Robust Regulation of Alkalinity in Highly Uncertain Continuous Anaerobic Digestion Processes

Abstract

In this paper, a multiple‐input multiple‐output (MIMO) model‐based robust control scheme is proposed for the indirect control of both total alkalinity and the ratio (intermediate alkalinity)/(total alkalinity) by regulating volatile fatty acid concentrations and strong ions concentration, while guaranteeing the so‐called operational stability in anaerobic digestion (AD) processes. The proposed MIMO regulator is an adaptive controller derived from an AD model which incorporates the physicochemical equilibrium of the system as well as the use of a robust interval observer to estimate key process bounds that are used in the computation of the control efforts. Numerical simulations were carried out for a number of operating conditions under the most uncertain scenarios. Results showed that the proposed multivariable control law is able to recover the system stability around a pre‐determined set point in the face of parameter uncertainty and load disturbances.

Influence of alkalinity and VFAs on the performance of an UASB reactor with recirculation for the treatment of Tequila vinasses

“…Automatic control of reactors is another important aspect developed to assess the effect of acidity and alkalinity in the anaerobic treatment of vinasse [7,14,20]. Mendez-Acosta et al Therefore, the high acidity of vinasses is associated to the VFAs concentration, especially…”

“…propionic and butyric acids that can affect the performance of the acetogenic bacteria and methanogenic archaea in the anaerobic digestion process [5,7,12,14,21]. Hence, the treatment of Tequila vinasse by anaerobic digestion requires an adequate control of operation parameters to avoid the VFAs accumulation and to profit the internal alkalinity generated by the anaerobic process itself to ensure the stability of the reactor.…”

“…Tequila vinasse is a dark brown liquid; it presents a pH of 3.5 and a high chemical oxygen demand (COD), which ranges from 60 to 100 g l -1 ; generating potential risks to the environment if it is discharged without treatment to water bodies [1][2][3][4]. Between the different treatments of vinasses, the anaerobic process stands out as the most viable; it has been used for the treatment of Tequila vinasse [2,[5][6][7] and for other distilled spirits [3,[8][9][10]. Anaerobic processes are considered energy, environmental and economically viable for the treatment of vinasses; biogas rich in methane generated during the anaerobic process could be used for electric energy generation.…”

“…Anaerobic sludge was capable to tolerate changes in OLR from 1 to 6 kgCOD m -3 d -1 , even with an unbalance of COD/N/P proportion; the automatic control of alkalinity ratio parameter α was maintained below 0.3 with continuous addition of NaOH, maintaining a stable performance of the reactor. Alcaraz-González et al[7] proposed a robust multivariable control model to guarantee the stable operation of the anaerobic process. Authors demonstrated that regulation of VFAs and the strong ionic concentration permit that the functional stability percentages in terms of intermediate and total alkalinity could be satisfied for any perturbation of the system.…”

Production of Bio-Energy from Pig Manure: A Focus on the Dynamics Change of Four Parameters under Sunlight-Dark Conditions

“…A study by Yin et al showed that sunlight-dark conditions can increase the biogas yield from PM [ 3 ]. However, the promoting influence of sunlight-dark conditions on physiological properties of digester, such as the VFAs, TAN, TA and pH, important parameters to be monitored in anaerobic digestion [ 17 – 20 ], and their effects on biogas production are unclear.…”