Bioresource Technology 102 (2011) 2523–2528

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Bioresource Technology

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Removal of nutrients from piggery wastewater using struvite precipitationand pyrogenation technology

Haiming Huang a,⇑, Chunlian Xu a,b, Wei Zhang a

a Center for Environmental Engineering Design, Chinese Academy of Environmental Sciences, Beijing, 100012, Chinab Graduate School of Life and Environmental Sciences, University of Tsukuba, Tennodai, Tsukuba, Ibaraki, 305-8572, Japan

a r t i c l e i n f o

Article history:Received 27 July 2010Received in revised form 11 November 2010Accepted 12 November 2010Available online 19 November 2010

Keywords:MagnesitePiggery wastewaterNutrientsRecycling struviteStruvite precipitation

0960-8524/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.biortech.2010.11.054

⇑ Corresponding author. Tel.: +86 10 84935398; faxE-mail address: huanghaiming52hu@163.com (H.

a b s t r a c t

In this paper, removal of nutrients from piggery wastewater by struvite crystallization was conductedusing a combined technology of low-cost magnesium source in struvite precipitation and recycling ofthe struvite pyrolysate in the process. In the present research, it was found that high concentrations ofK+ and Ca2+ present in the solution significantly affected the removal of nutrients. When the struvite crys-tallization formed at the condition of dosing the magnesite pyrolysate at a Mg:N:P molar ratio of 2.5:1:1,and having a reaction time of 6 h, a majority of nutrients in piggery wastewater can be removed. Surfacecharacterization analysis demonstrated that the main components of the pyrolysate of the obtainedstruvite were amorphous magnesium sodium phosphate (MgNaPO4) and MgO. When the struvite pyrol-ysate was recycled in the process at the pH range of 8.0–8.5, the precipitation effect was optimum. Whenthe struvite pyrolysate was recycled repeatedly at pH 8.5 or without any adjustment of pH, the outcomeof the removal of the nutrients in both cases was similar. With the increase in the number of recycletimes, the performance of struvite precipitation progressively decreased. An economic evaluation showedthat the combination of using low-cost material and recycling of struvite was feasible. Recycling struvitefor three process cycles could save the chemical costs by 81% compared to the use of pure chemicals.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Nitrogen is an essential nutrient for living organisms; however,it can provoke water eutrophication when it is present in excess.Therefore, ammonia–nitrogen removal from wastewaters is ofimportance to prevent environmental pollution. Piggery wastesare considered to be a type of waste with the greatest environmen-tal impact because of the presence of high concentrations of organ-ic matters, nitrogen, and phosphorous in it. Usually, anaerobicdigestion is accepted as a principal method of clearing up a major-ity of organic matters in piggery wastes, but the problem of nutri-ent enrichment of the digestion liquor still remains (Obaja et al.,2003). The most common and economical method to remove nutri-ents from wastewater is through the biological process (Cooperet al., 1994). However, high content of ammoniacal nitrogen hasa toxic effect on microorganisms (Kim et al., 2008), which may leadto a decrease in the treatment effectiveness of the biological pro-cess. Struvite precipitation is a valid alternative for the removalof high ammonia concentrations from the anaerobically digestedliquor of piggery wastes due to its high removal effectiveness, reac-tion rate, and solid–liquid separation capability. Struvite (MAP,

ll rights reserved.

: +86 10 84935653.Huang).

MgNH4PO4�6H2O) is a white crystalline compound composed ofmagnesium, ammonium, and phosphate in an equal molar ratio(Di Iaconi et al., 2010). It also has a very low solubility.

Removal of ammonia as struvite has been widely investigatedon the treatment of wastewaters that is rich in ammonia, such asrare-earth wastewater (Huang et al., 2009), landfill leachate (DiIaconi et al., 2010), coking wastewater (Chen et al., 2009), semicon-ductor wastewater (Kim et al., 2009; Warmadewanthi and Liu,2009), and human urine (Ganrot et al., 2007). The removal rateof ammonia could be reached to 85% within 30 min under a molarratio of Mg:N:P of 1:1:1 for treating landfill leachate (Ozturk et al.,2003). Since the amount of PO4

3� and Mg2+ in wastewaters areusually inadequate, a great amount of phosphate and magnesiumsalts are required for the effective removal of ammonia. This leadsto a high operating cost, which hampers the widespread applica-tion of the struvite process. To solve this problem, many research-ers have used low-cost materials containing magnesium asmagnesium source of struvite precipitation, such as the byproductsgenerated in the production of magnesium oxide (Chimenos et al.,2003; Quintana et al., 2005; Quintana et al., 2008), the pyrolysateof magnesite (Huang et al., 2010), magnesite mineral (Gunayet al., 2008), bittern (Lee et al., 2003), and seawater (Kumashiroet al., 2001). In addition, process recycling of the struvite pyroly-sate for the reduction of operation cost was proposed by someresearchers (He et al., 2007; Türker and Çelen, 2007; Huang

Table 1Composition of piggery wastewater supernatant after solid–liquid separation.

