Performance of a sponge MBR with a moving-cube sponge medium 20% v/v was evaluated at different hydraulic retention times HRTs for the specific example of catfish pond wastewater.. Key w
Trang 1Effects of Hydraulic Retention Time on Organic and Nitrogen Removal
in a Sponge-Membrane Bioreactor Bui Xuan Thanh,1,* Ha˚kan Berg,2
Le Nguyen Tuyet Nguyen,1and Chau Thi Da3
1 Faculty of Environment, Ho Chi Minh City University of Technology, Ho Chi Minh City, Vietnam.
2
Swedish International Biodiversity Program (SwedBio), Stockholm Resilience Center, Stockholm University, Stockholm, Sweden.
3
Faculty of Agriculture, An Giang University, Long Xuyen City, Vietnam.
Received: September 27, 2012 Accepted in revised form: January 1, 2013
Abstract
This is the first study on application of a sponge-membrane bioreactor (sponge MBR) for recirculation of aquaculture wastewater in the Mekong delta, Vietnam Performance of a sponge MBR with a moving-cube sponge medium (20% v/v) was evaluated at different hydraulic retention times (HRTs) for the specific example of catfish pond wastewater The sponge MBR was operated at HRT values of 8, 4, and 2 h, which correspond to membrane fluxes of 5, 10, and 20 L/m2per hour, respectively The average chemical oxygen demand (COD) removal efficiencies were maintained at 93%, 94%, and 87% at an HRT of 8, 4, and 2 h, respectively, while the average total nitrogen (TN) removal efficiencies were 84%, 70%, and 57% The COD and TN removal efficiencies decreased with a decrease in HRT (increase in membrane flux) Permeate concentrations of COD and TN were as low as 6.3 and 2.7 mg/L at the operated HRTs, respectively Compared to the conventional MBR, the sponge MBR had twice the TN removal capacity at the same HRT due to simultaneous nitrification–denitrification In addition, results implicated that the fouling rate (dTMP/dt) increased in an inverse proportion with HRT (h) according to the power equation (fouling rate = 4.2474 HRT- 2.225) Free movement of sponges in the reactor improved fouling due to sweeping of the cake layer on the membrane surface Results reveal that the sponge MBR was effective in terms of simultaneous organic and nitrogen removal, fouling control, and water recirculation
Key words: catfish farm; fouling rate; hydraulic retention time (HRT); nitrogen removal; sponge-membrane bioreactor (sponge MBR); wastewater
Introduction
In recent years, aquaculture production has increased
rapidly, mainly due to increasing catfish production in the
Mekong delta provinces in southern Vietnam This
develop-ment generates profit and income, but it also bears the risks of
a negative environmental impact such as pollution or
biodi-versity change (Anh et al., 2010; Konnerup et al., 2011) Catfish
production requires a large amount of fish feed, in the form of
wet homemade feed, trash fish, and pellets These feeds are
partly transformed into fish biomass and partly released into
the water as suspended solids or dissolved matters such as
organic carbon, nitrogen, and phosphorus These wastes
originate from surplus food, feces, and excretions via the gills
and kidneys Other pollutants are the residuals of drugs used
to cure or prevent diseases Unless the wastewater of catfish
ponds is treated before it is discharged directly into rivers, it adversely impacts the receiving waters with increased risks for eutrophication and declining water quality This may have
a direct negative effect on the catfish production itself, but also
on other water users relying on good water quality Aqua-culture development and management should take into ac-count the full range of ecosystem functions and services, and should not threaten the sustained delivery of these services to the society at large (Soto et al., 2008) Therefore, the selection of
a catfish wastewater treatment process for reuse and recycling
is necessary in sustainable catfish farming
Biological removal of organic compounds and nutrients from polluted aquaculture wastewater is an appropriate process for water quality and water reuse The common bio-logical methods include activated sludge process, biofilter, aerated lagoon, and constructed wetlands However, these approaches often demand a large area due to the requirement for a high hydraulic retention time (HRT) Some treatment processes also have to be operated during a limited time after harvesting fish, when the treated wastewater is discharged into the river In these situations, a compact and efficient
*Corresponding author: Faculty of Environment, Ho Chi Minh City
University of Technology (HCMUT), Vietnam Building B9, 268 Ly
Thuong Kiet St., District 10, Ho Chi Minh City 70000, Vietnam Tel/
Fax: + 84.8.3.863.9682; E-mail: bxthanh@hcmut.edu.vn
Volume 30, Number 4, 2013
ª Mary Ann Liebert, Inc.
