Water and the Circular Economy
Project Round
Project Number
9TR4 - 001
Research Organisation

Pathogen Die Off in Air Dried and Stockpiled Biosolids

Project Overview

Lagoon based systems are commonly used in Victoria for the processing of sewage sludge.  Most of these systems consist of a three open ponds, but the pre-treatment of the material, end use (if any) and time to harvesting varies considerably across Victoria. Some lagoons are de-sludged as frequently as every three years and the product used beneficially, while others are not de-sludged for 25 years.  This situation is not sustainable for several reasons.  Open ponds release large amounts of greenhouse gases, including methane and nitrous oxide, from anaerobic regions.  Moreover, long term storage is likely to result in loss of nutrients, which could otherwise be used beneficially on agricultural land.

A major factor restricting the recycling of lagoon-produced biosolids agricultural land is the lack of data on the microbiological safety of material produced in lagoon–based systems and the restrictions of the current Victorian EPA Biosolids Land Application Guidelines (2004).  Lagoon based systems are not prescribed in these guidelines as treatment processes capable of reliably reducing the numbers of a range of pathogens to sufficiently low levels to comply with Treatment Grade T1 (unrestricted use) or Treatment Grade T2 (restrictions on use apply).

The overall aim of this project is to provide data on the microbial safety and nutrient status of biosolids produced by air drying and stock piling of sludge from lagoon-based systems.

The levels of microbial indicators and nutrients will be determined in sludge taken from three regional plants that use lagoon processes, which are commonly used in most regional areas of Victoria.  Sludge harvested from lagoons will be treated in three different ways; pan-drying, stockpiling, and pan-covered.  Sludge will be analysed for microbiological, chemical and physical parameters on collection and at intervals during treatment.

The results of this project will extend the findings obtained from earlier studies at Melbourne metropolitan treatment plants to include lagoon systems.  The results from both studies are essential to inform future revision of the Vic EPA Biosolids Land Application Guidelines (2004) and the National Water Quality Guidelines (2004) management of sewage sludge. This is expected to lead to a substantial increase in land application of biosolids in Victoria.  This outcome supports government policy on the beneficial use of biosolids in Victoria (National Biosolids Partnership, 2010). If the project demonstrates that safety of biosolids can be achieved by harvesting lagoon sludge, followed by treatment for a shorter period of time, there will be significant benefits for the environment as well as considerable cost savings for water utilities.

Supporting documents