Removal of phosphorus usingAMD-treated lignocellulosic material

James S. Han

Soo-Hong Min

Yeong-Kwan Kim

AbstractExcess luitricnls, including phosphcirtis. can cause eutrophication in surface water and reservoirs. We tested the phosphate

removal capacity of juniper fiber through isotherm, kinetic, column, and field tests. Heavy metals from an acid mine drainage(AMD) site were precipitated on the surface of Juniper fiber. The modified fiber was tested in laboratory-scaled batch and colurnntests. Elemental analysis showed that soluble iron species deposited on the modified fiber acted as an inorganic adsorbent foranions; sorption capacity of this juniper fiber was higher than that of other conventional adsorbents. A pscudo second-orderkinetic model fitted well for sorption of phosphorus onto the modified medium. The modified lignocellulosic material was usedto remove phosphorus from wastewater from two dairy farms in the Catskill/Delaware watershed. The fiber was installed insidea filter box. Ibnning a nonwoven mat. Phosphorus removal efficiency ofthe material was about 41 percent at 59 mg.-'L of influentphosphorus concentration.

T,he quality of water reservoirs in the CatskJIl/Dclawarewatershed is afTeeted by run-off from approximately 350dairy and livestock farms and 90 other agricultural enter-prises. Small daily farms discharge a considerable amount ofphosphorus to the watershed; the total maximum daily load ofpho.sphate is not limited for individual farms. Wastewaterfrom the milking system is drained directly to the land. Inaddition to phosphorus, wastewater includes sediment andmay include parasites ofthe genus CrypfosporiJiuni.

Excess nutrients, including phosphorus, can cause culro-phication in surface water and reservoirs (NYCDEP 1991a.1991 b. 2001; Hammer and Hammer 2001). In natural, domes-tic, and industrial treatment systems, phosphorus can be re-moved by adsorption, chemical precipitation, and biologicaltreatment (Morse et a!. 1990). Among industrial treatmenttechnologies, adsorption on a fixed-bed filtration system iscommonly used to purify wastewater with a low concentra-tion of phosphorus {Hano et al.l997). Diverse adsorbents.such as red mud. activated alumina, polymeric ligand ex-changers, iron/aluminum-coaled sand, and calcium-based ad-sorbents, have been studied for their capacity to remove phos-phate (Hano etal. 1997. Lo etal. 1997. Akay et al. 1998. Zhaoand Sengupta 1998. Ayoub et al. 2001. Khadhraoui et al.2002).

Lignocellulosic materials have the capacity to adsorb pol-Umuits (Basso et al. 2002. Reddad et al. 2002). Chemicalmodification of these materials {i.e., saponification and phos-

phorylation) enhances their sorption capacity for heavy eat-ionic metals in water (Drake et al. 1996. Tiemann et al. 1999.Romero-Gonzalez etal. 2001, Nadaet al. 2002). For removalof anions such as phosphate, lignocellulosic materials havebeen cationized through hybridizing with inorganic chemicalsas well as grafting with ammonium-type chemicals. Zghida etal. (2002) used epoxy propyttrimethylammonium chloride(tiPTMAC) grafted lignocellulosic materials to remove chro-mium oxy-anioiis. DeMarco et al. (2003) developed a poly-meric/inorganic hybrid sorbent for removing arsenic. The hy-brid sorbent was a polymeric cation exchanger eontainitig ag-glomerates of nanoscale hydrated iron oxide. Likewise, iron(lll)-loaded carboxylated polyacrylamide-grafted sawdustwas tested for removing phosphate from an aqueous solution

"I'hc aulliors arc. respectively, l-'ornicr Research Chemist (retired)USDA Forest Serv,, Forest Products Lab,. Madison. WI (james,han(a runbc>x,coin): Research Associate. USDA Forest Serv.. ForestPniducts Lali,. Miidison, W! and Depl. of Civil and BnvironmcntalHngineering, Uni\. olW isconsin-Madison (sminu/fs.fed.iis); andProfessor. Division of Fn\ ironmcntiil and Geosystem Hnginccring,Kangvvon National tJniv.. Cluinchon. Korea (yeongfa kaiigvvon.ac.kr). This resc;irch was supported by funds from the USDA ForestServ. Large-Scalc Watershed Restoration Projeet - New York CityWatershed Study and the LSDA Forest Sorv, National Fire Program.This paper was teceived for publication in .lune 2004. Aniele No.9X93,

(Unnithan ct al. 2002). The motlitication consisted of twosteps: 1) graft copolymerization of aerylamide and N.N'-methylcnebisacrylamide onto sawdust; and 2) attachment ofiron (I i I) to the earboxyl ic acid moiety of tlic adsorbent. Theseiiicthod.s require at least one chemical treatment to activate thecapacity of lignocellulosie material to remove anions fromwater.

