Molecular sieve 13x packed column

Total COD (tCOD) and soluble COD (sCOD) were measured by the closed reflux colorimetric method [27 ]. Solids, total nitrogen (TN), and total carbon (TC) were determined as per the procedures described previously. Volatile fatty acids (VFAs, ≤C₆) were analyzed using a gas chromatograph (GC 2014, Shimadzu, Japan) equipped with a flame ionization detector and a carbowax packed column (Supelco, Bellefonte, PA, USA), with nitrogen as the carrier gas. Samples for sCOD and VFA measurements were prepared by filtration through a glass-fiber filter (Whatman GF/C; 1.2 μm pore size). Biogas composition was determined using a gas chromatograph (SRI 8610C; Torrance, CA, USA) equipped with a thermal conductivity detector and a molecular sieve 13X packed column (Restek, Bellefonte, PA, USA), with argon as the carrier gas. Total ammonia nitrogen (TAN) and lactic acid were quantified using a 7100 MBS analyzer (YSI Life Sciences, Yellow Springs, OH, USA). Phosphorous, calcium, potassium, and sodium were quantified using an inductively coupled plasma mass spectrometer (ICP-MS; Leeman Labs Inc., Hudson, NH, USA).

Samples were collected in the last three cycles of each batch. Biogas produced by the reactors was collected using water displacement for volume and rate measurement. After moisture removal, CH₄ concentration was determined using a GC-2014 Gas Chromatograph (Shimadzu) equipped with a Molecular Sieve 13X packed column (2000 × 2 mm, Restek) and a thermal conductivity detector. For chemical measurements, effluent samples were filtered through 0.22 µm membranes. Soluble COD was measured with a COD digestion kit and DR/4000 U Spectrophotometer (HACH). TOC was measured with a TOC-V Analyzer (Shimadzu). VFAs were measured with a 1200 Series HPLC System equipped with a Hi-Plex H column for organic acids (Agilent). Ethanol concentration was measured with a GC-2014 Gas Chromatograph (Shimadzu) equipped with a flame ionization detector. The pH of the effluent was measured using a benchtop pH meter (Fisher). Current production resulted from poised potential was recorded with the manufacturer's software (BioLogic), and CE was calculated as previously described^{68 (link)}.