Carbon Accounting Guidelines for Wastewater Treatment: CH4 and N2O

Executive Summary 

This document provides guidelines for accounting for methane (CH4) and nitrous oxide (N2O) emissions from municipal wastewater treatment, discharge and sludge processing in New Zealand. Emissions from on-site septic tanks are also covered. The guidelines were designed with certain objectives in mind:

• To help wastewater treatment providers to prepare a greenhouse gas (GHG) inventory through the use of standardized approaches and principles;

• To provide guidance on the scope and boundaries to be considered for activities in the wastewater industry;

• To provide more detailed guidance on GHG accounting for treatment processes used widely in New Zealand;

• To consider the current state of knowledge for wastewater GHG emissions and applicability of the methodology updates published by the Intergovernmental Panel on Climate Change (IPCC, 2019); and

• To increase consistency and transparency in GHG accounting and reporting among wastewater treatment providers.

The guidelines describe different levels of assessment depending upon the quality and extent of plant data available. They provide some default values that can be used in the absence of good data. The document provides details for improving data quality over time.