A new hybrid treatment system of bioreactors and electrocoagulation for superior removal of organic and nutrient pollutants from municipal wastewater

A new hybrid treatment system of bioreactors and electrocoagulationfor superior removal of organic and nutrient pollutants from municipal wastewater Dinh Duc Nguyena, Huu Hao Ngob, Yong

licensing copies, or posting to personal, institutional or third party

websites are prohibited.

In most cases authors are permitted to post their version of the article (e.g in Word or Tex form) to their personal website or institutional repository Authors requiring further information regarding Elsevier’s archiving and manuscript policies are

encouraged to visit:

http://www.elsevier.com/authorsrights

A new hybrid treatment system of bioreactors and electrocoagulation

for superior removal of organic and nutrient pollutants from municipal

wastewater

Dinh Duc Nguyena, Huu Hao Ngob, Yong Soo Yoona,⇑

a

Department of Chemical Engineering, Dankook University, Republic of Korea

b

School of Civil and Environmental Engineering, University of Technology, Broadway, Sydney, NSW 2007, Australia

h i g h l i g h t s

A new hybrid system consisting of RHMBR, MBR and EC was developed

Complete nitrification was achieved by the combination explored

T-N concentration in treated effluent of this system was low (3.81 ± 0.9 mg/L)

The system effectively eliminated phosphorus (0.03 ± 0.024 mg/L in treated effluent)

a r t i c l e i n f o

Article history:

Received 3 October 2013

Received in revised form 16 November 2013

Accepted 19 November 2013

Available online 27 November 2013

Keywords:

Integrated hybrid system

Municipal wastewater

Phosphorus

Nitrogen

Internal recycling ratio

a b s t r a c t

This paper evaluated a novel pilot scale hybrid treatment system which combines rotating hanging media bioreactor (RHMBR), submerged membrane bioreactor (SMBR) along with electrocoagulation (EC) as post treatment to treat organic and nutrient pollutants from municipal wastewater The results indicated that the highest removal efficiency was achieved at the internal recycling ratio as 400% of the influent flow rate which produced a superior effluent quality with 0.26 mgBOD5L1, 11.46 mgCODCrL1, 0.00 mgNHþ

4-N L1, and 3.81 mgT-N L1, 0.03 mgT-P L1 During 16 months of operation, NHþ

4-N was completely eliminated and T-P removal efficiency was also up to 100% It was found that increasing in internal recycling ratio could improve the nitrate and nitrogen removal efficiencies Moreover, the TSS and coliform bacteria concentration after treatment was less than 5 mg L1and 30 MPN mL1, respec-tively, regardless of internal recycling ratios and its influent concentration

Ó 2013 Elsevier Ltd All rights reserved

1 Introduction

The increase of inorganic nutrients in naturally receiving

non-point sources, especially nitrogen and phosphorus, can induce

eutrophication, causing negative effects on water resource quality

nutrient enrichment of surface waters, a number of wastewater

treatment plants have adopted various treatment systems that

can highly and simultaneously remove nitrogen and phosphorus

from wastewater Among those, biological nutrient removal

pro-cesses, such as suspended and attached growth biofilm techniques,

have been developed and widely applied due to their economic

Compared to the common activated sludge process, biofilm pro-cesses are increasingly being employed in wastewater treatment because of their advantages due to smaller facility operating areas footprints, ease of operation, short hydraulic retention time (HRT), insensitivity to organic and hydraulic shock loading, and higher

other work units Nowadays, several new biofilm technologies, based on the modification of existing processes, have attracted a great deal of attention from those responsible for treating

performance of the down-flow hanging sponge (DHS), which was preceded by an up-flow anaerobic sludge blanket (UASB) for treat-ing sewage and showed removal rates of 94.3%, 89.7% and 55.9% for

re-ported that the integrated fixed-film activated sludge (IFAS) with

a media of extruded high density polyethylene demonstrated

0960-8524/$ - see front matter Ó 2013 Elsevier Ltd All rights reserved.

⇑ Corresponding author Tel.: +82 31 8005 3539; fax: +82 31 8021 7216.

E-mail addresses: nguyensyduc@gmail.com (D.D Nguyen), chemyoon@unitel.

co.kr (Y.S Yoon).

