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Partitionable-space enhanced coagulation (PEC)reactor and its working mechanism: A newprospective chemical technology for phosphoruspollution control

Meng Zhang a, Ping Zheng a,*, Ghulam Abbas a,b, Xiaoguang Chen c

aDepartment of Environmental Engineering, Zhejiang University, Hangzhou 310058, ChinabDepartment of Chemical Engineering, University of Gujrat, Gujrat, PakistancCollege of Environmental Science and Engineering, Donghua University, Shanghai 201620, China

a r t i c l e i n f o

Article history:

Received 24 May 2013

Received in revised form

19 September 2013

Accepted 11 October 2013

Available online 23 October 2013

Keywords:

Phosphorus removal

Ferrous salt

Partitionable-space enhanced coag-

ulation (PEC) reactor

Working performance

Process mechanism

* Corresponding author. Tel.: þ86 517 889828E-mail address: pzheng@zju.edu.cn (P. Zh

0043-1354/$ e see front matter ª 2013 Elsevhttp://dx.doi.org/10.1016/j.watres.2013.10.031

a b s t r a c t

Phosphorus pollution control and phosphorus recycling, simultaneously, are focus of

attention in the wastewater treatment. In this work, a novel reactor named partitionable-

space enhanced coagulation (PEC) was invented for phosphorus control. The working

performance and process mechanism of PEC reactor were investigated. The results showed

that the PEC technology was highly efficient and cost-effective. The volumetric removal

rate (VRR) reached up to 2.86 � 0.04 kg P/(m3 d) with a phosphorus removal rate of over 97%.

The precipitant consumption was reduced to 2.60e2.76 kg Fe(II)/kg P with low operational

cost of $ 0.632e0.673/kg P. The peak phosphorus content in precipitate was up to 30.44% by

P2O5, which reveal the benefit of the recycling phosphorus resource. The excellent per-

formance of PEC technology was mainly attributed to the partitionable-space and ‘floc-

culation filter’. The partition limited the trans-regional back-mixing of reagents along the

reactor, which promoted the precipitation reaction. The ‘flocculation filter’ retained the

microflocs, enhancing the flocculation process.

ª 2013 Elsevier Ltd. All rights reserved.

1. Introduction extraction (Cordell et al., 2009), and it is beneficial to promote

The world is facing a threat of eutrophication of water bodies

nowadays (Guo, 2007; Qu and Fan, 2010; Stone, 2011). Phos-

phorus pollution is a widespread and challenging environ-

mental problem. So, it is necessary to remove phosphorus

from wastewaters (Camargo et al., 2005; Barca et al., 2012; Li

and Brett, 2012). On the contrary, phosphorus is a non-

renewable resource and the existing phosphate reserves will

be exhausted in the next 50e100 years at the current rate of

19; fax: þ86 571 88982819eng).

ier Ltd. All rights reserve

the phosphorus recycle (Abelson, 1999; Bennett et al., 2001;

Gilbert, 2009). As stressed by the UN Millennium Develop-

ment Project, the phosphorus pollution control should be

combined with the phosphorus recycle (UN Millennium

Project, 2005).

Chemical phosphorus removal using metal-salts is an

important technology to solve phosphorus pollution problem,

with obvious advantages of high removal rate, simple opera-

tion and reliable performance. Despite its widespread use,

.

d.

wat e r r e s e a r c h 4 9 ( 2 0 1 4 ) 4 2 6e4 3 3 427

several deficiencies limit its further development, such as

high chemical cost and low phosphorus content in the formed

precipitates (de-Bashan and Bashan, 2004; Lee et al., 2004;

Parsons and Smith, 2008; Rittmann et al., 2011). In recent

years, no effort was spared to refine the chemical phosphorus

removal process. Szabo et al. (2008) prolonged the settling

time in sedimentation tank to provide longer contact time and

more opportunity for formation of chemical flocs through

sorption reactions, and additional phosphorus removal was

achieved as a result. A similar result was obtained by Caravelli

et al. (2012). However, a longer settling time would lead to a

larger volume of settling tank and more construction cost. Li

et al. (2009) applied Fe2þ/H2O2 for phosphorus removal.

