Performance evaluation of novel cascade aerating trickling filter: contaminants removal and biodegradation model

This research assessed the effectiveness of a trickling filter wastewater treatment system using cocked stone (stone embedded with coal tar) as biofilm support. This study also explored influence of optimum hydraulic loading rates (HLRs) for the best operational parameters to remove suspended solids, biodegradable pollutants and pathogens, in accordance with Pak-EPA regulations for agricultural reuse. Two trickling filters have been installed in series, the first cascade aerated (CATF: 0.42 m³m⁻² h⁻¹) and the other unaerated (UATF). The selected HLRs (0.55, 1.20, and 1.35 m³m⁻²d¹) were evaluated for 200 days. The optimal HLR at which the TF presented a better treatment efficiency and fulfill regulatory guidelines intended for agriculture was 1.20 m³m⁻²d⁻¹, achieving treatment efficiencies of 90% BOD₅ (biochemical oxygen demand), 76% COD (chemical oxygen demand), 96% TSS (total suspended solids), and 4-log units of fecal coliforms. The effluent’s electrical conductivity certifies that it will not induce soil salinity. The BOD reaction kinetic model estimated the optimal volumetric design BOD loading rates (Bvd) of 1.7–2.3 kg BOD/m³ day for designing efficient trickling filter systems. As a result, cocked stone can be regarded as a novel material appropriate for use as a biofilm support in TFs treating wastewaters.