Investigating the potential origin and formation of humic substances in biological wastewater treatment systems from the forms of phosphorus

Abstract

ABSTRACT Origin of the humic substances formed in biological wastewater treatment system (abbreviated as bio-HS) still remains inconclusive. In this study, the bio-HS that contained humic acid (HA) and fulvic acid (FA) from effluent and activated sludge were isolated and purified with XAD-8 resin and ion exchange resin, and then the molecular weight, functional groups, contents and forms of phosphorus (P) using gel permeation chromatography (GPC), fourier transform infrared (FTIR), element analysis and P nuclear magnetic resonance (31P-NMR) were investigated. The results showed that HS was formed in biological wastewater treatment systems, and had a lower degree of humification than soil, peat, or marine HS, and mainly comprised diester and monoester P fragments. Specific signal peaks of intracellular materials and cell membranes (nucleic acid, phospholipids, and sugar phosphate) showed that microbial cell debris was the precursor of bio-HS. HA comprised diester P fragments and monoester P fragments that formed when diester P fragments degraded, while FA contained only diester P fragments. The monoester P fragments in HA may result from microbial degradation of diester P fragments, and FA may simultaneously condense into HA. These results show that microbial cell debris was first transformed into FA and then into HA.