Investigations on phosphorus recovery from aqueous solutions by biochars derived from magnesium-pretreated cypress sawdust

Journal of Environmental Management xxx (2017) 1e10

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Research article

Investigations on phosphorus recovery from aqueous solutions by biochars derived from magnesium-pretreated cypress sawdust Khouloud Haddad a, b, Salah Jellali a, *, Mejdi Jeguirim b, Aida Ben Hassen Trabelsi c, Lionel Limousy b a

Wastewaters and Environment Laboratory, Water Research and Technologies Center (CERTE), BP 273, Soliman, 8020, Tunisia Institut de Science des Mat
eriaux de Mulhouse, UMR CNRS 7361, 15 rue Jean Starcky, 68057, Mulhouse, France Laboratory of Wind Power Control and Energy Valorization of Waste, Research and Technology Centre of Energy (CRTEn), B.P 95, 2050, Hammam Lif, Tunisia b c

a r t i c l e i n f o

a b s t r a c t

Article history: Received 31 January 2017 Received in revised form 20 May 2017 Accepted 9 June 2017 Available online xxx

The ability of biochars, derived from the pyrolysis at 400
C; 500
C and 600
C of pretreated cypress sawdust with 20 wt% magnesium chloride (MgCl2) solutions, in recovering phosphorus from aqueous solutions was investigated under various experimental conditions in batch mode. The experimental results indicated that cypress sawdust pretreatment with MgCl2 induced important modifications of the physical and chemical biochars' properties favoring phosphorus recovery from the used synthetic solutions. Moreover, phosphorus recovery efficiency increased with the increase of the used pyrolysis temperature. Indeed, for an aqueous pH of 5.2 and a phosphorus concentration of 75 mg L1, the recovered amounts increased from 19.2 mg g1 to 33.8 mg g1 when the used pyrolysis temperature was raised from 400
C to 600
C. For all the tested biochars, the phosphorus recovery kinetics data were well fitted by the pseudo-second-order model, and the equilibrium state was obtained after 180 min of contact time. Furthermore, the phosphorus recovery data at equilibrium were well described by the Langmuir model with a maximal recovery capacity of 66.7 mg g1 for the magnesium pretreated biochar at 600
C. Phosphorus recovery by the used biochars occurred probably through adsorption onto biochars' active sites as well as precipitation with magnesium ions as magnesium phosphates components. All these results suggested that biochars derived from MgCl2 pretreated cypress sawdust could be considered as promising materials for phosphorus recovery from wastewaters for a possible further subsequent use in agriculture as amendments. © 2017 Elsevier Ltd. All rights reserved.

Keywords: Cypress sawdust Impregnation Magnesium salts Phosphorus Recovery Desorption Mechanisms

1. Introduction Wastewaters discharged from agriculture and urban activities are generally rich in phosphorus compounds (Li et al., 2016). Phosphorus (P), could be a potential pollutant of fresh water resources as it may contribute to the eutrophication of aquatic environments and be potentially toxic for aquatic organisms (Zhang et al., 2012). In the same time, phosphorus, which is an essential element for food production, is a finite resource on the earth and it €der may be depleted over the next 100 years. In this context, Schro

* Corresponding author. E-mail addresses: [email protected] (K. Haddad), [email protected]. tn (S. Jellali), [email protected] (M. Jeguirim), [email protected] (A. Ben Hassen Trabelsi), [email protected] (L. Limousy).

et al. (2011) have estimated that 2035 would be the date where phosphates demand exceed supply. Thus, P recovery from wastewaters has become a necessity in order to preserve the environment and to balance the intensively exhaustion of high-grade phosphates ores. Numerous P recovery methods such as chemical precipitation, enhanced chemical crystallization as struvite, biological uptake, and adsorption onto natural and modified materials have been developed and tested in the last decades. The chemical precipitation and crystallization processes have the drawback of the consumption of costly chemicals and the production of huge amounts of sludges (Nguyen et al., 2014). Likewise, biological P accumulation may be intensively reduced because of the difficulties of culturing adapted microorganisms and the lack of sufficient carbon contents which is necessary for their growth (Rittmann et al., 2011). Phosphorus recovery through adsorption onto natural/modified materials and wastes has been identified as a

http://dx.doi.org/10.1016/j.jenvman.2017.06.020 0301-4797/© 2017 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Haddad, K., et al., Investigations on phosphorus recovery from aqueous solutions by biochars derived from magnesium-pretreated cypress sawdust, Journal of Environmental Management (2017), http://dx.doi.org/10.1016/j.jenvman.2017.06.020

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K. Haddad et al. / Journal of Environmental Management xxx (2017) 1e10

promising research topic since it has the advantages of low reagents and energy consumption and offers the possibility of the Ploaded products use in agriculture as fertilizers (Vohla et al., 2011). Several mineral and organic natural materials have been tested for phosphorus recovery from both synthetic solutions or real urban/ industrials wastewaters such as powdered marble wastes (Jaouadi et al., 2014; Haddad et al., 2015), phosphates mine slimes (Jellali et al., 2010), Aleppo pine sawdust (Benyoucef and Amrani, 2011) and Posidonia Oceanica fibers (Jellali et al., 2011). These studies indicated that raw organic materials were not sufficient in recovering phosphorus compared to the mineral products. Indeed, the highest phosphorus recovery yields were obtained for alkaline pH and calcium-rich mineral products such as Sepiolite (Yin et al., 2013), crab shells (Jeon and Yeom, 2009) and calcinated powdered marble wastes (Haddad et al., 2015). Therefore, there was an urgent need for the development of novel, low cost and environmental-friendly organic materials which could be efficiently applied for phosphorus recovery from both low and highly concentrated phosphorus-containing effluents and then valorized in agriculture as fertilizers. Biochars are carbon-rich solid products which are generated by the thermal stabilization of organic agricultural and animal biomasses (Kung et al., 2014). Thanks to their stability and attractive physicochemical properties, biochars have been effectively applied for carbon sequestration (Lehmann et al., 2011), greenhouse-gas emissions reduction (Wang et al., 2013), soil quality and crop yields improvement (Zheng et al., 2013) and environmental pollution control (Tan et al., 2017). Therefore, the use of biochars as efficient sorbents of dissolved pollutants could be a promising solution in order to ensure a sustainable waste management and the preservation of the environment (Cao and Harris, 2010; Jellali et al., 2016). In order to enhance the biochars' efficiencies in removing and/or recovering pollutants from effluents, huge scientific efforts have been made this last decade regarding the improvement of their properties through their physical and/or chemical modification (Inyang et al., 2014; Mohan et al., 2014). The tested methods included steam-activation (Inyang et al., 2014), and the biomasses pre-impregnation with mineral functional additives such as aluminum, iron, calcium and magnesium (Zhang et al., 2012; Zhang and Gao, 2013; Wang et al., 2015a,b). The assessment of the ability of certain biochars generated from the pyrolysis of raw and saltspre-impregnated biomasses for P recovery from aqueous solutions has proved the role of such chemical modification in the enhancement of the P uptake under specific physicochemical conditions (Fang et al., 2014; Chen et al., 2011; Wang et al., 2015a,b). However, to the best of our knowledge, there were no studies reported in literature regarding the correlation of magnesium pretreated cypress sawdust biochars characteristics to their phosphorus recovery and release efficiencies for different pyrolysis temperatures. In this paper, biochars prepared from the slow pyrolysis of magnesium pretreated cypress sawdust at temperatures varying between 400 and 600
C were firstly well characterized using specific apparatus and then tested for phosphorus recovery and desorption under various experimental conditions. The main objectives of this work are: (1) to examine the effect of the pretreatment step with magnesium chloride on the main physicochemical characteristics of the produced biochars under different pyrolysis temperatures, (2) to assess the effects of contact time, initial phosphorus concentrations, pH solutions, biochars dosages and the presence of other anionic pollutants on the P recovery effectiveness, (3) to acquire further insights into the underlying recovery mechanisms and (4) to study the phosphorus release from the tested biochars and its implication for their reuse in agriculture.