In previous work (Shin et al. 2(K)4b), juniper chips wereproeessed into a mat-type filter medium to restore the water-shed affeeted by acid mine drainage (AMD) in the WayneNatitinal Forest in Oiiio. In general. AMD contains iron, sul-lates. aluminum, manganese, and other dissolved and sus-pended solids because of its low pH (Draver 1997). Iron spe-cies were found to be the primary metal deposited onto thejuniper filler mat, implying that juniper can be a natural andnovel inorganic lignocellulosic hybrid adsorbent.

.kiniper (Juiu])cnis monospcnna) fiber was ehosen becauseof its relatively high soiption capacity for heavy metals (Han1999). In addition, juniper is a small-diameter and underuti-lized wood as well as an invasive speeies, which contributes tofire loading. Another benefit is the fibrous character of juniperbark, which allows the bark to be proeessed with the wood; thewood does not need to be debarked before processing.

In the study reported here, we tested the phosphate removalcapacity of juniper liber through isotherm, kinetie. column,and field tests. The field tests consisted of installing small fil-tration systems on two dair>' farms in the Catskill/Delawarewatershed.

Materials and methodsMaterials

.luniper trunks and branches, including bark, were shreddedinto small chips, refined (fiberized or meehanically pulped),and made into a Rando mat using 10 percent of HC-105 binder(Hoechst C'elanese Ine. (iermany). which is the most widelyused polymer binder in the geotextile industry. The fiber waswashed with 0.5-M sodium hydroxide twice, after chippingand after fonnation ofthe Rando mat. Mat density was 0.109to 0.131 g'Cm and thickness was about 1.3 cm. "fhe mat wascul into 61-cm by 61-em pieces (mats). Mats were initiallyexposed to AMD for 3 days at the Wayne National Forest.They were then dried and shipped to the Forest ProductsLaboratory in Madison. Wisconsin. Mats were washed withdistilled water to remove excess water-soluble componentsand dried. All mats except those used for the laboratory-scaletests were shipped to the field site in New York State to bereused for removing phosphorus from water.

Unmodified and chemically modified filter mats were sub-jected to isothemi. kinetie. and column tests in the laboratory.The unmodified mats are simply designated as "juniper." Themodified mats are designated as base-lrealed juniper. Base-treated mats were treated with U.5 M sodium hydroxide for 24hours to improve cation exchange capacity (CEC). This in-ereased CEC eould enhance the binding ability of iron spe-eies. which can bind with phosphate in water. The mechanismofthe base treatment is described in detail in Min etal. (2004).The WNF-designated mats were treated with sodium hydrox-ide and exposed to AMD in the Wayne National Forest:WNFOl mats were untreated and WNF()2 mats were treatedwith water to remove soluble components and then redried.All mats were ground with a Wiley mill to pass a 20-mesh

screen and sieved again with a 20-mesh screen for adsorptiontests.

Elemental analysis and adsorption testsInductively eoupled plasma atomic emission spectrometry

(ICP-AES, ULTIMA, .lobin Yyon Inc.. lidison, NJ) was usedfor elemental analysis of inorganic components in solid andsolution samples. Phosphorus isotherms were acquiredthrough bateh experiments. The 20-mesh powdered samples,weighing 0.1 to 1.0 g, were placed in 125-mL bottles; 50 inLof 10 mg/L-phosphorus solutions was added. Ionie strength ofthe solution was maintained at 0.01 M using sodium nitrate.The samples were sealed and placed in a shaker (Bigger BillOscillator, Thermolyne, lA) and shaken at 150 qim for I dayat 25T. After 4H hours of shaking, the suspension was filteredimmediately through a 0.45- im tnicrofilter. and phosphorusconcentration in filtrate was analyzed by ICP-AES.

