Performance evaluation of phosphorus removal by apatite in constructed wetlands treating domestic wastewater: Column and pilot experiments

Abstract

In constructed wetlands (CWs) treating domestic wastewater, good treatment performance is obtained on mains parameters except phosphorus (P) which can cause eutrophication problems. In order to improve P removal from wastewater with a low specific filter surface per person equivalent (pe), different materials have been tested: man-made and natural materials, industrial by-products, and a mixture of these materials. The P removal by natural apatite has been studied by only a limited amount of work. Apatite materials appear to possess high and long-term removal capacity, thus a better knowledge is needed to determine the quality of apatite to be used and the P removal evolution with time and water quality. In this work the P removal rates were studied in two different scales (lab-experiments and pilot units) on different apatite qualities. Removal rate in the pilot units was smaller than the one found in lab-scale columns and the results suggested that a security coefficient might be applied while designing the apatite filter.

Full text

Performances evaluation of phosphorus removal by apatite in constructed wetlands
treating domestic wastewater: Column and pilot experiments
Najatte Harouiyaa, Stéphanie Prost-Bouclea, Catherine Morlayb, Dirk Esserc, Samuel Martin
Rueld, Pascal Mollea
a Cemagref, research unit: Water quality and pollution prevention, 3 bis, quai Chauveau-CP
220, 69336 Lyon Cedex 9- France (E-mail: najatte.harouiya@cemagref.fr;
pascal.molle@cemagref.fr; stephanie.prost-boucle@cemagref.fr)
b IRCE Lyon, CNRS-UMR 5256, université Claude Bernard Lyon 1-domaine scientifique de la
Doua-Villeurbanne- France (E-mail: catherine.morlay@univ-lyon1.fr)
c SINT, 5 rue Boyd, F- 73 100 Aix- Les- Bains, France (E-mail: dirk.esser@sint.fr)
d Cirsee, Suez Environnement, 38 rue du Président Wilson, 78230 Le Pecq, France (E-mail:
Samuel.MARTIN@suez-env.com)
Abstract
In constructed wetlands (CWs) treating domestic wastewater, good treatment performances
are obtained on mains parameters except phosphorus (P) which can cause eutrophication
problems. In order to improve P removal from wastewater with a low specific filter surface
per people equivalent (p. e.), different materials have been tested: man-made and natural
materials, industrial by-products, and a mixture of these materials. The P removal by natural
apatite have been studied by a very few works. Despite apatite materials appears to possess
high and long-term retention capacity, a better knowledge is needed to precise the quality of
apatite to be used and the P removal evolution with time and water quality. In this work the P
retention kinetics have been studied in two different scales (lab-experiments and pilots) on
different apatite qualities. Retention rate in pilots is smaller than the one found in lab-
experiments and the results suggested that a security coefficient might be applied while
designing apatite filter.
Keywords: constructed wetlands; phosphorus removal; apatite; experiments scale;
sustainable treatment.
*corresponding authors: najatte.harouiya@cemagref.fr; pascal.molle@cemagref.fr
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011
Author manuscript, published in "WETPOL, Barcelona : Spain (2009)"