Parameters Average values Standard deviation

pH 7.8 0.2COD (mg/L) 2388 238

2524 H. Huang et al. / Bioresource Technology 102 (2011) 2523–2528

et al., 2009; Zhang et al., 2009). However, the simultaneous use oflow-cost materials containing magnesium and the pyrolysate ofstruvite for ammonia removal has not yet been evaluated.

In earlier published literatures, there are some papers focusingon the pyrogenation and process recycling of struvite. For example,Kenichi et al. (1975) found that an ammonia removal of 86.3% wasachieved by recycling the pyrolysate of struvite, which was pro-duced in alkali solution and at 70–80 �C. Huang et al. (2009) intro-duced a technology of recycling struvite, which could achieve anammonia removal of 99% and remaining phosphorus of less than1 mg/L. He et al. (2007) reported that an ammonium-release ratiogreater than 96% could be reached when struvite was pyrolyzed inthe following conditions: OH�:NH4

+ = 1:1; decomposition temper-ature, 90 �C; heating time, 2 h. In addition, Zhang et al. (2009) con-sidered that the optimal condition for struvite pyrolysateproduction was controlled at an OH�:NH4

+ molar ratio of 2:1, aheating temperature of 110 �C, and a heating time of 3 h. The pyro-genation of struvite in NaOH solution could be depicted by the fol-lowing reaction equation:

MgNH4PO4 � 6H2OðsÞ þ NaOHðsÞ !MgNaPO4ðsÞ þ NH3ðgÞ þ 7H2OðgÞð4Þ

Zhang et al. (2009) reported that a NH4+–OH�–Mg2+–Na+–PO4

3�

solution system could be formed when struvite was mixed withNaOH solution. As the NH4

+–OH� structure was unstable, ammoniacould be released according to the Equation NH4

+ + OH� M NH3 +H2O when the NH4

+–OH�–Mg2+–Na+–PO43� solution system was

heated at a given temperature. As a result, the pyrogenation ofstruvite takes place, leading to the formation of MgNaPO4.

Struvite is an orthorhombic structure consisting of PO43� tetra-

hedral, Mg(6H2O)2+ octahedral and NH4+ groups held together by

hydrogen bands (Whitaker and Jeffery, 1970). MgNaPO4�7H2O isan isomorphous analogue with struvite. Besides, a large numberof other struvite analogues such as MgKPO4�6H2O, MgRbPO4�6H2O,MgTlPO4�6H2O, and MgCsPO4�6H2O have been reported (Mathewand Schroeder, 1979; Banks et al., 1975). As the stability of thestruvite analogues generally declines with the decrease in the sizeof the univalent ion (Banks et al., 1975), when MgNaPO4 was addedto a solution containing NH4

+, the Na+ in the MgNaPO4 could be re-placed by NH4

+ forming more stable MgNH4PO4�6H2O because thesize of NH4

+ is larger than that of Na+. Consequently, the reuse ofMgNaPO4 for ammonia removal was achieved.

The objective of this study is to investigate the struvite-precip-itation recycle technology with the use of low-cost magnesiumsources for ammonia removal, for the purpose of reducing thechemical cost of struvite precipitation. First, the effect of K+ andCa2+ in solution on struvite precipitation was evaluated by usingsynthetic swine wastewater. Second, the investigations focusedon the conditions of using the pyrolysate of magnesite as the mag-nesium source and the efficiency of ammonia removal from pig-gery wastewater by internally recycling struvite pyrolysate. Inaddition, the solid before and after the struvite pyrogenation werecharacterized by a scanning electron microscope (SEM), Fouriertransform infrared spectroscopy (FTIR), and X-ray diffraction(XRD). Finally, an economic evaluation of the recycle process wasperformed.

BOD5 (mg/L) 1035 164TN (mg/L) 1212 55NH3-N (mg/L) 985 31TP (mg/L) 182 19PO4

3–-P (mg/L) 161 11K (mg/L) 797 27Ca (mg/L) 135 23Mg (mg/L) 6.7 3.6Al (mg/L) 5.8 2.5Fe (mg/L) 2.1 0.8

2. Methods

2.1. Raw wastewater

The raw wastewater used in the experiments was the anaerobi-cally digested liquor of piggery wastewater, which was taken froma pig farm located in a city in Guangdong province. Before being

used, solid–liquid separation was performed. The composition ofthe supernatant is shown in Table 1.

