Review of Energy Audit and Benchmarking Tools to Study Energy Efficiency Through Reducing Consumption in Wastewater Treatment Systems

Abstract

Wastewater treatment systems are major consumers of electricity being responsible for 3 to 5% of global energy consumption, and 56% of greenhouse gas emissions into the atmosphere in the water treatment sector. Climate change currently imposes the definition of a new pattern of human behavior in the defense and sharing of a common space that is the planet, so the optimization of water treatment models plays a crucial role in the definition of sustainability strategies as part of the challenges for decarbonization by 2050. The physical-chemical characteristics of the influent, the treatment techniques and associated technologies and the unpredictability of external phenomena of inefficiency transform wastewater treatment plants (WWTPs) into complex systems, sometimes difficult to understand. The study of energy efficiency plays an important role in the emergence of a standard behavior model, which allows the correction of unbalanced situations in the expected energy consumption. Given the importance of the topic, the present review aims to study energy auditing techniques and benchmarking tools developed for the wastewater treatment sector to reduce the current electricity consumption, which could represent up to 90% of total energy consumption. The result of the research was organized according to the criteria defined for the characterization of auditing techniques and benchmarking tools. A review was conducted from 51 scientific papers from different reference research platforms published in the last 20 years according to the keywords. This literature review has shown that there are, in the classification of consumption reduction, energy auditing and benchmarking tools; energy management techniques and methods directed to the energy efficiency of the treatment stages and specific equipment; and, finally, decision support tools. According to the methodology followed, it was possible to conclude that although the concern is not recent, there are techniques and tools for assessing energy performance more suitable for the wastewater sector. However, the authors recognize that associated with the complexity of wastewater treatment systems, inefficiency phenomena still strongly impact energy efficiency assessment, so the contributions for their identification and quantification may represent an added value for data analysis, systematization, and optimization methodologies.

A Critical Review on Methodologies for the Energy Benchmarking of Wastewater Treatment Plants

“…Influent WW temperature affects the performance of the treatment process, in particular the biological ones [2,37,38]. Indeed, any temperature change may affect the energy consumption at WWTPs [2,15,38,39]. For instance, an increase in water temperature led to an increase in biological activities while reducing the oxygen solubility and a subsequent greater energy demand for aeration [2,15,40].…”

“…Indeed, any temperature change may affect the energy consumption at WWTPs [2,15,38,39]. For instance, an increase in water temperature led to an increase in biological activities while reducing the oxygen solubility and a subsequent greater energy demand for aeration [2,15,40]. It was reported that high temperatures during the summer season (T = 19.4 • C) led to an energy consumption approximately 5.6% lower than in winter (T = 11.5 • C) [2].…”

“…As a whole, a WWTP encompasses five main stages: preliminary, primary, secondary, tertiary, and sludge treatment [42]. The first one accounts for the smallest percentages (~10%) [2,15].…”

“…Aside from the aforementioned energy consumptions, WWTPs indirectly consume energy through various processes and activities associated with WW treatment [3,15,19].…”

“…Based on the latest technological advancements, modern WWTPs are expected to have a specific power consumption ranging from 20 to 45 kWh per population equivalent (PE) per year [3,15]. Additional data reveal that energy consumption in the EU varies between 0.3 and 2.1 kWh/m 3 of treated wastewater, while in the United States, the range is from 0.41 to 0.87 kWh/m 3 [3,16].…”