Molecular-level characterization of stratified extracellular polymeric substances of anammox sludge and its adsorption preference to refractory dissolved organic matter

Abstract

Anaerobic ammonium oxidation (anammox) is an energy saving and environmentally friendly technique for wastewater treatment. Sludge adsorption is an important process after organics enter the anammox reactor. The extracellular polymeric substances (EPS) of anammox sludge play a key role on the activity of anammox. This study utilized Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to investigate molecular-level compositional characteristics of the stratified EPS of the anammox sludge, and to explore the adsorption preference of each EPS layer to refractory dissolved organic matter (DOM) during anammox treatment. Results showed that the adsorbed component by the tightly bound EPS layer was dominantly composed of lipids and proteins, with nearly 80% of formulas being CHO and CHON. The outer layers (slime, loosely bound-EPS) preferentially adsorbed the compounds with comparatively higher aromatic and unsaturated degrees, with S-containing formulas and lignin being the predominant components. The newly produced formulas in the effluent were inferred to be associated with the anammox treatment performance. The refractory DOM, with smaller molecular weight and high reductive degree, seemed to experience a single adsorption by the stratified EPS, and became part of the anammox sludge.