1. Introduction
In constructed wetlands phosphorus can be assimilated by biomass and incorporated by
organic matter [1]. But in such systems it’s not possible to remove the sludge and P is
released back into water after organic matter mineralization [2]. On the other hand
phosphorus is used by reeds [3], however the quantity removed by plant assimilation can be
neglected when using small surfaces (30 to 150 kg.m-2.year-1) [4]. To avoid eutrophication
problems in surface waters many researches have been done to use specific materials in CWs.
In the previous works several materials were tested as iron, aluminium and calcium rich
materials [5-16].
The P removal by these materials is based on adsorption and/or precipitation mechanisms
onto particle surface. Recently researches have focused on the use of apatite to promote
irreversible sorption onto the material surface. Nevertheless, in the few works done on P
removal by apatite [17-20], the materials have been only evaluated in lab-scale experiments
(batch and/or column) under controlled conditions.
Apatite minerals are known to have a great stability and the particular crystalline structure
allows substitutions of different elements [21-24]. This material has been proposed as an
effective means for retaining metals and radionuclides [25-29]. For these reasons in this work
besides the evaluation of apatite capacity to remove P in CWs, the materials have been
characterized for metal content.
In this study five different apatite materials have been tested in column and pilot experiments.
In lab-scale columns, the objectives were to precise retention kinetics versus apatite qualities
and influence of water ionic composition. In pilots, fed with treated wastewaters in hydraulic
controlled conditions, the objectives were to point out the retention rate evolution with time,
scale transition effect and exhibit the reed effect on P removal. Other objectives were also
sought as:
- Evaluation of the process sustainability and design optimization.
- The capability of column experiments to predict P retention.
2. Material and methods
2.1. Apatites tested
P retention experiments were performed in the present study using five sedimentary apatites
from Morocco and Algeria (Table 1). Particle size distribution was determined using dry-
sieving techniques [30], to calculate d10, d60 (mesh diameter allowing, respectively, 10 or 60%
of the material mass to pass through), and the uniformity coefficient (UC= d60/d10). Porosity
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

was determined from the amount of water needed to saturate a known volume of component
(replicate number n=3) and the bulk density was measured by the volume of water displaced
by a known mass of medium (n=3). Geometric surface areas in the present study were
estimated from the particle size distribution, assuming spherical grains, according to:
()
∑
−
=+
⋅
+
⎟
⎠
⎞
⎜
⎝
⎛
=1
11
121 n
i
i
ii M
m
dd
S
ε
(1)
Where di represents the sphere diameter,
ε
stands for the sample density, mi correspond to the
mass passing across di diameter, and M to the total mass of sample.
Physical, chemical and mineralogical properties of materials used are shown in Tables 1, 2
and 3.
Table 1 Physical characteristics of tested materials
Particle size Porosity Density Geometric
surface area
d10 (mm) d60 (mm) UC (d60/d10)% kg.m
-3 m
2.kg-1
BT 1.27 4.02 3.15 50 2414 0.73
HT1 4.44 9.21 2.09 46 2160 0.17
HT2 0.19 9.21 47.54
(1) 53 2243 1.48
AM 0.37 2.79 7.46 58 2392 1.76
AT2 2.14 3.85 1.80 54 2447 0.33
(1) HT2 material contains 30 % of fine particles of clay that can be bonded to larger particles. As a consequence, particle size distribution is
modified and real grain distribution is masked. In reality we observe apatite grains of 0.1 – 0.3 µm and coarser grains with impurities.
Table 2 Mineralogical characteristics of materials
Mineralogical composition % (W/W) of materials
Apatite Calcite Quartz Ankerite(2) Dolomite Clay
BT 41.8 50.4 4.8 n.d(3) 3.0 0.0
HT160.2 35.1 0.0 n.d(3) 4.7 0.0
HT246.3 39.5 10.1 n.d(3) 2.5 1.5
AM 95.4 3.2 1.3 n.d(3) 0.0 0.0
AT258.1 0.0 0.2 41.7 0.0 0.0
(2) CaFe (CO3)2 and (3) not determined
Materials tested contain 40 % to 95 % of apatite associated with other impurities. In this paper
the term “quality of apatite” will be used to mean % content of apatite mineral. A good
quality of material is one with a high percent of apatite mineral.
Table 3 Chemical composition of materials
(a) Major constituents
% Mass Ca P Si Mg Fe Al
BT 36.3 8.4 3.1 0.5 0.3 0.4
HT1 35.3 10.1 3.3 0.2 0.3 0.2
HT2 32.3 8.2 6.5 0.5 0.6 1.0
AM 38.2 13.2 1.1 0.2 0.2 0.2
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

