Your Federal Quarterly Tax Payments are due April 15th Get Help Now >>

BIO-FOULING REDUCER IN SUBMERGED MEMBRANE BIOREACTOR FOR PALM - PDF by broverya77

VIEWS: 8 PAGES: 13

									Performance of Bio-Fouling Reducers In Aerobic
Submerged Membrane Bioreactor For Palm Oil Mill
Effluent Treatment
Adhi Yuniarto1, Zaini Ujang2, Zainura Zainon Noor3*
1,2,&3
       Institute of Environmental and Water Resource Management (IPASA),
       Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia.
     *
        Corresponding Author Email: zainura@fkkksa.utm.my

Published in
JURNAL TEKNOLOGI UTM
No. 49 (F), Dis. 2008
pp. 555-566




                                                                           1
Performance of Bio-Fouling Reducers in Aerobic
Submerged Membrane Bioreactor For Palm Oil Mill
Effluent Treatment
Adhi Yuniarto1, Zaini Ujang2, Zainura Zainon Noor3*
1,2,&3
       Institute of Environmental and Water Resource Management (IPASA),
       Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia.
     *
        Corresponding Author Email: zainura@fkkksa.utm.my

Abstract. Bio-fouling is one of the major challenges of submerged membrane
bioreactor operation, which reduces productivity and increases operational/main-
tenance cost. Powdered activated carbon, granular activated carbon and fine grained
zeolite were used as bio-fouling reducer (BFR) to reduce bio-fouling in membrane
and improve effluent qualities. A bench scale aerobic submerged membrane
bioreactor (ASMBR) was used to study bio-fouling behavior for palm oil mill
effluent (POME) treatment. A 20-liter reactor was set up using a flat sheet
microfiltration membrane equipped with continues fine air bubbles for bio-oxidation
and membrane scouring. Comparative result on ASMBR with and without BFR
adjunction was performed at constant flux and in a defined organic loading.
Experiments showed positive changes in trans membrane pressure (TMP), as well as
the improvement in effluent qualities. However a jelly-like biofilm layer was the
main reason for TMP increasing and bio-fouling.

Keywords : Bio-fouling reducer; membrane bioreactor; ASMBR; POME.


Abstrak. Bio-fouling merupakan salah satu daripada masalah utama di dalam
operasi membran bioreactor separa-tengelam. Serbuk karbon teraktif, granular karbon
teraktif dan serbuk halus zeolite telah digunakan untuk mengatasi masalah bio-
fouling di dalam membran dan juga untuk meningkatkan kualiti effluen. Membran
bioreaktor separa-tenggelam aerobik (ASMBR) telah digunakan di dalam kajian
berskala makmal untuk mengkaji ciri-ciri bio-fouling di dalam perawatan effluen air
sisa kelapa sawit. Reaktor bersaiz 20 liter telah dibina dengan mengggunakan 1
kepingan membrane penurasan mikro bersama gelembung udara halus secara
berterusan untuk proses bio-oksidasi dan untuk menggosok membrane. Perbandingan
ke atas ASMBR dengan Pengurang Bio-fouling (BFR) dan tiada BFR telah
dijalankan dengan aliran kekal dan pemuatan organik yang telah ditetapkan. Kajian
ini telah menunjukkan perubahan positif di dalam tekanan antara membran (TMP)
dan kualiti effluent. Walau bagaimanapun, didapati pembentukan lapisan lender pada
permukaan membrane masih merupakan punca utama peningkatan TMP dan
terjadinya bio-fouling.

Keywords : Pengurang Bio-fouling; membran bioreaktor; ASMBR; POME.




                                                                                 2
1.0. INTRODUCTION

Palm oil is the most important agriculture crop in Malaysia, covering about more than
three million hectares of the cultivated area. In 2007 Malaysia and Indonesia
remained as the world’s largest producers and exporters of palm oil, contributed for
87% of global production [1]. Unfortunately, this big agricultural and industry
activity generates a great amount of by product, known as palm oil mills effluent
(POME). Every ton of crude palm oil produced in factory, about 2.5-3.5 tons of
POME is generated [2]. In the year 2004, more than 40 million tonnes of POME was
generated from more than 370 mills in Malaysia. If the effluent is discharged
untreated properly, it can indisputably cause substantial environmental problems.
   Raw POME is a colloidal suspension that contains 95–96% of water, 0.6–0.7% of
oil and grease and 4–5% of total solids including 2–4% suspended solids originated
from the mixture of sterilized condensate, separator sludge and hydrocyclone
wastewater [3]. Typically with very high content of organic and oil, the resulting
POME is a thick brownish color liquid and discharged at a temperature between 80
and 90 oC. It is fairly acidic with pH ranging from 4.0 to 5.0. The POME
characteristic and standard discharge limit is summarized in Table 1.

