studied(Fig.3),which can be ex-plained by the fact that the colored substances would be more dif-?cult to be coagulated/?occulated than those contributing to COD and turbidity.

3.4.2.Effect of pH

An important factor affecting the alum-assisted coagulation/?occulation process is its pH.As shown in Fig.4,the removal of COD and turbidity in the post-coagulation/?occulation process had a minimum at about pH4.0and a maximum at about pH5–5.5.Similar phenomena have been observed by others in treating

Table3

Effect of wood extractives on the A.niger fermentation system and the activated sludge system.

Wood extractives, mg/l A.niger system*Activated sludge

system**

COD removal,%Solid biomass,%COD removal,%SV30,%

147.2600.655035 441.6400.452050

*Other fermentation conditions:3%inoculum,pH6.0,30°C,160rpm,72h. **Conditions were the same as in Fig.1.

T.Liu et al./Bioresource Technology102(2011)4712–47174715

pulp bleaching ef?uent with FeCl3as the coagulant(Rodrigues et al.,2008).A lower pH may favor lignin precipitation,but the for-mation of polymeric aluminum may be decreased.In terms of COD and turbidity removal,the optimal pH is5–5.5.The results in Fig.4 also showed that the removal of color was higher at a lower pH, which can be explained by the acidic precipitation of lignin that contributes to the color of APMP ef?uent.

https://www.wendangku.net/doc/2311123973.html,bined aerobic fermentation and post-coagulation/?occulation process

Under the optimum conditions of1000mg/l alum,2mg/l PAM,

pH5.0,50°C,250rpm,and5min,the results in Table4showed that the post-?occulation process removed82%COD,86%color, 96%turbidity,and53%MTBE extractives from the bio pre-treated sample.As a result,the total removal of COD,color,turbidity and MTBE extractives reached93%,92%,99%and99%,respectively from the two-stage process consisting of biological treatment and post-?occulation.These results were compared to a90%reduc-tion in COD of a paper and board mill ef?uent treated in a batch reactor,followed by coagulation/?ltration,as reported by Afzal et al.(2008).In another study by Chen et al.(2003)who treated a pulp mill bleaching ef?uent in a coagulation-anaerobic acidi?cat-ion-aeration package reactor,the total COD removal was88.1%. Therefore,it can concluded that our results from the combined aer-obic fermentation and post-coagulation/?occulation process are better than those reported in the literature(Afzal et al.,2008; Chaudhari et al.,2010;Chen et al.,2003;Shi et al.,2000),indicating that the proposed two-stage process is effective in eliminating the pollutants in the APMP pulping ef?uent.

For a typical300tons per day APMP pulping process,it is ex-pected that about10,000m3of ef?uent per day would be gener-ated,which will be treated in the combined two-stage process to decrease the COD,color and turbidity.Most of the treated ef?uent can then be recycled to the processes for reuse,and part of it will be discharged into the receiving water body after a tertiary treat-ment.About71.2tons of solid biomass will be generated per day as the byproduct,which may be used as the raw material for the production of organic fertilizers and animal feeds.

4.Conclusions

The proposed two-stage biological/?occulation process was effective in removing the pollutants from APMP ef?uent and the overall removal ef?ciencies of COD,color and turbidity were93%, 92%and99%,respectively.The bio-treatment with A.niger S13 can ef?ciently remove the pollutants and produce a large amount

Table4

Ef?uent characteristics of the2-stage biological-?occulation process.

CODcr, mg/l Turbidity,

NTU

Color,

C.U.

MTBE

extractives,

mg/l

Original APMP pulping ef?uent7521510977.2147.2

After bio-treatment2992116561.2 4.7

After?occulation554 4.476.43 2.2

Note:coagulation/?occulation conditions:1000mg/l Alum,2mg/l PAM,pH5.0,

50°C,250rpm and5min.

4716T.Liu et al./Bioresource Technology102(2011)4712–4717

of biomass that are rich in amino acids and minerals,and can be used to produce fertilizer and/or animal feed.In the second stage, under the optimal conditions(1000mg/l alum,2mg/l PAM,pH5 and50°C),the removal ef?ciencies of COD,color and turbidity reached82%,86%and96%,respectively.

Acknowledgements

The authors would like to acknowledge the?nancial supports from Tianjin Education Commission Project(Grant Nos. 2006ZD20and SW20080001).

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