Wellington stinky problem

Wellington is on the verge of a bizarre rubbish shortage, one that could leave us with a stinker of a problem.

This is arguably a nice problem to have but it remains an issue and one that the city’s ratepayers are set to spend $30 million or more to solve.

The root of the problem is that Wellington’s sewage goes through a ‘‘dewatering process’’ near the Southern Landfill above Owhiro Valley. This process theoretically removes liquids from the solids, with the liquids going back to the Moa Point sewage plant while the solids get buried at the landfill.

But, according to Wellington City Council’s city engineer, Derek Baxter, those ‘‘solids’’ are still 75 per cent liquid – of which, ‘‘tens of thousands of tonnes’’ went to the landfill each year.

The council’s consent to dump these solids says the landfill has to have a four-to-one ratio of general waste to sludgy sewage solids. To increase that ratio could make the general landfill too unstable.

Baxter said the amount of Wellington’s general waste was not keeping pace with what residents were sending down their toilets.

If this situation continued, in about seven years Wellington would not have sufficient general waste to achieve its four-to-one ratio and the council would have to look at other options – such as adding soil or compost to the landfill – to maintain its ratio.

A second option, with a pricetag of $30m or more, was to reduce the amount of ‘‘solid’’ sewage waste. The obvious solution was a better dewatering plant that could get more liquid out of the sewage.

Other options – each with their own fish-hooks – included using gas created at the landfill to run the dewaterer, getting microbes to eat the sludge, or using the waste to create electricity.

Councillor Iona Pannett, who holds the city’s infrastructure portfolio, said the amount of general rubbish in Wellington continued to rise but not to the same level as sewage.

The council’s expected spend, signalled in its draft Long-Term Plan, on a solution to the sludge problem was a sign of the ‘‘absolute commitment’’ it had to fixing this issue, she added.

Wellington Water spokesman Alex van Paassen said the company was looking at a region-wide solution for dealing with the sludge from Porirua, Hutt Valley, and Wellington’s two sewage plants.

Last May, Stuff revealed that ‘‘black boxes’’ at the Southern Landfill’s sewage plant were 10 years past their use-by dates and needed replacing.

Those black boxes are required to eliminate odours but were not working, leading to 15 complaints about the smell near the site. The council had to run an ‘‘odour suppression unit’’ to mask it.

Waste Operations landfill manager Darren Hoskins said yesterday that Veolia, the French-based multinational company contracted to run the capital’s sewage plant until 2020, had started work on replacing one of the black boxes and it would do the second one this year.

Wellington’s sewage flows to a treatment plant at Moa Point, from where non-contaminating parts of the city’s waste are treated and pumped out to sea. Leftover sludge is pumped to the sludge dewatering plant at the landfill.

The amount of Wellington’s general waste is not keeping pace with what we send down our toilets.

Wellington City Council city engineer Derek Baxter