Adsorption kinetie experiments were performed usinglOOO-mL solutions with 2.0 g of 2Q-mesh sample. Initialphosphorus concentration ofthe solution was 10 mg/L: pH ofthe solution was maintained al 6.4 using nitric acid or sodiumhydroxide solution. The suspension was stirred with a mag-netic bar, and samples were taken at various times over a pe-riod of 5 hours. Change in phosphorus concentration wasmeasured by ICP-AES.

Column testA column test was eondueted using an intact Rando mat

rather than powdered sample. Juniper mats eharged with ironspecies at the Wayne National Forest were removed from thefiltration boxes, washed with water, dried, and cut into 4.5-eni-diameter plugs. The pH ofthe phosphorus solution wasadjusted to 7 with 0.1 M nitric acid and sodium hydroxidesolution. Five plugs were weighed, packed into a 4.5-cm-diameter. 20-cm-long glass column, and ekited with 30 mg/Lphosphorus solution (potassium dihydrogenphosphate,+98%. Aldrich, Milwaukee, WI) with a Minipuls 3 fractioncollector (Gilson, Milwaukee, WI) pump at a flow rate of 4mL/niin. A 204 Gilson fraction collector was u.sed to eollect2()-niL aliqiiots. The weight ofthe plugs, phosphorus eoneen-tration, total volume of standard solution to be eluted, andHow rate were detennined on the basis of practical experi-ence: total elution time was arbitrarily limited to 15 hours sothai an experiment eould be finished overnight. The proeesswas replicated si.x times.

Field testThe filtration system was installed at two farms in the

Catski I I/Delaware watershed. The system with the WNK()2mats was connected to the wastewater drainage pipe from themilking system. The first field test was 3 days long at a farmthat diseharges phosphorus in a range of 60 mg/L. The secondfield test was 12 days long at a farm that discharges phospho-rus in a range of 100 mg/L.

The filtration box was designed at the Forest ProductsLaboratoiy and made of fiberglass by a eommercial builder(Empire Fiberglass Products Inc.. Little Falls, NY). The filterframes were fitted into slots in the box, and 10 filter mats wereplaced inside the box (Fig. 1). Flow through the filter matswas mathematically modeled by Hur et al. (2003). Watersamples were collected twice a day at the inlet ofthe filtrationbox. The samples were analyzed for total dissolved phospho-rus by ICP-AES.

FOREST PRODUCTS JOURNAL VOL. 55. NO. t t 49

Figure 1. Lignoceiluiosic filtration sysiem: a) filtration box: b) filter frames insiae filtration box.

Tabie 1. filter mats.

Sample

Juniper

Elemental analysis of

Al

0.112

Basc-trcalcd juniper 0.116

WNKIH

WNF02

0,103

0.076

Fe

4.670

6.533

129,5

134.9

inorganic

Contents

Pb

---(mg/g)--

0.177

0.IH4

0.169

0.254

components of

s

4.592

4.763

S.466

7.027

Zn

0.100

0.103

0.102

0.068

b

V

3.0

2.5

2.0

1.5

1,0

Results and discussion

Elemental analysisTable I shows inorganic component content of the filter

mats. Iron eontent of juniper and base-treated juniper matswas 4.670 and 6.533 mg/g, respectively. Iron content of matsexposed to AMD was 129.5 and 134.9 mg.'g for WNFOl andWNK02 mats, respectively, or about 13 percent by weight ofiron species. The content of other inorganic components wassimilar before and after exposure to AMD.

Several mechanisms might be responsible for the deposi-tion of iron species on filter mats (Tiemann et al. 1999, Red-dad et al. 2002). Iron species are deposited on the filter surfacethrough ehemical interactions such as replacement of calciumions and adsorption on active sites (e.g., phenolic or carbox-ylate sites). The mats also physically block solid particles byputting them into suspension.

Adsorption behaviorFigure 2 shows the kinetic behavior of each sample. As

expected, the phosphorus sorption capacity ofthe unmodifiedjuniper and base-treated juniper samples was almost nil. Incontrast, the kinetic data for WNFOl and WNF02 show thatmodification with iron greatly increased sorption capacity forphosphorus. Most uptake of phosphorus occurred within 100min., after which sorption of phosphorus reached an equilib-rium state.

