Rotorua District Council looks to gain value from biosolids

22 February 2010

Rotorua District Council (RDC) and Crown Research Institute, Scion, are joining forces to demonstrate a new approach to the management of organic wastes.

The Council has recently approved a proposal for Scion to build a pilot plant that will process biosolid wastes from Rotorua’s municipal wastewater treatment plant (WWTP) into value added products.

Scion’s Group Manager of Sustainable Design, Dr Trevor Stuthridge, says this is an exciting regional initiative that could be applied in other centres.

“There is increasing pressure on local councils to seek new disposal options for WWTP wastes, which currently account for up to 15% of all landfilled wastes in New Zealand.

“The technology that we have been developing with RDC’s support has the potential to slash biosolid volumes 30-fold and also substantially reduce greenhouse gas emissions and leachates that arise from this type of waste,” Dr Stuthridge explains.

The pilot plant will use a thermal deconstruction process that “cooks” the biosolids (sewage sludge) and breaks them down into re-useable nutrients and a range of other added value chemicals. In addition, methane can be produced for electricity production.

Scion is delighted that Rotorua District Council is taking a strong lead by backing this research programme for local and national benefit.

“Rotorua is a good model for many cities in New Zealand, with the same challenges regarding the disposal of biosolids and other municipal wastes. What works for the RDC can work for any other urban centre in the country, and not just for sewage sludge,” says Dr Stuthridge.

Research shows that the same technology could also be used for managing organic wastes from food and industrial processors.

“The Bay of Plenty contains some of New Zealand’s largest organic waste producers including pulp and paper, agriculture, dairy, meat and fruit processing.

“These waste streams represent a tremendous added-value resource for the region that can be tapped into by these types of environmental technologies. We are part of a trend that is rapidly growing throughout the world,” he explains.

The Council decision to fund the pilot plant, which is due to be operational by July 2010, is a bold response to the Government’s waste minimisation initiative.

If successful, a full-scale plant in Rotorua could remove up to 8,500 tonnes of waste going to landfill per year, and ultimately achieve net benefits (in terms of cost reduction and value creation) of around $4 million per year for the council and community.

The pilot plant project, which has a construction cost of $850,000, will be partly funded from the council’s share of the government’s waste levy fund.

Council works manager, Peter Dine, says the project could provide a solution to Council’s single largest waste disposal problem and even convert that waste stream into a revenue source.  

“In addition, there is potential to utilise the technology for the wider organic waste generated within the district. This could significantly extend landfill life and provide major environmental and financial benefits,” he says.

About Scion’s Waste 2 Gold programme

Scion’s Waste 2 Gold platform provides a sustainable solution to the disposal of solid organic wastes. It is based on a deconstruction process that uses heat, pressure and air to convert organic wastes. The results could benefit the council, the community and the environment. For example:

  • Acetic acid production: commercial ethanol is currently used to improve the sewage treatment system's ability to remove nitrogen. The acetic acid produced through Scion’s process could replace this ethanol, with potential savings of $367,000 per year.
  • Energy generation: the process is essentially a "wet combustion" and will generate excess heat for use in the deconstruction plant and elsewhere at the site. In addition, methane will be generated at several stages in the system for electricity production.
  • Environmental improvements: significant greenhouse gas reductions (>70%) will be achieved through deconstruction. In addition, high nutrient content leachates will no longer enter lake-bound waterways around the landfill.
  • The deconstruction stage leads to a 30-fold decrease in biosolids volumes - meaning a potential saving of $730,000 per year in transportation, landfill fees and waste levies.

Scion’s approach differs from others in this field in that it controls the deconstruction process to yield useful chemicals for downstream bioconversion, rather than complete breakdown to CO2 and water. Likely implementers of the technology include local councils and waste management companies.

Other possible customers for the technology include (1) industrial organic waste producers (e.g. primary industries), who are looking for reduced disposal costs and alternative use options; and (2) chemical companies that may want to generate and recover chemical intermediates from the waste stream as replacements for fossil fuel-derived equivalents.