Cromwell worm farmer Robbie Dick approached the QLDC to carry out trials on treated sludge from Project Pure in December, to see whether the effluent could be organically processed by worms to deliver a safe by-product.
The council is at pains to find an acceptable solution as to how to dispose of the potentially bio-hazardous sludge from Project Pure - it is currently being trucked to a Queenstown landfill at a cost to ratepayers.
QLDC solid waste manager Stefan Borowy said the council's preferred method of sludge disposal is to discharge the product to land.
While sludge had been provided to Mr Dick's Wormworx operations for testing, the QLDC was not actively involved with the trial process but was kept up to date with progress reports.
"As far as we're aware, the trial hasn't been successful, but it is something we have no control of," Mr Borowy said.
Mr Dick said his initial trials of introducing tiger worms to the treated sewage sludge had resulted in the invertebrates avoiding the substance.
For almost three weeks, the worms had been reluctant to venture into the sludge, after he placed them alongside the treated effluent.
Mr Dick decided to step things up.
"I put a [kilogram] of worms straight into a polystyrene box full of sludge ... It killed them all off in 24 hours - left them looking like they had been burnt by battery acid,"Mr Dick believed a polymer substance introduced as one of the final steps in the sludge treatment process had proved fatal to his worms, which otherwise would be able to handle the product.
If the "inorganic polymer" was swapped with an organic product, such as shredded cardboard, peat or vermicast (worm castings), then it could prove a more attractive food for worms, he said.
The Otago Daily Times understands the polymer is introduced to the sludge treatment process as one of the final steps to firm up the sludge to enable it to be more cleanly transported.
Mr Borowy said swapping the polymer with an organic material could be expensive.
"If we are talking about changing additives [to the treatment], it could possibly just make the wastewater process more costly." While the QLDC had evaluated other proposals, disposal to land of the treated sludge remained its preferred option.
