The unsatisfactory performance of the conventional swine wastewater treatment is drawing increasing attention due to the large amount of refractory chemical oxygen demand (COD), nitrogen, and phosphorus attached to the suspended solids (SS). In this study, for the first time, a novel process based on bio–coagulation dewatering followed by a bio–oxidation (BDBO) system was developed to treat swine wastewater containing high–strength SS, COD, TN, and TP. Firstly, after the bio–coagulation process, the removal efficiencies of SS, COD, NH₃–N, and TP reached as high as 99.94%, 98.09%, 61.19%, and 99.92%, respectively. Secondly, the filtrate of the bio–coagulation dewatering process was introduced into the subsequent bio–oxidation process, in which the residual COD and NH₃–N were further biodegraded in a sequence batch reactor. In addition, the dewatering performance of the concentrated swine slurry was substantially improved, with the specific resistance to filtration decreasing from 17.0 × 10¹² to 0.3 × 10¹² m/kg. Moreover, the concentrated swine slurry was pressed and filtered into a semi–dry cake after pilot–scale bio–coagulation dewatering treatment. Finally, the concentrations of COD and NH₃–N in the effluent after the BDBO process, ranging between 150–170 mg/L and 75–90 mg/L, met the relevant discharge standard. Compared to traditional treatments, the BDBO system has excellent large–scale potential for improving the treatment efficiency, shortening the operation period, and reducing the processing costs, and is emerging as a cost–effective alternative for the treatment of wastewater containing high concentrations of SS, COD, TN, and TP.

The use of bioleaching for anaerobically digested sludge (ADS) was found to be ineffective compared to using it for undigested sludge (UDS) for reasons elucidated in this study. Results showed that specific resistance to filtration of ADS increased during bioleaching. The pH value of ADS increased to 7.97 and remained unchanged during bioleaching, while it decreased to 2.98 for UDS. Added Fe²⁺ was not detected as the energy source for ADS. Higher alkalinity and unavailable Fe²⁺ in ADS prevented the growth of the Acidithiobacillus species. It was found that sludge pH increased to 8.40 and then stayed within an alkaline range, whereas slime EPS content rapidly increased to 8.13 mg DOC/g VSS. These results indicated that aeration seriously deteriorated the dewaterability of ADS through bioleaching due to the unexpected drastic increase of sludge pH and slime EPS content.