LABORATORY STUDIES OF THE FATE OF SEWAGE SLUDGE NITROGEN DURING COMBUSTION

The fate of sewage sludge nitrogen during combustion was investigated. Using a laboratory combustion apparatus, dried sewage sludge was combusted under different furnace temperatures and gas mixtures of oxygen and argon. The combustion product gases were sampled and analyzed for gaseous nitrogen species including NO, NO(,2), HCN, NH(,3) and N(,2). A complete nitrogen balance was performed. Over 90 percent of the sewage sludge nitrogen was converted to N(,2) during combustion, with the remaining 10 percent converted to NO. The sewage sludge nitrogen conversion to NO was found to increase with increasing oxygen levels and with increasing furnace temperature. NH(,3), HCN and organic nitrogen species were found to be stable intermediates pyrolyzed from the sludge bed and oxidized in the flame zone. Reaction paths leading from the initial sludge nitrogen compounds to NO and N(,2) have been postulated.; The sludge ash produced during these combustion studies was characterized. Combustion temperature had little effect on the major element composition of the ash. Evidence exists that several heavy metals were retained in the low temperature ash in greater concentration than in the high temperature ash.