Phosphorus recovery from aquaculture wastewater using thermally ...

Process Safety and Environmental Protection 9 8 ( 2 0 1 5 ) 296–308

Contents lists available at ScienceDirect

Process Safety and Environmental Protection journal homepage: www.elsevier.com/locate/psep

Phosphorus recovery from aquaculture wastewater using thermally treated gastropod shell N.A. Oladoja a,∗ , R.O.A. Adelagun b , A.L. Ahmad c , I.A. Ololade a a b c

Department of Chemistry, Adekunle Ajasin University, Nigeria Department of Chemistry, The Federal University, Wukari, Nigeria School of Chemical Engineering, Universiti Sains Malaysia, Malaysia

a r t i c l e

i n f o

a b s t r a c t

Article history:

In tandem with the quest for the development of sustainable strategies for the recovery of P

Received 23 July 2015

from P-rich aqua waste streams, thermally treated gastropod shell (GS) was investigated as a

Received in revised form 19 August

reactive material for P-recovery from aquaculture wastewater (AQW). The enhanced defects

2015

in the surficial physiognomies, imparted by the thermal treatment process, accounted for

Accepted 5 September 2015

the higher P-recovery efficiency. This contradicted the claim that the conversion of the car-

Available online 12 September 2015

bonate form of calcium to the oxide form was the reason for the higher P-recovery efficiency

Keywords:

files of the P-recovery process to different kinetic models and the determinations of the

Phosphorus recovery

thermodynamic parameters of the precipitation reaction showed that both adsorption and

of thermally treated calcium rich materials. The fittings of the time–concentration pro-

Aquaculture wastewater

precipitation were the underlying mechanism of the P-recovery process, using the thermally

Nutrients

treated GS. In addition to the removal of P, substantial amount of the total nitrogen in the

Resource recovery

AQW was also removed. The evaluation of the effects of the P-recovery process on the qual-

Gastropod shell

ity characteristics of the AQW showed that there was significant improvement in the overall

Eutrophication

physicochemical characteristics. © 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

1.

Introduction

Aquaculture wastewater (AQW) is one of the major anthropogenic sources of phosphorus (P) pollution in both land and water systems. For example, the production of a tonne of channel catfish releases an average of 9.2 kg of nitrogen, 0.57 kg of P, 22.5 kg of BOD and 530 kg of settleable solids into the environment (Rodhe, 1969). Amongst the constituents of AQW, P is one of the most scrutinized because it is the limiting nutrient for eutrophication onset. Premised on the negative environmental impact of P, different strategies are being developed for the removal and recovery from the waste stream. Furthermore, it has been shown that the use of P fertilizers is becoming more expensive and less sustainable because phosphate ores are limited, non-renewable resources; a fact that tends to increase the production costs of P derivates (Driver et al., 1999).

∗

On the basis of the operational simplicity and cost, the use of adsorption based water treatment technologies for P sequestration, has been pivotal in the quest for the development of sustainable strategies for P recovery. An overview of the array of P specific sorbents that have been studied showed that Al3+ , Fe3+ , and Ca2+ are the major elemental composition (Lindsay, 1979; Richardson, 1985; Faulkner and Richardson, 1989). In order to design a sustainable P-recovery system, it was advanced (Morse et al., 1998) that the choice of the metal ion is important because P that is too tightly bound cannot readily be reused in industrial and agricultural applications. Although, the removal of P from aqua stream, using Al3+ and Fe3+ rich materials is common, but it is less appealing for the recovery purpose. This is because the P recovered from these solids are tenaciously bound to the metal phase and aluminium has been found to be toxic to many plants and some soil organisms (Johnston and Richards, 2003). Consequently,

Corresponding author. Tel.: +234 8055438642. E-mail address: [email protected] (N.A. Oladoja). http://dx.doi.org/10.1016/j.psep.2015.09.006 0957-5820/© 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.


magnesium and calcium rich materials are most commonly used for P recovery because of the potential to be recycled as fertilizer. In our Laboratory, the ability of a Gastropod shell (GS), African land snail (Achatina achatina), was screened as a potential low cost sorbent for phosphate removal from aqua system in a batch and column reactor (Oladoja et al., 2012, 2013, 2014). Sequel to the promising findings from these investigations, the present studies aimed at optimizing the potential of GS for P-recovery via thermal treatment. The GS has got the same basic construction as other Mollusk shells and it contains, mainly, CaCO3 , as well as various organic compounds (Oladoja and Aliu, 2009; Oladoja et al., 2011). In the present study, the adoption of thermal treatment protocol hinged on the report (Vohla et al., 2011) that the common way to enhance the P removal efficiency of calcium-rich materials is via high temperature heating. It was advanced that during heating, CaO will probably form, which has a more reactive Ca2+ phase than commonly existing CaCO3 . The assertion, that the high Ca2+ content of a sorbent is not a guarantee of rapid reaction between Ca2+ and P and the fact that the reaction is many times easier if the Ca2+ in the material is in the form of CaO instead of CaCO3 , which has much lower dissolving ability, has been proven at different instances. Kaasik et al. (2008) showed that hydrated sediment of oil shale ash consists of CaCO3 (calcite), Ca6 Al2 (SO4 )3 (OH)12 ·26H2 O (ettringite) and Ca(OH)2 (portlandite). After the P sorption test, the calcite content remained the same, but the ettringite and portlandite content declined drastically. It has also been demonstrated that after the heating of Opoka, which naturally contained Ca2+ as CaCO3 , the sorption capacity increased significantly, from 0.1 g P/kg to 39.0 g P/kg (Brogowski and Renman, 2004; Johansson, 1999). Kwon et al. (2004) showed that pyrolizing oyster shell above the 650 ◦ C, the CaCO3 content fell and Premoval efficiency increased to 98% in the material, whereas the untreated material showed no P removal. The aim of the present study was to study, the P-recovery efficiency of thermally treated GS from AQW. The influence of the thermal treatment temperature on the surface properties and the P-affinity of the GS were studied. The time–concentration profiles and the effects of hydrochemistry on the P-recovery process were determined. The P-recovery efficiency of the thermally treated GS in real AQW was evaluated and the effects of the process on the other physicochemical characteristics of the AQW were examined.

