Method to calculate and express energy consumption of industrial wastewater treatment for the purpose of water reuse — Part 2: Accounting for energy recovery

This document sets out the general principles for, and provides guidance on, the quantitative characterization of energy recovery from wastewater and sludge treatment, and how to account for this in the total energy consumption calculation.

The scope of this document includes:

— a definition of the main energy recovery processes applicable to industrial wastewater treatment and sludge treatment for reuse, such as anaerobic digestion yielding biogas;

— an introduction to the possible forms of energy generated by energy recovery processes and systems, such as electricity, steam or heat, and how to account for intentional wasting or commercial utilization of biogas;

— guidance on the value to be taken into account as quantification of the energy generated, including the power actually generated on average;

— a limit level for contaminated components in biogas allowed before any utilization;

— principles to integrate the energy recovery results with the energy consumption in accordance with ISO 21939-1.

Energy production which is not recovered from wastewater or sludge treatment processes is not within the scope of this document and is not included in the calculations and result