BIOSOLIDS. A New Zealand Perspective (2015)

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Biowaste is an unavoidable end product of human communities - raw sewage.

Sludge is the residue remaining after raw sewage is processed.

Biosolids are the organic materials remaining after sludge is treated. They can contain bio-nutrients, and also microbiological and chemical contaminants, pharmaceuticals, parasites, radioactive material, heavy metals, nano-particulates, and other contaminants.

The treatment of wastewater and sewage - and the management of the biosolids that treatment produces - are issues of concern related to disease and environmental pollution. Because of the enormous volume of material involved and the difficulties associated with disposal, there is pressure to utilize the perceived benefits on a greater scale.

Biosolids are routinely dispersed on land in New Zealand. For example:

• Nelson Council has applied biosolids since 1996 on the 1000 ha forestry plantation, Rabbit Island (Moturoa). A higher tree growth rate has been recorded since 1996.

• New Plymouth's Treatment Plant produces Bioboost , a fertiliser sold for residential and commercial use that is made from treated sewage sludge.

• Thames/Coromandel District Council’s Biosolids Management Strategy claims composting is an economic method for it to deal with biosolids. However, biosolids composting operations ceased in 2014.

Among other countries, the US, Europe and Australia put around 40 per cent of treated biosolids on agricultural land, whereas New Zealand puts 90 percent into landfills. The application of biosolids to land is a contentious issue and the methane gas produced by sludge in landfills is inconsistent with New Zealand’s commitments to the Kyoto Protocol.

New Zealand regulations direct that untreated sewage may not be discharged within 500 metres from land, or in water less than five metres deep. Fewer restrictions apply to treated sewage. Sewage discharge is prohibited near marine farms, mataitai (traditional food collection) reserves or marine reserves.

During heavy rainfall sewage is discharged occasionally into the ocean approximately 1.8km from shore off Moa Point, Wellington. At Christchurch, after processing through oxidation ponds, cleaned water is discharged from a pipe 3 km off New Brighton beach; the pipe being 5.2 km long, 1.8m wide, and buried about 8m below the sea floor.
Guidelines for land application of biosolids

The conversion of sewage sludge into biosolids and the controlled application of biosolids to land are perceived to offer the advantage of the fertilising and soil conditioning properties of a resource that presents huge disposal problems and which is a sustainable resource. The ‘Guidelines for the safe application of biosolids to land in New Zealand’ acknowledges that protecting and enhancing the quality of the environment is essential for sustainable development:

“Biosolids have valuable fertilising and soil conditioning properties. They contain micronutrients and organic material and, worldwide, they are commonly applied to land as a means of restoring degraded soils or boosting the productivity of soils within areas of low natural fertility. Examples of beneficial use include the restoration of depleted cropping soils, maintenance or enhancement of soil fertility in forests, rehabilitation of mine tailings and quarry sites, landfill cover, golf courses, parks and gardens.”

The Guidelines also confirm biosolids contain microbiological and chemical contaminants that give legitimate concerns about public health, environmental and economic risks and includes a review of pathogens in New Zealand conditions, concluding directions that testing should be carried out for E. coli, campylobacter, salmonella, enteric virus, and helminth ova. However, the Guidelines are silent on the testing for a number of chemicals that have been found in wastewater, sewage sludge and biosolids around the world.

The Guidelines provide a biosolids grading system that is made up of two parts. The first part, which is denoted by a capital ‘A’ or ‘B’, represents the stabilisation (microbiological) grade. The second part, denoted by a lower case ‘a’ or ‘b’, represents the chemical contaminant grade. The Guidelines recommend that regular audits be commissioned to ensure top quality ‘A’ biosolids continue to meet requirements. Biosolids which fall short of an ‘Aa’ standard - for example, where contamination exceeds specified limits - can still be dumped if granted resource consent. Class ‘B’ biosolids would potentially contain pathogens at levels constituting a risk to human health. According to the Guidelines, additional protections in the ‘A’ grade may include a requirement that treated land cannot be used “directly” for residential activities and biosolids applied to land must not:

• Run off into water or contaminate streams;
• Occur on wahi tapu or sacred Maori sites;
• Create offensive smells;
• Be within 20m of property boundaries, water bores, geothermal and coastal marine areas.

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