Table 1 Characteristics of raw combine POME and its standard discharge limit by the
                      Malaysian Department of the Environment
          Parameters               Concentrations             Standart Limit,
                                        mg/L                      mg/L
   pH                                 4.2 – 5.1                    5-9
   BOD                            31,300 - 34,050                  100
   COD                            62,500 - 67,100                   ---
   Suspended solids               20,540 - 24,200                  400
   Total nitrogen                     872 - 912                    150
   Ammoniacal nitrogen                 36 - 46                      ---
   Oil and grease                 90,100 - 99,700                   50
   Temperature                         85 - 91                      45
  Except pH and temperature all other parameters are in mg/L, temperature in oC

   By increasing in number of replacing the conventional water and wastewater
treatment process, the membrane bioreactor (MBR) process has proved become a
feasible technology for water reclamation and producing of high quality treated water
[4]. MBR provides biological activated sludge treatment with filtration separation
where the membrane mainly uses to replace the clarifier as in the conventional
wastewater treatment. Among MBR are small footprint, low sludge production, and
high quality effluent. More specific advantages included complete separation of
suspended solids and bacteria by the membrane, possible to nitrify easily, reduce
hydraulic retention time (HRT) to a minimum by separating it with the sludge
retention time (SRT), uncomplicated operation especially because bulking



                                                                                   3
phenomenon does not effect to the liquid-solid separation, and MBR can also
function as a small-scale system [5].
    In the late of 1980s, submerged low pressure configurations of MBR was a
significant development to answer the lack of older MBR systems and also to reduce
operating cost. In this new configuration, membrane was directly submerged in
aeration tank containing the biological sludge and extracted the treated permeate [6].
Several methods that showed the development of submerged MBRs during 1980s -
1990s has been also affecting world-spread uses of submerged MBRs, including
submerged MBRs as an upgrade option for existing wastewater treatment plant [4, 7].
        It is generally known that fouling reduces the performance of the membrane.
When fouling occurs, a thick gel layer and cake layer is formed on and into the
membrane, resulting the permeate flux to decline, increase in hydraulic resistance and
operating costs due to the need for cleaning or changing the membrane. Fouling is
usually attributed to a number of parameters, such as sludge particle deposition,
adhesion of macromolecules such as extracellular polymeric substance (EPS), soluble
microbial products (SMP) and pore clogging by small molecules [8 - 11].
    A number of previous studies have focused on various factors that affect
membrane fouling in MBRs. Factors like the type of wastewater, sludge loading rate,
sludge age, mixed liquor suspended solid (MLSS) concentration, mechanical stress,
solid retention time, food-to-microorganism ratio and microbial growth phase are
known to affect the concentration of EPS and in turn to the evolution of membrane
fouling [12 - 14].
    Various techniques have been used to reduce membrane fouling. In aerobic
submerged membrane bioreactors, air bubbles can prevent the deposit forming on the
membrane surface [15]. Periodic backwashing improves membrane permeability and
reduces fouling, thus leading to optimal, stable hydraulic operating conditions [6, 10].
Adding flocculation–coagulation agents limits membrane fouling by aggrega-tion of
the colloidal fraction, thus reducing internal clogging of the membranes [16]. Several
materials have been added to the ASMBR to reduce bio-fouling. Previous studies
concerning activated carbon dosing in MBR have pointed out an increase in sludge
filterability and a decrease in the membrane fouling rate [17 – 21]. The addition of
zeolite on the membrane filter bioreactor has been enhanced the membrane
permeability [22].
    This paper aimed to conduct a better understanding on the effectiveness of Bio-
fouling Reducers in POME treatment, particularly to the membrane fouling
phenomenon and organic removal.

2.0. METHODOLOGY

The raw POME was obtained from Kilang Pertubuhan Petani Negeri Johor, Kahang
Johor, has a typical COD of about 65000 mg/L and had to be cooled and diluted
several times before feeding the reactor. Feed preparation in influent tanks and
sampling of its quality were done daily. The feeding characteristics are showed in
Table 2.