Bioresource Technology

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / b i o r t e c h

higher removal efficiencies of 90%, 90% and 85% for COD, TP

and ammonia, respectively, with a solids residence time (SRT) of

hybrid activated sludge/biofilm process for wastewater treatment

in a cold climate region: Influence of operating conditions The

results showed that the average removal efficiencies of total COD

and ammonium were higher than 76% and 70–99% for HRT of

3.5 h and 4.5 h, respectively One of the biofilm support media is

made of plastic They use various forms/types of plastic, such as

Hence, when selecting a suitable biofilm carrier media for use in

Gonzalez-Martinez, 2003; Levstek and Plazl, 2009; Nacheva and

surface area to support the high-density presence of active

micro-organism; (ii) it must have a low apparent specific weight per

square centimeter, yet be strong enough to support the added

weight of the cultured biomass; and (iii) the material used must

be durable and highly resistant to environmental conditions, for

effectiveness and longevity As PE & PP media met these conditions

well, they were chosen as the carrier media to be used for the

RHMBR in this study

In recent years, membrane bioreactor (MBR) processes have

been widely used to reduce or eliminate nutrients due to their

advantages over other conventional activated sludge systems

These advantages include a smaller footprint, less sludge

produc-tion, high organic loading rate, highly improved effluent quality,

water reuse and potential for removal of pathogenic

con-ventional submerged MBR is limited because its configuration does

not compensate for anaerobic or anoxic conditions that hinder

Phosphorus discharge standards for municipal wastewater in all

developed and developing countries have become increasingly

stringent, while the phosphorus concentrations in final effluent

from Biological Wastewater Treatment Systems has been difficult

to manage These limitations have caused levels to exceed more

technology Thus, there is a need to explore novel and applied

advanced technologies to create high efficiency in phosphorus

removal The criterion for these technologies is restrictive They

must use less space, lower capital investment; lower installation

cost; have lower operating and maintenance costs, and eliminate the need for additional, frequent, and expensive chemical use

pro-cess study was applied as a post treatment add-on, with potential for reasonably easy retrofitting to existing facilities

In this study, a hybrid system consisting of RHMBR – SMBR with

EC as post treatment was developed and implemented as a pilot scale unit to treat municipal wastewater The objectives of this study were: (1) to investigate the performance of an integrated hy-brid system to remove organics, nitrogen, and phosphorus with re-spect to the nitrogen and phosphorus loading rate as a function of operation time or hydraulic residence times; and biological and non-biological phosphorus removals in the hybrid system were also studied; (2) to determine the efficiency of T-N, and T-P removal at different initial concentrations; and (3) to evaluate the efficiency of denitrification and nitrification toward total nitrogen removal at different internal recycle ratios of a long-term, real-world operation

2 Methods 2.1 Experimental set-up and description Experiments were conducted using a large pilot-scale hybrid RHMBR MBR and EC located at the municipal wastewater treat-ment plant (WWTP) of Y City, Korea, for 475 days of continuous

using an external steel framework and pre-fabricated PDF wall pa-nel tank system, with a lining made of high-density polyethylene (HDPE) inside (Gentrol Co., LTD., Korea) The equalizing reactor (EQ) with functioned to reduce variation in influent flow, influent pollutant concentrations/loads, and reduced oxygen concentration

in the internal recycle flows, and was divided into three compart-ments: EQ1, EQ2, and EQ3 They were constructed with a working

with electrolysis time of approximately 2 min The influent waste-water was pumped continuously from WWTP using two sub-merged pumps (Wilo Pump, Korea) to the pilot system, which

was passed through a fine screen (FS), with 5 mm openings, to remove the larger materials and avoid damage to the work units beyond, especially the membrane, prior to the wastewater flow

