3.1. MBR configuration

There are two membrane-type alternatives: the first option is submerged MBR configuration such as operating under a vacuum, instead of direct pressure. This configuration may be named immersed as the membrane is placed directly into the liquid. The second option is sidestream MBR configuration such as operating under pressure. In this approach, the membrane is separated from the bioreactor, and a pump is required for pushing the bioreactor effluent into the membrane system and permeates through the membrane. This configuration may be named external cross flow membrane. Flat sheet (FS) and hollow fiber (HF) membranes are generally used for submerged MBR configuration [36]. The two main MBR configurations involve either submerged membranes or external circulation (sidestream configuration) (Figure 1) [32].

Efficient Removal Approach of Micropollutants in Wastewater Using Membrane Bioreactor http://dx.doi.org/10.5772/intechopen.75183 47

the WWTP. These metabolites are persistent due to their weaker sorption potential and high

Literature reported that the concentration of the metabolite in influent and effluent of WWTP is often higher than their parental compounds, and their fate depends on the environmental

Many studies on removal of pharmaceutical compounds from wastewater have been conducted, and many treatment technologies of hospital wastewater treatment have been developed.

Treatment of pharmaceutical residues using MBR processes was discussed in the following

Membranes have been used for many years as biological treatment (aerobic and anaerobic) and solid–liquid separation methods in physical applications. Nowadays, these methods are increasingly attracted to the name of membrane bioreactors combined with biological wastewater treatment [28]. Membrane bioreactor technology is emerging as a mature technology around the world with many full-scale installations for municipal and different wastewater treatments [29–31]. The reactor is operated in a similar manner to a conventional activated sludge process, and there is no need for tertiary stages such as secondary purification and sand filtration. Low-pressure membrane filters such as microfiltration (MF) or ultrafiltration (UF)

Several factors have been reported that may affect contamination in MBR membrane properties such as floc size, mixed liquid viscosity, mixed liquid viscosity, pH, solubility, associated polymeric compounds (EPS), pore size, porosity, surface charge, roughness, and hydrophilicity/hydrophobicity. Operating parameters such as hydraulic retention time (HRT), solid retention time (SRT), and food/mass (F/M) ratio do not have a direct effect on membrane contamination [33, 34]. They affect more sludge properties and therefore sludge filtration properties. Organic contamination is caused by contamination of the membrane during active sludge filtration compared

There are two membrane-type alternatives: the first option is submerged MBR configuration such as operating under a vacuum, instead of direct pressure. This configuration may be named immersed as the membrane is placed directly into the liquid. The second option is sidestream MBR configuration such as operating under pressure. In this approach, the membrane is separated from the bioreactor, and a pump is required for pushing the bioreactor effluent into the membrane system and permeates through the membrane. This configuration may be named external cross flow membrane. Flat sheet (FS) and hollow fiber (HF) membranes are generally used for submerged MBR configuration [36]. The two main MBR configurations involve either

submerged membranes or external circulation (sidestream configuration) (Figure 1) [32].

conditions such as salinity, temperature, pH, and microbial diversity [19, 27].

mobility and, thus, detected in environmental samples [26].

3. General features of MBR systems

to inorganic pollution [35].

3.1. MBR configuration

are used to separate wastewater from the activated sludge [32].

sections.

46 Wastewater and Water Quality

Figure 1. Configuration of MBR systems: (a) submerged (immersed) MBR and (b) sidestream (external) MBR configuration (adapted from [32, 37]).

Since submerged MBRs operate at lower operating fluxes, they have greater hydraulic efficiency due to greater permeability. Working with low flux is important in submerged MBR because this application minimizes membrane contamination or plugging. Membrane blockage is one of the major disadvantages of MBRs and requires cleaning mechanisms that increase cost and make operation difficult. While submerged MBRs require lower pumping costs than external MBRs, they require more aeration. The reason is that the aeration is the main method to prevent membrane clogging. In addition, low flux studies in submerged MBRs require more membrane surface area (and hence greater initial investment cost) when based on constant permeate flux production. Despite these disadvantages, however, the selected and implemented configuration for medium- and large-scale municipal wastewater treatment is the internal submerged MBR [38].

By the year 1990s, this existing accumulation has been rapidly increased by the MBR applications which are made as academic and field studies. MBR producers are Kubota from Japan, Zenon from Canada, Mitsubishi Rayon, and US Filtration [36, 39, 40] (Table 2).



