A

eseocacthsOtaoob©

K

1

ipdPpi

0d

Colloids and Surfaces A: Physicochem. Eng. Aspects 297 (2007) 154–162

Effect of organic matter on the sorption of dissolved organicand inorganic phosphorus in lake sediments

Shengrui Wang a, Xiangcan Jin a,∗, Haichao Zhao b, Xiaoning Zhou a, Fengchang Wu c

a State Environmental Protection Key Laboratory for Lake Pollution Control, Research Center of Lake Eco-environment,Chinese Research Academy of Environmental Sciences, Beijing 100012, PR China

b College of Agronomy, Inner Mongolia Agriculture University, Huhhot 010018, PR Chinac State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, PR China

Received 28 December 2005; received in revised form 7 October 2006; accepted 23 October 2006Available online 26 October 2006

bstract

The sorption of phosphate on lake sediments has a major influence on transport, degradation, and ultimate fate of phosphorus (P) in lakecosystem. Organic P is abundant in sediments and is an important P speciation for primary productivity. Organic P can also be transferred fromediments into the overlying water and supplies nutrition for aquatic organisms. Despite the importance of organic P, it remains poorly understood,specially the organic P sorption on sediments. This study evaluated dissolved organic phosphorus (DOP) and PO4

3− sorption on sediments, effectf organic matter on the sorption of DOP and PO4

3−, and differences of the sorption characteristics of DOP versus PO43− and dissolved organic

arbon (DOC) versus DOP. The results show that DOP and PO43− sorption kinetics can be satisfactorily fitted by the modified Langmuir model

nd linear model, respectively, organic matter did not significantly affect their general trend. For inorganic P, with the increasing of organic matterontent, sediments had lower sorption efficiency (m), higher amount of P naturally sorbed and higher risk of P release. While for organic P, withhe increasing of organic matter content, sediments had weaker binding strength, stronger ability of dissolved organic matter (DOM) release andigher sorption capacity. The results also show that the DOP and PO4

3− sorption process was composed of quick and slow sorption, the quickorption mainly occurred within 0.5 h. The DOP and PO4

3− sorption kinetics can be best fitted by both power function and simple Elovich models.rganic matter in sediments had a remarkable effect on DOP and PO4

3− sorption rates. But it did not affect the DOP and PO43−sorption trend, and

he effect of organic matter on PO43− sorption rate was more obvious than that on DOP. DOP was preferentially sorbed over PO4

3− in sediments3−

nd the DOP sorption increased more strongly with the increasing of organic matter content in sediments than the PO4 sorption. The sorption

f DOP and DOC increased similarly with the increasing of organic matter content in sediments, and DOC was preferentially absorbed. The rankrder of sorption strength of sediments was as follows: DOC < PO4

3− < DOP. This study has significant implication for the understanding of Piogeochemical cycling and its role in affecting eutrophication in lake ecosystem. 2006 Elsevier B.V. All rights reserved.

itrPwD

eywords: Phosphate; DOP; Sorption; Lake; Sediments; Organic matter

. Introduction

As a major nutrient for aquatic ecology, phosphorus (P) is anmportant factor for lake eutrophication [1–3]. The sorption ofhosphate on lake sediments has a major influence on transport,egradation and ultimate fate of P in lake system [4,5]. Organic

is abundant in lake sediments and is an important source for

rimary productivity [6]. The information about organic P in sed-ments is essential for understanding biogeochemical cycle of P

∗ Corresponding author. Tel.: +86 10 84915185; fax: +86 10 84915190.E-mail address: Jinxiang@public.bta.net.cn (X. Jin).

ssld

(s

927-7757/$ – see front matter © 2006 Elsevier B.V. All rights reserved.oi:10.1016/j.colsurfa.2006.10.040

n lake ecosystem, because it constitutes a large proportion ofotal P in sediments, and contributes to algal growth through theelease of orthophosphate by phosphatase enzymes [7]. Organic

can also be transferred from sediments into the overlyingater and contributes to the nutrition of aquatic organisms [8].espite the importance of organic P, it remains poorly under-

tood, especially the organic P sorption onto lake sediments andoil [9,10]. Most previous studies on P biogeochemical cyclingargely focused on dissolved inorganic phosphorus (DIP) and

issolved inorganic nitrogen (DIN) [1–5].