200 rpm for 2 h, samples were removed, filtered using 0.45 ␮m polypropylene membrane and the filtrate was analyzed for residual P concentration, using the molybdenum-blue ascorbic acid method with a UV–vis spectrophotometer. The amount of P uptake was determined using the mass balance procedure in each case. The effects of the thermal treatment temperatures on the elemental composition and the mineralogical assemblage of the samples were determined using X-ray fluorescence (XRF) and X-ray diffractometer (XRD), respectively. The BET surface areas of the TS samples were determined using an ASAP 2010 Micromeritics instrument, by Brunauer–Emmett–Teller (BET) method. The surface architecture and elemental composition were determined by a scanning electron microscope (SEM) and the surface functional groups were determined using an FTIR spectrophotometer (Thermo Scientific, USA).

2.2.

Materials and methods

2.1.

Material preparation and characterization

The GS was prepared as previously described (Oladoja et al., 2011, 2012, 2013, 2014; Oladoja and Aliu, 2009) and subjected to thermal treatment, in the furnace, at varying temperatures (100, 250, 500, 750 and 1000 ◦ C) for 2 h. The products were labelled TS100 , TS250 , TS500 , TS750 and TS1000 ; the subscript shows the temperature at which each material was thermally treated. The optimum temperature for the treatment of the GS, for P-recovery, was determined via batch sorption process viz.: 50 mL of synthetic P rich solution, derived from potassium dihydrogen phosphate (KH2 PO4 ) salt, of fixed concentration (40 mg/L) was contacted with 0.1 g of each thermally treated material (i.e., TS100 –TS1000 ). The mixture was agitated at

P-recovery in a synthetic P-rich water system

The time–concentration profiles of the P-recovery process were determined by the addition of 0.5 g of TS into 1.0 L of P solution of concentrations that ranged between 2.5 and 30 mg/L and stirred at a fixed agitation speed. Samples were withdrawn at intervals between 0 and 5 h, of stirring, centrifuged and the supernatant P concentration were determined in each case. The equilibrium isotherm analysis of the P-recovery process was evaluated by contacting 100 mL solution of known P concentration that ranged between 2.5 and 30 mg/L with 0.05 g of TS. The mixture was stirred at 200 rpm in thermostatic shaker at the equilibrium time, samples were withdrawn, centrifuged and the supernatant was analyzed for the residual P concentration. The influence of hydrochemistry (i.e., solution pH, presence of inorganic and organic ionic species and ionic strength) on the P-recovery process was simulated viz.: initial solution pH that ranged between pH 6.11and 11.12; presence of inorganic anions by the addition of varying concentrations (mg/L) (10, 50 and 100) of different anions (NO3 − , Cl− , PO4 2− , CO3 2− and SO3 2− ) derived from the potassium salts; organic load, simulated by the addition of humic acid (HA), of concentrations (mg/L) (5, 10, 20, 40 and 8 0); ionic strength (tested in NaCl solutions (%): 0, 0.05, 0.1, 0.2, 0.5 and 1, equivalent to ionic strengths (mol/L) of 0, 0.0085, 0.017, 0.0342, 0.085 and 0.17). All the studies were conducted in duplicate.

2.3.

2.

297

P-recovery in aquaculture wastewater

Grab sample of the real AQW was collected from an aquaculture farm that breeds catfish, characterized pending usage. The ability of the TS to recover P in the AQW was tested in a batch reactor by adding 0.5 g of the TS into a litre of the wastewater and the mixture was agitated for a period of 30 min before sample was withdrawn to determine the residual P concentration. The effects of the P-recovery process on the physicochemical characteristics of the wastewater were also evaluated.

3.

Results and discussion

3.1.

Preparation and characterization of materials

The elemental composition of the raw GS and the thermally treated samples are presented in Table 1. The assertion, in our

298


Fig. 1 – XRD pattern of raw and thermally treated GS.

Table 1 – Results of the XRD analysis of raw and thermally treated GS. Metal oxides Al2 O3 SiO2 P2 O5 SO3 Cl K2 O CaO Cr2 O3 Fe2 O3 NiO CuO ZnO SrO TnO

Raw GS

TS100

TS250

TS500

TS750

TS1000

0.37 1.66 0.12 0.06 0.02 0.19 96.38 0.11 0.36 0.20 0.06 0.20 0.69 ND

0.29 1.33 0.06 0.04 0.01 0.16 97.08 0.94 0.23 0.02 ND 0.09 0.69 ND

0.39 1.34 0.09 0.05 0.02 0.19 96.93 ND 0.29 0.16 ND 0.01 0.68 ND

0.53 1.85 0.11 0.05 0.01 0.20 96.22 ND 0.24 0.01 ND 0.01 0.68 0.24

0.39 1.18 0.08 0.05 0.01 0.16 97.19 ND 0.24 ND ND 0.03 0.66 ND

0.11 0.36 0.01 0.03 0.01 0.05 98.62 ND 0.24 ND ND 0.07 0.52 ND

previous reports (Oladoja et al., 2011, 2012, 2013, 2014; Oladoja and Aliu, 2009), that the GS is a calcium rich material was ascertained by the results of the XRF analysis. The diffractogram of the raw and thermally treated GS (Fig. 1) showed that the raw GS is a crystalline material and that the crystallinity was retained over the entire thermal treatment temperatures adopted. The number of peaks, produced from the interactions of each sample (i.e., GS and TS100 –TS1000 ) with X-ray, reduced with increasing thermal treatment temperature while the intensities of the prominent peaks was enhanced with increasing treatment temperature. The shells of Gastropods are known to be made up of CaCO3 and the form of CaCO3 in the shell of African land snail has been reported to be made up of largely aragonite (Vohla et al., 2011; Kaasik et al., 2008). Thus, the presence of the three polymorphs of CaCO3 (aragonite,

