# Removal of Organic UV Filters Using Enzymes in Spent Mushroom Composts from Fungicultures
## 4 Discussion  
Only a few intermediates were identified by GC/MS analysis. This may be due to the problem of sample collection, sample preparation and experimental technology. There are unknown reactions in the GC/MS results due to unidentified intermediates. Although the results shown in Figure 5 are incompletely hypothesized degradation pathways. However, these results indicate that EHS and HMS were degraded and EHMC was transformed by SMCs. More experiments need to be conducted to understand the detailed reaction mechanism of EHS and HMS biodegradation.  
EHS and HMS were degraded into benzoic acid (Figure 5A,B) by the extracellular enzymes in the SMCs. [PERSON] et al. (2020) indicated that benzoic acid can be degraded by the extracellular enzymes (lignin peroxidase and lacase) of the white-rot fungus _Hypocrea lixii_ AH [28]. [PERSON] et al. (2020) indicated that 3-phenoxyozoic acid can be degraded by _Aspergillus oryzae_ M-4 [29]. A study by [PERSON] et al. (2015) indicated that benzoic acid can be degraded by the endophytic fungus _Phomopsis liquidambari_[30]. Therefore, more investigations should be performed to ensure that the benzoic acid produced from EHS and HMS in this study can be further degraded by extracellular enzymes from _P. djamor_, _P._ ostreatus or _P. erygii_.  
The results in Figure 5 further support the proposal that the enzymes involved in the transformation of EHMC were different from the enzymes involved in the removal of EHS and HMS. The degradation of EHS and HMS may be associated with lacases because EHS and HMS were not degraded by enzyme extracts and SMCs of _A. polytricha_, which exhibit very low lacase activities (Figure 3D, Figure 4A, Figure 9E-H and Figure 10E,F) and evidenced by the study of [PERSON] et al. (2017) [31]. In contrast, EHMC was converted to an isomer (2-propenoic acid, 3-[4-methoxyphenylyl], 2-ethylhexyl ester, Figure 5C). The isomerization of EHMC may have nothing to do with lacase because the reaction occurred in both enzyme extracts and SMCs of _A. polytricha_ (Figure 3D, Figure 4A, Figure 9E-H and Figure 10E,F).  
There are at least three factors that affect the adsorption of UV filters on SMCs. First, as shown in Figure 1, the chemical structures of EHS and HMS are similar and are different from that of EHMC. Therefore, EHS and HMS exhibit similar adsorption abilities for all four SMCs and exhibit different adsorption abilities from EHMC. Second, the differences in adsorption abilities of the four SMCs to one UV filter may be due to different compositions of SMCs for different fungi (Figure 6). Third, the rates of water or wastewater (containing UV filters) used to flow through the SMCs may cause differences; a slow flow rate (500 mL/2 h) led to more UV filter adsorption on SMCs (Figures 7 and 9). These three factors should be considered in the real application of SMCs for wastewater treatments.  
The direct application of SMCs for UV filter treatment is better than the use of enzyme extracts of SMCs and has three advantages. First, there are living fungal mycelia in SMCs that can continuously secrete extracellular enzymes to degrade the organic UV filters adsorbed onto the SMCs. Second, some of the extracellular enzymes were flushed out with wastewater (containing UV filters). Organic UV filters can be continuously degraded by these enzymes in the effluents. Third, the preparation of enzyme extracts of SMCs requires a large amount of water. In contrast, there is no extra requirement for water with the direct application of SMCs, which saves considerable time and costs.