The performance of a laboratory scale ABR was investigated
using synthetic wastewater containing PNP which is
a toxic matter. In this study, in the start-up period, the ABR
was operated through 45 days without PNP under steadystate
conditions. The PNP and COD concentrations showed
that although the IC50 value of PNP (the p-NP concentration
caused 50% decrease in the methanogenic activity) was
found as 26.5 mg/L, the PNP and COD removal efficiencies
were 99 and 90% at PNP loading rates as high as 33.9 g/m3
day, through the acclimation of anaerobic granular sludge
to high PNP loadings. The COD removal efficiencies were
above 90% until a loading rate of 33.9 g/m3 day applied to the
reactor. After this loading rate, the COD removal efficiencies
started to drop and were measured as 79% at a PNP loading
rate of 67.9 g/m3 day. The maximum PNP removal efficiency
was measured as 99% at a loading rate of 8.32 g/m3 day. The
maximum methane contents were 50–58% at PNP loading
rates varying between 1.94 and 8.32 g/m3 day. The methane
yield (Y) increased to 0.41 from 0.21mL methane/g COD
as the PNP loading rates increased to 8.32 from 0.97 g/m3
day. The optimum PNP loading rate for maximum COD,
PNP removals methane percentage and methane yield were
8.32 g/m3 day.