| Abstract: | Abstract The ratio between non‐humified and humified fractions in pyrophosphate extracts is shown to vary during maturation of sewage sludge. The ratio is higher than 1 in the raw materials but lowers at 1 or less than 1 with the aging of sludge and is assumed to reflect quantitatively the degree of stabilization of organic matter in the sludge. Analytical isoelectrofocusing (IEF) experiments showed that humified fractions in raw sludge focalize only in the pH gradient regions lower than 5.0, whilst in older sludge samples a progressive strengthening of bands occurs in the region between pH 6.5 and 5.0, approaching at least partially IEF patterns of soil organic matter. IEF patterns are suggested to reflect the stabilization of organic matter in sewage sludge from a qualitative point of view. |
