Rosedale facility vital to healthy Shore

Toilet users of the North Shore might not like to give much thought as to what happens after pressing ‘‘flush’’.

But in fact, what comes next is a remarkably intricate process, essential to ensuring the North Shore’s environment and waterways are kept clean.

Basically it all ends up, all 240,000 people’s worth of it, at the Rosedale Treatment Facility every day, Auckland’s second largest treatment plant after Ma¯ ngere.

The 80 visitors who attended the facility’s open day on November 12, found the learning experience fascination and highlyrecommendable.

The process from raw sewage to clean and treated wastewater requires a network of experts, including an army of ‘‘bugs’’ grown on-site.

Operations controller Glenys Rule said bug-part of the process is the ‘‘coolest’’.

The bugs, which are good bacteria, eat most of the particles found in untreated wastewater or the ‘‘organic load’’ - otherwise known as poo.

‘‘We grow the bugs,’’ she said. ‘‘It’s like a little city, but we are the benevolent dictators that control the conditions these bugs live under.’’

The next step sends the bugcleansed water to the clarifiers, to make the water clear again.

After that, the water spends two weeks being naturally disinfected by sunlight, in the ponds on site. The ponds are visible from the Northern Motorway, just before the Greville off-ramp.

The treated wastewater is then discharged at Mairangi Bay, about 3 kilometres out to sea.

Importantly, despite the connotations the name might carry, the treated wastewater is actually extremely clean and safe.

In fact, the entire process is largely self-sustaining, and Rosedale is one of the top five most energy-efficient plants in Australasia. The plant creates biogas, which provides up to 80 per cent of the energy needed.

Currently, the treatment facility is in the process of expanding. When it opened in 1962, it served only 60,000 people. Now, it serves about 240,000 people who live from Devonport to Long Bay.

‘‘We are getting to capacity, which is why we have to expand it,’’ Kenny Williamson, Watercare plant manager, said. From Watercare’s $1 billion investment in the North Shore, $62 million has been assigned to the facility.

LAINE MOGER/ STUFF The ‘‘activated sludge’’ process is the second part of the cleaning process, which employs an army of bugs that is farmed on site.