To optimize the anaerobic digestion process of residual sludge, co-substrates addition and pre-treatments are increasingly being employed. Nevertheless, if these processes allow the optimization of biogas production, they can significantly impact the efficiency of mechanical dewatering processes for digested sludge. In this article, the impact of co-substrate addition (oily sludge) and thermal pre-treatment on the efficiency of mechanical dewatering of digested sludge was investigated. To this purpose, mechanical dewatering experiments were conducted at lab-scale by using a filtration-compression cell to determine the limit dryness of various digestates. In addition, control factors of the mechanical dewatering efficiency of digested sludge were investigated. Results highlight that 67% of the variance of the limit dryness of digestates is due to the variable 'volatile solid/total solid ratio