Rapid characterisation of agro-industrial effluents for environmental fate by UV–visible and infrared spectroscopy from fractions obtained by centrifugation

Abstract

Agro-industrial systems (e.g. dairy farms, feed lot, pig breeding and food processing plants) provide large quantity of organic wastes that could be recycled within the productive systems. However, the basic chemical characterisation is not enough to predict the effect that they may generate on the environment. In this study, a centrifugation process was applied at various speeds between 3000 and 15,000 rpm and carried out separately on two different livestock effluents (dairy farm and pig anaerobic digestate), in order to obtain supernatants and precipitates, which were studied separately. The more water soluble fractions, with lighter components and/or simpler structures, remained as liquid supernatants, while the more complex fractions, with higher molecular weight and/or water insoluble fractions, constituted the solid precipitates. An increase in the centrifugation rate did not produce the differential precipitation of dissimilar functional groups. Hence, 5000 rpm was the most adequate velocity since it generated clear supernatants without denaturation of the organic matter. A basic cost-effective chemical analysis, complemented with ultraviolet–visible and Fourier transform infrared spectroscopy, enables a set of properties to be established qualitatively and quickly for the multiple components of the organic matter for its later use as fertilisers or amendments. This rapid and economical technique allows for a characterisation prior to the reuse of the effluents, which is necessary to optimise their application and avoid environmental problems.