Green Energy in the Wastewater Industry: Moving to Net Zero Energy in Hawaii

Dr. Roger Babcock, Water Resources Research Center/Civil Engineering, University of Hawaii at Manoa.

The Hawaii Water Environment Association in collaboration with the Water Resources Research Center recently organized a one-day workshop on the use of green energy at wastewater treatment facilities, and how this might be implemented in Hawaii.

The workshop, entitled Green Energy in the Wastewater Industry: Moving to Net Zero Energy in Hawaii, was held on August 2 in Honolulu.

Hawaii’s water sector has the highest electricity costs in the USA (typically 300–400% of that on the mainland). Drinking water utilities use large quantities of energy to pump, treat, and convey water. The wastewater sector uses even more energy to pump and treat wastewater, and often to distribute recycled water. Together, these two utility sectors currently use approximately 4.5% of the electricity generated on Oahu (>95% of which is used for dealing with wastewater). The annual cost of this electricity, produced from imported oil, is in excess of $80 million. There is currently a widespread initiative in the wastewater industry to move from just treating and disposing of sewage, to recovering some of the valuable resources it contains, such as recycled water, nutrients, and energy. A basic first step has been the conversion of wastewater treatment plants with massive electricity demands into net positive energy production plants through the use of the methane- containing biogas that plants produce and usually flare off as a waste product.

Efforts are currently underway to upgrade and expand the two largest wastewater treatment plants in Hawaii—Sand Island and Honouliuli—to full secondary treatment capability. This increase in treatment level will require additional energy. Upgrades are also underway to wastewater treatment plants on the neighbor islands. Sustainable energy provisions incorporated into the upgrades will be very important for utility customers and the environment for the next 100 years.

By moving toward net zero energy use by wastewater treatment systems the utilities can play an important role in helping the state to meet Hawaii's Clean Energy Initiative goals (100% green energy by 2045) . The workshop included several speakers from outside of Hawaii sharing their experiences with the 80 or so attendees. They included the operator of the Gresham WWTP (Oregon, USA), which has been net zero energy for two years, and the manager of the Marselisborg WWTP in Aarhus, Denmark that has been net zero for four years. Consulting engineers from California, Colorado, and Idaho who have worked on sustainable energy WWTP projects across the mainland USA, and in Hawaii also gave presentations. Here Net Zero Wastewater workshop presentations is a list of the presentations heard at the workshop.