2.2. Chemicals for struvite formation

Piggery wastewaters generally contain negligible magnesiumand a low concentration of phosphate in comparison to ammonia(NH3-N) (see Table 1). For the effective removal of ammonia, somephosphate and magnesium salts are required to be added. In thisstudy, the pyrolysate of magnesite that calcined at 700 �C for1.5 h and with a 53% Mg content was used as a source of magne-sium in struvite precipitation (Huang et al., 2010). The originalmagnesite mineral was purchased from Xinxing Magnesium Pow-der Plant (Liaoning Province, China). As for the phosphate source,H3PO4 (85%) was used. In addition, KCl, CaCl2, NH4H2PO4,MgCl2�6H2O, and Na2HPO4�12H2O of analytical grade were usedin this study.

2.3. Experiments for the influence of K+ and Ca2+

To study the effect of K+ and Ca2+ on the struvite precipitation ofpiggery wastewater, synthetic swine wastewater with a NH3-Nconcentration of 985 mg/L prepared by dissolving NH4H2PO4 intodeionized water was used. The experimental procedures are shownin the following. First, 200 mL synthetic wastewater was fed into ajar with an airtight lid. Second, MgCl2�6H2O was added to thewastewater at the Mg2+:NH4

+:PO43� stoichiometric molar ratio of

1:1:1, and then KCl (or CaCl2) was fed into the wastewater atK+:Mg2+ (or Ca2+:Mg2+) molar ratio range of 0–0.75. Third, the reac-tion solution was stirred by a magnetic stirrer for 15 min at pH 9.Last, the solution supernatant after a precipitation of 10 min wasfiltered through a 0.45-lm membrane filter for componentanalysis.

2.4. Experiments for the use of the magnesite pyrolysate

The use of the pyrolysate of magnesite (its main compositionwas MgO) as the magnesium source of struvite precipitation wasperformed at different magnesium:ammonia molar ratios (1.5–3.5). Experimental procedures are depicted as follows. 500 mL pig-gery wastewater and a given dose of magnesite pyrolysate wereadded to a jar with an airtight lid, and H3PO4 was supplementedto the stoichiometric ratio of struvite formation. The pH value ofthe supernatant was measured after the agitation was intermittedfor 1 min, at different time intervals (0.5–8 h). Thereafter, thesupernatant of 5 mL was removed and filtered through a 0.45-lm membrane filter for the component analysis. In addition,control experiments using magnesite pyrolysate and H3PO4 asmagnesium and phosphate sources was conducted by using pureMgCl2�6H2O and Na2HPO4�12H2O. The experimental procedures

H. Huang et al. / Bioresource Technology 102 (2011) 2523–2528 2525

were similar to that described in Section 2.3 (reaction time,15 min; precipitation time, 10 min; Mg2+:NH4

+:PO43�, 1:1:1).

2.5. Experiments for the recycle of the struvite pyrolysate

The struvite formed in 500 mL piggery wastewater under opti-mum conditions was collected using a 0.45-lm membrane filterand washed for three times with pure water, and then decomposedunder the following conditions: pyrogenation temperature, 110 �C;pyrogenation time, 3 h; NaOH:NH4

+; 1:1. All the resulting pyroly-sate was added to 500 mL wastewater. The mixed solution was agi-tated for 1 h at given experimental pH, having a precipitation timeof 10 min. This process was repeated four more times. After eachexperiment, the supernatant of the effluent was filtered througha 0.45-lm membrane filter for component analysis.

All the experiments were performed in triplicate, at a wastewa-ter temperature range of 23–25 �C. To prevent the volatilization ofammonia, the jars were airproofed during the reaction and thesamples taken were diluted with deionized water to the desiredconcentration.

2.6. Analytical methods

The composition of the piggery wastewater, ammonia, andphosphate of the effluent were determined according to the Stan-dard Methods (SEPA, 2002). The struvite before pyrogenation andthe pyrolysate after pyrogenation were washed with deionizedwater three times, dried in an oven at 35 �C for 48 h, and then char-acterized by SEM (FEI Quanta 400, America), FTIR (Bruker VEN-TEX70, Germany), and XRD (Philips Model PW1830).

