Samples of clay-biosolids bricks. Source: RMIT University

Roughly 30% of worldwide biosolids generated as a by-product of the wastewater treatment process is stockpiled or landfilled. The EU produces over 9 million tons per year (tpy) of biosolids, while the U.S. produces about 7.1 million tpy. In Australia, 327,000 tonnes of biosolids are produced annually.

A sustainable use for this waste material is being pioneered at the RMIT University in Australia. Synthesis of fired-clay bricks with biosolids consumes only half of the energy required for conventional brick manufacture and yields a product with low porosity and low thermal conductivity, transferring less heat to potentially give buildings improved environmental performance.

The physical, chemical and mechanical properties of fired-clay bricks incorporating biosolids proportions between 10 and 25% were analyzed. Samples containing the sludge material passed compressive strength tests and were shown to immobilize heavy metals. Brick-firing energy demand was reduced up to 48.6% for bricks incorporating 25% biosolids. Inclusion of this material in bricks on a commercial scale would also reduce the need to mine clay for brick production.

About 5 million tpy of the biosolids produced in Australia, New Zealand, the EU, U.S. and Canada are now landfilled or stockpiled. Using a minimum 15% biosolids content in 15% of bricks produced could use up this 5 million tons.

The research is published in Buildings.