There were some reports on dissolved organic phosphorusDOP) sorption on soil. For example, Kaiser [11] compared theorption characteristics of DOP to those of DOC and found that

hysico

tQitstodpsoPobsicnassessD

astoiPlwcpccUwmtB

oPtc

2

2

TLisa

Jsiawsfems

2

aboortob

2.3. Sorption isotherm

Forest floor materials were used to make up stock DOM solu-tion. They were placed on netting and sprayed periodically with

Table 2Total organic carbon contents in the sediments before and after treatment withH2O2

Sediment samples TOC (%)

Before treatment After treatment

TP

I

EYW

S. Wang et al. / Colloids and Surfaces A: P

he overall retention of DOP was smaller than that of DOC [11].ualls (1991) reported that DOC/DOP ratios decreased with the

ncreasing of depth in soil profiles of the Appalachian Moun-ains, and concluded that DOC was preferentially sorbed on theoil. However, there were no comparison studies between sorp-ion isotherms of natural DOP and phosphate. There were alsother reports on the differences of the sorption characteristics ofissolved organic and inorganic P compounds [12]. For exam-le, Anderson et al. [13] found that inoccitol hexaphosphate wasorbed more strongly than inorganic phosphate in acid soil, andrganic P depressed the sorption of inorganic P, while inorganicdid not [13]. The sorption of organic P was stronger than that

f inorganic P [14]; this was probably due to the different num-ers of PO4

3− ester groups in organic molecules. Therefore, theorption of DOP on sediments is significant in the understand-ng of P transport between sediments and water because organiconstituents are often the major components of dissolved P inatural water, and these can be a major P source for algae if theyre hydrolyzed into its inorganic counterpart [15]. But the DOPorption on sediments was not often reported. Organic matter inediments strongly affected the phosphate sorption [1,3]. How-ver, little is known about the effect of organic matter on theorption of DOP, and little is known about the differences of theorption characteristics of DOP versus PO4

3− or DOC versusOP either.Different models were widely used to study P dynamics in

quatic sediments and to predict P release fluxes across theediment–water interface [16–18]. Those models focused onhe active layer below the sediment–water interface, consistingf aerobic and anaerobic layers [19]. The mechanisms involv-ng in the models included decomposition kinetics of organic

with different reactive fractions, kinetic sorption and non-inear partitioning of reactive inorganic P between the poreater and sediments, effective diffusion, mixing and burial pro-

esses of particulate P between sediment layers [18,19]. Theroposed P models had to be verified and validated before appli-ation, and this required a complete set of high quality andomprehensive data [20–22]. For example, Chesapeake Bay,SA, was perhaps the most intensively studied estuary in theorld, an extensive set of data on sediments was available forany years. Therefore, the sediment flux models were used

o simulate the budgets of sediment nutrients in Chesapeakeay [16].

The objective of this study was to investigate the effect of

rganic matter on the sorption of dissolved organic and inorganicin sediments of lakes from the lower and middle reaches of

he Yangtze River, China, and to provide some high quality andomprehensive data for future model studies.

EYW

able 1hysical and chemical characteristics of the studied sediments

tems TOC (%) CEC(mequiv. (100 g)−1)

TN (mg kg−1) TP (mg

ast Taihu Lake 0.90 13.33 932 441ue Lake 6.23 30.12 5213 1640uli Lake 1.67 22.15 1923 819

chem. Eng. Aspects 297 (2007) 154–162 155

. Materials and methods

.1. Sampling and analyses

Lake sediments used in this study were collected from Eastaihu Lake, Wuli Lake (Jiangshu Province, China) and Yueake (Hubei Province, China) using columnar sample thieves

n September 2003. The samples were taken to the laboratory inealed plastic bags that were put in iceboxes, then freeze-dried,nd sieved with a standard 100 mesh sieve for experiments.

X-ray fluorescence spectrometer (Model 3080E, Rigaku Co.,apan) was used to analyze the elemental composition in theediments. Organic matter content was estimated as losses ongnition at 550 ◦C. The grain size fractions were measured usingMastersizer 2000 laser size analyzer (Malvern Co., UK), andere classified into clay (<0.002 mm), silt (0.002–0.05 mm) and

and fractions (0.05–2 mm) [23]. The sediments were analyzedor total nitrogen (TN) [24] and total P (TP) [25]. Cationalxchange capacity (CEC) was analyzed using the EDTA-NH4

+

ethod [24]. All the physicochemical properties of the studiedediments are shown in Table 1.