3. Results and discussion

3.1. The effect of K+ and Ca2+

Fig. 1 reveals the removal efficiency of ammonia in the individ-ual presence of potassium and calcium ions as well as the remain-ing PO4-P as a function of the n(Cation):n(Mg2+) molar ratio. It canbe seen that there is an obvious decrease in ammonia removal andremaining PO4-P in the presence of Ca2+ and K+. At identical molarconcentration of metal ions, the ammonia-removal efficiency andremaining PO4-P concentration were lowest for Ca2+ present inthe solution, followed by K+. As shown in Fig. 1, when the molar ra-tios of Ca2+:Mg2+and K+:Mg2+ increased from 0 to 0.75, the removalefficiency of ammonia decreased from 87.7% to 58% and 79%,

0.00 0.15 0.30 0.45 0.60 0.7550

60

70

80

90

n(Cation):n(Mg2+)A

mm

onia

rem

oval

rat

io (

%)

0

20

40

60

Rem

. PO

4-P (

mg/

L)

K+ + NH4

+ Ca2+ + NH4

+

Fig. 1. Ammonia-removal ratio and remaining PO4-P concentration during struviteprecipitation at different n(Cation):n(Mg2+) molar ratios.

respectively, and there was a decrease in the remaining PO4-P con-centration from 58.7 mg/L to 0.3 mg/L and 48 mg/L, respectively.

The behavior of K+ in the solution could be explained by the fol-lowing reaction (Wilsenach et al., 2007):

Mg2þ þHPO3�4 þ Kþ !MgKPO4 þHþ ð1Þ

The K+ present in the solution could compete with NH4+ to form

the potassium struvite (Schuiling and Anrade, 1999; Di Iaconi et al.,2010). Nevertheless, the K-struvite is less stable than struvite anddecomposes with time when removed from the mother liquor(Banks et al., 1975). This may be a reason why the ammonia-removal ratio and remaining PO4-P concentration slowly decreasedwith the increase in the K+:Mg2+ ratio. As for Ca2+, its presencecould consume the PO4

3� available for struvite precipitationthrough the formation of calcium phosphate precipitation, inhibit-ing the generation of struvite crystal.

3.2. The use of the magnesite pyrolysate

The experimental results of the use of the magnesite pyrolysateas magnesium source are shown in Fig. 2(a–c). It was found thatwith increases in the Mg:N molar ratio and the reaction time, thesolution pH, ammonia-removal ratio, and PO4-P removal ratio alsoincreased. When the Mg:N molar ratio increased from 1.5 to 2.5 ata given reaction time, the ammonia and PO4-P removal ratio rap-idly increased, whereas further increases in the Mg:N range of2.5–3.5 caused a slow increase in the removal ratio of ammoniaand PO4-P. When the Mg:N molar ratio was 2.5 and the reactiontime was 6 h, the solution pH, the ammonia, and PO4-P removalratio were more than 8.6, 80%, and 96%, respectively. In order toobtain high removal efficiencies of nutrients, the struvite obtainedat the Mg:N molar ratio of 2.5 and reaction time of 6 h was adoptedin the subsequent recycle experiments.

The struvite formation with the use of magnesite pyrolysateproceeds by the following reactions:

MgOþ 2Hþ !Mg2þ þH2O ð2Þ

Mg2þ þHPO2�4 þ NHþ4 þ 6H2O!MgNH4PO4 � 6H2OþHþ ð3Þ

MgO has a very low solubility in the neutral solution. Neverthe-less, in this study, due to the presence of large amounts of H+

caused by the addition of phosphoric acid, the MgO present inthe magnesite pyrolysate can play a dual function on the struviteprecipitation perfectly, that is, neutralizing the H+ in solution andreleasing Mg2+ as magnesium source of struvite precipitation. Inthe previous literatures, there have been some papers reportingammonia removal by using low-grade MgO and the mechanismfor struvite formation involving the use of low-grade MgO has beendiscussed. Chimenos et al. (2003) proposed that the struvite forma-tion takes place on the surface of MgO particle instead of the bulksolution, which thereby stops further reaction of MgO. The mech-anism was also confirmed by Chen et al. (2009). In this work, in or-der to compare the ammonia-removal effect of the magnesitepyrolysate as magnesium source, pure MgCl2�6H2O was used andthe experimental results are shown in Fig. 3. From the figure, wecan observe that at the pH range of 8–8.5, the ammonia-removalratio reached the maximum of about 83%, with a residual concen-tration of PO4-P of 10 mg/L. Although the amount of active magne-sium in the experiments of using magnesite pyrolysate andMgCl2�6H2O as magnesium sources may be different, we can con-sider that using magnesite pyrolysate as the magnesium sourcecould achieve ammonia-removal efficiency, which may be closeto that of MgCl2�6H2O.

