Chemicals such as Ca(OH)2, Al2(SO4)3, and FeCl3 are used to precipitate and prevent phosphorus from escaping in effluents from sewage plants in Ontario. Since such chemicals affect the characteristics of anaerobically digested sludges, incubation experiments were conducted to determine if the nitrate production in soil treated with these sludges was also affected. Nitrate production of six anaerobically digested sewage sludges differed considerably when incubated with soil but not in a manner related to the chemical treatment of the sewage. Reduced nitrate production from whole sludge from one source was possibly attributable to relatively high lipid and petroleum hydrocarbon contents. With the exception of this sludge, 17 to 30% of the sludge N was nitrified in 16 weeks under laboratory conditions. Nitrate production lag periods of 2 weeks or more were observed with whole sludges. The lag period, if present, when reconstituted sludges (ammonium and soluble organic N removed) were incubated with soil was <1 week with the exception of the one sludge which probably had high lipid and petroleum hydrocarbon contents. Incubation of reconstituted sludges in soil resulted in 29 to 32% nitrification of the organic N during the first 16 weeks. Nitrate production was relatively rapid in the early part of the 49-week incubation period but slowed substantially later.; Nitrate production of six anaerobically digested sewage sludges differed considerably when incubated with soil but not in a manner related to the chemical treatment of the sewage. Reduced nitrate production from whole sludge from one source was possibly attributable to relatively high lipid and petroleum hydrocarbon contents. With the exception of this sludge, 17 to 30% of the sludge N was nitrified in 16 weeks under laboratory conditions. Nitrate production lag periods of 2 weeks or more were observed with whole sludges. The lag period, if present, when reconstituted sludges (ammonium and soluble organic N removed) were incubated with soil was less than one week with the exception of the one sludge which probably had high lipid and petroleum hydrocarbon contents.
