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Bioresource Technology xxx (2014) xxx–xxx Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech Review Modification of agricultural waste/by-products for enhanced phosphate removal and recovery: Potential and obstacles T.A.H Nguyen a, H.H Ngo a,⇑, W.S Guo a,b, J Zhang b, S Liang b, D.J Lee c, P.D Nguyen d, X.T Bui d,e a Centre for Technology in Water and Wastewater, School of Civil and Environmental Engineering, University of Technology, Sydney, Broadway, NSW 2007, Australia Shandong Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science & Engineering, Shandong University, Jinan 250100, PR China c Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan d Faculty of Environment and Natural Resources, Ho Chi Minh City University of Technology, District 10, Ho Chi Minh City, Viet Nam e Division of Environmental Engineering and Management, Ton Duc Thang University, District 7, Ho Chi Minh City, Viet Nam b h i g h l i g h t s Modification is critical in enhancing P removal ability of AWBs Review focuses on metal loading and quaternization with potentials and drawbacks P was adsorbed onto modified AWBs mainly via ligand and ion exchange mechanisms Little has been done on beneficial use of modified AWBs for P recovery Recommendations on proper use of modification methods were made a r t i c l e i n f o Article history: Received June 2014 Received in revised form July 2014 Accepted 10 July 2014 Available online xxxx Keywords: Agricultural waste/by-products Biosorbent Modification Phosphate Removal efficiency a b s t r a c t There is a growing trend to employ agricultural waste/by-products (AWBs) as the substrates for the development of phosphate biosorbents Nevertheless, due to the lack of anion binding sites, natural AWBs are usually inefficient in phosphate decontamination Consequently, modification plays a vital role in improving phosphate sorption’s property of raw AWBs This review paper evaluates all existing methods of modification The literatures indicate that modification can significantly improve phosphate removal ability of AWBs by retaining phosphate ion onto modified AWBs principally via ion exchange (electrostatic interaction) and ligand exchange mechanisms So far, little work has been done on the beneficial use of modified AWBs for the phosphorus recovery from aqueous solutions The poor recyclability of modified AWBs could be responsible for their limited application Hence, further study is essential to search for novel, cost-effective, and green methods of modification Ó 2014 Elsevier Ltd All rights reserved Introduction Phosphorus plays an important role to the development of plants, animals and the industrial manufacture (Choi et al., 2012; Karachalios, 2012; Mezenner and Bensmaili, 2009) However, due to the over-exploitation for these purposes, the global phosphate rock reserve is probably going to be exhausted in the next 50–100 years (Cooper et al., 2011; Eljamal et al., 2013; Ogata et al., 2012) In another perspective, the phosphorus concentration in the aqueous medium above 0.02 mg/L can cause eutrophication, ⇑ Corresponding author Address: School of Civil and Environmental Engineering, University of Technology, Sydney (UTS), P.O Box 123, Broadway, NSW 2007, Australia Tel.: +61 9514 2745; fax: +61 9514 2633 E-mail addresses: ngohuuhao121@gmail.com, h.ngo@uts.edu.au (H.H Ngo) leading to the deterioration of water quality and threatening the life of aquatic creatures (Ismail, 2012; Jyothi et al., 2012) Therefore, the excessive amounts of phosphorus need to be removed from the water medium to prevent water bodies from this undesirable phenomenon, as well as pave the way to the phosphorus recovery (Anirudhan et al., 2006; Zhang et al., 2012) Various technologies are available for controlling phosphorus pollution These processes can be classified as chemical methods (precipitation, crystallization, anion exchange, and adsorption), biological