.2. Oxidation of organic matter of the sediment samples

Approximately 200 g sediment samples were mixed withpproximately 300 mL 30% H2O2 solution in a 1.5 L Pyrexeaker and left to stand for 1 h, and then the beaker was placedn a sand bath at 400 ◦C to rapidly evaporate the hydrogen per-xide solution. After cooling down, the remaining residues wereemoved from the beaker and were freeze-dried, and regroundo pass through 100 meshes for further experiments [26]. Therganic matter contents in the sediments before and after treatedy H2O2 are listed in Table 2.

ast Taihu Lake 0.90 0.24uehu Lake 6.23 1.36uli Lake 1.67 0.46

kg−1) Al (%) Fe (%) Ca (%) Clay (%) Silt (%) Sand (%)

6.16 3.61 0.98 6.35 74.60 19.058.51 6.02 3.71 6.28 81.81 11.916.55 3.44 0.69 7.95 71.00 21.05

1 : Phys

dmm

ws10usp0facfcta

dTPcra

2

a0tsos1busw

2v

frsasritaio

3

3a

sttPDputpdfiia

Q

56 S. Wang et al. / Colloids and Surfaces A

eionized water for 12 h. In order to remove particulate organicatter solution was filtered through 0.45 �m cellulose acetateembrane filters (GN-6, Pall Corp., Ann Arbor, MI).0.5 g dried sediment was added in a series of 100 mL acid

ashed centrifuge tubes with 50 mL of solutions, the initialolutions containing 0, 0.02, 0.05, 0.10, 0.29, 0.49, 0.78, 0.98,.52, 2.31 PO4

3− mg L−1 of P and 0, 0.01, 0.02, 0.03, 0.06,.08, 0.13, 0.17, 0.21, 0.50 DOP mg L−1 of P, respectively, weresed. The solutions were prepared by diluting the stock DOMolution with a solution containing similar inorganic ion com-osition as the stock solution (pH 7.3, 0.54 mmol L−1 for K,.86 mmol L−1 for Ca, 0.08 mmol L−1 for Mg, 0.21 mmol L−1

or Na, 0.17 mmol L−1 for SO42−, 0.75 mmol L−1 for Cl−, for

n ionic strength of 1.97 mmol L−1). The centrifuge tubes wereapped and placed at 25 ± 1 ◦C in an orbital shaker at 250 rpmor 24 h to ensure the equilibrium [10]. After equilibrium andentrifugation (5000 rpm for 10 min) the suspension was filteredhrough 0.45 �m GF/C membranes, and PO4

3− in equilibriumnd total P were measured using the ascorbic acid method [27].

The quantity of sorbed phosphate was calculated through theecrease of the phosphate concentration in the solutions [28].he amount of total dissolved P was the sum of dissolved organic(DOP) and dissolved PO4

3−, and the quantity of sorbed DOPan also be calculated. Triplicate experiments showed the highepeatability of the sorption method, and the standard error devi-tion was within 6%.

.4. Sorption kinetic measurements

0.5 g dried sediment samples were added in a series of 100 mLcid washed centrifuge tubes with 50 mL of solution containing.23 DOP mg L−1 of P and of 0.94 PO4

3− mg L−1 of P. The cen-rifuge tubes were capped and placed at 25 ± 1 ◦C in an orbitalhaker at 250 rpm for various time intervals between 0 and 60 hf sorption (0.5, 1, 1.5, 2.5, 5, 9, 13, 18, 24, 36, 48 and 60 h). Theampled solution was immediately centrifuged at 5000 rpm for0 min, and was then filtered through 0.45 �m GF/C filter mem-

ranes. The filtrate was taken for the PO4

3− and total P analysessing the molybdenum blue/ascorbic acid method [20]. For allamples, triplicate experiments were performed, and the dataere reported as their average [28].

Q

Q

Fig. 1. The phosphate sorption

icochem. Eng. Aspects 297 (2007) 154–162

.5. Preferential sorption of PO43− versus DOP and DOC

ersus DOP

To test whether the degree of DOP sorption was differentrom that of DOC and PO4

3−, the PO43−/DOP and DOC/DOP

atios in the solution were compared before and after the batchorption experiments. The difference of the ratios before andfter sorption experiments was used to indicate a preferentialorption of one or the other. For examples, a higher DOC/DOPatio in the equilibrium solution than in the initial solution wouldndicate that more DOP was removed from the solution andherefore that it was preferentially sorbed over DOC. Similarly,higher PO4

3−/DOP ratio in the equilibrium solution than in thenitial solution would indicate that it was preferentially sorbedver PO4

3−.

. Results and discussion

.1. Effect of organic matter on sorption isotherm of DOPnd PO4

3−

The DOP and PO43− sorption isotherms on the sediments are

hown in Figs. 1 and 2, respectively. As shown, with the addi-ion of DOP or PO4

3− the amount of DOP or PO43− sorption on

he sediments increased. All studied sediments released DOP orO4

3− at low initial DOP or PO43− concentrations and sorbed

OP or PO43− at higher initial phosphate concentrations. The

rocess of DOP or PO43− sorption on sediments was analyzed

sing sorption isotherm models. The equilibrium (i.e., concen-ration after 24 h) DOP or PO4

3− concentration in solution waslotted against the mass of DOP or PO4

3− sorbed per kg ofry sediment. Linear model, Freundlich model and the modi-ed Langmuir model often were used to describe the sorption

sotherm of phosphate on sediments [29], and those three modelsre as follows [10,30]:

= KLCb − a (1)

1 + KLC

= mC − NAP (2)

= KFCn (3)

isotherms on sediments.