AT2 31.9 9.6 2.2 1.7 0.4 0.5
(b) Trace elements
mg.kg-1 As Cd Cr Cu Pb Se V Zn U
BT 11.4 76.8 182.1 6.4 2.3 3.2 115.5 109.9 61.5
HT1 11.6 34.5 196.0 18.9 3.3 <LQ(4) 152.0 196.0 106.0
HT2 9.5 31.5 321.0 21.3 3.8 <LQ(4) 242.0 237.0 78.9
AM 13.3 14.4 257.0 22.9 3.8 1.9 130.0 181.0 131.0
AT2 4.0 11.9 210.0 5.1 3.2 21.3 <DL(4) 82.1 40.1
(4) limit of quantification
2.2. Column experiments
The apatites materials have been tested in vertical downward flow columns of 9 cm of inner
diameter (Fig.1a). All columns consist of 20 cm high layers of apatite, equipped with five
sampling ports to study P removal evolution into the media and to have better model fitting.
The columns were fed with synthetic solution (table 4) with known P concentration (inlet P
concentrations ranged from 1 to 16 mg. l-1) and maintained in hydraulic saturation conditions
as in horizontal flow constructed wetlands (HFCW). The inlet pH of all synthetic solutions
was 7.6±0.2. The columns samples are taken regularly and analyzed for calcium, phosphorus,
alkalinity, and pH to observe the temporal evolution of effluent composition. Experiments
have lasted 3 months for each material.
Table 4 Inlet water characteristics and hydraulic loads tested in column experiments
Water Flow rate/ cross section
m.d-1
BT Tap water and wastewater 0.80-1.60
HT1 Tap water 0.85
HT2 Tap water and wastewater 0.80-1.60
AM Tap water 0.80-1.15
AT2 Tap water 0.80-1.15
2.3. Pilots
2.3.1 Pilot-scale description
BT and HT2 materials have been tested in three similar pilot-scale (HFCW) at Bagnols plant
(Rhône, France). The pilots consist of 1.5m² tanks and 40 cm in depth filled up with apatite.
The pilot units were fed with treated wastewater (except for P, table 5) from the outlet of
Bagnols plant (trickling filter) (Fig.1b). One apatite pilot (HT+r) is planted with Phragmites
australis to study the reeds effect on P retention.
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

2 cm Gravel
Apatite
filter
2 cm Gravel
Peristaltic pump
Inlet
Outlet
Sampling
ports
Pretreatment Primar y
settling
tank
Secondary
settling tank
Trickling
filters
St-Aygues river
3 - BT
2 – HT2
1 – HT2+ r
Inlet Phragmites
australis
Pretreatment Primar y
settling
tank
Secondary
settling tank
Trickling
filters
St-Aygues river
3 - BT
2 – HT2
1 – HT2+ r
Inlet Phragmites
australis
Fig. 1. Schematic representation of: (a) column experiments and (b) pilots at Bagnols
2.3.2 Pilots monitoring
The monitoring of pilots ran from April 2008 to September 2009 with continuous recording of
inlet and outlet flow, pH, redox potential and meteorological conditions. Weekly samples of
influent and effluent were taken and analyzed for COD, BOD, SS, Ca, Nitrogen and
Phosphorus forms. Moreover PO4-P analyses for inlet and outlet are performed continuously
with a TresCon WTW online analyser. The P removal evolution into the apatite filter was
performed by regular internal samples into the material. The hydraulic residence time,
preferential-flow paths and dead zones in the pilots have been determined by uranine tracer
experiments using a GGUN-FL30 Fluorometer. Tracer experiments were performed during 1
week approximately.
3. Results and discussion
3.1. P removal in column experiments
As example, the evolution of P removal by AM apatite is shown in the figure 2. The P
concentration is presented as a function of time at the inlet and the outlet of the column
(residence time =3.3 hours in that case). A slight change of pH is observed (pHinlet=7.6±0.2
and pHoutlet=7.4±0.3).
(a) (b)
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

