AbstractSafe biodegradable “green” alternatives with minimal environmental and health risks have received widespread research interest. Thirty different kinds of bio-based flocculants (modified starches, modified celluloses, native chitosan, and lignin-based flocculant) were pre-tested using a simple jar test for the examination of the applicability of new organic flocculants in papermaking and in conditioning of waste activated sludge from the pulp and paper industry. Three starch-based and two cellulose-based polymers were chosen for further flocculation and filtrations tests. Key optimization parameters for the polymer were identified as the increasing of molecular weight and nitrogen content. The starch-based polymer had the best performance in both applications, but in neither of the cases did it function as well as the commercial polyacrylamide-based polymers. The importance of the molecular weight came up in the experiments. The developed starch-based polymer was cationic and had the charge density used in industry. On the other hand, although cationic flocculants are the most used in sludge conditioning, also anionic and non-ionic polymers are needed, depending on the characteristics of the sludge to be flocculated. Overall action of the tailored polymers was also studied in order to predict their potential as papermaking retention and dewatering aids.