2. Materials and methods 2.1. Biochars preparation The raw cypress sawdust (RCS) used in this work was taken from a carpentry manufactory located in the city of Menzel Bouzelfa (North East of Tunisia). The RCS feedstock was firstly air-dried for 10 days until a constant weight and sieved for a particle size of 2 mm. Then, the RCS was chemically modified by immersing at once 40 g of RCS in 400 mL of 20 wt% magnesium chloride solution (MgCl2,6H2O). The resulting mixture was stirred at room temperature during 4 h. After filtering, the Mg-impregnated sample was dried in an oven at 60
C for 24 h and the obtained solid sample was referred to “Magnesium pretreated cypress sawdust (CS-Mg)”. Afterwards, the pretreated cypress sawdust was pyrolyzed in a fixedbed stainless reactor with a length of 30 cm and a diameter of 15 cm. During the pyrolysis tests, 600 g of CS-Mg were placed in the reactor and heated by an electric furnace from room temperature until the desired temperature (400
C; 500
C and 600
C) at a rate of 5 C
/min under 0.5 L min1 nitrogen flow. More details regarding this reactor are given by Kraiem et al. (2015). At the end of the pyrolysis operation, the biochars were recuperated from the reactor when its temperature becomes equal to the ambient one. The generated biochars at pyrolysis temperatures of 400; 500 and 600
C were labeled B-Mg400, B-Mg500, and B-Mg600, respectively and used for the study of phosphorus recovery from aqueous solutions and release. 2.2. Biochars characterization At a given pyrolysis temperature, the biochars production yield (Ybiochar) was determined as the ratio between the weight of collected biochar (Mbiochar (g)) and the weight of magnesium pretreated cypress sawdust (Mbiomass(g)) as follows:

Ybiochar ðwt%Þ ¼

Mbiochar *100 Mbiomass

(1)

Proximate analysis, including volatile matter (VM), fixed carbon (FC) and ash in biochars, was performed on the basis of the standard methods in ASTM D 1762-84 (ASTM, 2013). The pH of zero point charge (pHZPC) values of the studied biochars were determined according to the solid addition method using 0.01 M NaCl solutions, 1 g of solid matrix for initial pH values varying between 2 and 12 (Jellali et al., 2010). The surface chemistry of biochars was provided through Fourier transform infrared spectroscopy (FTIR) analyses using the KBr method with an IFTR-BX, Perkin Elmer apparatus. All biochars samples were carefully dried before mixing with KBr to avoid any additional effect due to the presence of water. The related spectral resolution is 1 cm-1 measured between 400 and 4000 cm1. The possible existence of any crystallographic structure in the tested biochars was assessed thanks to X-ray diffraction analysis (PW 1710). Furthermore, the mineral contents of the produced biochars were quantified by an X-ray fluorescence spectrophotometer (XRF: Philips PW2540) equipped with a rhodium target Xray tube and a 4 kW generator. During this analysis, 100 mg of the used biochars were ground and mixed with 200 mg of boric acid then pressed into a pellet under a 109 Pa pressure for 15 min. The morphologic and surface elemental composition of the biochars were characterized with a scanning electron microscopy (SEM) and energy dispersive EDX (X-ray spectrometry) (Philips XL 30 FEG). Finally, biochars textural properties were measured by nitrogen adsorption at 77 K using a Micromeritics ASAP 2420 instrument.

Please cite this article in press as: Haddad, K., et al., Investigations on phosphorus recovery from aqueous solutions by biochars derived from magnesium-pretreated cypress sawdust, Journal of Environmental Management (2017), http://dx.doi.org/10.1016/j.jenvman.2017.06.020

K. Haddad et al. / Journal of Environmental Management xxx (2017) 1e10

Prior to this analysis, the materials were degassed overnight in vacuum at 300
C. The BET specific surface areas (SSA) of the biochars were determined for relative pressure range of 0.01e0.05. The pore size distributions (PSD) were assessed from the adsorption branch of nitrogen isotherms using the 2D NLDFT heterogeneous surface model. 2.3. Phosphorus recovery experiments 2.3.1. Experimental protocol The assessment of phosphorus recovery capacities of the elaborated biochars was performed through batch experiments. A stock phosphorus synthetic solution of 1000 mg L1 was prepared by dissolving potassium dihydrogen phosphate (KH2PO4) acquired from Fisher Scientific with distilled water and used during this study. During this work, the impacts of contact time, initial P concentrations, solutions pH, biochars dosages and the presence of other anions on P recovery by the three tested Mg-biochars (BMg400, B-Mg500 and B-Mg600) were quantified. All These experiments were performed at 20 ± 02
C in 120 mL capped flasks. For each run, a given biochar mass was added into 50 mL solutions of a desired phosphorus concentration and shaken at 400 rpm using a Varimag-poly15 magnetic stirrer. The residual aqueous phosphorus contents were measured after the samples filtration through 0.45 mm filters. The analysis of phosphorus species concentrations was assessed according to (Fleury and Leclerc, 1943) method using a Thermo Spectronic UV1 model. At a given time, t, the recovered phosphorus amount (qt,P: mg g1) and the corresponding recovery efficiencies (Rt(%)) by the tested biochars were determined as follows:

qt;P ¼

C0;P  Ct;P *V M

Rt ð%Þ ¼

C0;P  Ct;P *100 C0;P

(2)

(3)

where C0,P and Ct,P (mg L1) are the initial and at time, t, phosphorus concentrations, respectively. V is the volume of the used solution and M is the weight of the used biochar (g). It is important to underline that each analysis point given in this study was an average of three independent parallel sample solutions with a standard deviation of ±3%. 2.3.2. Kinetic and isotherms studies Kinetic studies were performed in order to determine the effect of contact time on the phosphorus recovery process by the three tested biochars. The phosphorus recovery kinetic was monitored at different times between 10 and 180 min for fixed initial phosphorus concentration, biochars dosage and an aqueous pH of 75 mg L1, 2 g L1 and 5.2, respectively. The equilibrium P recovery data were assessed for the three studied magnesium pretreated biochars for initial phosphorus aqueous concentrations varying between 50 and 250 mg L1 at natural pH (without any adjustment), fixed biochars dosage of 2 g L1 and a constant contact time of 180 min. This time corresponds to an equilibrium state characterized by quasi-constant residual phosphorus concentrations. It was determined from preliminary experiments (data not shown). Numerous models have been already employed in scientific literature for the fitting of both kinetic and equilibrium experimental data of pollutants removal or recovery from solutions (Wang et al., 2015a,b; Chen et al., 2014). In the present work, the assessed kinetic and equilibrium data were fitted with the most