AM apatite
0
0.5
1
1.5
2
2.5
3
0 102030405060708090100110
Time (days)
Outlet PO4-P (mg.L-1)
0
5
10
15
20
Inlet PO4-P (mg.L-1)
Outlet P
Inlet P
Step 1 Step 2
Fig. 2. Evolution of P concentrations as a function of the time during the AM column experiment
Two steps can be noted:
Step 1: For 70 days 99% of phosphorus was removed and the P outlet concentration did not
exceed 0.1mg. l-1. The adsorption seems to be the predominant mechanism as proved by other
previous studies [31].
Step2: The outlet P concentration increased to reach lower but stable P retention kinetic. With
AM, this period starts after a storage level of about 5 g of P. kg-1 of apatite as found by Molle
et al. [18]. The precipitation becomes the predominant phenomenon of P retention in this step.
This points out how experiment duration is important to predict long term removal with such
material.
3.2. k-C* model and removal rates evolution
Using the internal sampling system, the P concentration in the apatite was modeled using k-
C* model [2]. The model has been chosen because it’s a simple way to model pollutant
removal in HFCW. The P concentration (C) at time t can be obtained by the following
expression:
(
)
*exp*)( 0CktCCC +
−
−= (2)
Where C0 is the inlet concentration of P, k the volumetric retention rate and C* the residual P
concentration.
The figure 3.a presents the P concentration evolution as a function of residence time in the
AM apatite material. The majority of P was retained in the first part of the apatite and the
retention rate k is about 4.2±0.2 h-1 in the beginning of the experiment (Fig.3b). Retention rate
for AM apatite decrease with time and with storage level of phosphorus in apatite material as
presented by the figure 4.b.
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

AM apatite
Inlet P= 15mg/L
0
2
4
6
8
10
12
14
16
18
20
00.511.522.533.544.55
Residence time (hours)
PO4-P mg.L-1
2 days
14 days
65 days
90 days
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
012345678
Storage level (g P.kg-1 of apatite)
k (h-1)
AM
AT2
BT
HT1
Fig. 3. (a) Variation of the phosphorus concentration with the reaction time for AM apatite. The symbols designate the
P experimental data, the curves drawn through this data represent the P concentrations calculated from k-C* model
and (b) Evolution of retention rates for all apatite materials studied as a function of P storage level per kilograms of
apatite
The comparison of retention rate evolution for all materials tested in this study as given by the
figure 4.b show that the retention rate k decreases systematically as adsorption mechanism
reduces until it reaches a steady state once precipitation becomes the major mechanism
involved in P removal. The stabilised k is about 0.9±0.1 h-1 and 0.3±0.1 h-1 for AM and BT
materials respectively. Indeed, the retention rates are different between materials used and the
differences observed could be related to material quality. This difference in k value is of great
importance in determination of the surface needed for P removal.
3.3. Surface observations
The AM apatite surface before and after column experiments was observed using an
Environmental Scanning Electron Microscopy (ESEM) equipped with a microanalysis
instrument EDS (Energy Dispersive X-ray System).
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

