4Waste Grease Biodiesel Production at a Wastewater Treatment Plant

Abstract

East Bay Municipal Utility District (EBMUD) conducted a pilot study to demonstrate the production and use of biodiesel from interceptor grease waste. Bench-scale testing was followed by pilot-scale production of 200 to 400-L batches. Brown grease with a free fatty acid (FFA) content of 54-100% was obtained from interceptor grease hauled to EBMUD's wastewater treatment plant. Free fatty acids were converted using a one or two step acid esterification reaction and triglycerides were converted using a sodium methoxide catalyzed transesterification reaction, both at ambient temperatures. Impurities associated with the brown grease, such as sulfur, proved to be problematic. Biodiesel was used to fuel heavy duty diesel trucks as B20 and B100 for multiple weeks. No operational or performance problems were reported. Preliminary energy and economic comparison to anaerobic digestion show a more favorable energy balance for biodiesel and a potentially more favorable economic value for biodiesel, but with significant risk.

A solvent-free approach to extract the lipid fraction from sewer grease for biodiesel production

“…FOG in the sewer grease was primarily in the form of FFA, which is consistent with other studies (Chakrabarti et al, 2008;Ngo et al, 2011). The moisture of a later batch of sewer grease averaged 56.3 ± 1.3%.…”

“…soap, food debris), higher FFA content (due to hydrolysis and prolonged residence in water), and emulsion (Stacy et al, 2014). Given the highly emulsified sewer grease from MSDGC, the reported lipid separation method for trap grease, primarily heating, (Chakrabarti et al, 2008;Wang et al, 2008;Ngo et al, 2011;Turner et al, 2011;Jolis and Martis, 2013;Watson, 2011;Noshadi et al, 2014) is insufficient to separate the lipid fraction (Chan, 2010;Chung and Young, 2013;Ducoste, 2013). In addition, the presence of calcium soap in the sewer grease that binds the lipids also adds to the challenge in separating the lipid fraction by heating (Keener et al, 2008;He et al, 2011).…”

Identification of Sulfur‐Containing Impurities in Biodiesel Produced From Brown Grease

“…BGL refers to the lipid components of wastewater residuals, such as GTW and SSG that are insoluble in water. A major challenge to producing biodiesel from wastewater residuals is the high sulfur content of BGL (Cairncross, Olson, & Spatari, ; Chakrabarti, Hake, Zarchi, & Gray, ; Gardner, Shang, Yuan, & Gray, ; Hums, Cairncross, & Spatari, ). BGL is often referred to as fats, oils, and greases (FOG) by the wastewater community.…”

“…In agreement with the observations made by He et al (), several researchers have reported that the sulfur content in FAME is less than the sulfur content in the parent oil (Alleman et al, ; Kim et al, ; Ma et al, ; Ragauskas et al, ). BGL typically contains 230–850 ppm S and in most cases, is reduced nearly into half upon transesterification to FAME (Cairncross et al, ; Chakrabarti et al, ; Gardner et al, ; Hums et al, ). Therefore, sulfur reduction is initially achieved via process steps involving transesterification and esterification reactions.…”

“…Therefore, sulfur reduction is initially achieved via process steps involving transesterification and esterification reactions. Employing chemical and physical methods, such as distillation, absorption, and oxidation, researchers have shown that it is possible to reduce the sulfur content in BGL‐derived FAME to 7–100 ppm (Cairncross et al, ; Chakrabarti et al, ; Gardner et al, ; Hums et al, ).…”