Materials and methods
UABF reactor operation
A lab-scale UABF reactor in continuous mode was used
for nitrogen removal from synthetic wastewater by the
Anammox process (Figure 1). The bioreactor was
inoculated with 400 mL of granule sludge. The volatile
suspended solid (VSS) of inoculated sludge in the beginning
was 12.3 g VSS/L (provided from an upflow anaerobic
sludge blanket (UASB) plant, Pegah Milk Factory,
Tehran, Iran). The culture of the Anammox sludge was
prepared by decreasing the COD/N ratio in the influent
gradually and lasted approximately 120 days [18]. The labscale
bioreactor with the effective volume of 1.8 L
consisted of a doubled wall plexiglass cylindrical column
(25 cm high), which was comprised of: an inner cylinder
(internal diameter of 11 cm and external diameter of
12 cm), the outer cylinder as water jacket (internal diameter
of 14 cm and external diameter of 15 cm).
Temperature was kept at 35±1C by a set including a recycling
pump used for pumping the circulated water from
the water tank to the outer cylinder (according to
Figure 1), and a thermostat was installed on the water
tank. The body of the reactor was covered with a dark
cover to prevent light penetration and algal growth. The
plastic media (bee-cell 2000) was filled to 50% of the total
reactor volume. This type of media was used as a biofilm
support material due to its large surface area (650 m2
/m3
)
and high porosity (pore volumes up to 87%).
Initially, the bioreactor was operated in a continuous
mode with the synthetic wastewater flow rate of 1.8 L/d.
pH was kept at a range of 7.5-8.0 by adding sodium bicarbonate.
The initial ammonium and nitrite concentrations
were 60 and 80 mgN/L, respectively. The operational
trend consisted of increasing the concentration of influent
nitrogen and decreasing the HRT stepwisely.