Application of designed enzymatic polysaccharide derivatives as a conditioning agent in wastewater sludge dewatering

Cationic polyacrylamides (CPAM) are the conditioning agents predominantly used in sludge dewatering at wastewater treatment plants but show a low biological degradability and unfavorable ecotoxicological effects. Paving the way for a circular economy, we seek to substitute CPAM with biopolymer derivatives produced from sustainable renewable feedstocks with an overall reduced environmental footprint. Therefore, an enzymatic-designed polysaccharide was utilized, and the appropriate cationic derivative was generated to compare with different conventional cationic acrylic polymers. Standard lab-scale dewatering tests, i.e., centrifugation, settling, capillary suction, and filtration were carried out for the polymers in this study. Besides, the ecotoxicity of investigated polymers was assessed using the triphenyl-tetrazolium chloride and nitrification inhibition test. As a result, the biopolymer derivatives (DP) showed good dewatering abilities but required 2–3 times higher dosages (15–30 g AS /kg DS ). Most notably, DP performed significantly better than the conventional CPAM in the centrifugation test, yielding higher dry content of sludge pellets and lower supernatant turbidity. The dry content of sludge with DP can be improved by 2.4 wt-%, while the turbidity was reduced by 30 % ( p < 0.05). In addition, it was observed in this study that the microbial inhibition and ecotoxicity of the biopolymer derivative were significantly lower than that of CPAM, which may provide further motivation to consider this new class of biopolymer derivative. • The biopolymer shows comparable dewatering performance to conventional polymers. • It achieves the best results in centrifugation test with +2.4 wt-% dry matter and -30% turbidity. • The biopolymer significantly lowers microbial inhibition in sludge treatment. • A 2–3 times higher dosage is needed compared to synthetic alternatives.