entering the EQ and then the RHMBR The primary-function of the

RHMBR is denitrification Secondly, it partially removes

phospho-rus, and, thirdly, it enhances contact between biomass with the

carbon source and nutrients in the wastewater The RHMBR

efflu-ent was treated using the MBR under aerobic conditions before

being discharged alternately through two automatic suction

pumps (P3, P4) Wastewater level in the MBR reactor was

con-trolled using level sensors The wastewater was allowed to flow

naturally from the EQ through the RHMBR to the MBR via gravity

flow to save capital costs

Both the equalizing reactor and RHMBR were agitated at

120 rpm and 0.16 rpm, respectively by a commercial agitator

(Hyup Dong Co., LTD., Korea) In RHMBR, fiber polypropylene

med-ia was hung on a mount and turned around the axis of the agitator

was 60 ± 5% based on the volume of the reactor for the attached

growth biomass The picture of polypropylene fiber media is

Two flat-sheet modules of submerged membrane in the MBR

were microfiltration membranes (model TC10A05, Yuasa

Corpora-tion, Korea) with outline dimensions of 1.3 m in length, 0.75 m in

width, and 1.52 m in height The number of membrane elements

was 75 per module The effective filtration area per membrane

operational trans-membrane pressure (TMP), in the range of 0.05

to 0.0 MPa, and the phenomenon of bio-fouling in the MBR were

monitored for changes in TMP via the vacuum gauge The

pri-mary-function of MBR is to maintain a high biomass density under

aerobic conditions and separation of particles larger than the

membrane pore size

Two air blowers (3 phase Ring blower, model HRB-402S, Hwang

Hae Electric Co., Ltd.) were operated alternately, maintaining an

uninterrupted air supply through an air diffuser system It was

in-stalled beneath the membrane modules to provide coarse bubble

oxi-dation and nitrification while helping to reduce the membrane

foul-ing and increase the sludge mixfoul-ing All pumps, agitators, air blowers,

electric valves, sensors, membrane backwashing system and other

equipment were automatically controlled by a programmable logic

controller (PLC) There was also a manual operating mode

A flow diagram of the EC process used in this study is shown in

hy-brid pilot plant was contained in a 200 L polypropylene tank From

this tank, wastewater was continuously pumped through the flow

meter in an upward axial flow through an annular region between

two coaxial cylinders of radius 5 cm and 9.5 cm in the EC reactor as

Supply (Sunchang Electronic Co., LTD., South Korea) which

in-cludes: voltage and current monitor, an on-off switch, and a

rheo-stat used to vary the desired output voltage In each channel of the

DC power supply, there are digital voltage meters with a voltage

response (0–30 V) monitor and current meter to set the applied

po-tential and current level

2.2 Operating conditions

Characteristics of raw and treated municipal wastewater used

The DO concentrations in the RHMBR and MBR were controlled

during the study period In addition, pH in each tank ranged from

6.6 to 8.0 Water flux and TMP were maintained in a range of

The MBR was operated for a 10 min cycle-filtration consisting of

9 min of filtration and 1 min of relaxation An internal recycle flow (R) rate from the MBR to the EQ (like a buffer tank) was performed

to carry out reduced oxygen concentration in the internal recycle, denitrification and phosphorus removal The recirculation flow rate was adjusted into the compartments (EQ1, EQ2, and EQ3) of EQ as

based on the influent flow rate, corresponding to Run 1, Run 2, Run 3 and Run 4, respectively The primary-function of MBR is to maintain a high biomass density under aerobic conditions and sep-aration of particles larger than the membrane pore size Through-out the study period, MLSS in the RHMBR and MBR was kept at

depending on the internal recycling ratio Excess sludge was dis-charged from the MBR tank to keep the MLSS concentrations at

HRTs of the individual reactors, recirculation ratios and other

The EC process consists of a pair of aluminum electrodes cyldrically shaped and placed in concentric cylinders together The in-side electrode has dimensions of 5 cm ID  45.5 cm H with a

dimen-sions of 9.5 cm OD  50 cm H with a geometric area of

constant electric potential of 10 volts (V) was applied with a hydraulic retention time of 2 min (more details are summarized

2.3 Analytical methods The influent, EQ, RHMBR, MBR and the effluent samples were collected 1–3 times per week to monitor the performance and kept

in a refrigerator prior to analyses The water quality parameters

liquor volatile suspended solids (MLVSS), mixed liquor suspended solids (MLSS), total suspended solids (TSS) and alkalinity were

Table 1 Characteristics of raw municipal wastewater.

NO 

3 -N mg L 1

NH þ

4 -N mg L 1

PO 3

Coliform bacterial MPN(100 mL) 1 1.5E + 6–2.0E + 7 7.56E + 06

Table 2 Distribution mechanism of internal recycle flows into the compartments of EQ Recirculation modes (internal recirculation value) EQ1 EQ2 EQ3

(PO34 -P) were analyzed with analyzer kits using

Spectrophotometer HS 3300, and an HS R200 Oven (Humas Co.,

LTD., Korea) Values for pH, and both dissolved oxygen (Martin &

Nerenberg) concentration and temperature were measured online

YSI 550A DO Instrument (YSI Environmental, US), respectively

All samples from EQ, RHMBR, MBR, and after EC treatment, were

3 Results and discussion

3.1 Ammonia nitrogen removal

ob-served that the nitrogen removal in this system was based on simple denitrification in RHMBR, followed by nitrification in MBR, where nitrifying bacteria convert nitrogen in the form of ammonia into nitrite and nitrate Nitrification is the important primary process in removing total nitrogen from influent waste-water However, its requirements of long SRT and high DO con-centration are usually considered as the limiting steps of the

means that the nitrification process in this system was fully

Table 3

Operational conditions of the hybrid pilot plant.

