Design of Feedback Control Strategies in a Plant-Wide Wastewater Treatment Plant for Simultaneous Evaluation of Economics, Energy Usage, and Removal of Nutrients

Abdul Sheik,Murali Seepana,Ramon Vilanova,Montse Meneses,Seshagiri Ambati,Eagalapati Tejaswini

doi:10.3390/en14196386

Abdul Sheik, Murali Seepana + Show 4 more

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https://doi.org/10.3390/en14196386

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Abstract

Simultaneous removal of nitrogen and phosphorous is a recommended practice while treating wastewater. In the present study, control strategies based on proportional-integral (PI), model predictive control (MPC), and fuzzy logic are developed and implemented on a plant-wide wastewater treatment plant. Four combinations of control frameworks are developed in order to reduce the operational cost and improve the effluent quality. As a working platform, a Benchmark simulation model (BSM2-P) is used. A default control framework with PI controllers is used to control nitrate and dissolved oxygen (DO) by manipulating the internal recycle and oxygen mass transfer coefficient (KLa). Hierarchical control topology is proposed in which a lower-level control framework with PI controllers is implemented to DO in the sixth reactor by regulating the KLa of the fifth, sixth, and seventh reactors, and fuzzy and MPC are used at the supervisory level. This supervisory level considers the ammonia in the last aerobic reactor as a feedback signal to alter the DO set-points. PI-fuzzy showed improved effluent quality by 21.1%, total phosphorus removal rate by 33.3% with an increase of operational cost, and a slight increase in the production rates of greenhouse gases. In all the control design frameworks, a trade-off is observed between operational cost and effluent quality.

Highlights

The increase in the global population and urbanization has emanated in an increase in the use of water and in the production of contaminated water
Many control applications like fuzzy logic controller (FLC), model predictive controller (MPC), proportional-integral (PI), and ammonia-based aeration control (ABAC) with different hierarchical combinations of PI, MPC, and fuzzy were studied, and it is observed that there is a trade-off between operational cost and effluent quality [18,19,20,21]
Shiek et al (2021) implemented an ammonia-based aeration control (ABAC) with four different combinations of controllers like PI-MPC, MPC-MPC, PI-fuzzy, and MPC-fuzzy, which resulted in a tradeoff between Operational Cost Index (OCI) and Effluent Quality Index (EQI)

Summary

Introduction

The increase in the global population and urbanization has emanated in an increase in the use of water and in the production of contaminated water (wastewater). It is perceived that valuable resources like clean water, energy, and nutrients can be recovered from wastewater [1] This leads to the progression of wastewater treatment plants (WWTP) into a water resource recovery facility (WRRF) [2]. Different plant-wide models are studied in the literature, which includes sludge control approaches, biogas production in primary settler, handling of the anaerobic digester, and phosphorus modeling with interactions of sulfur and iron cycles [10,11,12,13,14,15,16,17]. Many control applications like fuzzy logic controller (FLC), model predictive controller (MPC), proportional-integral (PI), and ammonia-based aeration control (ABAC) with different hierarchical combinations of PI, MPC, and fuzzy were studied, and it is observed that there is a trade-off between operational cost and effluent quality [18,19,20,21]. The ammonia removal rate was improved by 18% in the case of MPC-MPC but P removal was not affected much [23]

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