The results of fttting the adsorption data to several kinetieequations (Tiemann et al. 1999, Romero-Gonzalez et a!. 2001,Reddad et al. 2002) are shown in Tabie 2. Based on the de-tennination coefficients for each model, the pseudo second-

0.5

0

WNF01WNF02JuniperBase treated juniper

0 50 100 150 200 250 300Time (min)

Figure 2. Kinetics of phospfiorus adsorption for eacfisample (Shin et al. 2004a).

Table 2. Determination coefficients for eacfi modelequation.

Sample

WNFOl

WNF02

0.906

0.914

Pseudo 2nd

r K

fg/mg/min)

0.998 0.0526

0.983 0.0809

Powerfunction

r

0.923

0.769

SimpleElovich

0.911

0.769

Parabolicdiffusion

r

0.930

0.942

order model and the parabolic diffusion mode! matched wellwith the kinetic data. Since the parabolic diffusion equationwas indueed from diffusion-controlled adsorption, its good fitto the data suggests that the kinetics of pliosphorus sorption onWNFOl and WNF02 was controlled by diffusion. The pseudosecond-order model also fitted the kinetic data well, showinga kinelic constant K of 0.0526 and 0.0809 mg.'g/min forWNFOl and WNF()2, respectively, which indicates that ad-sorption on the filter medium is closer to chemisorption thanphysisorption (Ho and McKay 2000).

5O NOVEMBER 2OO5

Adsorption data were fitted to both Langnuiir andFreundlieh isotherms, as expressed in Hqualions [1] and [2].respectively:

where c/_,^ = amount adsorbed at equilibrium (mg/g); Q,,,^,^ ~maximum adsorbate loading (mg/g); C',,, - equilibrium eon-centration; b = eonstant.

where K and n are constants.

Isothenns for phosphorus adsorption and fitted results areshown in Figure 3 and Table 3. The determination eoeffi-

o.^3"Q.

Q.

0

WNFOlWNF02LangmuirFreundlieh

0 82 4 6Final concentration (mg/L)

Figure 3. Isotherms of phosphorus adsorption for eachsample and fitted lines (Shin et al. 2004a).

Table 3. Parameters from fit of isofherms to Freundlich andLangmuir models.

Freundlich Langmuir

Sample

WNFOl

WNF02

A'

1.76

1.12

///(

0.211

0.260

r

0.986

o.syi

(mg/g)

2.. I

h

6.41

2.06

r

0.947

0.942

Table 4. Phosphorus sorption capacity of diverse filter media.

Typi-' Q,SorhciU

Kaiidiuslalf

Malapeake

Tropohiinuills

Iroji and aluiniiuiin iixidc coaled sand

Iron and aluminum oxide coated olivinc

Gcothitc

AA300G

C-70

Kaulinite, Fe oxides

Chlorite, kaolinite. Fe oxides

Fe, Al oxides, kiiolinile

Fe, Al oxides

Fc, Al oxides

Fe oxides

y Al o.xides

a Al oxides

(mg/g)

0.394

0.465

2.060

0.011 10 0.033

0.015 10 0.035

1.3"

2.0''

l.Cf

"Calculated on basis of results reponed in the literature.

cients do not indicate whieh isotherm model is dominant inthe isotherm data. The Q,,,^^^ (maximum adsorbate loadingonto adsorbent) values of WNFOl and WNF02 (2.31 and 1.85mg/g, respectively) indicate ihat mild washing with water re-duced ihe phosphorus sorption capacity of the (liter medium.A similar phenomenon was observed in the kinetic results.The sorption capacity of the modified lignocellulosic filters,in particular of WNFOl, is superior to that of other inorganicfilter media. Tahle 4 lists the phosphorus soiption capacity ofvarious filters reported in the literature (Baker et al. 1998,Brady and Weil 1999. Ayoub ct al. 2(J01).

Column testA column test was eonducted to evaluate the adsorption ca-

paeity of the filter medium from Rowing water. As long asiron species were present in the medium, the medium was ableto adsorb phosphorus. In Figure 4, P is the concentration ofthe 3n-mg/L phosphorus solution after passing through thefilter medium. /'_,, is the amount of phosphorus adsorbed bythe medium, which is the differenee between 30 mg/L andP. As iron was depleted from the filter, adsorption of phos-phorus decreased. Phosphorus eoncentration started to in-crease after 20 niL of solution had passed through the filter.The maximum phosphorus adsorption capacity was ealeu-laled as 3 to 4 mg/g. Iron was adsorbed by the addition of thecation-exchanging base-treated juniper medium, as shown inFigure 5.