                                                                                      4
                    Table 2 Feeding characteristics (diluted POME)
        Parameter                         Range (mg/L, except pH)
           COD                                   1000  89
            TS                                    780  32
          Total N                                 14  2.1
          Total P                                3.2  1.29
   Ammoniacal Nitrogen                           0.83  0.23
          pH                                     6.11  0.12

   The laboratory experimental set-up is shown in Fig.1. The ASMBR consist of a
twenty liters reactor, where single module of flat sheet membrane was immersed in
the aerobic zone. The chlorinated polyethylene membrane module was provided by
Kubota Japan with nominal pore size of 0.4  m and effective area of 0.1 m2. The air
transported by the compressed air pipeline was fed into the reactor with a micro-
bubble diffuser installed beneath the membrane. It provided adequate oxygen to
maintain aerobic conditions for biomass growth as well as scoured the fouling on the
membrane surface to prevent cake accumulation on it. This air flow was monitored
with an air flow meter. The influent flow rate was controlled by a water level sensor
set in the reactor. Constant permeate flux was maintained with a variable speed
peristaltic pump. However the flux also controlled by measure it manually using a
calibrated cylinder and a stopwatch twice a day. A pressure transducer (PG-30 Copal
Elect.) measured trans membrane pressure and its data was recorded with RS232 Data
Logger software using a data logging system. The reactor was operated at room
temperature, and it was maintained to neutral pH.
   The working volume and operating condition of ASMBR are summarized in Table
3. The ASMBR was seeded with activated sludge obtained from a sewage treatment
plan in Kulai Johor Bahru. After run for achieving steady-state condition, the
experiments were initiated. The operational parameters during filtration process were
trans membrane pressure, organics removal (as COD) and permeate color. Initiate
experiment was the operation of BFR without bio-fouling reducer, and then followed
by BFR addition. No sludge was discharged during the operation period except
samplings and there was no further addition of BFR during ASMBR experimental
period.
                     Table 3 Operating conditions of the ASMBR
              Parameter                                  Value
Working volume, l                                          20
Temp., oC                                                25 – 27
pH                                                      6.8 – 7.7
Organicin, mg COD/l                                       1000
Qin, m3/d (l/h)                                         0.024 (1)
Organic loading, kg COD/m3.d                              0.024



                                                                                   5
Permeate Flux at constant rate, LMH                                  10
MLSS, mg/L                                                      4200 –
                                                          4000 to 8000 5400
HRT, h                                                               20
DO, mg/L                                                          6.6 – 7.9
Air flow, l/min                                                       6




                                                                            Computer
                                                  Pressure Gauge



                                  Water Leveler
       Influent Container
                                                                     Pump




                                             Flat sheet membrane




                                                                               Effluent Container




                            Air Diffuser


                                                                   Air Compressor

                        Figure 1 Flow diagram of ASMBR system

   Table 4 shows BFR type that used in this experiment. BFR have been dried for 24
hours and store in dry place before introduced it into ASMBR. Adsorption
experiment has been conducted as an approach method to determine BFR
concentration to be filled into ASMBR. A conventional jar apparatus with six-spindle
of steel paddles was used in this test. Six beakers with 0.5 liter of POME stirred
concurrently. Initial concentration of POME is 1000 mg COD/L. After adding BFR
into the suspension, the beakers were mixed for 1 min at 200 RPM and continued
with 20 hours at 50 RPM. After full stopped, suspensions were allowed to sediment
for 1 h with the supernatant being analyzed for organic concentrations. Variation of
BFR concentrations in the suspension were set in the range of 1 – 30 g/L.




                                                                                                    6
                            Table 4 BFR characteristics
      BFR type           Origin        Quality               Supplier
       BFR1          PAC, charcoal       PA         Fisher Scientific, Ltd.
       BFR2          GAC, charcoal       PA         Kanto Chemical Co. Inc.
       BFR3          Zeolite Powder Commercial Harta Semarak, Sdn. Bhd.

