(202a) Growing Lipid-Rich Microalgea in Wastewater for Biodiesel Production

1- Introduction

1-1 Background. The public is becoming increasingly aware of the need for alternatives to petroleum based fuels. The price of oil is increasing faster than new technologies such as gas-electric hybrids can compensate. Biofuels such as biodiesel are speculated to eventually replace petroleum fuels.

1-2 Biodiesel. Biodiesel is a renewable alternative to diesel fuel. It is made by the transesterification reaction of any lipid/oil with alcohol. Biodiesel can be burned in existing diesel engines with no modifications and can be blended in any proportion with petroleum diesel. Biodiesel has a strong sustainability perspective. It reduces the dependence on fossil fuels, produces far less carbon dioxide (CO2) and other greenhouse gases (GHGs) than petroleum oil, reduce other forms of air pollution such as carbon monoxide (CO) and sulfur dioxide (SO2), is a high-quality fuel, can be immediately used within the existing infrastructure, and support local agriculture and economic development.

1-3 Food Crop Challenges. Currently, biofuels such as biodiesel are produced from food crops such as soybeans, canola and corn. Soybean plants produce roughly 50 gallons of biodiesel per acre and Canola plants produce 90 gallons of biodiesel per acre. Huge amounts of land are needed to produce enough Biodiesel to meet the current US demands for Biodiesel (roughly 60 billion gallons of diesel per year). It would take over one billion acres of land growing soybeans to produce enough biodiesel for the United States. This strategy causes deforestation, and increases food prices as corn is being used to produce oil and ethanol instead of being used as food, and farmers are growing more corn to fuel demand for biofuels.

1-4 Microalgae as a Feedstock. Microalgae have the potential to solve many of the current problems with biofuels. Microalgae require light, nutrient and CO2 to grow. They grow faster than any food crop, and can produce between 5,000 and 15,000 gallons per acre. Based on an average of 10,000 gallons of biodiesel per acre, we would need 6 million acres of land containing algae to produce enough biodiesel for the United States, which would be close to the size of New Hampshire. Algae also have the ability to grow in closed bioreactors, which can be situated in areas that are unfit for farming. This is attractive both on a financial standpoint and an ethical standpoint.

1-5 Photobioreactors. These are closed vessels where the microalgae can grow under optimum conditions without the concern about contamination. A photobioreactor can be as simple as a lab scale conical transparent glass beaker exposed to light to a more sophisticated design, which tend to be costly. High lipid producing microalgae can be grown in a photobioreactor. The challenge in photobioreactors is to be able to achieve high growth rate of the microalgae in a cost-effective manner.

These promising high microalgae yields of lipids led to experiments concerning algae growth and the conversion of algae to biodiesel. The main objective is to grow microalgae with a high oil yield. The microalgae are simple single-cell plant-like organisms without roots or leaves. They are photoautotrophic organisms that undergo photosynthesis to sequester C from CO2. The microalgae uses the sequestered C to produce the lipids. The microalgae have the ability to grow at a fast rate. Our initial experiments indicated that algae grew best in solutions which contained salt. However, it is important to find the most economical medium in which to grow the algae in.

1-6 Wastewater Use Motivation. Hypotheses were made concerning wastewater and its use to help grow the algae. The hypothesis of this project promoted the notion that the nutrients contained in various types of wastewater would support microalgae growth and lipid production. This would be much more cost effective than constantly producing nutrient solution.

Wastewater is attractive because it is inexpensive and is readily available wherever there is a municipal wastewater treatment facility. If wastewater proves to be an effective medium, it may be possible to build algae biodiesel production facilities that would work directly of the effluent from wastewater treatment facilities.

2- Goal

The goal of this research project is to improve the process economics of producing biodiesel using microalgae-produced lipid/oil. This will be attempted by using wastewater to grow the microalgae.

3-Experimental Design

The water used in this experiment was obtained from the Durham Wastewater Treatment Facility in Durham, New Hampshire. Water samples used in our experiments included homogeneous untreated waste water, dechlorinated effluent, which was a treated wastewater suitable to be released into the environment, and finally a mixture of 50% wastewater and 50% dechlorinated effluent. Our photobioreactor was a two-liter clear glass conical flask in which the algae and water solution was placed. Air was bubbled to provide a source of CO2 and to stir the algae solution. The clear conical flask was placed in front of fluorescent light. All experiments were done indoors.

Initially, the untreated wastewater was observed to see any alien growth in the system. The solutions tested were wastewater alone (as a blank), wastewater plus algae, and finally wastewater plus algae and 0.1 Molar NaCl. It could be seen that there was contamination in the wastewater and this contamination would most likely lead to negative competition between the lipid-producing microalgae (which is highly desirable) and an alien algae or bacteria. Thus, the untreated wastewater would not be desirable to grow the algae in.

Next, the microalgae were grown in three main solutions: a nutrient solution containing 0.1 Molar NaCl, a dechlorintated effluent solution containing 0.1 Molar NaCl, and finally the mixture of 50% effluent and 50% wastewater plus 0.1 Molar NaCl. The outcomes are that the nutrient solution produced the algae with the highest oil yield, while the dechlorinated effluent showed the greatest promise.

In order to reach the above outcomes, the microalgae strain was tested at room temperature for two criteria over a time period of about 7-14 days per trial. The first criterion was growth rate, which was determined by measuring the solution absorbance using a spectrophotometer. Higher absorbance reading indicated higher algae concentration. The second is the lipid/oil concentration in the microalgae. This was by dying the algae in the solution with a Nile Red solution which stained the lipids. The solution was then put in the Spectrofluorometer which read the lipids concentration in the algae. When recording the data from the Spectrofluorometer, the quantity gradually increased to a certain point, and then decreased again. The data was recorded in 5 minute increments. When the data was analyzed, the highest and lowest values were subtracted from each other to find the microalgae lipid content.

4- Results

Once this data was obtained, the spectrophotometer absorbance readings and the spectrofluorometer lipid content were used to obtain the overall algal oil yield for the different water solutions used. The results showed that the mixture of 50% effluent and 50% wastewater had an oil content of about 5% that of the nutrient solution, while the dechlorinated effluent was about 19.9% that of the nutrient solution.

5- Conclusions

In conclusion, microalgae grown in nutrient and salt solution produced the greatest oil yield while the microalgae grown in effluent showed good promise. More tests will be taken with these various wastewaters to determine the best method of growing algae for the conversion to Biodiesel. The results will be reported in the November meeting. These results will be used in future planning for microalgal biodiesel research.