In recent years, there has been a notable increase in the number of swine farms worldwide. This rise is primarily driven by the growing demand for protein sources, leading to a substantial generation of swine or piggery wastewater. This wastewater is characterized by a high concentration of ammonia, which possesses a considerable risk of eutrophication and adverse environmental effects [1]. Consequently, researchers have increasingly focused on investigating secure and effective approaches for treating and disposing of swine wastewater.

This industry generates large volumes of wastewater which contains a high quantity of suspended solids content, organic matter (BOD₅ and COD), nutrients and fecal coliforms [2]. All these factors contribute to environmental degradation if it is discharged without proper treatment. Therefore, the aim of this work was the treatment of wastewater from swine farming using a coagulation-flocculation-decantation (CFD) process.

The CFD process was performed by organic coagulants derived from almond hull (AH) and cherry pit (CP). The CFD experiments were performed under a fast mix of 150 rpm/3 min and a slow mix of 20 rpm/20 min, at ambient temperature (25ºC). Four different coagulant concentrations were tested (0.1, 0.5, 1.0 and 2.0 g/L) and four different pH levels (3.0, 6.0, natural and 9.0). After sedimentation, samples were retrieved for analysis. The results showed that pH 3.0 allowed to achieve turbidity, total suspended solids (TSS) and chemical oxygen demand (COD) removals of 51.4, 67.3 and 15.9%, respectively, using AH coagulant. Regarding CP coagulant, the results showed that a pH of 3.0 achieved turbidity, TSS and COD removals of 55.0, 74.8 and 14.0% for SW. The variation of coagulant concentration was also assessed and the results showed that 0.1 g/L of AH achieved turbidity, TSS and COD removals of 43.3, 61.4 and 16.9%, respectively. The CP concentration of 0.1 g/L accomplished turbidity, TSS and COD removals of 61.7, 73.2 and 13.5%. Based on these results, the AH and CP were able to reduce the organic load of swine wastewater being its efficiency affected by the pH and coagulant concentration. The application of almond and cherry by-products as coagulants allowed to valorise the waste generated from these two food industries and, at the same time, treat the swine wastewater.

Acknowledgements

Authors acknowledge the OBTain project (NORTE-01-0145-FEDER-000084), co-financed by the European Regional Development Fund (ERDF) through NORTE 2020, and FCT for the financial support to CQVR (UIDB/00616/2020).

References

1. Nagarajan, D., et al., Current advances in biological swine wastewater treatment using microalgae-based processes. PloS one, 2019. 289: 121718.
2. Cheng, D.L., et al., Bioprocessing for elimination antibiotics and hormones from swine wastewater. Sci Total Environ, 2018. 621: 1664-1682.