3.3. Advantage and disadvantage of MBR

The best feature of MBRs is that they can easily convert existing activated sludge systems into MBR systems. This can be accomplished by placing submerged membranes in the aeration tank [46]. Membrane bioreactor is separating biological treatment of microorganisms and secondary cleaners from one site to another. The feed water is mixed with the biomass, the mixture is filtered from the membrane, and the biomass is separated from the treated water. Conventional activated sludge (CAS) units compared to the same operational conditions to provide better

Efficient Removal Approach of Micropollutants in Wastewater Using Membrane Bioreactor

http://dx.doi.org/10.5772/intechopen.75183

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At higher MLSS concentrations, the ability to work at higher SRT than conventional treatments, reduced biomass yield, higher quality waste, less hydraulic residence time and lower area footprint generation are advantages of MBRs compared to CAS units [48]. This means a small reactor volume and a reduction in the initial investment cost. They are also more resistant to sudden different hydraulic and organic loads and better respond to existing sustainability criteria for municipal wastewater systems [49]. Biomass separation is independent of the ability of the activated sludge to precipitate as it is achieved by microfiltration or ultrafiltration; in other words, there is no need for final sedimentation, no sludge swelling, and sedimentation problems caused by filament growth. Due to high MLSS concentrations, excess organic loading can be done in the system. MBRs are less likely to be negatively affected by nitrification or by business problems related to the toxic effects of toxic organisms [50]. Since the sludge from the membrane system is

MBRs are becoming increasingly common throughout the world, despite the fact that they can reduce their investment and operating costs and produce effluent that cannot be used despite their different reuse areas. One of the biggest causes of this is the clogging of the wastes, and the transmembrane pressure (TMP) increases to provide a constant flux. Occlusions may occur at the membrane surface or within the membrane pores. Membrane clogs

Meets sensitive discharge standards Cannot meet sensitive discharge standards Decreased reactor volume and foot print Large area is required for the secondary clarifier

Biomass retention is achieved by the membrane Biomass retention is accomplished by gravity

Long SRT and high MLSS imply low sludge yield Low SRT and low MLSS imply high sludge yield

) and low feed to microorganism ratio (F/M) MLSS is about four times less than that of MBR

Less quality effluent is obtained

recovery efficiency in the MBR. Using MBR has many advantages [22, 47] (Table 3).

less than the conventional system, the storage requirement is also reduced [51].

Complete retention of bacterial flocs by the membrane Needs disinfection step

Operated at elevated solid retention time (SRT) Usually operates with low SRT Better removal efficiency for slowly biodegradable micropollutants The low SRT in ASP cannot allow this

MBR CAS

Used as a pretreatment for reverse osmosis (RO) and nanofiltration

Table 3. Comparison of MBR and CAS (adapted from [52]).

(NF) with good effluent quality

High MLSS (10–15 g L<sup>1</sup>

a MLSS, Mixed liquor suspended solids.

b Although Kubota was not found very active in China, it was still referenced here in order to compare flat-sheet membranes made in China and those made in other countries.

Table 2. Summary comparison of membranes used in full-scale MBRs and MBR performance (adapted from [39, 41, 42]).

#### 3.2. Design and operating parameters

A number of parameters must be considered in order to activate an economically appropriate MBR system. These include membrane selection, membrane performance (permeate flow, transmembrane pressure, viscosity), biological performance of microorganisms (biomass concentration, ESS, HBS, F/M ratio), and economic factors (energy consumption, sludge treatment, and disposal cost). These parameters can influence each other, and a positive change can be observed in the other parameter by changing one parameter. For example, a high biomass concentration requires a long CIS, which in turn reduces the cost of sludge disposal and sludge disposal. On the other hand, at high sludge age, the cost of energy also increases as the sludge reaches a viscous structure, which leads to the decomposition of the organic fraction and the amount of oxygen needed to grow the microorganism [43–45].

These designed and operational parameters are used to design the reactor and to be able to differentiate in different configurations applied to the process, to give formulas which are used in the general working principles of MBRs, also in the definition and calculation.

The amount of liquid drained from the surface area of the membrane is called flux. MBRs are mostly 10–100 LMH flux values.