3

famous ones which are the pseudo-first-order and pseudo-secondorder; and Freundlich and Langmuir models, respectively. 2.3.3. Effect of pH, biochars dosages and ionic strength The pH influence on phosphorus recovery by the three studied biochars at equilibrium was performed for pH values varying between 3 and 11, an initial phosphorus concentration of 75 mg L1 and a fixed biochars dosage of 2 g L1. Besides, the impact of biochars dosages varying between 1 and 10 g L1 was performed for an initial phosphorus concentration of 75 mg/L and at natural pH. Finally, the influence of the ionic strength was monitored in presence of nitrates (10; 50 and 100 mg L1) and sulphates (100; 200; and 400 mg L1) for an initial constant concentration of 75 mg/L and at natural pH (without adjustment). 2.3.4. Phosphorus recovery mechanisms investigations The involved mechanisms during phosphorus recovery were explored through specific analyses. Indeed, scanning electron microscope images coupled with surface elemental composition analyses were conducted using a Philips XL 30 FEG apparatus in order to assess any modifications in the structure and the surface properties of the biochars after phosphorus recovery phase. Moreover, XRD analyses of the biochars before and after phosphorus recovery were performed with the aim to detect any new crystallographic structure induced by the phosphorus recovery by using a computer-controlled X-ray diffractometer. 2.4. Desorption experiments Phosphorus release experiments were performed in order to quantify the ability of the three tested biochars in releasing the prerecovered phosphorus and therefore their future reuse in agriculture as fertilizers. The phosphorus-loaded biochars (0.1 g) were added to 50 mL of distilled water solutions having adjusted pH values of 5.2, 7 and 9, and then shaken at 400 rpm for various times varying between 30 and 3600 min. At each time, three independent samples were firstly filtered through 0.45 mm filters, and then the corresponding phosphorus contents were measured through spectrometer analyses. At a given time, t, the released phosphorus amounts (qdes (mg/ g)) were calculated as follows:

qdes ¼

Ct; des V Ms

(4)

where Ct,des (mg/L) is the P concentration in the desorbed solution, V (L) is the volume of the used solution, and Ms (g) is the amount of used pre-loaded biochars. 3. Results and discussion 3.1. Effect of pyrolysis temperature on biochars properties 3.1.1. Biochars yields The pyrolysis of the magnesium pretreated cypress sawdust demonstrated that the biochars yields were very dependent on the used temperature (Table 1). Indeed, they decreased from about 52.5% to 33.3% when the temperature increased from 400
C to 600
C. This behavior is attributed to the fact that at low pyrolysis temperatures, lower condensation yields of aliphatic compounds and smaller transformations of biomass components to CH4, H2 and CO were achieved. In contrast, for high used temperatures, the dehydration of hydroxyl groups as well as the thermal degradation of cellulose and lignin structures significantly contributes to the decline of the generated biochars percentage (Novak et al., 2009;

Please cite this article in press as: Haddad, K., et al., Investigations on phosphorus recovery from aqueous solutions by biochars derived from magnesium-pretreated cypress sawdust, Journal of Environmental Management (2017), http://dx.doi.org/10.1016/j.jenvman.2017.06.020

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K. Haddad et al. / Journal of Environmental Management xxx (2017) 1e10

Table 1 Main physicochemical properties of the biochars produced from magnesium pretreated cypress sawdust at different pyrolysis temperatures.

Production yield (%) Volatile matter (%) Fixed carbon(%) Ash content (%) pHZPC Specific surface area (m2g1) Average pore size (nm)

B-Mg400 52.50 23.76 67.71 8.53 7.83 18.29 15.36

B-Mg500 45.00 18.87 72.06 9.07 8.25 7.37 19.67

B-Mg500 B-Mg600

B-Mg600 33.34 9.32 79.36 11.12 9.68 37.51 23.09

Wang et al., 2015a,b). Similar observations were reported by Wang et al. (2015a,b) and Zhang et al. (2015) when studying the pyrolysis of oak sawdust and wheat straw under different temperatures, respectively.

80

Adsorption Volume (Cm 3.g-1)

Parameter

B-Mg400 100

60

40

20

0 0

0.2

0.4

0.6

0.8

1

RelaƟve pressure (P/P0)

3.1.2. Biochars characterization The main physicochemical properties of the tested biochars, including ash contents, volatile matter, fixed carbon, pHZPC and specific area are summarized in Table 1. It can be noticed that the volatile matter contents of the biochars significantly decreased from about 23.8% to 9.3% when the applied pyrolysis temperature was increased from 400 to 600
C. On the contrary, the fixed carbon contents increased from about 67.7% to 79.36% when the temperature was raised from 400
C to 600
C. Indeed, at high temperature pyrolysis (600
C), the cellulose and hemicellulose were degraded. On the other hand, ash content increased from 8.5% to 11.1% as the pyrolysis temperature increased from 400
C to 600
C, respectively, which could be imputed to the catalytic degradation of more organic components in presence of magnesium chloride (MgCl2) at higher temperatures. It is worth mentioning that the pyrolysis temperature has also a significant effect on the pHZPC since it increases from 7.83 to 8.25 as the used temperature increased from 400
C to 500
C and it reaches 9.68 at 600
C. This behavior could be probably due to the separation of alkali salts from the pretreated cypress sawdust at high temperatures (Yuan et al., 2011). This finding is very promising since these biochars could contribute to the reduction of soils acidity when they are used as amendments. On the other hand, it can be noticed that the specific surface area of the biochars was approximately doubled when the used temperature was increased from 400
C to 600
C (Table 1). This result is most likely due to the increase in the degree of carbonization and also to the progressive destruction of aliphatic alkyl and ester groups which could hide the aromatic core at higher temperatures (Chen et al., 2008). However, the measured surface area at 500
C was lower than the one determined at 400
C which might be due to the blockage of some pores by the magnesium-formed-solidphases produced at this pyrolysis temperature. A similar result was obtained by Chen et al. (2014) when quantifying the impact of pyrolysis temperature on the characteristics of municipal sewage sludge' biochars. The N2 adsorption-desorption isotherms of all the used biochars corresponded to a typical Type IV isotherm and Type H2 hysteresis loop behavior (Fig. 1) indicating that the pores of the used biochars are mainly mesopores (with widths between 2 and 50 nm). This finding is comforted by the measured pore size of the used biochars (Table 1). 3.1.3. Inorganic elements contents The inorganic contents of the three studied biochars were determined thanks to X-ray fluorescence analyses (Table 2). The main metal constituents of the biochars were alkali and alkaline earth metals such as magnesium, calcium, potassium and iron. Besides, these biochars show high chloride contents which are

Fig. 1. Nitrogen adsorptionedesorption isotherms of the used biochars derived from magnesium pretreated cypress sawdust.