methods (assimilation, enhanced biological phosphorus removal, constructed wetlands, wastewater stabilization pond), and physical methods (microfiltration, reverse osmosis, electrodialysis, and magnetic separation) (Benyoucef and Amrani, 2011; Bhojappa, 2009) However, each method represents its own demerits (Jeon and Yeom, 2009) The physical methods have http://dx.doi.org/10.1016/j.biortech.2014.07.047 0960-8524/Ó 2014 Elsevier Ltd All rights reserved Please cite this article in press as: Nguyen, T.A.H., et al Modification of agricultural waste/by-products for enhanced phosphate removal and recovery: Potential and obstacles Bioresour Technol (2014), http://dx.doi.org/10.1016/j.biortech.2014.07.047 T.A.H Nguyen et al / Bioresource Technology xxx (2014) xxx–xxx disadvantages of being too expensive or inefficient (Karachalios, 2012) The chemical precipitation is often prone to additional sludge, high chemical expense, effluent neutralization requirement, and inadequate efficiency for dilute phosphorus solutions (Kumar et al., 2010; Mallampati and Valiyaveettil, 2013; Zhang et al., 2011) Similarly, the major concerns with biological removal technologies are complicated operation; high energy consumption and large footprint (Ning et al., 2008; Peleka and Deliyanni, 2009) The use of wastewater stabilization pond with the water hyacinth is also restricted by land scarcity and the difficulty in water hyacinth utilization (Xi et al., 2010) On the other hand, adsorption is proven to be affordable, effective and best suited for low levels of phosphate (Zhang et al., 2011) Especially, it is believed that, adsorption enables the recovery of phosphorus, owing to its high selectivity toward phosphorus (Loganathan et al., 2014) Previously, activated carbon or anion exchange resins are commonly used for phosphorus decontamination However, the problems associated with the high cost, no renewability, requirement of pre-concentration of anions, and disposal after use hinder their widespread application in developing countries (De Lima et al., 2012; Karachalios, 2012; Karthikeyan et al., 2004) Hence, increasing attention has been paid to AWBs based biosorbents in an attempt to search for a viable alternative option (Jyothi et al., 2012) The potential AWBs based phosphate biosorbents are expected to have low cost, high effectiveness, good selectivity, potential renewability, and high adaptability to various process parameters (Ning et al., 2008) AWBs have several properties that make them attractive as the substrate for developing phosphorus biosorbents To begin, AWBs are abundant, low-priced, and non-toxic Additionally, as lignocellulosic materials, AWBs contain large amounts of functional groups (e.g AOH, ACHO) in their cellulose, hemicellulose and lignin components Therefore, AWBs can easily get involved in chemical reactions (e.g condensation, etherification and polymerization) This provides a foundation for AWBs to be converted into some functional polymers (Benyoucef and Amrani, 2011; Xu et al., 2010b) Specifically, the AOH group of AWBs can combine with alkoxyamine ligands to improve their anion exchange abilities (Karthikeyan et al., 2002) The utilization of AWBs as phosphate biosorbents may result in many benefits Firstly, this practice can protect surface water from eutrophication Secondly, there are large amounts of AWBs produced worldwide annually, posing a challenge to solid waste disposal Thus, the recycling AWBs as phosphate biosorbents not only provides a viable solution to reduce waste materials in a cheap and eco-friendly way but also adds values to AWBs (Anirudhan et al., 2006; Eljamal et al., 2013; Ismail, 2012; Tshabalala et al., 2004) This also fits well with the principle ‘‘use of renewable resources’’ of Green Chemistry (Srivastava and Goyal, 2010) In addition, the production of anion exchange resins from abundant, cheap and renewable AWBs may help to the cost of phosphorus treatment (Liu et