Time (h)

pH

1.5

2

2.5

3

3.5M

agne

sium

:Am

mon

iaa

0.5 2 3.5 5 6.5 8

Time (h)

Ammonia removal ratio (%)

0.5 2 3.5 5 6.5 81.5

2

2.5

3

3.5

Mag

nesi

um:A

mm

onia

b

0.5 2 3.5 5 6.5 8

Time (h)

Phosphorus removal ratio (%)

1.5

2

2.5

3

3.5

Mag

nesi

um:A

mm

onia

c

Fig. 2. Struvite precipitation with magnesite pyrolysate as magnesium source at different Mg:N molar ratios and reaction time (a) the variation of solution pH, (b) thevariation of ammonia-removal ratio, and (c) the variation of PO4-P removal ratio.

2526 H. Huang et al. / Bioresource Technology 102 (2011) 2523–2528

3.3. Process recycling of the collected struvite

3.3.1. Struvite pyrogenation and surface characterization analysisIn this work, SEM, FITR, and XRD analysis before and after pyro-

genation were performed to identify the transformation of thestruvite collected at a Mg:N molar ratio of 2.5:1 and a reaction timeof 6 h. SEM images showed that the pyrolysate was coarse in com-parison with the nonpyrolyzed struvite and their sizes were irreg-ular (3–30 lm). The FITR pattern indicated that the ammoniumcharacteristic bands (1435 cm�1) of the pyrolysate almost com-pletely disappeared compared to the struvite. This suggests thatammonia releases from struvite (Stefov et al., 2004). Further, inthe XRD analysis, the comparison before and after the pyrogen-ation of the struvite precipitate indicated that the characteristicpeaks of struvite disappeared after heating, and only the peaks ofMgO remained. The main composition of the pyrolysate could beconsidered to be the nonreacted MgO and amorphous magnesiumsodium phosphate (MgNaPO4).

3.3.2. The optimum pH for the struvite pyrolysate reuseThe solution pH is one of the most important controlling factors

for struvite crystallization reaction (Song et al., 2007). H3PO4,H2PO4

�, HPO42�, MgOH+, MgNH4PO4, MgPO4

�, MgH2PO4+ and

MgHPO4 can be formed in the system involving Mg2+, PO43� and

NH4+ aqueous solutions when the pH varied (Mijangos et al.,

2004). The optimum pH of struvite precipitation has been widelyinvestigated. In the previous literatures concerning struvite precip-itation of piggery wastewater, the optimum pH of 8.5 (Suzuki et al.,2002; Çelen et al., 2007), 9 (Jaffer et al., 2002), 8.9–9.25 (Nelsonet al., 2003), 9.5–10.5 (Song et al., 2007) was reported. In thisstudy, to determine the optimum pH for the reuse of the struvitepyrolysate, experiments were performed at a pH range of 6.5–10,with a reaction time of 1 h. The experimental results are shownin Fig. 4. It is observed that the remaining PO4-P concentration de-creased rapidly with the increase of the pH and reached 1 mg/L atpH 10. The maximum ammonia-removal ratio appeared in therange of 8–8.5, which was in agreement with that of pureMgCl2�6H2O. When the pH was over the optimum range, Mg3(PO4)2

and Ca3(PO4)2 were formed instead of struvite with an increase inthe pH, which lead to the decrease of phosphate available for stru-vite crystallization. Finally, this brought a decrease in the ammo-nia-removal ratio. When the pH was below the optimum range,the increase of H+ in the solution inhibited the struvite crystalliza-tion, resulting in the decrease of the ammonia-removal ratio.

3.3.3. Multirecycles of the struvite pyrolysateFor determining the effect of multirecycle precipitation, two

modes of reuse of the struvite pyrolysate, with a reaction time of

6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.050

60

70

80

Am

mon

ia r

emov

al r

atio

(%

)

pH

0

40

80

120

160

Rem

. PO

4-P (

mg/

L)

Fig. 4. The effect of pH on the process recycling of struvite pyrolysate, with reactiontime of 1 h.

1 2 3 4 540

50

60

70

80

Am

mon

ia r

emov

al r

atio

(%

)

Recycle time

0

20

40

60

80

100

Rem

aini

ng P

O4-P

(m

g/L

)

At pH 8.5 Without any adjustment of pH

Fig. 5. The performance of the struvite pyrolysate recycles at different recycletimes.

