Rational and Significance

Shannon Ethier and Kevin WoisardBiological Systems Engineering Department, Virginia Tech

Acknowledgements: Z. Wen, D. Vaughan, D. Pyle, and R. Grisso

Objectives• Design a process for converting crude glycerol into omega-3 fatty acids.• Perform a mass balance to determine annual production capacity.• Determine equipment to be used in the conversion process at pilot scale.• Perform an economic analysis for the process.

Abstract Design Overview

Design Details

Schizochytrium limacinum

Future Work• Treatment of the waste water after the

fermentation process• Utilization of algal residue after DHA extraction

Figure 3. Overview of the design process.

Batch Fermentation:• 6 x 6000 L fermentors• 6 day growth period• Easy to operate

Continuous Fermentation:• An alternative design solution• High productivity• Complex to operate

Designing a Pilot Plant Converting Biodiesel Waste Crude Glycerol into Omega-3 Fatty Acids by Microalgae

Figure 6. Continuous pusher centrifuge.

Figure 4. Seed Fermentor.

• Biodiesel production has grown rapidly, producing more of the byproduct, crude glycerol.

• Crude glycerol has a low cost, but is expensive to purify.• A cost-effective option for crude glycerol is to use it as a carbon source

for omega-3 fatty acid producing algae.

Centrifugation:• 3,000 kg/h• Continuous pusher centrifuge• Compact machine with a high

throughput

The production of biodiesel has grown rapidly with increasing prices of crude oil worldwide. Crude glycerol is a major byproduct of biodiesel production. Recently, the price of glycerol has fallen significantly due to the large amount of biodiesel produced. This glycerol is relatively expensive to purify for use in the pharmaceutical, food, and cosmetic industries. As a cost-effective option, the glycerol at a less refined form can be used as a carbon source for growing the algae Schizochytrium limacinum.

S. limacinum is a heterotrophic producer of docosahexaenoic acid (DHA). DHA is an important fatty acid due to its many health benefits. It is an important factor in infant brain and retinal development. It has also been shown to reduce the effects of many neurological disorders such as Alzheimer’s disease and promote good cardiovascular health.

Fish oil is currently the main source of DHA, which is leading to overfishing and causing strain to the fish industry. The fish oil also has an undesirable odor and heavy metal contamination problems. As an alternative source of DHA, microalgae can avoid or reduce these problems. Using crude glycerol for algal culture to produce DHA will also provide a practical method for disposal of this waste material.

• An alternative source of DHA to fish oil• Fish oil may contain heavy

metal contaminants• Fish oil has poor taste

• Produces high levels of DHA with a high growth rate• 50% of the dry cell weight

is fatty acids• DHA is 30% of the total

fatty acids• Heterotrophic• Grows well using crude

glycerol as a carbon source

Figure 1. Fermentor Figure 2. Centrifugation

Drying:• Evaporation capacity of 40-220 kg water/h• Spray dryer• Quick process time• Cost effective

Figure 7. Spray dryer.

Pilot Plant Input and OutputAssuming a biodiesel plant produces 3.78 million liters (1 million gallons) of biodiesel each year, there will be 300,000 kg (238,000 L) of crude glycerol available for algal culture.

The expected algal yield is 0.25 g algae/g glycerol. The plant can therefore produce about 75,000 kg of algae per year. Assuming the DHA content is about 132 mg of DHA/g algae, the annual DHA production from algae will be approximately 9,900 kg.

Figure 8. Microalgae.

Glycerol

Algal Fermentation

Algal cell

Cheese

Aquaculture Fish

(DHA extraction)

(direct use of algal biomass)

Oilseeds

Biodiesel

Glycerol DHA

Figure 5. Production Fermentors.

Biodiesel to DHA

Cost Analysis:• 6 Fermentors: $240,000• Continuous Pusher Centrifuge: $60,000• Spray Dryer: $50,000• Total Equipment Cost: $350,000• Crude Glycerol: $25,000/yr• Artificial Sea Water: $25,000/yr