Effect of dissolved organic matter and goethite on removal of <italic>p</italic>-nitrophenol from biochar before and after water washing

Due to the abundance of dissolved organic matter (DOM) and iron minerals in the environment, they can affect the removal of p-nitrophenol (PNP) by biochar in the application. However, the studies on the effects of DOM or goethite on the PNP removal process by biochar are limited. In this study, the effects of DOM, goethite, and DOM-goethite mixtures on the adsorption and degradation process of PNP by biochar (BC700, WBC700, BC400 and WBC400) were examined. It was discovered that, whereas DOM had no discernible impact on PNP removal by BC700, it decreased PNP removal by BC400. The DOM-goethite mixtures reduced the removal of PNP by BC400, whereas goethite slightly increased the removal of PNP by biochar at two pyrolysis temperatures. Following washing, WBC700's specific surface area increased, more suitable for PNP adsorption; however, the decreased WBC400's specific surface area reduced PNP removal by biochar. DOM, goethite, and DOM-goethite mixtures decreased the electron utilization rate of BC400 for PNP degradation, but they had little effect on the electron utilization rate of BC700. Therefore, the results in this study could theoretically support the enhancement of the biochar’s effectiveness to remove PNP in the application.