The problem of water hyacinths in rivers and canals

Abstract

The cation exchange capacity (CEC) and content of COOH groups in bulky water hyacinth compost were estimated over the rotting period. The progressive increase observed in the estimates was ascribed to continuing oxidation processes in the composted materials.

Fractionation of organic carbon extracted with Na₄P₂O₇-NaOH from the composted materials over the rotting period on the basis of acid-soluble and -insoluble fractions, was carried out. The carbon of humic-like substances (precipitated at pH 2) in the dry matter was almost stable from 0- to 124-day composted materials. There were successive increases in total acidity, and content of carboxyl and phenolic hydroxyl groups in the humic substance extracts indicating progressive oxidation processes in these substances over the rotting period. Elementary analysis and IR spectra provided fürther support for the above inference and led us to conclude that humification of the water hyacinth consists mainly of structural modification of humic-like substances initially occurring rather than a condensation of simple organic carbon to form high molecular weight material. Such structural modification is dominated by biochemical oxidation and increases in oxygen-containing functional groups. This conclusion is consistent with the view that “humic acids are formed by processes involving oxidation of plant lignin and lignoprotein entering the soil.”