Removal processes of disinfection byproducts in subsurface-flow constructed wetlands treating secondary effluent

• The fate of DBPs in SSF CWs and the effect of aquatic macrophytes on DBPs removal were examined.
• Most of the DBPs were efficiently removed (>90% removal) in SSF CWs.
• The planted SSF CWs was more efficient for TCM removal than unplanted units.
• More than 23.8% of the TCM was removed by plant uptake, and volatilization only accounted for 1.3–1.8% in planted units.
• Anaerobic biodegradation of THMs via reductive dechlorination was observed in SSF CWs with cattail litter.

The removal efficiencies and the kinetics of disinfection byproducts (DBPs) were studied in six greenhouse laboratory-scale SSF CWs. Cattail (Typha latifolia) and its litter (collected from the aboveground samples of cattail in autumn) were used as a potential phytoremediation technology and as a primary substrate, respectively, for DBP removal. Results showed that most of the 11 DBPs (except chloroform and 1, 1-dichloropropanone) were efficiently removed (>90%) in six SSF CWs with hydraulic retention time of 5 d and there were no significant differences among the systems. Under the batch mode, the removal of DBPs in SSF CWs followed first-order kinetics with half-lives of 1.0–770.2 h. As a primary DBP in wastewater effluent, removal efficiencies for chloroform were higher in planted systems than in unplanted ones and plant uptake accounted for more than 23.8% of the removal. Plant litter greatly enhanced the removal of trihalomethanes (THMs) by supplying primary substrates and reducing conditions, and the formation of dichloromethane supported the anaerobic biodegradation of THMs via reductive dechlorination in SSF CWs. Trichloroacetonitrile was completely removed within 10 h in each system and hydrolysis was considered to be the dominant process as there was a rapid formation of the hydrolysis byproduct, trichloroacetamide.

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