Abstract
The performance of a feedback control strategy in the operation of a sequencing batch reactor was evaluated. This strategy uses the online biogas flow measurements to define the duration of the reaction phase of each operating cycle, thereby increasing the energy production of the system and maximizing the methane production rate. The reaction phase is ended when the biogas flow rate reaches a sustained value significantly lower value than the maximum flow rate achieved, as a consequence of the depletion of the soluble chemical oxygen demand. The implementation of the depletion-time control was successful and reached a maximum methane production rate of 1.22 L CH4/d, showing an average productivity of 0.73 ± 0.3 L CH4/d. The reaction phase varied from 1.2 to 6 days with hydraulic retention times from 6 to 30 days. The use of this feedback control strategy increased the methane production and the energy production in 80% of the evaluated cycles (from 10.4 to 43.8%) compared to the operation of conventional AD without a control strategy. Furthermore, the strategy is easy to implement since it does not require complex calculations and uses a readily available biogas flow rate sensor.
Highlights
Food waste (FW) may cause important social and environmental problems associated with its inefficient solid waste management, but it must be included in a circular economy to promote its energy recovery (Alias Meena et al 2020; Zhou et al 2020)
Feedback control strategies (FCS) are a possible solution to automatically find the optimal operating conditions that lead to an increase in the overall energy production of an anaerobic digestion (AD) process, and to make it less sensitive to external and internal disturbances; the use of feedback makes the process adapt to changes in the environmental conditions (Jimenez et al 2015; Gaida et al 2017)
H2S concentration in the biogas was 1,519 ppm in cycle 1; the H2S filter was implemented in cycle 2, reducing the H2S to less than 88 ppm for the cycles
Summary
Food waste (FW) may cause important social and environmental problems associated with its inefficient solid waste management, but it must be included in a circular economy to promote its energy recovery (Alias Meena et al 2020; Zhou et al 2020). Anaerobic digestion (AD) is a widely used process with social, environmental, and economic advantages that allow the valorization of FW through renewable energy production (Nguyen et al 2019; Panigrahi & Dubey 2019; Zhang et al 2019a; Ahmed & Rodríguez 2020). Feedback control strategies (FCS) are a possible solution to automatically find the optimal operating conditions that lead to an increase in the overall energy production of an AD process, and to make it less sensitive to external and internal disturbances; the use of feedback makes the process adapt to changes in the environmental conditions (Jimenez et al 2015; Gaida et al 2017)
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