al., 2012) Moreover, by converting phosphorus in wastewaters into fertilizers, this practice can generate revenues (Huang et al., 2010; Peng et al., 2012) Also, the successful exploitation of phosphorus from wastewaters will diminish the use of mineral phosphorus, and hence saving the global phosphorus rock resource Clearly, the use of AWBs based phosphate biosorbents may provide a sustainable, efficient and profitable solution for phosphorus pollution control There is increasing trend to use AWBs as phosphate biosorbents Nevertheless, very few studies have been made for the ability of raw AWBs to adsorb phosphorus Whereas some pristine AWBs can hardly remove any phosphorus from aqueous solutions (Huang et al., 2010; Namasivayam et al., 2005), others exhibit very low sorption abilities as compared to commercial adsorbents (Krishnan and Haridas, 2008; Marshall and Wartelle, 2004; Nguyen et al., 2013; Xu et al., 2011a; Zhang et al., 2012) (Table 1) The lack of efficiency in the phosphate removal of original AWBs can be explained by the abundant availability of negatively charged functional groups (e.g AOH, ACOOH), while absence of positively charged functional groups (e.g ANH2) on the surface of raw AWBs (Mallampati and Valiyaveettil, 2013; Nguyen et al., 2013) For these reasons, AWBs need to be modified to improve their phosphate sorption abilities Besides, modification of AWBs was found to increase the strength of lignocelluloses materials, and hence mitigating the release of organic matters into aqueous solutions (Anirudhan et al., 2006) Methods of modification of AWBs for better phosphate removal can be grouped into (i) cationization (e.g metal loading, grafting with ammonium type chemicals), (ii) anionization (e.g surface coating with sulphate), (iii) activation (e.g thermal, chemical and steam activation) (Fig 1) This paper aims to gain insight into each method of modification, with respect to the principle, procedure, Table The maximum phosphate adsorption capacity of commercial and natural AWBs based biosorbents Adsorbent Unmodified AWBs based biosorbents Oyster shell Oyster shell Giant reed Sugarcane bagasse Soybean milk residues (okara) Coir pith Date palm fibers Scallop shells Palm surface fibers Granular date stones Commercially available adsorbents Zr-MCM 41 Whatman QA-52 Zirconium ferrite Duolite A-7 Amberlite IRA-400 Aluminium oxide Zirconium ferrite Dowex Hydrotalcite Zirconium loaded MUROMAC Maximum adsorption capacity (mg PO4/g) 0 0.836 1.10 2.45 4.35 13.33 23.00 26.05 26.66 3.36 14.26 27.73 31.74 32.24 34.57 39.84 40.23 60.00 131.77 Reference Huang et al (2010) Namasivayam et al (2005) Xu et al (2011a) Zhang et al (2012) Nguyen et al (2013) Krishnan and Haridas (2008) Riahi et al (2009) Yeom and Jung (2009) Ismail (2012) Ismail (2012) Jutidamrongphan et al (2012) Marshall and Wartelle (2004) Jutidamrongphan et al (2012) Anirudhan et al (2006) Marshall and Wartelle (2004) Peleka and Deliyanni (2009) Biswas (2008) Anirudhan and Senan (2011) Peleka and Deliyanni (2009) Biswas (2008) Please cite this article in press as: Nguyen, T.A.H., et al Modification of agricultural waste/by-products for enhanced phosphate removal and recovery: Potential and obstacles Bioresour Technol (2014), http://dx.doi.org/10.1016/j.biortech.2014.07.047 T.A.H Nguyen et al / Bioresource Technology xxx (2014) xxx–xxx Fig Methods of modification of AWBs for better phosphate removal efficacy, mechanism, applicability and drawbacks Although this review paper has included all methods of modification that currently exist, the focus has been on two most widely used methods, namely metal loading and quaternization It is expected to enrich the fundamental theory and promote the practical application of modified AWBs based biosorbents in the future Cationization of AWBs by metal loading 2.1 Development of metal loaded AWBs based phosphate biosorbents 2.1.1 Background It was reported that metal (e.g Fe, Al, Mn) oxides in