City water energy-use study published in Australia

A major report on energy use in major cities by the Australian and New Zealand water industries has been produced by the Australian national research agency, CSIRO, and the Water Services Association of Australia.

It is the first time that energy use in the industry has been compared with other industries and total city use.

One finding of interest to promoters of desalination is that pumping water from sources located at considerable distance from cities contributes significantly to energy use in some cities because ongoing low rainfall periods have diminished local storages.

The report, completed in December 2009. finds that treating wastewater to a tertiary standard requires substantial energy compared with primary or secondary treatment. On average, energy intensity doubles between primary and secondary treatment and doubles again between secondary and tertiary treatment.

However, if tertiary treatment of wastewater is required, reuse opportunities may become more cost-effective as the additional energy required for reuse may be relatively minor depending on energy requirements after treatment (eg for pumping).

Total energy use by water utilities in Sydney, Melbourne, Perth, Brisbane, Gold Coast and Adelaide in 2006/07 was 7.1 petajoules (PJ) and met the needs of 12.5 million people (resulting in an Australian average of 590 megajoules per person per year (MJ/cap*y). This figure is approximately 0.2% of total urban energy use and less than 15% of the energy used for residential water heating – modelled as at least 46 PJ for 2006/07.

Energy use by Auckland water utilities comprised 0.43 PJ and met the needs of some 1.2 million people (349 MJ/cap*y).

Imported electricity, representing 76% of energy used by water utilities, is the main source of energy-related greenhouse gas emissions by the water industry. Maximising renewable energy opportunities such as biogas capture, mini-hydros and sourcing low emissions electricity from the grid will significantly reduce greenhouse gas emissions, says the report.

The full report can be downloaded from the CSIRO website.