Field testin the laboratoiy tests, only inorganic phosphorus was used

as an adsorbate. However, phosphorus in wastewater exists inseveral forms: particular, organic, inorganic, total, and so on.In the field test, phosphorus concentration refers to theamount of total dissolved phosphorus; each water sample wasfiltered by a 0.45-)ini filter prior to analysis. The mechanismof phosphorus removal in the field is more eomplicated thanthe physiochemical mechanism in the laboratory. In additionto adsorption, another possible nicehanism for phosphorus re-moval in the field is biological, by the action of microorgan-isms on the surface of lignocellulosic filter mats. Aecording toChiou et al. (2001) aiid Morgenroth and Wilderer (1998),phosphorus is removed by a biofllm fhat forms on a supportmaterial, in this case the lignocellulosic filter medium.

Table 5 shows the performance of filter mats installed on afarm for 3 days in 2002. Removal effieieney \aried in dailysampling; the average removal efficiency of WNF02 was41.51 percent at 59.19 mg/L of inlet phosphorus concentra-tion. This experiment was repeated in 2003 for an extended

period (12 days) on a farm where theinlet phosphorus concentration wasabout 100 nig/L (Table 6). Averageremoval efficiency on this farm wasonly 25 percent, which indicates thatthe capacity of the lllter medium wasdependent on phosphorus concen-tration.

The field test results suggest that afiltration system containing ligno-cellulosic-based filters could lowerthe amount of phosphorus load froma farm to the watershed by about 25to 40 pereent within the range ofphosphorus concentration expcri-

Brady clal. I WO

Brail>ctal. 1990

Brailyetal, 1990

Ayoub ctal. 2001

.Voiibctal. 2001

Baker el ;ii. 1998

Baker el al. I99S

Baker cial. 1998

FOREST PRODUCTS JOURNAL VOL. 55. NO. 1 t 51

3co

trat

ice

ni

coO

80

70

60

50

40

30

20

10

0

Table 5. Phosphorus analysis of water sample taken afinlet and outlet of fitter box in 2002.

0 20 80 10040 60Fraction (20 mL)

Figure 4. Elution of 30 mg/L phosphorus standard solutior]as a function of fraction.

80

70

60

50

40

30

20

10

0

--Fe-A-po Pnet

0 10040 60Fraction {20 mL)

Figure 5. Elution of 30 mg/L phosphorus standard solutionas a function of fraction. Cation exchanger added at end ofcolumn to control iron.

enced in this study. During the lest period, we did not observeany deterioration of the phosphorus-removal capacity of thefiber mats.

ConclusionThe capacity of jtinipcr fiber for removing phosphorus from

wastewater was evahiated in this sttidy. Phosphorus soiptioncapaeity was increased by modifying the lignoceilulosie filtermats with iron species. Further research on chemical modifi-cation would be necessary for enhancing phospiiorus re-moval. In the isotherm test, maximum adsorbate loading{Q,,,,,y) onto adsorbent was as high as 2.31 mg/g, which iscomparable to or better than that of other natural filter media.Maximum soiption eapacity was about 3.5 mg/g in the col-umn test, but some iron was released during the reaction. Infield tests, lignocellulosic filter mats removed about 40 per-cent of phosphorus from a waste stream containing around 60mg/L phosphorus and 25 percent phosphorus from a waste

Sampling in 2002

Day 1

Diiy 2

Day 3

a.m.

p.m.

a.m.

p.m.

a.m.

Avg. value

Inlet

Concentration o f totaldissolved phosphorus

Outlet Difference

(mg/L)

57.S5

57.57

59.76

64.68

59.19

34.89

19.87

31.4!

44.02

42.94

34.62

Table 6. Phosphorus analysis ofinlef and outlet of filter box in 2003.

Sampling in 2003

Day 1

Day 2

Day 3

Day 4

Day 5

Day 6

Day 7

p.m.

Day S

Day

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