Though, the Fe/P molar ratio was fairly decreased to 2.2 with

phosphorus removal efficiency of 96%. Additional H2O2 was

consumed, and strong oxidation of H2O2 would have adverse

effects on biological process. The procedural optimization is a

good way to reduce precipitant dose, and the effects of pH,

rapidmixing, settling time et al., on phosphorus removal were

carefully investigated (Lee et al., 2004; Banu et al., 2008; Szabo

et al., 2008; Zhang et al., 2013). The Fe/Pmolar ratio was hardly

achieved below 2.0 with phosphorus removal efficiency of

over 95%. Moreover, research on the phosphorus content in

the formed precipitates has rarely attracted attention, which

is essential for phosphorus reuse.

Solids-contact clarifier is a common found facility in

wastewater treatment plants (WWTP). Based on the contact

flocculation principle of solids-contact clarifier (Xu, 2000), a

novel reactor, called partitionable-space enhanced coagula-

tion (PEC) reactor was invented with a unique configuration to

overcome the weakness of traditional phosphorus removal

technologies. The PEC technology revealed an excellent per-

formance with regard to phosphorus removal and recycle,

owing to the partitionable-space and ‘flocculation filter’.

In this work, the working performances of traditional

phosphorus removal technology using batch experiments and

novel phosphorus removal technology with PEC reactor using

continuous experiments were investigated. A comparative

analysis between the two technologies was also conducted to

characterize the process mechanisms of the PEC reactor.

Fig. 1 e 1 e Schematic diagram of traditional system for

phosphorus removal by ferrous salt. 1. influent tank with

synthetic wastewater, 2. influent pump, 3. chemical

reagent tank with precipitant and NaOH, 4. chemical

reagent pump, 5. reaction tank, 6. impeller, 7. effluent. 2 e

Schematic diagram of PEC system for phosphorus removal

by ferrous salt. I. section (I) in reaction zone, II. section (II)

in reaction zone, III. section (III) in reaction zone, IV.

separation zone. 1. influent tank with synthetic

wastewater, 2. influent pump, 3. influent jet, 4. chemical

reagent tank with precipitant and NaOH, 5. chemical

reagent pump, 6. PEC reactor, 7. sediment discharge, 8.

effluent.

2. Materials and methods

2.1. Synthetic wastewater and precipitant

In both batch and continuous experiments, phosphorus was

supplied in the form of KH2PO4, and ferrous salt was supplied

as a precipitant in the form of FeSO4$7H2O. The concentra-

tions of KH2PO4 and FeSO4$7H2O were 10.0 g P/L and 20.1 g

Fe(II)/L, respectively, and they were diluted as needed before

the experiments.

2.2. Experimental set-up and analysis

The traditional phosphorus removal technology was carried

out through the jar test, which is shown in Fig. 1 e 1. In each

test, 150 ml of synthetic wastewater and ferrous salt were

taken into a 250ml glass beaker and theyweremixed for 1min

at 200 r/min followed by 15min at 50 r/min. Then, the reaction

products were allowed to settle for 30 min before the super-

natants were collected through a membrane filter with a

nominal pore diameter of 0.45 mm (APHA, 1998). A synthetic

wastewater with initial phosphorus concentration of

95.3 � 0.4 mg/L was prepared. The precipitant (FeSO4$7H2O

with concentration of 20.1 g/L) was added according to the Fe/

P molar ratio of 0.375, 0.75, 1.125, 1.50, 2.25, 3.00, 4.50,

respectively. NaOH with concentration of 2.0 mol/L was used

to alkalize the reaction pH. Pre-experiment was conducted to

estimate the necessary amount of NaOH for keeping the

effluent pH at about 7.0. The ferrous salt and NaOH were

added separately to the synthetic wastewater at the same

0 100 200 300 400 500 600 700 800 9000

20

40

60

80

100

Ferrous salt , (mg/L)

Phosphorus removal Phosphorus residual

Phos

phor

us r

emov

al (

%)

0

20

40

60

80

100

Phosphorus residual (mg/L

)

Fig. 2 e Performance of traditional technology for

wat e r r e s e a r c h 4 9 ( 2 0 1 4 ) 4 2 6e4 3 3428

time. A control without precipitant was set to assess the

physical phosphorus removal. All tests were run in triplicates.

The novel phosphorus removal technology was carried out

through the PEC reactor. As shown in Fig. 1 e 2, the PEC reactor

was made of plexiglass column with a distribution zone, a re-

action zone and a separation zone. The bottom part was the

distribution zonewith an influent jet to achieve reasonablyhigh

upward velocities. The middle part was the reaction zone,

which was partitioned into three sections, namely, section (I),

section (II) andsection (III), fromthecenter to thewall of reactor.

