Advanced coagulant strategies for urban municipal sludge treatment: balancing chemical and natural agents for optimal dewatering

Urbanization and population growth have led to increased production of municipal wastewater and sludge with high organic load and fine suspended solids. This situation highlights the urgent need for efficient, sustainable, and environmentally friendly sludge dewatering technologies. This situation highlights the urgent need for efficient, sustainable, and environmentally friendly sludge dewatering technologies. This study introduces an innovative combined coagulation strategy of ferric chloride with natural coagulants – marshmallow root and chitosan - for activated sludge dewatering, which aims to increase dewatering performance and reduce chemical consumption. Response surface methodology ( RSM ) and central composite design ( CCD ) were used to optimize the operating conditions and analyze the key influencing factors. The results indicated that under optimal conditions, moisture removal, turbidity reduction, and chemical oxygen demand ( COD ) removal reached 88.75 % , 91.70 % and 85.64 % , respectively. The optimal filtration time to achieve effective sludge dewatering was 2 minutes and 15 seconds. FTIR and SEM analyses confirmed the active role of natural polymers in floc formation. • Efficiency of combined natural and chemical coagulants (marshmallow, chitosan, FeCl₃) in urban sludge dewatering. • Use of natural coagulants to reduce chemical consumption and environmental impacts in sludge treatment. • Process optimization performed using Response Surface Methodology with Central Composite Design. • Optimal conditions achieved high efficiency: 88.75% moisture, 91.70% turbidity, 85.64% COD removal, TTF 2.1 min.