Fractionation of organic matter from wastewater treatment plants before and after a 21-day biodegradability test: A physical-chemical method for measurement of the refractory part of effluents

In order to study refractory organic matter (OM) from sewage treatment plants (STP), effluents were subjected to a 21-day biodegradation test. Mineral nutrient concentrations were adjusted to get an optimal growth of micro-organisms. This OM defined as the refractory part of biodegradation, was divided into hydrophobic and basic, acid and neutral hydrophilic fractions by passing through XAD-8, AGMP-50 and A-21 columns, respectively. Results obtained before and after the biodegradation test were then compared. This fractionation method, for determination of refractory OM, is an alternative physico-chemical technique to bioassay techniques. Our results foresee the possibility to study, without biological tests, refractory and labile OM and improve sewage treatment monitoring. Biodegradation results in a significant increase of the hydrophobic fraction (around 40%). This fraction is strictly equivalent to humic substances (HS) according to IHSS definition.