Closed Systems
Photobioreactors (PBR) are the most used closed systems for producing algae. In these cases, algae are grown in transparent vessels, which may be tanks, glass or plastic tubes, plastic sleeves or bags or as biofilm on different styles of substrates. Since they’re closed systems, algae grown in photobioreactors must be supplied with light, sterile water, nutrients, air and supplemental CO2. This means that the growing environment can be closely regulated, which is ideal for some pickier varieties of algae that don’t thrive in open ponds. The system is also protected from organisms and exposure to competing types of algae. Photobioreactors are a popular solution when open ponds are not a practical solution, but they are highly artificial and require more equipment and closer management than open ponds.
Fermentation
Light, typically sunlight, is considered an absolute requirement for growing algae, but an alternative approach is to skip the photosynthesis step and grow algae in the dark, providing them directly with the sugars needed to produce biomass and oil. These oils are suitable for conversion into biofuels, chemicals, nutritional products, cosmetics, and so on. Since sun exposure is no longer a concern, fermentation systems can be constructed vertically on a relatively small amount of land.
Hybrid Systems
Most algae producers use one of the above methods exclusively, but there is some advantage to developing a hybrid system that maximizes the advantages of each setup. Some strategies may include using small PBRs to continuously produce a consistent algae product used to inoculate certain open pond setups that are vulnerable to biological system crashes.
One of the potential goals in a hybrid system is to separate biomass growth from lipid accumulation. For example, a PBR may be used to produce algae without risk of contamination, and the product could then be transferred to open ponds where efficient stress induction techniques can be employed to maximize lipid production.
Sequential use of open ponds and fermenters would work in a similar fashion, where biomass is accumulated in the first phase with support of nutrients and CO2. In the second stage, algal cells are stressed and induced to use stored energy to produce fatty acids.
Integrated Systems
Integrated systems take advantage of several of algae’s unique abilities by linking them together to lower overall costs and multiply benefits. One example is to use algae to treat wastewater by removing nutrients and CO2, while breaking down organic waste and removing toxins. The biomass produced during this process is not a waste product - in fact, is still valuable (depending on what kind of toxins it was exposed to) to produce methane, fertilizer, and oils.
The key in any integrated system is that waste (polluted water or polluted air) is used during the growth stage where algae can consume the waste as it multiplies. For example, algae production facilities set up next to certain industrial plants that produce CO2 can create symbiotic relationships where factories are able to minimize carbon emissions while the algae enjoy rapid growth, producing more mass that can be converted to bio-fertilizer or other valuable products.
To Line or Not to Line?
A Question of Cost?
For decades, you could find most algae harvested out of unlined ponds and lakes whether for food or feed. Lining a pond can add cost to initial investing, and when dealing with a pond which has developed a natural sealed layer at its bottom, adding a liner may seem unnecessary. However, the vast majority of algaculture today is grown within lined reservoirs. Leakage, seepage, and various other unwanted algae are prevented through the addition of a waterproof lining. In an open-air, freshwater reservoir, the water-loss from evaporation can be counteracted by ensuring that no porous soils are soaking up extra moisture. Some chemicals or nutrients within the soil can be reactive or contaminating if allowed to come into contact with the water or algae. Stable conditions encourage productivity, making liners a common sight where efficiency is a concern. However, not every single algaculture design will technically require a pond liner.
Unlined ponds
The addition of a pond liner does add some cost to the initial investment and maintenance of a reservoir. Additionally, when dealing with algal biomass and biofuels, sustainability is typically a high priority. However, reactive or porous soil can reduce productivity and contaminate valuable nutritional coproducts found in the production of biofuel. A natural seal formed within a pond is typically a combination of settled solids, decaying organic material, and an underlying clay ‘liner’. If your pond is open to the elements, periods of freezing and melting can cause serious damage to even the oldest of river or lake beds. Storm damage and natural or man-made pollution may be more difficult to manage if settled sediment and porous soil or clay is exposed to the water. Water-loss is also more likely without an impermeable seal as water is allowed to seep into the soil.
Lined Ponds
A pond liner is a valuable way to mitigate water loss and stabilize the conditions of your pond. While it does cost more to add and maintain a liner than to go without, much of the algaculture industry today utilizes a liner. A liner for an algae pond can be made from plastics, concrete, fiberglass, or geomembranes like HDPE or RPE liners. Geomembrane liners are becoming increasingly more popular, as they are resistant to chemical leaching or reactivity, are UV-protected, and are virtually impermeable to water loss through seepage.
Loosely packed soil, or other forms of unlined ponds are not as effective at preventing the leakage and contamination of water, nutrients, algae, or waste as their lined competitors. A liner will also affect mixing within your algae pond. Pond mixing is typically required to reduce settling with the algae pond, as well as to expose cells to light, distribute nutrients, increase utilization of CO2, maintain temperature, and reduce the number of predatory microorganisms. If you’re using a rotor or paddlewheel to mix your algae pond, suspended sediment or waste can restrict movement, and reduce productivity.
When choosing the right liner for your pond, it’s important to make sure you consider your particular needs. What’s your budget? What conditions will your algae and water be exposed to? Is leakage a concern? If you’re building an open-air algae pond, evapotranspiration may make mitigating water loss a high priority. Additionally, exposure to sunlight or outside temperatures can damage unlined ponds, or liners which aren’t UV-resistant. To ensure the health of your water, and therefore your algae, a chemical-resistant and non-leaching liner will prevent contamination or degradation over time. At BTL, we specialize in long-term, impermeable, durable liners that can be custom fabricated for your new project. BTL’s AquaArmor products are UV and chemical resistant and made of a multi-layered geomembrane that is completely impermeable, massively reducing the risk of seepage or leakage within your algae pond. We’d be happy to discuss your algae pond project with you – get in touch with our team of designers today.
