Mestrado em Engenharia do Ambiente - Instituto Superior de AgronomiaThis work aims to evaluate the use of 4 different sewage sludges as a fertilizer:
mixed sewage sludge (primary+secondary sludge), dehydrated mixed sewage sludge;
anaerobically digested sewage sludge and anaerobically digested sewage sludge
treated with quicklime (CaO). Two aerobic incubations were performed with mixtures of
sludge and the top layer of a Haplic Pdzol, at a rate equivalent to 10 ton dry matter ha-
1. During 140 days, the CO2-C emissions and the mineral N in soil were periodically
measured. At the end of the incubation period, several soil properties were evaluated.
The higher CO2-C emission was found in the mixed sludges while the anaerobic
sludge presented the lower value. The treatment of anaerobic sludge with lime led to
an increase of CO2-C emission and nitrogen mineralization from the sludge, indicating
that lime treatment promoted more favorable conditions to sludge mineralization. At the
end of the incubation period, sludge-amended soil had higher pH, more evident on the
lime-treated sludge, and higher amounts of available nutrients, namely, nitrogen,
phosphorus, potassium and calcium. The balance between applied carbon and C-CO2
emission, proved that sewage sludge increases carbon accumulation in soil