Influent flow rate (m 3

day 1

MLSS (g L 1

Sludge waste (L day 1

Operation cycle (min) 9 min filtration + 1 min idle

Specific aeration (m 3

airh 1

Chemical cleaning reagents NaOCl solution 0.5–1.2%

The average value is show in parentheses.

Table 4

Nitrogen removal during the operational period of different Runs.

Run 1

NO 

NH þ

Run 2

T-N (mg L 1

NO 

3 -N (mg L 1

NH þ

4 -N (mg L 1

Alk (mg L 1

Run 3

NO 

NH þ

Run 4

T-N (mg L 1

NO 

NH þ

4 -N (mg L 1

Alk (mg L 1

Alk = Alkalinity (mg CaCo 3 L 1 ).

a The values measured after filtering through glass microfiber filters 1.2lm.

entire study (Fig 2a) This complete and constant removal of

be explained by the process of agitation in the RHMBR was not completely mixed

during operation of the hybrid pilot plant was also determined,

In addition, during the monitoring period of hybrid system, the average alkalinity concentration in influent, RHMBR and MBR were 163.43 ± 19.06, 103.28 ± 12.65 and 71.89 ± 11.45, respectively The alkalinity in RHMBR was higher than that in MBR as in addition to being available in the inflow of wastewater, alkalinity is also

Table 5

The influent and effluent T-P, PO 3

4 -P concentrations and various key parameters of ratios versus phosphorus during the operational period of different Runs.

T-P of influent (mg L 1

PO34 -P of influent (mg L 1

T-P of effluent (mg L 1

PO 3

4 -P of effluent (mg L 1

T-P of final effluent a

0.03 ± 0.024 mg/L (99.33 ± 0.56%) T-P loading rate (g m 3

day 1

COD Cr /T-P ratio b

T-N/T-P ratio b

PO 3

NO 

3 -N/T-P ratio c

a

Using Electrocoagulation at post-treatment.

b

The ratio of influent wastewater.

c

The ratio of total nitrate to total phosphorus entering anoxic/anaerobic tank Values in the above table is the average values.

Table 6

Summary of some key operating parameters and results during operation of EC

process.

2 T-P of effluent without EC (mg L 1 ) 1.28 ± 0.41 (0.04–2.09)

3 T-P of effluent with EC (mg L 1 ) 0.03 ± 0.02 (0.00–0.11)

5 Electrical conductivity (lS cm 1 ) 460.02 ± 0.07 (431.00–

548.00)

7 Current densities (A m 2

8 Specific energy consumption, SEC

(kWh m 3 ) a

0.2733 ± 0.0104 (0.2573–

0.3002)

9 Specific aluminum consumption, SAC

(g m 3 )

9.1725 ± 0.3489 (8.6349–

10.0741)

10 The mole ratio of Al to T-P 8.4416 ± 2.2729 (5.3293–

15.1614)

11 Sludge generated (kg m 3

0.0437)

13 Hydraulic retention time (min) 2

14 Applied electric potential (Volts, V) 10

a

Electric energy consumption of EC process.

0 2 4 6 8 10 20 30 40

0 20 40 60 80 100

0.1 0.2 0.3

0.004 0.006 0.008 0.010

Influent (mg/L)

+ -N

MBR* (mg/L) RHMBR* (mg/L) Effluent (mg/L)

Removal efficiency (%)

Run 4 Run 3

Run 2 Run 1

NH4+-N loading (kg/m3.day)

(c)

(a)

(b)

A: NH4-N loading rate (Kg/m3.day) base on the volume of MBR

NH 4+

-N/MLVSS ratio B: NH4-N/MLVSS ratio base on the MLVSS in MBR

0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 6

9 12 15

(d)

C: CODCr/NH4-N ratio of the influent wastewater

Operation time (days)

CODCr/NH4-N ratio

Fig 2 Variations of NH þ

-N concentrations, NH þ

-N conversion efficiency, NH þ

-N loading rate, NH þ

-N/MLVSS, and COD /NH þ

-N ratio in the hybrid system during operation.

