Nitrate and nitrite are ubiquitous ions in wastewater that affect the performance of advanced oxidation processes such as UV-activated persulfate (UV/PDS) and lead to the formation of by-products. Three structurally similar compounds with different substituent compounds, namely phenol (Ph), benzoic acid (BA) and salicylic acid (SA), were selected as target pollutants in this study, to explore these issues from a new perspective: the effect of substituents on contaminants. The results showed that both NO