DEVELOPMENT OF AN INNOVATIVE TOOL FOR MONITORING THE AERATION SYSTEM PERFORMANCE AND THE GREENHOUSE GAS EMISSIONS IN WRRFs

Abstract

Water Resources Recovery Facilities (WRRFs) are sources of greenhouse gases (GHGs) emission both direct (i.e. from biological processes) and indirect (i.e. due to the energy necessary for operating the treatment processes). Aeration of the biological tanks accounts for 50-60% of the total energy consumption of WRRFs. In light of this, and considering the worldwide concern for energy sustainability and adaptation strategies, there is a need to develop and implement innovative tools for reducing WRRFs carbon and energy footprint by optimizing treatment steps and lowering energy requirements from aeration systems.

Within the project LIFE LESSWATT (LIFE16 ENV/IT/000486) co-financed by the European Union, an innovative wireless tool for reducing energy consumption and GHGs emission of WRRFs has been manufactured and tested. The project consists of an innovative instrument (LESSDRONE) and a new protocol for converting LESSDRONE measures and specific WRRF data in actions aimed at optimizing the operation of the aerobic compartments of WRRFs. The project, started in October 2017, involves five partners: the Department of Civil and Environmental Engineering of the University of Florence, Cuoiodepur SpA, the Department of Mathematical Modelling, Statistics and Bioinformatics of the Ghent University, West System Srl and Utilitatis. The LESSDRONE instrument allow the real-time monitoring of the oxygen transfer efficiency (OTE) and GHGs emission from the aerated tanks in operating conditions in order to minimize WRRFs carbon footprint (CFP) and energy demand.

LESSDRONE is an automated, wireless and self-moving device. The automatic positioning of the hull, managed by Global Positioning System (GPS), and the instrumentation, are connected through a specific software that manages the different sampling phases. The sample collected by the hood passes through the sampling circuit equipped with silica gel cartridge, in order to dry the sample, and detectors for the measurement of CO₂, CH₄, N₂O, O₂, humidity, temperature and pressure, air velocity and dissolved oxygen (DO). One year of measurement campaigns using the LESSDRONE were carried out within the Cuoiodepur WRRF (Central Italy), that treats tannery and municipal wastewater, in order to assess the influence of operating parameters such as temperature and inlet load on the aeration efficiency and GHGs production. Moreover, the monitoring was aimed at evaluating the diffuser aging on the oxygen transfer efficiency (OTE).

Each measurement campaign consisted of:

• Points tests: measurements on several points of the oxidation tank with constant airflow. On each point the OTE and the GHGs (CO₂, N₂O and CH₄) were detected. Spatial distribution within the tanks of the off-gas flow rate and the concentration of DO were measured;


• Stationary tests: measurements in a single point of the tank for an extended period of time (up to one week). The OTE and the concentrations of the GHGs were measured in order to assess their temporal distribution in different operating conditions (working day/public holidays, night/day, high/low load, etc.);

During each test, sampling and analysis (COD, nitrogen compounds, mixed liquor suspended solids, etc.) of the inlet and outlet of the oxidation tanks were carried out.

In this paper, we present the results of the measurement campaigns carried out in Cuoiodepur WWRF. The new tool (LESSDRONE + protocol) will be tested in other 5 European WRRFs, with different characteristics in terms of treatment trains and loads, in order to validate the tool and make it applicable in a wide range of situations