The upper part was separation zone (IV). The influent jet in

distribution zone togetherwith thedifferent crossareas of three

sections in reaction zone gave rise to variable velocities in the

reactor, resulting in the enhancement of coagulation. Synthetic

wastewater with different initial phosphorus concentrations

(32.09, 64.01, 93.30 mg/L) was prepared in 50 L sealed buckets.

And the ferrous salt (FeSO4$7H2O as precipitant), with concen-

tration of 20.1 g Fe(II)/L was added according to the Fe/P molar

ratio of about 1.50. NaOH with concentration of 2.0 mol/L was

used to alkalize the reaction pH. Pre-experiment was also con-

ducted to estimate the necessary amount of NaOH for keeping

the effluent pH at about 7.0. The synthetic wastewater, ferrous

salt and NaOH were pumped into the bottom of section (I) in

reaction zone to develop a continuous mode. The PEC reactor

was operated for more than 20 h. The mixed liquid, along with

the precipitates formed ran through section (I), (II) and (III) in

sequence. After a solideliquid separation process in separation

zone (IV), the treatedwastewater released from the PEC reactor.

At the bottom of section (II) in reaction zone, part of the mixed

substrate would return to section (I) to form a circulation.

Excessive precipitateswere discharged through sludge outlet in

order to obtain an efficient continuous process. The configura-

tionparameters of PEC reactorwere: internal diameterF90mm,

the total height 270 mm, the total working volume 1.2 L. The

temperature of all the experiments was controlled at 25 � 1 �C(Yang et al., 2010; Zhang et al., 2013).

The volumetric removal rate (VRR, kg P/(m3 d)) was chosen

as an evaluation parameter to investigate the phosphorus

removal capacity of traditional and novel technologies. VRR

was calculated using Equation (1) where,Q (m3/d) is the flowof

influent,V (m3) is the volume of reactor, and Pin (kg/m3) and Pef

(kg/m3) are the phosphorus concentrations in the influent and

effluent, respectively.

VRR ¼ Q�Pin � Pef

�

V(1)

PV ¼ FeðIIÞaFeðIIÞd

� 100% ¼ 32�MFe

MP� Pa

FeðIIÞd� 100% (2)

3Fe2þ þ 2PO3�4 ¼ Fe3ðPO4Þ2ðsÞ (3)

The parameter precipitant validity percentage (PV, %,

Equation (2)) represents the validity of precipitant (ferrous

salt) for the phosphorus removal process in phosphorus

removal technologies (Zhang et al., 2013). In Equation (2),

Fe(II)a (mg/L) refers to the concentration of ferrous salt used

for reaction with phosphorus to form Fe3(PO4)2(S), Fe(II)d (mg/

L) refers to the initial dose of Fe(II), Pa (mg/L) refers to the

removed phosphorus to form Fe3(PO4)2(S) (Equation (3)). MFe

(56 g/mol) refers to the formula weight of iron. MP (31 g/mol)

refers to the formula weight of phosphorus.

2.3. Scanning electron microscopy (SEM)

Morphological characteristics of the precipitates were

observed using SEM model Ultra 55. The sample from tradi-

tional technology was obtained after treatment under the

condition of initial phosphorus concentration of 91.51 mg/L

and Fe/P ratio of 1.50. The sample from novel technology was

obtained from the section (III) in reaction zone, called ‘floc-

culation filter’, after treatment under the condition of initial

phosphorus concentration of 93.30mg/L and Fe/P ratio of 1.47.

All the precipitates were centrifuged at a speed of 5000 rpm,

and then vacuum dried for over 12 h, gold-coated by a sputter

and finally observed under scanning electron microscope.

2.4. Energy-dispersive X-ray spectroscopy (EDS) andanalysis

Elemental analysis of the precipitates was done using EDS

model 7426. The samples tested were the same as in SEM test.

Six points at the sample surface were chosen to determine

elemental contents. The elemental contents of phosphorus

were estimated using P (%) and P2O5 (%, Equation (4)) where,

MP2O5 (142 g/mol) and MP (31 g/mol) are the formula weight of

P2O5 and phosphorus, respectively.

