Emmanuel D. Revellame

Lipid storage compounds in raw activated sludge microorganisms for biofuels and oleochemicals production

Activated sludge contains a microbial population responsible for the biological treatment of wastewater. This microbial population mostly consists of heterothrophic bacteria which utilize the organic content of the wastewater for growth, either as part of their cellular structures or as energy and carbon storage compounds. These compounds are mostly lipidic in nature and are or could be important raw materials for a multitude of applications in biofuel and oleochemical industries. In this study, a municipal activated sludge was analyzed for lipid storage compounds and other compound classes present in significant concentrations. Three extraction techniques, namely; Bligh & Dyer (applied on dried and partially dewatered samples) and accelerated solvent extractions, were initially investigated to identify the one resulting in the highest gravimetric and biodiesel yields. The highest yields were obtained using the Bligh & Dyer of partially dewatered sludge samples and thus, the extracts from this extraction technique were subjected to a series of analytical procedures such as precipitation, solid phase extraction, thin layer chromatography (TLC), gas chromatography with flame ionization detector (GC-FID) and gas chromatography-mass spectrometry (GC-MS) to characterize the major compound classes present. Results indicated that the major compounds in the samples were polyhydroxyalkanoates, wax esters, steryl esters, triacylglycerides, free fatty acids, free sterols and phospholipids. Hydrocarbons, diacylglycerides and monoacylglycerides were also detected. These compounds are either synthesized by microorganisms or from exogenous contributions. Regardless of the source of these compounds, their persistent presence in activated sludge offers another feedstock for a wide range of applications.

Lipid-enhancement of activated sludges obtained from conventional activated sludge and oxidation ditch processes

Lipid-enhancement of activated sludges was conducted to increase the amount of saponifiable lipids in the sludges. The sludges were obtained from a conventional activated sludge (CAS) and an oxidation ditch process (ODP). Results showed 59-222% and 150-250% increase in saponifiable lipid content of the sludges from CAS and ODP, respectively. The fatty acid methyl ester (FAMEs) obtained from triacylglycerides was 57-67% (of total FAMEs) for enhanced CAS and 55-73% for enhanced ODP, a very significant improvement from 6% to 10% (CAS) and 4% to 8% (ODP). Regardless of the source, the enhancement resulted in sludges with similar fatty acid profile indicating homogenization of the lipids in the sludges. This study provides a potential strategy to utilize existing wastewater treatment facilities as source of significant amount of lipids for biofuel applications.

Parametric Study on the Production of Renewable Fuels and Chemicals from Phospholipid-Containing Biomass

Heterogeneous catalytic cracking of lipids into transportation fuels and other specialty chemicals offers a unique opportunity to provide sustainable energy while utilizing the current petroleum infrastructure. This study addresses a possible route for the utilization of phospholipid-containing biomass for production of renewable fuels and chemicals. The first part of the study focused on reaction pathways associated with the catalytic cracking of model phospholipid into fuel-type compounds. The results indicated that phospholipid cracking proceeds via acid-catalyzed mechanisms, which resulted to cleavage of fatty acids and glycerol moieties. Microbial lipids, which contain large concentrations of phospholipids, are a potential non-food related feedstock to displace petroleum. Among possible sources of microbial lipids, activated sludge offers a distinct advantage for its availability and abundance at a potential fee. The second part of this work dealt with the conversion of activated sludge to chemicals of value as fuel components through fluidized-bed catalytic cracking. The effect of moisture level and catalyst loading were determined. Results indicated that moisture level of up to 15 % (weight) has no effect on total product yield. On the other hand, higher catalyst loading resulted to a higher yield of gaseous product. Significant coke deposition was inferred as indicated by the high proportion of phenolic compounds produced from pyrolytic reactions. The results of this study provide a potential route of utilizing bulk lipid feedstocks, without the removal of phosphorus-containing molecules, to produce fuel components.

Microbial Lipid Accumulation Capability of Activated Sludge Feeding on Short Chain Fatty Acids as Carbon Sources through Fed-Batch Cultivation

The potential of activated sludge microbial lipid technology as a sustainable energy platform has been recognized in the past years, but it has been challenged by the cost of carbon sources. This study hypothesized that Short Chain Fatty Acids (SCFAs) that can be derived from organic wastes can be alternative carbon sources. Therefore, this work evaluated the capability of activated sludge microbial consortia to accumulate microbial lipid by fed-batch feeding of SCFAs acetic acid, propionic acid, and butyric acid that were fed every 12 h period in 5 liter bioreactors. Activated sludge microbial consortia can accumulate microbial lipid by feeding on acetic acid. Acetic acid at 1.5 g/L loading per feeding enhanced the lipid content of activated sludge up to around 20% (w/w) dry biomass. This is comparable to that of oleaginous microorganisms. The feeding of nitrogen source (ammonium) at molar C/N of 70 only at the start resulted in significant lipid accumulation as compared to that from feeding of nitrogen for every feeding of the carbon source (acid-substrates). Fatty Acid Methyl Esters (FAMEs) profiles of the extracted lipids changed during cultivation. A biodiesel volumetric yield increase of 325% (w/w) from initial culture was achieved. This microbial lipid enhancement was confirmed using fluorescence microscopy imaging of neutral lipids, which also showed that the neutral lipid-containing cells are in the size range of yeasts. This work proved the hypothesis that activated sludge microbial consortia can accumulate microbial lipid by feeding on SCFAs.