The insoluble organic fraction isolated from rice-hulls residues and animal fecal matter mixture is sulphonated in liquid SO3 at 200 degreesC to a water soluble sulphonate (111). 111 is compared to the sulphonate (IV) obtained from the same mix after composting. Both products have been found to contain mixtures of molecules with close molecular weight. These molecules consist of a central cicloaliphatic cluster with peripheral pending aromatic chains. III and IV appear to have the same sulphonation degree. However, the latter contains higher concentrations of cicloaliphatic fragments and of amide, phenol and ether bonds, but less carboxylic and amine functional groups. These differences may be reasonably traced back to the starting materials. By comparison with commercial lignosulphonates derived from the paper and pulp industry, the above arylsulphonates are likely candidates for a variety of applications in the chemical industry and in agriculture. We conclude that sulphonation, even under the drastic experimental conditions of this work, does not seem to erase the memory of the parent matter structure. This reaction is capable of upgrading recalcitrant organic matter in vegetable waste residues to an interesting variety of lignosulphonates. (C) 2003 Elsevier Ltd. All rights reserved.