some low cost materials played important roles in their phosphate removal ability (Liu et al., 2012; Penn et al., 2007) This suggests a solution to improve the phosphate uptake of AWBs based biosorbents, which is the saturation of AWBs with metal salts It is desirable that the metal treated AWBs with highly positive charges can sequester effectively phosphate anions (Cheng et al., 2013) Likewise, since Zr(IV) exhibits a good affinity toward PO3À ions, Zr(IV) loaded polymers can be a good choice for the removal of phosphate (Ruixia et al., 2002) 2.1.2 Metal loading procedure The cationization of AWBs is indented to improve their retention ability of PO3À ions through electrostatic interaction The process is implemented through the reaction of AWBs with metal salts Due to the abundance of negatively charged functional groups (e.g AOH, ACOOH) on their surfaces, AWBs can naturally adsorb metals Nevertheless, to further boost their metal sequestering ability, AWBs should be grafted with the carboxyl (ACOOH) group or pre-treated with bases prior to the reaction with metal salts (Eberhardt and Min, 2008) Accordingly, the metal loading procedure is proposed as follows: 2.1.2.1 Grafting carboxyl groups onto AWBs The carboxylic (ACOOH) group is considered as the most important functional group for metal sorption by AWBs (Min et al., 2004) Therefore, one of the well-known methods to improve metal sorption ability is through incorporation of carboxylic (ACOOH) groups into AWBs Nada and Hassan (2006) introduced three ways to incorporate carboxylic (ACOOH) groups into sugarcane bagasse to prepare cationic exchange resins, including etherification using monochloroacetic acid (Eq (1)), esterification using succinic anhydride, and oxidation using sodium chlorite They discovered that carboxymethylated bagasse displayed the highest cationic exchange ability and thermal stability over that of succinylated and oxidized bagasse Poly À OH ỵ Cl CH2 COOH ! Poly O À CH2 À COOH ð1Þ The efficacy of etherification method was confirmed by Carvalho et al (2011), who reported that the maximum Fe(II) adsorption capacity of sugarcane bagasse fibres rose from 16.0 to 75.4 mg/g (371.25%) after reaction with monochloroacetic acid As a consequence, the phosphate removal percentage of carboxymethylated sugarcane bagasse fibres rose 3% when compared to the raw material In the same way, Eberhardt and Min (2008) revealed that, the pre-treatment with carboxymethyl cellulose (CMC) augmented the phosphate uptake capacity of Fe(II) impregnated wood particles from 2.05 to 17.38 mg/g (748%) They Please cite this article in press as: Nguyen, T.A.H., et al Modification of agricultural waste/by-products for enhanced phosphate removal and recovery: Potential and obstacles Bioresour Technol (2014), http://dx.doi.org/10.1016/j.biortech.2014.07.047 T.A.H Nguyen et al / Bioresource Technology xxx (2014) xxx–xxx attributed the higher phosphate uptake capacity to additional binding sites to complex iron ions, which were formed by chemical reaction of wood particles with anionic polymer (CMC) Evidently, the integration of carboxylic (ACOOH) groups into AWBs prior to their reactions with metal salts significantly increases their metal adsorption capacities 2.1.2.2 Base treatment (saponification) Another method to enhance the metal sorption ability of AWBs is through base treatment Min et al (2004) examined the efficacy of base treatment on the Cd(II) sorption by juniper fibre It was found that base treatment enhanced the maximum Cd(II) adsorption capacity around 3.2 times (from 9.18 to 29.54 mg/g) They explained this enhancement by the fact that (AOH) ions, which derived from the reaction NaOH changed ester in the wood fibre to carboxylate, played a major role for binding Cd(II) onto AWBs (Eq (2)) R COO R0 ỵ H2 O ! R COO ỵ R0 OH 2ị Equally, the base treatment (saponification) was used prior to metal loading in many studies conducted by Biswas et al (2008, 2007), Han