attributed to the pretreatment of the raw cypress sawdust with MgCl2. As it can be seen in Table 2, the contents of Mg, Cl, Ca, Fe and K increased by about 19%, 13%, 14%, 84% and 103%, respectively, when the pyrolysis temperature was increased from 400 to 600
C. The same trend was observed by Titiladunayo et al. (2012) when they explored the effect of pyrolysis temperature on biochars production yields from selected lignocellulosic biomasses. They suggested that temperature increase upgrades ash elemental concentrations relative to its yield. 3.1.4. Surface functionalities FT-IR analyses (Fig. 2) indicated that the produced biochars at temperatures of 400; 500 and 600
C were rich in organic functional groups. The main functional groups were registered at approximately 3420 cm1, 1647, 1401, 1190 and 719 cm1 corresponding to CeOH linkages, C¼C aromatic ring stretching, CH3 and CH2 groups, CeO stretching vibration and the aromatic C-H wagging vibration (Vaughn et al., 2015; Zhao et al., 2016). The spectra of all the studied biochars were relatively similar and no significant differences were noticed. 3.1.5. SEM and EDS analyses Fig. 3 presents the EDS analyses of the three used biochars. SEM images (data not shown) showed the presence of very small aggregates/particles stabilized on the biochar surface. The EDS analyses showed that these nanoparticles were mainly formed by magnesium and oxygen and are imputed to the pre-treatment of cypress sawdust with MgCl2. Since the presence of magnesium ions is highly important in the recovery of phosphorus through precipitation processes, the three tested biochar (B-Mg400, B-Mg500, B-Mg600) could therefore be considered as attractive materials. Similar findings were reported by Takaya et al. (2016) when they studied phosphorus recovery from aqueous solutions by chemically modified biochar produced from holm oak. 3.2. Phosphorus recovery efficiencies 3.2.1. Kinetic behavior The impact of contact time between dissolved phosphorus and biochars particles generated at different pyrolysis temperatures on P recovery efficiencies is given by Fig. 4. It appears that for all the used biochars, phosphorus recovery efficiency is clearly a time dependent process. Indeed, the amounts of recovered phosphorus

Please cite this article in press as: Haddad, K., et al., Investigations on phosphorus recovery from aqueous solutions by biochars derived from magnesium-pretreated cypress sawdust, Journal of Environmental Management (2017), http://dx.doi.org/10.1016/j.jenvman.2017.06.020

K. Haddad et al. / Journal of Environmental Management xxx (2017) 1e10

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Table 2 Inorganic elemental composition of the studied biochars produced from magnesium pretreated cypress sawdust (wt%) (-: not detected).

B-Mg400 B-Mg500 B-Mg600

Mg

Cl

Ca

Fe

K

Cr

Ni

Zn

P

9.612 11.145 11.468

13.297 14.279 14.989

0.120 0.096 0.137

0.127 0.107 0.234

0.029 0.010 0.059

0.031 0.026 0.081

0.002 0.015 0.01

0.055 0.011 e

0.007 e 0.010

surface areas, pHZPC (see Table 1) and the biochars magnesium contents (see Table 2). The phosphorus recovery kinetics of Mg-biochar was fitted with the pseudo-first and pseudo-second order models. The related kinetic constant values of each model (K1 and K2), the correlation coefficients, R2, the predicted recovered phosphorus amounts at equilibrium in comparison with the experimental ones were given in Table 3. Furthermore, in order to compare the applicability of these two kinetic models and their goodness of fitting to the experimental data, the average percentage errors (APE) between the predicted recovered phosphorus amounts “qt,calc,i (mg g1)” and the experimental ones “qt,exp,i (mg g1)” for each used biochar were assessed as follows:

APEð%Þ ¼ Fig. 2. FTIR spectra of the biochars produced from magnesium pretreated cypress sawdust at different temperatures.

(qt) rapidly rose for contact times lower than 15 min. At this moment, they attained about 39%; 46% and 50% of the whole recovered amounts for B-Mg400; B-Mg500 and B-Mg600, respectively. For times superior to 15 min, the phosphorus recovery continued its increase but with a smaller slope. The equilibrium state, corresponding to quasi-constant recovered phosphorus amounts was observed at 180 min. The registered important phosphorus recovery rate at the beginning of the assays could be attributed to the fact that phosphorus ions were mainly adsorbed at the exterior surfaces of the biochars or precipitated with magnesium ions as magnesium phosphates solid precipitates (Yao et al., 2013). Afterwards, when the adsorption/precipitation at the exterior surfaces of the studied biochars attained entire saturation, the phosphorus ions diffuse inside the solid biochars particles and were adsorbed or precipitated with magnesium ions in the interior surface of the biochars. This diffusion process is generally constituted of two steps: i) the first one corresponds to phosphorus diffusion through the boundary layer where the surface groups were saturated, then ii) the second step is related to phosphorus diffusion through the intra-particular layer and the pores through the surface of the adsorbents for additional uptake (Haddad et al., 2015). The required time to attain the equilibrium state for the three tested biochars was faster in comparison with other biochars such as those produced from treated oak sawdust by Lanthanum (Wang et al., 2015a,b) and those derived from pyrolysis of Mg-corncob (Fang et al., 2015) where it was estimated to about 24 h. This low time is a very attractive finding for a future up scaling of set ups for phosphorus recovery by magnesium-pretreated cypress biochars' process. It is important to underline that phosphorus recovery efficiency at equilibrium significantly increased when raising the pyrolysis temperature. Indeed, the phosphorus recovered amounts were determined to about 19.2; 26.5 and 33.9 mg g1 for B-Mg400; BMg500 and B-Mg600, respectively. This behavior should be mainly due to the modification of the physicochemical properties of the biochars induced by the thermo-chemical treatment, especially the

  Pi¼N ðqt;exp;i  qt;calc;i Þ i¼1   qt;exp;i N

(5)

where N is the number of the experimental runs. From Table 3, it could be clearly noted that the correlation coefficients calculated for both pseudo-first-order and pseudosecond-order models were relatively high, indicating a good fitting to the experimental data. However, the calculated recovered phosphorus amounts at equilibrium (qe,I) for all the tested biochars by the pseudo-first order model were very low compared to the experimental ones and the related APE was important, presuming that phosphorus recovery kinetic is not a pseudo-first order process. At the contrary, the “qe,II” values corresponding to pseudosecond-order kinetic model were very close to the experimental data. Besides, its APE values were significantly lower than the ones determined for the pseudo-first-order kinetic model (Table 3). As a consequence, for all the tested biochars, the pseudo-second-order model is most appropriated for the restitution of the experimental data (Fig. 4). This finding suggests that phosphorus recovery by biochars derived from magnesium pretreated cypress sawdust might be mainly a chimisorption process including electronic bonding between surface biochars' functional groups and the phosphorus ions as well as its precipitation with magnesium ions. Similar finding has been pointed out by Trazzi et al. (2016) when they investigated the adsorption and desorption of phosphates on biochars produced from sugar cane bagasse and of Miscanhus giganteus biomasses. 3.2.2. Effect of initial phosphorus concentrations, isotherm modeling The phosphorus recovery capacities of the tested biochars increased when increasing its initial aqueous concentrations. For instance, raising initial phosphorus concentrations from 50 to 250 mg L1 allowed the B-Mg400, B-Mg500 and B-Mg600 to increase their recovery abilities from 14.2 to 34.9 mg g1 and from 18.0 to 49.3 mg g1 and from 23.7 to 62.2 mg g1, respectively (Fig. 5). This outcome could be explained by the presence of bigger diffusion rates as the initial aqueous phosphorus concentration increase. Besides, the contact probability between phosphorus contained in the aqueous phase, the biochars particles as well as magnesium ions that were used for the treatment of the raw cypress sawdust might be more favored for higher initial aqueous

