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Use for recycled wastewater will be economic in time

19 Jun 2009

Use for recycled wastewater will be economic in time

Using recycled wastewater for uses such as producing concrete, irrigating sports fields and flushing public toilets may be economical at some stage in the future if demand for drinking quality water continues to rise.

Project manager for the Gisborne Wastewater Project Peter McConnell says the cost of treating recycled wastewater to a higher level for use in industry and public sports fields and toilets may decrease as technology improves. The cost of producing water of drinking standard will increase, he says, if more water is required and treatment standards are increased.

"A tipping point will see it more economical to use the treated wastewater in some processes, and for that reason, the Alternative Use and Disposal research being undertaken as a wastewater resource consent condition has to be a continuous process." Mr McConnell told the Wastewater Management Committee today (Thursday).

Research to date shows that potential volumes required are just a small portion of the total output of the biological trickling filter plant. If the effluent was drawn off after the ultraviolet disinfection, it would require some form of filtration.

"Very preliminary capital costs for the additional treatment and reticulation to the users could be up to $2.5m. Preliminary operating costs could be up to $120,000 a year which for the volume identified is a production cost of $2 a cubic metre. At this stage, this does not compete with potable water at $0.80 a cubic metre."

Mr McConnell said that once the treatment plant was operating, council would be in a position to undertake filtration trials alongside the biotransformation study.

"This will help us determine more accurately the type of filtration equipment needed and likely costs for recycled effluent from the biological trickling filter plant.

"The basic work to date, undertaken over summer by an engineering student, will be refined over time and we will learn more as we proceed.