Dunedin City Council operates the only biosolids fluidised bed incinerator in Australasia. The system uses 3.5m3 of sand as the fluidising medium, which operates at a combustion temperature of 830°C.
This paper outlines the conclusion to the Tahuna Wastewater Treatment Plant upgrade project, being the biosolids disposal strategy. The original project had committed capital funding of $14.6 million for a biosolids beneficial re-use or disposal facility. However, by reusing the existing 1980 fluidised bed incinerator, DCC has been able to reduce this budget by $10 million and deliver several environmental benefits.
DCC is embarking on a project to optimise the existing incinerator, including re-conditioning the asset, automating the system for unmanned 24/7 operation and installing an ash removal system. Investment in an ash removal system has made the decision to reuse existing infrastructure an environmentally sustainable one. Without an ash removal system, the ash from combustion would accumulate in the treatment process, lowering the calorific value of the waste biosolids, resulting in the need to use diesel to augment combustion. In the absence of ash removal, only 36% of waste biosolids could be incinerated to prevent ash build up in the treatment plant; the remaining 64% requiring disposal to Landfill.