Increase pollutant removal efficiency of constructed wetlands in cold climates

Ouellet-Plamondon investigated the effect of artificial root zone aeration on removal performance in HSSFCWs (Horizontal subsurface flow constructed wetlands, Fig.1) treating a reconstituted trout farm effluent 5. Mesocosm experiments were conducted in a greenhouse, with a combination of planted, unplanted, aerated, and non-aerated beds. Adding an air diffuser at the front end of the bed would favor aerobic processes of organic matter oxidation and nitrification, while the remaining part of the beds could still offer conditions favorable to denitrification and the gain of artificial aeration would be greater in winter, when plants are dormant.

Under the experimental conditions, treatment performances in planted units were generally higher than in unplanted ones, even in winter, but no differences between common reed and cattail. Artificial aeration improved organic matter and nitrogen removal, especially in winter, where it apparently stimulated heterotrophic bacterial activity without reducing denitrification. Artificial aeration also slightly enhanced TSS removal in all beds in winter and summer, probably by physical action, like maintaining empty space in the head part of the gravel bed. The high efficiency that under all our treatment conditions (TKN removal rates of more than 70% for all beds) may have been the result of the relatively low organic load imposed. Yet, despite the already high removal in no-aerated bed, the addition of artificial aeration still showed significant improvement. The results are thus conservative, and under higher organic load conditions, the benefit of artificial aeration may even be more pronounced. The results suggest that artificial aeration represents a promising approach to improve removal efficiency in HSSFCW, especially for fresh water fish farms in cold climate, where artificial aeration is readily available