The use of diesel fuel in crop and transportation operations is responsible for one third of the carbon emissions in sugarcane biorefineries. A possible solution is to replace it with biodiesel from lipids, directly produced from sugarcane by highly productive heterotrophic microalgae. In this study a heterotrophic microalgae biodiesel plant, integrated with a typical Brazilian sugarcane bio-refinery, was designed and evaluated. Molasses, steam, and electricity from sugarcane processing were used as inputs for microalgae production. For a non-integrated plant, the production cost of the microalgae biodiesel was estimated at 2.51 and 2.27 $/liter for fed-batch and continuous processes, respectively. Equipment for cultivation and carbon sources was the highest cost affecting the financial feasibility of the proposed design. For the integrated plant, at present ethanol and biodiesel selling prices, the profitability would be lower than a first-generation sugarcane bio-refinery using fossil diesel fuel for its operations. However, the CO₂ emissions would be reduced by up to 50 000 × 10³ kg per year at a cost of $83 10⁻³ kg⁻¹ CO₂-eq. If carbon credits are considered, the process becomes economically profitable even at present fuel prices.

Emulsion formation is a major concern when dealing with multiphasic fermentations. Flocculants can be used together with other demulsification techniques to improve oil recovery in multiphasic fermentations. In this paper, the impact of adding flocculants during a multiphasic fermentation with 10 wt% dodecane, to destabilize the broth emulsion, improve creaming formation and enhance oil recovery is studied. Flocculants, CaCl₂ and (NH₄)₂SO₄ were shown to be the most promising flocculants. Flocculant addition, their time of addition, and its impact on multiphasic fermentations has been evaluated by comparing fermentation performance against reference fermentations and three oil recovery methods: gravity settling, gas enhanced oil recovery and centrifugation. When adding 75 mM of (NH₄)₂SO₄ during fermentation, the creaming rate during gravity settling increased 3-fold and the oil recovery by gas enhanced oil recovery was 35%, without altering fermentation performance. Addition of CaCl₂ during fermentation resulted in 88% and 67% oil recovery for early and late addition, which is a 4 and 3-fold increase in comparison with the reference. Yet, CaCl₂ deviated from standard fermentation performance when added immediately after second phase addition. In conclusion, flocculant addition during multiphasic fermentation can be used to destabilize microbial emulsions and potentially improve in situ oil recovery.

Multiphasic fermentations where an organic phase is spontaneously formed or when it is added for product removal are commonly used for production of valuable compounds. The turbulent conditions and the presence of surface-active compounds (SACs) during fermentation create a stable emulsion difficult to separate. A gas bubble/oil droplet separation method has been proposed to break such emulsion. In this paper, we propose a mathematical model to describe oil/bubble interaction in a region of high oil droplet concentration. Model validation was performed using a synthetic emulsion and an emulsion from a fermentation broth. By applying the optimal parameters predicted by the model, a 6- and 3-times oil recovery improvement was reached for the synthetic emulsion and the fermentation broth, respectively. In conclusion, the proposed mechanistic model allowed to improve oil recovery in the existing laboratory set-up, and can be used to optimize the separation and recovery method at large scale.

Sesquiterpenes are a group of versatile, 15-carbon molecules with applications ranging from fuels to fine chemicals and pharmaceuticals. When produced by microbial fermentation at laboratory scale, solvents are often employed for reducing product evaporation and enhancing recovery. However, it is not clear whether this approach constitutes a favorable techno-economic alternative at production scale. In this study empirical correlations, mass transfer and process flow sheeting models were used to perform a techno-economic assessment of solvent-based processes at scales typical for flavors and fragrances (25 MT year⁻¹) and the fuel market (25 000 MT year⁻¹). Different solvent-based process options were compared to the current state of the art, which employs surfactants for product recovery. The use of solvents did reduce the sesquiterpene evaporation rate during fermentation and improved product recovery but it resulted in costs that were higher than, or similar to, the base case due to the additional equipment cost for solvent-product separation. However, when selecting solvents compatible with the final product formulation (e.g. in a kerosene enrichment process), unit costs as low as $0.7 kg⁻¹ can be achieved while decreasing environmental impact.

Fossil carbon sources mainly contain hydrocarbons, and these are used on a huge scale as fuel and chemicals. Producing hydrocarbons from biomass instead is receiving increased attention. Achievable yields are modest because oxygen atoms need to be removed from biomass, keeping only the lighter carbon and hydrogen atoms. Microorganisms can perform the required conversions, potentially with high selectivity, using metabolic pathways that often end with decarboxylation. Metabolic and protein engineering are used successfully to achieve hydrocarbon production levels that are relevant in a biorefinery context. This has led to pilot or demo processes for hydrocarbons such as isobutene, isoprene, and farnesene. In addition, some non-hydrocarbon fermentation products are being further converted into hydrocarbons using a final chemical step, for example, ethanol into ethene. The main advantage of direct microbial production of hydrocarbons, however, is their potentially easy recovery because they do not dissolve in fermentation broth.

In multiphase fermentations where the product forms a second liquid phase or where solvents are added for product extraction, turbulent conditions disperse the oil phase as droplets. Surface-active components (SACs) present in the fermentation broth can stabilize the product droplets thus forming an emulsion. Breaking this emulsion increases process complexity and consequently the production cost. In previous works, it has been proposed to promote demulsification of oil/supernatant emulsions in an off-line batch bubble column operating at low gas flow rate. The aim of this study is to test the performance of this recovery method integrated to a fermentation, allowing for continuous removal of the oil phase. A 500 mL bubble column is successfully integrated with a 2 L reactor during 24 h without affecting cell growth or cell viability. However, higher levels of surfactants and emulsion stability are measured in the integrated system compared to a base case, reducing its capacity for oil recovery. This is related to release of SACs due to cellular stress when circulating through the recovery column. Therefore, it is concluded that the gas bubble-induced oil recovery method allows for oil separation and cell recycling without compromising fermentation performance; however, tuning of the column parameters considering increased levels of SACs due to cellular stress is required for improving oil recovery.

The exact knowledge of Drop Size Distributions (DSD) plays a major role in various fields of applications to control and optimize processes, as well as reduce waste. In the microbial production of advanced biofuels, oil droplets are produced under turbulent conditions in an aqueous medium containing many surface active components, making DSD knowledge essential for process optimization. The capability of a photo-optical measurement method for DSD measurement in fermentation broth and in plate separators is illustrated aiming at cost reduction in the microbial production of advanced biofuels. Measurements were carried out with model mixtures in a bioreactor, and at the inlet and outlet of a plate separator. In the bioreactor, the method was effective in detecting a broad range of droplet sizes and in differentiating other disperse components, e.g., microbial cells and gas bubbles. In the plate separator, photo-optical measurement effectively determined the influence of the varied parameters on the separation efficiency.