P2O5 ¼ MP2O5

2MPP ¼ 2:29P (4)

2.5. Analytical methods

The samples were filtered through a 0.45 mm pore diameter

membrane and analyzed immediately after collection. The

determinations of PO3�4 , Fe2þ and total iron were performed

according to the standard methods (APHA, 1998). Phosphorus

concentrationwasmeasured by the ascorbic acid photometric

method with a detection limit of 10 mg P/L. The ferrous and

total iron concentrations were measured colorimetrically

using 1,10-phenanthroline. The detection limit of dissolved or

total concentration of iron can be as low as 10 mg Fe/L.

phosphorus removal by ferrous salt.

Table 1 e Operation parameters for treatment of wastewater with different initial phosphorus concentrations by noveltechnology.

Type Low concentration (A) Medium concentration (B) High concentration (C)

Initial phosphorus concentration, mg/L 32.09 64.01 93.30

Concentrated ferrous salt (FeSO4$7H2O)

concentration, mg/L

8294 17,541 17,843

Diluted ferrous salt concentration, mg/L 85.0 170.3 265.5

Hydraulic retention time (HRT), h 0.78 0.78 0.78

Initial Fe/P molar ratio 1.466 1.473 1.575

Effluent pH 6.84 � 0.44 6.76 � 0.49 6.83 � 0.55

0 2 4 6 8 10 12 14 16 18 20 22 240

10

20

30

40

50

60

70

80

90

100

Phosphorus removal Phosphorus residual

A

Phos

phor

us r

emov

al (

%)

0

3

6

9

12

15

18

21

24

27

30

Phosphorus residual (mg/L

)

0 2 4 6 8 10 12 14 16 18 20 220

10

20

30

40

50

60

70

80

90

100B

Phos

phor

us r

emov

al (

%)

0

10

20

30

40

50

60

70

Phosphorus residual, (mg/L

)

0 2 4 6 8 10 12 14 16 18 20 22 240

10

20

30

40

50

60

70

80

90

100

Phosphorus residual ( m

g/L)

Time( h)

Phos

phor

us r

emov

al (

%)

0

10

20

30

40

50

60

70

80

90

100C

Fig. 3 e Performance of novel technology for phosphorus

removal by ferrous salt. A, B and C refer to wastewater with

low, medium and high initial phosphorus concentrations,

respectively.

wat e r r e s e a r c h 4 9 ( 2 0 1 4 ) 4 2 6e4 3 3 429

3. Results and discussion

3.1. Performance of phosphorus removal by traditionaltechnology

Batch experiments were carried out with typical jar test to

investigate the working performance of traditional phos-

phorus removal technology. At the effluent pH value of

7.07� 0.15,more phosphorouswas removedwith the increase

of ferrous concentration as shown in Fig. 2. The residual

phosphorus was dependent on the concentration of ferrous

salt in the liquid and was also constrained by the discharge

standard. When the initial concentration was fixed at

95.3 � 0.4 mg/L, the phosphorus removal rate rose from

15.10 � 2.96% to 99.62 � 0.16% with the increase in ferrous

concentration from 64.60 mg/L (Fe/P molar ratio ¼ 0.38) to

776.70 mg/L (Fe/P molar ratio ¼ 4.51). Meanwhile, the residual

phosphorus decreased from 80.91 � 2.82 mg/L to

0.36 � 0.15 mg/L, which was already lower than the discharge

standard (0.5 mg/L) (MEP, 2002). The corresponding VRR went

up from 0.45 kg P/(m3 d) to 2.97 kg P/(m3 d).

The PV decreased as the initial ferrous salt concentration

rose. When the residual phosphorus met the discharge stan-

dard of 0.5 mg/L, ferrous salt requirement was up to

776.70 mg/L, leading to a significant low PV of 33.12%.

3.2. Performance of phosphorus removal by noveltechnology

Continuous experiments were carried out with the PEC

reactor to investigate the working performance of novel

phosphorus removal technology. Three types of wastewater

with different initial phosphorus concentrations were treated.

The operation parameters are listed in Table 1. As depicted in

Fig. 3 (A/B/C), little phosphorus was removed during the first

2 h, with respective residual phosphorus concentrations of

11.12 mg/L, 29.94 mg/L and 75.71 mg/L. The corresponding

phosphorus removal rates were 65.34%, 53.22% and 18.85% for

wastewater with low (A), medium (B) and high (C) initial

phosphorus concentrations, respectively. The phosphorus

removal rates improved progressively during 2e12 h, and it

was over 90% in the end. The PEC reactor reached a steady

state in the order of 6e10 HRT after 14 h (Villadsen et al., 2011).

