A 7 L lab-scale
bioreactor with a working volume of 5 L was operated semi-continuously
as an anaerobic sequencing batch reactor (ASBR) for 339 days. The
ASBR was run on a 24 h cycle through four cycles: (1) feeding (8–10
min), (2) react phase with continuous mixing and pH adjustment (22
h 40 min), (3) settling (1 h), and (4) decanting for withdrawal of
effluent equal to the volume of the influent fed (8–10 min).
The bioreactor was temperature controlled at 40 ± 0.5 °C
until Day 73 and at 37 ± 0.5 °C from Days 74 to 339. The
bioreactor pH was maintained at 5.5 ± 0.1 by the automatic addition
of 3 M NaOH with the help of LabVIEW (National Instruments, Austin,
TX). The biogas was collected in a 5 L Tedlar gas bag. Rumen content
(17.1 ± 1.0 g volatile solids (VS) L–1), obtained
from a fistulated cow from a dairy farm at Michigan State University
(East Lansing, MI), was used as an inoculum. The bioreactor was operated
at a hydraulic retention time (HRT) of 2–4 days and an organic
loading rate (OLR) of (10.5 ± 7.0 g soluble chemical oxygen demand
(sCOD) L–1 d–1). The solids retention
time (SRT) was controlled around 9.7 ± 5.8 days from Days 20
to 81 by wasting suspended biomass from the bioreactor (during the
react phase) and effluent (after the decant phase). The volatile suspended
solids concentrations in both suspended biomass and effluent were
considered for SRT calculation. Additional operational details are
described by Shrestha et al.3 (link)A mixture
of waste beer containing ethanol and permeate extracted from an acidogenic
bioreactor20 treating food waste was fed
to the ASBR once a day. The influent was prepared once a week. Waste
beer was obtained from Jolly Pumpkin Brewery (Dexter, MI), where it
represents 2–19% of the total volumetric beer production (Doug
Knox, Sustainability Manager, personal communication). The sodium
salt of 2-BES (Sigma-Aldrich, St. Louis, MO) was added to the ASBR
at the beginning of the react phase roughly every 2 weeks, the first
two times on Days 230 and 246, and every 10 days (equivalent to approximately
three HRTs) after that on Days 259, 269, 278, 287, 296, 305, and 314
to reach a bioreactor concentration of 10 mM (∼10.8 g in 5
L working volume of the bioreactor) immediately after each addition.
The 2-BES dose was selected based on literature values obtained from
anaerobic mixed-culture studies.21 (link),22 (link) The change
in 2-BES concentration over time was estimated using the initial concentration
added, the volume of effluent wasted per day, and the bioreactor working
volume. Thermodynamic calculations were performed to evaluate the
feasibility of different reactions during the period 2-BES was added
(details are given in theSupporting Information [SI]).
bioreactor with a working volume of 5 L was operated semi-continuously
as an anaerobic sequencing batch reactor (ASBR) for 339 days. The
ASBR was run on a 24 h cycle through four cycles: (1) feeding (8–10
min), (2) react phase with continuous mixing and pH adjustment (22
h 40 min), (3) settling (1 h), and (4) decanting for withdrawal of
effluent equal to the volume of the influent fed (8–10 min).
The bioreactor was temperature controlled at 40 ± 0.5 °C
until Day 73 and at 37 ± 0.5 °C from Days 74 to 339. The
bioreactor pH was maintained at 5.5 ± 0.1 by the automatic addition
of 3 M NaOH with the help of LabVIEW (National Instruments, Austin,
TX). The biogas was collected in a 5 L Tedlar gas bag. Rumen content
(17.1 ± 1.0 g volatile solids (VS) L–1), obtained
from a fistulated cow from a dairy farm at Michigan State University
(East Lansing, MI), was used as an inoculum. The bioreactor was operated
at a hydraulic retention time (HRT) of 2–4 days and an organic
loading rate (OLR) of (10.5 ± 7.0 g soluble chemical oxygen demand
(sCOD) L–1 d–1). The solids retention
time (SRT) was controlled around 9.7 ± 5.8 days from Days 20
to 81 by wasting suspended biomass from the bioreactor (during the
react phase) and effluent (after the decant phase). The volatile suspended
solids concentrations in both suspended biomass and effluent were
considered for SRT calculation. Additional operational details are
described by Shrestha et al.3 (link)A mixture
of waste beer containing ethanol and permeate extracted from an acidogenic
bioreactor20 treating food waste was fed
to the ASBR once a day. The influent was prepared once a week. Waste
beer was obtained from Jolly Pumpkin Brewery (Dexter, MI), where it
represents 2–19% of the total volumetric beer production (Doug
Knox, Sustainability Manager, personal communication). The sodium
salt of 2-BES (Sigma-Aldrich, St. Louis, MO) was added to the ASBR
at the beginning of the react phase roughly every 2 weeks, the first
two times on Days 230 and 246, and every 10 days (equivalent to approximately
three HRTs) after that on Days 259, 269, 278, 287, 296, 305, and 314
to reach a bioreactor concentration of 10 mM (∼10.8 g in 5
L working volume of the bioreactor) immediately after each addition.
The 2-BES dose was selected based on literature values obtained from
anaerobic mixed-culture studies.21 (link),22 (link) The change
in 2-BES concentration over time was estimated using the initial concentration
added, the volume of effluent wasted per day, and the bioreactor working
volume. Thermodynamic calculations were performed to evaluate the
feasibility of different reactions during the period 2-BES was added
(details are given in the