calcite and vaterite) in the diffractogram of raw GS and thermally treated samples was determined using the following miller indices: 111 and 221 (for aragonite); 104 and 113 (for calcite) and 110, 112, 114, 300, 224 and 211 (for vaterite). In the GS, the aragonite peaks appeared at 26.26 (1 1 1) and 46.03 (2 2 1), the calcite peaks appeared at 52.89 (1 1 3) and the vaterite peak appeared at 37.93 (1 1 2). It has been posited (LBR, in press) that both aragonite and calcite have their highest-intensity peaks at different positions, and the general look of the two patterns is different. Aragonite has its greatest peak (1 1 1) at relatively small 2 angle and has several lesser peaks, whereas calcite has a booming (1 0 4) peak a bit to the right of the aragonite large peak, and few and comparatively small other peaks. Other notable peaks of aragonite (2 2 1) and calcite (1 0 4) have also been used for easy identification of these two minerals. The changes in the mineralogical assemblage, caused by the thermal treatment of the raw GS, are shown in the different diffractogram presented in Fig. 1 and the peak parameters of the salient peaks are presented in Table 2. The peak positions and parameters of the GS and the TS100 , are the same but in the TS250 , the disappearance of one of the Aragonite peaks, at 46.03 (2 2 1), and appearance of the vaterite peak, at 41.18 (2 1 1), were observed. The diffractogram of the TS500 and TS750 did not show any of the aragonite peaks while the presence of calcite and vaterite peaks were observed. The TS1000 showed the presence of all the three polymorphs of CaCO3 but the appearance of CaO peaks at 22.89 (1 1 2) and 28.95 (2 0 0) were noted. It has been postulated (Stanmore and Gilot, 2005) that when calcite crystals, are heated at a temperature of around 900 ◦ C, they will transform into CaO through the release of carbon dioxide gas. The calcination process of calcite begins when the partial pressure of CO2 in the gas above the solid surface

299


Table 2 – XRD peak parameters of raw and thermally treated GS. Samples

Aragonite

Raw GS

26.262 (1 1 1) 46.03 (2 2 1) 26.26 (1 1 1) 46.03 (2 2 1) 26.20 (1 1 1)

TS100 TS250 TS500

Calcite 52.89 (1 1 3)

37.93 (1 1 2)

52.89 (1 1 3)

37.93 (1 1 2)

52.55 (1 1 3) 29.46 (1 0 4) 39.41 (1 1 3)

41.18 (2 1 1) 35.97 (1 1 0) 54.64 (3 0 0) 56.55 (2 1 1) 63.19 (2 1 1) 72.68 (3 0 0) 15.15 (1 1 0)

43.70 (1 1 3)

TS750 TS1000

Vaterite

30.55 (2 2 1)

31.36 (1 1 3)

CaO

22.89 (1 1 2) 28.95 (2 0 0)

is less than the decomposition pressure of the CaCO3 . Evidences from the results of the XRD analysis showed that the formation of CaO was noted only in the TS1000 , which is an indication that the formation of CaO in the thermally activated may not have occurred below the calcination temperature of 1000 ◦ C. The presence of the three polymorphs of the CaCO3 in the diffractogram of the TS1000 (Fig. 1) is a pointer to the fact that the CaCO3 constituent of the raw GS was not completely transformed to CaO at this temperature. Amongst the CaCO3 polymorphs, vaterite is considered the less stable and it’s assumed to easily transform into either calcite or aragonite. Contrary to the claim that vaterite is thermodynamic unstable, the presence in both the raw GS and thermally treated samples were confirmed by the XRD analysis. Similarly, the presence of vaterite in some biological systems, sediments, and during oilfield drilling has been reported (Nehrke, 1971). Consequently, it was deduced that since vaterite forms and persists in a number of natural systems, the claim about the thermodynamic instability may not be tenable, at all the time. It was advanced that the stability observed in some cases could have been influenced by some mechanism which prevent the transformation of vaterite to other CaCO3 polymorphs. In nature, aragonite (a CaCO3 polymorph that is less stable than calcite) is often found to be stable in the shell of biological organisms or in hydrothermal deposits of hot springs, etc. It was reported that less-stable polymorphs were preserved through kinetic effects (Ogino et al., 1987; Xyla and Koutsoukos, 1987; Giannimaras and Koutsoukos, 1987, 1988) or were stabilized GS

TS10 00

TTS250

by impurities, such as some inorganic ions (Kitano, 1962) and organic matters (Kitano and Hood, 1965; Falini et al., 1996). At present, the material that is thermally treated, the GS, consist of three layers, namely Hypostracum, Ostracum and Periostracum. The Hypostracum is a form of Aragonite while the Ostracum is built by several layers of prism-shaped CaCO3 crystals with embedded proteid molecules. The Periostracum, the outermost shell layer, is not made of CaCO3 , but of an organic material called Conchin, a mixture of organic compounds, mostly of proteids. Conchin not only makes the outer shell layer, but also embedded between the CaCO3 crystals of deeper layers. In the raw and thermally treated GS, the stability of the different polymorphs of the CaCO3 was attributed to the naturally occurring organic and inorganic (Table 1) constituents of the shell. Aside the differences in the intensities of the FTIR peaks, the spectra patterns of the raw GS, TS100 and TS250 were similar (Fig. 2). Samples TS500 and TS750 also showed similar peaks with that of the raw GS and TS100 but the shape of the peaks were broadened and the intensities of the peaks were significantly reduced. The spectrum pattern of TS1000 completely was completely different, in terms of peaks positions and intensities, from the other samples. In both the raw and thermally treated GS, the presence of the peaks of the N H stretch of primary amines and ammonium ions were ascribed to the presence of Conchin, a complex protein that is secreted by the GS outer shell. These proteins are part of a matrix of organic macromolecules, mainly proteins and polysaccharides that assembled together to form the microenvironment, where the CaCO3 crystals nucleated and grew. The different carbonate peaks, identified in the FTIR spectra, were ascribed to the presence of the different polymorphs (i.e., calcite, aragonite and vaterite) of CaCO3 identified using the XRD. Aside the carbonate peaks that were present in all the samples, sample TS750 and TS1000 also showed the CaO peaks. In the X-ray diffractogram of sample TS750 , peaks synonymous with CaO was not identified; which informed the assumption that the transformation of CaCO3 to CaO did not occur below the treatment temperature of 1000 ◦ C. The non-visibility of the CaO peak in the X-ray diffractogram could be attributed to the fact that the amount of this oxide in the sample matrix was very low. The low concentration of the CaO in the TS750 matrix was evidenced in the appearance of a single CaO peak at 3630 cm−1 . TS500

TS750

TS10 000

80 0 70 0

%Transmitance

60 0 50 0 40 0 30 0 20 0 10 0 0 3800

3300

2800

2300

1800

1300

Wavenumb ber (cm-1)

Fig. 2 – FTIR pattern of the raw and thermally treated GS.