S. Wang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 297 (2007) 154–162 157

ion isotherms on sediments.

c(briacceweesodcantroDw

ooL

TT

S

WDEDYD

Na

Table 4The estimated parameters of DOP sorption using the modified Langmuir modelfitting

Sediments KL b a R2

Wuli Lake 15.54 44.85 2.29 0.97D-Wuli Lake 5.07 50.54 2.44 0.96East Taihu Lake 12.78 57.43 14.45 0.97D-East Taihu Lake 2.89 83.12 15.59 0.95YD

Kuaetiitrtm

bNAP and EPC0 decreased, and m increased. m was a measure

Fig. 2. The DOP sorpt

where C is the DOP or PO43− sorption equilibrium con-

entration (mg L−1), Q the DOP or PO43− sorption capacity

mg kg−1 dry weight), n, KL and KF the constants related to theinding strength, a the y-intercept which describes the DOMeleased at low initial concentrations of the added DOM, and bs the asymptote of the Langmuir model plus parameter a. Thesymptote of the Langmuir model was referred to as the sorptionapacity [10], because the modified Langmuir model includedonstant a. Thus, this model cannot be transformed into the lin-ar form as commonly done. Therefore, nonlinear regressionas used to estimate the parameters KL, b and a using a nonlin-

ar curve-fitting program, and the constant n, and KF were alsostimated using the nonlinear curve-fitting program [10]. m is thelope, which is a measure of the phosphate sorption efficiencyf sediments (L kg−1) [31,32], and NAP is the y-intercept whichescribes the phosphate released at low initial phosphate con-entrations [32,33]. EPC0 was also determined and was defineds the phosphate equilibrium concentration, at which there waso net sorption or release of phosphate on sediments. This washe x-intercept of the linear model and can be calculated by theegression equations [34,35]. To further investigate the effect ofrganic matter on DOP or PO4

3− sorption, and difference ofOP or PO4

3− sorption, stepwise multiple regression analysesere preformed.The parameters of m, NAP and EPC0 for PO4

3− sorption

btained by linear model are shown in Table 3, the parametersf KL, b and a for DOP sorption calculated using the modifiedangmuir model are shown in Table 4, and the parameters of

able 3he estimated parameters of phosphate sorption using linear model fitting

ediments m NAP EPC0 R2

uli Lake 116.11 16.14 0.14 0.94-Wuli Lake 175.40 14.10 0.08 0.94ast Taihu Lake 79.17 96.84 1.22 0.96-East Taihu Lake 113.80 56.28 0.49 0.94ue Lake 74.96 122.24 1.63 0.93-Yue Lake 134.04 16.49 0.12 0.97

ote: The studied samples were expressed as D-Wuli Lake, D-East Taihu Lakend D-Yue Lake after treated by H2O2.

oNu

TTm

S

WDEDYD

ue Lake 9.50 42.77 10.12 0.96-Yue Lake 8.54 48.72 11.42 0.98

F and n for DOP and PO43− sorption calculated using the Fre-

ndlich model are shown in Table 5. KL, KF, b and n reflected thebility of DOP and phosphate sorption on sediments at a certainxtent [36,37], while m (slope) and NAP also reflected the sorp-ion ability [31–33]. According to the results of Figs. 1 and 2,n contrast to the sorption isotherm of DOP, the PO4

3− sorptionsotherms were best described by the linear model, indicatinghat the PO4

3− concentration used in this experiment did noteach the capacity of the sediments (Fig. 1, Tables 3 and 5). Sorp-ion isotherms of DOP were best fitted to the modified Langmuir

odel (R2 = 0.92–0.99, Tables 4 and 5) [10].As shown in Tables 2 and 3, after the sediments were treated

y H2O2 (deprived organic matter partially), for PO43− sorption,

f the phosphate sorption efficiency of sediments [31,33], andAP was the P naturally sorbed by sediment [32,35], and thesefulness of EPC0 was highlighted when applying to the under-

able 5he estimated parameters of DOP and phosphate sorption using Freundlichodel fitting

ediments DOP Phosphate

KF n R2 KF a R2

uli Lake 249.04 1.18 0.99 0.10 0.70 0.89-Wuli Lake 145.58 1.18 0.97 −0.02 −1.36 0.53ast Taihu Lake 145.47 1.14 0.89 0.00 −4.07 0.15-East Taihu Lake 325.62 2.12 0.82 −0.07 −1.89 0.64ue Lake 371.29 1.87 0.46 0.10 0.87 0.84-Yue Lake 250.22 1.51 0.90 0.10 0.70 0.89

