Effect of Organic Content in Biosolids on the Properties of Fired-Clay Bricks Incorporated with Biosolids

Biosolids are produced following the treatment of wastewater sludge. Millions of metric tons of biosolids are produced around the world each year. This study has investigated the effect of biosolid organic content on the physical and mechanical properties of fired clay bricks. Biosolids produced at Melbourne water eastern treatment plant (ETP) and western treatment plant (WTP) have been used as a partial replacement material for brick soil producing raw mixtures with different amounts of organic content. The raw materials—brick soil and biosolids samples—were first characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), particle size distribution, Atterberg limits, specific gravity, organic content, and thermal analysis. The test results revealed that the organic content of ETP and WTP biosolids ranged from 6.3 to 23.3%. The green brick samples incorporating biosolids were fired at 1,050°C for three hours, and the fired samples were then tested for the compressive strength, density, cold and hot water absorption, the initial rate of absorption, and mass loss on ignition. The test results showed that all the physical and mechanical properties were highly dependent on the organic content of the raw materials. The compressive strength and density of fired bricks decreased as the organic content in the raw mixture increased. The initial rate of absorption, water absorption, and mass loss on ignition increased linearly with the increasing organic content in the raw brick mixtures. Furthermore, the test results demonstrated that the organic matter present in the raw brick mixtures significantly reduced the energy demand during the firing process of bricks proportionate to the percentage of organic content. The scanning electron microscopy results revealed that the intensity of pores increases with the increase in organic content. The leaching analysis was carried out for the manufactured bricks with different organic content and the results were compared with U.S. Environmental Protection Agency (EPA) regulatory limits.