800

300

300


Fig. 3 – Evaluation of P recovery capacity of raw and thermally treated GS.

The results of the BET analysis showed that the surface area (m2 /g) of the GS and the thermally treated samples (i.e., TS100 –TS1000 ) were 1.9666, 0.0030, 2.8070, 1.3301, 4.4409 and 50.0069, respectively. The effects of thermal treatment on the P-recovery efficiency of the materials (i.e., raw GS and TS100–1000 ) are presented in Fig. 3. The amount of P recovered slightly increased with increasing thermal activation temperature (◦ C) from zero (i.e., for raw GS) to 500 ◦ C and the amount of P recovered (mg/g) ranged between 7.45 and 8.11. A substantial increase (from 8.11 mg/g at 500 ◦ C to 19.17 mg/g at 750 ◦ C) in the values of P recovered was noted at temperatures of 750 ◦ C but the magnitude of P recovered when the thermal activation temperature was increased to 1000 ◦ C remained the same (Fig. 3). In the P-recovery systems, where TS750 and TS1000 were used as the reactive materials, the residual P concentrations were lower than the detectable limit of the P quantification procedure ( 0.99) to the experimental data than the pseudo first order kinetic model. In order to further confirm the kinetic equation that gave better description of the time–concentration profiles, the non-linear chi-square (2 ) error analysis was performed. The results obtained (Table 4b) also showed that pseudo second

302


Table 4b – Error analysis for the kinetic data. Initial conc. (mg/L)

2.5 5.0 10.0 20.0 30.0

qe(exp) (mg/g)

4.97 9.97 19.79 39.95 57.93

Pseudo 1st order

Pseudo 2nd order

qe(Mod) (mg/g)

R

0.815 0.80 1.60 15.65 2.01

0.9238 0.7721 0.627 0.8999 0.6491

21.18 105.11 206.80 37.73 1555.74

2

2

order model gave the better prediction of the experimental qe (mg/g) values. Consequent upon the calcium rich nature of the TS750 and the possible interaction between the Ca2+ content of the TS750 with the aqua P, to form insoluble calcium phosphate salts, the role of precipitation in the P-recovery process was determined. Considering the active ionic species in the P-recovery reactor (i.e., Ca and PO4 2− ), the simplest insoluble phosphate species that can be produced from the interactions within the system were used as the model insoluble phosphate salts (i.e., Ca3 (PO4 )2 with Ksp values of 2.07 × 10−33 ). The SI values of Ca3 (PO4 )2 was estimated via the determination of the activities of the two ionic species in solution, at equilibrium, in a batch process, at different initial phosphate solution concentrations (mg/L). The SI values of the insoluble phosphate species were calculated using Eq. (3) (Nath and Dutta, 2012):

SI = log 10

2

(activity of ca2+ )(activity of P)

2

qe(Mod) (mg/g)

R

4.97 9.96 19.76 40.00 57.80

1.000 1.000 1.000 1.000 1.000

Avrami kinetics

2

qe(Mod) (mg/g)

R2

2

4.96 9.43 19.37 39.95 54.63

0.8331 0.900 0.8714 0.9615 0.874

2.01−5 0.03 9.11−3 0.00 0.20

0.00 1.00−5 4.55−5 1.28−3 2.92−4

certainly mean the quick occurrence of a spontaneous precipitation. Between the under saturated zone and spontaneous precipitation zone there is still a metastable zone, where the solution is already supersaturated but no precipitation occurs over a relatively long period (Stumm and Morgan, 1996). The boundary between metastable zone and spontaneous precipitation zone can be called the critical supersaturation (Joko, 1984). The thermodynamic driving force to a chemical reaction is the Gibbs free energy G, and it is the criterion to judge whether a reaction is spontaneous, in equilibrium, or impossible, corresponding to G < 0, =0, or >0, respectively. The Gibbs free energy of a precipitation reaction is given by Song et al. (2002):

G = −

RT IAP ln n Ksp

(4)

(3)

solubility product of Ca3 (PO4 )2

The plot of the SI value against initial P concentrations, are presented in Fig. 6a. The value of the SI, which ranged between 30.6 and 34.5, increased, linearly, with increasing P concentrations (mg/L) from 2.5 to 30. A positive SI value has been attributed to supersaturation of the ionic species in solution which lead to precipitate formation while, a negative SI is an indication of a dominant adsorption process (Turner et al., 2005). Song et al. (2002) opined that SI value is a good indicator to show the deviation of a salt from its equilibrium state, i.e., the thermodynamic driving force for precipitation to occur. But considering the kinetics, supersaturation does not

where R is the ideal gas constant (8.314 J/mol), T is the absolute temperature (K), IAP and Ksp are, respectively, the free ionic activities product and the thermodynamic solubility product of the precipitate phase and, n is the number of ions in the precipitated compound. In order to judge supersaturation, which is a measure of the deviation of a dissolved salt from its equilibrium value, the SI of a solution with respect to a precipitate phase is defined

SI = log

SI

IAP Ksp

(5)

ΔG

35

-88000

34.5

-90000

34 -92000

33.5

-94000

ΔG

SI value

33 32.5

-96000

32 31.5

-98000

31 -100000

30.5 30

-102000 0

5

10

15

20

25

30

35

Inial P concentraons (mg/L)

Fig. 6 – Determination of the occurrence of precipitation in the P-recovery process.

