2.2 Measurements and calculations
The concentrations of NO3--N in the
SAMFCs were measured regularly with the time interval of 20 days. For
example, the first and second denitrification tests were performed at
t20 and t40 respectively. During the
whole period for denitrifers biofilm acclimation, the concentrations of
sodium nitrate keep at 1.21 g L-1, which is
corresponding to the NO3--N
concentration of 200 mg L-1. In order to obtain
optimal C/N ratio, three different concentrations of sodium acetate of
0.82 g L-1 (640 mg L-1 COD), 1.64 g
L-1 (1280 mg L-1 COD) and 2.05 g
L-1 (1600 mg L-1 COD) were used to
control the C/N weight ratio of 1.2, 2.4 and 3, respectively. The
denitrification tests under different C/N ratios were performed at
t20. Three different SSAMFCs were sampled at 1h, 2h, 3h,
4h and 5h and immediately filtered through disposable Millipore filter
with the pore size of 0.22μm for the analyses of nitrate, nitrite at the
same condition simultaneously. NO3--N
concentration measurements were conducted by applying a
spectrophotometer (SpectroDirect, Lovibond, Gremany) using standard
methods.
Denitrification rate (rDN) was fitting by pseudo-first
order reaction with respect to concentration and calculated as follows
according to Jia et al(Jiang et al., 2018),\(\text{Ln}\left(\frac{C_{t}}{C_{0}}\right)=-\text{Kt\ }\), where
C0 is the initial concentration of nitrogen in the form
of nitrate (NO3--N) (mg/L), t is the
time, Ct is the NO3--N
econcentration(mg/L) at t h. K is the observed reaction rate constant.