The co-combustion process may comprise the following unit operations: routing of hot gas (10) generated in the clinker cooling process to a rotary kiln (1); use of part of the rotary kiln exhaust gas to dry solid wastes in rotary dryers; leading the gases from both the dryer and the combustion kiln to the secondary combustion chamber (2); use of additional fuel to boost up the secondary combustion chamber reaction temperature to as high as 1200.degree. C.; primary dry gas scrubbing in a precalciner or precalciners (3, 3a); heat recovery (4) and power generation; secondary gas scrubbing (5) in a semi-dry scrubber; bag filtering after activated carbon injection and returning of all the collected ash and used carbon into the waste kiln and/or a cement kiln. Detrimental materials for cement processing generated by waste combustion can be by-passed to a scrubbing system and a cement kiln. Residue slag from waste kilns can be treated and reused.