158 S. Wang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 297 (2007) 154–162

rption

s(rvpstcsadosc

3a

csqmi

stsissWprvoP

spasesp

TD

S

W

D

E

D

Y

D

Fig. 3. The phosphate so

tanding of the direction and size of soluble reactive phosphorusSRP) flux [32,34], the higher EPC0, the higher risk of the Peleasing onto the overlying water from sediments [34]. As pre-iously reported, the amount of organic matter in sorbent waserceived to be one of the major factors controlling phosphateorption on sediments [38–41]. Our results are consistent withhose previous reports. With the increasing of organic matterontent, m decreased in the sediments; the higher amount of Porbed and the higher risk of P release. For the DOP sorption,and b increased in the sediments treated by H2O2, and KL

ecreased (Table 4). As discussed earlier, with the increasingf organic matter content, sediments had the weaker bindingtrength, stronger ability of DOM release and higher sorptionapacity.

.2. Effect of organic matter on sorption kinetics of DOPnd PO4

3−

Phosphate sorption on sediments was a complex kinetic pro-ess usually including quick and slow sorption [1]. It can be

een from Fig. 3 that DOP sorption on sediments also includeduick and slow sorption. For DOP and PO4

3− quick sorptionainly occurred within 0.5 h. The concept of sorption rate was

ntroduced to reflect the difference between DOP and PO43−

Dms(

able 6OP and PO4

3− sorption rate in different sediments (mg kg−1 h−1)

ediments Item Sampling internals (h)

0–0.5 0.5–1.5 1.5–3

ili LakePO4

3− 94.83 0.69 1.94DOP 28.06 0.44 0.53

-Wili LakePO4

3− 59.22 2.62 0.77DOP 20.9 1.35 0.35

ast Taihu LakePO4

3− 72.02 2.65 6.57DOP 22.91 1.02 0.05

-East Taihu LakePO4

3− −76.86 6.49 0.62DOP 18.7 0.15 1.03

ue LakePO4

3− 40.01 0.04 0.03DOP 21.51 0.18 0.19

-Yue LakePO4

3− −82.35 8.36 0.33DOP 12.11 3.16 0.14

kinetics on sediments.

orption on different sediments [1,30]. Table 6 shows the sorp-ion rates of DOP and PO4

3− on different sediments. The averageorption rates within 0.5 h were the highest. With the increas-ng of organic matter content in sediments DOP and PO4

3−orption rates increased for all studied sediments. The DOPorption rates within 0.5 h decreased 26%, 18% and 44% for

uli Lake, East Taihu Lake and Yue Lake as organic matter wasartially removed from the sediments, and the PO4

3− sorptionates decreased 38%, 207% and 306%, respectively. This pro-ides further support that organic matter had a remarkable effectn DOP and PO4

3− sorption, and the effect of organic matter onO4

3− sorption rate was stronger than on DOP (Fig. 4).The phosphate sorption kinetic curves can be fitted using

everal kinetic models, namely the power function and sim-le Elovich and parabolic diffusion models [1]. In this studyll the DOP and PO4

3− sorption kinetics can only be fittedatisfactorily by the power function and simple Elovich mod-ls, and the estimated parameters of the kinetic models arehown in Table 7. Based on R2 and S.E., it was found that theower function and simple Elovich models can best describe the

OP and PO4

3− sorption kinetics, but the parabolic diffusionodel cannot. There was no clear difference among different

ediments before and after the sediments was treated by H2O2Table 7).

3–5 5–7 7–12 12–24 24–48 48–60

0.86 1.65 0.04 0.03 0.16 0.090.01 0.25 0.17 0.05 0 0.050.9 0.89 0.09 0.29 0 0.170.04 0.17 0.04 0.14 0.02 0.01

0.4 0.45 0.86 0.13 0.07 0.080.65 0.38 0.07 0.09 0.02 0.042.55 0.15 0.64 0.4 0.36 0.130.07 0.04 0.09 0.16 0.03 0.02

0.69 0.23 0.03 0.05 0.04 0.291.92 0.19 0.03 0.04 0.04 0.130.34 3.11 0.07 0.08 0.1 0.250.24 0.01 0.33 0.07 0.02 0.08

S. Wang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 297 (2007) 154–162 159

Fig. 4. The DOP sorption k

Fi

3

stsstcitt

rtHwic

Pwps[otltsdtmog[

ig. 5. PO43−/DOP ratios in the equilibrium solution of the most concentrated

nitial solution.