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K. Haddad et al. / Journal of Environmental Management xxx (2017) 1e10 40

qt (mg/g)

30

20

10

B-Mg600

B-Mg600: PSO

B-Mg500

B-Mg500:PSO

B-Mg400

B-Mg400:PSO

0 0

20

40

60

80

100

120

140

160

180

200

Time ( min) Fig. 4. Phosphorus kinetic recovery by biochars produced from magnesium pretreated cypress sawdust at different temperatures and their fitting with the pseudo-second order model (C0,P ¼ 75 mg L1; pH ¼ 5.2; dosage ¼ 2 g L1; Temperature ¼ 20 ± 2).

concentrations (Jellali et al., 2010). The Langmuir and Freundlich constants, the corresponding correlation coefficients and APE are presented in Table 4. For all the tested biochars, the highest regression correlation coefficients (0.999) and the lowest APE values (2.95%) were observed for Langmuir model. Thus, this model successfully fits the experimental data (Fig. 5). This finding suggests that phosphorus recovery by the tested biochars occurs on a uniform surface with constant energy (Azzaz et al., 2015). The phosphorus Langmuir's recovery capacity, qmax, of B-Mg400; B-Mg500 and B-Mg600 were assessed to about 43.5; 58.8 and 66.7 mg g1, respectively, confirming that the pyrolysis temperature increase positively impacts the biochar ability in recovering phosphorus from aqueous solutions. The Langmuir's coefficients values (RL ¼ 1þK1L C ) for the studied aqueous concentrations range varied 0;P

from 0.14 to 0.44 for B-Mg400; from 0.11 to 0.38 for B-Mg500 and from 0.01 to 0.02 for B-Mg600, respectively. These values were lower than 1 showing that the phosphorus recovery by these biochars is a favorable process. About Freundlich model which supposes the presence of a heterogeneous surface, its “APE” values were about 1.8; 2.9 and 3.1 times higher than the ones determined for Langmuir's model (Table 4 and Fig. 5). On the other hand, the Freundlich exponent “n” values were estimated to 2.50; 2.44 and 4.03 for B-Mg400; BMg500 and B-Mg600, respectively (Table 5). These values were in the range of 1e10 which indicates a favourable recovery of phosphorus by the used biochars. Similar results were presented by Fang et al. (2015) when studying phosphorus recovery from biogas fermentation liquid by CaeMg loaded biochar. In order to situate the biochars generated from magnesium pretreated cypress sawdust's efficiencies in recovering phosphorus from aqueous solutions, a comparison with other biochars based on Langmuir's maximal recovery capacity “qmax” or otherwise its capacity at a given aqueous concentration was carried out (Table 5). According to this table, B-Mg600 has relatively higher recovery capacities compared to various biochars. This result could be imputed to the relatively high MgCl2used concentration for the pretreatment of the cypress sawdust. As a consequence, B-Mg600 could be considered as an attractive and promising material for nutrients and in particular phosphorus recovery from aqueous solutions. Fig. 3. EDS analyses of the tested biochars (B-Mg400 (a), B-Mg500 (b), B-Mg600 (c)) derived from magnesium pretreated cypress sawdust at different temperatures.

3.2.3. Effect of pH The effect of pH on phosphorus recovery from aqueous solutions was performed for the experimental conditions presented in

Please cite this article in press as: Haddad, K., et al., Investigations on phosphorus recovery from aqueous solutions by biochars derived from magnesium-pretreated cypress sawdust, Journal of Environmental Management (2017), http://dx.doi.org/10.1016/j.jenvman.2017.06.020

K. Haddad et al. / Journal of Environmental Management xxx (2017) 1e10

7

Table 3 Phosphorus recovery kinetics parameters of the tested biochars generated from magnesium pretreated cypress sawdust(C0,P ¼ 75 mgL1; pH ¼ 5; dosage ¼ 2 gL-1; T ¼ 20
C). qe,exp (mg g-1)

Sample

B-Mg400 B-Mg500 B-Mg600

Pseudo-First order model

19.15 26.53 33.86

qe,I (mg g1)

R2

APE (%)

K2 (g mg1 min1)

qe,II (mg g1)

R2

APE (%)

0.025 0.036 0.037

18.48 26.07 29.79

0.997 0.994 0.969

13.82 11.93 23.66

0.0013 0.0016 0.0015

22.99 30.12 37.59

0.996 0.995 0.996

4.42 8.33 9.29

80

B-Mg400 (Exp.) B-Mg500 (Exp.) B-Mg600 (Exp.) Freudlich Langmuir

70 60

qe (mg/g)

Pseudo-Second order model

K1 (min1)

50 40 30 20 10 0 0

20

40

60

80

100

120

140

160

180

200

Ce(mg/L)

Fig. 5. Phosphorus recovery at equilibrium by the biochars produced from magnesium pretreated cypress sawdust at different temperatures and their fitting by Langmuir and Freundlich isotherm models (contact time ¼ 180 min; pH ¼ 5.2; dosage ¼ 2 g L1; Temperature ¼ 20 ± 2
C).

Section 2.3.3. Fig. 6 indicates that for all the tested biochars, higher are the used aqueous pH values, higher are the phosphorus recovery capacities. For instance, for B-Mg600, the recovered phosphorus amount increases from about 29.5 mg g1 at pH ¼ 3, to 36.1 mg g1 at pH ¼ 7 and reaches about 37.9 mg g1 at pH ¼ 11. This finding proves that phosphorus recovery from aqueous solutions is partially attributed to its precipitation as magnesium phosphates compounds. Indeed, in presence of the adsorption phenomenon only, the phosphorus recovery should be more important for acidic pH values, since when the used aqueous pH were lower than the pHZPC of the used biochars (see Table 1), these solid particles should be positively charged and consequently

Fig. 6. Effect of pH on phosphorus recovery by the tested biochars produced from magnesium pretreated cypress sawdust at different temperatures (C0,P ¼ 75 mg L1; dosage ¼ 2 g L1; Temperature ¼ 20 ± 2
C).

adsorb easily the negatively charged phosphorus ions (Fang et al., 2014). It is important to underline that phosphorus precipitation as magnesium phosphates compounds is enhanced when the aqueous pH values increase (Darn et al., 2006). 3.2.4. Influence of biochars dosages The effect of the used biochars dosages on phosphorus recovery efficiencies was carried out under the experimental conditions cited in Section 2.3.3. Results (Fig. 7) indicated that for all the tested biochars, the phosphorus recovery efficiencies increased with the increase of biochars dosages. Moreover, all the tested biochars could be considered as promising materials for phosphorus recovery since even for a small dosage (3 g L1), relatively high

