Soybean Peroxidase Catalyzed Oligomerization of Acetaminophen and Selected Parabens for Wastewater Treatment

Esters of para-hydroxybenzoic acid (parabens) commonly used as universal preservatives, para-hydroxybenzoic acid, the degradation intermediate of parabens and the common analgesic/antipyretic pharmaceutically active ingredient, acetaminophen have been detected in the environment around the world largely because they are inefficiently removed by conventional wastewater treatment processes. These compounds are emerging contaminants, thus necessitating research for an alternative treatment regimen for their efficient removal from wastewater treatment plants effluent before discharge into receiving water bodies. Soybean peroxidase-catalyzed reaction in the presence of peroxide at appropriate pH was employed to treat these contaminants in synthetic wastewater with compound removal monitored using high performance liquid chromatography. Oligomers formed were determined with the aid of mass spectroscopy, using appropriate ionization techniques. The parameters influencing the removal process were optimized, both for single-compound treatment and in a mixture of the five compounds (mix-5), targeting ≥95% removal efficiency under both study conditions. Optimal pH for four single compounds was 6.5 while that for acetaminophen was 8.0; mix-5 showed optimal removal at pH 6.5. SBP requirement varied between 0.006 U/mL and 2.3 U/mL in the increasing order of Acetaminophenbutyl paraben≈propyl paraben\u3e para-hydroxybenzoic acid≈methyl paraben but followed the order of acetaminophen\u3ebutyl paraben\u3e para-hydroxybenzoic acid\u3epropyl paraben≈methyl paraben in mix-5. Mass spectroscopic analysis for single compounds showed the formation of oligomers of varying sizes ranging from dimers of para-hydroxybenzoic acid, to pentamers of acetaminophen, hexamers of propyl paraben and heptamers of methyl paraben and butyl paraben. Mass spectral analysis of mix-5 showed evidence of homo- and hetero-oligomers up to pentamers. The results support the possibility of soybean peroxidase-catalyzed treatment of the contaminants of emerging concern, both as single compounds and as a mixture. The possibility of mixture treatment is important for dealing with real wastewater effluents. These results show prospects for scaled-up processes with potential applications to hospital, industrial and pharmaceutical company wastes where these compounds may be predominantly found, before discharging such wastewaters to municipal treatment plants and thence receiving water bodies