Humic substances INDEX

SOM, soil organic matter HS, humic substances DH, degree of humification HAC, humic acid C FAC, fulvic acid C TEC, total extractable C HR, humification rate HI, humification index NHC, nonhumified C TOC, total organic C HA, humic acid FA, fulvic acids UV-Vis, ultraviolet-visible FT-IR, Fourier transform infrared NMR, nuclear magnetic resonance ESR, electron spin resonance EEM, excitation-emission matrix. 

Previous pilot plant operations have shown that the effectiveness of carbon adsorption processes in removing humic substances from raw water sources is limited. Most of the commercially available active carbons with high specific surface, iodine index and phenol index have a pore size distribution with a maximum of pores of a relatively low average diameter. For reason the adsorption capacity and rate towards larger-sized molecules is quite low. This was one of the incentives for the authors to start a search for alternative activated carbons. This paper will deal with the evaluation of a first generation of such activated carbons on the basis of widely used adsorption tests and an experimental comparison of their capacity towards several humic substances. 

However, the usual tests for characterizing active carbon — such as the phenol number, the surface area (BET 2)> tl tannin index or the iodine index — are inadequate for evaluating the potential removal of the humic substances by the carbon. Moreover the resulting adsorption may differ according to the source and previous treatment of those substances and the characteristics of the feed water used. 

In soils and clays the most generally present biopolymers that naturally occur in the adsorbed state on mineral and clay particles are humic substances , or humic acids these are decomposition products of lignin, whidi is the major non-cellulosic polymer in wood and other plant debris. Humic acids (also called allomelanins (Merck Index, 1989)) are for the greater part polyphenolic compounds, usueJly anionic polyelectrolytes, which can complex metal ions, and are surface active and thus capable, upon adsorption onto mineral particles, to enhance their suspension stability in aqueous media (Chheda and Grasso, 1994). 

The second approach consists of the study of both humic and fulvic fractions evolution. This way seems to be more operational. The evolution of the humic nature of the organic matter during composting or after mixture with soil can be estimated by one of the following methods C/N ratio [14-16], humification index [17-19] or biodegradability index [11,14]. Another parameter, based on the use of two wavelengths (465 and 665 nm), can also be used for the characterisation of the evolution of humic-like substances [20,21]. 

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