All of the current systems designed for algaculture, ranging from the most basic rural techniques to the most advanced laboratory equipment, fall into one of two production categories. Algae is either produced in an open production system or a closed one. Bioreactors and sealed containers make up the closed category, while all other ponds, tanks, raceways, and tubs fall into the open category. Choosing between the two is a little more complicated than just comparing costs and potential profit. Consider all of the benefits and disadvantages of each method before choosing one of them.
Control Over Conditions
It’s true that a closed bioreactor system offers far more control over the algae’s growth, exposure to contaminants, and other conditions. It’s easier to maintain a specific water temperature, pH level, or nutrient amount when you stop the evaporation and dilution process. If there’s only indoor growing environments available for algaculture, closed reactors are likely the best choice to control humidity levels. However, closed systems are highly expensive, require a lot of maintenance and are limited much more by size than open ponds. If you’re looking to produce as much algae as possible, a closed system shouldn’t be your first choice.
Risks of Contamination
Open ponds are at a higher risk for contamination from unwanted algae species or bacteria than closed reactors. However, these extra risks are easily mitigated with the right equipment. Pond covers can prevent the entrance of any fresh water or airborne particulates until the algae has fully colonized the water. Keeping water at the right salinity and pH level is often enough to keep the environment unfriendly to unwanted colonizers. Closed systems can still experience a contaminant issue if anything makes it into the reactor before it’s sealed. A closed system that is contaminated will quickly be overrun by the unwanted growth and must be drained and sanitized, while an open system can be treated to maintain the right balance of growth.
Volume of Production
Even the biggest bioreactor systems can only produce a fraction of the volume that comes from open pond algaculture. When the volume of the harvested algae product is the most important aspect of the system, open ponds or tanks are unbeatable. Entirely closed chambers simply can’t hold the water volume of an open pond, resulting in lower production even when using highly efficient algae species. Only thousands of acres of open ponds or raceways can create a sustainable food supply for humans and animals in a specific region.
Suitability of Algae Type
Not all algae can handle either the open or closed environment and still grow as expected. Seaweed, in particular, often struggles to grow in a closed environment with limited space. In contrast, open ponds aren’t a great idea for harvesting electrons for energy production yet. While the technology will likely eventually rise to the level where open ponds can generate energy, current technology requires the closed system design to help capture the electrical charge before it can dissipate. Before settling on either an affordable open system or a high-tech closed system, make sure you understand the limitations of your preferred algae species.
Cost for Setup
Open pond designs cost only a fraction of what it takes to build closed systems with the same volume. In fact, building a 200-gallon bioreactor may cost as much as a 2,000-gallon pond depending on the equipment and materials chosen for the project. Flexible pond liners and a little excavation are most of what you need to set up an open outdoor pond, while closed systems have dozens of individuals parts that must all work seamlessly together. Of course, sometimes investing in a closed bioreactor is the only option if you’re trying to produce algae that won’t grow well in open environments.
Lighting Sources
Another cost, related to running a closed algae system, is lighting. Closed systems and bioreactors are almost always located indoors to maintain a steady temperature and easier access to the equipment. This means that artificial lighting is necessary to keep the algae growing at a steady pace and subsequently producing electricity. Unfortunately, the cost of lighting the closed system can often exceed the power generated by the algae inside of it. Open ponds aren’t widely used for power generation yet, but they do take advantage of free access to sunlight to grow algae without high electrical costs for lighting. There’s still plenty of power needed for pumps and water mixers, but at least you aren’t paying for lighting when you choose an outdoor system.
Maintenance Requirements
An open algae pond does require cleaning and treatment on a weekly to monthly basis. However, this takes only about half an hour per pond per week at the most. In contrast, closed algae systems often need hours of daily maintenance to continue operating properly. From cleaning out filters to resetting water quality sensors, closed systems create a lot more work for you and your team than open ponds. Make sure the increased yield generated by the enclosed system is worth the extra manpower or choose open ponds whenever possible.
In general, open systems are less expensive, easier to set up and maintain, and more productive than closed ones. Closed systems only win in the categories of contamination control and water quality stabilization. Unless you have a specific need for a closed system, an open pond lined with materials from BTL Liners is likely your best choice.
