Production of Cationic Starch-Based Flocculants and Their Application in Thickening and Dewatering of the Municipal Sewage Sludge

Abstract

Polymer flocculants are used to promote solid–liquid separation processes in wastewater treatment technologies, and bio-based flocculants possess many advantages over conventional synthetic polymers. Potato starch microgranules were chemically modified and mechanically sheared to produce modified starch flocculants. The effectiveness of produced cationic starch (CS) and cross-linked cationic starch (CCS) flocculants in the thickening and dewatering of surplus activated sewage sludge was evaluated and compared with that of synthetic cationic flocculants (SCFs) The flocculation efficiency of SCF, CS, and CCS in sludge thickening was determined by measuring the filtration rate of treated surplus activated sludge. Comparing the optimal dose of SCFs and CCS flocculants needed for thickening, the CCS dose was more than 10 times higher, but a wide flocculation window was determined. The impact of used flocculants on the dewatering performance of surplus activated sludge at optimal dose conditions was investigated by measuring capillary suction time. The filtration efficiencies (dewaterability) of surplus activated sludge using SCF, CS, and CCS were 69, 67, and 72%, respectively. The study results imply that mechanically processed cross-linked cationic starch has a great potential to be used as an alternative green flocculant in surplus activated sludge thickening and dewatering operations in municipal sewage sludge treatment processes.

Could Plant-Based Flocculants Substitute the Conventional Synthetic Chemicals in the Sludge Dewatering Process?

“…Additionally, dewatering devices may be damaged as a result of the intensive use of corrosive ferric salts [50]. Moreover, due to their non-biodegradability, chemical residuals ascribed from synthetic flocculants may remain embedded in the dewatered sludge matrix, subsequently leading to secondary pollution and limiting the use of this sludge [51]. Consequently, sludge handling becomes much more costly as further treatment is required.…”

Investigation of the physicochemical properties of aqueous solutions of sodium salt of carboxymethyl starch obtained in the solid phase by viscometric methods

“…Na-CMS is a polymer produced on an industrial scale and is used in oil and gas [6,7], textile [8,9,10], pharmaceutical [11,12] industries, is used as a stabilizer for aqueous solutions, suspensions and emulsions, occulants, adhesive etc. [13,14,15]. In addition, aqueous solutions of Na-CMS are more stable and less prone to biodegradation compared to starch [16].…”