Fig. 4. Surface observation: (a) ESEM of AM apatite before experiment and (b) after experiment
Comparison of the photomicrographs illustrated in Figs. 4a and 4b shows a formation of
precipitate at the apatite surface. Precipitate formed are rich in Ca and P with Ca/P molar ratio
of 1.35±0.06. A presence of Zn in the precipitate was also observed and confirmed by water
analyze performed in column experiments (about 99% of Zn was retained by AM apatite). If
the Zn content is included as substitution of Calcium in the precipitate formed, the molar ratio
((Ca +Zn)/P) increase to 1.51±0.04. This composition obtained suggests a formation of tri-
calcium phosphate (TCP) and the precipitate could be considered as a precursor for
hydroxyapatite (HAP) phase. The formation of TCP as precursor of HAP precipitate could
have an effect on the evolution of P removal rates as observed in 3.2.
3.4. Hydraulic and treatment performances in pilots
The pilots were fed since April 2008 with residence time measured of about 2 days in the
whole pilots. The mean hydraulic and organic loads received by Bagnols pilots and inlet
wastewater characteristics are given in the table 5. Removal performances are similar in all
pilots and achieve about 70% and 98% for COD and SS respectively.
Table 5 Mean hydraulic and organic loads applied on the pilots and inlet wastewater characteristics.
Values for parameters are means/ (SD: standard deviation) of 34 samples
Conversely total nitrogen removal in the pilots is low (<40%) and this result could be related
to the longer time needed for nitrifying bacteria to develop in the beginning of experiments
and insufficient amounts of organic carbon available for denitrifying bacteria. The total
phosphorus removal is approximately 80% for HT2 material and 98% for BT material. No
HL (m/d) COD SS KN TN TP
Inlet wastewater (mg. l-1) 67.8/(31.2) 19.7/(16.1) 6.2/(4.3) 21.8/(8.0) 4.2/(1.7)
0.18/(0.08) HT+ r (g. m-2. d-1)/(SD) 11.6/(5.7) 3.1/(1.9) 1.0/(0.9) 3.6/(2.8) 0.7/(0.4)
0.18/(0.07) HT (g. m-2. d-1)/(SD) 11.8/(5.3) 3.0/(2.2) 1.1/(0.8) 4.0/(2.3) 0.7/(0.4)
0.13/(0.05) BT (g. m-2. d-1)/(SD) 8.3/(3.8) 2.2/(1.3) 0.7/(0.5) 2.5/(1.6) 0.5/(0.3)
(a) (b)
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

effect of reeds on phosphorus removal was observed in pilot experiments because the quantity
removed by reeds is very negligible compared to P loads applied on the HT+r pilot (30 to 150
kg. ha-1. year-1 [4]).
3.5. Scale transition effect
BT and HT2 materials have been tested in pilot system in order to evaluate the scale factor
effect and the biomass development on P retention rate. As presented in table 6, the retention
rates obtained in lab-experiments are different from those measured in pilots mostly for HT2
material.
Table 6 Comparison of retention rates between column experiments and pilots
Materials k (h-1) in column-scale k (h-1) in pilot-scale
BT 0.3 0.3
HT2 0.6 0.3
The differences might be caused by the hydraulic conditions. In pilots, hydrodynamic is less
controlled than in lab experiment. In another and longer study on BT apatite carried out in real
scale HFCW at Evieu plant [31], k value decreases to 0.07±0.02 h-1 after two years of
experiments. Stabilised k value for all materials might be smaller than the one stated in table 6
and in figure 3.b. Therefore designers have to be aware of it and apply security coefficient
while designing apatite filter. In real conditions the stabilised k values could be estimated two
to three times less than values in lab-scale experiments.
3.6. Design recommendations
To evaluate the process sustainability and optimize the design of apatite filter. In the figure 5
is given the surfaces needed per p.e. to respect 2 or 1 mg P.l-1 for the two extreme apatites
studied in this work (AM and BT). In this figure the surfaces are calculated for an inlet P
concentration of 10 mgP.l-1 and a retention rates of 0.9±0.1 h-1 and 0.3±0.1 h-1 for AM and BT
materials respectively.
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

