‘SolarMix’ - Innovation in Drying Technology

Abstract
The dramatic population increase in South East Queensland has seen a significant increase in the load placed upon our Sewage Treatment Plants (STPs) and a dramatic increase in the amount of biosolids produced at these STPs. Dewatered biosolids produced by most Water Authorities consists of 85 % water and only 15% solids and it is difficult to achieve a higher solids content with conventional equipment without sacrificing machine efficiency. At present Water Authorities in South East Queensland spend between $40 and $50 per wet tonne for removal and disposal of biosolids which generally represents the highest expenditure component of the total operational budget of an STP. Achieving a significantly higher solid content in the biosolids would obviously represent a major operational cost saving for the Water Authority. A secondary problem faced by these STPs is difficulty consistently meeting Stabilisation Grade B as the biosolids produced have not received the required digestion/treatment times to reach the Stabilisation Grade B requirements. As a result, Stabilisation Grade C biosolids is produced and is always a management problem to both biosolids producers and beneficial reuse end-users in high population growth areas. A simple, economical, and environmentally friendly method of volume/mass reduction and further biosolids stabilisation is air-drying, however, traditional air drying has a reputation for being labour intensive, sometimes odorous, and particularly susceptible to rainfall in coastal areas.