   Laboratory experiments associated with this study were carried out in the
Environmental Engineering Lab, Faculty of Civil Engineering, Universiti Teknologi
Malaysia. The activated sludge quality was regularly tested for mixed liquor
suspended solids (MLSS). Dissolved Oxygen (DO) concentration and temperature of
the activated sludge were measured using portable YSI 55 Dissolved Oxygen (YSI
Inc, Ohio USA). Also, pH was measured on site using Hanna pH211 pH meter
(Hanna Instruments, Bedfordshire UK). Color was analyzed using a
spectrophotometer (HACH/DR 5000). Parameter analyses were carried out according
to standard methods [23] immediately after samples were collected.

3.0. RESULTS AND DISCUSSION

Prior to the ASMBR experiment, adsorption experiment were carried out to
determine concentration of BFR. Figure 2 shows the organic removal percentage by
adsorption using BFR. BFR1 achieved the best performance in low concentration (1-
5 g/L) with 80 – 92% removal. The performance increased until almost 94.7% when
the BFR1 concentration was 8 gr/L, before the removal efficiency decreased even its
concentration increased to 30 gr/L. BFR2 removed 64% of organic at concentration 1
g/L and increased to 81% (8 g/L). Organic removal was only 83% when BFR2
concentration was 20 g/L. BFR3 had a better performance with 90.3% organic
removal on 8 g/L and still achieved higher organic removal when the concentration
was 30 g/L (93.3%).
   It was also proved that the concentration of BFR in the powder form was more
effective compared to the granular form. This is due to larger surface area of the BFR
powder and granular form. However the main reason why BFR2 considered to be
used in further experiment was in term of initial cost and ease of handle.
   From Figure 2 below, BFR1 of 8 g/L was selected to be filled into the ASMBR
because at higher concentration of BFR1, organic removal efficiency tended to
decrease. For BFR2 and BFR3, 8 g/L was also chosen as a dosage for further use,
because at higher BFR3 dosage there was no significant improvement of organic
removal.
   When the ASMBR operated without BFR, the increasing of TMP took place
gradually from the initiation to the end of the ASMBR operation at 120 hours, as
shows in Figure 3. The last TMP recorded was 13.6 kPa. The generation of gel layer
on the membrane surface of this operation was much thicker than other experiments
with BFR. This layer was observed in plain view after stopped the experiment and
removed the membrane. The layer generation was due to the production of SMP,




                                                                                    7
which could block membrane pores. Their accumulation demonstrated the natural
factor for membrane bio-fouling [11].

                                          100


                                          95


                                          90
           Organic (as COD) removal (%)




                                          85
                                                                                                   BFR1
                                                                                                   BFR2
                                          80                                                       BFR3


                                          75


                                          70


                                          65

                                                            Selected Dose
                                          60
                                                0   5        10             15      20        25      30   35
                                                                    BFR Concentration (g/L)
                                                        Figure 2 Organic removal by BFR

    Figure 3 also shows that the ASMBR with BFR had lower TMP development
compared to the system without BFR. TMP was remained stable at lowest pressure as
it was initiated when BFR1 and BFR2 were introduced into ASMBR; 2.8 kPa and 3.1
kPa, respectively. This is due to the direct adsorption of dissolved organic matters
onto BFR.
    BFR2, which is a granular form, tended to float or settle in the ASMBR. This
made it more difficult to disperse evenly in the activated sludge, resulting in a less
adsorption capacity to adsorb organic material. Therefore it is easier for organic
material to form cake layer on membrane surface, which made TMP in this system
higher than other BFR.
    On the other hand, the cake layer of the activated sludge was replaced by BF1 and
BF3 precoat layer with large porosity and non-compressibility, which reduced cake
resistance to water and oxygen transfer. As a result, TMP was decreased. These
phenomenon proved that the use of BFR mitigate the membrane fouling.
    Organic removal efficiency was measured during 120 hours of the ASMBR
system operation, which is shown in Figure 4. The results indicated that all systems
achieved excellent organic removals of over 94%. The addition of BFR increased the
ASMBR system to produce better permeate quality. This was due to the BFR
simultaneous functions of biodegradations (i.e. through attachment of biomass on its
surface) and adsorption of organic fractions. It was noted that BFR3 had a better
performance than other BFR.



                                                                                                                8
                     16


                     14


                     12


                     10
         TMP (kPa)


                                                                                   NoBFR
                             8


                             6
                                                                                                                          BFR2

                             4                                                                                                            BFR1


                             2

                                                                                                       BFR3
                             0
                                                  0            20                 40              60               80         100         120
                                                                                          Operation Time (hours)



                                            Figure 3 Trendline of Membrane Bio-fouling with BFR.

