Aeration is commonly identified as the highest energy use in water resource reclamation facilities (WRRF), so fine-bubble diffusers in municipal facilities are logical avenue to reduce energy use and therefore move towards energy neutrality because of their higher oxygen transfer efficiency. This research studied systematically the evolution of fine-bubble aeration diffuser efficiency over time, concurrently with the biological study of the biofilm fouling in order to understand the major factors contributing to diffuser fouling.
In this project the link between biofilm DNA concentration, reduced oxygen transfer efficiency, and energy consumption was clearly established. This was further connected with the energy usage per diffuser, which increases with time inexorably due to fouling. This showed a direct link between biological process conditions and an energy-sustainable infrastructure. Moreover, some strategies that treatment plants can utilize to supply more oxygen to the biological process with the same level of power consumption to improve aeration efficiency were studied, together with cleaning practices that can restore aeration efficiency.
At the end of the project a procedure to evaluate energy demand and recovery was developed to quantify the ability of a treatment facility to achieve energy neutrality, the effect of aeration efficiency on the process energy demand, as well as the effects of fouling for different diffusers and different process conditions. We projected that the potential energy savings achieved with fouling prevention could span from 18,000 USD/Month for a small plant (20 MGD, or 74,500 m3/d) to 90,000 USD/Month for a large plant (100 MGD, or 375,000 m3/d). This project helped to set a model for utilities to gain more insight in the process mechanisms leading to aeration energy consumption, thus allowing more targeted energy efficiency measures at existing facilities. Moreover, as the techniques employed in this project are adopted more within our industry, the upgrades of existing facilities and new designs will be able to fully integrate the results.