produced in denitrification under RHMBR condition and then is

partially consumed in the nitrification process under MBR

condi-tion The results indicated that there was enough buffering

avail-able in the wastewater for nitrogen, phosphorus removal process

in particular, and a biological process in general throughout all

runs

3.2 Total nitrogen removal and mechanism

The influent and effluent of T-N concentrations and T-N

nitrogen loading rater (NLR) based on the total volume of RHMBR

increased from 1.0 to 4.0, the T-N removal efficiencies increased

from 72.99 ± 5.95% to 90.42 ± 2.43%, which corresponds to the final

In this study, four recycle ratios 1, 2, 3, and 4 were investigated

The higher the recycle ratio (R), the better the nitrogen removal

was For example, the T-N removal efficiencies were increased

from 72.99 ± 5.59% (R = 1), 77.06 ± 5.99% (R = 2), 84.24 ± 4.09%

(R = 3) to 90.42 ± 2.43% (R = 4), respectively The results also

indi-cated that total nitrogen levels could be achieved less than

appropriate circulation rate should be used in Runs 3 or 4 in terms

of nutrient removal

However, the experimental results also demonstrated that the

the R strongly effected the T-N removal With an increase in the R,

nitrogen removal efficiency significantly improved The effect of

the R on nitrogen removal was also investigated in previous studies

shown that the T-N removal efficiency improved to 67% as the

internal recycle ratio was 300% of influent flow rate Similarly,

in-creased from 70 ± 9% to 89 ± 3% in a pre-denitrification membrane

process as the internal recycle ratio from aerobic to anoxic zone

in-creased from 2 to 6

Temperature is one of the important factors in the process of nitrification and denitrification During operation, the temperature was varied from 13.2 °C to 25.6 °C Depending on the variations of the internal cycling ratio, the biomass concentrations were

influ-ent flow rate were between 3.52 and 8.22, with an average

respectively The experimental results also suggested that there was enough carbon available in the municipal wastewater for re-moval of nitrogen in all runs, without adding an external carbon and energy source

con-centrations in the final effluent were low and significantly

demon-strated that the R influenced the nitrification and denitrification The increase in R improved the nitrification rate in MBR conditions

However, the nitrification efficiency was high enough to

the anoxic/anaerobic conditions of the RHMBR The RHMBR showed its important role in the denitrification process, which can provide media support for microbial growth utilizing excellent material, and agitation to increase contact with denitrifying bacte-ria In addition, these results also demonstrated that T-N removal efficiency increased with increasing in the internal recycling ratio

to the R However, an increased internal recycle ratio would in-crease the energy consumption, causing a subsequent inin-crease the operating costs

3 6 9 12 40 50 60 70

20 40 60 80 100

0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 0.05

0.10 0.15 0.20

0.05 0.10 0.15 0.20

T-N loading rate (kg/m3.day)

T-N Removal efficiency (%)

Run 1

Run 4 Run 3

Run 2

(a)

(c) (b)

Operation time (days)

4 6 8 10

4 6 8 10

Cr/T-N ratio of the influent wastewater

Fig 3 Variations of T-N concentrations, T-N removal efficiency, COD Cr /T-N ratio, and NLR in the pilot system during operation.

Consequently, it is suggested that the total recycling ratio can

be adjusted according to the effluent nitrogen requirements It is

important in choosing the best value internal recirculation by

requirements and a number of other parameters that would be

favorable to improving the effluent quality

3.3 Phosphorus removal

in influent, effluent, and in each tank’s total phosphorus removal

the influent wastewater in different phases throughout the study The influent T-P concentration fluctuation ranged between 3.00

ratio was in a range between 4.15 and 18.87 (average 7.87 ± 2.26)

In terms of the specific operating conditions, the average T-P

0.0 0.5 1.0

0.0 0.5 1.0 1.5

3 6 9 12

3 6 9 12

0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475

0.000 0.001 0.002 0.003

Influent (mg/L)

Run 4 Run 3

Run 2 Run 1

RHMBR* (mg/L)

- -N concentration (mg/

MBR* (mg/L)

Effluent (mg/L)

NO3--N/MLVSS ratio base on the MLVSS in RHMBR (e)

(d) (c) (b) (a)

Operation time (days)

- /MLVSS

Fig 4 Variations of NO 

3 -N concentrations, removal efficiency and NO 

3 -N/MLVSS in the pilot system during operation.

