Evaluation of the Main Parameters Influencing Sludge Treatment Processes in Activated Sludge Municipal Wastewater Treatment Plants Employing the Clay Material Nano Montmorillonite Conditioner

Objective: The efficient operation of excess biological sludge treatment processes including thickening, digestion, and dewatering is crucial to the overall performance of activated sludge wastewater treatment systems. This study aimed to evaluate key operational parameters across these stages in order to optimize the use of Nano
montmorillonite and its acid-thermal modified form as sludge conditioners. The objective was to assess their effectiveness in enhancing sludge dewaterability, digestibility, and methane production.
Methods: Laboratory-scale experiments were conducted using real sludge samples collected from the South Tehran Wastewater Treatment Plant. The primary parameters assessed included filtration time, specific resistance to filtration (SRF), capillary suction time (CST), zeta potential, bound water content, extracellular polymeric substances (EPS), and sludge digestibility. Pearson correlation analysis was applied to explore the relationships between the nanomaterials and these parameters. Additionally, a heatmap was generated to illustrate the interdependencies among them.
Results: The greatest reduction in SRF was observed with 300 mg/g dry solids of Nano montmorillonite, yielding SRF values of 6/65×10¹² and 52/75×10¹² m/kg for excess and digested sludge, respectively. Using 200 mg/g of the modified form produced SRF values of 6/22×10¹² and 45/3×10¹² m/kg. At the same optimal dosages, filtration time and CST were improved significantly: 31, 24, 2, and 6 seconds for excess sludge, and 192, 164, 2/3, and 6 seconds for digested sludge, respectively. The modified nanomaterial reduced zeta potential and bound water content by 93/75% and 80/38% in excess sludge and by 89/74% and 77/93% in anaerobically digested sludge. In addition, reductions in total organic carbon and protein content across all EPS layers were observed, contributing to enhanced sludge digestibility and increased methane production. The TOC in soluble EPS significantly decreased after conditioning by 31/58% in excess biological sludge and 60/52% in digested sludge. Similarly, the TOC in loosely bound EPS decreased by 56% and 19/23%, and in tightly bound EPS by 47.13% and 33.14%, respectively, which was directly associated with bound water reduction. The Protein depletion in the soluble EPS and an increase in both loosely and tightly bound EPS has been dedicated. The heatmap analysis at dosages of 0, 100, 150, 200, 250, 300, and 350 mg/g revealed strong correlations (97–98%) among filtration time, CST, and SRF. The addition of nanomaterials particularly Nano clays such as Nano montmorillonite and its modified variants has emerged as an effective approach to enhance anaerobic digestion and improve methane yield
Conclusion: Both nanomaterials demonstrated high efficacy despite differing optimal dosages. The strong intercorrelation among filtration time, capillary suction time, and specific resistance to filtration highlights their critical and interconnected roles in optimizing sludge dewatering performance.