Table 2The market prices of the chemicals used and

6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.550

60

70

80

Am

mon

ia r

emov

al r

atio

(%

)

pH

0

30

60

90

120

Rem

. PO

4-P

(mg/

L)

Fig. 3. The ammonia and PO4-P removal ratios with MgCl2 and Na2HPO4 asmagnesium and phosphate sources at different pHs: the Mg2+:NH4

+:PO43� molar

ratio for struvite precipitation was 1:1:1.

H. Huang et al. / Bioresource Technology 102 (2011) 2523–2528 2527

1 h, were investigated. In the first mode, the pyrolysate was reusedat pH 8.5. In the second mode, the pyrolysate was added to thewastewater without any adjustment of pH. It was found fromthe experiments that in the second mode, the supernatant pH atthe end of reaction decreased from the initial 9.38 to 8.45 in thefifth cycle. In addition, it was observed that the ammonia-removalratio and the remaining PO4-P concentration in both modes werebasically close per cycle (Fig. 5). With the increase in recycle times,the ammonia-removal ratio decreased gradually, and the remain-ing PO4-P concentration increased. The increases of inactiveMg3(PO4)2 and Mg2P2O7 in recycled pyrolysate (Schulze-Rettmeret al., 2001) and the losses of Mg2+ and PO4

3� in the supernatantper recycle time might be responsible for this present result.Besides, the accumulation of some components from wastewater(e.g. potassium, calcium, Section 3.1) might also be a factor inhib-iting the formation of struvite in later cycles.

energy consumed in the experiments.

Chemicals/energy Price

Magnesite 0.013 $/kgH3PO4 (85%) 0.61 $/kgMgCl2�6H2O 0.079 $/kgNa2HPO4�12H2O 0.36 $/kgNaOH 0.32 $/kgEnergy consumption 0.1 $/kW�h

3.4. Economic evaluation of recycling struvite

Economic analysis of process recycling of struvite obtained withthe magnesite pyrolysate was carried out and compared to thestruvite precipitation using pure chemicals (without internal recy-cling of struvite). In this assessment, the manpower costs, as wellas the market values of the recovered struvite and ammonia were

not taken into account, and only the costs of the chemicals usedand energy consumed were considered. The market prices ofchemicals used and energy consumed in the calculations are givenin Table 2. It can be calculated that the total cost of chemicals andenergy is $10.3/m3 of piggery wastewater when pure MgCl2�6H2Oand Na2HPO4�12H2O were used for the formation of struvite in pig-gery wastewater, whereas it is $4.9/m3 of piggery wastewaterwhen the magnesite pyrolysate and H3PO4 were used withoutinternal recycling of struvite (see Table 3). The results of the eco-nomic analysis for internal recycling of struvite (Table 3) indicatethat the average costs decrease progressively with the increase ofcycles of struvite recycle, and about 59% of the average cost couldbe reduced by recycling struvite for three cycles. Further, in com-parison to the costs of using pure chemicals, the cost of recyclingstruvite obtained with the magnesite pyrolysate and H3PO4 forthree process cycles could be reduced by 81%. Thus, it can be seenthat this process can greatly lower the costs of struvite precipita-tion. In addition, the use of MgO and H3PO4 in struvite precipita-tion does not increase the salinity of wastewater, which isbeneficial to the biological treatment of the effluents.

In previous literatures, there are some papers reporting thereduction of struvite-precipitation cost. He et al. (2007) reducedabout 44% of chemical costs by recycling struvite for three cycles.

Table 3Economic analysis of the nutrients removal process by struvite precipitationcompared to struvite pyrogenation and recycle technology.

Cost for struvite precipitation with MgCl2 and Na2HPO4 ($/m3 ofwastewater)

10.3

Cost for struvite precipitation with magnesite pyrolysate and H3PO4

($/m3 of wastewater)4.9

Average cost for recycling the pyrolysate of struvite obtained withmagnesite pyrolysate and H3PO4

The average cost for 1 recycle cycle ($/m3 of wastewater) 2.97The average cost for 2 recycle cycles ($/m3 of wastewater) 2.32The average cost for 3 recycle cycles ($/m3 of wastewater) 2.0The average cost for 4 recycle cycles ($/m3 of wastewater) 1.81The average cost for 5 recycle cycles ($/m3 of wastewater) 1.68

2528 H. Huang et al. / Bioresource Technology 102 (2011) 2523–2528

Huang et al. (2009) decreased 48.7% of struvite-precipitation costby using a struvite-recycle technology, and Gunay et al. (2008) re-duced the operation cost by about 18% by using magnesite as amagnesium source.