DOI: 10.1089/ees.2012.0385
194
Trang 2membrane bioreactor (MBR) is proposed to be the most
ap-propriate wastewater treatment solution
The MBR combines the aerobic degradation with a direct
solid–liquid separation of activated sludge using a
micro-filtration or ultramicro-filtration membrane MBR provides better
performance than conventional activated sludge, including a
smaller required area, higher quality of treated wastewater,
and long sludge retention time Further, high biomass
reten-tion in the MBR makes it able to operate at high loading rates,
with a comparable small reactor volume The filtration
pro-cess can remove microorganisms without chemical
disinfec-tion (Visvanathan et al., 2000) Moreover, the use of a medium
in the MBR could improve MBR operation, which may
in-crease the treatment performance by high biomass
concen-trations and reduced membrane fouling (Leiknes and
Ødegaard, 2001; Thanh et al., 2012) The presence of the
moving medium in the membrane tank can also reduce
fouling The mechanism reducing of the fouling membrane
can cause the moving medium in the MBR tank capable of
enhancing the combination of suspended and colloidal
par-ticles on the surface of the medium for reducing fouling and
clogging on the membrane surface
Jamal Khan et al (2011) studied the performance of the
MBR process in combination with a sponge medium at an
HRT of 8 h (representing 15% volume reaction tank) to
re-move chemical oxygen demand (COD), total nitrogen (TN),
and total phosphorus (TP) Results show that the effective
removal of COD, TN, and TP with the sponge MBR is 98%,
89%, and 58% This is higher than the standard MBR, which
had a removal of 98%, 74%, and 38% for COD, TN, and TP,
respectively Guo et al (2008b) found that the sponge MBR
(sponge occupies 10% of reactor volume) results in a twofold
enhancement of the filtration flux of the MBR This clearly
shows that the addition of sponges to MBR can reduce the
contamination loading of the MBR
Sponge has been considered as a suitable medium because
it can act as a mobile carrier for active biomass, resulting in
improved organic and nutrients removal, as well as reduce
membrane fouling (Chae et al., 2004; Ngo et al., 2006; Guo et al.,
2009) In addition, thick biofilm that is formed on the surface
of the sponge is regularly removed by friction of individual
sponge cubes with each other, whereas the fixed
microor-ganisms within the sponge are very stable and active (Chae
et al., 2004) Sombatsompop et al (2006) investigated the effect
of the HRT on membrane performance and sludge properties
MBRs were operated at different HRTs of 2, 4, 6, and 8 h The
MBRs consisted of three bioreactors that included suspended
growth without a medium, a moving medium, and a fixed
medium The removal efficiency of COD in the moving medium
was found to be 98% with a short HRT of 2 h The nitrogen
removal was accomplished by microorganism assimilation and
nitrification reaction in the MBR at all HRT values
This study aims to investigate the effect of different HRTs
on treatment performance and fouling of sponge MBR for
catfish wastewater treatment and recirculation
Materials and Methods
Wastewater
Wastewater was collected from a catfish farm located in
Long Xuyen City, An Giang province, Mekong delta,
Viet-nam In the later stage of the experiment (after day 88, at the
end of the 4-h HRT), serious flooding occurred in the prov-inces that inundated the pond Thus, synthetic wastewater was replaced for catfish farm wastewater The synthetic wastewater was made of catfish pellets with addition of