0
1
2
3
4
5
6
7
8
9
10
11
12
0.0 0.2 0.4 0.6 0.8 1.0
Surface needed (m².p.e-1)
PO4-P outlet (mgP.L-1) and storage level
(g P.kg-1 of apatite/year)
P outlet AM
P outlet BT
Storage level AM
Fig. 5. Effect of apatite quality on surface needed for P treatment and on final saturation of the apatite
filter
Using AM material a surface of 0.2 m²/p.e is sufficient to achieve 1 mgP.l-1 in the effluent.
However, due to hydraulic short-cutting it is not secure to use smaller surfaces and the best
window in term of application is to use about 0.5 m².p.e-1. It means that apatite materials like
BT with poor quality are not suitable. The use of 0.5 m².p.e-1 have also an important role to
delay final saturation of the filter. The actual storage level reached for AM material in lab-
experiments is about 7 g of P. kg-1 of apatite. As presented by grey curve, if the filter
accumulates 1g of P. kg-1 of apatite per year using a surface of 0.5 m².p.e-1, this level would
be reached after 7 years and the filter could work at least 7 years with high P retention
kinetics. The use of smaller filter surfaces would lead to earlier final saturation.
4. Conclusions
Main conclusion, except confirmation of the good P removal potential of apatite in
constructed wetlands, is the importance of apatite quality on long-term P removal. A better
insight of processes in term of adsorption/precipitation, precipitate formed, impact of reeds
and experiments scale allow to consolidate the design of apatite filters and its sustainability.
This work provides data in lab-scale experiments and in pilots for P removal by apatite.
Apatite materials have a high retention capacity and the results of lab-scale experiments could
be used to predict P removal in full-scale taking into account others factors as hydraulic
conditions. A decrease in retention rates with time was observed for all materials and the
apatite quality appears to be very important for sustainable P treatment. Using a good quality
of apatite the surface needed for P treatment is about 0.5 m² to respect 1 mgP.l-1 in the
effluent.
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

Acknowledgements: the Authors would like to thank the Rhône-Alpes Chemicals and Environment
competitiveness cluster “Axelera” in which this project takes place. We thank CERPHOS and
FERPHOS groups for providing the apatite used in this study.
References
[1] Vymazal, J. (2007). The Science of The Total Environment, 380 (1-3), 48-65.
[2] Kadlec R.H., Knight R.L. (1996). Boca Raton, Florida: CRC Press;893 pp.
[3] Vymazal, J. (1995). Chelsea, Michigan: Lewis Publishers; 698 pp.
[4] IWA (2000). Scientific and technical report no 8.
[5] Drizo, A., Frost, C.A., Grace, J., Smith, K.A. (1999). Water Research, 33, 3595–3602.
[6] Brix, H., Arias, C.A. and del Bubba, M. (2000). Proceedings, 7th International Conference
on Wetlands systems for water pollution control, IWA, Florida, 1, 65–74.
[7] Khadraoui, M., Watanabe, T., Kuroda, M. (2002). Water Research, 36, 3711-3718.
[8] Arias, C.A., Brix, H., Johansen, N.H. (2003). Water Science and Technology, 48 (5), 51–
58.
[9] Del Bubba, M., Arias, C.A., Brix, H. (2003). Water Research, 37, 3390–3400.
[10] Molle, P., Liénard, A., Grasmick, A. and Iwema, A. (2003). Water Science and
Technology, 48(5), 75-83.
[11] Karapinar, N., Hoffmann, E., Hahn, H. H. (2004). Water Research, 38, 3059-3066.
[12] Drizo, A., Forget, C., Chapuis, R.P. and Comeau, Y. (2006). Water Research, 40(8),
1547–1554.
[13] Johansson Westholm, L. (2006). Water Research. 40, 23–36.
[14] Shilton A.N., Elmetri I., Drizo A., Pratt S., Haverkamp R.G. and Bilby S.C. (2006).
Water Research, 40, 113-118.
[15] Àdàm, K., Krogstad, T., Vråle, L., Søvik, A.K., Jenssen, P.D. (2007). Ecological
Engineering, 29 (2), 200–208.
[16] Vohla, C., Kõiv, M., John Bavor, H. and Mander, Ü. (2009). Ecological Engineering (in
press).
[17] Jang, H., Kang, S.H. (2002). Water Research, 36 (5), 1324–1330.
[18] Molle, P., Liénard, A., Iwema, A., Kabbabi, A. (2005). Water Science and Technology,
51(9), 193–203.
[19] Bellier, N., Chazarenc, F. and Comeau, Y. (2006). Water research, 40(15), 2965-2971.
[20] Chazarenc, F, Filiatrault, M., Brisson, J. and Comeau, Y. (2008). Proceedings, 11th
International conference on Wetlands Systems for Water Pollution Control, IWA, India, 1,
1052–1059.
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

