NOVELTY - Treating sewage sludge comprises a pathogen reduction stage in which raw sludge is incubated at a temperature in the mesophilic temperature range. The sludge is incubated in sequential vessels comprising an upstream vessel which receives the raw sludge to be incubated and a downstream vessel which discharges the incubated sludge.    USE - For treating sewage sludge for use in the agricultural industry as a source of fertilizer and soil conditioner.    ADVANTAGE - The incubation of raw sludge ensures a high organic content which promotes the growth of hydrolytic bacteria and consequently, the reduction in pathogen content.    DETAILED DESCRIPTION - Treating sewage sludge comprises a pathogen reduction stage in which raw sludge is incubated at a temperature in the mesophilic temperature range. The sludge is incubated in sequential vessels comprising an upstream vessel which receives the raw sludge to be incubated and a downstream vessel which discharges the incubated sludge. The sludge is fed from the upstream vessel to the downstream vessel via any intermediate vessel and subsequently discharged after spending a predetermined residence time in each vessel. The total residence time is the predetermined incubation period.    An INDEPENDENT CLAIM is also included for a sewage sludge treatment apparatus comprising sludge incubation vessels (1a-1c) for incubating raw sewage sludge within the mesophilic temperature range, including an upstream vessel for receiving raw sludge and a downstream vessel for discharging incubated sludge; a heater (4) maintaining the sludge at the predetermined temperature range in the incubation vessels; and a transfer mechanism transferring the sludge sequentially from the upstream vessel to the downstream vessel via any intermediate vessels.    DESCRIPTION OF DRAWING(S) - The figure shows a sewage sludge treatment system.    Incubation vessels (1a-1c)    Mesophilic anaerobic digester (2)    Sludge feed line (3)    Heater (4)    Sludge transfer lines (5, 6)    Gas lines (7)    Digester input line (8)    Compressor (10)    Pressurized gas inlet (11)