The residual phosphorus for wastewater A, B and C decreased

to 0.01 � 0.02 mg/L, 1.52 � 0.87 mg/L and 2.87 � 1.37 mg/L,

respectively. The corresponding phosphorus removal rates for

wastewater A, B and C were 99.97 � 0.08%, 97.71 � 1.39% and

97.02 � 1.49%, respectively. With the increase of initial

wat e r r e s e a r c h 4 9 ( 2 0 1 4 ) 4 2 6e4 3 3430

phosphorus concentration, the VRR increased from 0.98 kg/

(m3 d) to 2.86 kg/(m3 d).

The novel technology offers obvious advantage over the

traditional technology with regard to PV. Taking wastewater C

with an initial phosphorus concentration of 93.30 mg/L as an

example, during the steady state of the PEC reactor, the

effluent pH value was 6.83 � 0.55 with the time. The ferrous

salt in the treated wastewater was beyond detection and the

phosphorus removal rate was 97.02� 1.49%. Therefore the Fe/

P molar ratio for reaction was calculated to be 1.528, which

well matched the theoretical stoichiometric ratio of 1.50,

shown as Equation (2) (Petrucci et al., 2004). The PV value was

97.02 � 1.49% according to Equation (1). Similar results were

obtained when wastewater A and B were treated with the PEC

reactor, and the PV values were 99.97 � 0.08% and

97.71 � 1.39%, respectively. In the traditional batch assays

with an initial phosphorus concentration of 95.30 mg/L and

initial Fe/P molar ratio of 1.50, the effluent pH value was

7.07 � 0.15. The ferrous salt and residual phosphorus in the

treated/supernatant wastewater were 8.25 � 1.14 mg/L and

28.39� 1.54mg/L, respectively. The PV value was decreased to

72.53% according to Equation (2), which was much lower than

that of the novel technology using PEC reactor.

The comparative results indicated that the PEC reactor was

applicable to treat wastewater with different initial phos-

phorus concentrations prior to traditional technology. More-

over, the high PV value led to operation cost of $ 0.632e0.673/

kg P by novel technology, which was much lower than that by

traditional technology (Lee et al., 2004; Banu et al., 2008; Szabo

et al., 2008), considering the price of FeSO4$7H2O to be $ 48.46/

ton (Global Chemical Network).

3.3. Process mechanism of the novel technology

3.3.1. Enhancement of precipitation reaction processThe phosphorus removal process by traditional technology

was investigated as a control to make clear the mechanism of

PEC reactor. The kinetics of phosphorus removal at different

Fe/P molar ratios was tested, starting with a similar initial

phosphorus concentration of about 92 mg/L. As shown in

0 5 10 15 200

10

20

30

40

50

60

70

80

90

100

(Phase I)

1000500100

Phos

phor

us R

esid

ual (

mg/

L)

Time (min)

Fe/P 1.0 Fe/P 1.5 Fe/P 3.01 min

50

(Phase II)

1

2

3

Fig. 4 e Kinetics of phosphorus removal at different ferrous

salt concentrations.

Fig. 4, two different phases were clearly observed in the

traditional technology, namely, fast reaction phase (I) and

slow reaction phase (II) (Szabo et al., 2008). Taking Fe/P molar

ratio of 1.50 as an example, the residual phosphorus concen-

tration reached the 27.08 mg/L within 1 min during the fast

reaction phase. But the residual phosphorus of 16.10mg/Lwas

achieved in 1140 min during the slow reaction phase.

Although the duration of phase (II) lasted thousands times

longer than that of phase (I), the amount of phosphorus

removal in fast reaction phase accounted for 85.53% in the

total phosphorus removal. So the fast reaction phase was far

more important than the slow reaction phase.

The comparison of wastewater treatment at different initial

Fe/Pmolar ratios is shown in Fig. 4. The amount of phosphorus

removal increased from 56.01 mg/L to 90.05 mg/L as the initial

Fe/P molar ratio increased from 1.0 to 3.0. In phase (I), the

amount of phosphorus removal was 79.80 mg/L at initial Fe/P

molar ratio of 3.0, much higher than 48.32 mg/L at initial Fe/P

molar ratio of 1.0. In phase (II) after 1140 min, the amount of

phosphorus removal was 9.88 mg/L (D3) at initial Fe/P molar

ratio of 3.0, only a little higher than 8.05 mg/L at initial Fe/P

molar ratio of 1.0 (D1). In other words, the amount of phos-

phorus removal increased significantly with the rise of initial

Fe/P molar ratio, especially for fast reaction phase (I). On the

contrary, the PV of ferrous salt decreased from 92.08% to 76.57%

as the initial Fe/P molar ratio increased from 1.0 to 3.0.

