COAL FLY-ASH AS A COMPOSTING MATERIAL FOR SEWAGE-SLUDGE - EFFECTS ON MICROBIAL ACTIVITIES

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 decomposi tion of sewage sludge. Lagoon ash and fly ash at 0, 2.5, 5, 10, 20, an d 50% w/w were mixed with dewatered sewage sludge and incubated at 25 degrees C for 3 months. Carbon dioxide evolution for all treatments fo llowed the same trend except 50% w/w amendment for both ash residues. When compared with the control (sludge only), higher levels of ash ame ndments had a lower CO2 evolution which may be due to the high entrain ed salt content and pH in both ash residues. The present results indic ate that fly ash has a more pronounced inhibition on sewage sludge dec omposition while 2.5% w/w and 5% w/w lagoon ash amendments demonstrate no significant inhibition. Therefore, lagoon ash would be a more suit able co-composting candidate for sewage sludge and the suitable amendm ent rate should be < 10%.