4.7. MBBR (moving biological bed reactor)
MBBR process is based on the use of suspended porous polymeric
carriers, kept in continuous movement in the aeration tank,
while the active biomass grows as a biofilm on the surfaces of them.
Its principle is the growing of a fixed biofilm on plastic elements
which move freely in the biological reactor. Main advantages of this
method compared to conventional suspended-growth processes
seems to be: higher biomass concentrations, no long sludgesettling
periods, lower sensitivity to toxic compounds and both
organic and high ammonia removals in a single process. Welander
et al. (1998) reported nearly 90% nitrogen removal while the COD
was around 20%. In case of treating high strength ammonia
leachate, no inhibition of nitrification is encountered. Moreover, the
use of granular activated carbon (GAC) as porous material offers an
appropriate surface to adsorb organic matter and optimized conditions
for enhanced biodegradation. Thus, steady-state equilibrium
is established between adsorption and biodegradation. Imai
et al. (1995) developed an efficient biological activated carbon
fluidized bed process. Nearly, 70% refractory organics were
removed by coupling biological treatment and adsorption process.
After optimizing the reactor operating regime, Horan et al. (1997)
proved possible to reach 85e90% ammonia and 60e81% COD
reduction.
5. Techniques