Municipal wastewater treatment produces vast amounts of sludge that is expensive to dispose. That’s why researchers in from Universiti Teknologi MARA in Malaysia are working on methods to use that sludge as a viable material in concrete that can be used in other infrastructure projects.
“Overall, there is potential for using domestic waste sludge powder (DWSP) as a partial cement replacement,” said Dr. Kartini Kamaruddin to ScienceDaily. “However, more detailed research should be conducted to yield methods for producing quality powder.”
While incineration, disposal in landfills, and land spreading are common sludge disposal options, increasingly these are under the scrutiny or regulators and the public. Strict environmental control regulations have resulted in limitations on sludge disposal options.
As well the costs of sludge management may be up to 50 per cent of the total running costs of a waste water treatment plant. Having obsevred these challenges, the research team set out to find an economic alternative disposal method, by making concrete.
The researchers first dried and burnt wet sludge to remove moisture, eventuall turning it into powder (DWSP). Using different proportions of DWSP (3, 5, 7, 10 and 15%), the researchers mixed it with cement to produce different types of concrete (normal strength Grade 30 and higher strength Grades 40 and 50). Then they compared each DWSP concrete mixture with normal concrete in terms of their compressive strength, water absorption, water permeability and rapid chloride ion penetration (i.e. permeability to salt).
The team found that the compressive strengths of DWSP concrete decreased as the proportion of DWSP increased in concrete mix, with the exception of Grade 40 concrete containing 7% DWSP. Also, both water absorption and water permeability increased as the percentage of DWSP increased. However, normal concrete was more permeable than DWSP concrete of Grade 40, suggesting that DWSP enhanced the durability of this concrete. Additionally, the resistance to chloride permeability increased for concretes with up to 15% DWSP.
The study was published in the Pertanika Journal of Science and Technology.