Table 4 Phosphorus recovery isotherms parameters of the biochars produced from magnesium pretreated cypress sawdust at different temperatures (C0,P ¼ 75 mgL1; pH ¼ 5.2; dosage ¼ 2 gL1; T ¼ 20
C). Sample

B-Mg400 B-Mg500 B-Mg600

Freundlich model

Langmuir model

Kf

n

R2

APE (%)

KL

qmax (mg g1)

R2

APE (%)

4.73 6.90 21.43

2.50 2.44 4.03

0.905 0.919 0.858

7.41 8.70 11.00

0.025 0.033 0.185

43.48 58.82 66.66

0.994 0.996 0.999

4.08 2.95 3.51

Table 5 Comparison of phosphorus recovery by biochars generated from the pyrolysis of magnesium pretreated cypress sawdust with other biochars. Material


Biochar generated from the pyrolysis at 600 C of magnesium pretreated cypress sawdust Mg-Oak biochar at 650
C Orange Peel biochar at 700
C Cornbiochar at 300
C Mg-modified corn biochar at 600
C Oak biochar at 450
C Sugar cane bagasse biochar at 500
C Miscanthus biochar at 500
C

C0 (mg L1)

Recovery capacity (mg g1)

Reference

50e250 400 10 100 100 400 25e400 25e400

66.66 64.6 0.3 35 50 1.0 7.18 6.98

This study Takaya et al. (2016) Chen et al. (2011) Fang et al. (2014) Fang et al. (2014) Takaya et al. (2016) Trazzi et al. (2016) Trazzi et al. (2016)

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8

K. Haddad et al. / Journal of Environmental Management xxx (2017) 1e10 100 90 Phosphorus recovery efficiency (%)

B-Mg600 80

B-Mg500

70

B-Mg400

60 50 40

Mg-600, Mg-500, and Mg-400, respectively which confirms the attractiveness of the used biochars. This finding is linked to both the existence of important available active sorption sites and also to the presence of high magnesium contents that could precipitate with phosphorus anions as magnesium phosphates compounds. Therefore, the three tested biochars could be considered as interesting products for phosphorus recovery from solutions even when compared to calcium-rich-minerals adsorbents such as dolomite (Karaca et al., 2004) and shell sand (Roseth, 2000).

30 20 10 0 1

1.5

2

3

4

6

8

Dosage (g/L)

Fig. 7. Effect of biochars dosage on phosphorus recovery by the tested biochars produced from magnesium pretreated cypress sawdust at different temperatures (C0,P ¼ 75 mg L1; pH ¼ 5.2; Temperature ¼ 20 ± 2
C).

efficiencies of 94%, 74%, and 66% were registered for B-Mg-600, BMg-500, and Mg-400, respectively. A complete phosphorus recovery was obtained with low biochars dosages of 4, 6, and 8 g L1f or

3.2.5. Influence of coexisting ions 2 Co-existing anions, such as NO 3 , SO4 , are commonly present in wastewaters, which could compete with phosphorus during its recovery by biochars. Fig. 8 gives the impact of nitrates and sulfates anions on the recovery of phosphorus from synthetic solutions under the experimental conditions cited in Section 2.3.3. Results indicated that for all the tested biochars, the presence of high nitrates concentrations (100 mg L1) could significantly reduce the phosphorus recovery. However, for typical urban wastewaters concentrations, these efficiencies decrease remained relatively low (Fig. 8). The presence of sulfates presented lower negative effect on the phosphorus recovery from aqueous solutions. For instance, for an initial sulfates concentration of 100 mg L1, the phosphorus 5000

Mg-600 before phosphorus recovery * Mg (OH)2

4000

* MgO

* Intensity

3000

*

*

2000

* *

1000

0

10

20

30

40

50

60

70

2 Theta

(a) 2500 Mg-600 aŌer phosphorus recovery * Mg(H2PO4)2 , 4H2O * MgHPO4 , 7H2O

2000

Intensity

*

*

1500

* *

*

* *

* *

*

1000 * 500

0 10

20

30

40

50

60

2 Theta Fig. 8. Effect of the presence of anions on phosphorus recovery by the tested biochars produced from magnesium pretreated cypress sawdust at different temperatures (C0,P ¼ 75 mg L1; dosage ¼ 2 g L1; pH ¼ 5.2; Temperature ¼ 20 ± 2
C).

(b) Fig. 9. XRD spectra of B-Mg600 before (a) and after (b) phosphorus recovery.

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K. Haddad et al. / Journal of Environmental Management xxx (2017) 1e10

3.3. Phosphorus recovery mechanism exploration SEM/EDS and DRX analyses on B-Mg600 before and after phosphorus recovery were carried out for a better understanding of the involved mechanisms during phosphorus recovery by the studied biochars (Figs. 9 and 10). It appears that the surfaces of the B-Mg600 before phosphorus recovery were dominated by Mg(OH) and MgO particles due to the pre-treatment of raw cypress sawdust with MgCl2 (Fig. 9). After phosphorus recovery, the XRD spectra showed strong signals of not only the preexisting Mg-hydroxides but also new Mg-P crystals in the form of Mg(HPO4) and Mg(H2PO4)2. This precipitation phenomenon is generally favored at alkaline pH (Yao et al., 2013). In our case, the used biochar has a relatively high pHZPC (9.68, see Table 1) which would induce an important increase of the aqueous solution pH and consequently significantly contribute to the phosphorus precipitation as magnesium phosphates compounds. Besides, the SEM/EDS of B-Mg600 after phosphorus recovery confirmed the presence of the formed

40 35

30

q des,t (mg /g)

recovery efficiency decreased by about 19%; 33% and 55% for BMg400; B-Mg500 and B-Mg600, respectively. This finding could is probably due to the presence of weaker affinity between the three biochars and the tested competing anions. Nitrates effect on the adsorption of phosphates is more important than sulphates because of its smaller atomic size as well as higher mobility (Haddad et al., 2015).

9

pH =5.2

25 20

pH=7

15

pH= 9

10 5

0 0

10

20

30

40

50

Temps (h) Fig. 11. Effect of pH on phosphorus desorption from B-Mg 600 (qe ¼ 37.6 mg g1, dosage ¼ 2 g L1; Temperature ¼ 20 ± 2
C).

precipitate Mg(HPO4) and Mg(H2PO4)2. Indeed, the surfaces of BMg600 were covered by crystalline shiny phases (Fig. 10a) that correspond to magnesium phosphates precipitates since according to the EDS analyses new peaks corresponding to phosphorus were detected (Fig. 10b). It is important to highlight that besides phosphorus precipitation, its adsorption onto biochar surface functional groups should be present (Takaya et al., 2016; Wang et al., 2013). 3.4. Phosphorus desorption Phosphorus release kinetic from pre-loaded B-Mg600
C at a concentration of 37.6 mg g1was investigated with distilled water at different initial pH values of 5.2; 7and 9 for the experimental conditions presented in Section 2.4. Results (Fig. 11) showed that the release of phosphorus was clearly a time dependent process. Indeed, for all the tested pH values, a complete phosphorus release was registered after about 24, 32, and 48 h for the used pH values of 9; 7 and 5.2 respectively. This slow release of phosphorus (especially in acidic media: pH ¼ 5.2) is very advantageous when using these phosphorus-loaded solid matrixes in agriculture, since the plants will take the necessary released phosphorus for their growth and the P leaching to groundwater will be very limited. These results are consistent with those obtained by Cui et al. (2011) and Morales et al. (2013) who found that the rate of phosphorus desorption from preloaded biochar produced from the pyrolysis of rice straw and sawdust, respectively was clearly dependent on the employed desorption conditions especially the phosphorus concentration gradient and the pH of the aqueous solutions. 4. Conclusions

Fig. 10. SEM (a) image and EDX (b) spectrum of B-Mg600 after phosphorus recovery.

