TECHNOLOGY FOCUS - POLYMERS - Preferred Polymers: The water-soluble cationic, amphoteric or zwitterionic polymers have a molecular weight of 2000-10000000 daltons. The cationic polymer is a copolymer of acrylamide and cationic monomer(s) selected from diallyldimethylammonium chloride, dimethylaminoethylacrylate methyl chloride quaternary salt (DMAEA-MCQ), dimethylaminoethylmethacrylate methyl chloride quaternary salt and dimethylaminoethylacrylate benzyl chloride quaternary salt, preferably diallyldimethylammonium chloride/acrylamide copolymer. The cationic polymer has a cationic charge of at least 5 mole%. The amphoteric polymer is selected from dimethylaminoethyl acrylate methyl chloride quaternary salt/acrylic acid copolymer, diallyldimethylammonium chloride/acrylic acid copolymer, dimethylaminoethyl acrylate methyl chloride salt/N,N-dimethyl-N-methacrylamidopropyl N-(3-sulfopropyl)-ammonium betaine copolymer, acrylic acid/N,N-methacrylamidopropyl N-(3-sulfopropyl)-ammonium betaine copolymer and DMAEA-MCQ/acrylic acid/N,N-dimethyl-N-methacrylamidopropyl N-(3-sulfopropyl)-ammonium betaine terpolymer. The amphoteric polymer has a molecular weight of 5000-2000000 daltons. The amphoteric polymer has a cationic charge equivalent to anionic charge equivalent ratio of 0.2:9.8-9.8:0.2. The cationic polymer has a cationic charge of 100 mole% and a molecular weight of 2000-500000 dalton. The water-soluble cationic polymer selected from polydiallyldimethylammonium chloride, polyethyleneimine, polyepiamine, polyepiamine crosslinked with ammonia or ethylenediamine, condensation polymer of ethylenedichloride and ammonia, condensation polymer of triethanolamine and tall oil fatty acid, poly(dimethylaminoethylmethacrylate sulfuric acid salt) and poly(dimethylaminoethylacrylate methyl chloride quaternary salt). The water-soluble zwitterionic polymer is composed of 1-99 mole% of N,N-dimethyl-N-methacrylamidopropyl N-(3-sulfopropyl)-ammonium betaine and 99-1 mole% of nonionic monomer(s), such as acrylamide.