ACID-BASE PROPERTIES OF FULVIC-ACIDS EXTRACTED FROM AN UNTREATED SEWAGE-SLUDGE AND FROM COMPOSTED SLUDGE

The acid-base properties of two samples of anthropogenic fulvic acids (FA) extracted from the untreated sewage sludge (rsFA) of a municipal wastewater treatment plant and from the compost (csFA) obtained in the aerobical digestion of this sludge were studied. Potentiometric titri metry, infrared spectroscopy and synchronous molecular fluorescence (S yF) spectroscopy were used to obtain experimental information about th e acid-base properties of the samples. Moreover, the SyF spectral data which were collected as function of the pH were analysed by a self-mo delling curve resolution technique, evolving factor analysis with a gr adient concentration window (EFA-GCW), to calculate the number of acid -base systems, their SyF spectra and the corresponding distribution di agrams, from which the pK(a) values were estimated. Two acid-base syst ems with pK(a) values about 6.2 and 8.9 were detected for rsFA and thr ee systems with pK(a) values about 3.8, 6.6 and 9.4 for csFA. The amou nts of acid groups directly titrated in water were (standard deviation s in brackets) about 6.8(1) for rsFA and 6.73(3) for csFA. This inform ation for rsFA and csFA was compared with similar information for natu ral soil FA samples extracted from a pinewood soil. Beyond different s tructural composition, this comparison showed that the anthropogenic s amples have a higher amount of acid structures, but the structures of natural samples have stronger acid properties. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.