NH4Cl The concentrations of COD, NH4+-N, NO2--N,
NO3--N, and TP were similar to those of the real catfish pond wastewater (Table 1)
MBR and operating conditions The MBR has a working volume of 40 L with a submerged hollow-fiber membrane module (Tianjin Motimo Membrane Technology, Tianjin, China; surface area of 1 m2, nominal pore size of 0.2 lm) The MBR was operated in a cyclic condition (8 min on/2 min off) The sponge MBR was operated at HRTs
of 8, 4, and 2 h The solid retention time was controlled at 30 days for all HRTs (Table 2) Dissolved oxygen was maintained
at a level higher than 4 mg/L by stone diffusers The trans-membrane pressure (TMP) was recorded daily by a pressure gauge When the TMP reached a set-point value of 40 kPa (membrane fouling), a backwash pump (Blue-White In-dustries, Huntington Beach, CA) was automatically operated
to flush off the caked layer formed on the membrane surface The flow rate of the backwash pump was set at 20 L/h for
5 min However, in this study, the backwash only occurred at the highest HRT of 2 h Before the system started a new run, the membrane was cleaned by chemicals (0.5% NaOH and 0.5% NaOCl) for 4 h Seed sludge for the sponge MBR was taken from a conventional activated sludge process (70% v/v) and sediment from the bottom of a catfish pond (30% v/v) The initial mixed liquor suspended solids (MLSS) concentra-tion was approximately of 6000 mg/L
Sponge medium Polyurethane sponge, with a density of 18.2 kg/m3, and a sponge cube of 2 cm · 2 cm · 2 cm were used as a moving
Table1 Composition of Wastewater Used
The real catfish farm wastewater was used at the beginning of the study From day 88 onward, similar synthetic wastewater compo-nent was substituted due to serious natural flooding that occurred in the study area.
COD, chemical oxygen demand; TP, total phosphorus.
Table2 Operational Periods of Sponge
Membrane Bioreactor
HRT, hydraulic retention time.
Trang 3medium The sponges were added in the MBR proportional to
20% of the reactor volume (Guo et al., 2010)
Analytical methods
Analyzed parameters were COD, nitrite, nitrate, ammonia,
TP, MLSS, and mixed liquor volatile suspended solids
(MLVSS) The biomass concentration in the sponges was
es-timated according to Guo et al (2010) Analytical methods
were done according to the standard methods (APHA, 1998)
Nitrogen balance was estimated by Equation (1):
TNin¼ TNoutþ TNassimilatedþ TNdenitrification ð1Þ
Nitrogen assimilated into the cell biomass was estimated
based on the produced volatile-suspended solids (VSS) The
assimilated nitrogen was equal to 12% VSS (Metcalf & Eddy,
Inc., 2003) The nitrogen balance was conducted to estimate
the simultaneous nitrification–denitrification (SND) that
oc-curred in the sponge medium
All results were statistically compared by one-way analysis
of variance using Minitab 16
Results and Discussion
COD removal
The average COD removal efficiency during the operating
period is shown in Table 3 The removal efficiency of COD
ranges between 87% and 94% with an HRT ranging from 2 to
8 h The average COD concentrations in the permeate were
*6.3 mg/L for the operated HRTs A similar observation was
reported by Coˆte´ et al (1997), who suggested the effluent COD
from a hollow-fiber MBR was maintained at a level below
16 mg/L, despite a five-stage change in the HRT from 2 to
24 h, and Guo et al (2008b) found the COD removal efficiency
over 97% The COD removal was maintained at 93% and 94%
at an HRT of 8 and 4 h, respectively, but was 87% at an HRT of
2 h, which indicates that the HRT affects the permeate quality