[21] Kreidler, E. R. and Hummel, F. A. (1970). Am Mineral. 55, 170-184.
[22] McConnel, D. (1973). Springer, New York.
[23] Roy, D. M., Drafall, L. E. and Roy, R. (1978). In phase diagrams, material sciences and
technology 6-V. Alper AM (ed) Academic Press, New York, p 186-239.
[24] Elliott, J. C. (1994). Elsevier, Amsterdam.
[25] Lindsay, W.L. (1979). 449 p. Wiley, New York.
[26] Gauglitz, R., Holterdorf, M., Franke, W. and Marx, G. (1992). Radiochim. Acta .58/59,
253-257.
[27] Valsami-Jones, E., Ragnarsdottir, K. V., Putnis, A., Bosbach, D., Kemp, A. J. and
Cressey G. (1998). Chem. Geo. 151, 215-233.
[28] Manecki, M., Maurice, P.A. and Traina, S.J. (2000). American Mineralogist. 85, 932–
942.
[29] Arnich, N., Lanhers, M, Laurensot, F., Podorc, R. Montiel, A. and Burnel, D. (2003).
Environmental Pollution. 124,139–149.
[30] European norm EN 933-1 (1997). Tests for geometrical properties of aggregates – Part 1:
Determination of particle size distribution – sieving method.
[31] Harouiya, N., Molle, P., Prost-Boucle, S., and Liénard, A. (2008). Proceedings, 11th
International conference on Wetlands Systems for Water Pollution Control, IWA, India, 2,
746–753.
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

FIGURES
2 cm Gravel
Apatite
filter
2 cm Gravel
Peristaltic pump
Inlet
Outlet
Sampling
ports
Pretreatment Primar y
settling
tank
Secondary
settling tank
Trickling
filters
St-Aygues river
3 - BT
2 – HT2
1 – HT2+ r
Inlet Phragmites
australis
Pretreatment Primar y
settling
tank
Secondary
settling tank
Trickling
filters
St-Aygues river
3 - BT
2 – HT2
1 – HT2+ r
Inlet Phragmites
australis
Fig. 1. Schematic representation of: (a) column experiments and (b) pilots at Bagnols
AM apatite
0
0.5
1
1.5
2
2.5
3
0 102030405060708090100110
Time (days)
Outlet PO4-P (mg.L-1)
0
5
10
15
20
Inlet PO4-P (mg.L-1)
Outlet P
Inlet P
Step 1 Step 2
Fig. 2. Evolution of P concentrations as a function of the time during the AM column experiment
(a) (b)
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

AM apatite
Inlet P= 15mg/L
0
2
4
6
8
10
12
14
16
18
20
00.511.522.533.544.55
Residence time (hours)
PO4-P mg.L-1
2 days
14 days
65 days
90 days
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
012345678
Storage level (g P.kg-1 of apatite)
k (h-1)
AM
AT2
BT
HT1
Fig. 3. (a) Variation of the phosphorus concentration with the reaction time for AM apatite. The symbols designate the
P experimental data, the curves drawn through this data represent the P concentrations calculated from k-C* model
and (b) Evolution of retention rates for all apatite materials studied as a function of P storage level per kilograms of
apatite
Fig. 4. Surface observation: (a) ESEM of AM apatite before experiment and (b) after experiment
(a) (b)
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

0
1
2
3
4
5
6
7
8
9
10
11
12
0.0 0.2 0.4 0.6 0.8 1.0
Surface needed (m².p.e-1)
PO4-P outlet (mgP.L-1) and storage level
(g P.kg-1 of apatite/year)
P outlet AM
P outlet BT
Storage level AM
Fig. 5. Effect of apatite quality on surface needed for P treatment and on final saturation of the apatite
filter
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