Although the flash mixing with impeller is a common

operation for traditional coagulation technology, it can exert a

negative effect on the phosphorus removal due to a sharp

decrease of precipitant concentration. So a unique internal

structure was designed in the novel PEC reactor to avoid the

mixing over the whole reactor. The partition of reaction zone

limited the trans-regional back-mixing of reagents along the

reactor, increased the precipitant concentration in the micro-

domain of section (I), and so, accelerated the precipitation re-

action, especially in the fast reaction phase. The formation of

large amount of precipitates in the micro-domain of section (I)

and section (II), in turn, promoted the subsequent flocculation.

The influent jet in distribution zone achieved a reasonably

high upward velocity. A negative pressure domain at the

bottom of section (I) would be created according to Bernoulli

equation (Spurk and Aksel, 2008). The negative pressure cause

part of the mixed liquid and precipitates in section (II) to re-

turn to section (I). A circulation of the substances between

section (I) and section (II) in reaction zone was produced,

Fig. 5 e The precipitates accumulation in section (III) of

novel PEC reactor.

Fig. 6 e Scanning electron micrograph of precipitate from the novel technology (A) and traditional technology (B). The

elements showed in the right EDS spectra were the elemental contents surpass 1% (wt).

Fig. 7 e Schematic diagram of enhancement of phosphorus

removal by the PEC reactor.

wat e r r e s e a r c h 4 9 ( 2 0 1 4 ) 4 2 6e4 3 3 431

which provided longer contact time and more opportunity for

formation of chemical flocs through during the sorption and

precipitation (Szabo et al., 2008; Caravelli et al., 2012). As a

result, additional phosphorus was removed.

3.3.2. Enhancement of flocculation processIn the novel PEC reactor, the precipitates produced in section

(I) and section (II) accumulated in section (III), which formed

the ‘flocculation filter’, as shown in Fig. 5. Comparing Fig. 5

with Fig. 3, it was found that the phosphorus removal rate

rose in 2e12 h with the progressive formation of ‘flocculation

filter’, implying a relationship between phosphorus removal

rate and precipitant accumulation in the PEC reactor.

The morphological characteristic of precipitates were

observed using SEM to characterize the phosphorus removal

by the ‘flocculation filter’. As shown in Fig. 6, the precipitate

from the ‘flocculation filter’ possessed larger particle size,

looser packing and rougher surface, which were largely

different from the precipitate in the traditional technology.

According to the principles of minimum Gibbs free energy

(Xi et al., 2007), substances have a favorable characteristics to

obtain a state of low energy. As for large particles with greater

surface area, there are saturation differences on the surface

possessing higher surface energy, which lead to the growth of

particles for attaining an equilibrium state (Jiang et al., 2013).

Therefore the precipitates in ‘flocculation filter’ can grow

easily into new large precipitates through agglomeration of

more ferrous ions and orthophosphate (from the liquid) on the

precipitates surface as shown in Fig. 7. In addition, the pro-

gressive formation of new precipitates induces a concentra-

tion gradient at the micro-domain of precipitates surface,

promoting the diffusion of solutes (ferrous and phosphorus).

Thus, higher phosphorus removal efficiency is achieved. The

rough surface of precipitates in ‘flocculation filter’ containing

diverse pores that ranges from micro to macro implies rela-

tively more adsorption sites exposed to adsorbates, resulting

in higher adsorption capacity of phosphorus (Xu, 2000; Shin

et al., 2004; Yang et al., 2010). On the whole, all the charac-

teristics enhanced the phosphorus removal and flocculation

process in the PEC reactor.

