Use of headspace solid-phase microextraction to characterize odour compounds in subsurface flow constructed wetland for wastewater treatment.

A headspace solid-phase microextraction (HS-SPME) preconcentration method was applied to the analysis of some of the major odorous compounds occurring in wastewater using GC/MS or GC/NPD detection. The detection limit for volatile amines, volatile fatty acids, and volatile alkylsulphides ranged from 3 to 100, 2 to 150, and 0.0006 to 0.035 microg/L, respectively. The SPME method was used to examine the fate of odorous compounds in the subsurface flow constructed wetlands (SFCW) operated under different hydraulic loading rate (HLR), bed aspect ratio, and granular medium size. Among the experimental conditions evaluated in the SFCW beds, HLR was found to be the most important factor influencing the evolution of the studied compounds. There were also significant differences among bed types in the behaviour of ammonia (NH3), acetic acid (Ac), isovaleric acid (IsoA), propionic acid (PrA), and dimethylsulphide. Aspect ratio and medium granular size were minor factors influencing SFCW performance. The major odour compounds by mass in the effluent of SFCW with different operational conditions were NH3 and Ac. Further removal of these two compounds is considered as very important from the viewpoint of chemical composition. On the other hand, Relative Odour Intensity (ROI: ratio between the absolute concentration to the odour threshold concentration) suggested that PrA and IsoA were the two major compounds responsible for odour intensity. Thus, further removal of these two compounds is viewed as very important for the effluent deodorization, especially for PrA. From our results, this compound appears to be produced by processes occurring in the SFCW.