TABLES
Table 1 Physical characteristics of tested materials
Particle size Porosity Density Geometric
surface area
d10 (mm) d60 (mm) UC (d60/d10)% kg.m
-3 m
2.kg-1
BT 1.27 4.02 3.15 50 2414 0.73
HT1 4.44 9.21 2.09 46 2160 0.17
HT2 0.19 9.21 47.54
(1) 53 2243 1.48
AM 0.37 2.79 7.46 58 2392 1.76
AT2 2.14 3.85 1.80 54 2447 0.33
(1) HT2 material contains 30 % of fine particles of clay that can be bonded to larger particles. As a consequence, particle size distribution is
modified and real grain distribution is masked. In reality we observe apatite grains of 0.1 – 0.3 µm and coarser grains with impurities.
Table 2 Mineralogical characteristics of materials
Mineralogical composition % (W/W) of materials
Apatite Calcite Quartz Ankerite(2) Dolomite Clay
BT 41.8 50.4 4.8 n.d(3) 3.0 0.0
HT160.2 35.1 0.0 n.d(3) 4.7 0.0
HT246.3 39.5 10.1 n.d(3) 2.5 1.5
AM 95.4 3.2 1.3 n.d(3) 0.0 0.0
AT258.1 0.0 0.2 41.7 0.0 0.0
(2) CaFe (CO3)2 and (3) not determined
Table 3 Chemical composition of materials
(a) Major constituents
% Mass Ca P Si Mg Fe Al
BT 36.3 8.4 3.1 0.5 0.3 0.4
HT1 35.3 10.1 3.3 0.2 0.3 0.2
HT2 32.3 8.2 6.5 0.5 0.6 1.0
AM 38.2 13.2 1.1 0.2 0.2 0.2
AT2 31.9 9.6 2.2 1.7 0.4 0.5
(b) Trace elements
mg.kg-1 As Cd Cr Cu Pb Se V Zn U
BT 11.4 76.8 182.1 6.4 2.3 3.2 115.5 109.9 61.5
HT1 11.6 34.5 196.0 18.9 3.3 <DL(4) 152.0 196.0 106.0
HT2 9.5 31.5 321.0 21.3 3.8 <DL(4) 242.0 237.0 78.9
AM 13.3 14.4 257.0 22.9 3.8 1.9 130.0 181.0 131.0
AT2 4.0 11.9 210.0 5.1 3.2 21.3 <DL(4) 82.1 40.1
(4) Detection limit
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

Table 4 Inlet water characteristics in column experiments
Water Flow rate/ cross section
m.d-1
BT Tap water and wastewater 0.80-1.60
HT1 Tap water 0.85
HT2 Tap water and wastewater 0.80-1.60
AM Tap water 0.80-1.15
AT2 Tap water 0.80-1.15
Table 5 Mean hydraulic and organic loads applied on the pilots and inlet wastewater characteristics.
Values for parameters are means/ (SD: standard deviation) of 34 samples
Table 6 Comparison of retention rates between column experiments and pilots
Materials k (h-1) in column-scale k (h-1) in pilot-scale
BT 0.3 0.3
HT2 0.6 0.3
HL (m/d) COD SS KN TN TP
Inlet wastewater (mg. l-1) 67.8/(31.2) 19.7/(16.1) 6.2/(4.3) 21.8/(8.0) 4.2/(1.7)
0.18/(0.08) HT+ r (g. m-2. d-1)/(SD) 11.6/(5.7) 3.1/(1.9) 1.0/(0.9) 3.6/(2.8) 0.7/(0.4)
0.18/(0.07) HT (g. m-2. d-1)/(SD) 11.8/(5.3) 3.0/(2.2) 1.1/(0.8) 4.0/(2.3) 0.7/(0.4)
0.13/(0.05) BT (g. m-2. d-1)/(SD) 8.3/(3.8) 2.2/(1.3) 0.7/(0.5) 2.5/(1.6) 0.5/(0.3)
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011

Figures captions
WETPOL, Barcelona, ESP, 2009
hal-00619050, version 1 - 5 Sep 2011