0 1 2 3 4 5 6 7 8 9

0 20 40 60 80 100 0

1 2 3 4 5 6 7

(d) (c)

(b)

T-P remv _without EC (%) T-P remv _with EC (%)

T-P conc eff._with EC (mg/L) T-P conc eff._without EC (mg/L) T-P con influent (mg/L) T-P con in RHMBR (mg/L)* T-P con in MBR (mg/L)*

Run 4 Run 3

Run 2 Run 1

40 60 80

(e)

Starting EC

T-P LR: T-P loading rate (kg/m 3 day)

CODCr/T-P ratio

0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 4

8 12 16

Operation time (days)

T-N/T-P ratio

10 20

3- -P con influent

PO

4 3- -P con influent (mg/L) PO

4 3- -P con effluent (mg/L)

-40 -20 0 20 40 60 80 100

PO43--P removal efficiency (%)

Fig 5 Variations of T–P concentrations and PO 3

4 -P concentrations, and removal efficiencies, T-P loading rate, COD Cr /T-P ratio, and T-N/T-P ratio in the pilot system during

removal efficiencies of the hybrid system without an EC process

73.44 ± 6.03%, corresponding to Rs 1, 2, 3 and 4, respectively These

results showed the influence of the internal recirculation flow on

the phosphorus removal performance of the system, and in

partic-ular, the effect of dissolved oxygen and nitrate concentrations,

T-P removal efficiency in the first phase was attributed to the effect

of high biomass production which occurred through assimilation

RHMBR as phosphorus was taken up under aerobic conditions in

the MBR by poly-phosphate accumulating organisms (PAOs), and

released under anoxic/anaerobic conditions in the RHMBR Although

these occurred simultaneously under the same conditions of anoxic/

anaerobic conditions, there was also a small portion of phosphorus

discharged from the MBR tank to keep the MLSS concentration at

nitrate to total phosphorus entering anoxic/anaerobic tank in

plant treated municipal wastewater throughout the study with

44.60:7.81:1.00, and 40.99:7.07:1.00 corresponding to Runs 1Q,

2Q, 3Q and 4Q, respectively

70.52 ± 11.33% with the values corresponding to Runs 1, 2, 3 and

the system was in ranged between 0.42 and 1 (average of

0.82 ± 0.17) It was found that T-P the most appropriate circulation

rate should be used in runs 2 or 3

This system also was successful in reducing the fouling of the membrane, as the membrane was only chemically cleaned in place during its year of operation using sodium hypochlorite (NaOCl) solution 0.5–1.2% (v/v) for 2 h without aeration This stabilized the system operation at a constant membrane permeation flux of 22.77 ± 2.19 LMH under ambient temperature conditions This reduced overall maintenance needs and increased operational efficiency of the system

3.4 Enhanced phosphorus removal by EC The hybrid pilot plant was operated without adding supple-mental reactive compounds (carbon sources, chemicals, etc.) to the solution which resulted in relatively good phosphorus

stringent regulations and wastewater reuse strategies, it is neces-sary to achieve phosphorus concentrations after treatment below

needed to achieve better efficiency in phosphorus removal

the membrane bioreactor averaged 0.94 ± 0.16, indicating that phosphorus in the effluent exists mainly as orthophosphate

(EC) process using cylindrical aluminum electrodes, was carried out continuously in the 145th to 316th day in post-treatment During that time, T-P concentration in final effluent showed that excellent T-P removal was achieved in the 145th to 316th inves-tigation days The highest effluent concentration detected during the course of the experiment using the EC process was

the T-P removal efficiency of the hybrid system combined with

EC process at post-treatment has now been shown, in practice,

as an excellent method with removal percentages of T-P main-tained stably and constantly at a high level of 97.23–100% (aver-age of 99.33 ± 0.56%) The corresponding concentration of T-P in

process, the efficiency was only in the range of 73.30 ± 8.65%

140 160 180 200 220 240 260 280 300 320

0.0 0.1 0.2 0.3 0.4 0.5

140 160 180 200 220 240 260 280 300 320 0.0

0.4 0.8 1.2 1.6 3 4 5 6 7 8 9

Current densities (A/m2) Removal efficiency (%)

Α Current (A)

Sludge generated (Kg/m3)

SAC (kg Al/m3)

The mole ratio of Al to T-P

SEC(kWh/m3)

Operation time (days)

0 5 10 15 20 25 30

0.0

2.0x

-3

4.0x

-3

6.0x

-3

8.0 x10

-3

1.0x

-2

3 )

0.0 0.1 0.2 0.3 0.4 0.5

(8)

(7) (7)

(6)

(5) (5)

3)

Run 4

discharge limit, 0.2mg/l

T-P conc influent (mg/L) Whithout EC treatment (mg/L) Whith EC treatment (mg/L) Conductivity (microS/cm)

0 20 40 60 80 100

0 1 2 3 4 5 6 7 8 9 10

Α Current (A)

0 80 160 240 320 400 480 560

(b)

(a)

(2) (2) (2)

(4)

(4)

(3)

(3)

(1)

(2) (2)

(1) (1)

Fig 6 Effect of the EC process on phosphorous removal, and variation of specific energy consumption (SEC), specific aluminum consumption (SAC), mole ratio of Al to T-P and sludge generated during operation of EC process.

