Pretreatment of water-based seed coating wastewater by combined coagulation and sponge-iron-catalyzed ozonation technology

Coagulation–sedimentation combined with sponge iron/ozone (CS-SFe/O3) technology was applied to pretreat water-based seed coating wastewater (WSCW) from pesticide manufacturing. Coagulation with polyferric sulfate at a dosage of 1.5 g L−1 and a pH of 8.0 was effective, with color and chemical oxygen demand (COD) removal rates of 96.8 and 83.4%, respectively. SFe/O3 treatment further reduced the organic content in the effluents, especially concerning the degradation of aromatic pollutants, as demonstrated via ultraviolet–visible spectrophotometry (UV–vis), excitation-emission matrix (EEM) fluorescence spectrometry, and gas chromatography-mass spectrometry (GC/MS) analyses. The residual color and COD values of the effluent were 581.0 times and 640.0 mg L−1, respectively, under optimal conditions (ozone concentration of 0.48 mg L−1, SFe dosage of 20.0 g L−1, initial pH of 9.0, and reaction time of 30 min). Organic pollutants were also degraded by the high amounts of HO, which may have been generated via the transformation of ozone into HO on the SFe's surface and in the solution. Meanwhile, the biochemical oxygen demand (BOD5)/COD ratio of the WSCW increased, which indicates that the biodegradability improved significantly. The amount of iron leached from SFe particles was 4.5 mg L−1, which shows that the SFe catalyst has good stability. The operating cost of the combined CS-SFe/O3 technology was estimated at approximately 2.79 USD t−1. The results of this study suggest that the application of the combined CS-SFe/O3 technology in WSCW pretreatment can be beneficial for removing suspended solids, degrading recalcitrant pollutants, and enhancing biodegradability for the subsequent bioprocessing treatment.