New algae sensor system developed

Posted Dec. 29, 2010

A research team at Texas AgriLife Research, a division of the Texas A&M University System, is developing an optical-electronic sensor to aid in commercial-scale algae production. The system is designed to monitor algae growth in real-time, allowing for increased efficiency.

According to Alex Thomasson, the AgriLife Research engineer leading the project, the sensor system essentially emits a beam of energy that interacts with an algae culture. The response is measured at multiple wavelengths to determine the optical density of the algae. While handheld sensor devises do exist on the market to complete similar evaluations, Thomasson said his team has identified commercial need for an automated, real-time, highly repeatable measurement solution. "The eventual success of the algae industry is going to depend on high-level commercial production," he said. "For that to work, you need to optimize inputs and outputs, and you need real-time methods to measure that process."

Thomasson said his team designed the sensor system to utilize multiple wavelengths of light. This increases reliability, he said. While the actual wavelengths measured by the system have not been released, information released by Texas AgriLife Research states that Thomasson and his team experimented with wavelengths ranging from 250 to 2,500 nanometers.

In research applications, algae cultures are usually evaluated using labor-intensive methods, Thomasson said. This includes manually collecting samples and transporting them to the lab for evaluation using a spectrophotometer. On a commercial scale, these methods would be prohibitively expensive and time consuming. "It's not economically feasible for industrial production," Thomasson continued, noting that the sensor his team has developed is designed to automate that process.

In order for an optical sensor system to be suitable for use in open ponds, it needs to be mountable at a fixed location in a production facility. It also has to operate without human intervention and provide accurate measurements that could be used to adjust and tweak production in real-time. The sensor developed by Thomasson has been specifically designed to meet these requirements.

Initial field testing of the system was completed in mid-2010 at the AgriLife Algae Research and Development Facility near Pecos, Texas. Over the course of several days, a prototype sensor was used to measure the optical density of an algae culture being grown in an open raceway pond. According to Thomasson, data gathered by the sensor was compared to data gathered through sample collection and laboratory testing. The results were overwhelmingly positive. "Compared with the lab data, we found good repeatable agreement," he said. "We could also see that as media was added, there was a large drop in the optical density." The system was also able to detect changes in optical density as the number of algae cells within the culture grew.

While the initial field testing lasted only a few days, Thomasson said more extensive long-term testing on the optical-electronic sensor is currently underway. The research team is also working on a second sensor project for algae production. According to Thomasson, that research focuses on evaluating the lipid content of algae cells as well as nutrient levels within the algal biomass. Most algae-oil production scenarios consist of two stages, he said. The first stage involves promoting growth to rapidly increase the number of algae cells within a culture. The second stage involves limiting nutrients at exactly the right time in order to help maximize lipid production. Thomasson and his team are working to develop a sensor technology to aid optimization of lipid production.

Additional members of Thomasson's research team include USDA engineer Ruixiu Sui, Texas A&M University assistant research engineer Yufeng Ge, and Texas A&M University graduate research assistant Yao Yao.