Headspace gas chromatography with flame ionization detection (HS-GC-FID) for the determination of dissolved methane in wastewater

There is currently a need for a simple, accurate and reproducible method that quantifies the amount of dissolved methane in wastewater in order to realize the potential methane that can be recovered and account for any emissions. This paper presents such a method, using gas chromatography with flame ionization detection fitted with a GS-Gas PRO column coupled with a headspace auto sampler. A practical limit of detection for methane of 0.9 mg L⁻¹, with a retention time of 1.24 min, was obtained. It was found that the reproducibility and accuracy of the method increased significantly when samples were collected using an in-house constructed bailer sampling device and with the addition of 100 μL hydrochloric acid (HCl) and 25% sodium chloride (NaCl) and sonication for 30 min prior to analysis. Analysis of wastewater samples and wastewater sludge collected from a treatment facility were observed to range from 12.51 to 15.79 mg L⁻¹ (relative standard deviation (RSD) 8.1%) and 17.56 to 18.67 mg L⁻¹ (RSD 3.4%) respectively. The performance of this method was validated by repeatedly measuring a mid-level standard (n = 8; 10 mg L⁻¹), with an observed RSD of 4.6%.