Biosolids are the treated, dried sludge produced from sewage treatment and, until recently, these have been stored onsite at Melbourne Water’s sewage treatment plants at Bangholme and Werribee.
The minimum storage time is three years to ensure that public health and environmental guidelines are met. Stockpiling Victoria’s biosolids is not sustainable and Melbourne Water is looking at new and beneficial uses for biosolids.
Melbourne Water is responsible for treating about 92 per cent of Melbourne’s sewage, and from this produces over 40,000 tonnes of dried and treated biosolids a year.
Melbourne Water has approximately 95 per cent of the State’s stored biosolids. Due to low levels of nutrients and the presence of other contaminants, biosolids are currently only being used in the production of blended soil improvement products, landscaping and site rehabilitation.
It is of great importance that further innovative uses of this waste material are investigated and developed.
An innovative South Australian company, Re-Brick Pty Ltd, was awarded a Smart Water Fund grant to use biosolids as a core ingredient in the manufacturing of bricks and pavers destined for use in the building industry.
Following the design and construction of a portable brick-making machine, Re-Brick experimented with different combinations of biosolid waste and binding agents to produce the best quality brick.
As part of the program, 50,000 pavers were produced, some of which were used to construct a demonstration path at Melbourne Water’s Western Treatment Plant ‘Discovery Centre’. The bricks are currently being assessed for durability.
Re-Brick was concerned that the market may respond negatively to a brick made of biosolids. As industry attitudes to using waste products in building materials were unknown, Re-Brick undertook research to determine them – and the results were surprisingly positive.
The building and construction industry has shown real interest in using products that benefit the environment.
The sample bricks passed strict tests for contaminant concentration (SCC) and leaching (TCLP). The bricks at the Discovery Centre, however, have shown signs of stress and wear and tear during high durability testing, and future product development will need to use these findings to improve durability before such a product is commercially viable.
The Smart Water Fund encourages innovation in the reduction and reuse of biosolids as a way of leading to a sustainable level of waste and protecting Victoria’s water resources.
Re-Brick Project Manager, Brian Rohan says, “The potential for expanding this to a commercial operation could see up to 3,000 tonnes of biosolids used every year and a significant reduction of the Western Treatment Plant’s current stockpile.”