303


Therefore 2.303RT G = − SI n

(6)

When SI = 0, hence G = 0, the solution is in equilibrium; when SI < 0, G > 0, the solution is under saturated and precipitation is impossible; when SI > 0, G < 0, the solution is supersaturated and precipitation is spontaneous. The G values obtained (Fig. 6) were all negative (range between −88764.5 and −100183.0) which indicated the spontaneity of precipitate formation in the system. Consequent upon the role of precipitation reaction in the P recovery process, the time- concentration profile was analyzed to determine the kinetics of the possible precipitate formation, using the Avrami fractional kinetic equation (Eq. (7)). The theoretical basis of the Avrami fractional kinetic equation hinged on the description of changes in the volume of crystals as a function of time during the process of crystallization (Avrami, 1939). The linearized form of this equation by simple linear regression is presented in Eq. (7) below: ln[− ln(1 − F) = ln(B) + k ln(t)

(7)

where F is the fraction adsorbed (qt /qe ) at time, t, B, is a temperature dependent constant (similar to a rate constant), while, k, is the Avrami exponent (which reflects the dimensionality of crystal growth). The Avrami exponent, k, value can be 3 ≤ k ≤ 4 (for three-dimensional growth); 2 ≤ k ≤ 3 (for two-dimensional growth) or 1 ≤ k ≤ 2 (for one-dimensional growth). The kinetic parameters obtained using Avrami kinetic equation are presented in Table 2. The values of the linear correlation coefficient (r2 ) obtained were high (r2 value ranged between 0.8331 and 0.9615) and the error analysis using the non-linear chi-square (2 ) test showed a good prediction of the qe values (Table 4b). The values of the Avrami exponent, k, which ranged between 0.1779 and 0.7715, showed that the dimensionality of the growth of the precipitate occurred in one dimension.

3.3. Equilibrium isotherm analysis of the P-recovery process The affinity of the TS750 for P and the characteristics of the mode of interactions were determined (Table 3) using the linear forms of the following three equilibrium isotherm equations: Langmuir :

ce 1 1 = + qe qm ce ka qm

Freundlich :

log qe = log kf +

Temkin :

(8) 1 log ce n

qe = B1 ln kT + B1 ln Ce

(9) (10)

where Ce is the equilibrium concentration of P in solution (mg/L), qe is the amount of P adsorbed at equilibrium (mg/g), qm is the theoretical maximum monolayer sorption capacity (mg/g), and Ka is the Langmuir constant (L/mg). Kf is the Freundlich constant (mg/g) (L/mg)1/n and 1/n is the heterogeneity factor. The results of the equilibrium isotherm analysis showed that the TS750 possess heterogeneous site for the interaction with the P species in the aqua system. This fact was ascertained by the highest value of the correlations coefficient

Table 5 – Equilibrium isotherm parameters of P-recovery process. Langmuir isotherm

Freundlich isotherm

Temkin isotherm

1/n = 0.551 Kf = 39.976 r2 = 0.9377

B1 = 10.732 KT = 46.353 r2 = 0.7443

qm = 84.746 Ka = 1.192 r2 = 0.6374

(r2 = 0.9377), when the experimental data were analyzed with the Freundlich equilibrium isotherm equation (Table 5). The equilibrium adsorption curves, relating the TS750 and aqua phase concentration of P, at equilibrium for each of the equilibrium isotherm equations are presented below: Langmuir = qe =

101.02ce 1 + 1.192ce

Freundich = qe = 39.98ce0.551 Temkin = qe = 10.732 ln(46.353ce )

3.4. Effects of hydrochemistry on the P-recovery process The results presented in the Supplementary Information section (see SIF 1–4) showed the effects of hydrochemistry, simulated in the synthetic P-rich water, on the P-recovery ability of the TS750. Considering the elemental composition of TS750 and the tendency for loss of integrity in acidic medium, the effects of pH on the recovery process was monitored between solution pH 6 and 11. The amount (mg/g) of P recovered were in the same range (47.30 and 49.09), despite the difference in the initial solution pH values (see SIF 1). The similarities in the amount of P recovered were ascribed to the fact that the presence of the TS750 in the synthetic P solution caused an increase in the solution pH and the equilibrium pH of all the solution ranged between pH 10.11 and 11.18, irrespective of the value of the initial solution pH. Since the sorbate speciation in aqueous system and the surface chemistry of an adsorbent are all pH dependent, the similarities in the magnitude of the P recovered were attributed to the fact that the surface chemistry of the TS750 and the speciation of the P species in the aqua system were all the same in all the system studied, hence the mode of interactions between the TS750 and the aqua P were similar, despite the difference in the initial solution pH. The influence of variations in the ionic strength of aqua system on the P-recovery process showed that the increase in the ionic strength of the aqua matrix, from a value that ranged between 0.025 and 0.5 M, caused reduction in the amount of the P recovered (see SIF 2). The amount (mg/g) of P recovered reduced from a value of 57.93, when the ionic strength was not enhanced (i.e., raw synthetic P-rich water sample), to a value of 21.19, at the maximum ionic strength studied (i.e., 0.5 mol/L). The reduction in the magnitude of P recovered is an indication that the interaction between the TS750 and the aqua matrix P occurred via an outer sphere complexation reaction or electrostatic attraction, which made it possible for the anionic specie in the aqua matrix to compete with the P for the active sites on the TS750. The effects of anionic interference on the P-recovery by the TS750 showed that the presence of carbonate and chloride negatively impacted the process (see SIF 3) while the other anionic species had minimal influence, within the limit of the

304


TTS750

PTS750

80 0 70 0

Phopshate peak

50 0 40 0

Phosphate peak

Transmiance (%)

60 0

30 0 20 0 10 0 0 3800

3300

2800

2300

1800

1300

800

300

W avenumber (Cm-1) (

Fig. 7 – Comparison of the FTIR spectra of TS750 with PTS750 . concentrations of the anionic species studied. The presence of organic ions, simulated via HA dissolution in the synthetic feed water, showed that the amount of P recovered significantly reduced with increase in the organic load (see SIF 4). The organic load simulator, HA, contains both hydrophilic and hydrophobic molecules as well as many functional groups such as carboxyl, phenolic and hydroxyl groups connected to a skeleton of aliphatic or aromatic units. It has been posited that the carboxylic and phenolic group on the HA are deprotonated in weakly acidic to basic media, thereby conferring negative charge on the HA molecule (Anirudhan et al., 2008). This negative charge promotes competition between the HA and the aqua matrix P for the adsorption sites on the TS750 , thereby causing a reduction in the magnitude of P recovered.

