Last Sunday, we introduced the first mixture into our polycarbonate tubing on the inclined face of the platform. As our group is lacking an initial source of algae, we decided to use a mixture of water from Strawberry Creek and tap water to attempt to grow algae. We have added nutrients and soil as well to this mixture, as well as bubbled up air from the bottom of the tubes from an air pump in order to keep circulation up inside of the tubes. We measured the pH around 7.5 for both of the mixtures.
The next step in the project is to obtain the solar panels, battery, and inverter in order to make this system sustainable and self-powering by the time we have to move the reactor outside in mid-May.
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Today, we began the construction of the photobioreactor on our steel platform in the Oxford Tract. Most of our team members showed up to drill holes in the platform in order to fix the polycarbonate tubing onto it. For now, we just have two tubes installed on the incline. The tubes have our rubber stoppers in them to hold the water/algae mix inside. Additionally, we have thin rubber tubing with check valves to feed air/carbon dioxide into the tubes. Over spring break, we aim to continue to build the reactor and set up a fully functioning prototype to circulate and grow the algae.
Last week, my dad and I moved the steel platform into the Oxford Tract near the northwest end of the UC Berkeley campus. It's currently being stored in the greenhouse there, which provides access our initial energy demands. There are also grow lights in the greenhouse (pictured) that will help our photobioreactor function. Later this week we will be constructing and installing the reactor set up.
A special thanks to Berlin Food Equipment in South San Francisco for constructing the reactor and providing transport for it to get here to Berkeley. The steel platform that will be brought within the next week to the Oxford Tract into a greenhouse area. The reactor will then be set up and start growing microalgae.
We are also considering various methods to extract the oil/lipids from the algae. A couple of possibilities are: 1. Oil Press Extraction This method involves drying the algae and then pushing it through an oil press like the one shown below. The machine would press out the oil which we could easily collect. This procedure would require purchasing an oil press which would be around $150 and it can extract up to about 75% or the oil in the algae. 2. Solvent Extraction This method involves mixing the algae slurry with an organic solvent such as hexane or benzene. The chemical will break down the algae cell walls and dissolve the oil from the algae which can in turn be extracted through distillation or filtration. This process is more dangerous than the previous mechanical process due to the use of toxic chemicals but it does have the potential to extract 95% of the oil from the algae. The solvent and oil press extractions can be used together to achieve a higher extraction yield, but it may not be cost effective for us to invest in both procedures. The finished steel platform: the platform was painted and primed in order to improve light reflection as well as deter rusting. Platform is about six feet long on the inclined side. The polycarbonate tubes will be clamped onto the inclined face of the platform and the algae will be grown there. Air pumps and carbon dioxide will be stored and locked in the inside of the platform. Platform before paint: the platform was constructed using steel on all sides, with galvanized steel on the bottom. The steel was bent and welded by my dad at a South San Francisco sheet metal shop. (Berlin Food Equipment) The platform will be placed somewhere on campus within the next month and a small scale tubing design will be constructed.
We are currently looking at the most efficient and effective way to filter the algae once it has accumulated in the tubes. Two possible options are shown below: a very small sieve or a cheesecloth. Since the sieve is exponentially more expensive, we are thinking of purchasing the cheesecloth and testing its effectiveness. If it is not a viable option we will go ahead and purchase the sieve to compare test results. If neither of these methods are effective we will have to research more and find some new options to test.
We have also looked into creating a built-in system that can automatically strain the algae and recycle the water; at this point in our prototype, that seems to be a lofty goal. Once we find the right straining mechanism, we will then go on to improve our manual straining system into an automatic one. Above is a rough sketch of what our final reactor is going to look like. We will be using materials like solar panels, polycarbonate tubing, air pumps, and stainless steel in order to form a foundation for our design. The inside of the reactor will be a storage type area for materials as well as a place to keep our air pumps and wiring supplies. BACK of the envelope energy/water calculations for reactor For our Polycarbonate Tubing (ID 2.75 inches, OD 3 inches, L 4 feet):
Total Volume (one tube) = (pi)(radius^2)(height) --> (pi)(1.375 inch)^2*(48 inches) = 285 inches^3 of water volume per tube or 4.67L/tube when filled completely. For two tubes: maximum 9.34 L needed For four tubes: maximum 18.68 L needed For five tubes: maximum 23.35 L needed Water would need to be recycled or resupplied each complete algal growth cycle (about 10 to 14 days). For our Air Pumps (Max Power 5.5 W/pump, 15 L/air/minute for four outlets combined) Total Energy Demand w/Two Pumps on Max Power*: 5.5W/pump * 2 pumps = 11 W If 11 W is running 24 hours a day, then we would need 864000 J/day or 0.24 kWh/day. Using average Berkeley commercial electricity rates (14 cents/kWh), the total cost of our energy demand would be 0.0336 cents/day or $12.26/year if we are hooked up to the Berkeley electricity grid. Total Air Supplied: 15 L/min/pump * 2 pumps = 30 L/min / 8 outlets = 3.75 L air/min/outlet at max power*. *We will not be operating the pumps at max power during our experiments. These calculations are just to show the maximum energy demands for our reactor using two air pumps. Solar Panels: Using the above calculations, if we want to power the air pumps using solar energy completely, we need a solar panel output of greater than 11 W, probably around 15 W just to be safe. We will either have to use a battery system to supply power to the pumps at night or just use the outlet out in the courtyard. **These are not experimental numbers, just rough back of the envelope calculations from measurements made from the supplies already purchased. Updated data will be posted once prototype is tested. This past fall, our project group formed and started formulating ideas on what our reactor would look like. Before we could actually get started on building our reactor, however, we needed to familiarize ourselves with algal growth and under what conditions algae grew best. So we set up several experiments in the courtyard of Wurster Hall with varying conditions in different bottles to test how algae growth responded. Our experimental setup in the Wurster Courtyard. Figure 1 shows the growth in the bottles after seven days outside, while Figure 2 shows the growth in the bottles after 10 days of growth. Significant growth was shown after about two weeks in some bottles. Platform 1: Plastic bottle that started out with a high algae concentration. Most significant growth was shown in this bottle with much biomass forming on the sides/top of the bottle. Platform 2: Glass bottles were used for this platform. Each bottle started out with one scoop of algae, but the bottle on the left was given a small pinch of sugar and yeast to produce carbon dioxide. As the second image shows, much more growth was shown in that bottle. Platform 3: A case where too much sugar and yeast was added to a bottle. This bottle grew minimal algae and started to form an orange layer on the top with a foul smell. Platforms 4, 5, 6: More variables test here including fertilizer (far left with red ring on top) and no reflector surface (middle images). Some bottles were capped or left uncapped to see what atmospheric exposure would do for algal growth. The far right images had a reflector wall set up to maximize solar rays hitting the bottles. All images on the top row were taken after seven days and all on the bottom row after ten days.
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SUSTAINABLE ALGAE PHOTOBIOREACTORThe Sustainable Algae Photobioreactor Project is one of the various projects developed through the UC Berkeley division of Engineers for a Sustainable World (ESW). A special thanks to The Green Initiative Fund (TGIF) here at UC Berkeley for providing the grant to make this project possible.
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