and chlorinated solvents, and high organic pollution which are present in vegetable
oil refining wastes can be treated with MBR.
Hybrid Coagulation/Flocculation-Membrane Filtration
Membrane fouling is a major challenge for the development of membrane technologies due to the high operation and maintenance cost resulting from increased
energy and chemical demand for cleaning and the frequency of membrane replacement [60, 71]. Therefore, in order to overcome membrane fouling during oily
wastewater treatment, the hybrid processes uniting the advantages of pretreatment
methods such as pre-coagulation, pre-adsorption, pre-filtration, and pre-oxidation
with membrane processes are often preferred [60, 72, 73]. Among the various
pretreatments, coagulation/flocculation is the most applied method since it is easy
to operate and relatively inexpensive and can improve UF performance significantly
[74]. During coagulation, oil droplets and colloids destabilize and form larger flocs;
hence, they can be easily held by UF membranes [75].
In a recent bench-scale experiment, Khouni et al. [76] investigated several
technologies to identify the most efficient one for complete removal of oil from
synthetic and industrial oily wastewaters. They employed various treatment processes such as coagulation/flocculation and membrane filtrations such as UF directly
or in hybrid mode. The treatment processes were compared based on their efficiency
in COD, TOC, and turbidity removals. The experiment was done using a commercial
ceramic UF membrane (0.245 m
2 and 150 kDa) in cross-flow filtration mode with
flow rate of 3000 L/h and a trans-membrane pressure at 1.2 bars. However, UF
membrane is susceptible to fouling and not efficient for reusable quality water.
Therefore, in that study, the aim was to improve the purification performances of
UF by investigating its combination with other treatment options such as optimized
coagulation/flocculation as pretreatment and dead-end filtration as post-treatment for
high-quality reusable effluent [76]. When coagulation/flocculation was used as
pretreatment under optimal conditions (defined as 2.4 g/L of aluminum sulfate,
60 mg/L of CHT flocculant, initial pH of 9.2), the hybrid process uniting coagulation/flocculation with UF membrane provided the highest-quality effluent in terms of
turbidity, COD, and TOC removals at about 100%, 98%, and 97%, respectively,
compared to those of coagulation/flocculation and UF membrane processes when
used separately, with membrane permeability of 135 L/(h.m
2 .bar) [76]. The membrane permeability for cases of direct UF and hybrid coagulation/flocculation/UF
was in agreement with an industrial application. However, Khouni et al. [76] found
that the coagulation/flocculation pretreatment was inefficient in terms of reducing
membrane fouling since it did not improve the membrane permeability, 135 L/(h.m
2 .
bar), compared to that attained with direct UF (150 L/(h.m
2 .bar)). The findings of the
study in terms of water quality and membrane performance indicated that the hybrid
coagulation/flocculation/UF process is a promising alternative to water recovery and
pollution removal despite the fact that it does not offer the advantage for valorization
and vegetable oil recovery.
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D. Kaya and Y.-T. Hung
oil refining wastes can be treated with MBR.
Hybrid Coagulation/Flocculation-Membrane Filtration
Membrane fouling is a major challenge for the development of membrane technologies due to the high operation and maintenance cost resulting from increased
energy and chemical demand for cleaning and the frequency of membrane replacement [60, 71]. Therefore, in order to overcome membrane fouling during oily
wastewater treatment, the hybrid processes uniting the advantages of pretreatment
methods such as pre-coagulation, pre-adsorption, pre-filtration, and pre-oxidation
with membrane processes are often preferred [60, 72, 73]. Among the various
pretreatments, coagulation/flocculation is the most applied method since it is easy
to operate and relatively inexpensive and can improve UF performance significantly
[74]. During coagulation, oil droplets and colloids destabilize and form larger flocs;
hence, they can be easily held by UF membranes [75].
In a recent bench-scale experiment, Khouni et al. [76] investigated several
technologies to identify the most efficient one for complete removal of oil from
synthetic and industrial oily wastewaters. They employed various treatment processes such as coagulation/flocculation and membrane filtrations such as UF directly
or in hybrid mode. The treatment processes were compared based on their efficiency
in COD, TOC, and turbidity removals. The experiment was done using a commercial
ceramic UF membrane (0.245 m
2 and 150 kDa) in cross-flow filtration mode with
flow rate of 3000 L/h and a trans-membrane pressure at 1.2 bars. However, UF
membrane is susceptible to fouling and not efficient for reusable quality water.
Therefore, in that study, the aim was to improve the purification performances of
UF by investigating its combination with other treatment options such as optimized
coagulation/flocculation as pretreatment and dead-end filtration as post-treatment for
high-quality reusable effluent [76]. When coagulation/flocculation was used as
pretreatment under optimal conditions (defined as 2.4 g/L of aluminum sulfate,
60 mg/L of CHT flocculant, initial pH of 9.2), the hybrid process uniting coagulation/flocculation with UF membrane provided the highest-quality effluent in terms of
turbidity, COD, and TOC removals at about 100%, 98%, and 97%, respectively,
compared to those of coagulation/flocculation and UF membrane processes when
used separately, with membrane permeability of 135 L/(h.m
2 .bar) [76]. The membrane permeability for cases of direct UF and hybrid coagulation/flocculation/UF
was in agreement with an industrial application. However, Khouni et al. [76] found
that the coagulation/flocculation pretreatment was inefficient in terms of reducing
membrane fouling since it did not improve the membrane permeability, 135 L/(h.m
2 .
bar), compared to that attained with direct UF (150 L/(h.m
2 .bar)). The findings of the
study in terms of water quality and membrane performance indicated that the hybrid
coagulation/flocculation/UF process is a promising alternative to water recovery and
pollution removal despite the fact that it does not offer the advantage for valorization
and vegetable oil recovery.
352
D. Kaya and Y.-T. Hung