a range of OLR at which constant values of methane yield were obtained
(0.3–1.3 kg VS m3 d1 resulted in methane yields of
0:3 m3 kg VS1
added). However, lower values of OLR resulted in significantly
lower methane yields.
With regard to R2, a decrease in HRT had no effect on methane
yield. Average weekly volumetric methane production is presented
in Fig. 1A. Although methane yield remained constant during the
experiment, an increase in the volumetric methane production
with decreasing HRT (OLR increase) was observed.
It has been demonstrated that low pH [16], free ammonia concentration
[10] and TVFA accumulation [17] are the main parameters
responsible of methanogenic processes inhibition. Due to the
acidity of VPW, pH in R2 feed was lower than in R1 feed (Table
1). However, SM buffered the system providing average pH values
of 8.1 and 7.8 for R1 and R2, respectively, throughout the experimental
time (Table 3).
Due to the high nitrogen content of this substrate, N—NHþ4
concentration
was mainly dependent on the content of SM in the feeding
mixture (Table 1). Free ammonia concentrations at the end of
the experiments were calculated for all treatments in accordance
a range of OLR at which constant values of methane yield were obtained(0.3–1.3 kg VS m3 d1 resulted in methane yields of0:3 m3 kg VS1added). However, lower values of OLR resulted in significantlylower methane yields.With regard to R2, a decrease in HRT had no effect on methaneyield. Average weekly volumetric methane production is presentedin Fig. 1A. Although methane yield remained constant during theexperiment, an increase in the volumetric methane productionwith decreasing HRT (OLR increase) was observed.It has been demonstrated that low pH [16], free ammonia concentration[10] and TVFA accumulation [17] are the main parametersresponsible of methanogenic processes inhibition. Due to theacidity of VPW, pH in R2 feed was lower than in R1 feed (Table1). However, SM buffered the system providing average pH valuesof 8.1 and 7.8 for R1 and R2, respectively, throughout the experimentaltime (Table 3).Due to the high nitrogen content of this substrate, N—NHþ4concentrationwas mainly dependent on the content of SM in the feedingmixture (Table 1). Free ammonia concentrations at the end ofthe experiments were calculated for all treatments in accordance
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