Modelling and pH Control in Raceway and Thin-Layer Photobioreactors for Wastewater Treatment

María José Rodríguez-Torres, Ainoa Morillas-España, José Luis Guzmán and Francisco Gabriel Acién
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María José Rodríguez-Torres: Department of Informatics, University of Almería, CIESOL-ceiA3, 04120 Almería, Spain
Ainoa Morillas-España: Department of Chemical Engineering, University of Almería, CIESOL-ceiA3, 04120 Almería, Spain
José Luis Guzmán: Department of Informatics, University of Almería, CIESOL-ceiA3, 04120 Almería, Spain
Francisco Gabriel Acién: Department of Chemical Engineering, University of Almería, CIESOL-ceiA3, 04120 Almería, Spain

Energies, 2021, vol. 14, issue 4, 1-14

Abstract: One of the most critical variables in microalgae-related processes is the pH; it directly determines the overall performance of the production system especially when coupling with wastewater treatment. In microalgae-related wastewater treatment processes, the adequacy of pH has a large impact on the microalgae/bacteria consortium already developing on these systems. For cost-saving reasons, the pH is usually controlled by classical On/Off control algorithms during the daytime period, typically with the dynamics of the system and disturbances not being considered in the design of the control system. This paper presents the modelling and pH control in open photobioreactors, both raceway and thin-layer, using advanced controllers. In both types of photobioreactors, a classic control was implemented and compared with a Proportional–Integral (PI) control, also the operation during only the daylight period and complete daily time was evaluated. Thus, three major variables already studied include (i) the type of reactors (thin-layers and raceways), (ii) the type of control algorithm (On/Off and PI), and (iii) the control period (during the daytime and throughout the daytime and nighttime). Results show that the pH was adequately controlled in both photobioreactors, although each type requires different control algorithms, the pH control being largely improved when using PI controllers, with the controllers allowing us to reduce the total costs of the process with the reduction of CO 2 injections. Moreover, the control during the complete daily cycle (including night) not only not increases the amount of CO 2 to be injected, otherwise reducing it, but also improves the overall performance of the production process. Optimal pH control systems here developed are highly useful to develop robust large-scale microalgae-related wastewater treatment processes.

Keywords: microalgae; thin-layer; raceway; photobioreactor; PI control; On/Off control (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
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