Quantifying Fugitive CH4 Emissions from Facultative Sludge Lagoons

As part of WERF's U2R08 project, NASA Ames Research Center (ARC) and Brown and Caldwell researchers performed liquid and gaseous phase sample collection at two different sites to focus on the methane (CH4) emissions from facultative sludge lagoons (FSLs) and Photo+ synthetic oxidation ponds (PSOPs). This paper presents a case study on the CH4 emissions from wastewater treatment in facultative sludge lagoons. The Owner of the site preferred to remain anonymous for this paper.The effort under U2R08 was limited to one sampling event. These estimates are based on this sampling event and largely represent an order of magnitude estimate for FSLs receiving and storing anaerobically digested sludge during fall.Overall CH4 fluxes were highly variable for the four FSLs (mean 3.6±3.1 g/m2/d) with the highest fluxes coming from the two lagoons being fed digested biosolids on a daily basis. High CH4 bubble concentrations indicated that methanogens are quite active in these lagoons in the fall. Ebullitive fluxes are significant; contributing at least 75% of the total flux into the atmosphere. However, Since CH4 escaping in bubbles substantially avoids oxidation, ponds with higher oxygen concentrations will be characterized by higher oxidation rates, lower diffusive fluxes, and relatively higher proportions of flux attributable to ebullition. Considering the large surface areas, fugitive CH4 emissions from FSLs can be significant, especially for the lagoons where undigested solids are stored.This investigation was a step in the direction of providing a better understanding of the wastewater treatment industry's true impacts from a GHG standpoint by taking into consideration the emissions from FSLs and PSOPs. Further comprehensive research and year-round measurements will provide much better understanding of the full impact and may lead to develop better solutions to remediate their impact as warranted by their significance.