4. Conclusions

The presence of high contents of K+ and Ca2+ in solution could in-hibit the formation of pure struvite. When the pyrolysate of magne-site was used as magnesium sources, a Mg:N molar ratio of 2.5:1 andreaction time of 6 h is required for a satisfactory nutrients removalfrom piggery wastewater (i.e. 80% of NH3-N and 96% of PO4-P).The multi-recycling of struvite pyrolysate in the recovery processwithout any pH adjustment may provide a sustainable method toremove nutrient from piggery wastewater. Using low-cost materialin combination with the process recycling of the struvite pyrolysateis as effective as and less costly than using pure chemicals.

Acknowledgements

The authors are indebted the anonymous reviewers for theirinsightful comments and suggestions that significantly improvedthe manuscript. This work was financially supported by Major Spe-cific Projects of National Science and Technology of China, ‘‘Controland Treatment of Water Pollution’’ (Grant Nos. 2009ZX07529-007).

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.biortech.2010.11.054.

References

Banks, E., Chianelli, R., Korenstein, R., 1975. Crystal chemistry of struvite analogs ofthe type MgMPO4 6H2O (M+ = potassium (1+), rubidium (1+), cesium (1+),thallium (1+), ammonium (1+). Inorg. Chem. 14 (7), 1634–1639.

Chen, T., Huang, X., Pan, M., Jin, S., Peng, S., Fallgren, P.H., 2009. Treatment of cokingwastewater by using manganese and magnesium ores. J. Hazard. Mater. 168,843–847.

Chimenos, J.M., Fernández, A.I., Villalba, G., Segarra, M., Urruticoechea, A., Artaza, B.,Espiell, F., 2003. Removal of ammonium and phosphates from wastewaterresulting from the process of cochineal extraction using MgO-containing by-product. Water Res. 37, 1601–1607.

Cooper, P., Day, M., Thomas, V., 1994. Process options for phosphorus and nitrogenremoval from wastewater. J. Inst. Water Environ. Manage. 8, 84–92.

Çelen, I., Buchanan, J.R., Burns, R.T., Robinson, R.B., Raman, D.R., 2007. Using achemical equilibrium model to predict amendments required to precipitatephosphorus as struvite in liquid swine manure. Water Res. 41, 1689–1696.

Di Iaconi, C., Pagano, M., Ramadori, R., Lopez, A., 2010. Nitrogen recovery from astabilized municipal landfill leachate. Bioresour. Technol. 101, 1732–1736.

Ganrot, Z., Dave, G., Nilsson, E., 2007. Recovery of N and P from human urine byfreezing, struvite precipitation and adsorption to zeolite and active carbon.Bioresour. Technol. 98, 3112–3121.

Gunay, A., Karadag, D., Tosun, I., Ozturk, M., 2008. Use of magnesit as a magnesiumsource for ammonium removal from leachate. J. Hazard. Mater. 156, 619–623.

He, S.L., Zhang, Y., Yang, M., Du, W., Harada, H., 2007. Repeated use of MAPdecomposition residues for the removal of high ammonium concentration fromlandfill leachate. Chemosphere 66, 2233–2238.

Huang, H.M., Xiao, X.M., Yan, B., 2009. Recycle use of magnesium ammoniumphosphate to remove ammonium nitrogen from rare-earth wastewater. WaterSci. Technol. 59 (6), 1093–1099.

Huang, H.M., Xiao, X.M., Yang, L., Yan, B., 2010. Removal of ammonium as struviteusing magnesite as a source of magnesium ions. Water Pract. Technol. 5.doi:10.2166/WPT.2010.007.

Jaffer, Y., Clark, T.A., Pearce, P., Parsons, S.A., 2002. Potential phosphorus recovery bystruvite formation. Water Res. 36, 1834–1842.

Kenichi E., Kaoru I., Kyoji T., 1975. Ammonia removal from wastewaters. JapanKokai 77 04 649, App1. 75/80, 538.

Kim, H.S., Choung, Y., Ahn, S., Oh, H.S., 2008. Enhancing nitrogen removal of piggerywastewater by membrane bioreactor combined with nitrification reactor.Desalination 223, 194–204.

Kim, D., Kim, J., Ryu, H.D., Lee, S., 2009. Effect of mixing on spontaneous struviteprecipitation from semiconductor wastewater. Bioresour. Technol. 100, 74–78.

Kumashiro, K., Ishiwatari, H., Nawamura, Y., 2001. A pilot plant study on usingseawater as a magnesium source for struvite precipitation. In: Paper Presentedat Second International Conference on the Recovery of Phosphorus from Sewageand Animal Wastes, Noordwijkerhout, The Netherlands, March 12–13.

