‘SolarMix’ - Innovation in Drying Technology

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Courtesy of IST-Anlagenbau GmbH

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.

Cabwater recently commissioned the ‘SolarMix’ process at the Burpengary East STP where solar energy & air drying is used to enhance the solids content and the stability of the biosolids in a manner that is protected from rainfall. The ‘SolarMix’ technology has taken the traditional method of bed air-drying and used modern technology to remove the traditional problems. This process has not only had a positive impact on the operational budget by reducing the amount of biosolids removed from the STP but has also significantly increased the stability of the biosolids which presents Cabwater with a number of other options for beneficial reuse.

The results collected to date confirm that the process is capable of continually producing biosolids with a solid content in excess of 65% (during both summer and winter) as well as reducing the levels of bacteria and pathogens to the point that it meets stabilisation grade A. The end result is dependant on the initial solid content, the biosolids type (STP treatment process), and climatic conditions.

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