title: Energy audit in small wastewater treatment plants: methodology, energy consumption indicators, and lessons learned.
abstract: Energy audits in wastewater treatment plants (WWTPs) reveal large differences in the energy consumption in the various stages, depending also on the indicators used in the audits. This work is aimed at formulating a suitable methodology to perform audits in WWTPs and identifying the most suitable key energy consumption indicators for comparison among different plants and benchmarking. Hydraulic-based stages, stages based on chemical oxygen demand, sludge-based stages and building stages were distinguished in WWTPs and analysed with different energy indicators. Detailed energy audits were carried out on five small WWTPs treating less than 10,000 population equivalent and using continuous data for 2 years. The plants have in common a low designed capacity utilization (52% on average) and equipment oversizing which leads to waste of energy in the absence of controls and inverters (a common situation in small plants). The study confirms that there are several opportunities for reducing energy consumption in small WWTPs: in addition to the pumping of influent wastewater and aeration, small plants demonstrate low energy efficiency in recirculation of settled sludge and in aerobic stabilization. Denitrification above 75% is ensured through intermittent aeration and without recirculation of mixed liquor. Automation in place of manual controls is mandatory in illumination and electrical heating.
authors.affiliation: Department of Civil, Environmental and Mechanical Engineering, University of Trento, via Mesiano 77, 38123 Trento, Italy E-mail: paola.foladori@ing.unitn.it.
authors.forename: P
authors.initials: P
authors.lastname: Foladori
authors.affiliation: Department of Civil, Environmental, Architectural Engineering and Mathematics, University of Brescia, via Branze 43, 25123 Brescia, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Vaccari
authors.affiliation: Department of Civil, Environmental, Architectural Engineering and Mathematics, University of Brescia, via Branze 43, 25123 Brescia, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Vitali
mesh_terms: D057919:Biological Oxygen Demand Analysis; D003246:Conservation of Energy Resources / Q000191:economics*; D012722:Sewage; D064091:Waste Disposal Facilities / Q000191:economics*; D014865:Waste Disposal, Fluid / Q000379:methods; D062065:Wastewater
chemical_list: D012722:Sewage; D062065:Wastewater