four basic phenomena, which are hydrolysis, acidogenesis, acetogenesis, and
methanogenesis. This process produces a high content of methane as a side product
and can be used as fuel.
Activated sludge and biological filter methods have been the most commonly
used biological treatment for the oily wastewater treatment applications (Yu et al.
2017). Activated sludge is an aerobic process whereby the oil particles and other
organic matters are adsorbed on the surface of the microorganisms in which the
organic matters will be decomposed. While in the biological filter method, the
microorganisms are attached to the filter surface. The wastewater flows through
the filter surface and the adsorption of organic pollutants occurs. The adsorbed
organic matters are then decomposed into simpler compounds by the microorganisms. These biological methods are usually employed as a secondary treatment after
the wastewater pretreatment process (Kulkarni 2016; Wan Ikhsan et al. 2017). In
most cases, a consortium of microorganisms is used in removing hazardous pollutants in oily wastewater. The synergistic interactions among different microorganisms in the consortium may lead to the complete decomposition of the organic
matters, hence it is more advantageous compared to pure bacterial culture (Cerqueira
et al. 2011). Song et al. (2011) treated oily wastewater by combining a whole-cell
lipase together with fungal lipase and a Yarrowia lipolytica. The results showed that
97.6% of chemical oxygen demand and 96.9% of the oil were successfully removed
after 72 h of treatment. Nevertheless, lower chemical oxygen demand and oil
removals of 91.8% and 87.1%, respectively were observed when only Yarrowia
lipolytica was applied. Meanwhile, 45.1% and 67.5% of oil and chemical oxygen
demand were respectively removed from the control system when no cell was added.
Another study by Cerqueira et al. (2011) also reported that the bacterial consortium
of Stenotrophomonas acidaminiphila, Bacillus megaterium, Bacillus cibi, Pseudomonas aeruginosa, and Bacillus cereus demonstrated an excellent oily sludge
degradation capacity with the aliphatic and aromatic fractions degradation efficiencies of 90.7% and 51.8%, respectively, compared to the pure bacterial cultures.
However, the biological treatment is not practically well embraced in the oily
wastewater treatment due to high difficulty in handling the diverse microbe behaviors under different environmental conditions. Yet, recent research in this area has
yielded remarkable contaminant removal rates from oily wastewater. Khondee et al.
(2012) investigated the treatment of lubricants in wastewater by using an internal
loop airlift bioreactor containing chitosan immobilized-Sphingobium sp. The
chitosan immobilized bacteria demonstrated high efficiency in removing the automotive oils from both synthetic and carwash wastewaters. In fact, the semicontinuous test showed 80–90% of the hydrocarbons was successfully removed
from both synthetic and carwash wastewaters. Moreover, 85% of the petroleum
hydrocarbons and 73% of the chemical oxygen demand were removed from the
carwash wastewater using an airlift bioreactor via the internal loop bioreactor
containing 4 g/L immobilized bacteria. Xie et al. (2007) applied a biological aerated
filter for the treatment of polluted oily wastewater at the optimum operating conditions with the flow volume ratio of air to water of 5:1, 1 h cycle time and with
backwash cycling of 4–7 days. The outcomes showed the average chemical oxygen
364
M. H. D. Othman et al.
methanogenesis. This process produces a high content of methane as a side product
and can be used as fuel.
Activated sludge and biological filter methods have been the most commonly
used biological treatment for the oily wastewater treatment applications (Yu et al.
2017). Activated sludge is an aerobic process whereby the oil particles and other
organic matters are adsorbed on the surface of the microorganisms in which the
organic matters will be decomposed. While in the biological filter method, the
microorganisms are attached to the filter surface. The wastewater flows through
the filter surface and the adsorption of organic pollutants occurs. The adsorbed
organic matters are then decomposed into simpler compounds by the microorganisms. These biological methods are usually employed as a secondary treatment after
the wastewater pretreatment process (Kulkarni 2016; Wan Ikhsan et al. 2017). In
most cases, a consortium of microorganisms is used in removing hazardous pollutants in oily wastewater. The synergistic interactions among different microorganisms in the consortium may lead to the complete decomposition of the organic
matters, hence it is more advantageous compared to pure bacterial culture (Cerqueira
et al. 2011). Song et al. (2011) treated oily wastewater by combining a whole-cell
lipase together with fungal lipase and a Yarrowia lipolytica. The results showed that
97.6% of chemical oxygen demand and 96.9% of the oil were successfully removed
after 72 h of treatment. Nevertheless, lower chemical oxygen demand and oil
removals of 91.8% and 87.1%, respectively were observed when only Yarrowia
lipolytica was applied. Meanwhile, 45.1% and 67.5% of oil and chemical oxygen
demand were respectively removed from the control system when no cell was added.
Another study by Cerqueira et al. (2011) also reported that the bacterial consortium
of Stenotrophomonas acidaminiphila, Bacillus megaterium, Bacillus cibi, Pseudomonas aeruginosa, and Bacillus cereus demonstrated an excellent oily sludge
degradation capacity with the aliphatic and aromatic fractions degradation efficiencies of 90.7% and 51.8%, respectively, compared to the pure bacterial cultures.
However, the biological treatment is not practically well embraced in the oily
wastewater treatment due to high difficulty in handling the diverse microbe behaviors under different environmental conditions. Yet, recent research in this area has
yielded remarkable contaminant removal rates from oily wastewater. Khondee et al.
(2012) investigated the treatment of lubricants in wastewater by using an internal
loop airlift bioreactor containing chitosan immobilized-Sphingobium sp. The
chitosan immobilized bacteria demonstrated high efficiency in removing the automotive oils from both synthetic and carwash wastewaters. In fact, the semicontinuous test showed 80–90% of the hydrocarbons was successfully removed
from both synthetic and carwash wastewaters. Moreover, 85% of the petroleum
hydrocarbons and 73% of the chemical oxygen demand were removed from the
carwash wastewater using an airlift bioreactor via the internal loop bioreactor
containing 4 g/L immobilized bacteria. Xie et al. (2007) applied a biological aerated
filter for the treatment of polluted oily wastewater at the optimum operating conditions with the flow volume ratio of air to water of 5:1, 1 h cycle time and with
backwash cycling of 4–7 days. The outcomes showed the average chemical oxygen
364
M. H. D. Othman et al.