The Emergent Integrated Constructed Wetland-Reservoir (CW-R) Is Being Challenged by 2-Methylisoborneol Episode—A Case Study in Yanlonghu CW-R

Abstract

Integrated constructed wetland-reservoirs (referred to as CW-Rs) are being built for ensuring drinking water supply in plain areas where the source water often cannot meet the quality criteria for drinking water. CW-Rs consist of a series of treatment units and have been reported to reduce the concentration of major nutrients. The efficiency of CW-Rs in mitigating odor compounds and their producer(s) remains largely unclear. In this study, Yanlonghu CW-R located in Jiangsu province, eastern China, was selected to monitor the occurrence and dynamics of 2-methylisoborneol (2-MIB). Two peaks of 2-MIB, attributed mainly to Pseudanabaena in April, and Pseudanabaena and Oscillatoria in July, were observed. This indicated that benthic Oscillatoria is also a threatening factor and should be considered. The concentrations of 2-MIB at the inlet and outlet were 9.75 and 50.08 ng/L in April and 73.11 and 25.21 ng/L in July, respectively. Yanlonghu CW-R was reported to be effective in reducing the content of major nutrients (total phosphorus in particular) throughout the year. In addition, it was effective in mitigating the levels of 2-MIB-producers/2-MIB during the summer season. It is proposed that qPCR for mic gene detection can be performed to screen and establish an early warning method. We revealed that the 2-MIB episode is related to the function of the CW-R, which is shown to be different from what is known in lakes or reservoirs. It is emphasized that each treatment unit of CW-R should be maintained at full capacity so that the frequency and hazardous effects caused by 2-MIB in the system can be controlled or reduced. This finding is implicated in the control strategy selection and contributes to the better management and improvement of future applications.