Authors
1
Animal Science Research Department, Isfahan Agricultural and Natural Resources Research and Education Center, AREEO, Isfahan
2
PhD student in Department of Animal Sciences, Isfahan University of Technology
3
Faculty member of Department of Animal Sciences (Retired), Isfahan University of Technology
4
MSc student in Molecular Cell Biology-Microbiology, Isfahan University
Abstract
Background and objective: As a result of the water scarcity, the use of unconventional water in the country, especially municipal wastewater, is inevitable. However, worries have always been existing about the possible contamination of these sources and the entry of these contaminants into the human food chain. Corn silage is regarded as one of the candidate products for irrigation with wastewater due to the possible reduction of microbial contamination resulting from various processing steps. The objective of this study was to investigate the quality and hygienic characteristics of corn silage irrigated by well water and treated wastewater.
Materials and methods: For this purpose, information of 11 industrial dairy herds that provided their corn forage from lands located around of northern Isfahan water treatment plant were compared with 11 other dairy herds whit source of purchased corn forage from lands irrigated with well water. The chemical composition of the silage samples, including dry matter, ash, crude protein, and ether extract, were measured using the approximate degradation. Also, neutral detergent fiber and acid detergent fiber were measured based on the Van Soest method. Furthermore, the net energy for lactation and non-fiber carbohydrates were calculated using Adams’ equation and the subtraction method, respectively. Volatile fatty acids were measured using gas chromatography, while microbial population were measured according to the instructions of microbiological tests. The comparison of the mean values of the two groups of corn silage irrigated with the well water and treated wastewater was performed using SAS statistical software and the T-test procedure.
Results: There was no significant difference between the two groups of corn silage in dry matter, ether extract, neutral detergent fiber, acid detergent fiber, net energy for lactation and ash. However, the percentage of crude protein and the amount of acetic acid in the corn silage irrigated with treated wastewater were significantly lower than the control group (P<0.01). In contrast, samples irrigated with treated wastewater had higher levels of non-fiber carbohydrates, along with propionic and butyric volatile fatty acids, which ultimately decreased the pH of silage (P<0.01). In terms of hygienic indicators, despite no significant difference in the amount of E. coli and Salmonella colonies between the two groups, the number of gram-negative bacteria, lactobacilli and the total bacterial count in the silage irrigated with treated wastewater were higher (P<0.05).
Conclusion: When treated sewage wastewater is utilized for irrigating corn forage, it alters the type of fermentation that takes place in the corn silage, leading to an increase in the levels of propionic and butyric acids, while decreasing the levels of acetic acid. As a result, the pH of the corn silage decreases further. According to this research, using treated sewage wastewater can negatively impact the quality of corn silage fermentation. This can result in a reduction of crude protein levels and an increase in certain microbial components. Therefore, it is crucial to improve the urban wastewater treatment process by reducing the concentration of ammonium nitrogen.
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