The MBR Book: Principles and Applications of Membrane

Table 2.5 System facets of denitrification MBR configurations
Configuration Advantages Disadvantages
Fundamentals 59
Extractive Separation of biomass Requires further downstream processing
microporous and carbon source from Carbon source breakthrough
product water Pumping costs
Extractive Dense membrane Requires further downstream processing
ion-exchange significantly reduces risk Potentially complex operation
of carbon source Unknown impact of fouling
breakthrough Comparatively high membrane cost
Pumping costs
Diffusive Non-toxic and low Requires further downstream processing
cost electron donor Biomass breakthrough
Good nitrate removal Potential for fouling to limit mass transfer
Low biomass yield Health and safety risk with respect to
hydrogen gas dissolution
Autotrophs, slow to adapt
Biomass Retention of biomass/ Potential for carbon source
rejection active denitrifiers breakthrough
Limited further downstream
processing
High rate nitrate removal
Proven at full scale
Appropriate dose control to
limit breakthrough
Comparatively low cost
Comparatively simple to operate
Limited knowledge of fouling potential
organic chemical dosed to substitute for the C 10H 19O 3N in Equation (2.21). Electron
donors trialled have included methanol (Mansell and Schroeder, 1999), ethanol
(Fuchs et al., 1997), acetic acid (Barrieros et al., 1998), hydrogen (Haugen et al., 2002)
and sulphur (Kimura et al., 2002), all designed to promote the appropriate heterotrophic
(organic carbon-based electron donor) or autotrophic conditions necessary
for denitrification, and each having its own limitations. As already stated, MBRs can
be employed in three different configurations to augment denitrification (Table 2.5):
● selective extraction of nitrate with porous (Fuchs et al., 1997; Mansell and
Schroeder, 1999) or dense (ion-exchange) membranes (Velizarov et al., 2003);
● supply of gas in molecular form (Ho et al., 2001; Lee and Rittmann, 2002), or
● rejection of biomass (Nuhoglu et al., 2002; Urbain et al., 1996).
2.3.3.1 Extractive microporous MBR
In this configuration (Fig. 2.24a), also known as a “confined cell” or “fixed membrane
biofilm reactor”, nitrate is extracted from the pumped raw water by molecular diffusion
through a physical barrier to a recirculating solution containing the denitrifying biomass.
Pressure should ideally be equalised to reduce the influence of diffusion (Mansell
and Schroeder, 2002). Various materials have been researched to separate effectively
the solutions, including calcium alginate gel, polyacrylamide/alginate copolymer, an
agar/microporous membrane composite structure and various microporous membranes