But one group of scientists and the environmental lobby Friends of the Earth are urging caution. They say the council should proceed carefully, given that the grade of wastes allowed to be spread could still contain low levels of pathogens as well as new-generation materials not included in current safety guidelines. These molecular-sized waste particles, known as manufactured nano-materials or MNM and found in everyday shampoos or cleansers, end up in the waste stream.
Toxicological studies on nano-particles have found adverse reactions including deaths in animals and fish.
The draft plan defines biosolids as "sewage sludges" which often are mixed with materials such as pumice or sawdust and treated and stabilised to the extent that "they are able to be beneficially applied to the land".
Biosolids which fall short of the highest "Aa" standard - because, for example, contaminants exceed specified limits - could be dumped if granted resource consent. Additional protections covering this grade of wastes include a requirement that the land cannot be used "directly" for residential activities.
At present, Watercare, the Auckland Council-owned utility, dumps biosolids at Puketutu Island near its Mangere waste treatment plant. The company says it doesn't produce Aa grade biosolids, so the proposed plan change would not effect its operations. While most councils bury biosolids in landfills, some have tried to recycle the nutrient-rich waste. Nelson has sprayed it on land in a council-owned forest. Impressive tree growth rates have been recorded in the Rabbit Island plantation, where biosolids have been used since 1997.
Taranaki City Council has been making a product called Bioboost for more than 10 years and which it sells as a domestic fertiliser.
During its manufacture sewage waste is heated to 600°C to destroy pathogens. The council says its product is 100 per cent safe, though its use had to overcome what one report called "faecal phobia".
The Auckland draft plan notes that the practice of dumping biosolids in landfills was costly and was filling up space.
"More sophisticated wastewater treatment plants have enabled the production of more highly treated biosolids and more flexibility in their disposal to land," the draft says.
Scientist Peter Wills, a trustee of Physicians and Scientists for Global Responsibility, said his group wanted a precautionary approach.
"Generally we agree that recycling biosolids is a good idea. But you need to be careful what you're throwing around. Nano-particles have entered our domestic and industrial environment without a lot of scrutiny regarding their breakdown or persistence," Dr Wills, an associate physics professor at Auckland University, said.
Bob Tait, co-director of Friends of the Earth and a member of the panel which drew up the national biosolids guidelines, said before any policy change the public needed reassurance that industrial wastes including heavy metals were removed.
Mr Tait said the "Aa" standard did not mean wastes were free of pathogens, which meant they potentially could spread diseases such as norovirus. He too urged the council to proceed with caution.
Concerns raised by Friends of the Earth and PGSR were put to the council. In response John Duguid, manager Unitary Plan, said the new provisions were "consistent with national guidance on the management of biosolids, including their land-based application".
The issue was also being dealt with through Auckland Regional Plan appeals regarding air, land and water.
"It is expected that the provisions of the notified Auckland Unitary Plan will reflect both the resolution of this appeal and the feedback we receive on the draft provisions."
He encouraged feedback on the draft plan before the deadline of May 31.
A Ministry for the Environment spokesperson said: "There are actual and potential health risks when disposing of biosolids on to land and this process needs to be carefully managed."
The new rules
Biosolids (treated sewage waste) could be dumped on Auckland land provided it does not
• Run off into water or contaminate streams.
• Occur on wahi tapu or sacred Maori sites.
• Create offensive smells.
• Take place within 20m of property boundaries, water bores, geothermal features and coastal marine areas.
