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Water 2017, 9(6), 426; doi:10.3390/w9060426

Dual-Control of Autothermal Thermophilic Aerobic Digestion Using Aeration and Solid Retention Time

Electrical Engineering Department, University of La Rioja, c/San José de Calasanz 31, 26004 Logroño, Spain
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Academic Editor: José Manuel Poyatos
Received: 11 March 2017 / Revised: 16 May 2017 / Accepted: 9 June 2017 / Published: 13 June 2017
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Abstract

Autothermal thermophilic aerobic digestion (ATAD) is an advanced sewage sludge treatment which allows compliance with increasingly demanding regulations. Concerning sludge pasteurization, a certain average temperature must be assured in the digester during batch treatment. Aeration flow is the variable most manipulated to regulate the digester temperature. Additionally, the manipulation of the batch sludge flow—which is related to the solid-retention-time—is considered to improve temperature regulation despite variations in air and sludge temperatures and the variability of raw sludge organic content. Thus, a dual-input control structure was provided where the aeration and solid-retention-time contributed as faster and slower inputs, respectively. Two controllers intervened, and the set-point for the batch average temperature was chosen to meet the minimum effluent quality established by the US regulations or European recommendations, considering that lower set point temperatures save aeration costs. A set-point for the aeration allowed us to achieve an extra goal, which aimed at either reducing operation costs or increasing production rates. The two feedback controllers were designed following the robust control methodology known as quantitative feedback theory (QFT). Improvements were compared with single-input (aeration-flow) control strategy and open-loop control strategy. Simulations were performed on a benchmark non-linear simulation model for ATAD. View Full-Text
Keywords: Autothermal Thermophilic Aerobic Digestion (ATAD); sludge pasteurization; wastewater treatment (WWT); mid-ranging control; quantitative feedback theory (QFT); process control Autothermal Thermophilic Aerobic Digestion (ATAD); sludge pasteurization; wastewater treatment (WWT); mid-ranging control; quantitative feedback theory (QFT); process control
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Nájera, S.; Gil-Martínez, M.; Rico-Azagra, J. Dual-Control of Autothermal Thermophilic Aerobic Digestion Using Aeration and Solid Retention Time. Water 2017, 9, 426.

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