Fig 6a showed that the effluent quality could stably and

signifi-cantly be maintained for phosphorus removal when the EC

fluctuations in the concentration of influent T-P

During the course of operating with the EC process in

continu-ous-flow, electrical energy consumption cost, amount of aluminum

used, and sludge generated per cubic meter of wastewater were

elec-trode used per cubic meter of wastewater treated would enable

operators to have a predictable plan for replacement of used

electrodes

The activity of the anode can decrease over time due to the

4, HCO3, SO24 , etc., in wastewa-ter This is caused by the precipitation of ions or the formation of

insoluble hydroxides, or sludge layers on the surface of the

elec-trodes These layers insulate the surface of the electrodes,

conse-quently reducing amperage and preventing the needed anode

2004; Chen, 2004; Martin and Nerenberg, 2012; Nguyen et al.,

operated to avoid these above concerns To find and establish the

optimum operating parameters for effective EC processing in this

experiment, a series of lab-scale experiments were done using both

synthetic wastewater and real municipal wastewater In this way,

the ideal operating conditions for effective EC processing were

prede-termined optimum condition for T-P removal with the advanced

aluminum electrodes in continuous mode, a hydraulic retention

time of 2 min, and application of a constant electric potential of

10 V, some of the highest removal rates ever achieved were

re-corded Other parameters measured during the course of the

EC experiment, the temperature and pH value were not altered

much, and remained in the range of 13.2–25.6 °C and 7.10–7.92,

respectively

In spite of the fact that a hybrid system with RHMBR and a

submerged MBR performed well in the biological treatment of

wastewater, some cases require stringent quality control of T-P

concentration after treatment These initial results show that this

method of combined EC processing as post-treatment promises to

be essential in meeting those requirements and extant stringent

regulations Consequently, further investigation is critically and

urgently needed for the broad implementation of this pragmatic

and effective methodological tool in the struggle to contain the

negative anthropomorphic impacts of phosphorus and related

wastewater pollution on surface and groundwater resources

worldwide

4 Conclusions

An integrated hybrid RHMBR and MBR system together with an

advanced EC process as post treatment performed extremely well

significantly affected on the nitrogen removal efficiency Due to the

completed nitrification, T-N in effluent was mainly in the form of

The EC process as post treatment proved highly efficient in

produc-ing high and stable levels of T-P removal

References

Ahn, Y.T., Kang, S.T., Chae, S.R., Lim, J.L., Lee, S.H., Shin, H.S., 2005 Effect of

treatment in the combined UBF/MBR system Water Sci Technol 51, 241–247

AWWA, WEF, APHA, 1998 Standard Methods for the Examination of Water and Wastewater, 20th ed American Public Health Association, Washington DC, USA.

Baeza, J.A., Gabriel, D., Lafuente, J., 2004 Effect of internal recycle on the nitrogen removal efficiency of an anaerobic/anoxic/oxic (A2/O) wastewater treatment plant (WWTP) Process Biochem 39, 1615–1624

Bektasß, N., Akbulut, H., Inan, H., Dimoglo, A., 2004 Removal of phosphate from aqueous solutions by electro-coagulation J Hazard Mater 106, 101–105

Chen, G., 2004 Electrochemical technologies in wastewater treatment Sep Purif Technol 38, 11–41

Chen, Y., Peng, C., Wang, J., Ye, L., Zhang, L., Peng, Y., 2011 Effect of nitrate recycling ratio on simultaneous biological nutrient removal in a novel anaerobic/anoxic/ oxic (A2/O)-biological aerated filter (BAF) system Bioresour Technol 102, 5722–5727

Cresson, R., Carrère, H., Delgenès, J.P., Bernet, N., 2006 Biofilm formation during the start-up period of an anaerobic biofilm reactor-impact of nutrient complementation Biochem Eng J 30, 55–62

Defrance, L., Jaffrin, M.Y., Gupta, B., Paullier, P., Geaugey, V., 2000 Contribution of various constituents of activated sludge to membrane bioreactor fouling Bioresour Technol 73, 105–112

