Environmental and Agronomical Aspects of Sludge Produced from Tannin-Based Coagulants in Dairy Industry Wastewater Treatment

A study was carried out of the environmental and agronomic features of the sludge generated by a dissolved air flotation process applying a tannin-based coagulant in a dairy factory. First, the chemical and physical characteristics of the sludge were examined. Subsequently, a solubilization test was performed to evaluate the potential of groundwater contamination after the application of sludge on soil. The data obtained were compared to the United States Environmental Protection Agency (US-EPA) criteria for evaluation and classification of solid residues for land application. The results show that the studied sludge is a non-hazardous waste, and all evaluated parameters are lower than the maximum reference values according to international criteria. Based on the set of parameters which were evaluated, no organic pollutants were found. Additionally, the agronomic characterization shows good potential for agricultural purposes. However, in the solubilization test, chemicals such as phenols, cyanide, nitrate and fluoride were solubilized from the studied residue. As a result, the water showed concentrations above the limits required by the international criteria for drinking water established by US-EPA and World Health Organization. In conclusion, although tannin-based coagulants produce sludge with the potential for agronomic applications, some limits have to be considered to avoid environmental impacts.