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A. Z. Yaser and N. N. Safie
There are two types of constructed wetlands namely, free surface flow and subsurface flow. Free surface flow requires larger areas than subsurface flow, but it has
lower costs, while subsurface flow depends on the wastewater discharge in media. In
urban areas subsurface flow is more suitable to be used because of the availability of
areas (ElZein et al. 2016). There are two hydraulic flow systems in subsurface flow
constructed wetland, horizontal flow type, and vertical flow type. In horizontal flow
system, the water laterally flows beneath the surface through the gravel bed, while in
vertical flow system, the water downwardly flows through the increased particle size
layers. The vertical flow system is an efficient, and small-scale wastewater alternative
treatment (approximately 30 people) Randerson (2006).
Generally, CW removes about 80–99% of organic matter, 92–95% of bacteria,
30–80% of nitrogen, and 20–70% of phosphorus from domestic wastewaters depending on the plant type used and flow regime (Ayaz and Akca 2000). Despite its benefits,
the performance of CW may be less consistent than in conventional treatments due
to the environmental changes at different seasons. During the normal flow, high rate
pollutants removal was achieved but the performance was decreased during the heavy
rainfall due to surface overflow. Under normal flow conditions, the removal of pollutants may occur extensively but during the heavy rainfall the surface overflow may
occur and disrupt the effectiveness of CW.
3.1.4 Combined Systems
Membrane Bioreactor (MBR)
Membrane bioreactor is commonly known as the combination of membrane filtration
and biological treatment such as in activated sludge, where the membrane primarily
serves to replace the clarifier in the water treatment (Meng et al. 2009). There are
three types of membranes that are commonly used namely flat sheet (FS), hollow
fiber membrane (HFM) and multi tubular (MT). As compared with the conventional
wastewater treatment processes, MBR has smaller footprint and reactor requirements,
higher effluent quality, better disinfection capability, higher volumetric loading, and
less sludge production (Sari Erkan et al. 2018). Basically, there are two types of
membrane bioreactor (MBR) which are submerged membrane bioreactor and external membrane bioreactor. Even though external MBR is robust and flexible and both
can be used for aerobic and anaerobic process (provided this compartment is added to
the system), but submerged MBR is mostly used in municipal wastewater compared
to external MBRs. This is because submerged MBR has constant permeate flux, less
equipment, easier membrane cleaning and low energy requirements (Sari Erkan et al.
2018).
MBR has been used in treating sewage in North China University, China and
reported average removal for COD and NH 3 –N is 82.6% and 72.2%, respectively
(Sun and Shi 2014). Despite its advantages, MBR is subjected to several disadvantages starting from high operation costs to the membrane fouling problem which
reduces both water quantity and quality as well as increasing the operating costs by
A. Z. Yaser and N. N. Safie
There are two types of constructed wetlands namely, free surface flow and subsurface flow. Free surface flow requires larger areas than subsurface flow, but it has
lower costs, while subsurface flow depends on the wastewater discharge in media. In
urban areas subsurface flow is more suitable to be used because of the availability of
areas (ElZein et al. 2016). There are two hydraulic flow systems in subsurface flow
constructed wetland, horizontal flow type, and vertical flow type. In horizontal flow
system, the water laterally flows beneath the surface through the gravel bed, while in
vertical flow system, the water downwardly flows through the increased particle size
layers. The vertical flow system is an efficient, and small-scale wastewater alternative
treatment (approximately 30 people) Randerson (2006).
Generally, CW removes about 80–99% of organic matter, 92–95% of bacteria,
30–80% of nitrogen, and 20–70% of phosphorus from domestic wastewaters depending on the plant type used and flow regime (Ayaz and Akca 2000). Despite its benefits,
the performance of CW may be less consistent than in conventional treatments due
to the environmental changes at different seasons. During the normal flow, high rate
pollutants removal was achieved but the performance was decreased during the heavy
rainfall due to surface overflow. Under normal flow conditions, the removal of pollutants may occur extensively but during the heavy rainfall the surface overflow may
occur and disrupt the effectiveness of CW.
3.1.4 Combined Systems
Membrane Bioreactor (MBR)
Membrane bioreactor is commonly known as the combination of membrane filtration
and biological treatment such as in activated sludge, where the membrane primarily
serves to replace the clarifier in the water treatment (Meng et al. 2009). There are
three types of membranes that are commonly used namely flat sheet (FS), hollow
fiber membrane (HFM) and multi tubular (MT). As compared with the conventional
wastewater treatment processes, MBR has smaller footprint and reactor requirements,
higher effluent quality, better disinfection capability, higher volumetric loading, and
less sludge production (Sari Erkan et al. 2018). Basically, there are two types of
membrane bioreactor (MBR) which are submerged membrane bioreactor and external membrane bioreactor. Even though external MBR is robust and flexible and both
can be used for aerobic and anaerobic process (provided this compartment is added to
the system), but submerged MBR is mostly used in municipal wastewater compared
to external MBRs. This is because submerged MBR has constant permeate flux, less
equipment, easier membrane cleaning and low energy requirements (Sari Erkan et al.
2018).
MBR has been used in treating sewage in North China University, China and
reported average removal for COD and NH 3 –N is 82.6% and 72.2%, respectively
(Sun and Shi 2014). Despite its advantages, MBR is subjected to several disadvantages starting from high operation costs to the membrane fouling problem which
reduces both water quantity and quality as well as increasing the operating costs by