Abstract
One of the largest surveys in Europe about energy consumption in Italian wastewater treatment plants (WWTPs) is presented, based on 241 WWTPs and a total population equivalent (PE) of more than 9,000,000 PE. The study contributes towards standardised resilient data and benchmarking and to identify potentials for energy savings. In the energy benchmark, three indicators were used: specific energy consumption expressed per population equivalents (kWh PE-1 year-1), per cubic meter (kWh/m3), and per unit of chemical oxygen demand (COD) removed (kWh/kgCOD). The indicator kWh/m3, even though widely applied, resulted in a biased benchmark, because highly influenced by stormwater and infiltrations. Plants with combined networks (often used in Europe) showed an apparent better energy performance. Conversely, the indicator kWh PE-1 year-1 resulted in a more meaningful definition of a benchmark. High energy efficiency was associated with: (i) large capacity of the plant, (ii) higher COD concentration in wastewater, (iii) separate sewer systems, (iv) capacity utilisation over 80%, and (v) high organic loads, but without overloading. The 25th percentile was proposed as a benchmark for four size classes: 23 kWh PE-1 y-1 for large plants > 100,000 PE; 42 kWh PE-1 y-1 for capacity 10,000 < PE < 100,000, 48 kWh PE-1 y-1 for capacity 2,000 < PE < 10,000 and 76 kWh PE-1 y-1 for small plants < 2,000 PE.
Highlights
More than 2% of the world’s electrical energy is a rough estimation of the energy used for water supply and wastewater treatment worldwide (Olsson ; Plappally & Lienhard )
This paper presents the outcomes derived from the largest survey conducted in Italy about energy consumption in wastewater treatment plants (WWTPs)
The benchmark value depends on the size class: energy consumption of or below 23 kWh PEÀ1 yÀ1 is the objective of large plants with more than 100,000 population equivalent (PE), while a higher benchmark of 76 kWh PEÀ1 yÀ1 is reasonable for small plants
Summary
More than 2% of the world’s electrical energy is a rough estimation of the energy used for water supply and wastewater treatment worldwide (Olsson ; Plappally & Lienhard ). A large amount of primary energy, mainly originated from fossil sources, is used in WWTPs to meet stringent targets on effluent water quality, but contributes to environmental problems such as global warming and climate change. In this context, measures simultaneously aimed at maintaining. The benchmark of energy consumption in WWTPs represents a powerful management tool which uses specific indicators to find the optimal performance or to evaluate the energy efficiency of a plant in comparison with other plants or a standard value (inter alia Lindtner et al ; Krampe ; Torregrossa et al ). A universal benchmarking of energy performance in WWTPs does not exist yet at an international level (Belloir et al ; Longo et al ), and the rare benchmarking studies appear very fragmented and piecemeal because they were carried out locally on the basis of national/regional surveys
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