.3. Preferential sorption of PO43− or DOP

To determine whether DOP or PO43− was preferentially

orbed, the PO43−/DOP ratios of the equilibrium concentra-

ions of the highest initial concentration were calculated for alltudied sediments [10]. The PO4

3−/DOP ratios of the initialolution were 4.2 (Fig. 5). Although the initial solution con-ained more PO4

3− than DOP, and the equilibrium solution still

ontained more inorganic than organic P after the sorption exper-ments, the higher PO4

3−/DOP ratio in the equilibrium solutionhan in the initial solution indicates that DOP was preferen-ially sorbed (Fig. 6). As shown in Figs. 5 and 6, PO4

3−/DOP

3

h

Fig. 6. PO43−/DOP ratios in the equilibrium

inetics on sediments.

atios significantly decreased with the deceasing of organic mat-er content in the sediments. But for the sediments treated by

2O2, PO43−/DOP ratios before and after sorption experiments

ere not significant (Fig. 6). This suggests that DOP sorptionncreased more strongly with the increasing of organic matterontent in sediments than the PO4

3− sorption.Our results show the preferential sorption of DOP over

O43−, and this is consistent with those of experiments in

hich model organic P compounds were used. For exam-les, Anderson et al. [13] found that inoccitol hexaphosphateorbed more strongly than inorganic phosphate in acid soil13]. Frossard et al. [14] found that sorption depended on therganic P compound, and the sorption of organic P was strongerhan inorganic P [14]. The strength, with which a particu-ar organic P compound was sorbed, was closely related tohe numbers of phosphate ester groups per unit of molecularize [10]. In the case of DOP in natural DOM, although theensity of phosphate ester groups per molecule is unknown,he DOP/DOC ratio in lakes varied greatly [42], and this

ay also result in variation in the sorption characteristicsf DOP. Moreover, other functional groups such as carboxylroups may influence the sorption behavior of DOM as well12].

.4. Preferential sorption of DOC or DOP

DOC/DOP ratios of the equilibrium concentrations of theighest initial concentration were also compared in all stud-

solution of the different initial solution.

1 : Phys

iiatTDoisst

weti(

s

TT

S

P

P

S

60 S. Wang et al. / Colloids and Surfaces A

ed sediments. As shown in Fig. 7, DOC/DOP ratio of thenitial solution (the highest initial concentration) was 91.3,nd DOC/DOP ratio of the equilibrium solution after sorp-ion experiment was higher than before sorption experiment.his indicates that DOP was also preferentially absorbed.OC/DOP ratios decreased significantly with the deceasingf organic matter content in the sediments. But for the sed-

ments treated by H2O2, DOC/DOP ratios before and afterorption experiments was significantly different (Fig. 7). Thisuggests that the sorption of DOP and DOC increased almosthe same as the increase in organic matter content, and DOC

cacD

able 7he evaluated kinetic model parameters for DOP and PO4

3− sorption on different se

amples Item a

ower function model (q = atb)

Wuli LakePO4

3− 41.18DOP 14.34

D-Wuli LakePO4

3− 48.39DOP 11.13

East Taihu LakePO4

3− −35.34DOP 12.03

D-East Taihu LakePO4

3− 40.75DOP 9.52

Yue LakePO4

3− −36.82DOP 11.31

D-Yue LakePO4

3− 19.62DOP 7.84

arabolic diffusion model (q/t = a + b/t1/2)

Wuli LakePO4

3− 0.04DOP 0.02

D-Wuli LakePO4

3− 0.02DOP 0.25

East Taihu LakePO4

3− 0.00DOP 1.68

D-East Taihu LakePO4

3− 0.08DOP 2.79

Yue LakePO4

3− 0.09DOP 0.74

D-Yue LakePO4

3− 0.02DOP 1.92

imple Elovich model (q = a + b ln t)b

Wuli LakePO4

3− 41.08DOP 14.32

D-Wuli LakePO4

3− 48.31DOP 11.09

East Taihu LakePO4

3− −36.05DOP 11.97

D-East Taihu LakePO4

3− 40.16DOP 9.49

Yue LakePO4

3− −36.56DOP 11.16

D-Yue LakePO4

3− 19.65DOP 7.64

a q-sorbed DOP or PO43− (mg kg−1) at time t (h). DOP and PO4

3− were initially ab The simple Elovich parameters were estimated without using the origin (q = 0; t =

icochem. Eng. Aspects 297 (2007) 154–162

as preferentially absorbed [43]. DOC/PO43− ratios of the

quilibrium concentrations of the highest initial concentra-ion were also compared for all the sediments. As shownn Fig. 8, PO4

3− and DOC were not preferentially sorbedFigs. 5, 7 and 8).

