As a coal producer, Solid Energy isn’t a company you’d automatically attribute to environmental stewardship. After all, it is collaborating with Bathurst Resources on plans to mine the Denniston plateau on the West Coast of the South Island. But the company does devote some of its efforts to the development of biodiesel and it has recently found success with a wastewater treatment process that recycles biodiesel glycerol and produces renewable energy.
The process, which is the result of three years of testing and research between the Christchurch City Council and Solid Energy, is currently being used at the Council's Wastewater Treatment Plant in Bromley, New Zealand's second largest wastewater treatment facility.
The glycerol recycling process uses a combination of wastewater sludge from Christchurch City and biodiesel glycerol to produce biomethane gas. The biomethane is being used at the wastewater treatment plant to generate electricity and heat, and there are plans to use the gas created during the process at community facilities such as the Christchurch Art Gallery and Civic Offices.
"Research and testing has confirmed a method which uses the glycerol by-product to supercharge the plant's gas production, delivering much more gas, and therefore energy, than it would normally," said Christchurch City Council City water and waste manager, Mark Christison.
It's not the first time sewage sludge has been converted into a useful product. In July a thermal oxidation pilot plant was installed at Rotorua District Council’s Wastewater Treatment Plant to test an innovative process that converts biosolid waste (sewage sludge) into valuable chemical products. The pilot plant uses thermal deconstruction to “cook” the biosolids and break them down into re-useable chemicals and a range of other by products. These can be used for fertilisers or in the production of bioplastics and biofuels.