Di Trapani, D., Christensso, M., Odegaard, H., 2011 Hybrid activated sludge/biofilm process for the treatment of municipal wastewater in a cold climate region: a case study Water Sci Technol 63, 1121–1129

Fan, J., Tao, T., Zhang, J., You, G.-L., 2009 Performance evaluation of a modified anaerobic/anoxic/oxic (A2/O) process treating low strength wastewater Desalination 249, 822–827

Guo, W., Ngo, H.-H., Palmer, C.G., Xing, W., Hu, A.Y.-J., Listowski, A., 2009 Roles of sponge sizes and membrane types in a single stage sponge-submerged membrane bioreactor for improving nutrient removal from wastewater for reuse Desalination 249, 672–676

Jou, C.-J.G., Huang, G.-C., 2003 A pilot study for oil refinery wastewater treatment using a fixed-film bioreactor Adv Environ Res 7, 463–469

Judd Simon, Claire, J., 2010 The MBR Book: Principles and Applications of Membrane Bioreactors for Water and Wastewater Treatment Elsevier, Oxford, UK

Khoshfetrat, A.B., Nikakhtari, H., Sadeghifar, M., Khatibi, M.S., 2011 Influence of organic loading and aeration rates on performance of a lab-scale upflow aerated submerged fixed-film bioreactor Process Saf Environ Prot 89, 193–197

Kim, H.-S., Gellner, J.W., Boltz, J.P., Freudenberg, R.G., Gunsch, C.K., Schuler, A.J.,

2010 Effects of integrated fixed film activated sludge media on activated sludge settling in biological nutrient removal systems Water Res 44, 1553–1561

Le-Clech, P., Chen, V., Fane, T.A.G., 2006 Fouling in membrane bioreactors used in wastewater treatment J Membr Sci 284, 17–53

Lee, W.S., Hong, S.H., Chung, J.S., Ryu, K., Yoo, I.-K., 2010 Comparison of the operational characteristics between a nitrifying membrane bioreactor and a pre-denitrification membrane bioreactor process J Ind Eng Chem 16, 546–

550

Levstek, M., Plazl, I., 2009 Influence of carrier type on nitrification in the moving-bed biofilm process Water Sci Technol 59, 875–882

Markus, John.A., Santroch, James.A., Tumuluri, Sailaja., Xi, Yun., Arifin, Anderson., Portman, D., 2011 Technical and Economic Evaluation of Nitrogen and Phosphorus Removal at Municipal Wastewater Treatment Facilities Engineering & Architecture Services Tetra Tech Inc .

Martin, K.J., Nerenberg, R., 2012 The membrane biofilm reactor (MBfR) for water and wastewater treatment: principles, applications, and recent developments Bioresour Technol 122, 83–94

Monclús, H., Sipma, J., Ferrero, G., Rodriguez-Roda, I., Comas, J., 2010 Biological nutrient removal in an MBR treating municipal wastewater with special focus on biological phosphorus removal Bioresour Technol 101, 3984–3991

Nacheva, P.M., Chavez, G.M., 2010 Wastewater treatment using a novel bioreactor with submerged packing bed of polyethylene tape Water Sci Technol 61, 481–

489 Nguyen, D.D., Kim, S.D., Yoon, Y.S., 2013 Enhanced phosphorus and COD removals for retrofit of existing sewage treatment by electro coagulation process with cylindrical aluminum electrodes Desalin Water Treat http://dx.doi.org/ 10.1080/19443994.2013.794707

Nguyen, T.T., Ngo, H.H., Guo, W., Johnston, A., Listowski, A., 2010 Effects of sponge size and type on the performance of an up-flow sponge bioreactor in primary treated sewage effluent treatment Bioresour Technol 101, 1416–1420

Oleszkiewicz, J.A., Barnard, J.L., 2006 Nutrient removal technology in North America and the European Union: a review Water Qual Res J Canada 41, 449–462

Orantes, J.C., Gonzalez-Martinez, S., 2003 A new low-cost biofilm carrier for the treatment of municipal wastewater in a moving bed reactor Water Sci Technol.

48, 243–250

Ozgur Yagci, N., Tasli, R., Artan, N., Orhon, D., 2003 The effect of nitrate and different substrates on enhanced biological phosphorus removal in sequencing batch reactors J Environ Sci Health A 38 (8), 1489–1497

Peng, Y.-Z., Wang, X.-L., Li, B.-K., 2006 Anoxic biological phosphorus uptake and the effect of excessive aeration on biological phosphorus removal in the A2O process Desalination 189, 155–164