Samples for various chemical analyses
were collected once a week from the influent and the bioreactor content
during the ASBR mixing phase and two to three times a week from the
effluent during the ASBR settling phase. sCOD analyses were conducted
using Lovibond medium-range (0–1500 mg L–1) COD digestion vials (Tintometer, Germany). Carboxylic acids (C2–C8,
including iso-forms of C4 and C5) and ethanol concentrations were
determined by an Agilent Technologies 7890B gas chromatograph (Santa
Clara, CA) equipped with a stabilwax-DA column (Restex) and a flame
ionization detector (GC-FID). The samples for GC-FID and sCOD were
acidified with phosphoric acid and sulfuric acid, respectively, centrifuged,
and filtered through 0.45 μm nylon membrane filters (TISCH Scientific,
North Bend, OH) before analyses. The concentrations of SCCAs and MCCAs
are reported as the sum of undissociated carboxylic acids and dissociated
carboxylates, even though we refer to them by their dissociated carboxylate
names for simplicity. The concentrations of SCCAs (including acetate,
propionate, n-butyrate, and n-valerate) and MCCAs (including caproate,
enanthate, and caprylate) are expressed on a molar basis. To determine
net acetate concentrations, the influent concentrations were subtracted
from the corresponding effluent concentrations. Gas collected in the
Tedlar gas bag was measured daily with a 0.1 L gas-tight glass syringe.
Gas composition (H2, CO2, and CH4) was determined two to three times a week using a Gow-Mac Series
gas chromatography (Bethlehem, PA) equipped with a thermal conductivity
detector. PH2 was calculated by considering the H2 percentages in the gas and assuming that the headspace in the bioreactor
was at atmospheric pressure. Detailed information on both of the gas
chromatographs is given in theSI .
were collected once a week from the influent and the bioreactor content
during the ASBR mixing phase and two to three times a week from the
effluent during the ASBR settling phase. sCOD analyses were conducted
using Lovibond medium-range (0–1500 mg L–1) COD digestion vials (Tintometer, Germany). Carboxylic acids (C2–C8,
including iso-forms of C4 and C5) and ethanol concentrations were
determined by an Agilent Technologies 7890B gas chromatograph (Santa
Clara, CA) equipped with a stabilwax-DA column (Restex) and a flame
ionization detector (GC-FID). The samples for GC-FID and sCOD were
acidified with phosphoric acid and sulfuric acid, respectively, centrifuged,
and filtered through 0.45 μm nylon membrane filters (TISCH Scientific,
North Bend, OH) before analyses. The concentrations of SCCAs and MCCAs
are reported as the sum of undissociated carboxylic acids and dissociated
carboxylates, even though we refer to them by their dissociated carboxylate
names for simplicity. The concentrations of SCCAs (including acetate,
propionate, n-butyrate, and n-valerate) and MCCAs (including caproate,
enanthate, and caprylate) are expressed on a molar basis. To determine
net acetate concentrations, the influent concentrations were subtracted
from the corresponding effluent concentrations. Gas collected in the
Tedlar gas bag was measured daily with a 0.1 L gas-tight glass syringe.
Gas composition (H2, CO2, and CH4) was determined two to three times a week using a Gow-Mac Series
gas chromatography (Bethlehem, PA) equipped with a thermal conductivity
detector. PH2 was calculated by considering the H2 percentages in the gas and assuming that the headspace in the bioreactor
was at atmospheric pressure. Detailed information on both of the gas
chromatographs is given in the