The present work proved that biochars produced from magnesium-pretreated cypress sawdust could be considered as high effective, attractive and promising materials for phosphorus recovery from solutions compared to various previously studied biochars in term of both rapid kinetic and equilibrium recovery capacity. The various analyses prove that the phosphorus recovery process is a combination between adsorption onto the active surface sites and also precipitation with magnesium as magnesium phosphates compounds (Mg(HPO4)2), and Mg(HPO4). Desorption study of P-laden biochars showed that the phosphorus desorption is complete and also relatively slow especially in acidic media which indicates that these biochars could be used as a slow phosphorus release fertilizer when applied to soils as amendments.

Please cite this article in press as: Haddad, K., et al., Investigations on phosphorus recovery from aqueous solutions by biochars derived from magnesium-pretreated cypress sawdust, Journal of Environmental Management (2017), http://dx.doi.org/10.1016/j.jenvman.2017.06.020

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K. Haddad et al. / Journal of Environmental Management xxx (2017) 1e10

Acknowledgments This work was financially supported by the “PHC Utique” program of the French Ministry of Foreign Affairs and Ministry of Higher Education and Research and the Tunisian Ministry of higher education and scientific research in the GEDURE Project (No 16G1119/34863VB) and the authors gratefully acknowledge the
Mixte Franco-Tunisien pour la Coope
ration Universitaire “Comite (CMCU)” for their support. Khouloud Haddad thanks the World Bank for its financial support through the Robert S. McNamara Fellowships Program. References ASTM (American Society for Testing and Materials) D1762-84, 2013. Standard Test Method for Chemical Analysis of Wood Charcoal. ASTM International, Pennsylvania, USA. Azzaz, A.A., Jellali, S., Assadi, A.A., Bousselmi, L., 2015. Chemical treatment of orange tree sawdust for a cationic dye enhancement removal from aqueous solutions: kinetic, equilibrium and thermodynamic studies. Desalin. Water Treat. 11, 1e13. Benyoucef, S., Amrani, M., 2011. Adsorption of phosphate ions onto low cost Aleppo pine adsorbent. Desalination 275, 231e236. Cao, X., Harris, W., 2010. Properties of dairy-manure-derived biochar pertinent to its potential use in remediation. Bioresour. Technol. 101, 5222e5228. Chen, B., Chen, Z., Lv, S., 2011. A novel magnetic biochar efficiently sorbs organic pollutants and phosphate. Bioresour. Technol. 102, 716e723. Chen, M., Wang, J., Zhang, M., Chen, M., Zhu, X., Min, F., Tan, Z., 2008. Catalytic effects of eight inorganic additives on pyrolysis of pine wood sawdust by microwave heating. J. Anal. Appl. Pyrolysis 82, 145e150. Chen, T., Zhang, Y., Wang, H., Lu, W., Zhou, Z., Zhang, Y., Ren, L., 2014. Influence of pyrolysis temperature on characteristics and heavy metal adsorptive performance of biochar derived from municipal sewage sludge. Bioresour. Technol. 164, 47e54. Cui, L., Li, L., Zhang, A., Pan, G., Bao, D., Chang, A., 2011. Biochar amendment greatly reduces rice cd uptake in a contaminated paddy soil: a two-year field experiment. Bio Resour. 6, 2605e2618. Darn, S.M., Sodi, R., Ranganath, L.R., Roberts, N.B., Duffield, J.R., 2006. Experimental and computer modelling speciation studies of the effect of pH and phosphate on the precipitation of calcium and magnesium salts in urine. Clin. Chem. Lab. Med. 44, 185e191. Fang, C., Zhang, T., Li, P., Jiang, R., Wang, Y., 2014. Application of magnesium modified corn biochar for phosphorus removal and recovery from swine wastewater. Int. J. Environ. Res. Public. Health 11, 9217e9237. Fang, C., Zhang, T., Li, P., Jiang, R., Wu, S., Nie, H., Wang, Y., 2015. Phosphorus recovery from biogas fermentation liquid by CaeMg loaded biochar. J. Environ. Sci. 29, 106e114.
thode nitro-vanado-molybdique pour le dosage Fleury, P., Leclerc, M., 1943. La me
trique du phosphore. Son inte
re ^t Biochim. Bull Soc. Chim. Biol. 25, colorime 201e205. Haddad, K., Jellali, S., Jaouadi, S., Benltifa, M., Mlayah, A., Hamzaoui, A.H., 2015. Raw and treated marble wastes reuse as low cost materials for phosphorus removal from aqueous solutions: efficiencies and mechanisms. Comptes Rendus Chim. 18, 75e87. Inyang, M., Gao, B., Zimmerman, A., Zhang, M., Chen, H., 2014. Synthesis, characterization, and dye sorption ability of carbon nanotubeebiochar nanocomposites. Chem. Eng. J. 236, 39e46. Jaouadi, S., Wahab, M.A., Anane, M., Bousselmi, L., Jellali, S., 2014. Powdered marble wastes reuse as a low-cost material for phosphorus removal from aqueous solutions under dynamic conditions. Desalin. Water Treat. 52, 1705e1715. Jellali, S., Diamantopoulos, E., Haddad, K., Anane, M., Durner, W., Mlayah, A., 2016. Lead removal from aqueous solutions by raw sawdust and magnesium pretreated biochar: experimental investigations and numerical modelling. J. Environ. Manage. 180, 439e449. Jellali, S., Wahab, M.A., Anane, M., Riahi, K., Jedidi, N., 2011. Biosorption characteristics of ammonium from aqueous solutions onto Posidonia oceanica (L.) fibers. Desalination 270, 40e49. Jellali, S., Wahab, M.A., Anane, M., Riahi, K., Bousselmi, L., 2010. Phosphate mine wastes reuse for phosphorus removal from aqueous solutions under dynamic conditions. J. Hazard. Mater. 184, 226e233. Jeon, D.J., Yeom, S.H., 2009. Recycling wasted biomaterial, crab shells, as an adsorbent for the removal of high concentration of phosphate. Bioresour. Technol. 100, 2646e2649. Karaca, S., Gürses, A., Ejder, M., Açıkyıldız, M., 2004. Kinetic modeling of liquidphase adsorption of phosphate on dolomite. J. Colloid Interface Sci. 277, 257e263. Kraiem, T., Ben Hassen-Trabelsi, A., Naoui, S., Belayouni, H., Jeguirim, M., 2015. Characterization of the liquid products obtained from Tunisian waste fish fats using the pyrolysis process. Fuel Process Technol. 138, 404e412.

