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

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.

Why do We Know So Much and Yet So Little? A Scoping Review of Willingness to Pay for Human Excreta Derived Material in Agriculture

“…We suggest that the product heterogeneity resulting from the nascence of the commercialization of HEDM and the infancy of the regulatory environment may explain this dearth of information in scientific/academic publications. However, while the technologies to recover a more consistent product are being explored, it is imperative to explore the market demand if the green fertilizers and other HEDM are to cross the 'innovation chasm' or what is often stylized as 'bridging the valley of death' [106,107]. We discuss these among other issues hindering wide-scale commercialization in the following sections.…”

Aerobic and Anaerobic Sewage Biodegradable Processes: The Gap Analysis

“…High strength wastewater contains enough energy for auto-thermal process and therefore no exogenous heat is required. The thermophilic aerobic technique has been used in wastewater treatment from livestock's, industry and other wastewater sources [6][7][8]. Anaerobic treatment on the other hand, is used to treat high concentration of biodegradable contaminants in wastewater such as domestic sewage, animal manure slurry, and wastes from biosolids and food processing.…”

“…This is very useful due to increased cost for production, treatment, and burning of fossil fuels [3,11]. Though conventional aerobic and anaerobic techniques have been applied previously in most wastewater treatment, high rate anaerobic bioreactor systems have been used recently to treat wastewater with high COD level [8,10,12].…”

Feedforward of Measurable Disturbances to Improve Multi-Input Feedback Control

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“…Whenever external disturbances are measurable, the contribution of this work can be of importance in a great variety of fields where multi-input control has been successfully applied. Remarkable application fields include bioprocesses [14,15], thermal systems [18], medical systems [19,20], scanner imaging [21,22], massive data storage devices [23,24], fuel engines [25] and electrical vehicles [26], robotics [27][28][29], and unmanned aerial vehicles [30].…”