Table 2 and Fig. 6 show the elemental contents of iron and

phosphorus in precipitates. The average phosphorus contents

in precipitate from ‘flocculation filter’ were 10.94% by P,

25.06% by P2O5 with the peak value of 13.29% by P, 30.44% by

P2O5. And this phosphorus content (30.44%) was so high that it

equaled P2O5 contents of the standard rich-phosphate rock

(�30%) (Hao et al., 2011). Whereas the precipitates obtained

from traditional technology under similar condition con-

tained obviously lower phosphorus. Besides, the Fe/P molar

ratio of precipitates from ‘flocculation filter’ was lower by

38.27% than that from traditional technology. The result was

Table 2 e Elemental contents of Fe and P in theprecipitate.

Sample Aa Ba

Phosphorus,wt%

Iron,wt%

Phosphorus,wt%

Iron,wt%

1 11.45 48.76 12.03 29.51

2 8.70 36.03 8.81 29.11

3 12.63 31.81 8.62 32.70

4 7.22 40.88 4.02 57.21

5 12.36 37.60 4.81 51.74

6 13.29 41.82 4.49 50.33

Average 10.94 39.48 7.13 41.77

Fe/P mole

ratio

2.00 3.24

a A and B refer to precipitates from ‘flocculation filter’ in novel

technology and traditional technology, respectively.

wat e r r e s e a r c h 4 9 ( 2 0 1 4 ) 4 2 6e4 3 3432

in accordance with the high PV value of ferrous salt in the

novel technology.

4. Conclusions

The PEC reactor was invented and applied successfully to treat

phosphorus-containing wastewater with excellent perfor-

mances, suchasvolumetric removal rate (VRR)of2.86�0.04kgP/

(m3 d), phosphorus removal rate of over 97%, precipitant validity

(PV) of over 97%, and low operation cost of $ 0.632-0.673/kg P,

respectively.Theexcellentperformancewasmainlyattributed to

the partitionable-space and ‘flocculation filter’ which enhanced

the coagulation process. The partition limited the trans-regional

back-mixing of reagents along the reactor, and so promoted the

precipitation reaction. The ‘flocculation filter’ retained the

microflocs, and so promoted the precipitation, filtration and

adsorption processes. In addition, the phosphorus content in

precipitate was up to 30.44% by P2O5, which could be helpful for

phosphorus recycling. In further research, a prolonged operation

was necessary to test the feasibility of achieving an efficient,

stable and continuous phosphorus removal before imple-

mentation of the new chemical technology. Performance of PEC

reactor using real wastewater and the bioavailability of recycled

precipitates from the reactor for plants should also be investi-

gated to achieve the final goal of simultaneous phosphorus

pollution control and phosphorus recycling.

Acknowledgment

Financial supports of this work by Natural Science Foundation

of China (51278457) and Zhejiang Provincial National Science

Foundation (Z5110094) are greatly appreciated.

r e f e r e n c e s

Abelson, P.H., 1999. A potential phosphate crisis. Science 283(5410), 2015.

APHA (American Public Health Association), 1998. StandardMethods for the Examination of Water and Wastewater,twentieth ed. American Public Health Association,Washington D.C.

Banu, J.R., Do, K.U., Yeom, I.T., 2008. Effect of ferrous sulphate onnitrification during simultaneous phosphorus removal fromdomestic wastewater using a laboratory scale anoxic/oxicreactor. World J. Microbiol. Biotechnol. 24 (12), 2981e2986.

Barca, C., Gerente, C., Meyer, D., Cliazarenc, F., Andres, Y., 2012.Phosphate removal from synthetic and real wastewater usingsteel slags produced in Europe. Water Res. 46 (7), 2376e2384.

Bennett, E.M., Carpenter, S.R., Caraco, N.F., 2001. Human impacton erodible phosphorus and eutrophication: a globalperspective. Bioscience 51 (3), 227e234.

Camargo, J.A., Alonso, K., de la Puente, M., 2005. Eutrophicationdownstream from small reservoirs in mountain river ofCentral Spain. Water Res. 39 (14), 3376e3384.

Caravelli, A.H., Gregorio, C.D., Zaritzky, N.E., 2012. Effect ofoperating conditions on the chemical phosphorus removalusing ferric chloride by evaluating orthophosphateprecipitation and sedimentation of formed precipitates inbatch and continuous systems. Chem. Eng. J. 209, 469e477.

Cordell, D., Drangert, J.O., White, S., 2009. The story ofphosphorus: global food security and food for thought. Glob.Environ. Change-Human Policy Dimen. 19 (2), 292e305.

de-Bashan, L.E., Bashan, Y., 2004. Recent advances in removingphosphorus from wastewater and its future use as fertilizer(1997e2003). Water Res. 38 (19), 4222e4246.

