Remediacion De Suelos

Bioresource Technology 40 (1992) 275-282

Chemical Characterization of Humic Substances Extracted from Organic-Waste-Amended Softs
A. Piccolo
Istituto Sperimentale per 1o Studio e la Difesa del Suolo, Piazza M. D'Azeglio 30, Firenze, Italy

E Zaccheo & P. G. Genevini
Istituto Chimica Agraria, Universitfi di Milano, Via della Celoria, Milano, Italy (Received 24 October 1990; accepted 18June 1991) Key words: Humus, soil, organic waste.

Abstract

Humic substances were extracted from a soil treated, in a 4-year experiment, at different rates with a sludge from anaerobic treatment of combined civil and industrial wastes, and with agricultural manure. Elemental and chemical analyses, molecular weight (MW) distribution and infrared (IR) spectroscopy were performed on the purifiedhumic acids (HA). Organic wastes significantly increased the HA content of the treated soils and improved CEC. The C/N, C/H and C/O ratios of HA extracted from the original wastes showed a higher degree of humification for sludge than for manure. This difference was also noticed for the C/N ratio of soil humic extracts, indicating a faster humification process for the sludges in soil. The content ofoxygen-containing functional groups was lower than the 'model' HA reported in the literature, and even more so for HA from sludges, reflecting their anaerobic formation. M W distribution and E4/E 6 ratios showed that the sludge material had a higher molecular complexity than manure, supporting the high degree of humification attributed to the former. HA extracted from sludgetreated soils revealeda molecular dimension increasing with the application doses of waste material. Infrared spectra showed that HA formed in soils after waste additions reflected the chemical composition of the original organic material, which was rich in aliphatic groups and peptides for sludge and in carbohydrates for manure. On the basis of this study, it is concluded that not only are organic waste additionsable to build up the HA content in soils but the HA formed assume the chemical characteristics and the degree of humification of the original material.

INTRODUCTION The worldwide growing demand for means of disposing organic wastes derived from agricultural productions and urban and industrial refuses has increasingly turned to soils as a highly suitable acceptor. It is claimed that the soilchemical and biological activity may efficiently and safely incorporate organic wastes into the soil organic components. This practice often results in an improvement in the chemical and physical properties of the soil (Marchesini et al., 1988; Mbagwu & Piccolo, 1989, 1990), although there is an increasing awareness of the risk of groundwater contamination by pollutants such as heavy metals leacheddown in soluble organic matter complexes (Campanella et al., 1989). The realization that organic matter introduced into soils by waste additions may alter the soil capacity to prevent pollutants from a downward mobility has led to increased research on organic matter characterization, since information on humus chemical properties may be useful to predict the fate of a pollutant in the soilenvironment. Sugahara & Inoko (1981) reported on humic acid properties of a city refuse compost, Petronio et al. (1989) proposed a fractionation scheme of the organic components of urban and industrial sludges for a better evaluation of the chemical properties, Petrussi et al. (1988) investigated the characteristics of organic matter from animal manures after digestion by earthworms, Inbar et aL (1990)followed the chemical changes of humus during the compost-

275 Bioresource Technology 0960-8524/92/S05.00 © 1992 Elsevier Science Publishers Ltd, England. Printed in Great Britain

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A. Piccolo, P. Zaccheo, P. G. Genevini

ing of solid wastes from wineries. Other works studied the strength of metal complexes with soluble fulvic acids extracted from anaerobically digested sewage sludges...