in terms of COD removal This is in contrast to the result of
Sombatsompop (2006), who reported that the MBR provided
an excellent and stable effluent quality at HRT values between
2 and 8 h
The permeate COD not only complies with the Vietnam
National Technical Regulation on the effluent of
aquaculture-processing industry, QCVN 11:2008/BTNMT (50 mg COD/
L), but also reaches the Vietnam National Technical
Regula-tion for surface water quality, QCVN 08:2008/BTNMT
(100 mg COD/L) Moreover, the organic content in treated
wastewater was removed to a level that would make the
water acceptable for such uses as park irrigation, vehicle washing, firewater, flushing a toilet, or aquaculture re-circulation, according to the U.S Environmental Protection Agency (USEPA, 2004) Based on these guidelines, the treated wastewater can be recycled directly to the catfish pond Nitrogen removal
Characteristics of catfish pond wastewater are mainly ammonia (NH3) with its derivatives, NH4+-N, NO2--N, and
NO3--N Ammonia and nitrite are harmful substances for aquatic animals In a catfish pond, ammonia is generated by the natural decomposition of proteins, which are residues from various sources including zooplankton, fish excrement, and uneaten food The average concentrations of NH4+-N,
NO2--N, NO3--N, and TN in catfish wastewater treated with the sponge MBR are summarized in Table 4 During the op-erational period, the NH4+-N removal efficiencies at HRTs of
8, 4, and 2 h were 100%, 99%, and 86% in the sponge MBR, respectively, which implies slightly better nitrification at a higher HRT Guo et al (2009) reported ammonia nitrogen removal of > 99% with 10% sponge medium at an influent ammonia nitrogen concentration of 15–20 mg/L Jamal Khan
et al (2011) mentioned NH4+-N removal of 95.6% with 15% sponge medium at an HRT of 8 h Liu et al (2010) reported that increasing HRT from 2 to 4 h could enhance the NH4+-N re-moval from 47.2% to 98.1% Table 4 indicates that there was
no significant improvement between HRTs of 4 h and 8 h in terms of NH4+-N elimination, as almost all (99%) had been removed after 4 h
The average nitrite concentration was *0.03 mg/L with HRTs of 8 and 4 h, but > 1.0 mg/L with an HRT of 2 h This indicates a limited nitrification capacity of the MBR during a short retention time An HRT of 2 h is too short to achieve complete nitrification This result is similar to the result of Sombatsompop (2006) The results infer that changes of HRT affect the nitrogen removal efficiency of the sponge MBR
TN removal efficiencies of the sponge MBR were 84% – 8%, 70% – 18%, and 57% – 21% at HRTs of 8, 4, and 2 h, respec-tively This indicates that TN removal of the sponge MBR increases with an increasing HRT In the sponges, nitrification probably takes place on the surface of the sponge, whereas anaerobic/anoxic conditions inside the sponge provide a suitable environment for denitrification (Nguyen et al., 2010) This phenomenon is SND A higher HRT enriches slow-growing microorganisms and creates effective contacts be-tween microorganisms and substrates SND occurs in the sponge medium because of the biomass captured within the pores of the sponge and a limited oxygen concentration inside
Table3 Chemical Oxygen Demand Removal Performance in Sponge-Membrane Bioreactor
COD concentration and removal efficiency at different HRTs
QCVN 08:2008/BTNMT
USEPA, 2004
Data was analyzed by Minitab 16 Statistical Software.
abc
Superscript letters denote significant differences among periods of operation Means in the same row that do not share the same letter are significant different ( p < 0.05).
