Coal fly ash as a composting material for sewage sludge: Effects on microbial activities

J. W. C. WONG, S. W. Y. LI, Ming Hung WONG

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Coal fly ash has a strong alkaline buffering capacity which may render heavy metals in sewage sludge unavailable and the aim of this project is to study the potential of coal fly ash as a co- composting material for sewage sludge by evaluating its effect on the microbial decomposition of sewage sludge. Lagoon ash and fly ash at 0, 2.5, 5, 10, 20, and 50% w/w were mixed with dewatered sewage sludge and incubated at 25°C for 3 months. Carbon dioxide evolution for all treatments followed the same trend except 50% w/w amendment for both ash residues. When compared with the control (sludge only), higher levels of ash amendments had a lower CO₂ evolution which may be due to the high entrained salt content and pH in both ash residues. The present results indicate that fly ash has a more pronounced inhibition on sewage sludge decomposition while 2.5% w/w and 5% w/w lagoon ash amendments demonstrate no significant inhibition. Therefore, lagoon ash would be a more suitable co-composting candidate for sewage sludge and the suitable amendment rate should be < 10%. Copyright © 1995 Informa UK Limited.

Original languageEnglish
Pages (from-to)527-537
JournalEnvironmental Technology (United Kingdom)
Issue number6
Publication statusPublished - 1995



Wong, J. W. C., Li, S. W. Y., & Wong, M. H. (1995). Coal fly ash as a composting material for sewage sludge: Effects on microbial activities. Environmental Technology, 16(6), 527-537. doi: 10.1080/09593331608616294


  • Sewage sludge
  • Fly ash
  • Lagoon ash
  • Composting
  • Microbial activity