Gilbert, N., 2009. Environment: the disappearing nutrient. Nature461 (7265), 716e718.

Global Chemical Network. http://net.chemnet.com.Guo, L., 2007. Ecology e doing battle with the green monster of

Taihu Lake. Science 317 (5842), 1166.Hao, X.D.,Wang, C.C., Jin,W.B., 2011. Overview of Phosphorus Crisis

andTechnologiesof ItsRecovery.HigherEducationPress, Beijing.Jiang, C., Jia, L.Y., He, Y.L., Zhang, B., Kirumba, G., Xie, J., 2013.

Adsorptive removal of phosphorus from aqueous solutionusing sponge iron and zeolite. J. Colloid Interf. Sci. 402, 246e252.

Lee, S.H., Iamchaturapatr, J., Polprasert, C., Ahn, K.H., 2004.Application of chemical precipitation for piggery wastewatertreatment. Water Sci. Technol. 49 (5e6), 381e388.

Li, B., Brett, M.T., 2012. The impact of alum based advancednutrient removal processes on phosphorus bioavailability.Water Res. 46 (3), 837e844.

Li, C.J., Ma, J., Shen, J.M., Wang, P., 2009. Removal of phosphatefrom secondary effluent with Fe2þ enhanced by H2O2 at naturepH/neutral pH. J. Hazard. Mater. 166 (2e3), 891e896.

MEP (Ministry of Environmental Protection), 2002. DischargeStandard of Pollutants for Municipal Wastewater TreatmentPlant. Ministry of Environmental Protection, Beijing.

Parsons, S.A., Smith, J.A., 2008. Phosphorus removal and recoveryfrom municipal wastewaters. Elements 4 (2), 109e112.

Petrucci, R.H., Harwood, W.S., Herring, F.G., 2004. GeneralChemistry: Principles and Modern Applications, eighth ed.Higher Education Press, Beijing, China.

Qu, J.H., Fan, M., 2010. The current state of water quality andtechnology development for water pollution control in China.Crit. Rev. Environ. Sci. Technol. 40 (6), 519e560.

Rittmann, B.E., Mayer, B., Westerhoff, P., Edwards, M., 2011.Capturing the lost phosphorus. Chemosphere 84 (6), 846e853.

Shin, E.W., Han, J.S., Jang, M., Min, S.H., Park, J.K., Rowell, R.M.,2004. Phosphate adsorption on aluminum-impregnatedmesoporous silicates: surface structure and behavior ofadsorbents. Environ. Sci. Technol. 38 (3), 912e917.

Spurk, J.H., Aksel, N., 2008. Fluid Mechanics, second ed. Springer,Verlag Berlin and Heidelberg.

Stone, R., 2011. China aims to turn tide against toxic lakepollution. Science 333 (6047), 1210e1211.

wat e r r e s e a r c h 4 9 ( 2 0 1 4 ) 4 2 6e4 3 3 433

Szabo, A., Takcas, I., Murthy, S., Daigger, G.T., Licsko, I., Smith, S.,2008. Significance of design and operational variable in chemicalphosphorus removal. Water Environ. Res. 80 (5), 407e416.

UN millennium project, 2005. Investing in Development: aPractical Plan to Achieve the Millennium Development Goals.Earthscan, New York.

Villadsen, J., Nielsen, J., Liden, G., 2011. Bioreaction Engineering,third ed. Springer Science þ Business Media, New York.

Xi, H.D., Sun, J., Tsourapas, V., 2007. A control oriented low orderdynamic model for planar SOFC using minimum Gibbs freeenergy method. J. Power Sourc. 165 (1), 253e266.

Xu, B.J., 2000. Water Treatment Theories and Principles. ChinaBuilding Industry Press, Beijing.

Yang, K., Li, Z.H., Zhang, H.Y., Qian, J.F., Chen, G., 2010. Municipalwastewater phosphorus removal by coagulation. Environ.Technol. 31 (6), 601e609.

Zhang, M., Zheng, K., Jin, J.J., Yu, X.Q., Qiu, L., Ding, S., Lu, H.F.,Cai, J., Zheng, P., 2013. Effects of Fe(II)/P ratio and pH onphosphorus removal by ferrous salt and approach tomechanisms. Separat. Purif. Technol. 118, 801e805.