Removal of dimethylphenols from an artificial wastewater in a laboratory-scale wetland system planted with Juncus effusus

•Dimethylphenols were removed using a laboratory-scale constructed wetland.•Isomer removal performance was determinated to be in the order of 3,4- > 3,5- > 2,6.•An increase in the dimethylphenol concentration was accompanied by the formation of CH4 and decrease of removal intensities.

A laboratory-scale planted fixed bed reactor planted with the helophyte Juncus effusus was utilized for long-term experiments in the treatment of an artificial industrial wastewater using a mixture of 2,6-, 3,4-, and 3,5-dimethylphenol (DMP) in equimolar ratios (total DMPs of 20, 40 and 100 mg L−1), and only adding the isomer 2,6-DMP. The permanent circulation flow of the process water in the reactor enabled the simulation of the rooted zone of a constructed wetland (CW). Removal performance of the DMP isomers varied, and was determined to be in the order of 3,4- > 3,5- > 2,6. A stepwise increase in the inflow concentration of the total DMPs from 20 to 100 mg L−1 caused a decrease in the removal of total DMPs by more than 90%, and ultimately led to nearly complete removal inhibition. The results showed that DMP removal performance was dependent on concentration and specific isomer. At a DMP inflow concentration of 100 mg L−1, methane appeared in the pore water with a concentration of approximately 1.5 mg L−1 using a DMP mixture and 0.7 mg L−1 by only 2,6-DMP addition. Whether the carbon source for methanogenesis come either from the rhizodeposition products or/and the DMPs, has yet to be discovered. These experimental results, and further studies with higher effluent complexity, will assist in developing new treatment strategies for industrial effluents from the petro-chemical and, in particular, the carbo-chemical industry using CWs.