Mehlika A. Kiser’s research while affiliated with University of Girona and other places

This paper introduces the application of a fully dynamic air distribution model integrated with a biokinetic process model and a detailed process control model. By using a fully dynamic air distribution model, it is possible to understand the relationships between aeration equipment, control algorithms, process performance, and energy consumption, thus leading to a significantly more realistic prediction of water resource recovery facility (WRRF) performance. Consequently, this leads to an improved design of aeration control strategies and equipment. A model-based audit has been performed for the Girona WRRF with the goal of providing a more objective evaluation of energy reduction strategies. Currently, the Girona plant uses dissolved oxygen control and has been manually optimised for energy consumption. Results from a detailed integrated model show that the implementation of an ammonia-based aeration controller, a redistribution of the diffusers, and the installation of a smaller blower lead to energy savings between 12 and 21%, depending on wastewater temperature. The model supported the development of control strategies that counter the effects of current equipment limitations, such as tapered diffuser distribution, or over-sized blowers. The latter causes an intermittent aeration pattern with blowers switching on and off, increasing wear of the equipment.

A model-based treatment performance and energy audit of the Girona WRRF in Spain was conducted using advanced and fully dynamic air supply models. The focus of the study was on the aeration system, which represents 63% of the plant's energy consumption. A dynamic model consisting of a process, a realistic controller, and a very detailed air supply model, was developed and calibrated to be used as the baseline for testing various scenarios. Results show that the implementation of an ammonia-based controller and a redistribution of the diffusers led to energy savings between 12 and 21%, depending on wastewater temperature. In addition, the model demonstrated that the current blower is too large, which causes an intermittent behaviour, endangering the equipment and shortening its lifetime , plus limiting the minimum air-supply. The applied aeration system models enable engineers to identify bottlenecks by modelling equipment constraints (e.g. blower turn-down). Ignoring the air supply side in an assessment could result in an overestimation of energy savings or treatment performance and consequently in non-optimal control solutions or equipment selection. INTRODUCTION One of the largest urban consumers of energy are water resource recovery facilities (WRRFs, formerly wastewater treatment plants). Within a WRRF, aeration energy consumption typically accounts for 50% of the facility's total operating costs (Olsson, 2012). WRRFs are therefore important targets for reducing municipal energy demands. Energy audits, which identify opportunities to reduce energy use, are typically based on the average energy consumption of a facility; they include benchmarking with similar plants or comparison against standard performance indicators. However, significant saving potential lies in the variability of wastewater treatment and the resulting process dynamics. Current energy audits should therefore include dynamic models that integrate water and sludge lines and their respective energy consumption.