The livestock industry has an important economic role in nearly all developing countries, and it is expected that these activities intensify in the coming decades [1]. Moreover, inadequate livestock management provides several environmental consequences at different levels which have not been sufficiently addressed in developing countries. This industry generates large volumes of wastewater which contains a high quantity of suspended solids content, organic matter (BOD₅ and COD), nutrients and faecal coliforms [2]. All these factors contribute to environmental degradation if it is discharged without proper treatment. Taking these factors into account, the aim of this work was the treatment of livestock wastewater from cattle (CW) 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 60.8, 73.1 and 52.1%, respectively, using AH coagulant. Regarding CP coagulant, the results showed that a pH of 3.0 achieved turbidity, TSS and COD removal of, respectively, 59.3, 77.2 and 38.9%. Regarding the variation of coagulants concentrations, the results showed that 0.1 g/L of AH achieved turbidity, TSS and COD removals of, respectively, 38.3, 52.9 and 39.1% for CW. The CP concentration of 0.1 g/L accomplished turbidity, TSS and COD removals of, respectively, 88.8, 22.7 and 42.4%.

Based on these results, the AH and CP coagulants were able to reduce the organic load of cattle wastewaters being its efficiency affected by the pH and coagulant concentration. Moreover, the application of almond and cherry by-products as coagulants allows to reduce the waste resulting from these two food industries and treat the cattle 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. Bodirsky, B.L., et al., Global food demand scenarios for the 21 st century. PloS one, 2015. 10(11): p. e0139201.
2. Cheng, D.L., et al., Bioprocessing for elimination antibiotics and hormones from swine wastewater. Sci Total Environ, 2018. 621: p. 1664-1682.