Abstract Dewatering of sludge at wastewater treatment plants is an essential and costly step in the subsequent sludge processing. Prior to dewatering, sludge is conditioned by addition of expensive organic and inorganic conditioners. The present study aimed at developing an effective biological process for sludge dewatering in comparison with commercial polyacrylamide polymers. A complex ferric biogenic flocculant produced by Acidithiobacillus ferrooxidans was used for dewatering of sludge generated after the Chemically Enhanced Primary Treatment process from municipal sewage. Within 1 h of treatment, the ferric biogenic flocculant reduced the capillary suction time (CST) and specific resistant to filtration (SRF) of sludge by 92 and 91%, respectively, as compared to the 89 and 72% respectively achieved by using polymer. The acidification of the sludge after the addition of ferric biogenic flocculant caused charge neutralization of sludge particles and led to enhanced dewaterability. It also enhanced the floc structure of sludge with much bigger sized flocs as compared to the control, which facilitate its dewatering capacity. Ferric biogenic flocculant treatment improved the calorific value of the sludge by 27% due to improved settlement of organic matter into the sludge pellet. The small scale mechanical filter press study confirmed that the ferric biogenic flocculant is effective in reducing sludge moisture content to 69% as well as improving the effluent quality in terms of total suspended solids and total dissolved solids removal compared with polymer treatment.