Cost-effective evaluation of modified ochre soil and its combination with cationic polyacrylamide for municipal wastewater sludge conditioning.

Abstract

One of the most costly stages of activated sludge wastewater treatment plants is the treatment and dewatering of waste sludge. Chemical conditioning of sludge, as one of the most widespread methods to enhance sludge dewaterability, accounts for a significant portion of operational expenses due to the consumption of expensive polymeric compounds. This research aims to assess the cost-effectiveness of ochre soil, modified with hydrochloric acid, as an affordable mineral for conditioning waste sludge in an activated sludge system. The optimal conditions for acid modifications are obtained using response surface methodology. Then, its performance is compared with conventional coagulants (ferric chloride and alum) and in combination with cationic polyacrylamide (CPAM). To assess the conditioning process efficiency, the specific resistance to filtration (SRF) parameter was employed. At an optimal dose of modified ochre soil (MOS) equal to 300 (mg/g dry solids), the SRF value decreased from 31.96 to 2.7 Tm/kg. The combination of 100 (mg/gDS) MOS with 0.5 (mg/gDS) CPAM showed as the most cost-effective among the coagulants tested, with a 31% greater SRF reduction compared to CPAM used alone. This study shows the practical efficacy of an eco-friendly natural mineral as a polymer alternative, with the potential for sludge dewatering.