Trang 4the pores This explains the comparatively high TN removal
in the sponge MBR (Yang et al., 2009) Therefore, an HRT of
4–8 h could be the appropriate operating time for nitrogen
removal in this system Figure 1 provides a simplified
illus-tration of the possible mechanism for nitrogen removal
through SND in the sponge MBR
The nitrification reaction occurs nearly completely at HRTs
of 8 and 4 h, as the concentrations of TN are low in the
membrane permeate of the sponge MBR The TN
concentra-tion in the permeate at 2-h HRT is almost twofold higher than
those at other HRTs These results indicate that the reaction
time of 2-h HRT is not enough for SND to occurr in the sponge
MBR The HRT influences the nitrogen removal capacity of
the sponge MBR Fig 1 also shows that the amount of TN
denitrified at HRTs of 8 and 4 h in the sponge MBR is 72% and
62% higher than at HRTs of 8 and 4 h in a conventional MBR
(no sponge in the MBR), where the amount of TN denitrified
was 40% and 27% It is inferred that the sponge medium can
achieve complete nitrogen removal through SND The
per-centage of denitrification in sponge MBR is twice that in a
conventional MBR at the same HRT
Table 4 presents the average removal of TP in the sponge
MBR, which is 82%, 56%, and 64% at HRTs of 8, 4, and 2 h,
respectively TP removal at a 4-h HRT is lower than that at a
2-h HRT probably because the concentration of TP in the
in-fluent at a 4-h HRT was lower than that at a 2-h HRT The TP
removal efficiency in this study is 82% higher in comparison
with a conventional MBR: 58% in the sponge MBR, and 38% in
the MBR without sponge in the studies of Jamal Khan et al (2011)
Biomass in sponge MBR Figure 2 shows that the biomass accumulated in the MBR with time from 8- to 4-h HRT The trend was similar for bio-mass in sponges The rate of biobio-mass formation in sponges was higher than that in suspended growth; thus, the ratio of MLSS in sponge/total MLSS increased with the operation time, showing that the shorter the HRT, the higher the ratio More biomass in sponges enhanced more TN removal and fouling control It is observed that when operated at a 2-h HRT (high flux of 20 L/m2 per hour), the biomass started releasing from the sponges, and a large amount of biomass attached strongly to the membrane module This resulted in total biomass reduction in the reactor since day 138, and se-rious fouling occurred in the 2-h HRT operating period (as described in the Fouling propensity of sponge MBR section) The average total biomass in sponges and in suspension was
3908 – 813 mg/L during this stage The level sensor had a problem on day 148; the biomass was lost, and the total MLSS remained 2882 mg/L Then, the total MLSS started increasing and reached 5136 mg/L on day 158
The MLVSS/MLSS ratio ranged from 0.21 to 0.69 during operation The ratio reduced from 0.43 to 0.21 during the 8-h HRT This was due to the endogenous respiration in the sponge MBR (F/M = 0.07–0.52 mg COD/mg VSS per day) The ratio increased from 0.24 to 0.6 at 2- and 4-h HRTs The
Table4 Concentrations of Nitrogen and Total Phosphorus in Wastewater
Treated with the Sponge-Membrane Bioreactor Concentration in permeates (% removal efficiency) at different HRTs [mg/L (%)]
QCVN 08:2008/BTNMT
TP 0.11 – 0.16a(82 – 26b) 1.18 – 0.47b(56 – 8c) 0.31 – 0.29a(64 – 20c) 0.1–0.5 (PO4-)
TN = NH 4+-N + NO 2--N + NO 3--N Data was analyzed by Minitab 16 Statistical Software.
abc
Superscript letters denote a significant differences among periods of operation Means in the same row that do not share the same letter are significantly different ( p < 0.05).
TN, total nitrogen.
FIG 1 Nitrogen balance in a sponge-membrane bioreactor
Trang 5MLVSS/MLSS ratio in the sponge MBR was lower than that
in a conventional MBR
Fouling propensity of sponge MBR
Figure 3 shows the variation of the TMP during the
oper-ation of the sponge MBR The results show that TMP
devel-opment fluctuated from 3.5 to 6 kPa in 58 days, from 6 to
18 kPa in 43 days, and from 20 to 40 kPa in 15 days for HRTs of
8, 4, and 2 h, respectively (Table 5) The TMPs fluctuated at an
