Fungal removal of humic acids from treated wastewater

Abstract

In order to address the ambiguities and knowledge gaps in the HA removal by WRF, mechanisms of removal were explored in chapter 2. It was shown that the mechanisms of HA removal by WRF involves the degradation of HA to smaller molecules, conversion to FA and also biosorption of HA by fungal mycelia. Furthermore, the ability of laccase to effectively degrade HA was demonstrated and it was shown that the presence of suitable mediators, such as ABTS, have a crucial effect on the degradation process. Also, the contribution of the membrane-bond CYP 450 enzymes to the rate of the HA degradation by fungi was demonstrated. In addition, addressing the ambiguities in the measurement techniques mentioned in chapter 1, it was shown that decolorization was not necessarily representing the degradation of HA, but removal of HA in the general context. This removal could be due to biosorption, in-complete or complete degradation of HA to smaller molecules. Also, it was shown that the degradation or depolymerization of the HA is not necessarily reflected by a change in the average MW of the HA in the wastewater. The reason is that the depolymerization and/or degradation of HA could basically result in three products, smaller HA molecules, smaller non-aromatic molecules, and FA. Except for the first group, the other products from the degradation of HA could not be detected by the SEC analysis (at 254 nm) and were therefore not considered in the calculation of the average MW. Also, it was shown (chapter 2 and 3) that the biosorption of HA to fungal mycelia was not uniform among large, medium and small size HA. The large HA molecules were shown to be more susceptible to biosorption. Therefore, sole biosorption of HA to fungal mycelia could result in a change in MW distribution of the HA, even when no degradation or polymerization have occurred...