3.5.

Characterization of the P-laden TS750

The FTIR spectrum of the P-laden TS750 (PTS750 ) (Fig. 7) showed, in addition to the original diagnostic peaks of the virgin TS750 , strong phosphate band at 1041 cm−1 and weak phosphate bands at 578 cm−1 . Increase in the intensity of the original peaks, identified in the TS750 , were observed in the PTS750 . The comparison of the surface architecture of the

virgin TS750 (Fig. 4B) with that of the PTS750 (Fig. 8) showed the formation of thick mass of a new material, covering the surface in the PTS750 . The presence of this surface coverage was confirmed by the substantial reduction in the intensity of the original diagnostic XRD peaks found on the virgin TS750 , after the P-recovery process (i.e., in the PTS750 ) (Fig. 9). Aside the different diagnostic peaks, originally reported in the TS750 , no new peaks were detected in the PTS750 . The reduction in the XRD peak intensity in the PTS750 is an indication that the product formed (i.e., the surface coverage) from the recovery of P by the TS750 is amorphous to X-ray. It has been posited that phosphate and Ca2+ in aqueous system solution can form octacalcium phosphate (OCP), dicalcium phosphate dehydrate (DCPD) and hydroxylapatite (HAP). It was opined that the poorly crystallized or amorphous DCPD and OCP formed, as precursor phases, in solution containing Ca and P, and they are recrystallized into thermodynamically stable HAP over time (Kaasik et al., 2008; Koiv et al., 2010).

3.6.

Mechanistic insight into the P-recovery process

The affinity of metal oxides for P has been attributed to the presence of multiple charges on the metallic species, high

Fig. 8 – Surficial architecture of P-laden TS750 in synthetic feed water.

305


PTS750

TSS750

2600

2100

Intensity (a.u.)

1600

1100

600

100 10

20

30

40

-400

50

60

70

80

90

100

2 Theta

Fig. 9 – Comparison of the XRD pattern of TS750 and PTS750 . positive surface charge densities at near-neutral pH, and a propensity to hydroxylate in aqueous systems (Michael et al., 1998). Specifically, it was posited that the reaction between P and Ca2+ rich materials (e.g., calcium oxide, calcite, or gypsum) surface involves the adsorption of small amounts of P and subsequent precipitation of calcium phosphate (Moon et al., 2007). Initial adsorption is thought to occur at sites where lateral interaction with phosphate ions produces surface clusters that then act as nuclei for subsequent crystal growth. The kinetic analysis of the time–concentration profiles showed that chemisorption (due to conformance with the pseudo second order kinetic equation) was the underlying mechanism of the process but the occurrence of precipitation reaction, due to the thermodynamic parameters (i.e., the −G values) of precipitation also lend credence to the occurrence of precipitation during the P-recovery process. Additionally, the effects of ionic strength on the P-recovery indicated that the mode of interaction between TS750 and P occurred via outer sphere complexation (a form of non-specific interaction) while the effects of anionic interference showed that the interaction occurred via specific adsorption. Thus, it could be inferred that both that both the non-specific and specific adsorption were the underlying mode of interaction in the P-recovery process. In order to elucidate the possible mode of interactions, between the ionic species, during the P-recovery process, the speciation of the aqua P and the surface chemistry of the TS750 , was elucidated, using the computer software, MEDUSA

(Make Equilibrium Diagrams Using Sophisticated Algorithms) and HYDRA (Hydrochemical Equilibrium Constant Database) computer software (Chemical Equilibrium Diagrams, in press) to determine the chemical equilibrium data. Taking the operational pH for P-recovery into cognizance, the chemical equilibrium data (Fig. 10) showed that the ionic species that exist at the inception of the process included Ca2+ , PO4 3− , HPO4 2− and H2 PO4 − , while the interactions between these ionic species produced the following molecular species, at varying concentrations: CaHPO4 , Ca5 (PO4 )3 OH and CaPO4 − . Taking into cognizance the experimental evidences that showed that both adsorption (specific and non-specific adsorption) and precipitation reaction were the underlying mechanisms of P-recovery, using the TS750 reactive material, the following reaction schemes are proposed as the possible underlying mechanism of interaction in the P-recovery process viz.: Specific adsorption Ca2+ + HPO4 2− → CaHPO4 Ca2+ + PO4 3− → CaPO4 − Non-specific adsorption Ca2+ + HPO4 2− → Ca2+ . . .. . .HPO4 2−

Fig. 10 – Chemical equilibrium data of interaction of TS750 with aqueous P.

306


Table 6 – Physicochemical parameters of the raw AQW and product water. Parameters pH Turbidity (NTU) EC (␮s/cm) P TS DS SS COD TN K Ca Na

Raw AQW

Product water

6.61 20.2 92.5 0.15 643 460 183 135 19.76 6.01 5.43 3.64

10.11 8.70 192.5 0.06 261 191 70 54 10.4 6.88 23.10 3.86

Fig. 11 – SEM image of P-laden TS750 in real AQW. Precipitation reaction 2+

5Ca

+ 3PO4

3−

→ Ca5 (PO4 )3 OH

In the chemical equations presented above the specific adsorption process occurred via covalent bonding while the non-specific adsorption process occurred via electrostatic attraction between the oppositely charged species.

3.7.