et al (2005), Mallampati and Valiyaveettil (2013) Han et al (2005) claimed that treatment juniper mats with 0.5 M NaOH improved their cationic exchange capacity (CEC), and hence enhancing the binding ability of Fe irons As a result, the capture of PO3À ions onto juniper mats was strengthened Mallampati and Valiyaveettil (2013) saponified apple peels with NaOH before its impregnation with Zr(IV) salt They suggested that the base treatment broke up ester bonds and produced more (AOH) groups, which were responsible for metal binding onto AWBs 2.1.2.3 Deposition of metal ions onto AWBs It is well-recognized that metals can attach to AWBs via chemical reactions with cationic binding sites on their surfaces, e.g hydroxyl (AOH) groups, carboxylic (ACOOH) groups (Han et al., 2005; Min et al., 2004) Besides, Shin et al (2005) claimed that ion exchange mechanism might be responsible for the La(III) attachment to juniper bark fibre This assumption is supported by XRD patterns, indicating that after La(III) treatment, the height of Ca peak declined as compared to the reference peak, while Ca(II) concentration in the solution increased From the data obtained, they concluded that La(III) was retained to the bark by replacing some of Ca(II) in the bark as follows: La3ỵ ỵ H2 O $ LaOH2ỵ ỵ Hỵ 3ị LaOH2ỵ ỵ H2 O $ LaOHịỵ2 þ Hþ ð4Þ þ 2þ 2þ bark À C2 O2À þ 2LaðOHÞþ2 ! bark À C2 O2À Ca ẵLaOHị2 ỵ Ca 5ị 2.1.3 Characterization of metal loaded AWBs based biosorbents The immobilization of metal ions onto AWBs surface can be confirmed by using various techniques, such as FTIR, SEM, XPS, XRD, EDXA, elementary analysis FTIR spectrum of wood fibre treated with carboxymethyl cellulose (CMC) and FeCl2 had the carboxyl (ACOOH) group at 1600 cmÀ1, implying the penetration of CMC into the fibre (Eberhardt and Min, 2008) Similarly, the presence of a new band at 1057 cmÀ1 for FeAOH in FTIR spectrum validated the deposition of iron on coir pith (Krishnan and Haridas, 2008) The SEM image of apple peels after treatment revealed that there were Zr nanoparticles immobilized on the surface (Mallampati and Valiyaveettil, 2013) XRD patterns of juniper bark fibre before and after treatment with La showed that, La was bounded to the bark by replacement of Ca in the bark This hypothesis is validated by EDXA results, which indicated that the Ca peak intensity decreased, while that of La increased after treatment (Shin et al., 2005) Based on XPS profile of Zr loaded apple peel, Mallampati and Valiyaveettil (2013) discovered that, Zr was anchored to the apple peel surface in oxidation state of (+4) and with the binding energy of 179 eV (Mallampati and Valiyaveettil, 2013) Using elemental analysis, Han et al (2005) proved that the content of Fe increased after impregnation of mats into acid mine drainage (AMD) By exploring that the iron content of CMC pre-treated wood particles was 7-fold higher than that for untreated one, Eberhardt and Min (2008) suggested that CMC pre-treatment form additional sites to complex iron ions 2.1.4 Factors influencing the metal loading The efficacy of AWBs metal loading is found to rely on the type and concentration of metal salts, as well as method of metal loading Wang et al (2012) reported that, the maximum phosphate adsorption capacity of AC/NÀFe(II) (14.12 mg/g) was greater than AC/NÀFe(III) (8.73 mg/g) The authors ascribed this to the higher intra-particle diffusion and binding energy of AC/NÀFe(II) in comparison with AC/NÀFe(III) Shin et al (2005) revealed that the increase in La(NO3)3Á6H2O concentration from 0.01 to 0.1 M led to a rise of phosphate capture ability of La(III) loaded juniper bark fibre, from 20.05 to 33.35 mg/g Nada and Hassan (2006) discovered that, etherification was more efficient than oxidation and esterification in deposition of four heavy metals (i.g Cu, Fe, Ni, Cr) onto carboxymethylated bagasse 2.1.5 Effect of metal loading on phosphate biosorption Table summarizes the performance of metal