Characterization of humic substances recovered from the sewage sludge and validity of their removal from this waste

Abstract

Being an inevitable byproduct of the operation of wastewater treatment plants (WWTPs), sewage sludge may cause serious environmental problems. Thus, the proper treatment and management of such waste is currently a challenge of great importance. Due to the significant concentration of various contaminants, the direct application of sewage sludge in agriculture is often limited. Nevertheless, this waste is rich in valuable compounds, among which humic substances (HS) are recognized to be one of the most important. A plethora of studies have shown the extensive application potential of HS. However, literature data also evidenced that HS may constitute obstacles for efficient wastewater treatment and sewage sludge management. The current review article discusses the fate of HS in WWTPs. Moreover, the necessity of removing and recovering such compounds from wastewater treatment systems was highlighted. Attention was also drawn to the beneficial features of humic compounds and avenues for their various possible applications.