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Removal of Contaminants and Pathogens
from Secondary Wastewater Effluents using
Hollow Fiber Microfiltration Membranes
Mahmoud Bali* and Soumaya Farhat
Higher Institute of Sciences and Techniques of Water, University of Gabès, Tunisia
Submission: January 10, 2020; Published: January 24, 2020
*Corresponding author: Mahmoud Bali, Higher Institute of Sciences and Techniques of Water, University of Gabès, Tunisia
How to cite this article: Mahmoud Bali, Soumaya Farhat. Removal of Contaminants and Pathogens from Secondary Wastewater Effluents using Hollow Fiber Microfiltration Membranes. Int J Environ Sci Nat Res. 2020; 23(3): 556112. DOI: 10.19080/IJESNR.2020.23.556112
The main purpose of this study was to investigate the ability of cross-flow microfiltration technique to treat urban wastewater effluents. Experimental results demonstrated that this technique is reliable and very effective in removing wastewater impurities. Results showed that hollow fiber membranes achieved a significant removal rate of all parameters tested except ammonium nitrogen. This study confirmed that cross-flow microfiltration process is very efficient concerning the abatement of suspended solids and organic matter. All pathogenic bacteria indicators were removed by this process. The experimental study demonstrated that quality of permeate produced by hollow fiber microfiltration membranes is suitable for industrial reuse.
During the last few years there has been a continuous and important growth in water consumption and consequently a strong increase of the domestic and industrial wastewater potential sources of environmental problems. Reclamation of wastewater in thus becoming a major goal in several countries where there is water scarcity . Conventional water and wastewater treatment processes have been long established in removing many chemical and microbial contaminants of concern to public health and the environment. However, the effectiveness of these processes has become limited over the last two decades .
Development of new technologies has extended the possibilities of wastewater reuse . At the same time, norms regarding the quality of water to be reused have become increasingly stringent, while tertiary treatments have in turn become increasingly sophisticated as they strive to obtain effluents of high quality . Advanced treatment technologies have been demonstrated to remove various potentially harmful compounds that could not be effectively removed by conventional treatment process . Membrane based separation processes have gradually become an attractive alternative to the conventional separation processes in the treatment of wastewater. The advantages of membrane technology over conventional separation methods are high removal capacity, flexibility of operation and cost effectiveness. However, the main limitation to the greater use of membrane technology is membrane fouling . The application of membrane filtration processes not only enables high removal efficiencies, but also allows reuse of water and some of the valuable waste constituents . Membrane technologies obtain effluents which meet the standards established in wastewater reuse  and are extensively employed as wastewater tertiary treatments . Membrane technologies provide an important solution in environmental fields such as pollution reduction and water reuse [8-10]. Membrane filtration is one of the most promising technologies used for the advanced treatment of secondary effluents . Among membrane processes, microfiltration (MF) is a widely used technique in treating contaminated water and wastewater . MF is operated in the cross-flow as well as the dead-end mode. In cross-flow microfiltration (CFMF), the suspension is pumped tangentially over the membrane surface. Clear liquid permeates the filtration medium and is recovered as the permeate, while the solids accumulate at the filtration barrier to form a fouling layer, or cake. The tangential suspension flow tends to limit the growth of the cake. For this reason, CFMF is preferably applied for the filtration of liquids having high solids content. In dead-end filtration, the suspension flows perpendicular to the membrane surface so that the retained particles accumulate at the membrane surface and form a cake which decreases the permeate flux.
Cross-flow microfiltration is an efficient and energy-saving process that has been widely used in separating fine particles . A membrane filtration unit can be placed at the very end of
the wastewater treatment line, treating wastewater from various
sources after traditional pretreatment and biological degradation
. It is expected that the use of membrane filtration for treatment
of municipal wastewater will steadily increase with more stringent
discharge regulations and fresh water supply limitations. In
response, ultrafiltration and microfiltration membrane suppliers
have developed a number of different membrane structures and
operating procedures for wastewater treatment . Hollowfiber
membranes have been widely employed for water and
wastewater treatment . However, the major obstacle is the
flux decline due to the membrane fouling , which remains
one of the most problematic issues surrounding membrane use in
water and wastewater treatment applications .
The main objective of this study is to evaluate the applicability
of cross-flow microfiltration technique in treating secondary
effluent of urban wastewater for industrial reuse.
We carried out filtration trials using secondary wastewater
effluents produced by the treatment plant of the town of Gabès
(south-east of Tunisia) which uses activated sludge treatment.
The capacity of this plant is about 17.000m3 per day. The average
characteristics of the secondary wastewater effluent are given in
Cross-flow microfiltration experiments under constant
pressure mode were carried out using a Pall AriaTM Mobile C60
(PAM C60) (Figure 1) water treatment unit. It’s a high-volume and
automated microfiltration membrane system in a 12.2m (40ft)
high cube container. The PAM C60 can produce up to 7000m3 of
water per day, filtered to 0.1μm for industrial reuse. It contains 60
microfiltration membrane modules ranged into two independent
racks. The modules are equipped with Microza (trademark of
Asahi Kasei Corporation) polyvinylidene fluoride (PVDF) hollow
fiber membranes. Each module provides high active surface area
of up to 538ft2. The operating trans-membrane pressure is about
3 bars. In order to avoid membranes fouling, which would shorten
the membranes lifetime dramatically, a filter with 300 μm pore
size was used as a pre-treatment for the cross-flow microfiltration
Membrane fouling causes a decrease in filtration productivity
resulting in a decrease in flux with time under constant trans membrane operation . To restore membrane performance
two cleaning methods were used: air/water flush and chemical
The so-called air/water flush is a forward flush during which
air is injected in the supplier pipe. Because air is used, a much
more turbulent cleaning system is created. Using air flush means
flushing the inside of membranes with an air/ water mixture. The
forward flush intervals are from 45 to 60 minutes, and durations
are from 40 seconds to 1 minute, depending on the water quality.