HRT of 4 h because the biomass concentration in the MBR was
lost due to the malfunctioning water-level sensor
In the last period, the TMP reached 40 kPa, and the
mem-brane was backwashed by permeate water The need for
membrane backwash after a comparatively short period
op-eration (15 days) at a 2-h HRT was due to a high fouling speed
because of a high flux (20 L/m2per hour) This flux is slightly
over the maximum allowable flux for the sponge membrane
This indicates that a reduction in the HRT (increasing
mem-brane flux) results in an increase in memmem-brane fouling, which
is in agreement with previous studies (Cho et al., 2005;
Kok-Kwang et al., 2011) In this study, the relationship between the
fouling rate (kPa/day) and the HRT (h) in the sponge MBR
was found to follow the power equation (dTMP/dt = 4.2474
HRT- 2.225, R2= 0.9992)
Table 5 shows the comparison of the average fouling rates
of some other reports The lowest fouling rate of 0.04 kPa/day
is for the sponge MBR treating catfish pond wastewater at a
flux of 5 L/m2per hour It indicates that the flux (and thus the HRT) strongly influences the fouling propensity of the sponge MBR The results imply that the fluxes < 10 L/m2per hour are suitable operating conditions of the sponge MBR for treating and reuse of catfish pond wastewater If the fouling rate is slow, the membrane will be expanded, and the operation and lifetime investment for replacement and chemicals for back-washing membrane will be reduced
Conclusion This study investigated the organic compounds, nitrogen, and phosphorous removal performance of a sponge MBR at HRTs of 2, 4, and 8 h (fluxes of 20, 10, and 5, L/m2per hour, respectively) It demonstrated that the sponge MBR exhibited the best treatment performance at an HRT of 8 h for COD, TN, and TP removal efficiencies of 93%, 84%, and 82%, respec-tively The COD removal at HRTs of 8 and 4 h was not sig-nificantly different An HRT of 4–8 h was required to stimulate an SND process, which is important to allow for a high reduction in the TN content of the catfish farm waste-water The fouling rate was as slow as 0.04 and 0.20 kPa/day
at a flux of 5 and 10 L/m2per hour, respectively The optimal flux for catfish farm wastewater should be in the range of 5–10 L/m2per hour for a sponge MBR In addition, the small size, high organic and nutrient removal efficiencies, and slow fouling rate of sponge MBR make this technology a poten-tially attractive alternative to conventional wastewater
FIG 3 Profile of
trans-membrane pressure (TMP)
with time (left) and fouling
rate (right)
Table5 Comparison of Fouling Rate in the Sponge-Membrane Bioreactor to Other Systems
TMP increase [kPa (days)]
Fouling rate (kPa/day)
Flux (L/m2
MBR (Mitsubishi
a
Sponge percentages are % (v/v).
MBR, membrane bioreactor; TMP, transmembrane pressure.
Trang 6treatment methods The treated wastewater can be recycled
directly to the catfish pond during the culture period Thus, it
is clear that sponge MBR technology could contribute to a
more environmentally sustainable development of catfish
farming in the Mekong delta, Vietnam
Acknowledgments
The authors would like to thank the Swedish International
Cooperation Agency, the Partner Driver Cooperation Project
on Sustainable Management of Ecosystem Services, for long
term aquaculture production in the Mekong Delta, and the Ho
Chi Minh City University of Technology for financial support
for this study
Author Disclosure Statement
No competing financial interests exist
References
Anh, P.T., Kroeze, C., Bush, S.R., and Mol, A.P.J (2010) Water
pollution by Pangasius production in the Mekong Delta—
Vietnam: Causes and options for control Aquac Res 42, 108
American Public Health Association (APHA) (1998) Standard
Methods for the Examination of Water and Wastewater, 20th ed
Washington, DC: APHA
Chae, K.J., Yim, S.K., and Choi, K.H (2004) Application of a
sponge media (BioCube) process for upgrading and expansion
of existing caprolactam wastewater treatment plant for
nitro-gen removal Water Sci Tech 50, 163
Cho, J., Song, K.G., Lee, S.H., and Anh, K.H (2005) Sequencing
