Energy Neutral WWTPs – A Dream or a Reality for New Zealand?

There has been much coverage recently at conferences and in technical publications about “resource recovery” in wastewater treatment plants. The term “green factories” is being used to describe wastewater facilities which are manufacturing “green” energy or biofuels, recovering nutrients and recycling water for reuse. Many utilities globally have achieved – or are at least aiming for – “energy neutrality” at their wastewater facilities and, in some instances, a net positive energy balance has been achieved across the plant site.

In an investigation to see how different WWTPs in the USA are achieving a positive energy balance or at least energy neutrality – or are taking initiatives towards this goal – one of the authors visited six utilities on the west and east coasts of the USA in late 2016:

• Gresham, Oregon
• Columbia Boulevard, Oregon
• South East WPCP, San Francisco, California
• East Bay MUD WWTP, Oakland, California
• Blue Plains WWTP, Washington DC
• Alexandria RENEW, Virginia

The plants were very different in terms of their scale and treatment processes, and with a range of effluent standards based on their specific receiving environments, spanning from relatively straightforward BOD removal to advanced biological nutrient removal. The energy demands for liquid stream treatment processes and for the treatment of solids streams – which is driven by the enduse of the biosolids – have a huge influence on total energy utilisation and potential generation of biogas at a particular site, and hence on the net energy balance across the site.

This paper will summarise the key energy aspects of these six “Water Resource Recovery Facilities”, and will then relate their similarities and differences to a range of New Zealand counterparts to assess whether energy neutrality is a realistic goal for them – or is a dream which will be difficult to achieve.