Abstract
Oxidation ditches are popularly used in rural areas and decentralized treatment facilities where energy deficiency is of concern. Aeration control technologies are well established for diffusion systems in order to improve energy efficiency, but there are still challenges in their application in oxidation ditches because surface aerators have unique characteristics with respect to oxygen transfer and energy consumption. In this paper, an integral energy model was proposed to include the energy, aeration, and fluidic effects of surface aerators, by which the energy for aeration of each aerator can be estimated using online data. Two types of rotating disks with different diameters (1800 mm and 1400 mm) were monitored in situ to estimate the model parameters. Furthermore, a feedforward–feedback loop control strategy was proposed using the concept of energy analysis and optimization. The simplified control system was implemented in a full-scale Orbal oxidation ditch, achieving an approximately 10% saving in full-process energy consumption. The cost–benefit analysis and carbon emission assessment confirmed the economic feasibility and environmental contribution of the control system. The energy model can help process designers and operators to better understand and optimally control the aeration process in oxidation ditches.
Highlights
The energy performance in wastewater treatment plants (WWTPs) is generally sub-optimal in most countries [1], the optimal water–energy nexus has been intensively studied in sustainable development [2]
We proposed an energy consumption model and demonstrated how to derive the aeration energy from the online process data
An energy consumption model with single and multiple surface aerators was developed which can be used as an energy-saving control system
Summary
The energy performance in wastewater treatment plants (WWTPs) is generally sub-optimal in most countries [1], the optimal water–energy nexus has been intensively studied in sustainable development [2]. As one of the oldest wastewater treatment processes, the oxidation ditch is still used in about 30% of running wastewater facilities in China, especially in rural areas and decentralized stations [4]. The typical energy consumption of an oxidation ditch is close to 0.40 kWh·m−3 , which is around 33% higher than for activated sludge processes [4,5]. High energy intensity and poor maintenance prevent such processes from application in energy neutral initiatives, e.g., next-generation urban water systems in China [6]. Energy-saving techniques and processes are necessary to upgrade WWTPs for a sustainable society
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