loaded AWBs based phosphate biosorbents About the effect of metal loading on the phosphate sorption of AWBs, Krishnan and Haridas (2008) found that impregnation of coir pith with Fe(III) solution enhanced its level of phosphate capture 5–6 times Supporting the Eberhardt and Min’s (2008) argument that the amount of loaded Fe(II) governed the phosphate adsorption capacity (qmax) of the modified wood particles, Carvalho et al (2011) reported that qmax of Fe(II) treated sugarcane bagasse increased 2.25 times as compared to the reference These results are in harmony with the finding by Shin et al (2005), who observed that the phosphate uptake by raw juniper bark (JB) was marginal, whilst that of La(III) treated JB was 22.14 mg/g Apparently, the cationization of AWBs considerably improved their sorption capacities of phosphate The maximum adsorption capacity (qmax) of metal loaded AWBs based phosphate biosorbents in this review varied in a wide range (2.05–174.68 mg/g) This variation can be ascribed to the difference in the nature, composition of AWBs as the substrate and type, concentration of metal salts used for loading Among them, the potential metal loaded AWBs with the qmax value higher than 50 mg/g include Fe(II) treated carboxymethylated sugarcane baggage fibre (152 mg/g) and saponified Zr(IV) treated orange waste gel (172 mg/g) (Biswas, 2008; Carvalho et al., 2011) These two metal loaded biosorbents are even better as compared to commercially available adsorbents listed in Table 1, in term of the qmax This comparison result is a sound proof of the potential of metal loading in improving the phosphate sorption capacity of AWBs 2.2 Adsorption mechanisms of metal loaded AWBs based phosphate biosorbents 2.2.1 Ligand exchange The ligand exchange is considered as chemical sorption, which is characterized by fast, strong and less reversible adsorption (Loganathan et al., 2014) It may occur through inner sphere complex, when PO3À anions create a covalent chemical bond with a metallic cation on the surface of the metal loaded AWBs, leading Please cite this article in press as: Nguyen, T.A.H., et al Modification of agricultural waste/by-products for enhanced phosphate removal and recovery: Potential and obstacles Bioresour Technol (2014), http://dx.doi.org/10.1016/j.biortech.2014.07.047 T.A.H Nguyen et al / Bioresource Technology xxx (2014) xxx–xxx Table Performance of metal loaded AWBs based phosphate biosorbents Mechanisms Side effects Phosphate uptake Desorption efficiency capacity (mg/g) (%) Type of reactor or operation mode Reference Apple peels NaOH + 0.1 M ZrO2ClÁ8H2O Electrostatic interaction No release of Zr(IV) during adsorption 20.35 BSR Okara NaOH + 0.25 M FeCl3 – Vigorous leakage of Fe 14.66 during adsorption and desorption tests Mallampati and Valiyaveettil (2013) Nguyen et al (2013) Bagasse fibres Eggshell Monochloroacetic acid + FeCl2 0.9%, 1.8%, 3.6%, and 5.3% FeCl3.2H2O mg/L Orange waste gel Ca(OH)2 + 0.1 M ZrOCl2.8H2O Wood particles Carboxymethyl cellulose Complexation (CMC) 4% + FeCl2 12% 17.38 Coir pith Fe(NO3)3Á9H2O 70.92 (BSR) 68 (PBR) Orange waste gel Ca(OH)2 + 0.01 M La(III)À/Ce(III)À/Fe(III)solutions Juniper fiber Acid mine drainage (AMD) No Biosorbents Modifying agents 152 Distilled water pH 2, 4, BSR 6, 8, 10 (94%) – – 14.49 – BSR BSR 0.2 M NaOH (95%) PBR HCl (70%) Carvalho et al (2011) Mezenner and Bensmaili (2009) Biswas et al (2008) BSR Eberhardt and Min (2008) – BSR + PBR (sewage) Krishnan and Haridas (2008) 42.72 for all types of gels 0.4 M HCl (85%) Biswas et al (2007) 7.08 – BSR + PBR (with La(III)loaded SOW gel only) BSR + PBR (synthetic WW) + Field (real WW) BSR Significant desorption 20.045 (La/JB01) Ion 33.35(La/JB02) exchange + complexation of La(III) occurred under acidic condition +precipitation (pH < 4.5) Chemisorption + ion 5.1 exchange Reduced 8.9% of qm 28.79 after cycles Sorbent weight loss 3% after NaOH treatment – Distilled water pH (30%) pH 11 (50%) pH 3–11 (