During a chemical cleaning process, membranes are soaked
with a solution of sodium hypochlorite, citric acid or sodium
hydroxide. The solution soaks into the membranes for a number
of minutes and after that a forward flush or backward flush is
applied. The chemical cleaning step is applied after each 12 hours
operation for 60 minutes duration.
The secondary effluent and permeate were analyzed for
suspended solids (SS), chemical oxygen demand (COD), 5- day
biochemical demand (BOD5), ammonium nitrogen (NH4-N), total
coliforms (TC), faecal coliforms (FC) and faecal streptococci
(FS). Temperature, pH, electric conductivity and turbidity were
measured. All parameters were measured according to the AFNOR
The retention (R) of the MF membrane was calculated using
the following equation:
Where Cf and Cp are respectively the feed and the permeate
St.dv.: Standard deviation; NS: Number of samples.
Results obtained from statistical analyses of the applied
secondary wastewater effluent and permeate produced by the
cross-flow microfiltration unit are summarized in Table 2. The
maximum, minimum, and mean values as well as the standard
deviation are presented. Analyses showed that the secondary
effluent characteristics varied within a wider range and exhibited
relatively higher variability than the treated water for the
parameters tested. Variability in the secondary effluent quality
may be taken as an indication of an inherent in- plant treatment
problem or a problem caused by diurnal variations in influent
wastewater flow and characteristics as well as process control
The physico-chemical characteristics of the secondary
wastewater effluent and filtered water are depicted in Figure 2.
Analyses showed an increase of pH values in the filtered water
(Figure 2(a)). This increase could be explained by the abatement
of organic acids present in the applied wastewater effluent.
Results showed a good efficiency of the microfiltration process
regarding the remove of impurities from secondary wastewater
effluent. The PVDF hollow-fiber membrane was a total barrier for
the suspended solids. The average concentration of suspended
solids observed in the influent during the period of study was
about 100.5mg/L. Despite the fluctuation of SS contents in
the secondary wastewater effluent, cross-flow microfiltration
process allowed a total removal of these pollutants (Figure 2(b)).
Consequently, the turbidity abatement exceeded 92% (Figure 3).
Similar results were reported by Vera et al.  and Sorlini et
al. . In fact, the particulate matters which their sizes exceed
0.1μm were retained by this membrane. Experimental results
showed that cross-flow MF process allowed efficiently eliminating
all pollutants except ammonium nitrogen (Figure 2(d)). In fact,
the average NH4-N concentration in the treated water was about
154mg/L, corresponding to a removal rate of 10.64% (Figure 3).
Consequently, the risk of eutrophication of surface waters is very high. In fact, nitrogen poses a major environmental problem due
to its high contribution to eutrophication of freshwater bodies.
Eutrophication is a condition of an aquatic ecosystem where
high nutrient concentrations, such as nitrogen and phosphorus,
stimulate algal blooms, degrading the water quality in these
aquatic ecosystems . Therefore, controlling phosphorus and
nitrogen discharged from municipal and industrial wastewater
treatment plants is a key factor in preventing eutrophication of
surface waters. In addition to its contribution to eutrophication
phenomenon, ammonium nitrogen in wastewater can reduce the
effectiveness of chemical cleaning by converting hypochlorite into
less active chloramine’s species.
The removal efficiency of the technique of cross-flow
microfiltration regarding the total coliforms (TC), faecal
coliforms (FC), and faecal streptococci (FS) was investigated.
Microorganism contents in the secondary wastewater effluent
and permeate were measured. Bacteriological characteristics of
the applied wastewater effluent and treated water are presented
in Table 3. Average contents of pathogenic microorganisms in
the secondary effluent were 5.62, 2.78 and 0.92 log unit for total
coliforms, faecal coliforms, and faecal streptococci, respectively.
Results demonstrated the good disinfection performances of the
cross-flow MF technique. All pathogenic bacteria indicators (TC,
FC and FS) were efficiently removed from the applied wastewater.
Therefore, the PVDF membrane represents a total barrier for
this group of bacteria. These results can be explained by the
size of microbial cells which is bigger than the pore size of the
membrane. Similar results were presented by Sorlini et al. ,
who demonstrated that CFMF using hollow fiber membranes is
able to achieve removal rates higher than 98% for a large number
of species of bacteria. The bacteriological quality of permeate was
good enough to allow industrial reuse.
Cross-flow microfiltration seems to be an efficient technique
to polish urban wastewater effluents. Results confirmed that
this process is performed as an advanced treatment system
for the suspended solids and organic matter. However, it is less
efficient concerning the reduction of ammonium nitrogen. Data
obtained during this study are evidences of the high disinfection
capacity of microfiltration membranes. Therefore, the MF process
is considered as an interesting issue for the treatment of urban
wastewater effluent and it can be an attractive alternative for
reusing a significant part of all incoming fresh water.
This process can be used as a tertiary treatment with the aim
of removing contaminants from the effluents of conventional
wastewater treatment plants. Reuse of tertiary-treated effluent
is an economically viable and environmentally sound option for
water resource development in the state of Tunisia.
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