EFFECTS OF IRRADIATION ON SLUDGE ORGANIC-CARBON AND NITROGEN MINERALIZATION

Irradiation used to eliminate pathogens in sewage sludge may deleterio usly affect properties of sludge organic matter. Three anaerobically d igested, dewatered sewage sludges were irradiated with gamma-irradiati on at absorption doses of 0, 6 and 12 kGy, respectively, then mixed wi th a soil and incubated for 16 wk. Evolved CO2 and concentrations of N H4+-N and NO3--N in the sludge-soil mixture were measured. The effects of irradiation were not consistent in the three sludges tested. Irrad iation did not significantly affect sludge organic C nor N mineralizat ion in Guelph sludge (GS). However, in sludges from Ottawa (OS) and To ronto (TS), C mineralized in irradiated treatments was less than from the non-irradiated treatments. In response to slower organic matter de composition caused by irradiation in the OS and TS, the inorganic N co ncentrations;were higher with irradiated than with non-irradiated in t he OS, but the converse was true for the TS. This was probably related to the difference in C-to-N ratio of the organic matter (19.5 in OS a nd 9.5 in TS). Increasing the irradiation doses did not significantly affect inorganic N concentrations;with the OS, but with the TS, the hi gh dose (12 kGy) treatment resulted in higher C and N mineralization t han did the low dose (6 kGy). (C) 1997 Elsevier Science Ltd.