P-recovery from real aquaculture wastewater

The ability of the TS750 to recover P from real aquaculture wastewater (AQW) was tested in a batch reactor. The physicochemical characteristics of the real aquaculture and the product water (PW) from the P-recovery process are presented in Table 6. The TS750 removed 60% of the original P content (0.15 mg/L) from the AQW, which is equivalent to 0.18 mg/g of the TS750 . The quality characteristics of the PW showed that the P-recovery process appreciably improved the quality characteristics of the PW which was considered as a positive step towards the save disposal of the AQW, after the P-recovery process. Aside the values of the pH and EC that increased, appreciably, in the PW, the magnitude of other parameters reduced after the P-recovery process. The magnitude of the solids (TS, DS and SS) in the AQW substantially reduced after the P-recovery process. The reduction in the solids was attributed to the effects of the occurrence of precipitation 000 30

reaction during the P-recovery process. The removal of the solid from the aqua matrix, via the precipitation reaction, was ascribed to a phenomenon known as sweep coagulation, in coagulation–flocculation process. The reduction in the values of solids in the PW also manifested in the value of the COD, which reduced from the value of 15 mg/L to a value of 54 mg/L in the PW. In the P recovery process, appreciable amount of the TN content of the AQW was also removed (47.4% i.e., 18.72 mg/g of TS750 ) which showed that in the process of P recovery, substantial amount of the TN was also removed. The synchronous attenuation of both the P and N in the aqua matrix is an indication that the solid fraction, recovered from the P-recovery process, can be used as a very good source of these two nutrients in agricultural practice. The sodium and potassium content of the PW was not influenced by the process but substantial amount of calcium was added into the PW after the P recover process. The elevation of the magnitude of calcium in the aqua matrix was assumed to be responsible for the higher values of the pH and EC in the PW.

3.8. Characterization of P-laden TS750 from AQW system The surface architecture of the P-laden TS750 in the AQW (AQWTS750 ) (Fig. 11) showed that the particle surface remained crystalline after the P-recovery process and the deposition of

RPPTS750

TS750

500 25

Intensity (a.u.)

000 20

500 15

10 000

5 500

0 0 -500

20

40

60

80

1000

2 Theta

Fig. 12 – Comparison of the XRD pattern of TS750 and AQWTS750 .

120

307


RX

TS750

70 60

% Transmiance

50 40 30 20 10 0 3800

3300

2800

2300

1800

1300

800

300

Wavenumber (Cm-1)

Fig. 13 – Comparison of the FTIR spectra of TS750 and AQWTS750 . speckles of extraneous materials on the surface of the reactive material was observed. The XRD patterns (Fig. 12) of the AQWTS750 were similar to that of the virgin TS750 but the values of the miller indices showed that during the P-recovery process, significant structural changes occurred in the CaCO3 crystallite. In the TS750 , only the peaks of calcite (43.70 (1 1 3)) and vaterite (63.19 (2 1 1), 72.68 (3 0 0)) were observed while in the diffractogram of AQWTS750 , the vaterite peaks appeared at 21.09 (1 1 0), 37.93 (1 1 2), 41.20 (2 1 1), 69.14 (1 1 4) and 81.05 (2 2 4), calcite peaks appeared at 52.50 (1 1 3), 67.96 (1 0 4) and aragonite peaks appeared at 26.24 (1 1 1), 45.89 (2 2 1). The structural changes in the CaCO3 crystallites were attributed to the hydration or solvation of the thermally treated material in the AQW during the P-recovery process. It was noted that despite the similarities in the peaks positions, the intensity of the peaks in the AQWTS750 were higher than that of the TS750 . This showed that the P-recovery process enhanced the crystallinity of the TS750 . The enhanced crystallinity was ascribed to the occurrence of the structural changes in the crystallites of CaCO3 in the presence of array of ionic constituents of the real AQW. The comparison of the FTIR spectra of the AQWTS750 and that of virgin TS750 (Fig. 13) showed that they were similar, aside the reduction in the intensity of the different peaks. In the AQWTS750 , the disappearance of some carbonate peaks, which appeared at 1624 cm−1 , 2314 cm−1 and 2372 cm−1 , CaO peaks, which appeared at 3630 cm−1 in the TS750 and appearance of phosphate peak at 605 cm−1 were noted.

4.

Conclusion

The P-recovery ability of a GS can be improved significantly via thermal treatment and the optimum treatment temperature can be achieved at a temperature of 750 ◦ C. The higher Precovery ability of the TS was caused by the enhanced defects in the surficial physiognomies. Kinetic analysis showed that chemisorption was the underlying mechanism of the process while thermodynamic analysis showed that precipitation also contributed to the P-recovery process. Avrami fractional kinetic analysis showed that the precipitate growth occurred in one direction. In addition to the removal of P, substantial amount of the total nitrogen in the AQW was also removed and the process produced water with significant improvement in the overall physicochemical characteristics.

Acknowledgements The Authors wish to express gratitude to the Membrane Cluster, School of Chemical Engineering, Universiti Sains Malaysia, Penang (Grant Number: 1001/PSF/861001) and the International Foundation for Science (IFS), Sweden (Grant Number: W/4212-2) for the financial supports granted to undertake this research.

Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j. psep.2015.09.006.

References Anirudhan, T.S., Suchithra, P.S., Rijith, S., 2008. Amine-modified polyacrylamide bentonite composite for the adsorption of humic acid in aqueous solutions. Colloids Surf. A Physicochem. Eng. Asp. 326, 147–156. Avrami, M., 1939. Kinetics of phase change. I. General theory. J. Chem. Phys. 7, 1103–1112. Brogowski, Z., Renman, G., 2004. Characterization of opoka as a basis for its use in wastewater treatment. Pol. J. Environ. Stud. 13, 15–20. Chemical Equilibrium Diagrams. http://www.kemi.kth.se/medusa/. Driver, J., Lijmbach, D., Steen, I., 1999. Why recover phosphorus for recycling, and how? Environ. Technol. 20 (7), 651–662. Falini, G., Albeck, S., Weiner, S., Addadi, L., 1996. Science 271, 67. Faulkner, S.P., Richardson, B.C., 1989. Physical and chemical characteristic of freshwater wetlands. In: Hammer, D.A. (Ed.), Constructed Wetlands for Wastewater Treatment: Municipal Industrial and Agricultural. Lewis Publishers, Chelsea, pp. 41–72. Giannimaras, E.K., Koutsoukos, P.G., 1987. J. Colloid Interface Sci. 116, 423. Giannimaras, E.K., Koutsoukos, P.G., 1988. Langmuir 4, 855. Johansson, L., 1999. Industrial by-products natural substrata as phosphorus sorbents. Environ. Technol. 20, 309–316. Johnston, A.E., Richards, I.R., 2003. Effectiveness of different precipitated phosphates as phosphorus sources for plants. Soil Manage. 19, 45–49. Joko, I., 1984. Phosphorus removal from wastewater by the crystallization method. Water Sci. Technol. 17, 121–132.