Lee, S.I., Weon, S.Y., Lee, C.W., Koopman, B., 2003. Removal of nitrogen andphosphate from wastewater by addition of bittern. Chemosphere 51, 265–271.

Mathew, M., Schroeder, L.W., 1979. Crystal structure of a struvite analogue,MgNH4PO4 6H2O. Acta Crystallogr. B35, 11–13.

Mijangos, F., Kamel, M., Lesmesa, G., Muraviev, D.N., 2004. Synthesis of struvite byion exchange isothermal supersaturation technique. React. Funct. Polym. 60,151–161.

Nelson, N.O., Mikkelsen, R.L., Hesterberg, D.L., 2003. Struvite precipitation inanaerobic swine lagoon liquid: effect of pH and Mg:P ratio and determination ofrate constant. Bioresour. Technol. 89, 229–236.

Obaja, D., Macé, S., Costa, J., Sans, C., Mata-Alvarez, J., 2003. Nitrification,denitrification and biological phosphorus removal in piggery wastewaterusing a sequencing batch reactor. Bioresour. Technol. 87, 103–111.

Ozturk, I., Altinbas, M., Koyuncu, I., Arikan, O., Gomec-Yangin, C., 2003. Advancedphysico-chemical treatment experiences on young municipal landfill leachates.Waste Manage. 23, 441–446.

Quintana, M., Colmenarejo, M.F., Barrera, J., Sánchez, E., García, G., Travieso, L., Borja,R., 2008. Removal of phosphorus through struvite precipitation using a by-product of magnesium oxide production (BMP): Effect of the mode of BMPpreparation. Chem. Eng. J. 136, 204–209.

Quintana, M., Sanchez, E., Colmenarejo, M.F., Barrera, J., Garcia, G., Borja, R., 2005.Kinetics of phosphorus removal and struvite formation by the utilization of by-product of magnesium oxide production. Chem. Eng. J. 45, 2211–2216.

Schuiling, R.D., Anrade, A., 1999. Recovery of struvite from calf manure. Environ.Technol. 20 (7), 765–768.

Schulze-Rettmer, R., von Fircks, R., Simbach, B., 2001. MAP precipitation pilot plantinvestigation in Germany. In: Proc. 2nd International Conference onPhosphorous Recovery for Recycling from Sewage and Animal Wastes,Noordwijkerhout, The Netharlands, March 12–14.

Song, Y., Yuan, P., Zheng, B., Peng, J., Yuan, F., Gao, Y., 2007. Nutrients removal andrecovery by crystallization of magnesium ammonium phosphate from syntheticswine wastewater. Chemosphere 69, 319–324.

Stefov, V., Soptrajanov, B., Spirovski, F., Kuzmanovski, I., Lutz, H.D., Engelen, B., 2004.Infrared and Raman spectra of magnesium ammonium phosphate hexahydrate(struvite) and its isomorphous analogues. I. Spectra of protiated and partiallydeuterated magnesium potassium phosphate hexahydrate. J. Mol. Struct. 689,1–10.

Suzuki, K., Tanaka, Y., Osada, T., Waki, M., 2002. Removal of phosphate, magnesiumand calcium from swine wastewater through crystallization enhanced byaeration. Water Res. 36, 2991–2998.

The State Environmental Protection Administration of China (SEPA), 2002. Editorialcommittee of ‘‘monitoring and analytical methods of water and wastewater’’.Monitoring and analytical methods of water and wastewater, 4th ed. ChinaEnvironmental Science Press, Beijing.

Türker, M., Çelen, I., 2007. Removal of ammonia as struvite from anaerobic digestereffluents and recycling of magnesium and phosphate. Bioresour. Technol. 98,1529–1534.

Warmadewanthi, Liu, J.C., 2009. Recovery of phosphate and ammonium as struvitefrom semiconductor wastewater. Sep. Purif. Technol. 64, 368–373.

Whitaker, A., Jeffery, J.W., 1970. The crystal structure of struvite, MgNH4PO4 6H2O.Acta Crystallogr.B 26, 1429–1440.

Wilsenach, J.A., Schuurbiers, C.A.H., van Loosdrecht, M.C.M., 2007. Phosphate andpotassium recovery from source separated urine through struvite precipitation.Water Res. 41, 458–466.

Zhang, T., Ding, L., Ren, H., Xiong, X., 2009. Ammonium nitrogen removal fromcoking wastewater by chemical precipitation recycle technology. Water Res. 43,5209–5215.