Drain dumpers cause city waste log jam

Monitoring of waste in the pipe network entering the region's main treatment plant at Mangere has revealed items ranging from wet wipes, building rags, dental floss and more. Photo / iStock

Dental floss and nappies flushed down household toilets are among the indestructible items causing costly blockages to an Auckland sewerage system that has been designed for only human and domestic waste.

Monitoring of waste in the pipe network entering the region's main treatment plant at Mangere has revealed items ranging from wet wipes, building rags, dental floss, cellphones, false teeth and cash.

Items have to be removed because the Watercare Services plant uses biological processes rather than chemicals to treat effluent before it is discharged into the Manukau Harbour.

All of these items travelled many kilometres through household drains, street sewers, pump stations and holding tanks before reaching the screening room at Mangere, said Watercare Services.

"We ask people not to dispose of foreign matter that our system is not designed to cope with and just results in a failure in facilities or overflows into the environment or on private property," said network operations manager Anin Nama.

"Nappies have been around for a time but the population seems to find it easier to put theses things down the system.

"Wet wipes is another product that does not break down."

Mr Nama said dental floss did not rot and when caught in other material had the potential to cause major problems.

Watercare had 120 employees working directly with wastewater, excluding contractors' teams to investigate and clear blockages in the network.

Another growing problem is cooking fat and oil tipped down the kitchen sink, which staff call "Fat-bergs".

About 90 tonnes of fat was mechanically sucked from street grit tanks in Auckland last year.

Mr Nama said Watercare has a team dedicated for education, who visit areas where a lot of fat is found.

"It should be put in the rubbish but the natural tendency is to wash it down the drain and ... a large volume ... solidifies and causes a problem in our system.

Flushing nappies and wet wipes down the toilet is keeping household drain unblocking firms busy.

"They don't move in the pipes and form a log jam," said Drain Patrol company director Mark Rollinson.

Dumping food particles and other debris down the drain was the main cause of blockages, along with tree roots invading pipes.

He said tree roots trapped insoluble material and even toilet paper.It cost from $150 to unblock a drain, including travel and the first hour's labour, but some emergencies took longer to remedy.

Mr Rollinson said that hot cooking juices poured down the kitchen sink cooled in the pipes and turned into a hard obstacle.

The trend for households to save water by taking a shower instead of a bath had deprived drains of a rush of bath water to clear pipes.

Waste Water Worries

• Nappies
• Wet wipes
• Building rags
• Dental floss
• Cellphones
• Home phones
• Toys
• False teeth
• Crockery
• Cash
• Cooking fat

Auckland's Waste Water System

• 90 tonnes of fat a year trapped in street grit tanks
• 120 Watercare employees maintain sewer network and treatment
• 60 minutes' minimum response by crews to overflow callouts
• 400 million litres of wastewater treated daily
• 7834 km wastewater pipes500 pump stations
• 18 treatment plants in Auckland region