308


Kaasik, A., Vohla, C., Motlep, R., Mander, U., Kirsimae, K., 2008. Hydrated calcareous oil-shale ash as potential filter media for phosphorus removal in constructed wetlands. Water Res. 42, 1315–1323. Kitano, Y., 1962. Bull. Chem. Soc. Jpn. 35, 1973. Kitano, Y., Hood, D.W., 1965. Geochim. Cosmochim. Acta 29, 29. Koiv, M., Liira, M., Mander, U., Motlep, R., Vohla, C., Kirsimae, K., 2010. Phosphorus removal using Ca-rich hydrated oil shale ash as filter material – the effect of different phosphorus loadings and wastewater compositions. Water Res. 44, 5232–5239. Kwon, H.-B., Lee, C.-W., Jun, B.-S., Yun, J.-D., Weon, S.-Y., Koopman, B., 2004. Recycling waste oyster shells for eutrophication control. Resour. Conserv. Recycl. 41, 75–82. Lagergren, S., 1898. About the theory of so-called adsorption of soluble substances. K. Sven. Vetenskapsakad. Handl. Band. 24, 1–39. LBR A&CmixturesXRD01.odg 7/2012, X-ray diffraction (XRD) of aragonite and calcite. Lindsay, W.L., 1979. Phosphate Chemical Equilibria in Soils. John Wiley & Sons, New York. McKay, G., 1984. The adsorption of basic dye onto silica from aqueous solution–solid diffusion model. Chem. Eng. Sci. 39 (1), 129–138. Michael, J.B., David, W.B., Carol, J.P., 1998. Laboratory development of permeable reactive mixtures for the removal of phosphorus from onsite wastewater disposal systems. Environ. Sci. Technol. 32, 2308–2316. Mishakov, I.V., Bedilo, A.F., Richards, R.M., Chesnokov, V.V., Volodin, A.M., Zaikovskii, V.I., Buyanov, R.A., Klabunde, K.J., 2002. Nanocrystalline MgO as a dehydrohalogenation. J. Catal. 206, 40–48. Moon, Y.H., Kim, J.G., Ahn, J.S., Lee, G.H., Moon, H.S., 2007. Phosphate removal using sludge from fuller’s earth production. J. Hazard. Mater. 143, 41–48. Morse, G.K., Brett, S.W., Guy, J.A., Lester, J.N., 1998. Review: phosphorus removal and recovery technologies. Sci. Total Environ. 212, 69–81. Nath, S.K., Dutta, R.K., 2012. Acid-enhanced limestone defluoridation in column reactor using oxalic acid. Process Saf. Environ. Prot. 90, 65–75. Nehrke, G., (PhD Thesis) 1971. Calcite Precipitation from Aqueous Solution: Transformation from Vaterite and Role of Solution Stoichiometry. Universiteit Utrecht.

Ogino, T., Suzuki, T., Sawada, K., 1987. Geochim. Cosmochim. Acta 51, 2757. Oladoja, N.A., Aliu, Y.D., 2009. Snail shell as coagulant aid in the alum precipitation of malachite green from aqua system. J. Hazard. Mater. 164, 1494–1502. Oladoja, N.A., Aliu, Y.D., Ofomaja, A.E., 2011. Evaluation of Snail shell as coagulant aid in the alum precipitation of aniline blue from aqua system. Environ. Technol. 32 (6), 639–652. Oladoja, N.A., Ahmad, A.L., Adesina, O.A., Adelagun, R.O.A., 2012. Low-cost biogenic waste for phosphate capture from aqueous system. Chem. Eng. J. 209, 170–179. Oladoja, N.A., Ololade, I.A., Adesina, A.O., Adelagun, R.O.A., Sani, Y.M., 2013. Appraisal of gastropod shell as calcium ion source for phosphate removal and recovery in calcium phosphate minerals crystallization procedure. Chem. Eng. Res. Des. 91, 810–818. Oladoja, N.A., Adesina, A.O., Adelagun, R.O.A., 2014. Gastropod shell column reactor as on-site system for phosphate capture and recovery from aqua system. Ecol. Eng. 69, 83–92. Richardson, C.J., 1985. Mechanisms controlling P retention capacity in fresh water wetlands. Science 228, 1424. Rodhe, W., 1969. Crystallization of eutrophication concepts in North Europe. In: Eutrophication, Causes, Consequences, Correctives. National Academy of Sciences, Washington, DC, pp. 50–64, ISBN 309-01700-9. Song, Y., Hahn, H.H., Hoffmann, E., 2002. Effects of solution conditions on the precipitation of phosphate for recovery: a thermodynamic evaluation. Chemosphere 755 (48), 1029–1034. Stanmore, B.R., Gilot, P., 2005. Review – calcination and carbonation of limestones during thermal cycling for CO2 sequestration. Fuel Proc. Technol. 86, 1707–1743. Stumm, W., Morgan, J.J., 1996. Aquatic Chemistry, third ed. John Wiley & Sons, Inc, New York, pp. 356. Turner, B.D., Binning, P.J., Stipp, S.L.S., 2005. Fluoride removal by calcite: evidence for fluoride precipitation and surface adsorption. Environ. Sci. Technol. 39, 9561–9568. Vohla, C., Koiv, M., Bavor, H.J., Chazarenc, F., Mander, U., 2011. Filter materials for phosphorus removal from wastewater in treatment wetlands – a review. Ecol. Eng. 37, 70–89. Xyla, A.G., Koutsoukos, P.G., 1987. J. Chem. Soc., Faraday Trans. 1 83, 1477.