Sequencing batch airlift reactors (SBAR): a suitable technology for treatment and valorization of mineral oil wastewaters towards lipids production.

Produced water (PW) and spent oil-based wastewaters are some of the largest mineral oil wastewaters produced. Due to the high toxicity of hydrocarbons, several countries set stringent discharge limits and its treatment is compulsory before discharge. In this work, biological treatment of mineral oil wastewaters coupled with the production of bacterial lipids is demonstrated in sequential batch airlift reactors (SBAR). Two SBAR (2 L working volume) were used for treatment of PW and lubricant-based wastewater (LW), inoculated with Alcanivorax borkumensis SK2 (SBARAb+PW) and Rhodococcus opacus B4 (SBARR.o+LW), respectively. A total petroleum hydrocarbon removal (TPH) efficiency up to 96% and 80% were achieved for SBARAb+PW and SBARR.o+LW, respectively. Intracellular lipids production in SBARAb+PW increased when lower TPH/N ratios and higher feast stage duration were applied (up to 0.74 g g-1 cell dry weight (CDW)), whereas in SBARR.o+LW higher lipids production was observed for higher TPH/N ratios (0.94 g g-1 in CDW). Triacylglycerols (TAG) were the main intracellular lipid accumulated in both SBARAb+PW and SBARR.o+LW operations, while wax ester (WE) production was only observed extracellularly in the SBARAb+PW.

Conversion of waste cooking oil into biogas: perspectives and limits.

Each year, large quantities of waste cooking oils are produced worldwide which are currently reused mainly for biodiesel production. Since lipids have a very high potential for biomethanation, the production of biogas is a possible alternative for the recycling of edible used oils. The digestion of fats is hindered mainly by their hydrophobicity, which implies a biphasic system with problems of floating and foaming of the oily materials, and by the accumulation of long-chain fatty acids, which are toxic to microbial consortia. The objectives of this review were to highlight the recycling potential of waste cooking oil to biogas production and to facilitate the application of the technology by identifying solutions to overcome biological and engineering limits to its diffusion. Particular attention was paid to the microbial populations involved, to the process factors whose control is important to improve the digestion of fats such as lipid concentration, pH, temperature, and agitation, and to technological solutions whose application also aims to improve digestion, such as pretreatment of raw materials and co-digestion of fats with other feedstocks. The state of the art in reactor designs suitable for lipid digestion was also examined.

Pig slurry improves the anaerobic digestion of waste cooking oil.

Recycling of waste cooking oil greatly reduces the environmental impact of its disposal. As fats can give rise to high methane yields, the use of waste cooking oil for biogas production seems a promising solution. The aim of this work was to test the anaerobic digestion performances of waste cooking oil in co-digestion with pig slurry, the fat degradation dynamics and the relationships between digestion performances and pig slurry compositional properties. In laboratory batch, static, mesophilic anaerobic conditions, the treatments waste cooking oil in synthetic hydration medium (WCO + HM) and waste cooking oil in pig slurry (WCO + PS) were compared. Pig slurry alone was included for reference. Co-digestion with pig slurry greatly shortened the lag phase (by 58.3%) and increased the overall methane production per reactor (by 15.5%). An increase in emulsion stability of the biphasic system and an earlier triglyceride degradation were associated with the better anaerobic digestion performances in the WCO + PS reactors. A negative, however reversible, effect of palmitic acid accumulation on methane production was also observed. These results are encouraging for the application of co-digestion of waste cooking oil and pig slurry in agricultural biogas plants.