Those observations show that DOC, DOP and PO43− were

orbed differently after the sediments treated by H2O2, this indi-

ates that the organic matter content of sediments significantlyffected their sorption behavior. According to the above dis-ussion, the rank order of sorption strength on sediments wasOC < PO4

3− < DOP.

dimentsa

S.E. b S.E. R2

0.37 0.06 0.00 0.980.14 0.05 0.00 0.970.68 0.06 0.01 0.950.16 0.08 0.01 0.97

2.22 −0.24 0.04 0.870.17 0.09 0.01 0.981.35 0.10 0.01 0.910.22 0.10 0.01 0.96

0.98 −0.15 0.01 0.950.56 0.12 0.02 0.870.62 0.06 0.01 0.770.32 0.14 0.01 0.94

0.02 −0.01 0.01 0.160.06 0.00 0.00 −0.670.01 0.00 0.00 −0.260.26 −0.02 0.02 −0.50

0.03 −0.01 0.02 0.520.57 −0.25 0.09 0.260.03 −0.05 0.01 0.591.00 −0.64 0.22 0.46

0.08 −0.16 0.08 0.660.33 −0.09 0.03 0.630.01 −0.01 0.00 −0.090.82 −0.33 0.14 0.22

0.39 2.77 0.16 0.980.15 0.85 0.06 0.970.72 3.06 0.29 0.940.19 0.99 0.07 0.96

1.22 6.39 0.49 0.960.19 1.21 0.08 0.97

1.19 4.91 0.48 0.940.29 1.18 0.12 0.94

1.02 4.25 0.41 0.940.59 1.68 0.24 0.88

0.67 1.22 0.27 0.750.29 1.49 0.12 0.96

dded at 0.23 and 0.94 mg L−1 P sorbent.0).

S. Wang et al. / Colloids and Surfaces A: Physico

Fig. 7. DOC/DOP ratios in the equilibrium solution of the most concentratedinitial solution.

Fi

4

(

(

(

A

bcG

R

[

[[[[

[

[[[[[[[[

[

[

[[

[

[

[[[

[

ig. 8. DOC/ PO43− ratios in the equilibrium solution of the most concentrated

nitial solution.

. Conclusions

1) The DOP and PO43− sorption kinetics can be best fitted

by the modified Langmuir model and linear model, respec-tively. The organic matter content in sediments did notsignificantly affected their general trend. For inorganic P,with the increasing of organic matter content, m decreased,the higher the amount of P sorbed, the higher the risk of Prelease. While for organic P, with the increasing of organicmatter content, the sediments had weak binding strength, thestrong ability of DOM release and higher sorption capacity.

2) The DOP and PO43− sorption by sediments all included

quick and slow sorption and the quick sorption mainlyoccurred within 0.5 h; All DOP and PO4

3− sorption kinet-ics were best fitted by both power function and the simpleElovich models. Organic matter content in sediments had aremarkable effect on DOP and PO4

3− sorption rates. But,it did not affect the DOP and PO4

3− sorption trend, and theeffect of organic matter on PO4

3− sorption rate was moreobvious than on DOP.

3) The preferential sorption of DOP was over PO43−, and

the DOP sorption increased more strong with the increas-

ing of organic matter content in sediments than the PO4

3−sorption, and DOC was preferentially absorbed. The rankorder of sorption strength of sediments was as follows:DOC < PO4

3− < DOP.

[[[[

chem. Eng. Aspects 297 (2007) 154–162 161

cknowledgements

This research was financially supported by China’s nationalasic research program: “Studies on the Process of Eutrophi-ation of Lakes and the Mechanism of the Blooming of Bluereen Alga” (2002CB412304) and NSF of China (40403011).

eferences

[1] S.R. Wang, X.C. Jin, Y. Pang, H.C. Zhao, X.N. Zhou, J. Colloid InterfaceSci. 285 (2005) 448.

[2] R.A. Dorich, D.W. Nelson, L.E. Sommers, J. Environ. Qual. 14 (1985) 400.[3] C.E. Gibson, The dynamics of phosphorus in freshwater and marine envi-

ronments, in: H. Tunney, et al. (Eds.), Phosphorus Loss from Soil to Water,CAB International, Oxon, 1997, p. 121.

[4] A.G. Brinkman, Hydrobiologia 253 (1993) 31.[5] R. Emil, B.W. Eugene, Water Res. 32 (1998) 2969.[6] E. Gunnar, C. Rolf, Chemosphere 45 (20011053).[7] B.A. Whitton, S.L.J. Grainger, G.R.W. Hawley, J.W. Simon, Microbial

Ecol. 21 (1991) 85.[8] L.C. Kolowith, E.D. Ingall, R. Benner, Limnol. Oceanogr. 46 (2001)

309.[9] E.J. Frossard, L.M. Condron, A. Oberson, S. Sinaj, J.C. Fardeau, J. Environ.