anoxic/anaerobic membrane bioreactor (SAM) pilot plant for
advanced wastewater treatment Desalination 178, 219
Coˆte´, P., Buisson, H., Pound, C., and Arakaki, G (1997)
Im-mersed membrane activated sludge for the reuse of municipal
wastewater Desalination 113, 189
Guo, J., Xia, S., Wang, R.C., and Zhao, J (2008a) Study on
membrane fouling of submerged membrane bioreactor in
treating bathing wastewater Environ Sci 20, 1158
Guo, W., Ngo, H.H., Dharmawan, F., and Palmer, C.G (2010)
Roles of polyurethane foam in aerobic moving and fixed bed
bioreactors Bioresour Technol 101, 1435
Guo, W., Ngo, H.H., Palmer, C.G., Xing, W., Hu, A.Y.J., and
Listowski, A (2009) Roles of sponge sizes and membrane
types in a single stage sponge-submerged membrane
biore-actor for improving nutrient removal from wastewater for
reuse Desalination 249, 672
Guo, W.S., Vigneswaran, S., Ngo, H.H., Kandasamy, J., and
Yoon, S (2008b) The role of a membrane performance
en-hancer in a membrane bioreactor: A comparison with other
submerged membrane hybrid systems Desalination 231, 305
Jamal Khan, S., Shazia, I., Sadaf, J., Visvanathan, C., and
Je-gatheesan, V (2011) Performance of suspended and sponge
MBR systems in treating high strength synthetic wastewater
Bioresour Technol 102, 5331
Kok-Kwang, N., Cheng-Fang, L., Sri, C.P., Pui-Kwan, A.H., and Ping-Yi, Y (2011) Reduced membrane fouling in a novel bio-entrapped membrane reactor for treatment of food and bev-erage processing wastewater Water Res 45, 4269
Konnerup, D., Trang, N.T.D., and Brix, H (2011) Treatment of fish pond water by recirculating horizontal and vertical flow constructed wetlands in the tropics Aquaculture 313, 57 Leiknes, T., and Ødegaard, H (2001) The development of a biofilm membrane bioreactor Desalination 202, 135
Liu, Y.X., Yang, T.O., Yuan, D.X., and Wu, X.Y (2010) Study of municipal wastewater treatment with oyster shell as biological aerated filter medium Desalination 254, 149
Metcalf & Eddy, Inc (2003) Wastewater Engineering: Treatment and Reuse, 4th ed Singapore: McGraw-Hill, Inc
Ngo, H.H., Guo, W., and Xing, W (2008) Evaluation of a novel sponge-submerged membrane bioreactor (SSMBR) for sus-tainable water reclamation Bioresour Technol 99, 2429 Ngo, H.H., Nguyen, M.C., Sangvikar, N.G., Hoang, T.T.L., and Guo, W.S (2006) Simple approaches towards a design of an attached-growth sponge bioreactor (AGSB) for wastewater treatment and reuse Water Sci Tech 54, 191
Nguyen, T.T., Ngo, H.H., Guo, W., Johnston, A., and 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
QCVN 08:2008/BTNMT Vietnam national technical regulation for surface water quality Available at: http://vea.gov.vn/vn/ vanbanphapquy/tcmt/Pages/default.aspx
QCVN 11:2008/BTNMT Vietnam national technical regulation
on the effluent of aquatic products processing industry Available at: http://vea.gov.vn/vn/vanbanphapquy/tcmt/ Pages/default.aspx
Sombatsompop, K., Visvanathan, C., and Ben Aim, R (2006) Evaluation of biofouling phenomenon in suspended and at-tached growth membrane bioreactor systems Desalination 201, 138
Soto, D., Aguilar-Manjarrez, J., and Hishamunda, N (2008) Building an ecosystem approach to aquaculture FAO/Uni-versitat de les Illes Balears Expert Workshop May 7–11, 2007, Palma de Mallorca, Spain FAO Fisheries and Aquaculture Pro-ceedings No 14 Rome, FAO, 2008, p 221
Thanh, B.X., Dan, N.P., and Binh, N.T (2012) Fouling mitigation
in submerged membrane bioreactor treating dyeing and tex-tile wastewater Desalination Water Treat 47, 150
U.S Environmental Protection Agency (USEPA) (2004) Guide-lines for Water Reuse, U.S Environmental Protection Agency, Municipal Support Division, Office of Wastewater Management Washington, DC, No 625/R-04/108
Visvanathan, C., Benaim, R., and Parameshwaran, K (2000) Membrane separation bioreactor for wastewater treatment Crit Rev Environ Sci Tech 30, 1
Yang, S., Yang, F., Fu, Z., and Lei, R (2009) Comparison be-tween a moving bed membrane bioreactor and a conventional membrane bioreactor on organic carbon and nitrogen re-moval Bioresour Technol 100, 2369