c the rate of heating of the biological sludge to the foregoing temperature may be determined by best engineering practice preferably the biological sludge is heated to the aforementioned temperature as rapidly as possible the retention time is preferably about 0 to about 15 minutes and more preferably about 0 to about 10 minutes thus the retention time used is the minimum time required to allow the biological sludge to come to a uniform temperature compared to current heat treating processes a shorter retention time is advantageous because it reduces the size of the reaction vessel required and results in lower b o d in the filtrate because this process uses lower temperatures and pressures than prior art heat treatment processes reaction vessel 16 may be constructed from less expensive metals and with less rugged construction after heating the biological sludge is then transported in the direction of arrow 18 to centrifuge 20 in step b of the present process the heated biological sludge from step a is centrifuged to isolate the solids of the heated biological sludge from the liquid of the heated biological sludge a conventional solid bowl decanter centrifuge is preferably used for this purpose because the benefits derived from this centrifugal isolation step are proportional to the separation degree of liquid and solids.