Qual. 29 (2000) 15.10] L. Juliane, G.Q. Robert, M.U. Shauna, D.B. Scott, Soil Sci. Soc. Am. J. 68

(2) (2004) 620.11] K. Kaiser, Eur. J. Soil Sci. 52 (2001) 489.12] R.G. Qualls, B.L. Haines, Soil Sci. Soc. Am. J. 55 (1991) 1112.13] G. Anderson, E.G. Williams, J.O. Mori, J. Soil Sci. 25 (1974) 51.14] E.J. Frossard, W.B. Stewart, R.J. Arnaud, Can. J. Soil Sci. 69 (1989)

401.15] A. Kuhl, Algal Physiology and Biochemistry, University of California

Press, Berkeley, CA, 1974, p. 636.16] H. Wang, A. Adhityan, S.G. John, Water Res. 37 (2003) 3939.17] L.R. Pomeroy, E.E. Smith, C.M. Grant, Limnol. Oceanogr. 10 (1965) 167.18] J.G.C. Smits, D.T. van der Molen, Hydrobiologia 253 (1993) 281.19] H. Furumai, S. Ohgaki, Water Res. 23 (1989) 677.20] W.A. House, F.H. Denison, Environ. Sci. Technol. 36 (2002) 4295.21] T. Hiemstra, W.H. Van Riemsdijk, J. Colloid Interface Sci. 179 (1996) 488.22] L.H. Kim, E. Choi, M.K. Stenstrom, Chemosphere 50 (2003) 53.23] B.M. Das, Principles of Geotechnical Engineering, 2nd ed., PWS-KENT,

Boston, MA, 1990, p. 35.24] V.J.F. Ruban, S. Lopez, P. Pardo, G. Rauret, H. Muntau, Fresenius J. Anal.

Chem. 370 (2001) 224.25] Institute of Soil Science, Chinese Academy of Sciences, Physico-chemical

Analysis of Soils, Institute of Soil Science, Chinese Academy of Sciences,Shanghai, 1978, p. 35.

26] J.B. Angus, C.J. Kevin, Chemosphere 32 (1996) 2345.27] AWWA, WPCE, APHA, Standard Methods for the Examination Water and

Wastewater, 18th ed., AWWA, APHA, WPCE, Washington, DC, 1998, p.458.

28] B.V. Nwoke, J. Diels, N. Sanginga, O. Osonubi, R. Merckx, Agric. Ecosyst.Environ. 100 (2003) 285.

29] X.C. Jin, S.R. Wang, Y. Pang, H.C. Zhao, X.N. Zhou, Colloid Surf. A:Physicochem. Eng. Aspect 254 (2005) 241.

30] S.R. Wang, X.C. Jin, Y. Pang, Res. Environ. Sci. 18 (1) (2005) 53.31] M. Liu, L.J. Hou, S.X. Xu, Acta Geogr. Sin. 57 (4) (2002) 397.32] P. Lopez, X. Lluch, M. Vidal, J.A. Morguı́, Estuar. Coast. Shelf Sci. 42

(1996) 185.33] S.R. Wang, X.C. Jin, H.C. Zhao, Y. Pang, X.N. Zhou, J.Z. Chu, Environ.

Sci. 26 (3) (2005) 38.

34] E.D. Naoml, L.B. Patrick, Environ. Sci. Technol. 25 (1991) 395.35] A.M. Zhou, H.X. Tang, D.S. Wang, Water Res. 39 (2005) 1245.36] M. Mozaffari, J.T. Sims, Soil Sci. 157 (2) (1994) 97.37] T.E. Boub, E.A. Rochette, Commun. Soil Sci. Plant Anal. 34 (7/8) (2003)

1177.

1 : Phys

[

[[

62 S. Wang et al. / Colloids and Surfaces A

38] H.L. Golterman, Zonation of mineralization in stratified lakes, in: J.M.Anderson, A. Macfayden (Eds.), The Role of Terrestrial and Aquatic Organ-ism in Decomposition Processes, vol. 1, 1976, p. 3.

39] W. Davison, S.I. Heany, Limnol. Oceanogr. 23 (6) (1978) 1194.40] H. Verdouw, E.M.J. Dekkers, Arch. Hydrobiol. 89 (4) (1980) 509.

[

[[

icochem. Eng. Aspects 297 (2007) 154–162

41] J. Pizarro, N. Belzile, M. Filella, G.G.J.C. Leppard, P.D. Negre, J. Bule,Water Res. 29 (2) (1995) 617.

42] H. Kimmo, P. Juhani, P. Kalevi, Environ. Int. 24 (5/6) (1998) 527.43] J. Lilienfein, R.G. Qualls, S.M. Uselan, S.D. Bridgham, Soil Sci. Soc. Am.

J. 68 (2004) 292.