Kung, C.-C., McCarl, B.A., Chen, C.-C., Chen, L.-J., 2014. Environmental impact and bioenergy potential: evaluation of agricultural commodity and animal waste based biochar application on Taiwanese set-aside land. Energy Procedia 61, 679e682. Lehmann, J., Rillig, M.C., Thies, J., Masiello, C.A., Hockaday, W.C., Crowley, D., 2011. Biochar effects on soil biotaeA review. Soil Biol. Biochem. 43, 1812e1836. Li, R., Liam, M., Gavin, C., Li, A., Zhan, X., 2016. Simultaneous nitrate and phosphate removal from wastewater lacking organic matter through microbial oxidation of pyrrhotite coupled to nitrate reduction. Water Res. 96, 32e41. Mohan, D., Kumar, S., Srivastava, A., 2014. Fluoride removal from ground water using magnetic and nonmagnetic corn stover biochars. Ecol. Eng. 73, 798e808. ~o, N.P.S., Reeves, J.B., 2013. SorpMorales, M.M., Comerford, N., Guerrini, I.A., Falca tion and desorption of phosphate on biochar and biocharesoil mixtures. Soil Use Manag. 29, 306e314. Nguyen, T.A.H., Ngo, H.H., Guo, W.S., Nguyen, T.V., Zhang, J., Liang, S., Chen, S.S., Nguyen, N.C., 2014. A comparative study on different metal loaded soybean milk by-product “okara” for biosorption of phosphorus from aqueous solution. Bioresour. Technol. 169, 291e298. Novak, J.M., Lima, I., Xing, B., Gaskin, J.W., Steiner, C., Das, K.C., Ahmedna, M., Rehrah, D., Watts, D.W., Busscher, W.J., Schomberg, H., 2009. Characterization of designer biochar produced at different temperatures and their effects on a loamy sand. Ann. Environ. Sci. 3, 123e132. Rittmann, B.E., Mayer, B., Westerhoff, P., Edwards, M., 2011. Capturing the lost phosphorus. Chemosphere Phosphorus Cycle 84, 846e853. Roseth, R., 2000. Shell sand: a new filter medium for constructed wetlands and wastewater treatment. J. Environ. Sci. Health Part A 35, 1335e1355. €der, J.J., Smith, A.L., Cordell, D., Rosemarin, A., 2011. Improved phosphorus use Schro efficiency in agriculture: a key requirement for its sustainable use. Chemosphere 84, 822e831. Takaya, C.A., Fletcher, L.A., Singh, S., Okwuosa, U.C., Ross, A.B., 2016. Recovery of phosphate with chemically modified biochars. J. Environ. Chem. Eng. 4, 1156e1165. Tan, X., Liu, S., Liu, Y., Gu, Y., Zeng, G., Hu, X., Wang, X., Liu, S., Jiang, L., 2017. Biochar as potential sustainable precursors for activated carbon production: multiple applications in environmental protection and energy storage. Bioresour. Technol. 227, 359e372. Titiladunayo, I.F., McDonald, A.G., Fapetu, O.P., 2012. Effect of temperature on biochar product yield from selected lignocellulosic biomass in a pyrolysis process. Waste Biomass Valorization 3, 311e318. Trazzi, P.A., Leahy, J.J., Hayes, M.H.B., Kwapinski, W., 2016. Adsorption and desorption of phosphate on biochars. J. Environ. Chem. Eng. 4, 37e46. Vaughn, S.F., Kenar, J.A., Eller, F.J., Moser, B.R., Jackson, M.A., Peterson, S.C., 2015. Physical and chemical characterization of biochars produced from coppiced wood of thirteen tree species for use in horticultural substrates. Ind. Crops Prod. 66, 44e51. ~ iv, M., Bavor, H.J., Chazarenc, F., Mander, Ü., 2011. Filter materials for Vohla, C., Ko phosphorus removal from wastewater in treatment wetlandsda review. Ecol. Eng. 37, 70e89. Wang, W.-L., Ren, X.-Y., Chang, J.-M., Cai, L.-P., Shi, S.Q., 2015a. Characterization of bio-oils and bio-chars obtained from the catalytic pyrolysis of alkali lignin with metal chlorides. Fuel Process. Technol. 138, 605e611. Wang, Z., Guo, H., Shen, F., Yang, G., Zhang, Y., Zeng, Y., Wang, L., Xiao, H., Deng, S., 2015b. Biochar produced from oak sawdust by Lanthanum (La)-involved pyrolysis for adsorption of ammonium (NH4þ), nitrate (NO3), and phosphate (PO43). Chemosphere 119, 646e653. Wang, Z., Zheng, H., Luo, Y., Deng, X., Herbert, S., Xing, B., 2013. Characterization and influence of biochars on nitrous oxide emission from agricultural soil. Environ. Pollut. 174, 289e296. Yao, Y., Gao, B., Chen, J., Yang, L., 2013. Engineered biochar reclaiming phosphate from aqueous solutions: mechanisms and potential application as a slowrelease fertilizer. Environ. Sci. Technol. 47, 8700e8708. Yin, H., Kong, M., Fan, C., 2013. Batch investigations on P immobilization from wastewaters and sediment using natural calcium rich sepiolite as a reactive material. Water Res. 47, 4247e4258. Yuan, J.-H., Xu, R.-K., Zhang, H., 2011. The forms of alkalis in the biochar produced from crop residues at different temperatures. Bioresour. Technol. 102, 3488e3497. Zhang, J., Liu, J., Liu, R., 2015. Effects of pyrolysis temperature and heating time on biochar obtained from the pyrolysis of straw and lignosulfonate. Bioresour. Technol. 176, 288e291. Zhang, M., Gao, B., 2013. Removal of arsenic, methylene blue, and phosphate by biochar/AlOOH nanocomposite. Chem. Eng. J. 226, 286e292. Zhang, M., Gao, B., Yao, Y., Xue, Y., Inyang, M., 2012. Synthesis of porous MgObiochar nanocomposites for removal of phosphate and nitrate from aqueous solutions. Chem. Eng. J. 210, 26e32. Zhao, Y., Feng, D., Zhang, Y., Huang, Y., Sun, S., 2016. Effect of pyrolysis temperature on char structure and chemical speciation of alkali and alkaline earth metallic species in biochar. Fuel Process. Technol. 141, 54e60. Zheng, H., Wang, Z., Deng, X., Herbert, S., Xing, B., 2013. Impacts of adding biochar on nitrogen retention and bioavailability in agricultural soil. Geoderma 206, 32e39.

Please cite this article in press as: Haddad, K., et al., Investigations on phosphorus recovery from aqueous solutions by biochars derived from magnesium-pretreated cypress sawdust, Journal of Environmental Management (2017), http://dx.doi.org/10.1016/j.jenvman.2017.06.020