                                                  100

                                                                    BFR3




                                                                           BFR1
                     Removal Efficiency (% COD)




                                                      95
                                                               BFR2



                                                               NoBFR



                                                      90

                                                                                                                        CODrem NoBFR
                                                                                                                        CODrem BFR1
                                                                                                                        CODrem BFR2
                                                                                                                        CODrem BFR3


                                                      85
                                                           0        20             40             60          80        100         120
                                                                                        SMBR Operation Time (hours)

                                                                         Figure 4 Organic Removal

   The average organic removal during ASMBR operation without BFR, with BFR1,
BFR2 and BFR3 were 94.38%, 96.89%, 95.25% and 98.18%, respectively. It means
that organic removal for ASMBR with BFR1, BFR2 and BFR3 were increased by




                                                                                                                                                 9
2.46%, 0.87%, and 3.80%, respectively. It seems that these increments were not
significant, but it would be rewarded by the ASMBR longer operation time.

                               200

                               180

                               160
                                                                                                    NoBFR
                               140
       Effluent Color (PtCu)




                               120

                               100
                                                                                                     BFR2
                                80                                                     BFR3
                                                                                       BFR1
                                60

                                40
                                                                                             Color Eff NoBFR
                                                                                             Color Eff BFR1
                                20                                                           Color Eff BFR2
                                                                                             Color Eff BFR3
                                 0
                                     0     20       40             60           80     100            120
                                                         SMBR Operation Time (hours)

                                         Figure 5 Effluent color of ASMBR system

The ASMBR without BFR produced higher effluent color then others. This soluble
natural color is known as the other problem in POME treatment. By adding BFR into
the ASMBR, the quality of effluent color improved as indicated in Figure 5. This was
due to adsorption of the small molecule material onto BFR surface or BFR-biomass
surface.
Effluent color in ASMBR without BFR was decreasing even the gel layer was
generated on membrane surface. It was possibly because the gel layer blocked
membrane pore, made the pore size smaller, so that bigger substances was rejected. It
also explained why its organic removal still tended to increase. As illustrated in
Figure 6(a). When BFR added into the ASMBR, it was found that the organic
removal remained high during the experiment, it probably due to the BFR adsorption
of SMP produced. This adsorption could improve the organic removal and improved
the quality of permeate. Even though with the use of BFR1 and BFR3, effluent color
tended to increase again after 20 hours of operation, despite high organic removal.
The color remains high because the membrane layer was not blocked by the
formation of gel layer or cake, thus soluble organic which not attached to BFR could
pass through the membrane pore to permeate side as illustrated in Figure 6(b).




                                                                                                               10
                         (a)                   (b)




       Figure 6 Conceptual removal of soluble materials in ASMBR operation
                              (Adapted from [17])


4.0. CONCLUSIONS

From these experiments, it can be concluded that BFR demonstrated a significant role
in bio-fouling reduction by maintained TMP as low as 2.3 – 3.6 kPa at the end of
ASMBR operations. It was also found that the organic removal of ASMBR with
BFR1, BFR2 and BFR3 was further improved by 2.46%, 0.87% and 3.80%
respectively, compared to the operation of ASMBR without BFR. In addition, the
reduction of the thickness of gel layer and the organic cake formation on membrane
surface thereafter demonstrated the capability of BFR in adsorption and reducing bio-
fouling.

                           ACKNOWLEDGEMENT
The authors wish to express gratitude the Research Management Center (RMC) of
Universiti Teknologi Malaysia for the financial assistance under VOT no. 79903.

                                   REFERENCES
[1]   USDA, Foreign Agricultural Service (2007) Indonesia : Palm Oil Production
      Prospects Continue to Grow. http://www.pecad.fas.usda.gov /highlights/2007/
      12/Indonesia_palmoil.
[2]   Ahmad, A.L., Ismail, S. and Bhatia, S. (2005) Membrane treatment for palm
      oil mill effluent: effect of transmembrane pressure and crossflow velocity.
      Desalination 179:245-255.




