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Autonomous Benthic Algal Cultivator Under Feedback Control of Ecosystem Metabolism

David M. Blersch, Patrick C. Kangas, Walter Mulbry
Environmental Engineering Science 2013 v.30 no.2 pp. 53-60
turbulent flow, metabolism, hybrids, energy, primary productivity, variance, algorithms, pollutants, carbon, species diversity, biomass production, ecosystems, benthic plants, autotrophs, cultivators
An autonomous and internally-controlled techno-ecological hybrid was developed that controls primary production of algae in a laboratory-scale cultivator. The technoecosystem is based on an algal turf scrubber (ATS) system that combines engineered feedback control programming with internal feedback patterns within the ecosystem. An ATS is an engineered, highly-turbulent aquatic system used to cultivate benthic filamentous algae while removing pollutants from an overlying water stream. The feedback control system is designed to monitor the carbon metabolism of the algal turf and manipulate the turbulence regime experienced by the algae to automatically optimize for maximum biomass production. The feedback control algorithm converged quickly on the state of maximum primary production when the variance of the input data was low. However, the convergence rate was slow at moderate levels of input variance. Results show that the system can converge on the maximum algal productivity at the lowest level of turbulence, the most efficient state from an engineering perspective, but in practice the system was confounded by measurement noise. Investigation into the species composition of the dominant algae showed shifting relative abundance for those units under automated control, suggesting that certain species are more suited for utilizing the technological feedback pathways for manipulating the energy signature of their environment. The results have implications for further design of techno-ecological hybrids for the testing of principles of organization for self organizing systems.