Influence of Nitrogen to Phosphorus Ratio and CO2 Concentration on Lipids Accumulation of Scenedesmus dimorphus for Bioenergy Production and CO2 Biofixation.

The potential of Scenedesmus dimorphus microalgae for CO2 biofixation and lipid biosynthesis for bioenergy applications was evaluated in this study. Batch experiments were conducted using synthetic tertiary municipal wastewater samples at several nitrogen to phosphorus (NP) ratios (1 : 1 to 8 : 1) and CO2 concentrations (∼0%, 2%, 4%, and 6% CO2 in supplied air). Scenedesmus dimorphus was cultivated for 25 days and the growth is highly dependent on the CO2 concentration and the NP ratio. An NP ratio of 2 : 1 produces a biomass yield of 733 mg/L when the microalga culture was supplied with air enriched with 2% CO2 . The maximum CO2 biofixation rate of 49.6 mg L-1 d-1 is at an NP ratio of 8 : 1 with 4% CO2 . A colorimetric technique depending on sulpho-phospho-vanillin (SPV) was utilized for the determination of the intracellular lipid content. The highest lipid content of 31.6% as the dry weight of the biomass is at an NP ratio of 1 : 1 and 6% CO2 . These results indicate that supplementation of suitable CO2 with favorable NP ratio has a considerable effect on lipid accumulation in the microalgae Scenedesmus dimorphus biomass.

Characterization of aerobic oil and grease-degrading bacteria in wastewater.

A bacterial consortium that degrades cooking oil (CO) has been isolated in wastewater (WW) samples, by enrichment in olive CO. This consortium could degrade 90% of CO within 7-9 days (from an initial 1% [w/v]), and it is more active at alkaline conditions. The 16S ribonucleic acid (RNA) gene analysis showed that it contains five bacterium species: Stenotrophomonas rhizophila, Sphingobacterium sp., Pseudomonas libanensis, Pseudomonas poae and Pseudomonas aeruginosa. This consortium can degrade the free fatty acids (FFA): palmitic, stearic, oleic, linoleic and linolenic acids; glycerol, glucose and amylose; and albumin, but could not efficiently degrade carboxymethyl-cellulose. Each strain could also degrade CO and FFAs. The level of bacterial crude-activity of extracellular lipases was found to be between 0.2 and 4U/ml. Using synthetic WW, the consortium could reduce 80% of the chemical oxygen demand [from 10550 ± 2828 mg/l], 80% of nitrogen (from 410 ± 78 mgl/l) and 57% of phosphorus (from 93 ± 25 mg/l). Thus, this consortium can be utilized in the removal of CO from WW.