                                                                                  11
[3]    Ma, A.N. (2000) Environmental management for the palm oil industry. Palm
       Oil Developments 30:1-10.
[4]    Judd, S, (2007) The status of membrane bioreactor technology. Trends in
       biotechnology 26(2):109-116.
[5]    Jeong, T.Y., Cha, G.C., Yoo, I.K. and Kim, D.J. (2007) Characteristics of bio-
       fouling in a submerge MBR. Desalination 207:107-113.
[6]    Cote, P., Buisson, H. and Praderie, M. (1998) Immersed membranes activated
       sludge process applied to the treatment of municipal wastewater. Water Sci.
       Technol. 38:437–442.
[7]    Buisson, H., Cote, P., Praderie, M. and Paillard, H. (1998) The use of immersed
       membranes for upgrading wastewater treatment plants. Water Sci. Technol.
       37:89–95.
[8]    Nagaoka, H., Ueda, S. and Miya, A. (1996) Influence of bacterial extracellular
       polymers on the membrane separation activated sludge process. Wat. Sci. Tech.
       34:165–172.
[9]    Bouhabila, E.H., Aim, R.B. and Buisson, H. (2001) Fouling characterisation in
       membrane bioreactors. Sep. Purif. Tech. 22–23:123–132.
[10]   Bouhabila, E.H., Aim, R.B. and Buisson, H. (1998) Microfiltration of activated
       sludge using submerged membrane with air bubbling: application to wastewater
       treatment. Desalination 118:315–322.
[11]   Drews, A., Lee, C.H. and Kraume, M. (2006) Membrane fouling - a review on
       the role of EPS, Desalination 200:186–188.
[12]   Chang, I.S. and Lee, C.H. (1998) Membrane filtration characteristic in
       membrane coupled activated sludge system the effect of physiological states of
       activated sludge on membrane fouling. Desalination 120:221–233.
[13]   Chang, I.S., Le Clech, P., Jefferson, B. and Judd, S. (2002) Membrane fouling
       in membrane bioreactors for wastewater treatment, J. Environ. Eng. 128:1018–
       1029.
[14]   Li, X.Y. and Yang, S.F. (2007) Influence of loosely bound extracellular
       polymeric substances (EPS) on the flocculation, sedimentation and
       dewaterability of activated sludge. Water Res. 41(5):1022–1030.
[15]   Ueda, T., Hata, K., Kikuoka, Y. and Seino, O. (1997) Effects of aeration on
       suction pressure in a submerged membrane bioreactor. Water Res. 31(3):489–
       494.
[16]   Bhatia, S., Othman, Z. and Ahmad, A.L. (2007) Coagulation–flocculation
       process for POME treatment using Moringa oleifera seeds extract:
       Optimization studies. Chem. Eng. Journal 133:205–212.
[17]   Ujang, Z., Au, Y.L. and Nagaoka, H. (2002) Comparative study on microbial
       removal in immersed membrane filtration (IMF) with and without powdered
       activated carbon (PAC). Water Sci. Technol. 46(9):109–115.
[18]   Seo, G.T., Moon, C.D., Chang, S.W. and Lee, S.H. (2004) Long term operation
       of high concentration powdered activated carbon membrane bio-reactor for
       advanced water treatment. Water Sci. Technol. 50(8):81–87.




                                                                                   12
[19] Liu, Y., Wang, L., Wang, B., Cui, H. and Zhang, J. (2005) Performance
     improvement of hybrid membrane bioreactor with PAC addition for water
     reuse. Wat. Sci. Tech. 52(10–11):383–391.
[20] Munz, G., Gori, R., Mori, G. and Lubelloa, C. (2007) Powdered activated
     carbon and membrane bioreactors (MBR-PAC) for tannery wastewater
     treatment: long term effect on biological and filtration process performances.
     Desalination 207:349–360.
[21] Guojun, Z., Shulan, J., Xue, G. and Zhongzhou, L. (2008) Adsorptive fouling
     of extracellular polymeric substances with polymeric ultrafiltration membranes.
     J. Membrane Science 309:28–35.
[22] Lee, J.C., Kim, J.S, Kang, I.J., Cho, M.H., Park, P.K. and Lee, C.H. (2001)
     Potential and limitations of alum or zeolite addition to improve the performance
     of a submerged membrane bioreactor. Water Sci. Technol. 43(11):59–66.
[23] APHA (1992). Standard Methods for Examination of Water and Wastewater.
     18th ed. American Public Health Association, American Water Works
     Association and Water Environment Federation, Washington DC, USA.




                                                                                  13

								
To top